| 0/0 |
2026/05/25 04:29 |
flow |
assessment-security |
51m
Results: map[DenialOfService:true Explanation:**Analysis of the Bug Report**
The bug report indicates a hung task (`syz.0.17`) blocked in
`nilfs_transaction_begin` while waiting for the `nilfs->ns_segctor_sem`
semaphore. Another task (`syz.3.20`) is holding this semaphore and is stuck
printing a large number of warnings to the console, which is a slow operation
and causes the system to hang.
By examining the stack trace and the source code, we can trace the issue to the
`NILFS_IOCTL_CLEAN_SEGMENTS` ioctl. This ioctl is used by the `nilfs_cleanerd`
garbage collection daemon to clean segments. It takes an array of segment
numbers to be freed from user space.
The ioctl eventually calls `nilfs_sufile_updatev()` in `fs/nilfs2/sufile.c`,
which contains the following loop:
```c
for (seg = segnumv; seg < segnumv + nsegs; seg++) {
if (unlikely(*seg >= nilfs_sufile_get_nsegments(sufile))) {
nilfs_warn(sufile->i_sb,
"%s: invalid segment number: %llu",
__func__, (unsigned long long)*seg);
nerr++;
}
}
```
If a user provides a very large `nsegs` value and populates the array with
invalid segment numbers, the kernel will print a warning for every single
invalid segment. Because console output (especially serial console) is extremely
slow, printing thousands or millions of warnings will block the task for a long
time, triggering the hung task watchdog and causing a Denial of Service (DoS).
**Security Impact Assessment**
While this bug causes a Denial of Service, it is **not a security
vulnerability** because it is completely inaccessible to unprivileged users.
Looking at the entry point for the ioctl in `fs/nilfs2/ioctl.c`:
```c
static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
unsigned int cmd, void __user *argp)
{
...
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
...
```
The very first check in the ioctl handler is `capable(CAP_SYS_ADMIN)`. The
`capable()` function checks for the capability in the **initial user
namespace**. This means that:
1. An unprivileged user cannot trigger this bug.
2. An unprivileged user inside a new user namespace (where they might have
`CAP_SYS_ADMIN` relative to that namespace) also cannot trigger this bug,
because `capable()` strictly checks the initial namespace (unlike
`ns_capable()`).
Furthermore:
* **Exploitable:** No. This is not a memory corruption issue; it is merely a
slow path causing a hung task.
* **Malicious Filesystem Trigger:** No. The bug is triggered by the ioctl
arguments provided by the user-space process, not by the kernel parsing
malicious filesystem metadata during mount or normal operations.
In conclusion, this is a root-only Denial of Service bug and does not cross any
privilege boundaries. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/05/25 04:29 |
action |
syz-repro-to-c-repro |
0m
Results: map[SimplifiedCRepro:// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <setjmp.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <linux/loop.h>
#ifndef __NR_memfd_create
#define __NR_memfd_create 319
#endif
static unsigned long long procid;
//% This code is derived from puff.{c,h}, found in the zlib development. The
//% original files come with the following copyright notice:
//% Copyright (C) 2002-2013 Mark Adler, all rights reserved
//% version 2.3, 21 Jan 2013
//% This software is provided 'as-is', without any express or implied
//% warranty. In no event will the author be held liable for any damages
//% arising from the use of this software.
//% Permission is granted to anyone to use this software for any purpose,
//% including commercial applications, and to alter it and redistribute it
//% freely, subject to the following restrictions:
//% 1. The origin of this software must not be misrepresented; you must not
//% claim that you wrote the original software. If you use this software
//% in a product, an acknowledgment in the product documentation would be
//% appreciated but is not required.
//% 2. Altered source versions must be plainly marked as such, and must not be
//% misrepresented as being the original software.
//% 3. This notice may not be removed or altered from any source distribution.
//% Mark Adler madler@alumni.caltech.edu
//% BEGIN CODE DERIVED FROM puff.{c,h}
#define MAXBITS 15
#define MAXLCODES 286
#define MAXDCODES 30
#define MAXCODES (MAXLCODES + MAXDCODES)
#define FIXLCODES 288
struct puff_state {
unsigned char* out;
unsigned long outlen;
unsigned long outcnt;
const unsigned char* in;
unsigned long inlen;
unsigned long incnt;
int bitbuf;
int bitcnt;
jmp_buf env;
};
static int puff_bits(struct puff_state* s, int need)
{
long val = s->bitbuf;
while (s->bitcnt < need) {
if (s->incnt == s->inlen)
longjmp(s->env, 1);
val |= (long)(s->in[s->incnt++]) << s->bitcnt;
s->bitcnt += 8;
}
s->bitbuf = (int)(val >> need);
s->bitcnt -= need;
return (int)(val & ((1L << need) - 1));
}
static int puff_stored(struct puff_state* s)
{
s->bitbuf = 0;
s->bitcnt = 0;
if (s->incnt + 4 > s->inlen)
return 2;
unsigned len = s->in[s->incnt++];
len |= s->in[s->incnt++] << 8;
if (s->in[s->incnt++] != (~len & 0xff) ||
s->in[s->incnt++] != ((~len >> 8) & 0xff))
return -2;
if (s->incnt + len > s->inlen)
return 2;
if (s->outcnt + len > s->outlen)
return 1;
for (; len--; s->outcnt++, s->incnt++) {
if (s->in[s->incnt])
s->out[s->outcnt] = s->in[s->incnt];
}
return 0;
}
struct puff_huffman {
short* count;
short* symbol;
};
static int puff_decode(struct puff_state* s, const struct puff_huffman* h)
{
int first = 0;
int index = 0;
int bitbuf = s->bitbuf;
int left = s->bitcnt;
int code = first = index = 0;
int len = 1;
short* next = h->count + 1;
while (1) {
while (left--) {
code |= bitbuf & 1;
bitbuf >>= 1;
int count = *next++;
if (code - count < first) {
s->bitbuf = bitbuf;
s->bitcnt = (s->bitcnt - len) & 7;
return h->symbol[index + (code - first)];
}
index += count;
first += count;
first <<= 1;
code <<= 1;
len++;
}
left = (MAXBITS + 1) - len;
if (left == 0)
break;
if (s->incnt == s->inlen)
longjmp(s->env, 1);
bitbuf = s->in[s->incnt++];
if (left > 8)
left = 8;
}
return -10;
}
static int puff_construct(struct puff_huffman* h, const short* length, int n)
{
int len;
for (len = 0; len <= MAXBITS; len++)
h->count[len] = 0;
int symbol;
for (symbol = 0; symbol < n; symbol++)
(h->count[length[symbol]])++;
if (h->count[0] == n)
return 0;
int left = 1;
for (len = 1; len <= MAXBITS; len++) {
left <<= 1;
left -= h->count[len];
if (left < 0)
return left;
}
short offs[MAXBITS + 1];
offs[1] = 0;
for (len = 1; len < MAXBITS; len++)
offs[len + 1] = offs[len] + h->count[len];
for (symbol = 0; symbol < n; symbol++)
if (length[symbol] != 0)
h->symbol[offs[length[symbol]]++] = symbol;
return left;
}
static int puff_codes(struct puff_state* s,
const struct puff_huffman* lencode,
const struct puff_huffman* distcode)
{
static const short lens[29] = {
3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258};
static const short lext[29] = {
0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0};
static const short dists[30] = {
1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
8193, 12289, 16385, 24577};
static const short dext[30] = {
0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
7, 7, 8, 8, 9, 9, 10, 10, 11, 11,
12, 12, 13, 13};
int symbol;
do {
symbol = puff_decode(s, lencode);
if (symbol < 0)
return symbol;
if (symbol < 256) {
if (s->outcnt == s->outlen)
return 1;
if (symbol)
s->out[s->outcnt] = symbol;
s->outcnt++;
} else if (symbol > 256) {
symbol -= 257;
if (symbol >= 29)
return -10;
int len = lens[symbol] + puff_bits(s, lext[symbol]);
symbol = puff_decode(s, distcode);
if (symbol < 0)
return symbol;
unsigned dist = dists[symbol] + puff_bits(s, dext[symbol]);
if (dist > s->outcnt)
return -11;
if (s->outcnt + len > s->outlen)
return 1;
while (len--) {
if (dist <= s->outcnt && s->out[s->outcnt - dist])
s->out[s->outcnt] = s->out[s->outcnt - dist];
s->outcnt++;
}
}
} while (symbol != 256);
return 0;
}
static int puff_fixed(struct puff_state* s)
{
static int virgin = 1;
static short lencnt[MAXBITS + 1], lensym[FIXLCODES];
static short distcnt[MAXBITS + 1], distsym[MAXDCODES];
static struct puff_huffman lencode, distcode;
if (virgin) {
lencode.count = lencnt;
lencode.symbol = lensym;
distcode.count = distcnt;
distcode.symbol = distsym;
short lengths[FIXLCODES];
int symbol;
for (symbol = 0; symbol < 144; symbol++)
lengths[symbol] = 8;
for (; symbol < 256; symbol++)
lengths[symbol] = 9;
for (; symbol < 280; symbol++)
lengths[symbol] = 7;
for (; symbol < FIXLCODES; symbol++)
lengths[symbol] = 8;
puff_construct(&lencode, lengths, FIXLCODES);
for (symbol = 0; symbol < MAXDCODES; symbol++)
lengths[symbol] = 5;
puff_construct(&distcode, lengths, MAXDCODES);
virgin = 0;
}
return puff_codes(s, &lencode, &distcode);
}
static int puff_dynamic(struct puff_state* s)
{
static const short order[19] =
{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
int nlen = puff_bits(s, 5) + 257;
int ndist = puff_bits(s, 5) + 1;
int ncode = puff_bits(s, 4) + 4;
if (nlen > MAXLCODES || ndist > MAXDCODES)
return -3;
short lengths[MAXCODES];
int index;
for (index = 0; index < ncode; index++)
lengths[order[index]] = puff_bits(s, 3);
for (; index < 19; index++)
lengths[order[index]] = 0;
short lencnt[MAXBITS + 1], lensym[MAXLCODES];
struct puff_huffman lencode = {lencnt, lensym};
int err = puff_construct(&lencode, lengths, 19);
if (err != 0)
return -4;
index = 0;
while (index < nlen + ndist) {
int symbol;
int len;
symbol = puff_decode(s, &lencode);
if (symbol < 0)
return symbol;
if (symbol < 16)
lengths[index++] = symbol;
else {
len = 0;
if (symbol == 16) {
if (index == 0)
return -5;
len = lengths[index - 1];
symbol = 3 + puff_bits(s, 2);
} else if (symbol == 17)
symbol = 3 + puff_bits(s, 3);
else
symbol = 11 + puff_bits(s, 7);
if (index + symbol > nlen + ndist)
return -6;
while (symbol--)
lengths[index++] = len;
}
}
if (lengths[256] == 0)
return -9;
err = puff_construct(&lencode, lengths, nlen);
if (err && (err < 0 || nlen != lencode.count[0] + lencode.count[1]))
return -7;
short distcnt[MAXBITS + 1], distsym[MAXDCODES];
struct puff_huffman distcode = {distcnt, distsym};
err = puff_construct(&distcode, lengths + nlen, ndist);
if (err && (err < 0 || ndist != distcode.count[0] + distcode.count[1]))
return -8;
return puff_codes(s, &lencode, &distcode);
}
static int puff(
unsigned char* dest,
unsigned long* destlen,
const unsigned char* source,
unsigned long sourcelen)
{
struct puff_state s = {
.out = dest,
.outlen = *destlen,
.outcnt = 0,
.in = source,
.inlen = sourcelen,
.incnt = 0,
.bitbuf = 0,
.bitcnt = 0,
};
int err;
if (setjmp(s.env) != 0)
err = 2;
else {
int last;
do {
last = puff_bits(&s, 1);
int type = puff_bits(&s, 2);
err = type == 0 ? puff_stored(&s) : (type == 1 ? puff_fixed(&s) : (type == 2 ? puff_dynamic(&s) : -1));
if (err != 0)
break;
} while (!last);
}
*destlen = s.outcnt;
return err;
}
//% END CODE DERIVED FROM puff.{c,h}
#define ZLIB_HEADER_WIDTH 2
static int puff_zlib_to_file(const unsigned char* source, unsigned long sourcelen, int dest_fd)
{
if (sourcelen < ZLIB_HEADER_WIDTH)
return 0;
source += ZLIB_HEADER_WIDTH;
sourcelen -= ZLIB_HEADER_WIDTH;
const unsigned long max_destlen = 132 << 20;
void* ret = mmap(0, max_destlen, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANON, -1, 0);
if (ret == MAP_FAILED)
return -1;
unsigned char* dest = (unsigned char*)ret;
unsigned long destlen = max_destlen;
int err = puff(dest, &destlen, source, sourcelen);
if (err) {
munmap(dest, max_destlen);
errno = -err;
return -1;
}
if (write(dest_fd, dest, destlen) != (ssize_t)destlen) {
munmap(dest, max_destlen);
return -1;
}
return munmap(dest, max_destlen);
}
static int setup_loop_device(unsigned char* data, unsigned long size, const char* loopname, int* loopfd_p)
{
int err = 0, loopfd = -1;
int memfd = syscall(__NR_memfd_create, "syzkaller", 0);
if (memfd == -1) {
err = errno;
goto error;
}
if (puff_zlib_to_file(data, size, memfd)) {
err = errno;
goto error_close_memfd;
}
loopfd = open(loopname, O_RDWR);
if (loopfd == -1) {
err = errno;
goto error_close_memfd;
}
if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
if (errno != EBUSY) {
err = errno;
goto error_close_loop;
}
ioctl(loopfd, LOOP_CLR_FD, 0);
usleep(1000);
if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
err = errno;
goto error_close_loop;
}
}
close(memfd);
*loopfd_p = loopfd;
return 0;
error_close_loop:
close(loopfd);
error_close_memfd:
close(memfd);
error:
errno = err;
return -1;
}
static void reset_loop_device(const char* loopname)
{
int loopfd = open(loopname, O_RDWR);
if (loopfd == -1) {
return;
}
if (ioctl(loopfd, LOOP_CLR_FD, 0)) {
}
close(loopfd);
}
static long syz_mount_image(
volatile long fsarg,
volatile long dir,
volatile long flags,
volatile long optsarg,
volatile long change_dir,
volatile unsigned long size,
volatile long image)
{
unsigned char* data = (unsigned char*)image;
int res = -1, err = 0, need_loop_device = !!size;
char* mount_opts = (char*)optsarg;
char* target = (char*)dir;
char* fs = (char*)fsarg;
char* source = NULL;
char loopname[64];
if (need_loop_device) {
int loopfd;
memset(loopname, 0, sizeof(loopname));
snprintf(loopname, sizeof(loopname), "/dev/loop%llu", procid);
if (setup_loop_device(data, size, loopname, &loopfd) == -1)
return -1;
close(loopfd);
source = loopname;
}
mkdir(target, 0777);
char opts[256];
memset(opts, 0, sizeof(opts));
if (strlen(mount_opts) > (sizeof(opts) - 32)) {
}
strncpy(opts, mount_opts, sizeof(opts) - 32);
if (strcmp(fs, "iso9660") == 0) {
flags |= MS_RDONLY;
} else if (strncmp(fs, "ext", 3) == 0) {
bool has_remount_ro = false;
char* remount_ro_start = strstr(opts, "errors=remount-ro");
if (remount_ro_start != NULL) {
char after = *(remount_ro_start + strlen("errors=remount-ro"));
char before = remount_ro_start == opts ? '\0' : *(remount_ro_start - 1);
has_remount_ro = ((before == '\0' || before == ',') && (after == '\0' || after == ','));
}
if (strstr(opts, "errors=panic") || !has_remount_ro)
strcat(opts, ",errors=continue");
} else if (strcmp(fs, "xfs") == 0) {
strcat(opts, ",nouuid");
} else if (strncmp(fs, "gfs2", 4) == 0 && (strstr(opts, "errors=panic") || strstr(opts, "debug"))) {
strcat(opts, ",errors=withdraw");
}
res = mount(source, target, fs, flags, opts);
if (res == -1) {
err = errno;
goto error_clear_loop;
}
res = open(target, O_RDONLY | O_DIRECTORY);
if (res == -1) {
err = errno;
goto error_clear_loop;
}
if (change_dir) {
res = chdir(target);
if (res == -1) {
err = errno;
}
}
error_clear_loop:
if (need_loop_device)
reset_loop_device(loopname);
errno = err;
return res;
}
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// syz_mount_image$nilfs2 arguments: [
// fs: ptr[in, buffer] {
// buffer: {6e 69 6c 66 73 32 00} (length 0x7)
// }
// dir: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 30 00} (length 0x8)
// }
// flags: mount_flags = 0x90 (8 bytes)
// opts: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// union ANYUNION {
// ANYBLOB: buffer: {00 01 de f4 77 47 74 36 6f 0b 8a 20 db 13 db 64 e8 5f c9 32 2c 3f e0 18 b9 1f f1 29 1b 4f 4c 56 de 7e 45 43 f4 98 18 e1 30 7d 98 d0 9d aa 1e 2a 7d bf 88 00 3e 94 01 dc 73 aa d0 b7 db b5 68 55 65 c7 82 5b a8 34 06 21 fa ea e9 2a be d1 9c 52 4a b0 6c 43 03 25 8d 25 37 22 e1 59 64 2a f4 47 ae b0 96 c6 a2 6d 34 5d 82 f2 92 51 63 33 1b 0e 91 57 44 1a 9c 61 dd 10 51 d3 b9 70 f9 ac 12 f5 97 5c f1 ad 4e 45 ac ef 1a 54 92 1c 49 2a 77 bc b1 85 8b 68 75 8e d3 39 60 8b 8e 43 c7 33 21 9f 1f 9e 0b 86 78 40 f8 21 e0 3b c0 e8 a4 97 c4 d5 dd e4 36 00 00 90 a3 97 63 7d ed b2 f3} (length 0xbd)
// }
// }
// }
// chdir: int8 = 0x1 (1 bytes)
// size: len = 0xd99 (8 bytes)
// img: ptr[in, buffer] {
// buffer: (compressed buffer with length 0xd99)
// }
// ]
// returns fd_dir
memcpy((void*)0x200000000dc0, "nilfs2\000", 7);
memcpy((void*)0x200000000400, "./file0\000", 8);
memcpy((void*)0x200000003280, "... [truncated large byte array] ...", 189);
memcpy((void*)0x200000006900, "... [truncated large byte array] ...", 3481);
syz_mount_image(/*fs=*/0x200000000dc0, /*dir=*/0x200000000400, /*flags=MS_SYNCHRONOUS|MS_DIRSYNC*/0x90, /*opts=*/0x200000003280, /*chdir=*/1, /*size=*/0xd99, /*img=*/0x200000006900);
// openat arguments: [
// fd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 00} (length 0x2)
// }
// flags: open_flags = 0x0 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x200000000240, ".\000", 2);
res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x200000000240ul, /*flags=*/0, /*mode=*/0);
if (res != -1)
r[0] = res;
// ioctl$NILFS_IOCTL_CLEAN_SEGMENTS arguments: [
// fd: fd (resource)
// cmd: const = 0x40786e88 (4 bytes)
// arg: ptr[in, nilfs_ioctl_clean_segments_args] {
// nilfs_ioctl_clean_segments_args {
// argv0: nilfs_argv_typed[nilfs_vdesc, in, NILFS_VDESC_SIZE] {
// v_base: nil
// v_nmembs: len = 0x0 (4 bytes)
// v_size: const = 0x40 (2 bytes)
// v_flags: int16 = 0xb (2 bytes)
// v_index: int64 = 0x430 (8 bytes)
// }
// argv1: nilfs_argv_typed[nilfs_period, in, NILFS_PERIOD_SIZE] {
// v_base: nil
// v_nmembs: len = 0x0 (4 bytes)
// v_size: const = 0x10 (2 bytes)
// v_flags: int16 = 0x20c (2 bytes)
// v_index: int64 = 0x47 (8 bytes)
// }
// argv2: nilfs_argv_typed[int64, in, 8] {
// v_base: nil
// v_nmembs: len = 0x0 (4 bytes)
// v_size: const = 0x8 (2 bytes)
// v_flags: int16 = 0x1 (2 bytes)
// v_index: int64 = 0x10000000004 (8 bytes)
// }
// argv3: nilfs_argv_typed[nilfs_bdesc, in, NILFS_BDESC_SIZE] {
// v_base: nil
// v_nmembs: len = 0x0 (4 bytes)
// v_size: const = 0x28 (2 bytes)
// v_flags: int16 = 0xfffe (2 bytes)
// v_index: int64 = 0x1000000000000101 (8 bytes)
// }
// argv4: nilfs_argv_typed[int64, in, 8] {
// v_base: ptr[in, array[int64]] {
// array[int64] {
// int64 = 0x20000000000009 (8 bytes)
// }
// }
// v_nmembs: len = 0x1 (4 bytes)
// v_size: const = 0x8 (2 bytes)
// v_flags: int16 = 0x98f (2 bytes)
// v_index: int64 = 0xffff (8 bytes)
// }
// }
// }
// ]
*(uint64_t*)0x200000000640 = 0;
*(uint32_t*)0x200000000648 = 0;
*(uint16_t*)0x20000000064c = 0x40;
*(uint16_t*)0x20000000064e = 0xb;
*(uint64_t*)0x200000000650 = 0x430;
*(uint64_t*)0x200000000658 = 0;
*(uint32_t*)0x200000000660 = 0;
*(uint16_t*)0x200000000664 = 0x10;
*(uint16_t*)0x200000000666 = 0x20c;
*(uint64_t*)0x200000000668 = 0x47;
*(uint64_t*)0x200000000670 = 0;
*(uint32_t*)0x200000000678 = 0;
*(uint16_t*)0x20000000067c = 8;
*(uint16_t*)0x20000000067e = 1;
*(uint64_t*)0x200000000680 = 0x10000000004;
*(uint64_t*)0x200000000688 = 0;
*(uint32_t*)0x200000000690 = 0;
*(uint16_t*)0x200000000694 = 0x28;
*(uint16_t*)0x200000000696 = 0xfffe;
*(uint64_t*)0x200000000698 = 0x1000000000000101;
*(uint64_t*)0x2000000006a0 = 0x2000000003c0;
*(uint64_t*)0x2000000003c0 = 0x20000000000009;
*(uint32_t*)0x2000000006a8 = 1;
*(uint16_t*)0x2000000006ac = 8;
*(uint16_t*)0x2000000006ae = 0x98f;
*(uint64_t*)0x2000000006b0 = 0xffff;
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0x40786e88, /*arg=*/0x200000000640ul);
// fchmodat arguments: [
// dirfd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 30 00} (length 0x8)
// }
// mode: open_mode = 0x17f (8 bytes)
// ]
memcpy((void*)0x200000000300, "./file0\000", 8);
syscall(__NR_fchmodat, /*dirfd=*/0xffffff9c, /*file=*/0x200000000300ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|0x100*/0x17ful);
return 0;
}
]
|
| 2/1 |
2026/05/25 04:29 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/316e237849c78635c7c5ae4b5398d0fa5c963d95]
|
| 3/1 |
2026/05/25 04:30 |
action |
kernel-builder |
26m
Results: map[KernelObj:/app/workdir/cache/build/c82a8f7fa3c8ce695be82c740e323952b33935e5]
|
| 4/1 |
2026/05/25 04:57 |
action |
codesearch-prepare |
20m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/05/25 05:18 |
agent |
expert |
2m
Model:
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Instruction:
You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by greeping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption or elevated privileges.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completly wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control tranfers, that's also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitabability depends on how exactly the uninit value
is used in the code, and what it affects.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidetial Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Don't make assumptions about the kernel source code (it may be different from what you assume it is).
Extensively use the provided code access tools (codesearch-*, git-*, grepper, etc)
to examine the actual source code, and confirm any assumptions.
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.
Prompt:
The kernel bug report is:
INFO: task syz.0.17:5918 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.17 state:D stack:25832 pid:5918 tgid:5911 ppid:5833 task_flags:0x400040 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5387 [inline]
__schedule+0x17b4/0x5680 kernel/sched/core.c:7188
__schedule_loop kernel/sched/core.c:7267 [inline]
schedule+0x164/0x360 kernel/sched/core.c:7282
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7339
rwsem_down_read_slowpath+0x6d9/0x940 kernel/locking/rwsem.c:1114
__down_read_common kernel/locking/rwsem.c:1291 [inline]
__down_read kernel/locking/rwsem.c:1304 [inline]
down_read+0x99/0x2e0 kernel/locking/rwsem.c:1570
nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221
nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921
notify_change+0xc1a/0xf40 fs/attr.c:556
chmod_common+0x273/0x4a0 fs/open.c:637
do_fchmodat+0x12d/0x230 fs/open.c:682
__do_sys_fchmodat fs/open.c:701 [inline]
__se_sys_fchmodat fs/open.c:698 [inline]
__x64_sys_fchmodat+0x7d/0x90 fs/open.c:698
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc71999cdd9
RSP: 002b:00007fc71a8fe028 EFLAGS: 00000246
ORIG_RAX: 000000000000010c
RAX: ffffffffffffffda RBX: 00007fc719c16090 RCX: 00007fc71999cdd9
RDX: 000000000000017f RSI: 0000200000000300 RDI: ffffffffffffff9c
RBP: 00007fc719a32d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc719c16128 R14: 00007fc719c16090 R15: 00007fffbf6a8c68
</TASK>
Showing all locks held in the system:
1 lock held by khungtaskd/31:
#0: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#0: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
#0: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
2 locks held by getty/5375:
#0: ffff888035c970a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc9000321e2e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x45c/0x13a0 drivers/tty/n_tty.c:2211
2 locks held by syz.0.17/5912:
4 locks held by syz.0.17/5918:
#0: ffff888079e74410 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:493
#1: ffff88805f4f0ec0 (&type->i_mutex_dir_key#8){++++}-{4:4}, at: inode_lock_killable include/linux/fs.h:1034 [inline]
#1: ffff88805f4f0ec0 (&type->i_mutex_dir_key#8){++++}-{4:4}, at: chmod_common+0x191/0x4a0 fs/open.c:629
#2: ffff888079e74600 (sb_internal#2){.+.+}-{0:0}, at: nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921
#3: ffff888078880288 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221
3 locks held by syz.1.18/6027:
4 locks held by syz.1.18/6029:
#0: ffff888076484410 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:493
#1: ffff88805f41ddf8 (&type->i_mutex_dir_key#8){++++}-{4:4}, at: inode_lock_killable include/linux/fs.h:1034 [inline]
#1: ffff88805f41ddf8 (&type->i_mutex_dir_key#8){++++}-{4:4}, at: chmod_common+0x191/0x4a0 fs/open.c:629
#2: ffff888076484600 (sb_internal#2){.+.+}-{0:0}, at: nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921
#3: ffff8880316d2288 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221
2 locks held by syz.2.19/6067:
4 locks held by syz.2.19/6069:
#0:
ffff888032d1a410
(
sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:493
#1: ffff88805f4f3968 (&type->i_mutex_dir_key#8){++++}-{4:4}, at: inode_lock_killable include/linux/fs.h:1034 [inline]
#1: ffff88805f4f3968 (&type->i_mutex_dir_key#8){++++}-{4:4}, at: chmod_common+0x191/0x4a0 fs/open.c:629
#2: ffff888032d1a600 (sb_internal#2
){.+.+}-{0:0}
, at: nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921
#3:
ffff888079970288
(
&nilfs->ns_segctor_sem
){++++}-{4:4}
, at: nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221
2 locks held by syz.3.20/6113:
4 locks held by syz.3.20/6115:
#0:
ffff88802539c410
(
sb_writers
#12
){.+.+}-{0:0}
, at: mnt_want_write+0x41/0x90 fs/namespace.c:493
#1:
ffff88806f1d0290
(
&type->i_mutex_dir_key
#8
){++++}-{4:4}
, at: inode_lock_killable include/linux/fs.h:1034 [inline]
, at: chmod_common+0x191/0x4a0 fs/open.c:629
#2:
ffff88802539c600
(sb_internal#2){.+.+}-{0:0}, at: nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921
#3:
ffff88802512c288
(
&nilfs->ns_segctor_sem
){++++}-{4:4}, at: nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221
7 locks held by syz.4.21/6161:
4 locks held by syz.4.21/6163:
#0: ffff888067cac410
(sb_writers
#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:493
#1: ffff88806f1d5df8
(&type->i_mutex_dir_key
#8
){++++}-{4:4}
, at: inode_lock_killable include/linux/fs.h:1034 [inline]
, at: chmod_common+0x191/0x4a0 fs/open.c:629
#2:
ffff888067cac600
(
sb_internal
#2){.+.+}-{0:0}, at: nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921
#3:
ffff888076c65288
(
&nilfs->ns_segctor_sem
){++++}-{4:4}
, at: nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221
2 locks held by syz.5.22/6208:
4 locks held by syz.5.22/6210:
#0:
ffff88807c43a410
(
sb_writers
#12
){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:493
#1: ffff88806f01a720 (&type->i_mutex_dir_key#8
){++++}-{4:4}
, at: inode_lock_killable include/linux/fs.h:1034 [inline]
, at: chmod_common+0x191/0x4a0 fs/open.c:629
#2:
ffff88807c43a600
(
sb_internal
#2
){.+.+}-{0:0}
, at: nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921
#3: ffff88802990c288 (
&nilfs->ns_segctor_sem
){++++}-{4:4}
, at: nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221
3 locks held by syz.6.23/6263:
4 locks held by syz.6.23/6265:
#0:
ffff88802ba72410
(
sb_writers
#12
){.+.+}-{0:0}
, at: mnt_want_write+0x41/0x90 fs/namespace.c:493
#1:
ffff88806f01a108 (&type->i_mutex_dir_key#8){++++}-{4:4}, at: inode_lock_killable include/linux/fs.h:1034 [inline]
ffff88806f01a108 (&type->i_mutex_dir_key#8){++++}-{4:4}, at: chmod_common+0x191/0x4a0 fs/open.c:629
#2: ffff88802ba72600 (sb_internal#2){.+.+}-{0:0}, at: nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921
#3: ffff88802877f288 (&nilfs->ns_segctor_sem){++++}-{4:4}, at: nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221
1 lock held by modprobe/6273:
=============================================
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
__sys_info lib/sys_info.c:157 [inline]
sys_info+0x135/0x170 lib/sys_info.c:165
check_hung_uninterruptible_tasks kernel/hung_task.c:353 [inline]
watchdog+0xfd3/0x1030 kernel/hung_task.c:561
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 6113 Comm: syz.3.20 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:srso_alias_safe_ret+0x0/0x7 arch/x86/lib/retpoline.S:210
Code: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc <48> 8d 64 24 08 c3 cc e8 f4 ff ff ff 0f 0b cc cc cc cc cc cc cc cc
RSP: 0018:ffffc900000075d8 EFLAGS: 00000292
RAX: 0000000091643301 RBX: ffffc900000076a0 RCX: 0000000000000102
RDX: 0000000000000007 RSI: ffffffff8e216b62 RDI: ffff88802e838000
RBP: ffffc90000007670 R08: ffffc90000007d98 R09: ffffc90000007638
R10: dffffc0000000000 R11: fffff52000000ec9 R12: ffff88802e838000
R13: 00000000000000f0 R14: ffffffff81b0d880 R15: ffffc900000075e8
FS: 00007faaf1ac36c0(0000) GS:ffff888125295000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7ac9347e20 CR3: 0000000077017000 CR4: 0000000000350ef0
Call Trace:
<IRQ>
srso_alias_return_thunk+0x5/0xfbef5 arch/x86/lib/retpoline.S:220
arch_stack_walk+0x11b/0x150 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0xa9/0x100 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
unpoison_slab_object mm/kasan/common.c:340 [inline]
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4569 [inline]
slab_alloc_node mm/slub.c:4898 [inline]
kmem_cache_alloc_node_noprof+0x384/0x690 mm/slub.c:4950
__alloc_skb+0x1d0/0x7d0 net/core/skbuff.c:702
skb_copy+0x188/0x800 net/core/skbuff.c:2182
mac80211_hwsim_tx_frame_no_nl+0xe82/0x1650 drivers/net/wireless/virtual/mac80211_hwsim.c:1991
mac80211_hwsim_tx_frame+0x1b5/0x200 drivers/net/wireless/virtual/mac80211_hwsim.c:2400
mac80211_hwsim_beacon_tx+0x3e8/0x870 drivers/net/wireless/virtual/mac80211_hwsim.c:2501
__iterate_interfaces+0x2ab/0x590 net/mac80211/util.c:772
ieee80211_iterate_active_interfaces_atomic+0xdb/0x180 net/mac80211/util.c:808
mac80211_hwsim_beacon+0xbb/0x180 drivers/net/wireless/virtual/mac80211_hwsim.c:2531
__run_hrtimer kernel/time/hrtimer.c:1930 [inline]
__hrtimer_run_queues+0x3c0/0xa20 kernel/time/hrtimer.c:1994
hrtimer_run_softirq+0x17a/0x240 kernel/time/hrtimer.c:2011
handle_softirqs+0x22a/0x840 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0xca/0x220 kernel/softirq.c:735
irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1061
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:console_flush_one_record arch/x86/include/asm/irqflags.h:-1 [inline]
RIP: 0010:console_flush_all+0x801/0xb20 kernel/printk/printk.c:3343
Code: ff ff e8 42 e1 20 00 90 0f 0b 90 e9 85 fc ff ff e8 34 e1 20 00 e8 9f f2 02 0a 48 85 db 74 c0 e8 25 e1 20 00 fb 48 8b 5c 24 08 <48> 8b 44 24 20 42 80 3c 20 00 4c 8b 74 24 18 74 08 4c 89 f7 e8 f6
RSP: 0018:ffffc90003236c40 EFLAGS: 00000293
RAX: ffffffff81a4c28b RBX: ffffc90003236da0 RCX: ffff88802e838000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90003236d50 R08: ffffffff903096f7 R09: 1ffffffff20612de
R10: dffffc0000000000 R11: fffffbfff20612df R12: dffffc0000000000
R13: 0000000000000001 R14: 0000000000000000 R15: ffffffff8f2195a0
__console_flush_and_unlock kernel/printk/printk.c:3373 [inline]
console_unlock+0xd1/0x1c0 kernel/printk/printk.c:3413
vprintk_emit+0x485/0x560 kernel/printk/printk.c:2479
_printk+0xdd/0x130 kernel/printk/printk.c:2504
__nilfs_msg+0x373/0x450 fs/nilfs2/super.c:78
nilfs_sufile_updatev+0x21c/0x6d0 fs/nilfs2/sufile.c:186
nilfs_sufile_freev fs/nilfs2/sufile.h:93 [inline]
nilfs_free_segments fs/nilfs2/segment.c:1140 [inline]
nilfs_segctor_collect_blocks fs/nilfs2/segment.c:1261 [inline]
nilfs_segctor_collect fs/nilfs2/segment.c:1547 [inline]
nilfs_segctor_do_construct+0x1f55/0x76c0 fs/nilfs2/segment.c:2122
nilfs_segctor_construct+0x17b/0x690 fs/nilfs2/segment.c:2462
nilfs_clean_segments+0x3bd/0xa50 fs/nilfs2/segment.c:2536
nilfs_ioctl_clean_segments fs/nilfs2/ioctl.c:922 [inline]
nilfs_ioctl+0x261f/0x2780 fs/nilfs2/ioctl.c:1352
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+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7faaf0b9cdd9
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:00007faaf1ac3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007faaf0e15fa0 RCX: 00007faaf0b9cdd9
RDX: 0000200000000640 RSI: 0000000040786e88 RDI: 0000000000000004
RBP: 00007faaf0c32d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007faaf0e16038 R14: 00007faaf0e15fa0 R15: 00007ffe90caddb8
</TASK>
It is reproducible with the followint program.
Keep in mind that it may lack the precise threading, sandboxing, and some arguments of a working reproducer.
But it should give an idea of the involved syscalls.
// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <setjmp.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <linux/loop.h>
#ifndef __NR_memfd_create
#define __NR_memfd_create 319
#endif
static unsigned long long procid;
//% This code is derived from puff.{c,h}, found in the zlib development. The
//% original files come with the following copyright notice:
//% Copyright (C) 2002-2013 Mark Adler, all rights reserved
//% version 2.3, 21 Jan 2013
//% This software is provided 'as-is', without any express or implied
//% warranty. In no event will the author be held liable for any damages
//% arising from the use of this software.
//% Permission is granted to anyone to use this software for any purpose,
//% including commercial applications, and to alter it and redistribute it
//% freely, subject to the following restrictions:
//% 1. The origin of this software must not be misrepresented; you must not
//% claim that you wrote the original software. If you use this software
//% in a product, an acknowledgment in the product documentation would be
//% appreciated but is not required.
//% 2. Altered source versions must be plainly marked as such, and must not be
//% misrepresented as being the original software.
//% 3. This notice may not be removed or altered from any source distribution.
//% Mark Adler madler@alumni.caltech.edu
//% BEGIN CODE DERIVED FROM puff.{c,h}
#define MAXBITS 15
#define MAXLCODES 286
#define MAXDCODES 30
#define MAXCODES (MAXLCODES + MAXDCODES)
#define FIXLCODES 288
struct puff_state {
unsigned char* out;
unsigned long outlen;
unsigned long outcnt;
const unsigned char* in;
unsigned long inlen;
unsigned long incnt;
int bitbuf;
int bitcnt;
jmp_buf env;
};
static int puff_bits(struct puff_state* s, int need)
{
long val = s->bitbuf;
while (s->bitcnt < need) {
if (s->incnt == s->inlen)
longjmp(s->env, 1);
val |= (long)(s->in[s->incnt++]) << s->bitcnt;
s->bitcnt += 8;
}
s->bitbuf = (int)(val >> need);
s->bitcnt -= need;
return (int)(val & ((1L << need) - 1));
}
static int puff_stored(struct puff_state* s)
{
s->bitbuf = 0;
s->bitcnt = 0;
if (s->incnt + 4 > s->inlen)
return 2;
unsigned len = s->in[s->incnt++];
len |= s->in[s->incnt++] << 8;
if (s->in[s->incnt++] != (~len & 0xff) ||
s->in[s->incnt++] != ((~len >> 8) & 0xff))
return -2;
if (s->incnt + len > s->inlen)
return 2;
if (s->outcnt + len > s->outlen)
return 1;
for (; len--; s->outcnt++, s->incnt++) {
if (s->in[s->incnt])
s->out[s->outcnt] = s->in[s->incnt];
}
return 0;
}
struct puff_huffman {
short* count;
short* symbol;
};
static int puff_decode(struct puff_state* s, const struct puff_huffman* h)
{
int first = 0;
int index = 0;
int bitbuf = s->bitbuf;
int left = s->bitcnt;
int code = first = index = 0;
int len = 1;
short* next = h->count + 1;
while (1) {
while (left--) {
code |= bitbuf & 1;
bitbuf >>= 1;
int count = *next++;
if (code - count < first) {
s->bitbuf = bitbuf;
s->bitcnt = (s->bitcnt - len) & 7;
return h->symbol[index + (code - first)];
}
index += count;
first += count;
first <<= 1;
code <<= 1;
len++;
}
left = (MAXBITS + 1) - len;
if (left == 0)
break;
if (s->incnt == s->inlen)
longjmp(s->env, 1);
bitbuf = s->in[s->incnt++];
if (left > 8)
left = 8;
}
return -10;
}
static int puff_construct(struct puff_huffman* h, const short* length, int n)
{
int len;
for (len = 0; len <= MAXBITS; len++)
h->count[len] = 0;
int symbol;
for (symbol = 0; symbol < n; symbol++)
(h->count[length[symbol]])++;
if (h->count[0] == n)
return 0;
int left = 1;
for (len = 1; len <= MAXBITS; len++) {
left <<= 1;
left -= h->count[len];
if (left < 0)
return left;
}
short offs[MAXBITS + 1];
offs[1] = 0;
for (len = 1; len < MAXBITS; len++)
offs[len + 1] = offs[len] + h->count[len];
for (symbol = 0; symbol < n; symbol++)
if (length[symbol] != 0)
h->symbol[offs[length[symbol]]++] = symbol;
return left;
}
static int puff_codes(struct puff_state* s,
const struct puff_huffman* lencode,
const struct puff_huffman* distcode)
{
static const short lens[29] = {
3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31,
35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258};
static const short lext[29] = {
0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0};
static const short dists[30] = {
1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
8193, 12289, 16385, 24577};
static const short dext[30] = {
0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6,
7, 7, 8, 8, 9, 9, 10, 10, 11, 11,
12, 12, 13, 13};
int symbol;
do {
symbol = puff_decode(s, lencode);
if (symbol < 0)
return symbol;
if (symbol < 256) {
if (s->outcnt == s->outlen)
return 1;
if (symbol)
s->out[s->outcnt] = symbol;
s->outcnt++;
} else if (symbol > 256) {
symbol -= 257;
if (symbol >= 29)
return -10;
int len = lens[symbol] + puff_bits(s, lext[symbol]);
symbol = puff_decode(s, distcode);
if (symbol < 0)
return symbol;
unsigned dist = dists[symbol] + puff_bits(s, dext[symbol]);
if (dist > s->outcnt)
return -11;
if (s->outcnt + len > s->outlen)
return 1;
while (len--) {
if (dist <= s->outcnt && s->out[s->outcnt - dist])
s->out[s->outcnt] = s->out[s->outcnt - dist];
s->outcnt++;
}
}
} while (symbol != 256);
return 0;
}
static int puff_fixed(struct puff_state* s)
{
static int virgin = 1;
static short lencnt[MAXBITS + 1], lensym[FIXLCODES];
static short distcnt[MAXBITS + 1], distsym[MAXDCODES];
static struct puff_huffman lencode, distcode;
if (virgin) {
lencode.count = lencnt;
lencode.symbol = lensym;
distcode.count = distcnt;
distcode.symbol = distsym;
short lengths[FIXLCODES];
int symbol;
for (symbol = 0; symbol < 144; symbol++)
lengths[symbol] = 8;
for (; symbol < 256; symbol++)
lengths[symbol] = 9;
for (; symbol < 280; symbol++)
lengths[symbol] = 7;
for (; symbol < FIXLCODES; symbol++)
lengths[symbol] = 8;
puff_construct(&lencode, lengths, FIXLCODES);
for (symbol = 0; symbol < MAXDCODES; symbol++)
lengths[symbol] = 5;
puff_construct(&distcode, lengths, MAXDCODES);
virgin = 0;
}
return puff_codes(s, &lencode, &distcode);
}
static int puff_dynamic(struct puff_state* s)
{
static const short order[19] =
{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
int nlen = puff_bits(s, 5) + 257;
int ndist = puff_bits(s, 5) + 1;
int ncode = puff_bits(s, 4) + 4;
if (nlen > MAXLCODES || ndist > MAXDCODES)
return -3;
short lengths[MAXCODES];
int index;
for (index = 0; index < ncode; index++)
lengths[order[index]] = puff_bits(s, 3);
for (; index < 19; index++)
lengths[order[index]] = 0;
short lencnt[MAXBITS + 1], lensym[MAXLCODES];
struct puff_huffman lencode = {lencnt, lensym};
int err = puff_construct(&lencode, lengths, 19);
if (err != 0)
return -4;
index = 0;
while (index < nlen + ndist) {
int symbol;
int len;
symbol = puff_decode(s, &lencode);
if (symbol < 0)
return symbol;
if (symbol < 16)
lengths[index++] = symbol;
else {
len = 0;
if (symbol == 16) {
if (index == 0)
return -5;
len = lengths[index - 1];
symbol = 3 + puff_bits(s, 2);
} else if (symbol == 17)
symbol = 3 + puff_bits(s, 3);
else
symbol = 11 + puff_bits(s, 7);
if (index + symbol > nlen + ndist)
return -6;
while (symbol--)
lengths[index++] = len;
}
}
if (lengths[256] == 0)
return -9;
err = puff_construct(&lencode, lengths, nlen);
if (err && (err < 0 || nlen != lencode.count[0] + lencode.count[1]))
return -7;
short distcnt[MAXBITS + 1], distsym[MAXDCODES];
struct puff_huffman distcode = {distcnt, distsym};
err = puff_construct(&distcode, lengths + nlen, ndist);
if (err && (err < 0 || ndist != distcode.count[0] + distcode.count[1]))
return -8;
return puff_codes(s, &lencode, &distcode);
}
static int puff(
unsigned char* dest,
unsigned long* destlen,
const unsigned char* source,
unsigned long sourcelen)
{
struct puff_state s = {
.out = dest,
.outlen = *destlen,
.outcnt = 0,
.in = source,
.inlen = sourcelen,
.incnt = 0,
.bitbuf = 0,
.bitcnt = 0,
};
int err;
if (setjmp(s.env) != 0)
err = 2;
else {
int last;
do {
last = puff_bits(&s, 1);
int type = puff_bits(&s, 2);
err = type == 0 ? puff_stored(&s) : (type == 1 ? puff_fixed(&s) : (type == 2 ? puff_dynamic(&s) : -1));
if (err != 0)
break;
} while (!last);
}
*destlen = s.outcnt;
return err;
}
//% END CODE DERIVED FROM puff.{c,h}
#define ZLIB_HEADER_WIDTH 2
static int puff_zlib_to_file(const unsigned char* source, unsigned long sourcelen, int dest_fd)
{
if (sourcelen < ZLIB_HEADER_WIDTH)
return 0;
source += ZLIB_HEADER_WIDTH;
sourcelen -= ZLIB_HEADER_WIDTH;
const unsigned long max_destlen = 132 << 20;
void* ret = mmap(0, max_destlen, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANON, -1, 0);
if (ret == MAP_FAILED)
return -1;
unsigned char* dest = (unsigned char*)ret;
unsigned long destlen = max_destlen;
int err = puff(dest, &destlen, source, sourcelen);
if (err) {
munmap(dest, max_destlen);
errno = -err;
return -1;
}
if (write(dest_fd, dest, destlen) != (ssize_t)destlen) {
munmap(dest, max_destlen);
return -1;
}
return munmap(dest, max_destlen);
}
static int setup_loop_device(unsigned char* data, unsigned long size, const char* loopname, int* loopfd_p)
{
int err = 0, loopfd = -1;
int memfd = syscall(__NR_memfd_create, "syzkaller", 0);
if (memfd == -1) {
err = errno;
goto error;
}
if (puff_zlib_to_file(data, size, memfd)) {
err = errno;
goto error_close_memfd;
}
loopfd = open(loopname, O_RDWR);
if (loopfd == -1) {
err = errno;
goto error_close_memfd;
}
if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
if (errno != EBUSY) {
err = errno;
goto error_close_loop;
}
ioctl(loopfd, LOOP_CLR_FD, 0);
usleep(1000);
if (ioctl(loopfd, LOOP_SET_FD, memfd)) {
err = errno;
goto error_close_loop;
}
}
close(memfd);
*loopfd_p = loopfd;
return 0;
error_close_loop:
close(loopfd);
error_close_memfd:
close(memfd);
error:
errno = err;
return -1;
}
static void reset_loop_device(const char* loopname)
{
int loopfd = open(loopname, O_RDWR);
if (loopfd == -1) {
return;
}
if (ioctl(loopfd, LOOP_CLR_FD, 0)) {
}
close(loopfd);
}
static long syz_mount_image(
volatile long fsarg,
volatile long dir,
volatile long flags,
volatile long optsarg,
volatile long change_dir,
volatile unsigned long size,
volatile long image)
{
unsigned char* data = (unsigned char*)image;
int res = -1, err = 0, need_loop_device = !!size;
char* mount_opts = (char*)optsarg;
char* target = (char*)dir;
char* fs = (char*)fsarg;
char* source = NULL;
char loopname[64];
if (need_loop_device) {
int loopfd;
memset(loopname, 0, sizeof(loopname));
snprintf(loopname, sizeof(loopname), "/dev/loop%llu", procid);
if (setup_loop_device(data, size, loopname, &loopfd) == -1)
return -1;
close(loopfd);
source = loopname;
}
mkdir(target, 0777);
char opts[256];
memset(opts, 0, sizeof(opts));
if (strlen(mount_opts) > (sizeof(opts) - 32)) {
}
strncpy(opts, mount_opts, sizeof(opts) - 32);
if (strcmp(fs, "iso9660") == 0) {
flags |= MS_RDONLY;
} else if (strncmp(fs, "ext", 3) == 0) {
bool has_remount_ro = false;
char* remount_ro_start = strstr(opts, "errors=remount-ro");
if (remount_ro_start != NULL) {
char after = *(remount_ro_start + strlen("errors=remount-ro"));
char before = remount_ro_start == opts ? '\0' : *(remount_ro_start - 1);
has_remount_ro = ((before == '\0' || before == ',') && (after == '\0' || after == ','));
}
if (strstr(opts, "errors=panic") || !has_remount_ro)
strcat(opts, ",errors=continue");
} else if (strcmp(fs, "xfs") == 0) {
strcat(opts, ",nouuid");
} else if (strncmp(fs, "gfs2", 4) == 0 && (strstr(opts, "errors=panic") || strstr(opts, "debug"))) {
strcat(opts, ",errors=withdraw");
}
res = mount(source, target, fs, flags, opts);
if (res == -1) {
err = errno;
goto error_clear_loop;
}
res = open(target, O_RDONLY | O_DIRECTORY);
if (res == -1) {
err = errno;
goto error_clear_loop;
}
if (change_dir) {
res = chdir(target);
if (res == -1) {
err = errno;
}
}
error_clear_loop:
if (need_loop_device)
reset_loop_device(loopname);
errno = err;
return res;
}
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// syz_mount_image$nilfs2 arguments: [
// fs: ptr[in, buffer] {
// buffer: {6e 69 6c 66 73 32 00} (length 0x7)
// }
// dir: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 30 00} (length 0x8)
// }
// flags: mount_flags = 0x90 (8 bytes)
// opts: ptr[inout, array[ANYUNION]] {
// array[ANYUNION] {
// union ANYUNION {
// ANYBLOB: buffer: {00 01 de f4 77 47 74 36 6f 0b 8a 20 db 13 db 64 e8 5f c9 32 2c 3f e0 18 b9 1f f1 29 1b 4f 4c 56 de 7e 45 43 f4 98 18 e1 30 7d 98 d0 9d aa 1e 2a 7d bf 88 00 3e 94 01 dc 73 aa d0 b7 db b5 68 55 65 c7 82 5b a8 34 06 21 fa ea e9 2a be d1 9c 52 4a b0 6c 43 03 25 8d 25 37 22 e1 59 64 2a f4 47 ae b0 96 c6 a2 6d 34 5d 82 f2 92 51 63 33 1b 0e 91 57 44 1a 9c 61 dd 10 51 d3 b9 70 f9 ac 12 f5 97 5c f1 ad 4e 45 ac ef 1a 54 92 1c 49 2a 77 bc b1 85 8b 68 75 8e d3 39 60 8b 8e 43 c7 33 21 9f 1f 9e 0b 86 78 40 f8 21 e0 3b c0 e8 a4 97 c4 d5 dd e4 36 00 00 90 a3 97 63 7d ed b2 f3} (length 0xbd)
// }
// }
// }
// chdir: int8 = 0x1 (1 bytes)
// size: len = 0xd99 (8 bytes)
// img: ptr[in, buffer] {
// buffer: (compressed buffer with length 0xd99)
// }
// ]
// returns fd_dir
memcpy((void*)0x200000000dc0, "nilfs2\000", 7);
memcpy((void*)0x200000000400, "./file0\000", 8);
memcpy((void*)0x200000003280, "... [truncated large byte array] ...", 189);
memcpy((void*)0x200000006900, "... [truncated large byte array] ...", 3481);
syz_mount_image(/*fs=*/0x200000000dc0, /*dir=*/0x200000000400, /*flags=MS_SYNCHRONOUS|MS_DIRSYNC*/0x90, /*opts=*/0x200000003280, /*chdir=*/1, /*size=*/0xd99, /*img=*/0x200000006900);
// openat arguments: [
// fd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 00} (length 0x2)
// }
// flags: open_flags = 0x0 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x200000000240, ".\000", 2);
res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x200000000240ul, /*flags=*/0, /*mode=*/0);
if (res != -1)
r[0] = res;
// ioctl$NILFS_IOCTL_CLEAN_SEGMENTS arguments: [
// fd: fd (resource)
// cmd: const = 0x40786e88 (4 bytes)
// arg: ptr[in, nilfs_ioctl_clean_segments_args] {
// nilfs_ioctl_clean_segments_args {
// argv0: nilfs_argv_typed[nilfs_vdesc, in, NILFS_VDESC_SIZE] {
// v_base: nil
// v_nmembs: len = 0x0 (4 bytes)
// v_size: const = 0x40 (2 bytes)
// v_flags: int16 = 0xb (2 bytes)
// v_index: int64 = 0x430 (8 bytes)
// }
// argv1: nilfs_argv_typed[nilfs_period, in, NILFS_PERIOD_SIZE] {
// v_base: nil
// v_nmembs: len = 0x0 (4 bytes)
// v_size: const = 0x10 (2 bytes)
// v_flags: int16 = 0x20c (2 bytes)
// v_index: int64 = 0x47 (8 bytes)
// }
// argv2: nilfs_argv_typed[int64, in, 8] {
// v_base: nil
// v_nmembs: len = 0x0 (4 bytes)
// v_size: const = 0x8 (2 bytes)
// v_flags: int16 = 0x1 (2 bytes)
// v_index: int64 = 0x10000000004 (8 bytes)
// }
// argv3: nilfs_argv_typed[nilfs_bdesc, in, NILFS_BDESC_SIZE] {
// v_base: nil
// v_nmembs: len = 0x0 (4 bytes)
// v_size: const = 0x28 (2 bytes)
// v_flags: int16 = 0xfffe (2 bytes)
// v_index: int64 = 0x1000000000000101 (8 bytes)
// }
// argv4: nilfs_argv_typed[int64, in, 8] {
// v_base: ptr[in, array[int64]] {
// array[int64] {
// int64 = 0x20000000000009 (8 bytes)
// }
// }
// v_nmembs: len = 0x1 (4 bytes)
// v_size: const = 0x8 (2 bytes)
// v_flags: int16 = 0x98f (2 bytes)
// v_index: int64 = 0xffff (8 bytes)
// }
// }
// }
// ]
*(uint64_t*)0x200000000640 = 0;
*(uint32_t*)0x200000000648 = 0;
*(uint16_t*)0x20000000064c = 0x40;
*(uint16_t*)0x20000000064e = 0xb;
*(uint64_t*)0x200000000650 = 0x430;
*(uint64_t*)0x200000000658 = 0;
*(uint32_t*)0x200000000660 = 0;
*(uint16_t*)0x200000000664 = 0x10;
*(uint16_t*)0x200000000666 = 0x20c;
*(uint64_t*)0x200000000668 = 0x47;
*(uint64_t*)0x200000000670 = 0;
*(uint32_t*)0x200000000678 = 0;
*(uint16_t*)0x20000000067c = 8;
*(uint16_t*)0x20000000067e = 1;
*(uint64_t*)0x200000000680 = 0x10000000004;
*(uint64_t*)0x200000000688 = 0;
*(uint32_t*)0x200000000690 = 0;
*(uint16_t*)0x200000000694 = 0x28;
*(uint16_t*)0x200000000696 = 0xfffe;
*(uint64_t*)0x200000000698 = 0x1000000000000101;
*(uint64_t*)0x2000000006a0 = 0x2000000003c0;
*(uint64_t*)0x2000000003c0 = 0x20000000000009;
*(uint32_t*)0x2000000006a8 = 1;
*(uint16_t*)0x2000000006ac = 8;
*(uint16_t*)0x2000000006ae = 0x98f;
*(uint64_t*)0x2000000006b0 = 0xffff;
syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/0x40786e88, /*arg=*/0x200000000640ul);
// fchmodat arguments: [
// dirfd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 2f 66 69 6c 65 30 00} (length 0x8)
// }
// mode: open_mode = 0x17f (8 bytes)
// ]
memcpy((void*)0x200000000300, "./file0\000", 8);
syscall(__NR_fchmodat, /*dirfd=*/0xffffff9c, /*file=*/0x200000000300ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|0x100*/0x17ful);
return 0;
}
Reply: **Analysis of the Bug Report**
The bug report indicates a hung task (`syz.0.17`) blocked in `nilfs_transaction_begin` while waiting for the `nilfs->ns_segctor_sem` semaphore. Another task (`syz.3.20`) is holding this semaphore and is stuck printing a large number of warnings to the console, which is a slow operation and causes the system to hang.
By examining the stack trace and the source code, we can trace the issue to the `NILFS_IOCTL_CLEAN_SEGMENTS` ioctl. This ioctl is used by the `nilfs_cleanerd` garbage collection daemon to clean segments. It takes an array of segment numbers to be freed from user space.
The ioctl eventually calls `nilfs_sufile_updatev()` in `fs/nilfs2/sufile.c`, which contains the following loop:
```c
for (seg = segnumv; seg < segnumv + nsegs; seg++) {
if (unlikely(*seg >= nilfs_sufile_get_nsegments(sufile))) {
nilfs_warn(sufile->i_sb,
"%s: invalid segment number: %llu",
__func__, (unsigned long long)*seg);
nerr++;
}
}
```
If a user provides a very large `nsegs` value and populates the array with invalid segment numbers, the kernel will print a warning for every single invalid segment. Because console output (especially serial console) is extremely slow, printing thousands or millions of warnings will block the task for a long time, triggering the hung task watchdog and causing a Denial of Service (DoS).
**Security Impact Assessment**
While this bug causes a Denial of Service, it is **not a security vulnerability** because it is completely inaccessible to unprivileged users.
Looking at the entry point for the ioctl in `fs/nilfs2/ioctl.c`:
```c
static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
unsigned int cmd, void __user *argp)
{
...
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
...
```
The very first check in the ioctl handler is `capable(CAP_SYS_ADMIN)`. The `capable()` function checks for the capability in the **initial user namespace**. This means that:
1. An unprivileged user cannot trigger this bug.
2. An unprivileged user inside a new user namespace (where they might have `CAP_SYS_ADMIN` relative to that namespace) also cannot trigger this bug, because `capable()` strictly checks the initial namespace (unlike `ns_capable()`).
Furthermore:
* **Exploitable:** No. This is not a memory corruption issue; it is merely a slow path causing a hung task.
* **Malicious Filesystem Trigger:** No. The bug is triggered by the ioctl arguments provided by the user-space process, not by the kernel parsing malicious filesystem metadata during mount or normal operations.
In conclusion, this is a root-only Denial of Service bug and does not cross any privilege boundaries.
|
| 6/2 |
2026/05/25 05:18 |
llm |
expert |
0m
Model:
Tokens:
input: 21763
output: 49
thoughts: 754
Thoughts: **Analyzing a Nilfs2 Hang**
Okay, I'm looking at a hang in the `nilfs2` filesystem. The task `syz.0.17` is stuck in `nilfs_transaction_begin`, specifically waiting on the `nilfs->ns_segctor_sem` semaphore. I'm familiar with this semaphore; it's central to segment construction and cleaning.
Meanwhile, task `syz.3.20` is actively executing `nilfs_ioctl_clean_segments`. My initial thought is that `nilfs_clean_segments`, which calls `nilfs_segctor_do_construct` and ultimately uses the semaphore, might be holding `ns_segctor_sem` for write access. The stack traces seem to confirm this suspicion, as `nilfs_clean_segments` is the one calling the IOCTL. Furthermore, the stack traces indicate a lot of print statements going on within `nilfs_clean_segments`, it is possibly in an infinite loop while printing messages.
Given this, I need to understand what's happening within `nilfs_sufile_updatev` and `nilfs_sufile_freev` because these seem to be involved in the `nilfs_clean_segments` path and the likely cause of the hang. They could be the source of the deadlock, perhaps by calling an operation that conflicts with segment construction or is causing the printing loop. Time to dive into those functions and see what's going on with the super usage file.
|
| 7/2 |
2026/05/25 05:18 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/sufile.c IncludeLines:true Name:nilfs_sufile_updatev]
Results: map[SourceCode: 144: /**
145: * nilfs_sufile_updatev - modify multiple segment usages at a time
146: * @sufile: inode of segment usage file
147: * @segnumv: array of segment numbers
148: * @nsegs: size of @segnumv array
149: * @create: creation flag
150: * @ndone: place to store number of modified segments on @segnumv
151: * @dofunc: primitive operation for the update
152: *
153: * Description: nilfs_sufile_updatev() repeatedly calls @dofunc
154: * against the given array of segments. The @dofunc is called with
155: * buffers of a header block and the sufile block in which the target
156: * segment usage entry is contained. If @ndone is given, the number
157: * of successfully modified segments from the head is stored in the
158: * place @ndone points to.
159: *
160: * Return: 0 on success, or one of the following negative error codes on
161: * failure:
162: * * %-EINVAL - Invalid segment usage number
163: * * %-EIO - I/O error (including metadata corruption).
164: * * %-ENOENT - Given segment usage is in hole block (may be returned if
165: * @create is zero)
166: * * %-ENOMEM - Insufficient memory available.
167: */
168: int nilfs_sufile_updatev(struct inode *sufile, __u64 *segnumv, size_t nsegs,
169: int create, size_t *ndone,
170: void (*dofunc)(struct inode *, __u64,
171: struct buffer_head *,
172: struct buffer_head *))
173: {
174: struct buffer_head *header_bh, *bh;
175: unsigned long blkoff, prev_blkoff;
176: __u64 *seg;
177: size_t nerr = 0, n = 0;
178: int ret = 0;
179:
180: if (unlikely(nsegs == 0))
181: goto out;
182:
183: down_write(&NILFS_MDT(sufile)->mi_sem);
184: for (seg = segnumv; seg < segnumv + nsegs; seg++) {
185: if (unlikely(*seg >= nilfs_sufile_get_nsegments(sufile))) {
186: nilfs_warn(sufile->i_sb,
187: "%s: invalid segment number: %llu",
188: __func__, (unsigned long long)*seg);
189: nerr++;
190: }
191: }
192: if (nerr > 0) {
193: ret = -EINVAL;
194: goto out_sem;
195: }
196:
197: ret = nilfs_sufile_get_header_block(sufile, &header_bh);
198: if (ret < 0)
199: goto out_sem;
200:
201: seg = segnumv;
202: blkoff = nilfs_sufile_get_blkoff(sufile, *seg);
203: ret = nilfs_mdt_get_block(sufile, blkoff, create, NULL, &bh);
204: if (ret < 0)
205: goto out_header;
206:
207: for (;;) {
208: dofunc(sufile, *seg, header_bh, bh);
209:
210: if (++seg >= segnumv + nsegs)
211: break;
212: prev_blkoff = blkoff;
213: blkoff = nilfs_sufile_get_blkoff(sufile, *seg);
214: if (blkoff == prev_blkoff)
215: continue;
216:
217: /* get different block */
218: brelse(bh);
219: ret = nilfs_mdt_get_block(sufile, blkoff, create, NULL, &bh);
220: if (unlikely(ret < 0))
221: goto out_header;
222: }
223: brelse(bh);
224:
225: out_header:
226: n = seg - segnumv;
227: brelse(header_bh);
228: out_sem:
229: up_write(&NILFS_MDT(sufile)->mi_sem);
230: out:
231: if (ndone)
232: *ndone = n;
233: return ret;
234: }
SourceFile:fs/nilfs2/sufile.c]
|
| 8/2 |
2026/05/25 05:18 |
llm |
expert |
0m
Model:
Tokens:
input: 24389
output: 49
thoughts: 217
Thoughts: **Analyzing a Potential Performance Bottleneck**
Okay, so I'm looking at this snippet of code, specifically the `nilfs_warn` on line 186. It's inside a loop that iterates through an array of segment numbers, `segnumv`, with `nsegs` indicating the number of elements in the array. My immediate concern is the potential for a flood of warnings.
If `nsegs` is very large, and, critically, if *many* of the segment numbers are invalid (i.e., greater or equal to `nilfs_sufile_get_nsegments(sufile)`), then `nilfs_warn` will get called *a lot*. And that's where things get dicey. I know from experience that console printing, particularly over a serial connection, is surprisingly slow. A thousand or more warnings can take an unacceptably long time, effectively stalling the task and giving the user a false impression of a system hang. That's unacceptable.
Therefore, I need to understand where `nsegs` and `segnumv` are coming from. The comments point me to `nilfs_sufile_freev` as the caller, which Iβll need to investigate further to understand the circumstances under which this loop is executed and how `nsegs` is derived. This seems like a potential hotspot. I need to figure out the likely magnitude of `nsegs` under normal and problematic conditions and see if this warning flood is really a concern, or if there are other mitigation strategies.
|
| 9/2 |
2026/05/25 05:18 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/sufile.h IncludeLines:true Name:nilfs_sufile_freev]
Results: map[SourceCode: 81: /**
82: * nilfs_sufile_freev - free segments
83: * @sufile: inode of segment usage file
84: * @segnumv: array of segment numbers
85: * @nsegs: size of @segnumv array
86: * @ndone: place to store the number of freed segments
87: *
88: * Return: 0 on success, or a negative error code on failure.
89: */
90: static inline int nilfs_sufile_freev(struct inode *sufile, __u64 *segnumv,
91: size_t nsegs, size_t *ndone)
92: {
93: return nilfs_sufile_updatev(sufile, segnumv, nsegs, 0, ndone,
94: nilfs_sufile_do_free);
95: }
SourceFile:fs/nilfs2/sufile.h]
|
| 10/2 |
2026/05/25 05:18 |
llm |
expert |
0m
Model:
Tokens:
input: 25269
output: 44
thoughts: 11
Thoughts: Okay, here's my interpretation of what's going on, summarized from the perspective of someone deeply familiar with filesystem internals, specifically concerning the `nilfs_free_segments` function:
**Analyzing the `nilfs_free_segments` Caller**
So, I'm looking at the caller to `nilfs_free_segments`. Based on context, it must be some kind of operation that's freeing up disk space in a NILFS2 filesystem. "Freeing segments" immediately flags a focus on how the log-structured nature is managed. This function is *critical* because it directly influences garbage collection, how we reclaim old data, and keep the disk from filling up completely with stale versions of data. I'll need to know whether the caller is related to a file delete, a filesystem sync, a checkpoint creation or a recovery. The caller's context will be key to understanding the intent of *why* we're freeing these segments right now. What triggers this specific call is of utmost importance. Is it driven by some high-level user action, or more a low-level internal housekeeping?
|
| 11/2 |
2026/05/25 05:18 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/segment.c IncludeLines:true Name:nilfs_free_segments]
Results: map[SourceCode:1109: /**
1110: * nilfs_free_segments - free the segments given by an array of segment numbers
1111: * @nilfs: nilfs object
1112: * @segnumv: array of segment numbers to be freed
1113: * @nsegs: number of segments to be freed in @segnumv
1114: *
1115: * nilfs_free_segments() wraps nilfs_sufile_freev() and
1116: * nilfs_sufile_cancel_freev(), and edits the segment usage metadata file
1117: * (sufile) to free all segments given by @segnumv and @nsegs at once. If
1118: * it fails midway, it cancels the changes so that none of the segments are
1119: * freed. If @nsegs is 0, this function does nothing.
1120: *
1121: * The freeing of segments is not finalized until the writing of a log with
1122: * a super root block containing this sufile change is complete, and it can
1123: * be canceled with nilfs_sufile_cancel_freev() until then.
1124: *
1125: * Return: 0 on success, or one of the following negative error codes on
1126: * failure:
1127: * * %-EINVAL - Invalid segment number.
1128: * * %-EIO - I/O error (including metadata corruption).
1129: * * %-ENOMEM - Insufficient memory available.
1130: */
1131: static int nilfs_free_segments(struct the_nilfs *nilfs, __u64 *segnumv,
1132: size_t nsegs)
1133: {
1134: size_t ndone;
1135: int ret;
1136:
1137: if (!nsegs)
1138: return 0;
1139:
1140: ret = nilfs_sufile_freev(nilfs->ns_sufile, segnumv, nsegs, &ndone);
1141: if (unlikely(ret)) {
1142: nilfs_sufile_cancel_freev(nilfs->ns_sufile, segnumv, ndone,
1143: NULL);
1144: /*
1145: * If a segment usage of the segments to be freed is in a
1146: * hole block, nilfs_sufile_freev() will return -ENOENT.
1147: * In this case, -EINVAL should be returned to the caller
1148: * since there is something wrong with the given segment
1149: * number array. This error can only occur during GC, so
1150: * there is no need to worry about it propagating to other
1151: * callers (such as fsync).
1152: */
1153: if (ret == -ENOENT) {
1154: nilfs_err(nilfs->ns_sb,
1155: "The segment usage entry %llu to be freed is invalid (in a hole)",
1156: (unsigned long long)segnumv[ndone]);
1157: ret = -EINVAL;
1158: }
1159: }
1160: return ret;
1161: }
SourceFile:fs/nilfs2/segment.c]
|
| 12/2 |
2026/05/25 05:18 |
llm |
expert |
0m
Model:
Tokens:
input: 26517
output: 47
thoughts: 14
Thoughts: Okay, here's my interpretation of that.
**Analyzing `nilfs_segctor_collect_blocks`**
Alright, so the caller we're looking at is `nilfs_segctor_collect_blocks`. That immediately tells me we're deep within the NILFS file system's segmentation construction process. This function's name strongly suggests it's responsible for, well, *collecting* blocks β specifically, blocks that are going to be incorporated into a new segment. This is crucial for NILFS's log-structured approach. I need to understand *how* it's collecting them, and what logic it's using to decide which blocks are chosen. I'm going to want to know:
* **What criteria are being applied?** Is it time-based, size-based, data-locality based? Is this part of the allocation heuristic? Are there other functions being called during this process?
* **What data structures is it interacting with?** We're probably dealing with bitmaps, block lists, and segment descriptors, but I need to pinpoint the exact ones and how they're being managed. Understanding how this function interfaces with other NILFS components will be key to understanding the whole segment construction system.
* **What are the performance implications?** How efficient is this collection process? Any bottlenecks or areas for optimization? This is a core function, so any inefficiency here will cascade across the file system.
* **What error handling is present?** What happens if block allocation fails or a data structure is corrupted? I want to know how robust this function is.
My immediate focus will be tracing the execution flow of this function, digging into the associated data structures, and assessing its overall impact on NILFS's performance and reliability. I need to see how the segment construction process actually works.
|
| 13/2 |
2026/05/25 05:18 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/segment.c IncludeLines:true Name:nilfs_segctor_collect_blocks]
Results: map[SourceCode:1163: static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
1164: {
1165: struct the_nilfs *nilfs = sci->sc_super->s_fs_info;
1166: struct list_head *head;
1167: struct nilfs_inode_info *ii;
1168: int err = 0;
1169:
1170: switch (nilfs_sc_cstage_get(sci)) {
1171: case NILFS_ST_INIT:
1172: /* Pre-processes */
1173: sci->sc_stage.flags = 0;
1174:
1175: if (!test_bit(NILFS_SC_UNCLOSED, &sci->sc_flags)) {
1176: sci->sc_nblk_inc = 0;
1177: sci->sc_curseg->sb_sum.flags = NILFS_SS_LOGBGN;
1178: if (mode == SC_LSEG_DSYNC) {
1179: nilfs_sc_cstage_set(sci, NILFS_ST_DSYNC);
1180: goto dsync_mode;
1181: }
1182: }
1183:
1184: sci->sc_stage.dirty_file_ptr = NULL;
1185: sci->sc_stage.gc_inode_ptr = NULL;
1186: if (mode == SC_FLUSH_DAT) {
1187: nilfs_sc_cstage_set(sci, NILFS_ST_DAT);
1188: goto dat_stage;
1189: }
1190: nilfs_sc_cstage_inc(sci);
1191: fallthrough;
1192: case NILFS_ST_GC:
1193: if (nilfs_doing_gc()) {
1194: head = &sci->sc_gc_inodes;
1195: ii = list_prepare_entry(sci->sc_stage.gc_inode_ptr,
1196: head, i_dirty);
1197: list_for_each_entry_continue(ii, head, i_dirty) {
1198: err = nilfs_segctor_scan_file(
1199: sci, &ii->vfs_inode,
1200: &nilfs_sc_file_ops);
1201: if (unlikely(err)) {
1202: sci->sc_stage.gc_inode_ptr = list_entry(
1203: ii->i_dirty.prev,
1204: struct nilfs_inode_info,
1205: i_dirty);
1206: goto break_or_fail;
1207: }
1208: set_bit(NILFS_I_COLLECTED, &ii->i_state);
1209: }
1210: sci->sc_stage.gc_inode_ptr = NULL;
1211: }
1212: nilfs_sc_cstage_inc(sci);
1213: fallthrough;
1214: case NILFS_ST_FILE:
1215: head = &sci->sc_dirty_files;
1216: ii = list_prepare_entry(sci->sc_stage.dirty_file_ptr, head,
1217: i_dirty);
1218: list_for_each_entry_continue(ii, head, i_dirty) {
1219: clear_bit(NILFS_I_DIRTY, &ii->i_state);
1220:
1221: err = nilfs_segctor_scan_file(sci, &ii->vfs_inode,
1222: &nilfs_sc_file_ops);
1223: if (unlikely(err)) {
1224: sci->sc_stage.dirty_file_ptr =
1225: list_entry(ii->i_dirty.prev,
1226: struct nilfs_inode_info,
1227: i_dirty);
1228: goto break_or_fail;
1229: }
1230: /* sci->sc_stage.dirty_file_ptr = NILFS_I(inode); */
1231: /* XXX: required ? */
1232: }
1233: sci->sc_stage.dirty_file_ptr = NULL;
1234: if (mode == SC_FLUSH_FILE) {
1235: nilfs_sc_cstage_set(sci, NILFS_ST_DONE);
1236: return 0;
1237: }
1238: nilfs_sc_cstage_inc(sci);
1239: sci->sc_stage.flags |= NILFS_CF_IFILE_STARTED;
1240: fallthrough;
1241: case NILFS_ST_IFILE:
1242: err = nilfs_segctor_scan_file(sci, sci->sc_root->ifile,
1243: &nilfs_sc_file_ops);
1244: if (unlikely(err))
1245: break;
1246: nilfs_sc_cstage_inc(sci);
1247: /* Creating a checkpoint */
1248: err = nilfs_cpfile_create_checkpoint(nilfs->ns_cpfile,
1249: nilfs->ns_cno);
1250: if (unlikely(err))
1251: break;
1252: fallthrough;
1253: case NILFS_ST_CPFILE:
1254: err = nilfs_segctor_scan_file(sci, nilfs->ns_cpfile,
1255: &nilfs_sc_file_ops);
1256: if (unlikely(err))
1257: break;
1258: nilfs_sc_cstage_inc(sci);
1259: fallthrough;
1260: case NILFS_ST_SUFILE:
1261: err = nilfs_free_segments(nilfs, sci->sc_freesegs,
1262: sci->sc_nfreesegs);
1263: if (unlikely(err))
1264: break;
1265: sci->sc_stage.flags |= NILFS_CF_SUFREED;
1266:
1267: err = nilfs_segctor_scan_file(sci, nilfs->ns_sufile,
1268: &nilfs_sc_file_ops);
1269: if (unlikely(err))
1270: break;
1271: nilfs_sc_cstage_inc(sci);
1272: fallthrough;
1273: case NILFS_ST_DAT:
1274: dat_stage:
1275: err = nilfs_segctor_scan_file(sci, nilfs->ns_dat,
1276: &nilfs_sc_dat_ops);
1277: if (unlikely(err))
1278: break;
1279: if (mode == SC_FLUSH_DAT) {
1280: nilfs_sc_cstage_set(sci, NILFS_ST_DONE);
1281: return 0;
1282: }
1283: nilfs_sc_cstage_inc(sci);
1284: fallthrough;
1285: case NILFS_ST_SR:
1286: if (mode == SC_LSEG_SR) {
1287: /* Appending a super root */
1288: err = nilfs_segctor_add_super_root(sci);
1289: if (unlikely(err))
1290: break;
1291: }
1292: /* End of a logical segment */
1293: sci->sc_curseg->sb_sum.flags |= NILFS_SS_LOGEND;
1294: nilfs_sc_cstage_set(sci, NILFS_ST_DONE);
1295: return 0;
1296: case NILFS_ST_DSYNC:
1297: dsync_mode:
1298: sci->sc_curseg->sb_sum.flags |= NILFS_SS_SYNDT;
1299: ii = sci->sc_dsync_inode;
1300: if (!test_bit(NILFS_I_BUSY, &ii->i_state))
1301: break;
1302:
1303: err = nilfs_segctor_scan_file_dsync(sci, &ii->vfs_inode);
1304: if (unlikely(err))
1305: break;
1306: sci->sc_curseg->sb_sum.flags |= NILFS_SS_LOGEND;
1307: nilfs_sc_cstage_set(sci, NILFS_ST_DONE);
1308: return 0;
1309: case NILFS_ST_DONE:
1310: return 0;
1311: default:
1312: BUG();
1313: }
1314:
1315: break_or_fail:
1316: return err;
1317: }
SourceFile:fs/nilfs2/segment.c]
|
| 14/2 |
2026/05/25 05:18 |
llm |
expert |
0m
Model:
Tokens:
input: 29545
output: 46
thoughts: 59
Thoughts: Here's my take on the thought process, as if it were my own:
**Investigating `nilfs_free_segments`**
Okay, so I'm looking at `nilfs_free_segments`. The function call itself isn't the interesting bit; it's the inputs. It's called with `sci->sc_freesegs` and `sci->sc_nfreesegs`. Right, those are clearly segment-related, but where are they *coming* from? I need to trace back their origin. What sets these values up?
Aha! The `NILFS_IOCTL_CLEAN_SEGMENTS` ioctl. That's the likely culprit. It makes sense β segment cleaning would involve determining which segments are free and available for reuse. So, I need to dig into the implementation of that ioctl to understand how `sci->sc_freesegs` and `sci->sc_nfreesegs` are being populated. That's where I'll find the logic behind which segments get put on the free list and how the free segment count is calculated. This Ioctl is the key.
|
| 15/2 |
2026/05/25 05:18 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/ioctl.c IncludeLines:true Name:nilfs_ioctl_clean_segments]
Results: map[SourceCode: 820: /**
821: * nilfs_ioctl_clean_segments - clean segments
822: * @inode: inode object
823: * @filp: file object
824: * @cmd: ioctl's request code
825: * @argp: pointer on argument from userspace
826: *
827: * Description: nilfs_ioctl_clean_segments() function makes garbage
828: * collection operation in the environment of requested parameters
829: * from userspace. The NILFS_IOCTL_CLEAN_SEGMENTS ioctl is used by
830: * nilfs_cleanerd daemon.
831: *
832: * Return: 0 on success, or a negative error code on failure.
833: */
834: static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
835: unsigned int cmd, void __user *argp)
836: {
837: struct nilfs_argv argv[5];
838: static const size_t argsz[5] = {
839: sizeof(struct nilfs_vdesc),
840: sizeof(struct nilfs_period),
841: sizeof(__u64),
842: sizeof(struct nilfs_bdesc),
843: sizeof(__u64),
844: };
845: void *kbufs[5];
846: struct the_nilfs *nilfs;
847: size_t len, nsegs;
848: int n, ret;
849:
850: if (!capable(CAP_SYS_ADMIN))
851: return -EPERM;
852:
853: ret = mnt_want_write_file(filp);
854: if (ret)
855: return ret;
856:
857: ret = -EFAULT;
858: if (copy_from_user(argv, argp, sizeof(argv)))
859: goto out;
860:
861: ret = -EINVAL;
862: nsegs = argv[4].v_nmembs;
863: if (argv[4].v_size != argsz[4])
864: goto out;
865:
866: /*
867: * argv[4] points to segment numbers this ioctl cleans. We
868: * use kmalloc() for its buffer because the memory used for the
869: * segment numbers is small enough.
870: */
871: kbufs[4] = memdup_array_user(u64_to_user_ptr(argv[4].v_base),
872: nsegs, sizeof(__u64));
873: if (IS_ERR(kbufs[4])) {
874: ret = PTR_ERR(kbufs[4]);
875: goto out;
876: }
877: nilfs = inode->i_sb->s_fs_info;
878:
879: for (n = 0; n < 4; n++) {
880: ret = -EINVAL;
881: if (argv[n].v_size != argsz[n])
882: goto out_free;
883:
884: if (argv[n].v_nmembs > nsegs * nilfs->ns_blocks_per_segment)
885: goto out_free;
886:
887: if (argv[n].v_nmembs >= UINT_MAX / argv[n].v_size)
888: goto out_free;
889:
890: len = argv[n].v_size * argv[n].v_nmembs;
891: if (len == 0) {
892: kbufs[n] = NULL;
893: continue;
894: }
895:
896: kbufs[n] = vmemdup_user(u64_to_user_ptr(argv[n].v_base), len);
897: if (IS_ERR(kbufs[n])) {
898: ret = PTR_ERR(kbufs[n]);
899: goto out_free;
900: }
901: }
902:
903: /*
904: * nilfs_ioctl_move_blocks() will call nilfs_iget_for_gc(),
905: * which will operates an inode list without blocking.
906: * To protect the list from concurrent operations,
907: * nilfs_ioctl_move_blocks should be atomic operation.
908: */
909: if (test_and_set_bit(THE_NILFS_GC_RUNNING, &nilfs->ns_flags)) {
910: ret = -EBUSY;
911: goto out_free;
912: }
913:
914: ret = nilfs_ioctl_move_blocks(inode->i_sb, &argv[0], kbufs[0]);
915: if (ret < 0) {
916: nilfs_err(inode->i_sb,
917: "error %d preparing GC: cannot read source blocks",
918: ret);
919: } else {
920: if (nilfs_sb_need_update(nilfs))
921: set_nilfs_discontinued(nilfs);
922: ret = nilfs_clean_segments(inode->i_sb, argv, kbufs);
923: }
924:
925: nilfs_remove_all_gcinodes(nilfs);
926: clear_nilfs_gc_running(nilfs);
927:
928: out_free:
929: while (--n >= 0)
930: kvfree(kbufs[n]);
931: kfree(kbufs[4]);
932: out:
933: mnt_drop_write_file(filp);
934: return ret;
935: }
SourceFile:fs/nilfs2/ioctl.c]
|
| 16/2 |
2026/05/25 05:18 |
llm |
expert |
0m
Model:
Tokens:
input: 31689
output: 46
thoughts: 1006
Thoughts: **Analyzing a Potential Kernel Bug**
Okay, so I'm looking at this `ioctl` for `NILFS_IOCTL_CLEAN_SEGMENTS`. The code explicitly checks for `CAP_SYS_ADMIN`, which is what I'd expect. But wait, `capable(CAP_SYS_ADMIN)` operates on the *initial* user namespace. That means this `ioctl` is only accessible to root in the initial user namespace. Good, I'll confirm that `capable` is definitely the function being used, not `ns_capable`. Yep, `capable(CAP_SYS_ADMIN)` it is. So, based on this, the bug isn't exploitable by unprivileged processes or within user namespaces, which would typically be a lower severity.
But, hang on, let's look at the provided bug report. It shows a hung task, `syz.0.17`, blocked for a significant amount of time, and the trace suggests it's getting stuck during an `fchmodat` operation. Crucially, the task holding the lock is `syz.3.20`, and this task is currently executing `ioctl(NILFS_IOCTL_CLEAN_SEGMENTS)`. Since `ioctl(NILFS_IOCTL_CLEAN_SEGMENTS)` requires `CAP_SYS_ADMIN`, the syzkaller process, the origin of these tasks, *must* have `CAP_SYS_ADMIN` in the initial user namespace to even *call* this `ioctl`.
Now, Syzkaller usually runs either as root or inside a user namespace. If it's root, it has the capability. If it's in a user namespace, it *doesn't* have `CAP_SYS_ADMIN` in the initial namespace, which is the crucial point here. I need to make sure I am correct, in my assumption. To be safe, I'll go back and double check how `capable(CAP_SYS_ADMIN)` is used within the code to verify this hypothesis.
|
| 17/2 |
2026/05/25 05:18 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/ioctl.c IncludeLines:true Name:nilfs_ioctl_clean_segments]
Results: map[SourceCode: 820: /**
821: * nilfs_ioctl_clean_segments - clean segments
822: * @inode: inode object
823: * @filp: file object
824: * @cmd: ioctl's request code
825: * @argp: pointer on argument from userspace
826: *
827: * Description: nilfs_ioctl_clean_segments() function makes garbage
828: * collection operation in the environment of requested parameters
829: * from userspace. The NILFS_IOCTL_CLEAN_SEGMENTS ioctl is used by
830: * nilfs_cleanerd daemon.
831: *
832: * Return: 0 on success, or a negative error code on failure.
833: */
834: static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
835: unsigned int cmd, void __user *argp)
836: {
837: struct nilfs_argv argv[5];
838: static const size_t argsz[5] = {
839: sizeof(struct nilfs_vdesc),
840: sizeof(struct nilfs_period),
841: sizeof(__u64),
842: sizeof(struct nilfs_bdesc),
843: sizeof(__u64),
844: };
845: void *kbufs[5];
846: struct the_nilfs *nilfs;
847: size_t len, nsegs;
848: int n, ret;
849:
850: if (!capable(CAP_SYS_ADMIN))
851: return -EPERM;
852:
853: ret = mnt_want_write_file(filp);
854: if (ret)
855: return ret;
856:
857: ret = -EFAULT;
858: if (copy_from_user(argv, argp, sizeof(argv)))
859: goto out;
860:
861: ret = -EINVAL;
862: nsegs = argv[4].v_nmembs;
863: if (argv[4].v_size != argsz[4])
864: goto out;
865:
866: /*
867: * argv[4] points to segment numbers this ioctl cleans. We
868: * use kmalloc() for its buffer because the memory used for the
869: * segment numbers is small enough.
870: */
871: kbufs[4] = memdup_array_user(u64_to_user_ptr(argv[4].v_base),
872: nsegs, sizeof(__u64));
873: if (IS_ERR(kbufs[4])) {
874: ret = PTR_ERR(kbufs[4]);
875: goto out;
876: }
877: nilfs = inode->i_sb->s_fs_info;
878:
879: for (n = 0; n < 4; n++) {
880: ret = -EINVAL;
881: if (argv[n].v_size != argsz[n])
882: goto out_free;
883:
884: if (argv[n].v_nmembs > nsegs * nilfs->ns_blocks_per_segment)
885: goto out_free;
886:
887: if (argv[n].v_nmembs >= UINT_MAX / argv[n].v_size)
888: goto out_free;
889:
890: len = argv[n].v_size * argv[n].v_nmembs;
891: if (len == 0) {
892: kbufs[n] = NULL;
893: continue;
894: }
895:
896: kbufs[n] = vmemdup_user(u64_to_user_ptr(argv[n].v_base), len);
897: if (IS_ERR(kbufs[n])) {
898: ret = PTR_ERR(kbufs[n]);
899: goto out_free;
900: }
901: }
902:
903: /*
904: * nilfs_ioctl_move_blocks() will call nilfs_iget_for_gc(),
905: * which will operates an inode list without blocking.
906: * To protect the list from concurrent operations,
907: * nilfs_ioctl_move_blocks should be atomic operation.
908: */
909: if (test_and_set_bit(THE_NILFS_GC_RUNNING, &nilfs->ns_flags)) {
910: ret = -EBUSY;
911: goto out_free;
912: }
913:
914: ret = nilfs_ioctl_move_blocks(inode->i_sb, &argv[0], kbufs[0]);
915: if (ret < 0) {
916: nilfs_err(inode->i_sb,
917: "error %d preparing GC: cannot read source blocks",
918: ret);
919: } else {
920: if (nilfs_sb_need_update(nilfs))
921: set_nilfs_discontinued(nilfs);
922: ret = nilfs_clean_segments(inode->i_sb, argv, kbufs);
923: }
924:
925: nilfs_remove_all_gcinodes(nilfs);
926: clear_nilfs_gc_running(nilfs);
927:
928: out_free:
929: while (--n >= 0)
930: kvfree(kbufs[n]);
931: kfree(kbufs[4]);
932: out:
933: mnt_drop_write_file(filp);
934: return ret;
935: }
SourceFile:fs/nilfs2/ioctl.c]
|
| 18/2 |
2026/05/25 05:18 |
llm |
expert |
0m
Model:
Tokens:
input: 34964
output: 24
thoughts: 64
Thoughts: **Analyzing the Vulnerability's Accessibility**
Okay, so I see `capable(CAP_SYS_ADMIN)` is definitely involved here. That's good; it immediately suggests this isn't something a standard, unprivileged process or user namespace can just stumble upon. This significantly limits the attack surface. Now, the key question is, are there *any* other ways to trigger `nilfs_free_segments` besides the typical path? It's essential to meticulously explore all possibilities. Let's dig into the code and systematically hunt down all references to `nilfs_free_segments`. I need to ensure there are no subtle, unexpected calls lurking somewhere that bypass the expected privilege checks. Thoroughness is paramount when dealing with security vulnerabilities like this.
|
| 19/2 |
2026/05/25 05:18 |
tool |
codesearch-find-references |
0m
Args: map[Name:nilfs_free_segments]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_segctor_collect_blocks SourceFile:fs/nilfs2/segment.c SourceLine:1261]] TruncatedOutput:false]
|
| 20/2 |
2026/05/25 05:18 |
llm |
expert |
0m
Model:
Tokens:
input: 35285
output: 27
thoughts: 48
Thoughts: Okay, here's my interpretation of that logic, presented as a first-person thought process, keeping in mind my expertise:
**My Deductive Reasoning on Segment Allocation**
Right, let me break this down. It's clear that the responsibility for freeing segments within this `nilfs` file system construct falls squarely on the shoulders of `nilfs_segctor_collect_blocks`. I see that function as the point person for calling `nilfs_free_segments`. It's essentially the cleanup crew, handling the release of resources.
And tracing that call back up the chain, I see that the function that *initiates* that cleanup, or at least calls the function that does, is `nilfs_segctor_do_construct`. `nilfs_segctor_collect_blocks` is clearly a helper function of `nilfs_segctor_do_construct`. So, it's `do_construct` that's managing the overall segment construction and then, crucially, directing the collection and freeing of blocks via `collect_blocks`. This confirms my understanding.
|
| 21/2 |
2026/05/25 05:18 |
tool |
codesearch-find-references |
0m
Args: map[Name:nilfs_segctor_collect_blocks]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_segctor_collect SourceFile:fs/nilfs2/segment.c SourceLine:1547]] TruncatedOutput:false]
|
| 22/2 |
2026/05/25 05:18 |
llm |
expert |
0m
Model:
Tokens:
input: 35661
output: 25
thoughts: 23
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Diving into the Segmentation Constructor**
Alright, so I'm focusing in on the segmentation constructor. Specifically, I see that the `nilfs_segctor_collect` function is being invoked by `nilfs_segctor_do_construct`. This is crucial. It means `nilfs_segctor_collect` is a core building block *within* the construction process. It's not the driver itself, but it's clearly performing an essential collection task β a part of a larger construct. Now I have to figure out what it's *collecting*, and why this process is considered so essential. Is it gathering data blocks? Metadata? Free space information? I'll need to dig into `nilfs_segctor_collect` to understand the data gathering and how it feeds into the larger construction steps outlined in `nilfs_segctor_do_construct`. I assume that this is likely related to the overall performance of the file system.
|
| 23/2 |
2026/05/25 05:19 |
tool |
codesearch-find-references |
0m
Args: map[Name:nilfs_segctor_collect]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_segctor_do_construct SourceFile:fs/nilfs2/segment.c SourceLine:2122]] TruncatedOutput:false]
|
| 24/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 36006
output: 27
thoughts: 23
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm an expert in file systems and journaling:
**Understanding the Construction Process**
Right, so I'm focusing on the low-level mechanics here, specifically within the NILFS file system. My thought process is circling around the relationship between two specific functions: `nilfs_segctor_do_construct` and `nilfs_segctor_construct`. The obvious implication is that `nilfs_segctor_construct` serves as some sort of entry point or orchestrator. It's likely that it handles the overall high-level logic for segment construction within NILFS. My attention is drawn to `nilfs_segctor_do_construct` because it is called by the other. It seems highly likely that this latter function is the workhorse. It probably carries out the actual heavy lifting required to construct a new segment. The first function sets things in motion, while the second does the building. I'll need to dig deeper into the code to really understand the exact responsibilities of each, but that relationship is a good starting point for understanding how a new segment gets created. It could be important when tracing a bug or trying to understand the inner workings of the system.
|
| 25/2 |
2026/05/25 05:19 |
tool |
codesearch-find-references |
0m
Args: map[Name:nilfs_segctor_do_construct]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_construct_dsync_segment SourceFile:fs/nilfs2/segment.c SourceLine:2380] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_segctor_construct SourceFile:fs/nilfs2/segment.c SourceLine:2462] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_segctor_do_immediate_flush SourceFile:fs/nilfs2/segment.c SourceLine:2593]] TruncatedOutput:false]
|
| 26/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 36502
output: 23
thoughts: 41
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm an expert in file system internals:
**Investigating `nilfs_segctor_collect_blocks` and its Data Dependencies**
Alright, let's zoom in on `nilfs_segctor_collect_blocks`. I see it's using `sci->sc_freesegs` and `sci->sc_nfreesegs`. Hang on a second... that's interesting. I know those are related to free segment management, presumably a critical part of the NILFS design. I understand the general purpose, and it makes sense this function would be involved.
But now my brain is saying, "hold on, where are these `sc_freesegs` and `sc_nfreesegs` fields *initialized* and *updated*? This function is *using* them, but if I want to thoroughly understand its behavior and potential issues, I need to trace back and identify the code responsible for *setting* the values that `nilfs_segctor_collect_blocks` is consuming. Are we talking about a race, a bug, or an optimisation? It's essential to understand the data flow, the context, and the conditions under which these values are being modified and how their integrity is guaranteed. Time to go hunting for the producers of these fields.
|
| 27/2 |
2026/05/25 05:19 |
tool |
codesearch-find-references |
0m
Error:
Args:
Results: map[References:<nil> TruncatedOutput:false]
|
| 28/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 36870
output: 19
thoughts: 24
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Investigating `sc_freesegs` in the NILFS2 Filesystem**
Alright, I'm thinking I need to refresh my memory on how free segments are managed within NILFS2. My gut feeling tells me that if I want to understand the lifecycle of freed segments, the place to start is likely in the core segment management code. I'll search for the function `sc_freesegs` directly within `fs/nilfs2/segment.c`. That should give me the entry point and at least the initial context for tracing the execution path that deals with marking, tracking, and perhaps ultimately reusing freed segments. I expect this to lead to other key functions as well. I'm hoping to get a clear picture of how NILFS2 reclaims those blocks.
|
| 29/2 |
2026/05/25 05:19 |
tool |
grepper |
0m
Args: map[Expression:sc_freesegs]
Results: map[Output:fs/nilfs2/segment.c=1163=static int nilfs_segctor_collect_blocks(struct nilfs_sc_info *sci, int mode)
--
fs/nilfs2/segment.c-1260- case NILFS_ST_SUFILE:
fs/nilfs2/segment.c:1261: err = nilfs_free_segments(nilfs, sci->sc_freesegs,
fs/nilfs2/segment.c-1262- sci->sc_nfreesegs);
--
fs/nilfs2/segment.c=1532=static int nilfs_segctor_collect(struct nilfs_sc_info *sci,
--
fs/nilfs2/segment.c-1563- err = nilfs_sufile_cancel_freev(nilfs->ns_sufile,
fs/nilfs2/segment.c:1564: sci->sc_freesegs,
fs/nilfs2/segment.c-1565- sci->sc_nfreesegs,
--
fs/nilfs2/segment.c=1859=static void nilfs_segctor_abort_construction(struct nilfs_sc_info *sci,
--
fs/nilfs2/segment.c-1877- ret = nilfs_sufile_cancel_freev(nilfs->ns_sufile,
fs/nilfs2/segment.c:1878: sci->sc_freesegs,
fs/nilfs2/segment.c-1879- sci->sc_nfreesegs,
--
fs/nilfs2/segment.c=2508=int nilfs_clean_segments(struct super_block *sb, struct nilfs_argv *argv,
--
fs/nilfs2/segment.c-2530-
fs/nilfs2/segment.c:2531: sci->sc_freesegs = kbufs[4];
fs/nilfs2/segment.c-2532- sci->sc_nfreesegs = argv[4].v_nmembs;
--
fs/nilfs2/segment.c-2546- if (nilfs_test_opt(nilfs, DISCARD)) {
fs/nilfs2/segment.c:2547: int ret = nilfs_discard_segments(nilfs, sci->sc_freesegs,
fs/nilfs2/segment.c-2548- sci->sc_nfreesegs);
--
fs/nilfs2/segment.c-2557- out_unlock:
fs/nilfs2/segment.c:2558: sci->sc_freesegs = NULL;
fs/nilfs2/segment.c-2559- sci->sc_nfreesegs = 0;
--
fs/nilfs2/segment.h=71=struct nilfs_segsum_pointer {
--
fs/nilfs2/segment.h-84- * @sc_iput_work: work struct to defer iput call
fs/nilfs2/segment.h:85: * @sc_freesegs: array of segment numbers to be freed
fs/nilfs2/segment.h:86: * @sc_nfreesegs: number of segments on @sc_freesegs
fs/nilfs2/segment.h-87- * @sc_dsync_inode: inode whose data pages are written for a sync operation
--
fs/nilfs2/segment.h=119=struct nilfs_sc_info {
--
fs/nilfs2/segment.h-129-
fs/nilfs2/segment.h:130: __u64 *sc_freesegs;
fs/nilfs2/segment.h-131- size_t sc_nfreesegs;
]
|
| 30/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 38055
output: 24
thoughts: 112
Thoughts: **Analyzing the Vulnerability's Accessibility**
Okay, so I've traced the path of `sc_freesegs`. It looks like it's *only* set within `nilfs_clean_segments`. And that's called exclusively by `nilfs_ioctl_clean_segments`. The crucial point is `nilfs_ioctl_clean_segments` demands `CAP_SYS_ADMIN` in the *initial* user namespace. That's a pretty significant restriction. My initial read suggests this bug is completely out of reach for any unprivileged users and, just as importantly, those operating within user namespaces. That's a strong start for the analysis; it appears to significantly limit the impact.
But hold on a second... I need to be absolutely certain. There's always a chance I'm missing something, some subtle alternative trigger. Let me quickly double-check. I need to exhaustively examine all references to `nilfs_clean_segments`. I'll run a quick cross-reference check to eliminate any doubt. Gotta be thorough.
|
| 31/2 |
2026/05/25 05:19 |
tool |
codesearch-find-references |
0m
Args: map[Name:nilfs_clean_segments]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_ioctl_clean_segments SourceFile:fs/nilfs2/ioctl.c SourceLine:922]] TruncatedOutput:false]
|
| 32/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 38487
output: 27
thoughts: 274
Thoughts: **Analyzing the `nilfs_ioctl_clean_segments` Bug**
Okay, so the code shows that the `nilfs_clean_segments` function is only called through `nilfs_ioctl_clean_segments`. And, crucially, `nilfs_ioctl_clean_segments` requires `CAP_SYS_ADMIN` β that makes things interesting.
Right, the syzkaller reproducer, it mounts a nilfs2 image and then calls `ioctl(NILFS_IOCTL_CLEAN_SEGMENTS)`. If syzkaller is running as root (which is its typical configuration), that means it has `CAP_SYS_ADMIN`. So, this bug is definitely triggered by a privileged user, which changes the threat model.
But, hang on, is this *just* a denial of service? Yes, the hung task clearly indicates denial of service. If this requires `CAP_SYS_ADMIN`, then this isn't a *security* vulnerability in the sense of privilege escalation if it's strictly limited to root.
Hold on... could there be a scenario where the filesystem is mounted by root, but then an *unprivileged* user somehow manages to call the ioctl? Nope, the ioctl itself checks for `capable(CAP_SYS_ADMIN)`, so it's a dead end. An unprivileged user is blocked.
Hmm, but are there other code paths to those key `nilfs_sufile_freev` or `nilfs_sufile_updatev` functions? Time to check the references to `nilfs_sufile_freev` to make sure there are no other vectors.
|
| 33/2 |
2026/05/25 05:19 |
tool |
codesearch-find-references |
0m
Args: map[Name:nilfs_sufile_freev]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_free_segments SourceFile:fs/nilfs2/segment.c SourceLine:1140]] TruncatedOutput:false]
|
| 34/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 39208
output: 27
thoughts: 27
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Focusing on NILFS Free Segment Management**
Alright, the core issue seems to be centered around `nilfs_free_segments`. That's where the rubber meets the road in managing free space, especially concerning segment allocation and deallocation in NILFS2. So, what's triggering this train of thought? Is there a problem there? Or, are we just trying to optimize things?
To understand the broader implications and potential side effects related to segment management, I need to check how the code interacts with related operations. Specifically, I should look for the places in the code where `nilfs_sufile_updatev` is called, because that function deals with super-block update. Understanding the calls to this function will let me understand segment management on super-block update, which should provide a good path for root-causing any issues that might be present.
|
| 35/2 |
2026/05/25 05:19 |
tool |
codesearch-find-references |
0m
Args: map[Name:nilfs_sufile_updatev]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_sufile_cancel_freev SourceFile:fs/nilfs2/sufile.h SourceLine:110] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_sufile_freev SourceFile:fs/nilfs2/sufile.h SourceLine:93]] TruncatedOutput:false]
|
| 36/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 39599
output: 51
thoughts: 1565
Thoughts: **Analyzing the NILFS2 Hung Task Bug**
Okay, so I'm looking at this bug report involving a hung task in the NILFS2 filesystem, specifically triggered by `NILFS_IOCTL_CLEAN_SEGMENTS`. My initial thought is that both `nilfs_sufile_updatev` and `nilfs_sufile_cancel_freev` are used for freeing segments, and that this code path is only reachable through that specific IOCTL, during garbage collection/clean segments. I briefly considered if `nilfs_sufile_updatev` could be called elsewhere but then remembered we checked the references earlier and it's isolated to the IOCTL.
The bug report shows the task, `syz.0.17`, is blocked, waiting on `nilfs->ns_segctor_sem`, which the `NILFS_IOCTL_CLEAN_SEGMENTS` task holds. The cleaner task is also spamming warnings via `nilfs_sufile_updatev`. The warning originates from a check within `nilfs_sufile_updatev` where the code validates segment numbers against the number of segments in the sufile.
Now, the vulnerability lies in the fact that the number of segments to process, `nsegs`, is user-controlled via the IOCTL arguments. It can be potentially very large, up to `UINT_MAX / sizeof(__u64)`. There's a check that seems like it should prevent this (where the number of segments is compared to the number of blocks in the segment). However, on closer inspection, the test is actually flawed in the check of `nsegs`. It's possible to pass very large values for `nsegs` to the IOCTL if those segments are invalid. If this happens, `nilfs_sufile_updatev` enters a loop and for each invalid segment, it prints a warning to the console, leading to a huge number of console outputs.
This excessive console output is the root cause: because console output is relatively slow, this process can get blocked, triggering the "hung task" warning. It's essentially a denial-of-service condition.
So, is it a security vulnerability? Not really. It requires `CAP_SYS_ADMIN` in the initial user namespace, so unprivileged users and user namespaces are protected. However, it *is* a denial-of-service, as an administrator can use the IOCTL to cause a system hang by triggering the print statements. And the filesystem itself doesn't trigger this bug; the IOCTL, which takes the number of segments as an argument does.
|
| 37/2 |
2026/05/25 05:19 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/sufile.h IncludeLines:true Name:nilfs_sufile_cancel_freev]
Results: map[SourceCode: 97: /**
98: * nilfs_sufile_cancel_freev - reallocate freeing segments
99: * @sufile: inode of segment usage file
100: * @segnumv: array of segment numbers
101: * @nsegs: size of @segnumv array
102: * @ndone: place to store the number of cancelled segments
103: *
104: * Return: 0 on success, or a negative error code on failure.
105: */
106: static inline int nilfs_sufile_cancel_freev(struct inode *sufile,
107: __u64 *segnumv, size_t nsegs,
108: size_t *ndone)
109: {
110: return nilfs_sufile_updatev(sufile, segnumv, nsegs, 0, ndone,
111: nilfs_sufile_do_cancel_free);
112: }
SourceFile:fs/nilfs2/sufile.h]
|
| 38/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 42087
output: 47
thoughts: 46
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing `nilfs_segctor_abort_construction` Usage**
Right, so this function is apparently only called from `nilfs_free_segments` and `nilfs_segctor_abort_construction`. I need to figure out the exact context of this call from `nilfs_segctor_abort_construction`. It's a bit of a code smell to have a function call itself, so let's delve into what's happening within `nilfs_segctor_abort_construction` itself. What specific conditions necessitate this self-call? I need to understand the error paths or exceptional scenarios it's designed to handle. This deeper dive will illuminate the logic and potential implications of its use.
|
| 39/2 |
2026/05/25 05:19 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/segment.c IncludeLines:true Name:nilfs_segctor_abort_construction]
Results: map[SourceCode:1859: static void nilfs_segctor_abort_construction(struct nilfs_sc_info *sci,
1860: struct the_nilfs *nilfs, int err)
1861: {
1862: LIST_HEAD(logs);
1863: int ret;
1864:
1865: list_splice_tail_init(&sci->sc_write_logs, &logs);
1866: ret = nilfs_wait_on_logs(&logs);
1867: nilfs_abort_logs(&logs, ret ? : err);
1868:
1869: list_splice_tail_init(&sci->sc_segbufs, &logs);
1870: if (list_empty(&logs))
1871: return; /* if the first segment buffer preparation failed */
1872:
1873: nilfs_cancel_segusage(&logs, nilfs->ns_sufile);
1874: nilfs_free_incomplete_logs(&logs, nilfs);
1875:
1876: if (sci->sc_stage.flags & NILFS_CF_SUFREED) {
1877: ret = nilfs_sufile_cancel_freev(nilfs->ns_sufile,
1878: sci->sc_freesegs,
1879: sci->sc_nfreesegs,
1880: NULL);
1881: WARN_ON(ret); /* do not happen */
1882: }
1883:
1884: nilfs_destroy_logs(&logs);
1885: }
SourceFile:fs/nilfs2/segment.c]
|
| 40/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 42815
output: 27
thoughts: 94
Thoughts: Okay, here's my breakdown of this.
**Investigating a Potential Trigger for `sci->sc_freesegs` Usage**
Alright, so I'm digging into this code, specifically looking at how `sci->sc_freesegs` and `sci->sc_nfreesegs` are being used. It seems like the primary, and potentially *only*, way to get at these variables is through the `NILFS_IOCTL_CLEAN_SEGMENTS` ioctl. That's the expected path, and that makes sense... but I have this nagging feeling I'm missing something.
Hang on a minute... could `nilfs_sufile_updatev` be getting called with a bigger-than-expected `nsegs` value from *elsewhere*? If that were happening, it would bypass my initial assumption. I need to make *absolutely* sure there aren't any sneaky calls to `nilfs_sufile_updatev` with unusual parameters that are somehow triggering unexpected behavior with these `sci` fields. Right, I need to check all the places in the codebase where `nilfs_sufile_updatev` is called, and review the context surrounding each call. I need to make sure that `nsegs` is always what I believe it to be. Time to do some digging.
|
| 41/2 |
2026/05/25 05:19 |
tool |
codesearch-find-references |
0m
Args: map[Name:nilfs_sufile_updatev]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_sufile_cancel_freev SourceFile:fs/nilfs2/sufile.h SourceLine:110] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nilfs_sufile_freev SourceFile:fs/nilfs2/sufile.h SourceLine:93]] TruncatedOutput:false]
|
| 42/2 |
2026/05/25 05:19 |
llm |
expert |
0m
Model:
Tokens:
input: 43356
output: 42
thoughts: 1059
Thoughts: **Analysis of the NILFS_IOCTL_CLEAN_SEGMENTS Issue**
Okay, so the crux of this problem lies with `nilfs_sufile_cancel_freev` and `nilfs_sufile_freev`, and how they're called only through `sci->sc_freesegs` and `sci->sc_nfreesegs`. These are populated solely within `nilfs_clean_segments`, which in turn is driven by the `NILFS_IOCTL_CLEAN_SEGMENTS` ioctl. So it's very targeted.
Initially, I thought this was a non-issue because `NILFS_IOCTL_CLEAN_SEGMENTS` mandates `CAP_SYS_ADMIN` in the initial user namespace. This makes it inaccessible to unprivileged users, and also from user namespaces, which eliminates the obvious security vulnerability angle. It appears to just be a bug that can be triggered by root. But the plot thickens.
The question then becomes: what if `nilfs_cleanerd` calls this ioctl? It's a user-space daemon running as root. If it's compromised, that's already a problem, but it already has the required permissions. The real threat is a malicious filesystem being mounted and potentially tricking `nilfs_cleanerd`.
If a malicious filesystem could feed bad data to `nilfs_cleanerd`, could that then cause `NILFS_IOCTL_CLEAN_SEGMENTS` to be called with a large `nsegs` value and invalid segment numbers? That daemon reads info from the filesystem and determines what to clean, so it's a plausible scenario.
However, if `nilfs_cleanerd` crashes or hangs, it is a user-space issue. The kernel bug is the ioctl taking a long time and causing a hung task. But can a malicious filesystem *cause* this? If a user plugs in a malicious USB drive with a nilfs2 filesystem, and the system automounts it, does it trigger `nilfs_cleanerd`? Yes, mount.nilfs2 automatically starts `nilfs_cleanerd`. So now, the pieces are falling into place!
The system might run `mount.nilfs2`, which then starts `nilfs_cleanerd`. If `nilfs_cleanerd` reads a malicious filesystem, gets confused, and then makes that call to `NILFS_IOCTL_CLEAN_SEGMENTS` with bad data, it leads to kernel warnings and a hang. Is that a plausible attack vector? Yes, if `nilfs_cleanerd` actually *does* that.
`nilfs_cleanerd` reads segment usage info using `NILFS_IOCTL_GET_SUINFO`. If the filesystem is malicious, `NILFS_IOCTL_GET_SUINFO` could feed back bad data. Then `nilfs_cleanerd` could call `NILFS_IOCTL_CLEAN_SEGMENTS` with bad data. This is still indirect though. The syzkaller reproducer, as I understand it, calls the ioctl directly and requires root or `CAP_SYS_ADMIN`.
But... I need to be sure there isn't another way to trigger this. The ioctl is the only way this can be triggered.
Now, let's evaluate this in terms of severity.
* **Exploitable:** No. This is a hung task due to excessive console output.
* **Denial of Service:** Yes, it does cause a hung task, so it is a DoS.
* **Accessible From Unprivileged Processes:** No. Requires `CAP_SYS_ADMIN`.
* **Accessible From User Namespaces:** No. `capable(CAP_SYS_ADMIN)` checks the initial user namespace.
* **VM Guest Trigger:** No.
* **VM Host Trigger in the Confidential Computing Context:** No.
* **Ethernet Network Trigger:** No.
* **Other Remote Trigger:** No.
* **Peripheral Trigger:** Maybe, if auto-mount starts `nilfs_cleanerd` and it triggers the bug. But, because the bug *is* in the ioctl which requires root, I will say No.
* **Malicious Filesystem Trigger:** Same as above. The filesystem itself does not trigger it, the ioctl does. Therefore, No.
I should double-check that `capable(CAP_SYS_ADMIN)` is the *only* check. Yes, it's the very first check in `nilfs_ioctl_clean_segments`.
Okay, any other ioctls that can cause this? Let's check `nilfs_ioctl`.
|
| 43/2 |
2026/05/25 05:20 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/ioctl.c IncludeLines:true Name:nilfs_ioctl]
Results: map[SourceCode:1319: long nilfs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
1320: {
1321: struct inode *inode = file_inode(filp);
1322: void __user *argp = (void __user *)arg;
1323:
1324: switch (cmd) {
1325: case FS_IOC_GETVERSION:
1326: return nilfs_ioctl_getversion(inode, argp);
1327: case NILFS_IOCTL_CHANGE_CPMODE:
1328: return nilfs_ioctl_change_cpmode(inode, filp, cmd, argp);
1329: case NILFS_IOCTL_DELETE_CHECKPOINT:
1330: return nilfs_ioctl_delete_checkpoint(inode, filp, cmd, argp);
1331: case NILFS_IOCTL_GET_CPINFO:
1332: return nilfs_ioctl_get_info(inode, filp, cmd, argp,
1333: sizeof(struct nilfs_cpinfo),
1334: nilfs_ioctl_do_get_cpinfo);
1335: case NILFS_IOCTL_GET_CPSTAT:
1336: return nilfs_ioctl_get_cpstat(inode, filp, cmd, argp);
1337: case NILFS_IOCTL_GET_SUINFO:
1338: return nilfs_ioctl_get_info(inode, filp, cmd, argp,
1339: sizeof(struct nilfs_suinfo),
1340: nilfs_ioctl_do_get_suinfo);
1341: case NILFS_IOCTL_SET_SUINFO:
1342: return nilfs_ioctl_set_suinfo(inode, filp, cmd, argp);
1343: case NILFS_IOCTL_GET_SUSTAT:
1344: return nilfs_ioctl_get_sustat(inode, filp, cmd, argp);
1345: case NILFS_IOCTL_GET_VINFO:
1346: return nilfs_ioctl_get_info(inode, filp, cmd, argp,
1347: sizeof(struct nilfs_vinfo),
1348: nilfs_ioctl_do_get_vinfo);
1349: case NILFS_IOCTL_GET_BDESCS:
1350: return nilfs_ioctl_get_bdescs(inode, filp, cmd, argp);
1351: case NILFS_IOCTL_CLEAN_SEGMENTS:
1352: return nilfs_ioctl_clean_segments(inode, filp, cmd, argp);
1353: case NILFS_IOCTL_SYNC:
1354: return nilfs_ioctl_sync(inode, filp, cmd, argp);
1355: case NILFS_IOCTL_RESIZE:
1356: return nilfs_ioctl_resize(inode, filp, argp);
1357: case NILFS_IOCTL_SET_ALLOC_RANGE:
1358: return nilfs_ioctl_set_alloc_range(inode, argp);
1359: case FITRIM:
1360: return nilfs_ioctl_trim_fs(inode, argp);
1361: case FS_IOC_GETFSLABEL:
1362: return nilfs_ioctl_get_fslabel(inode->i_sb, argp);
1363: case FS_IOC_SETFSLABEL:
1364: return nilfs_ioctl_set_fslabel(inode->i_sb, filp, argp);
1365: default:
1366: return -ENOTTY;
1367: }
1368: }
SourceFile:fs/nilfs2/ioctl.c]
|
| 44/2 |
2026/05/25 05:20 |
llm |
expert |
0m
Model:
Tokens:
input: 46485
output: 51
thoughts: 55
Thoughts: Okay, here's my take on those thoughts, framed as my own:
**Analyzing NILFS Cleaning Operations**
Alright, so the core of this seems straightforward enough. It appears that `NILFS_IOCTL_CLEAN_SEGMENTS` is the only relevant IOCTL for the cleaning process β that's a key piece of information. I need to make sure I understand that interaction completely.
My next line of thinking, and a very important one in this design, is to look at the relationship between `nilfs_sufile_updatev` and `nilfs_sufile_set_suinfo`. Can the former be invoked from within the latter? That's going to be essential for understanding the data flow and potential synchronization issues, as this is a very sensitive area. I need to dig into the code and determine the exact calling structure. This is a critical point that needs to be clarified for this specific implementation.
|
| 45/2 |
2026/05/25 05:20 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/sufile.c IncludeLines:true Name:nilfs_sufile_set_suinfo]
Results: map[SourceCode: 916: /**
917: * nilfs_sufile_set_suinfo - sets segment usage info
918: * @sufile: inode of segment usage file
919: * @buf: array of suinfo_update
920: * @supsz: byte size of suinfo_update
921: * @nsup: size of suinfo_update array
922: *
923: * Description: Takes an array of nilfs_suinfo_update structs and updates
924: * segment usage accordingly. Only the fields indicated by the sup_flags
925: * are updated.
926: *
927: * Return: 0 on success, or one of the following negative error codes on
928: * failure:
929: * * %-EINVAL - Invalid values in input (segment number, flags or nblocks).
930: * * %-EIO - I/O error (including metadata corruption).
931: * * %-ENOMEM - Insufficient memory available.
932: */
933: ssize_t nilfs_sufile_set_suinfo(struct inode *sufile, void *buf,
934: unsigned int supsz, size_t nsup)
935: {
936: struct the_nilfs *nilfs = sufile->i_sb->s_fs_info;
937: struct buffer_head *header_bh, *bh;
938: struct nilfs_suinfo_update *sup, *supend = buf + supsz * nsup;
939: struct nilfs_segment_usage *su;
940: size_t offset;
941: unsigned long blkoff, prev_blkoff;
942: int cleansi, cleansu, dirtysi, dirtysu;
943: long ncleaned = 0, ndirtied = 0;
944: int ret = 0;
945:
946: if (unlikely(nsup == 0))
947: return ret;
948:
949: for (sup = buf; sup < supend; sup = (void *)sup + supsz) {
950: if (sup->sup_segnum >= nilfs->ns_nsegments
951: || (sup->sup_flags &
952: (~0UL << __NR_NILFS_SUINFO_UPDATE_FIELDS))
953: || (nilfs_suinfo_update_nblocks(sup) &&
954: sup->sup_sui.sui_nblocks >
955: nilfs->ns_blocks_per_segment))
956: return -EINVAL;
957: }
958:
959: down_write(&NILFS_MDT(sufile)->mi_sem);
960:
961: ret = nilfs_sufile_get_header_block(sufile, &header_bh);
962: if (ret < 0)
963: goto out_sem;
964:
965: sup = buf;
966: blkoff = nilfs_sufile_get_blkoff(sufile, sup->sup_segnum);
967: ret = nilfs_mdt_get_block(sufile, blkoff, 1, NULL, &bh);
968: if (ret < 0)
969: goto out_header;
970:
971: for (;;) {
972: offset = nilfs_sufile_segment_usage_offset(
973: sufile, sup->sup_segnum, bh);
974: su = kmap_local_folio(bh->b_folio, offset);
975:
976: if (nilfs_suinfo_update_lastmod(sup))
977: su->su_lastmod = cpu_to_le64(sup->sup_sui.sui_lastmod);
978:
979: if (nilfs_suinfo_update_nblocks(sup))
980: su->su_nblocks = cpu_to_le32(sup->sup_sui.sui_nblocks);
981:
982: if (nilfs_suinfo_update_flags(sup)) {
983: /*
984: * Active flag is a virtual flag projected by running
985: * nilfs kernel code - drop it not to write it to
986: * disk.
987: */
988: sup->sup_sui.sui_flags &=
989: ~BIT(NILFS_SEGMENT_USAGE_ACTIVE);
990:
991: cleansi = nilfs_suinfo_clean(&sup->sup_sui);
992: cleansu = nilfs_segment_usage_clean(su);
993: dirtysi = nilfs_suinfo_dirty(&sup->sup_sui);
994: dirtysu = nilfs_segment_usage_dirty(su);
995:
996: if (cleansi && !cleansu)
997: ++ncleaned;
998: else if (!cleansi && cleansu)
999: --ncleaned;
1000:
1001: if (dirtysi && !dirtysu)
1002: ++ndirtied;
1003: else if (!dirtysi && dirtysu)
1004: --ndirtied;
1005:
1006: su->su_flags = cpu_to_le32(sup->sup_sui.sui_flags);
1007: }
1008:
1009: kunmap_local(su);
1010:
1011: sup = (void *)sup + supsz;
1012: if (sup >= supend)
1013: break;
1014:
1015: prev_blkoff = blkoff;
1016: blkoff = nilfs_sufile_get_blkoff(sufile, sup->sup_segnum);
1017: if (blkoff == prev_blkoff)
1018: continue;
1019:
1020: /* get different block */
1021: mark_buffer_dirty(bh);
1022: put_bh(bh);
1023: ret = nilfs_mdt_get_block(sufile, blkoff, 1, NULL, &bh);
1024: if (unlikely(ret < 0))
1025: goto out_mark;
1026: }
1027: mark_buffer_dirty(bh);
1028: put_bh(bh);
1029:
1030: out_mark:
1031: if (ncleaned || ndirtied) {
1032: nilfs_sufile_mod_counter(header_bh, (u64)ncleaned,
1033: (u64)ndirtied);
1034: NILFS_SUI(sufile)->ncleansegs += ncleaned;
1035: }
1036: nilfs_mdt_mark_dirty(sufile);
1037: out_header:
1038: put_bh(header_bh);
1039: out_sem:
1040: up_write(&NILFS_MDT(sufile)->mi_sem);
1041: return ret;
1042: }
SourceFile:fs/nilfs2/sufile.c]
|
| 46/2 |
2026/05/25 05:20 |
llm |
expert |
0m
Model:
Tokens:
input: 48910
output: 44
thoughts: 920
Thoughts: **My Analysis of the NILFS2 Hung Task Bug**
Okay, here's what I've got so far. The key issue is `nilfs_sufile_updatev`. This function, specifically when passed invalid segment numbers, leads to a hung task due to excessive warnings being printed to the console. These invalid segment numbers are supplied by the user via the `NILFS_IOCTL_CLEAN_SEGMENTS` ioctl. This ioctl, thankfully, requires `CAP_SYS_ADMIN` within the initial user namespace. That's good, because it means unprivileged users or those within user namespaces cannot trigger this.
So, in essence, it's a denial-of-service vulnerability, but only root can exploit it. It's not exploitable in the sense that it doesn't lead to memory corruption or anything like that. It's not a malicious filesystem trigger since the vulnerability is tied directly to the ioctl itself and not some filesystem event. I need to see if `nilfs_warn` could be rate-limited, or if a patch has addressed this. But, I don't need that for this analysis.
Now, I was a bit worried that `nilfs_sufile_updatev` might be called from somewhere else, and that's the only way invalid segment numbers could be passed. So, I went back to make sure I followed the trace. I re-traced from `nilfs_sufile_freev` to confirm. That calls `nilfs_free_segments`, which calls `nilfs_segctor_collect_blocks`, and `nilfs_segctor_collect`, and then `nilfs_segctor_do_construct`. All calls eventually trace to `nilfs_clean_segments`. I double-checked if `sci->sc_freesegs` was populated anywhere else. Nope, just `nilfs_clean_segments`. And the only place `nilfs_clean_segments` gets called is from `nilfs_ioctl_clean_segments`.
Therefore, the only path is indeed the ioctl. I checked `nilfs_ioctl_clean_segments` is only called from `nilfs_ioctl`. I confirmed there is no compat ioctl path.
In conclusion, it looks like:
* **Exploitable: False**
* **DenialOfService: True**
* **Unprivileged: False**
* **UserNamespace: False**
* **VMGuestTrigger: False**
* **VMHostTrigger: False**
* **NetworkTrigger: False**
* **RemoteTrigger: False**
* **PeripheralTrigger: False**
* **FilesystemTrigger: False**
|
| 47/2 |
2026/05/25 05:20 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/ioctl.c IncludeLines:true Name:nilfs_compat_ioctl]
Results: map[SourceCode:1371: long nilfs_compat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
1372: {
1373: switch (cmd) {
1374: case FS_IOC32_GETVERSION:
1375: cmd = FS_IOC_GETVERSION;
1376: break;
1377: case NILFS_IOCTL_CHANGE_CPMODE:
1378: case NILFS_IOCTL_DELETE_CHECKPOINT:
1379: case NILFS_IOCTL_GET_CPINFO:
1380: case NILFS_IOCTL_GET_CPSTAT:
1381: case NILFS_IOCTL_GET_SUINFO:
1382: case NILFS_IOCTL_SET_SUINFO:
1383: case NILFS_IOCTL_GET_SUSTAT:
1384: case NILFS_IOCTL_GET_VINFO:
1385: case NILFS_IOCTL_GET_BDESCS:
1386: case NILFS_IOCTL_CLEAN_SEGMENTS:
1387: case NILFS_IOCTL_SYNC:
1388: case NILFS_IOCTL_RESIZE:
1389: case NILFS_IOCTL_SET_ALLOC_RANGE:
1390: case FITRIM:
1391: case FS_IOC_GETFSLABEL:
1392: case FS_IOC_SETFSLABEL:
1393: break;
1394: default:
1395: return -ENOIOCTLCMD;
1396: }
1397: return nilfs_ioctl(filp, cmd, (unsigned long)compat_ptr(arg));
1398: }
SourceFile:fs/nilfs2/ioctl.c]
|
| 48/2 |
2026/05/25 05:20 |
llm |
expert |
0m
Model:
Tokens:
input: 50944
output: 51
thoughts: 51
Thoughts: Okay, here's my take on those thoughts, framed as my own:
**Analyzing `nilfs_ioctl` and Namespace Capabilities**
Right, so it's straightforward β this comes down to the `nilfs_ioctl` call. That means, the original assessment is correct: we are going to need `CAP_SYS_ADMIN` within the initial user namespace. The requirement is pretty clear-cut there. I will quickly check over how `nilfs_sufile_get_nsegments` works, just to be sure there isn't something sneaky happening somewhere else, but I would assume this is all there is to it.
|
| 49/2 |
2026/05/25 05:20 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nilfs2/sufile.h IncludeLines:true Name:nilfs_sufile_get_nsegments]
Results: map[SourceCode: 18: static inline unsigned long nilfs_sufile_get_nsegments(struct inode *sufile)
19: {
20: return ((struct the_nilfs *)sufile->i_sb->s_fs_info)->ns_nsegments;
21: }
SourceFile:fs/nilfs2/sufile.h]
|
| 50/2 |
2026/05/25 05:20 |
llm |
expert |
0m
Model:
Tokens:
input: 51291
output: 66
thoughts: 251
Thoughts: **My Analysis of the `nilfs_sufile_updatev` Warning Loop**
Okay, so the function in question just returns `ns_nsegments`, which isn't particularly insightful. My main concern right now is how we can repeatedly trigger `nilfs_warn` in a tight loop within `nilfs_sufile_updatev`. Looking at the code snippet, it's clear the loop iterates through a segment number vector:
```c
for (seg = segnumv; seg < segnumv + nsegs; seg++) {
if (unlikely(*seg >= nilfs_sufile_get_nsegments(sufile))) {
nilfs_warn(sufile->i_sb,
"%s: invalid segment number: %llu",
__func__, (unsigned long long)*seg);
nerr++;
}
}
```
The issue is that if `nsegs` (the number of segments) is very large, this will generate a flood of warnings. We need to mitigate that. My initial thoughts on solutions are: we could break out of the loop after the first warning, return `-EINVAL` immediately without printing the warning, or, perhaps the best option, use `nilfs_warn_ratelimited`. I'll want to carefully weigh the pros and cons of each.
I've checked the important point that `nsegs` is controlled by the user through an ioctl and that the ioctl requires `CAP_SYS_ADMIN`. Since the user needs that capability, it doesn't appear to be a security vulnerability, but we should be mindful of how this impacts the end-user experience.
Now that I've analyzed this, I'm ready to move on to setting the results and formulating the final response.
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| 51/2 |
2026/05/25 05:20 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
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| 52/2 |
2026/05/25 05:20 |
llm |
expert |
0m
Model:
Tokens:
input: 52064
output: 708
thoughts: 240
Thoughts: **Final Thoughts on the Hung Task Bug**
Okay, the analysis is complete, and it's time to craft the final response. This comes down to a clear explanation of that pesky hung task. I've pinned down the root cause to a tight loop within `nilfs_sufile_updatev`. It's all stemming from that `NILFS_IOCTL_CLEAN_SEGMENTS` ioctl. It's essentially a DOS caused by excessive console logging.
Here's the scenario: the user, via the ioctl, provides an array of segment numbers. The code iterates through this array, and if it encounters invalid segment numbers, it helpfully prints a warning to the console for each one. The problem? When a massive number of invalid segments are supplied, the console output becomes the bottleneck. Itβs slow, and the tight loop becomes a hang β a denial-of-service condition.
However, and this is crucial, triggering this bug demands `CAP_SYS_ADMIN` in the initial user namespace. That's a key mitigation. This means this vulnerability isn't exploitable by unprivileged users or within user namespaces β and therefore it's not a security vulnerability. There's no memory corruption, no possibility of exploitation beyond, essentially, stopping the kernel. Finally, this isn't a malicious filesystem trigger as itβs the ioctl, not the filesystem itself that sets things off. It's a root-only denial of service.
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| 53/1 |
2026/05/25 05:20 |
action |
format-explanation |
0m
Results: map[Explanation:**Analysis of the Bug Report**
The bug report indicates a hung task (`syz.0.17`) blocked in
`nilfs_transaction_begin` while waiting for the `nilfs->ns_segctor_sem`
semaphore. Another task (`syz.3.20`) is holding this semaphore and is stuck
printing a large number of warnings to the console, which is a slow operation
and causes the system to hang.
By examining the stack trace and the source code, we can trace the issue to the
`NILFS_IOCTL_CLEAN_SEGMENTS` ioctl. This ioctl is used by the `nilfs_cleanerd`
garbage collection daemon to clean segments. It takes an array of segment
numbers to be freed from user space.
The ioctl eventually calls `nilfs_sufile_updatev()` in `fs/nilfs2/sufile.c`,
which contains the following loop:
```c
for (seg = segnumv; seg < segnumv + nsegs; seg++) {
if (unlikely(*seg >= nilfs_sufile_get_nsegments(sufile))) {
nilfs_warn(sufile->i_sb,
"%s: invalid segment number: %llu",
__func__, (unsigned long long)*seg);
nerr++;
}
}
```
If a user provides a very large `nsegs` value and populates the array with
invalid segment numbers, the kernel will print a warning for every single
invalid segment. Because console output (especially serial console) is extremely
slow, printing thousands or millions of warnings will block the task for a long
time, triggering the hung task watchdog and causing a Denial of Service (DoS).
**Security Impact Assessment**
While this bug causes a Denial of Service, it is **not a security
vulnerability** because it is completely inaccessible to unprivileged users.
Looking at the entry point for the ioctl in `fs/nilfs2/ioctl.c`:
```c
static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
unsigned int cmd, void __user *argp)
{
...
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
...
```
The very first check in the ioctl handler is `capable(CAP_SYS_ADMIN)`. The
`capable()` function checks for the capability in the **initial user
namespace**. This means that:
1. An unprivileged user cannot trigger this bug.
2. An unprivileged user inside a new user namespace (where they might have
`CAP_SYS_ADMIN` relative to that namespace) also cannot trigger this bug,
because `capable()` strictly checks the initial namespace (unlike
`ns_capable()`).
Furthermore:
* **Exploitable:** No. This is not a memory corruption issue; it is merely a
slow path causing a hung task.
* **Malicious Filesystem Trigger:** No. The bug is triggered by the ioctl
arguments provided by the user-space process, not by the kernel parsing
malicious filesystem metadata during mount or normal operations.
In conclusion, this is a root-only Denial of Service bug and does not cross any
privilege boundaries.]
|