| 0/0 |
2026/05/23 06:42 |
flow |
assessment-security |
38m
Results: map[DenialOfService:true Explanation:**Bug Analysis**
The crash is a NULL pointer dereference in `bvec_set_page()` called from
`__bio_add_page()`. It occurs because a `bio` structure is created with a `NULL`
`bi_io_vec` array but a non-zero `bi_max_vecs` count.
This is caused by a bug in `bio_alloc_bioset()` in `block/bio.c`. When
allocating a bio and its associated `bvec` array, the function first attempts a
fast-path slab allocation. If that fails, it falls back to allocating from the
`bio_set`'s mempools:
```c
gfp = try_alloc_gfp(gfp);
// ...
if (unlikely(!bio)) {
if (!(saved_gfp & __GFP_DIRECT_RECLAIM))
return NULL;
// ...
p = mempool_alloc(&bs->bio_pool, gfp);
bio = p + bs->front_pad;
if (nr_vecs > BIO_INLINE_VECS) {
nr_vecs = BIO_MAX_VECS;
bvecs = mempool_alloc(&bs->bvec_pool, gfp);
}
}
```
The issue is that `try_alloc_gfp(gfp)` strips the `__GFP_DIRECT_RECLAIM` flag
from the `gfp` mask. In the fallback path, `mempool_alloc()` is called with this
modified `gfp` mask instead of the original `saved_gfp`.
Because `__GFP_DIRECT_RECLAIM` is cleared, `mempool_alloc()` is not allowed to
sleep and wait for memory reclaim. If the `bvec_pool` is currently empty (due to
high concurrent I/O) and the underlying slab allocation fails (due to memory
pressure), `mempool_alloc()` will return `NULL`.
If `mempool_alloc` succeeds for the `bio_pool` but fails for the `bvec_pool`,
`bvecs` becomes `NULL`. `bio_alloc_bioset()` does not check for this failure and
proceeds to initialize the bio with `bvecs = NULL` and `nr_vecs = 256`.
When the caller (e.g., ext4 writeback) subsequently tries to add a page to this
bio via `bio_add_page()`, it executes
`bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], ...)`. Since `bi_vcnt` is `0`, it
attempts to write to index 0 of a `NULL` pointer, resulting in a direct write to
memory address `0x0` and an immediate kernel crash.
**Security Impact**
* **Exploitable:** **False**. The crash always occurs on the very first page
addition when `bi_vcnt` is `0`. It is impossible to advance the index to write
to an arbitrary memory offset. The bug strictly results in a NULL pointer
dereference (writing to address `0x0`), which is mitigated by `mmap_min_addr` on
modern systems and cannot be exploited for privilege escalation or arbitrary
code execution.
* **Denial of Service:** **True**. Triggering the bug causes a kernel
oops/panic, leading to a system crash.
* **Accessible From Unprivileged Processes:** **True**. Any unprivileged user
can trigger this by generating a massive amount of concurrent block I/O (e.g.,
writing to files, using `pipe2`, `epoll`, or loop devices) while inducing memory
pressure to exhaust the `bvec_pool` and force the allocation failure.
* **Accessible From User Namespaces:** **True**. Unprivileged users inside user
namespaces can perform the same I/O operations.
* **VM Guest Trigger:** **True**. A typical KVM guest can trigger this bug
within its own guest kernel by issuing heavy block I/O. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:true VMHostTrigger:false]
|
| 1/1 |
2026/05/23 06:42 |
action |
syz-repro-to-c-repro |
0m
Results: map[SimplifiedCRepro:// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <arpa/inet.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <linux/genetlink.h>
#include <linux/if_addr.h>
#include <linux/if_link.h>
#include <linux/in6.h>
#include <linux/neighbour.h>
#include <linux/net.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <linux/veth.h>
#ifndef __NR_epoll_pwait2
#define __NR_epoll_pwait2 441
#endif
struct nlmsg {
char* pos;
int nesting;
struct nlattr* nested[8];
char buf[4096];
};
static void netlink_init(struct nlmsg* nlmsg, int typ, int flags,
const void* data, int size)
{
memset(nlmsg, 0, sizeof(*nlmsg));
struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg->buf;
hdr->nlmsg_type = typ;
hdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | flags;
memcpy(hdr + 1, data, size);
nlmsg->pos = (char*)(hdr + 1) + NLMSG_ALIGN(size);
}
static void netlink_attr(struct nlmsg* nlmsg, int typ,
const void* data, int size)
{
struct nlattr* attr = (struct nlattr*)nlmsg->pos;
attr->nla_len = sizeof(*attr) + size;
attr->nla_type = typ;
if (size > 0)
memcpy(attr + 1, data, size);
nlmsg->pos += NLMSG_ALIGN(attr->nla_len);
}
static int netlink_send_ext(struct nlmsg* nlmsg, int sock,
uint16_t reply_type, int* reply_len, bool dofail)
{
if (nlmsg->pos > nlmsg->buf + sizeof(nlmsg->buf) || nlmsg->nesting)
exit(1);
struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg->buf;
hdr->nlmsg_len = nlmsg->pos - nlmsg->buf;
struct sockaddr_nl addr;
memset(&addr, 0, sizeof(addr));
addr.nl_family = AF_NETLINK;
ssize_t n = sendto(sock, nlmsg->buf, hdr->nlmsg_len, 0, (struct sockaddr*)&addr, sizeof(addr));
if (n != (ssize_t)hdr->nlmsg_len) {
if (dofail)
exit(1);
return -1;
}
n = recv(sock, nlmsg->buf, sizeof(nlmsg->buf), 0);
if (reply_len)
*reply_len = 0;
if (n < 0) {
if (dofail)
exit(1);
return -1;
}
if (n < (ssize_t)sizeof(struct nlmsghdr)) {
errno = EINVAL;
if (dofail)
exit(1);
return -1;
}
if (hdr->nlmsg_type == NLMSG_DONE)
return 0;
if (reply_len && hdr->nlmsg_type == reply_type) {
*reply_len = n;
return 0;
}
if (n < (ssize_t)(sizeof(struct nlmsghdr) + sizeof(struct nlmsgerr))) {
errno = EINVAL;
if (dofail)
exit(1);
return -1;
}
if (hdr->nlmsg_type != NLMSG_ERROR) {
errno = EINVAL;
if (dofail)
exit(1);
return -1;
}
errno = -((struct nlmsgerr*)(hdr + 1))->error;
return -errno;
}
static int netlink_query_family_id(struct nlmsg* nlmsg, int sock, const char* family_name, bool dofail)
{
struct genlmsghdr genlhdr;
memset(&genlhdr, 0, sizeof(genlhdr));
genlhdr.cmd = CTRL_CMD_GETFAMILY;
netlink_init(nlmsg, GENL_ID_CTRL, 0, &genlhdr, sizeof(genlhdr));
netlink_attr(nlmsg, CTRL_ATTR_FAMILY_NAME, family_name, strnlen(family_name, GENL_NAMSIZ - 1) + 1);
int n = 0;
int err = netlink_send_ext(nlmsg, sock, GENL_ID_CTRL, &n, dofail);
if (err < 0) {
return -1;
}
uint16_t id = 0;
struct nlattr* attr = (struct nlattr*)(nlmsg->buf + NLMSG_HDRLEN + NLMSG_ALIGN(sizeof(genlhdr)));
for (; (char*)attr < nlmsg->buf + n; attr = (struct nlattr*)((char*)attr + NLMSG_ALIGN(attr->nla_len))) {
if (attr->nla_type == CTRL_ATTR_FAMILY_ID) {
id = *(uint16_t*)(attr + 1);
break;
}
}
if (!id) {
errno = EINVAL;
return -1;
}
recv(sock, nlmsg->buf, sizeof(nlmsg->buf), 0);
return id;
}
static long syz_open_dev(volatile long a0, volatile long a1, volatile long a2)
{
if (a0 == 0xc || a0 == 0xb) {
char buf[128];
sprintf(buf, "/dev/%s/%d:%d", a0 == 0xc ? "char" : "block", (uint8_t)a1, (uint8_t)a2);
return open(buf, O_RDWR, 0);
} else {
unsigned long nb = a1;
char buf[1024];
char* hash;
strncpy(buf, (char*)a0, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = 0;
while ((hash = strchr(buf, '#'))) {
*hash = '0' + (char)(nb % 10);
nb /= 10;
}
return open(buf, a2 & ~O_CREAT, 0);
}
}
static long syz_open_procfs(volatile long a0, volatile long a1)
{
char buf[128];
memset(buf, 0, sizeof(buf));
if (a0 == 0) {
snprintf(buf, sizeof(buf), "/proc/self/%s", (char*)a1);
} else if (a0 == -1) {
snprintf(buf, sizeof(buf), "/proc/thread-self/%s", (char*)a1);
} else {
snprintf(buf, sizeof(buf), "/proc/self/task/%d/%s", (int)a0, (char*)a1);
}
int fd = open(buf, O_RDWR);
if (fd == -1)
fd = open(buf, O_RDONLY);
return fd;
}
static long syz_genetlink_get_family_id(volatile long name, volatile long sock_arg)
{
int fd = sock_arg;
if (fd < 0) {
fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
if (fd == -1) {
return -1;
}
}
struct nlmsg nlmsg_tmp;
int ret = netlink_query_family_id(&nlmsg_tmp, fd, (char*)name, false);
if ((int)sock_arg < 0)
close(fd);
if (ret < 0) {
return -1;
}
return ret;
}
uint64_t r[7] = {0xffffffffffffffff, 0xffffffffffffffff, 0x0, 0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff, 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)) {}
// pipe2$9p arguments: [
// pipefd: ptr[out, pipe_9p] {
// pipe_9p {
// rfd: rfd9p (resource)
// wfd: wfd9p (resource)
// }
// }
// flags: pipe_flags = 0x80 (8 bytes)
// ]
res = syscall(__NR_pipe2, /*pipefd=*/0x200000000000ul, /*flags=O_NOTIFICATION_PIPE*/0x80ul);
if (res != -1) {
r[0] = *(uint32_t*)0x200000000000;
r[1] = *(uint32_t*)0x200000000004;
}
// write$P9_RLCREATE arguments: [
// fd: wfd9p (resource)
// data: ptr[in, p9_msg[P9_RLCREATE, p9_ropen]] {
// p9_msg[P9_RLCREATE, p9_ropen] {
// size: bytesize = 0x18 (4 bytes)
// type: const = 0xf (1 bytes)
// tag: int16 = 0x1 (2 bytes)
// payload: p9_ropen {
// qid: p9_qid {
// type: p9_qid_types = 0x80 (1 bytes)
// version: int32 = 0x4 (4 bytes)
// path: int64 = 0x4 (8 bytes)
// }
// iounit: int32 = 0x1 (4 bytes)
// }
// }
// }
// size: bytesize = 0x18 (8 bytes)
// ]
*(uint32_t*)0x200000000040 = 0x18;
*(uint8_t*)0x200000000044 = 0xf;
*(uint16_t*)0x200000000045 = 1;
*(uint8_t*)0x200000000047 = 0x80;
*(uint32_t*)0x200000000048 = 4;
*(uint64_t*)0x20000000004c = 4;
*(uint32_t*)0x200000000054 = 1;
syscall(__NR_write, /*fd=*/r[1], /*data=*/0x200000000040ul, /*size=*/0x18ul);
// ioctl$BLKTRACESETUP arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0xc0481273 (4 bytes)
// arg: ptr[inout, blk_user_trace_setup] {
// blk_user_trace_setup {
// name: buffer: {00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00} (length 0x20)
// act_mask: int16 = 0x1 (2 bytes)
// pad = 0x0 (2 bytes)
// buf_size: int32 = 0x5b (4 bytes)
// buf_nr: int32 = 0xfffffffa (4 bytes)
// pad = 0x0 (4 bytes)
// start_lba: int64 = 0xbe6c (8 bytes)
// end_lba: int64 = 0x5a (8 bytes)
// pid: pid (resource)
// pad = 0x0 (4 bytes)
// }
// }
// ]
memset((void*)0x200000000080, 0, 32);
*(uint16_t*)0x2000000000a0 = 1;
*(uint32_t*)0x2000000000a4 = 0x5b;
*(uint32_t*)0x2000000000a8 = 0xfffffffa;
*(uint64_t*)0x2000000000b0 = 0xbe6c;
*(uint64_t*)0x2000000000b8 = 0x5a;
*(uint32_t*)0x2000000000c0 = -1;
res = syscall(__NR_ioctl, /*fd=*/(intptr_t)-1, /*cmd=*/0xc0481273, /*arg=*/0x200000000080ul);
if (res != -1)
r[2] = *(uint32_t*)0x2000000000c0;
// syz_open_procfs arguments: [
// pid: pid (resource)
// file: ptr[in, buffer] {
// buffer: {67 69 64 5f 6d 61 70 00} (length 0x8)
// }
// ]
// returns fd
memcpy((void*)0x200000000100, "gid_map\000", 8);
res = -1;
res = syz_open_procfs(/*pid=*/r[2], /*file=*/0x200000000100);
if (res != -1)
r[3] = res;
// ioctl$BLKTRACESTART arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1274 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x1274, /*arg=*/0ul);
// syz_open_dev$loop arguments: [
// dev: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 6c 6f 6f 70 23 00} (length 0xb)
// }
// id: intptr = 0x100000000 (8 bytes)
// flags: open_flags = 0x103000 (8 bytes)
// ]
// returns fd_loop
memcpy((void*)0x200000000180, "/dev/loop#\000", 11);
res = -1;
res = syz_open_dev(/*dev=*/0x200000000180, /*id=*/0x100000000, /*flags=O_SYNC|FASYNC*/0x103000);
if (res != -1)
r[4] = res;
// ioctl$BLKTRACESETUP arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0xc0481273 (4 bytes)
// arg: ptr[inout, blk_user_trace_setup] {
// blk_user_trace_setup {
// name: buffer: {00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00} (length 0x20)
// act_mask: int16 = 0x1 (2 bytes)
// pad = 0x0 (2 bytes)
// buf_size: int32 = 0x18148795 (4 bytes)
// buf_nr: int32 = 0x7 (4 bytes)
// pad = 0x0 (4 bytes)
// start_lba: int64 = 0x6 (8 bytes)
// end_lba: int64 = 0x0 (8 bytes)
// pid: pid (resource)
// pad = 0x0 (4 bytes)
// }
// }
// ]
memset((void*)0x2000000001c0, 0, 32);
*(uint16_t*)0x2000000001e0 = 1;
*(uint32_t*)0x2000000001e4 = 0x18148795;
*(uint32_t*)0x2000000001e8 = 7;
*(uint64_t*)0x2000000001f0 = 6;
*(uint64_t*)0x2000000001f8 = 0;
*(uint32_t*)0x200000000200 = r[2];
syscall(__NR_ioctl, /*fd=*/r[4], /*cmd=*/0xc0481273, /*arg=*/0x2000000001c0ul);
// ioctl$XFS_IOC_ERROR_CLEARALL arguments: [
// fd: fd (resource)
// cmd: const = 0x40085875 (4 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x40085875, 0);
// epoll_create1 arguments: [
// flags: epoll_flags = 0x0 (8 bytes)
// ]
// returns fd_epoll
res = syscall(__NR_epoll_create1, /*flags=*/0ul);
if (res != -1)
r[5] = res;
// epoll_pwait2 arguments: [
// epfd: fd_epoll (resource)
// events: ptr[out, array[epoll_event]] {
// array[epoll_event] {
// epoll_event {
// ev: epoll_ev = 0x0 (4 bytes)
// data: const = 0x0 (8 bytes)
// }
// }
// }
// maxevents: len = 0x1 (8 bytes)
// timeout: ptr[in, timespec] {
// timespec {
// sec: time_sec (resource)
// nsec: time_nsec (resource)
// }
// }
// sigmask: nil
// size: bytesize = 0x0 (8 bytes)
// ]
*(uint64_t*)0x2000000002c0 = 0;
*(uint64_t*)0x2000000002c8 = 0;
syscall(__NR_epoll_pwait2, /*epfd=*/r[5], /*events=*/0x200000000240ul, /*maxevents=*/1ul, /*timeout=*/0x2000000002c0ul, /*sigmask=*/0ul, /*size=*/0ul);
// ioctl$OCFS2_IOC_UNRESVSP arguments: [
// fd: fd (resource)
// cmd: const = 0x40305829 (4 bytes)
// arg: ptr[in, ocfs2_space_resv] {
// ocfs2_space_resv {
// l_type: ocfs2_l_type = 0x2 (2 bytes)
// l_whence: ocfs2_l_whence = 0x1 (2 bytes)
// pad = 0x0 (4 bytes)
// l_start: int64 = 0xfffffffffffffff9 (8 bytes)
// l_len: int64 = 0x5 (8 bytes)
// l_sysid: int32 = 0x7 (4 bytes)
// l_pid: int32 = 0x10 (4 bytes)
// l_pad: buffer: {00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00} (length 0x10)
// }
// }
// ]
*(uint16_t*)0x200000000340 = 2;
*(uint16_t*)0x200000000342 = 1;
*(uint64_t*)0x200000000348 = 0xfffffffffffffff9;
*(uint64_t*)0x200000000350 = 5;
*(uint32_t*)0x200000000358 = 7;
*(uint32_t*)0x20000000035c = 0x10;
memset((void*)0x200000000360, 0, 16);
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x40305829, /*arg=*/0x200000000340ul);
// fcntl$setstatus arguments: [
// fd: fd (resource)
// cmd: const = 0x4 (8 bytes)
// flags: fcntl_status = 0x40000 (8 bytes)
// ]
syscall(__NR_fcntl, /*fd=*/r[0], /*cmd=*/4ul, /*flags=O_NOATIME*/0x40000ul);
// ioctl$BLKTRACETEARDOWN arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1276 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x1276, /*arg=*/0ul);
// getsockopt$inet_IP_IPSEC_POLICY arguments: [
// fd: sock_in (resource)
// level: const = 0x0 (4 bytes)
// optname: const = 0x10 (4 bytes)
// optval: nil
// optlen: ptr[inout, len] {
// len = 0x0 (4 bytes)
// }
// ]
*(uint32_t*)0x2000000004c0 = 0;
syscall(__NR_getsockopt, /*fd=*/r[3], /*level=*/0, /*optname=*/0x10, /*optval=*/0ul, /*optlen=*/0x2000000004c0ul);
// ioctl$BLKTRACETEARDOWN arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1276 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[4], /*cmd=*/0x1276, /*arg=*/0ul);
// syz_genetlink_get_family_id$nl80211 arguments: [
// name: ptr[in, buffer] {
// buffer: {6e 6c 38 30 32 31 31 00} (length 0x8)
// }
// fd: sock_nl_generic (resource)
// ]
// returns nl80211_family_id
memcpy((void*)0x200000000640, "nl80211\000", 8);
syz_genetlink_get_family_id(/*name=*/0x200000000640, /*fd=*/r[3]);
// ioctl$sock_SIOCGIFINDEX_80211 arguments: [
// fd: sock (resource)
// cmd: const = 0x8933 (4 bytes)
// arg: ptr[out, ifreq_dev_t[nl80211_devnames, nl80211_ifindex]] {
// ifreq_dev_t[nl80211_devnames, nl80211_ifindex] {
// ifr_ifrn: buffer: {77 6c 61 6e 31 00 00 00 00 00 00 00 00 00 00 00} (length 0x10)
// elem: nl80211_ifindex (resource)
// pad = 0x0 (20 bytes)
// }
// }
// ]
memcpy((void*)0x200000000680, "wlan1\000\000\000\000\000\000\000\000\000\000\000", 16);
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x8933, /*arg=*/0x200000000680ul);
// sendmsg$NL80211_CMD_SET_MULTICAST_TO_UNICAST arguments: [
// fd: sock_nl_generic (resource)
// msg: ptr[in, msghdr_netlink[netlink_msg_t[nl80211_family_id, msg_nl80211_payload[NL80211_CMD_SET_MULTICAST_TO_UNICAST, nl80211_wdev_payload], nl80211_policy$set_mcast_to_ucast]]] {
// msghdr_netlink[netlink_msg_t[nl80211_family_id, msg_nl80211_payload[NL80211_CMD_SET_MULTICAST_TO_UNICAST, nl80211_wdev_payload], nl80211_policy$set_mcast_to_ucast]] {
// addr: ptr[in, sockaddr_nl_t[AF_NETLINK, const[0, int32], flags[netlink_group_bitmap, int32]]] {
// sockaddr_nl_t[AF_NETLINK, const[0, int32], flags[netlink_group_bitmap, int32]] {
// nl_family: const = 0x10 (2 bytes)
// nl_pad: const = 0x0 (2 bytes)
// nl_pid: const = 0x0 (4 bytes)
// nl_groups: netlink_group_bitmap = 0x400000 (4 bytes)
// }
// }
// addrlen: len = 0xc (4 bytes)
// pad = 0x0 (4 bytes)
// vec: nil
// vlen: const = 0x1 (8 bytes)
// ctrl: const = 0x0 (8 bytes)
// ctrllen: const = 0x0 (8 bytes)
// f: send_flags = 0x40080 (4 bytes)
// pad = 0x0 (4 bytes)
// }
// }
// f: send_flags = 0x24000004 (8 bytes)
// ]
*(uint64_t*)0x200000000740 = 0x200000000600;
*(uint16_t*)0x200000000600 = 0x10;
*(uint16_t*)0x200000000602 = 0;
*(uint32_t*)0x200000000604 = 0;
*(uint32_t*)0x200000000608 = 0x400000;
*(uint32_t*)0x200000000748 = 0xc;
*(uint64_t*)0x200000000750 = 0;
*(uint64_t*)0x200000000758 = 1;
*(uint64_t*)0x200000000760 = 0;
*(uint64_t*)0x200000000768 = 0;
*(uint32_t*)0x200000000770 = 0x40080;
syscall(__NR_sendmsg, /*fd=*/r[3], /*msg=*/0x200000000740ul, /*f=MSG_ZEROCOPY|MSG_FASTOPEN|MSG_DONTROUTE*/0x24000004ul);
// ioctl$BLKTRACESTART arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1274 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/(intptr_t)-1, /*cmd=*/0x1274, /*arg=*/0ul);
// ioctl$KVM_CREATE_VM arguments: [
// fd: fd_kvm (resource)
// cmd: const = 0xae01 (4 bytes)
// type: intptr = 0x1e (8 bytes)
// ]
// returns fd_kvmvm
res = syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0xae01, /*type=*/0x1eul);
if (res != -1)
r[6] = res;
// ioctl$KVM_CREATE_IRQCHIP arguments: [
// fd: fd_kvmvm (resource)
// cmd: const = 0xae60 (4 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[6], /*cmd=*/0xae60, 0);
// preadv arguments: [
// fd: fd (resource)
// vec: ptr[in, array[iovec[out, array[int8]]]] {
// array[iovec[out, array[int8]]] {
// iovec[out, array[int8]] {
// addr: ptr[out, buffer] {
// buffer: (DirOut)
// }
// len: len = 0x17 (8 bytes)
// }
// }
// }
// vlen: len = 0x1 (8 bytes)
// off_low: int32 = 0x1 (4 bytes)
// off_high: int32 = 0x0 (4 bytes)
// ]
*(uint64_t*)0x200000000800 = 0x2000000007c0;
*(uint64_t*)0x200000000808 = 0x17;
syscall(__NR_preadv, /*fd=*/r[6], /*vec=*/0x200000000800ul, /*vlen=*/1ul, /*off_low=*/1, /*off_high=*/0);
// setsockopt$ax25_int arguments: [
// fd: sock_ax25 (resource)
// level: const = 0x101 (4 bytes)
// optname: ax25_option_types_int = 0x9 (4 bytes)
// optval: ptr[in, int32] {
// int32 = 0x9 (4 bytes)
// }
// optlen: len = 0x4 (8 bytes)
// ]
*(uint32_t*)0x200000000840 = 9;
syscall(__NR_setsockopt, /*fd=*/(intptr_t)-1, /*level=*/0x101, /*optname=AX25_IDLE*/9, /*optval=*/0x200000000840ul, /*optlen=*/4ul);
// ioctl$BLKTRACETEARDOWN arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1276 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x1276, /*arg=*/0ul);
return 0;
}
]
|
| 2/1 |
2026/05/23 06:42 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/cf00e7e1bf032f4f2bab40eca7cf2bde41d10736]
|
| 3/1 |
2026/05/23 06:43 |
action |
kernel-builder |
15m
Results: map[KernelObj:/app/workdir/cache/build/e380001f84a99d4bbb4ff8d90862d27997854458]
|
| 4/1 |
2026/05/23 06:58 |
action |
codesearch-prepare |
17m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/05/23 07:15 |
agent |
expert |
5m
Model:
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:true 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:
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 UID: 0 PID: 35 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: writeback wb_workfn (flush-8:0)
RIP: 0010:bvec_set_page include/linux/bvec.h:44 [inline]
RIP: 0010:__bio_add_page block/bio.c:992 [inline]
RIP: 0010:bio_add_page+0x462/0x6e0 block/bio.c:1048
Code: fd 48 8b 1b 48 8b 44 24 30 42 0f b6 04 30 84 c0 0f 85 c3 01 00 00 48 8b 14 24 0f b7 02 c1 e0 04 48 01 c3 48 89 d8 48 c1 e8 03 <42> 80 3c 30 00 74 0c 48 89 df e8 5f da a3 fd 48 8b 14 24 48 8b 44
RSP: 0000:ffffc90000ab6b80 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88801eac3d00
RDX: ffff88802cd6ea78 RSI: 00000000ffffefff RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffea0001b06147 R09: 1ffffd4000360c28
R10: dffffc0000000000 R11: fffff94000360c29 R12: 1ffff110059add4f
R13: 0000000000001000 R14: dffffc0000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888124de1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9bc55ed6b8 CR3: 00000000769ea000 CR4: 00000000003526f0
Call Trace:
<TASK>
bio_add_folio+0x64/0x90 block/bio.c:1084
io_submit_add_bh fs/ext4/page-io.c:465 [inline]
ext4_bio_write_folio+0x1446/0x1ea0 fs/ext4/page-io.c:603
mpage_map_and_submit_buffers fs/ext4/inode.c:2326 [inline]
mpage_map_and_submit_extent fs/ext4/inode.c:2516 [inline]
ext4_do_writepages+0x207e/0x46e0 fs/ext4/inode.c:2928
ext4_writepages+0x241/0x3b0 fs/ext4/inode.c:3022
do_writepages+0x32e/0x550 mm/page-writeback.c:2554
__writeback_single_inode+0x133/0x11a0 fs/fs-writeback.c:1750
writeback_sb_inodes+0x992/0x1a20 fs/fs-writeback.c:2042
__writeback_inodes_wb+0x111/0x240 fs/fs-writeback.c:2118
wb_writeback+0x46a/0xb70 fs/fs-writeback.c:2229
wb_check_start_all fs/fs-writeback.c:2355 [inline]
wb_do_writeback fs/fs-writeback.c:2381 [inline]
wb_workfn+0x95b/0xf50 fs/fs-writeback.c:2414
process_one_work+0x9ab/0x1780 kernel/workqueue.c:3288
process_scheduled_works kernel/workqueue.c:3379 [inline]
worker_thread+0xba8/0x11e0 kernel/workqueue.c:3465
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:bvec_set_page include/linux/bvec.h:44 [inline]
RIP: 0010:__bio_add_page block/bio.c:992 [inline]
RIP: 0010:bio_add_page+0x462/0x6e0 block/bio.c:1048
Code: fd 48 8b 1b 48 8b 44 24 30 42 0f b6 04 30 84 c0 0f 85 c3 01 00 00 48 8b 14 24 0f b7 02 c1 e0 04 48 01 c3 48 89 d8 48 c1 e8 03 <42> 80 3c 30 00 74 0c 48 89 df e8 5f da a3 fd 48 8b 14 24 48 8b 44
RSP: 0000:ffffc90000ab6b80 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88801eac3d00
RDX: ffff88802cd6ea78 RSI: 00000000ffffefff RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffea0001b06147 R09: 1ffffd4000360c28
R10: dffffc0000000000 R11: fffff94000360c29 R12: 1ffff110059add4f
R13: 0000000000001000 R14: dffffc0000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888124ee1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005577be56a168 CR3: 000000002552e000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: fd std
1: 48 8b 1b mov (%rbx),%rbx
4: 48 8b 44 24 30 mov 0x30(%rsp),%rax
9: 42 0f b6 04 30 movzbl (%rax,%r14,1),%eax
e: 84 c0 test %al,%al
10: 0f 85 c3 01 00 00 jne 0x1d9
16: 48 8b 14 24 mov (%rsp),%rdx
1a: 0f b7 02 movzwl (%rdx),%eax
1d: c1 e0 04 shl $0x4,%eax
20: 48 01 c3 add %rax,%rbx
23: 48 89 d8 mov %rbx,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 80 3c 30 00 cmpb $0x0,(%rax,%r14,1) <-- trapping instruction
2f: 74 0c je 0x3d
31: 48 89 df mov %rbx,%rdi
34: e8 5f da a3 fd call 0xfda3da98
39: 48 8b 14 24 mov (%rsp),%rdx
3d: 48 rex.W
3e: 8b .byte 0x8b
3f: 44 rex.R
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 <arpa/inet.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <linux/genetlink.h>
#include <linux/if_addr.h>
#include <linux/if_link.h>
#include <linux/in6.h>
#include <linux/neighbour.h>
#include <linux/net.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <linux/veth.h>
#ifndef __NR_epoll_pwait2
#define __NR_epoll_pwait2 441
#endif
struct nlmsg {
char* pos;
int nesting;
struct nlattr* nested[8];
char buf[4096];
};
static void netlink_init(struct nlmsg* nlmsg, int typ, int flags,
const void* data, int size)
{
memset(nlmsg, 0, sizeof(*nlmsg));
struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg->buf;
hdr->nlmsg_type = typ;
hdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | flags;
memcpy(hdr + 1, data, size);
nlmsg->pos = (char*)(hdr + 1) + NLMSG_ALIGN(size);
}
static void netlink_attr(struct nlmsg* nlmsg, int typ,
const void* data, int size)
{
struct nlattr* attr = (struct nlattr*)nlmsg->pos;
attr->nla_len = sizeof(*attr) + size;
attr->nla_type = typ;
if (size > 0)
memcpy(attr + 1, data, size);
nlmsg->pos += NLMSG_ALIGN(attr->nla_len);
}
static int netlink_send_ext(struct nlmsg* nlmsg, int sock,
uint16_t reply_type, int* reply_len, bool dofail)
{
if (nlmsg->pos > nlmsg->buf + sizeof(nlmsg->buf) || nlmsg->nesting)
exit(1);
struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg->buf;
hdr->nlmsg_len = nlmsg->pos - nlmsg->buf;
struct sockaddr_nl addr;
memset(&addr, 0, sizeof(addr));
addr.nl_family = AF_NETLINK;
ssize_t n = sendto(sock, nlmsg->buf, hdr->nlmsg_len, 0, (struct sockaddr*)&addr, sizeof(addr));
if (n != (ssize_t)hdr->nlmsg_len) {
if (dofail)
exit(1);
return -1;
}
n = recv(sock, nlmsg->buf, sizeof(nlmsg->buf), 0);
if (reply_len)
*reply_len = 0;
if (n < 0) {
if (dofail)
exit(1);
return -1;
}
if (n < (ssize_t)sizeof(struct nlmsghdr)) {
errno = EINVAL;
if (dofail)
exit(1);
return -1;
}
if (hdr->nlmsg_type == NLMSG_DONE)
return 0;
if (reply_len && hdr->nlmsg_type == reply_type) {
*reply_len = n;
return 0;
}
if (n < (ssize_t)(sizeof(struct nlmsghdr) + sizeof(struct nlmsgerr))) {
errno = EINVAL;
if (dofail)
exit(1);
return -1;
}
if (hdr->nlmsg_type != NLMSG_ERROR) {
errno = EINVAL;
if (dofail)
exit(1);
return -1;
}
errno = -((struct nlmsgerr*)(hdr + 1))->error;
return -errno;
}
static int netlink_query_family_id(struct nlmsg* nlmsg, int sock, const char* family_name, bool dofail)
{
struct genlmsghdr genlhdr;
memset(&genlhdr, 0, sizeof(genlhdr));
genlhdr.cmd = CTRL_CMD_GETFAMILY;
netlink_init(nlmsg, GENL_ID_CTRL, 0, &genlhdr, sizeof(genlhdr));
netlink_attr(nlmsg, CTRL_ATTR_FAMILY_NAME, family_name, strnlen(family_name, GENL_NAMSIZ - 1) + 1);
int n = 0;
int err = netlink_send_ext(nlmsg, sock, GENL_ID_CTRL, &n, dofail);
if (err < 0) {
return -1;
}
uint16_t id = 0;
struct nlattr* attr = (struct nlattr*)(nlmsg->buf + NLMSG_HDRLEN + NLMSG_ALIGN(sizeof(genlhdr)));
for (; (char*)attr < nlmsg->buf + n; attr = (struct nlattr*)((char*)attr + NLMSG_ALIGN(attr->nla_len))) {
if (attr->nla_type == CTRL_ATTR_FAMILY_ID) {
id = *(uint16_t*)(attr + 1);
break;
}
}
if (!id) {
errno = EINVAL;
return -1;
}
recv(sock, nlmsg->buf, sizeof(nlmsg->buf), 0);
return id;
}
static long syz_open_dev(volatile long a0, volatile long a1, volatile long a2)
{
if (a0 == 0xc || a0 == 0xb) {
char buf[128];
sprintf(buf, "/dev/%s/%d:%d", a0 == 0xc ? "char" : "block", (uint8_t)a1, (uint8_t)a2);
return open(buf, O_RDWR, 0);
} else {
unsigned long nb = a1;
char buf[1024];
char* hash;
strncpy(buf, (char*)a0, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = 0;
while ((hash = strchr(buf, '#'))) {
*hash = '0' + (char)(nb % 10);
nb /= 10;
}
return open(buf, a2 & ~O_CREAT, 0);
}
}
static long syz_open_procfs(volatile long a0, volatile long a1)
{
char buf[128];
memset(buf, 0, sizeof(buf));
if (a0 == 0) {
snprintf(buf, sizeof(buf), "/proc/self/%s", (char*)a1);
} else if (a0 == -1) {
snprintf(buf, sizeof(buf), "/proc/thread-self/%s", (char*)a1);
} else {
snprintf(buf, sizeof(buf), "/proc/self/task/%d/%s", (int)a0, (char*)a1);
}
int fd = open(buf, O_RDWR);
if (fd == -1)
fd = open(buf, O_RDONLY);
return fd;
}
static long syz_genetlink_get_family_id(volatile long name, volatile long sock_arg)
{
int fd = sock_arg;
if (fd < 0) {
fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
if (fd == -1) {
return -1;
}
}
struct nlmsg nlmsg_tmp;
int ret = netlink_query_family_id(&nlmsg_tmp, fd, (char*)name, false);
if ((int)sock_arg < 0)
close(fd);
if (ret < 0) {
return -1;
}
return ret;
}
uint64_t r[7] = {0xffffffffffffffff, 0xffffffffffffffff, 0x0, 0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff, 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)) {}
// pipe2$9p arguments: [
// pipefd: ptr[out, pipe_9p] {
// pipe_9p {
// rfd: rfd9p (resource)
// wfd: wfd9p (resource)
// }
// }
// flags: pipe_flags = 0x80 (8 bytes)
// ]
res = syscall(__NR_pipe2, /*pipefd=*/0x200000000000ul, /*flags=O_NOTIFICATION_PIPE*/0x80ul);
if (res != -1) {
r[0] = *(uint32_t*)0x200000000000;
r[1] = *(uint32_t*)0x200000000004;
}
// write$P9_RLCREATE arguments: [
// fd: wfd9p (resource)
// data: ptr[in, p9_msg[P9_RLCREATE, p9_ropen]] {
// p9_msg[P9_RLCREATE, p9_ropen] {
// size: bytesize = 0x18 (4 bytes)
// type: const = 0xf (1 bytes)
// tag: int16 = 0x1 (2 bytes)
// payload: p9_ropen {
// qid: p9_qid {
// type: p9_qid_types = 0x80 (1 bytes)
// version: int32 = 0x4 (4 bytes)
// path: int64 = 0x4 (8 bytes)
// }
// iounit: int32 = 0x1 (4 bytes)
// }
// }
// }
// size: bytesize = 0x18 (8 bytes)
// ]
*(uint32_t*)0x200000000040 = 0x18;
*(uint8_t*)0x200000000044 = 0xf;
*(uint16_t*)0x200000000045 = 1;
*(uint8_t*)0x200000000047 = 0x80;
*(uint32_t*)0x200000000048 = 4;
*(uint64_t*)0x20000000004c = 4;
*(uint32_t*)0x200000000054 = 1;
syscall(__NR_write, /*fd=*/r[1], /*data=*/0x200000000040ul, /*size=*/0x18ul);
// ioctl$BLKTRACESETUP arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0xc0481273 (4 bytes)
// arg: ptr[inout, blk_user_trace_setup] {
// blk_user_trace_setup {
// name: buffer: {00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00} (length 0x20)
// act_mask: int16 = 0x1 (2 bytes)
// pad = 0x0 (2 bytes)
// buf_size: int32 = 0x5b (4 bytes)
// buf_nr: int32 = 0xfffffffa (4 bytes)
// pad = 0x0 (4 bytes)
// start_lba: int64 = 0xbe6c (8 bytes)
// end_lba: int64 = 0x5a (8 bytes)
// pid: pid (resource)
// pad = 0x0 (4 bytes)
// }
// }
// ]
memset((void*)0x200000000080, 0, 32);
*(uint16_t*)0x2000000000a0 = 1;
*(uint32_t*)0x2000000000a4 = 0x5b;
*(uint32_t*)0x2000000000a8 = 0xfffffffa;
*(uint64_t*)0x2000000000b0 = 0xbe6c;
*(uint64_t*)0x2000000000b8 = 0x5a;
*(uint32_t*)0x2000000000c0 = -1;
res = syscall(__NR_ioctl, /*fd=*/(intptr_t)-1, /*cmd=*/0xc0481273, /*arg=*/0x200000000080ul);
if (res != -1)
r[2] = *(uint32_t*)0x2000000000c0;
// syz_open_procfs arguments: [
// pid: pid (resource)
// file: ptr[in, buffer] {
// buffer: {67 69 64 5f 6d 61 70 00} (length 0x8)
// }
// ]
// returns fd
memcpy((void*)0x200000000100, "gid_map\000", 8);
res = -1;
res = syz_open_procfs(/*pid=*/r[2], /*file=*/0x200000000100);
if (res != -1)
r[3] = res;
// ioctl$BLKTRACESTART arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1274 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x1274, /*arg=*/0ul);
// syz_open_dev$loop arguments: [
// dev: ptr[in, buffer] {
// buffer: {2f 64 65 76 2f 6c 6f 6f 70 23 00} (length 0xb)
// }
// id: intptr = 0x100000000 (8 bytes)
// flags: open_flags = 0x103000 (8 bytes)
// ]
// returns fd_loop
memcpy((void*)0x200000000180, "/dev/loop#\000", 11);
res = -1;
res = syz_open_dev(/*dev=*/0x200000000180, /*id=*/0x100000000, /*flags=O_SYNC|FASYNC*/0x103000);
if (res != -1)
r[4] = res;
// ioctl$BLKTRACESETUP arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0xc0481273 (4 bytes)
// arg: ptr[inout, blk_user_trace_setup] {
// blk_user_trace_setup {
// name: buffer: {00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00} (length 0x20)
// act_mask: int16 = 0x1 (2 bytes)
// pad = 0x0 (2 bytes)
// buf_size: int32 = 0x18148795 (4 bytes)
// buf_nr: int32 = 0x7 (4 bytes)
// pad = 0x0 (4 bytes)
// start_lba: int64 = 0x6 (8 bytes)
// end_lba: int64 = 0x0 (8 bytes)
// pid: pid (resource)
// pad = 0x0 (4 bytes)
// }
// }
// ]
memset((void*)0x2000000001c0, 0, 32);
*(uint16_t*)0x2000000001e0 = 1;
*(uint32_t*)0x2000000001e4 = 0x18148795;
*(uint32_t*)0x2000000001e8 = 7;
*(uint64_t*)0x2000000001f0 = 6;
*(uint64_t*)0x2000000001f8 = 0;
*(uint32_t*)0x200000000200 = r[2];
syscall(__NR_ioctl, /*fd=*/r[4], /*cmd=*/0xc0481273, /*arg=*/0x2000000001c0ul);
// ioctl$XFS_IOC_ERROR_CLEARALL arguments: [
// fd: fd (resource)
// cmd: const = 0x40085875 (4 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x40085875, 0);
// epoll_create1 arguments: [
// flags: epoll_flags = 0x0 (8 bytes)
// ]
// returns fd_epoll
res = syscall(__NR_epoll_create1, /*flags=*/0ul);
if (res != -1)
r[5] = res;
// epoll_pwait2 arguments: [
// epfd: fd_epoll (resource)
// events: ptr[out, array[epoll_event]] {
// array[epoll_event] {
// epoll_event {
// ev: epoll_ev = 0x0 (4 bytes)
// data: const = 0x0 (8 bytes)
// }
// }
// }
// maxevents: len = 0x1 (8 bytes)
// timeout: ptr[in, timespec] {
// timespec {
// sec: time_sec (resource)
// nsec: time_nsec (resource)
// }
// }
// sigmask: nil
// size: bytesize = 0x0 (8 bytes)
// ]
*(uint64_t*)0x2000000002c0 = 0;
*(uint64_t*)0x2000000002c8 = 0;
syscall(__NR_epoll_pwait2, /*epfd=*/r[5], /*events=*/0x200000000240ul, /*maxevents=*/1ul, /*timeout=*/0x2000000002c0ul, /*sigmask=*/0ul, /*size=*/0ul);
// ioctl$OCFS2_IOC_UNRESVSP arguments: [
// fd: fd (resource)
// cmd: const = 0x40305829 (4 bytes)
// arg: ptr[in, ocfs2_space_resv] {
// ocfs2_space_resv {
// l_type: ocfs2_l_type = 0x2 (2 bytes)
// l_whence: ocfs2_l_whence = 0x1 (2 bytes)
// pad = 0x0 (4 bytes)
// l_start: int64 = 0xfffffffffffffff9 (8 bytes)
// l_len: int64 = 0x5 (8 bytes)
// l_sysid: int32 = 0x7 (4 bytes)
// l_pid: int32 = 0x10 (4 bytes)
// l_pad: buffer: {00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00} (length 0x10)
// }
// }
// ]
*(uint16_t*)0x200000000340 = 2;
*(uint16_t*)0x200000000342 = 1;
*(uint64_t*)0x200000000348 = 0xfffffffffffffff9;
*(uint64_t*)0x200000000350 = 5;
*(uint32_t*)0x200000000358 = 7;
*(uint32_t*)0x20000000035c = 0x10;
memset((void*)0x200000000360, 0, 16);
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x40305829, /*arg=*/0x200000000340ul);
// fcntl$setstatus arguments: [
// fd: fd (resource)
// cmd: const = 0x4 (8 bytes)
// flags: fcntl_status = 0x40000 (8 bytes)
// ]
syscall(__NR_fcntl, /*fd=*/r[0], /*cmd=*/4ul, /*flags=O_NOATIME*/0x40000ul);
// ioctl$BLKTRACETEARDOWN arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1276 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x1276, /*arg=*/0ul);
// getsockopt$inet_IP_IPSEC_POLICY arguments: [
// fd: sock_in (resource)
// level: const = 0x0 (4 bytes)
// optname: const = 0x10 (4 bytes)
// optval: nil
// optlen: ptr[inout, len] {
// len = 0x0 (4 bytes)
// }
// ]
*(uint32_t*)0x2000000004c0 = 0;
syscall(__NR_getsockopt, /*fd=*/r[3], /*level=*/0, /*optname=*/0x10, /*optval=*/0ul, /*optlen=*/0x2000000004c0ul);
// ioctl$BLKTRACETEARDOWN arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1276 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[4], /*cmd=*/0x1276, /*arg=*/0ul);
// syz_genetlink_get_family_id$nl80211 arguments: [
// name: ptr[in, buffer] {
// buffer: {6e 6c 38 30 32 31 31 00} (length 0x8)
// }
// fd: sock_nl_generic (resource)
// ]
// returns nl80211_family_id
memcpy((void*)0x200000000640, "nl80211\000", 8);
syz_genetlink_get_family_id(/*name=*/0x200000000640, /*fd=*/r[3]);
// ioctl$sock_SIOCGIFINDEX_80211 arguments: [
// fd: sock (resource)
// cmd: const = 0x8933 (4 bytes)
// arg: ptr[out, ifreq_dev_t[nl80211_devnames, nl80211_ifindex]] {
// ifreq_dev_t[nl80211_devnames, nl80211_ifindex] {
// ifr_ifrn: buffer: {77 6c 61 6e 31 00 00 00 00 00 00 00 00 00 00 00} (length 0x10)
// elem: nl80211_ifindex (resource)
// pad = 0x0 (20 bytes)
// }
// }
// ]
memcpy((void*)0x200000000680, "wlan1\000\000\000\000\000\000\000\000\000\000\000", 16);
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x8933, /*arg=*/0x200000000680ul);
// sendmsg$NL80211_CMD_SET_MULTICAST_TO_UNICAST arguments: [
// fd: sock_nl_generic (resource)
// msg: ptr[in, msghdr_netlink[netlink_msg_t[nl80211_family_id, msg_nl80211_payload[NL80211_CMD_SET_MULTICAST_TO_UNICAST, nl80211_wdev_payload], nl80211_policy$set_mcast_to_ucast]]] {
// msghdr_netlink[netlink_msg_t[nl80211_family_id, msg_nl80211_payload[NL80211_CMD_SET_MULTICAST_TO_UNICAST, nl80211_wdev_payload], nl80211_policy$set_mcast_to_ucast]] {
// addr: ptr[in, sockaddr_nl_t[AF_NETLINK, const[0, int32], flags[netlink_group_bitmap, int32]]] {
// sockaddr_nl_t[AF_NETLINK, const[0, int32], flags[netlink_group_bitmap, int32]] {
// nl_family: const = 0x10 (2 bytes)
// nl_pad: const = 0x0 (2 bytes)
// nl_pid: const = 0x0 (4 bytes)
// nl_groups: netlink_group_bitmap = 0x400000 (4 bytes)
// }
// }
// addrlen: len = 0xc (4 bytes)
// pad = 0x0 (4 bytes)
// vec: nil
// vlen: const = 0x1 (8 bytes)
// ctrl: const = 0x0 (8 bytes)
// ctrllen: const = 0x0 (8 bytes)
// f: send_flags = 0x40080 (4 bytes)
// pad = 0x0 (4 bytes)
// }
// }
// f: send_flags = 0x24000004 (8 bytes)
// ]
*(uint64_t*)0x200000000740 = 0x200000000600;
*(uint16_t*)0x200000000600 = 0x10;
*(uint16_t*)0x200000000602 = 0;
*(uint32_t*)0x200000000604 = 0;
*(uint32_t*)0x200000000608 = 0x400000;
*(uint32_t*)0x200000000748 = 0xc;
*(uint64_t*)0x200000000750 = 0;
*(uint64_t*)0x200000000758 = 1;
*(uint64_t*)0x200000000760 = 0;
*(uint64_t*)0x200000000768 = 0;
*(uint32_t*)0x200000000770 = 0x40080;
syscall(__NR_sendmsg, /*fd=*/r[3], /*msg=*/0x200000000740ul, /*f=MSG_ZEROCOPY|MSG_FASTOPEN|MSG_DONTROUTE*/0x24000004ul);
// ioctl$BLKTRACESTART arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1274 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/(intptr_t)-1, /*cmd=*/0x1274, /*arg=*/0ul);
// ioctl$KVM_CREATE_VM arguments: [
// fd: fd_kvm (resource)
// cmd: const = 0xae01 (4 bytes)
// type: intptr = 0x1e (8 bytes)
// ]
// returns fd_kvmvm
res = syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0xae01, /*type=*/0x1eul);
if (res != -1)
r[6] = res;
// ioctl$KVM_CREATE_IRQCHIP arguments: [
// fd: fd_kvmvm (resource)
// cmd: const = 0xae60 (4 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[6], /*cmd=*/0xae60, 0);
// preadv arguments: [
// fd: fd (resource)
// vec: ptr[in, array[iovec[out, array[int8]]]] {
// array[iovec[out, array[int8]]] {
// iovec[out, array[int8]] {
// addr: ptr[out, buffer] {
// buffer: (DirOut)
// }
// len: len = 0x17 (8 bytes)
// }
// }
// }
// vlen: len = 0x1 (8 bytes)
// off_low: int32 = 0x1 (4 bytes)
// off_high: int32 = 0x0 (4 bytes)
// ]
*(uint64_t*)0x200000000800 = 0x2000000007c0;
*(uint64_t*)0x200000000808 = 0x17;
syscall(__NR_preadv, /*fd=*/r[6], /*vec=*/0x200000000800ul, /*vlen=*/1ul, /*off_low=*/1, /*off_high=*/0);
// setsockopt$ax25_int arguments: [
// fd: sock_ax25 (resource)
// level: const = 0x101 (4 bytes)
// optname: ax25_option_types_int = 0x9 (4 bytes)
// optval: ptr[in, int32] {
// int32 = 0x9 (4 bytes)
// }
// optlen: len = 0x4 (8 bytes)
// ]
*(uint32_t*)0x200000000840 = 9;
syscall(__NR_setsockopt, /*fd=*/(intptr_t)-1, /*level=*/0x101, /*optname=AX25_IDLE*/9, /*optval=*/0x200000000840ul, /*optlen=*/4ul);
// ioctl$BLKTRACETEARDOWN arguments: [
// fd: fd_block_trace (resource)
// cmd: const = 0x1276 (4 bytes)
// arg: const = 0x0 (8 bytes)
// ]
syscall(__NR_ioctl, /*fd=*/r[3], /*cmd=*/0x1276, /*arg=*/0ul);
return 0;
}
Reply: **Bug Analysis**
The crash is a NULL pointer dereference in `bvec_set_page()` called from `__bio_add_page()`. It occurs because a `bio` structure is created with a `NULL` `bi_io_vec` array but a non-zero `bi_max_vecs` count.
This is caused by a bug in `bio_alloc_bioset()` in `block/bio.c`. When allocating a bio and its associated `bvec` array, the function first attempts a fast-path slab allocation. If that fails, it falls back to allocating from the `bio_set`'s mempools:
```c
gfp = try_alloc_gfp(gfp);
// ...
if (unlikely(!bio)) {
if (!(saved_gfp & __GFP_DIRECT_RECLAIM))
return NULL;
// ...
p = mempool_alloc(&bs->bio_pool, gfp);
bio = p + bs->front_pad;
if (nr_vecs > BIO_INLINE_VECS) {
nr_vecs = BIO_MAX_VECS;
bvecs = mempool_alloc(&bs->bvec_pool, gfp);
}
}
```
The issue is that `try_alloc_gfp(gfp)` strips the `__GFP_DIRECT_RECLAIM` flag from the `gfp` mask. In the fallback path, `mempool_alloc()` is called with this modified `gfp` mask instead of the original `saved_gfp`.
Because `__GFP_DIRECT_RECLAIM` is cleared, `mempool_alloc()` is not allowed to sleep and wait for memory reclaim. If the `bvec_pool` is currently empty (due to high concurrent I/O) and the underlying slab allocation fails (due to memory pressure), `mempool_alloc()` will return `NULL`.
If `mempool_alloc` succeeds for the `bio_pool` but fails for the `bvec_pool`, `bvecs` becomes `NULL`. `bio_alloc_bioset()` does not check for this failure and proceeds to initialize the bio with `bvecs = NULL` and `nr_vecs = 256`.
When the caller (e.g., ext4 writeback) subsequently tries to add a page to this bio via `bio_add_page()`, it executes `bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], ...)`. Since `bi_vcnt` is `0`, it attempts to write to index 0 of a `NULL` pointer, resulting in a direct write to memory address `0x0` and an immediate kernel crash.
**Security Impact**
* **Exploitable:** **False**. The crash always occurs on the very first page addition when `bi_vcnt` is `0`. It is impossible to advance the index to write to an arbitrary memory offset. The bug strictly results in a NULL pointer dereference (writing to address `0x0`), which is mitigated by `mmap_min_addr` on modern systems and cannot be exploited for privilege escalation or arbitrary code execution.
* **Denial of Service:** **True**. Triggering the bug causes a kernel oops/panic, leading to a system crash.
* **Accessible From Unprivileged Processes:** **True**. Any unprivileged user can trigger this by generating a massive amount of concurrent block I/O (e.g., writing to files, using `pipe2`, `epoll`, or loop devices) while inducing memory pressure to exhaust the `bvec_pool` and force the allocation failure.
* **Accessible From User Namespaces:** **True**. Unprivileged users inside user namespaces can perform the same I/O operations.
* **VM Guest Trigger:** **True**. A typical KVM guest can trigger this bug within its own guest kernel by issuing heavy block I/O.
|
| 6/2 |
2026/05/23 07:15 |
llm |
expert |
0m
Model:
Tokens:
input: 17222
output: 20
thoughts: 664
Thoughts: **Kernel Bug Deep Dive**
Okay, here's what's running through my mind. I've got a kernel bug report that's screaming "general protection fault," specifically a null-pointer dereference. The KASAN report pinpoints the problem within `bvec_set_page` (inline within `include/linux/bvec.h`), and the crash happens in `__bio_add_page` then `bio_add_page` within `block/bio.c`. That's the immediate problem. The address in question (0xdffffc0000000000) looks non-canonical, which raises an eyebrow, but the KASAN report is the more immediate concern with that null pointer dereference.
I need to understand the context. The call trace shows this originated from within the ext4 filesystem, specifically in `ext4_do_writepages`, which is called as part of the writeback process. It seems that during writeback, `ext4_do_writepages` calls `bio_add_page` which triggers the bug via `bvec_set_page` and, thus, the dereference. The `ext4` filesystem context is a strong hint that the problem is specific to how ext4 handles page I/O, or a generic function being used by ext4.
I need to dig into `bvec_set_page` first. What are the assumptions it's making about the `page` it's given? What are the implications of a null pointer here? Since it's inline, I need to understand exactly what's going on within that macro. Then, I need to correlate that back to `__bio_add_page`, and then `bio_add_page`, to see what's passing a null pointer here. I should also check the `ext4_bio_write_folio` function, the likely source, to understand its parameters.
This whole thing smells like a page accounting issue during writeback β maybe a race condition where the page is freed before it's properly added to the bio, or perhaps some corruption in the page list. My initial guess would be a problem in the synchronization between page allocation/deallocation and the block device layer. The writeback path is a known area of complexity, with multiple threads and asynchronous operations interacting, so that's a prime suspect. Let me start by reviewing the code around the `page` argument in the functions listed.
|
| 7/2 |
2026/05/23 07:15 |
tool |
grepper |
0m
Args: map[Expression:bvec_set_page]
Results: map[Output:block/bio-integrity.c=67=void bio_integrity_alloc_buf(struct bio *bio, bool zero_buffer)
--
block/bio-integrity.c-82- memset(page_address(page), 0, len);
block/bio-integrity.c:83: bvec_set_page(&bip->bip_vec[0], page, len, 0);
block/bio-integrity.c-84- bip->bip_flags |= BIP_MEMPOOL;
block/bio-integrity.c-85- } else {
block/bio-integrity.c:86: bvec_set_page(&bip->bip_vec[0], virt_to_page(buf), len,
block/bio-integrity.c-87- offset_in_page(buf));
--
block/bio-integrity.c=225=int bio_integrity_add_page(struct bio *bio, struct page *page,
--
block/bio-integrity.c-253-
block/bio-integrity.c:254: bvec_set_page(&bip->bip_vec[bip->bip_vcnt], page, len, offset);
block/bio-integrity.c-255- bip->bip_vcnt++;
--
block/bio-integrity.c=335=static unsigned int bvec_from_pages(struct bio_vec *bvec, struct page **pages,
--
block/bio-integrity.c-360-
block/bio-integrity.c:361: bvec_set_page(&bvec[nr_bvecs], pages[i], size, offset);
block/bio-integrity.c-362- offset = 0;
--
block/bio.c=983=void __bio_add_page(struct bio *bio, struct page *page,
--
block/bio.c-991-
block/bio.c:992: bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], page, len, off);
block/bio.c-993- bio->bi_iter.bi_size += len;
--
drivers/block/drbd/drbd_transport_lb-tcp.c=1631=static int _dtl_send_page(struct dtl_transport *dtl_transport, struct dtl_flow *flow,
--
drivers/block/drbd/drbd_transport_lb-tcp.c-1643-
drivers/block/drbd/drbd_transport_lb-tcp.c:1644: bvec_set_page(&bvec, page, len, offset);
drivers/block/drbd/drbd_transport_lb-tcp.c-1645- iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, len);
--
drivers/block/drbd/drbd_transport_tcp.c=1488=static int dtt_send_page(struct drbd_transport *transport, enum drbd_stream stream,
--
drivers/block/drbd/drbd_transport_tcp.c-1505-
drivers/block/drbd/drbd_transport_tcp.c:1506: bvec_set_page(&bvec, page, len, offset);
drivers/block/drbd/drbd_transport_tcp.c-1507- iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, len);
--
drivers/block/rbd.c=3075=static int setup_copyup_bvecs(struct rbd_obj_request *obj_req, u64 obj_overlap)
--
drivers/block/rbd.c-3093-
drivers/block/rbd.c:3094: bvec_set_page(&obj_req->copyup_bvecs[i], page, len, 0);
drivers/block/rbd.c-3095- obj_overlap -= len;
--
drivers/infiniband/sw/siw/siw_qp_tx.c=323=static int siw_tcp_sendpages(struct socket *s, struct page **page, int offset,
--
drivers/infiniband/sw/siw/siw_qp_tx.c-341- msg.msg_flags &= ~MSG_SPLICE_PAGES;
drivers/infiniband/sw/siw/siw_qp_tx.c:342: bvec_set_page(&bvec, page[i], bytes, offset);
drivers/infiniband/sw/siw/siw_qp_tx.c-343- iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, bytes);
--
drivers/nvme/host/tcp.c=1139=static int nvme_tcp_try_send_data(struct nvme_tcp_request *req)
--
drivers/nvme/host/tcp.c-1164-
drivers/nvme/host/tcp.c:1165: bvec_set_page(&bvec, page, len, offset);
drivers/nvme/host/tcp.c-1166- iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, len);
--
drivers/nvme/target/io-cmd-file.c=120=static bool nvmet_file_execute_io(struct nvmet_req *req, int ki_flags)
--
drivers/nvme/target/io-cmd-file.c-141- for_each_sg(req->sg, sg, req->sg_cnt, i) {
drivers/nvme/target/io-cmd-file.c:142: bvec_set_page(&req->f.bvec[bv_cnt], sg_page(sg), sg->length,
drivers/nvme/target/io-cmd-file.c-143- sg->offset);
--
drivers/nvme/target/tcp.c=354=static void nvmet_tcp_build_pdu_iovec(struct nvmet_tcp_cmd *cmd)
--
drivers/nvme/target/tcp.c-384-
drivers/nvme/target/tcp.c:385: bvec_set_page(iov, sg_page(sg), iov_len,
drivers/nvme/target/tcp.c-386- sg->offset + sg_offset);
--
drivers/nvme/target/tcp.c=655=static int nvmet_try_send_data(struct nvmet_tcp_cmd *cmd, bool last_in_batch)
--
drivers/nvme/target/tcp.c-672-
drivers/nvme/target/tcp.c:673: bvec_set_page(&bvec, page, left, cmd->offset);
drivers/nvme/target/tcp.c-674- iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, left);
--
drivers/scsi/iscsi_tcp.c=293=static int iscsi_sw_tcp_xmit_segment(struct iscsi_tcp_conn *tcp_conn,
--
drivers/scsi/iscsi_tcp.c-321- offset += segment->sg_offset + sg->offset;
drivers/scsi/iscsi_tcp.c:322: bvec_set_page(&bv, sg_page(sg), copy, offset);
drivers/scsi/iscsi_tcp.c-323- } else {
--
drivers/scsi/sd.c=961=static void *sd_set_special_bvec(struct scsi_cmnd *cmd, unsigned int data_len)
--
drivers/scsi/sd.c-978- clear_highpage(page + n);
drivers/scsi/sd.c:979: bvec_set_page(&rq->special_vec, page, data_len, 0);
drivers/scsi/sd.c-980- rq->rq_flags |= RQF_SPECIAL_PAYLOAD;
--
drivers/target/iscsi/iscsi_target_util.c=1090=int iscsit_fe_sendpage_sg(
--
drivers/target/iscsi/iscsi_target_util.c-1139-send_pg:
drivers/target/iscsi/iscsi_target_util.c:1140: bvec_set_page(&bvec, sg_page(sg), sub_len, sg->offset + offset);
drivers/target/iscsi/iscsi_target_util.c-1141- iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, sub_len);
--
drivers/target/target_core_file.c=266=fd_execute_rw_aio(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
--
drivers/target/target_core_file.c-283- for_each_sg(sgl, sg, sgl_nents, i) {
drivers/target/target_core_file.c:284: bvec_set_page(&aio_cmd->bvecs[i], sg_page(sg), sg->length,
drivers/target/target_core_file.c-285- sg->offset);
--
drivers/target/target_core_file.c=312=static int fd_do_rw(struct se_cmd *cmd, struct file *fd,
--
drivers/target/target_core_file.c-329- for_each_sg(sgl, sg, sgl_nents, i) {
drivers/target/target_core_file.c:330: bvec_set_page(&bvec[i], sg_page(sg), sg->length, sg->offset);
drivers/target/target_core_file.c-331- len += sg->length;
--
drivers/target/target_core_file.c=428=fd_execute_write_same(struct se_cmd *cmd)
--
drivers/target/target_core_file.c-462- for (i = 0; i < nolb; i++) {
drivers/target/target_core_file.c:463: bvec_set_page(&bvec[i], sg_page(&cmd->t_data_sg[0]),
drivers/target/target_core_file.c-464- cmd->t_data_sg[0].length,
--
drivers/vhost/vringh.c=1039=static int iotlb_translate(const struct vringh *vrh,
--
drivers/vhost/vringh.c-1081-
drivers/vhost/vringh.c:1082: bvec_set_page(&bvec[ret], pfn_to_page(pfn), io_len,
drivers/vhost/vringh.c-1083- io_addr & (PAGE_SIZE - 1));
--
fs/ceph/file.c=85=static ssize_t __iter_get_bvecs(struct iov_iter *iter, size_t maxsize,
--
fs/ceph/file.c-109-
fs/ceph/file.c:110: bvec_set_page(&bvecs[bvec_idx], pages[idx], len, start);
fs/ceph/file.c-111- bytes -= len;
--
fs/coredump.c=1276=static int dump_emit_page(struct coredump_params *cprm, struct page *page)
--
fs/coredump.c-1296- pos = file->f_pos;
fs/coredump.c:1297: bvec_set_page(&bvec, page, PAGE_SIZE, 0);
fs/coredump.c-1298- iov_iter_bvec(&iter, ITER_SOURCE, &bvec, 1, PAGE_SIZE);
--
fs/dlm/lowcomms.c=1363=static int send_to_sock(struct connection *con)
--
fs/dlm/lowcomms.c-1384-
fs/dlm/lowcomms.c:1385: bvec_set_page(&bvec, e->page, len, offset);
fs/dlm/lowcomms.c-1386- iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, len);
--
fs/netfs/iterator.c=36=ssize_t netfs_extract_user_iter(struct iov_iter *orig, size_t orig_len,
--
fs/netfs/iterator.c-91- len = ret > PAGE_SIZE ? PAGE_SIZE : ret;
fs/netfs/iterator.c:92: bvec_set_page(bv + npages + i, *pages++, len - offset, offset);
fs/netfs/iterator.c-93- ret -= len;
--
fs/nfs/localio.c=470=nfs_local_iters_init(struct nfs_local_kiocb *iocb, int rw)
--
fs/nfs/localio.c-484- len = min_t(size_t, total, PAGE_SIZE - base);
fs/nfs/localio.c:485: bvec_set_page(&iocb->bvec[v], *pagevec, len, base);
fs/nfs/localio.c-486- total -= len;
--
fs/nfsd/vfs.c=1112=nfsd_direct_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
--
fs/nfsd/vfs.c-1136- len = min_t(size_t, total, PAGE_SIZE);
fs/nfsd/vfs.c:1137: bvec_set_page(&rqstp->rq_bvec[v], *rqstp->rq_next_page,
fs/nfsd/vfs.c-1138- len, 0);
--
fs/nfsd/vfs.c=1191=__be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
--
fs/nfsd/vfs.c-1225- len = min_t(size_t, total, PAGE_SIZE - base);
fs/nfsd/vfs.c:1226: bvec_set_page(&rqstp->rq_bvec[v], *rqstp->rq_next_page,
fs/nfsd/vfs.c-1227- len, base);
--
fs/splice.c=662=iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
--
fs/splice.c-726-
fs/splice.c:727: bvec_set_page(&array[n], buf->page, this_len,
fs/splice.c-728- buf->offset);
--
fs/splice.c=795=ssize_t splice_to_socket(struct pipe_inode_info *pipe, struct file *out,
--
fs/splice.c-863-
fs/splice.c:864: bvec_set_page(&bvec[bc++], buf->page, seg, buf->offset);
fs/splice.c-865- remain -= seg;
--
include/linux/bvec.h=28=struct bio_vec {
--
include/linux/bvec.h-34-/**
include/linux/bvec.h:35: * bvec_set_page - initialize a bvec based off a struct page
include/linux/bvec.h-36- * @bv: bvec to initialize
--
include/linux/bvec.h-40- */
include/linux/bvec.h:41:static inline void bvec_set_page(struct bio_vec *bv, struct page *page,
include/linux/bvec.h-42- unsigned int len, unsigned int offset)
--
include/linux/bvec.h=56=static inline void bvec_set_folio(struct bio_vec *bv, struct folio *folio,
--
include/linux/bvec.h-61- WARN_ON_ONCE(len > UINT_MAX);
include/linux/bvec.h:62: bvec_set_page(bv, folio_page(folio, nr), len, offset % PAGE_SIZE);
include/linux/bvec.h-63-}
--
include/linux/bvec.h=71=static inline void bvec_set_virt(struct bio_vec *bv, void *vaddr,
--
include/linux/bvec.h-73-{
include/linux/bvec.h:74: bvec_set_page(bv, virt_to_page(vaddr), len, offset_in_page(vaddr));
include/linux/bvec.h-75-}
--
io_uring/rsrc.c=762=static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
--
io_uring/rsrc.c-838- vec_len = min_t(size_t, size, (1UL << imu->folio_shift) - off);
io_uring/rsrc.c:839: bvec_set_page(&imu->bvec[i], pages[i], vec_len, off);
io_uring/rsrc.c-840- off = 0;
--
io_uring/rsrc.c=1322=static int io_vec_fill_bvec(int ddir, struct iov_iter *iter,
--
io_uring/rsrc.c-1363-
io_uring/rsrc.c:1364: bvec_set_page(&res_bvec[bvec_idx],
io_uring/rsrc.c-1365- src_bvec->bv_page, seg_size, offset);
--
lib/iov_iter.c=1898=ssize_t iov_iter_extract_bvecs(struct iov_iter *iter, struct bio_vec *bv,
--
lib/iov_iter.c-1931- len = get_contig_folio_len(&pages[i], &nr_to_add, left, offset);
lib/iov_iter.c:1932: bvec_set_page(&bv[*nr_vecs], pages[i], len, offset);
lib/iov_iter.c-1933- i += nr_to_add;
--
lib/tests/kunit_iov_iter.c=217=static void __init iov_kunit_load_bvec(struct kunit *test,
--
lib/tests/kunit_iov_iter.c-241- } else {
lib/tests/kunit_iov_iter.c:242: bvec_set_page(&bvec[i], page, pr->to - pr->from, pr->from);
lib/tests/kunit_iov_iter.c-243- }
--
net/ceph/messenger_v1.c=40=static int ceph_tcp_recvpage(struct socket *sock, struct page *page,
--
net/ceph/messenger_v1.c-47- BUG_ON(page_offset + length > PAGE_SIZE);
net/ceph/messenger_v1.c:48: bvec_set_page(&bvec, page, length, page_offset);
net/ceph/messenger_v1.c-49- iov_iter_bvec(&msg.msg_iter, ITER_DEST, &bvec, 1, length);
--
net/ceph/messenger_v1.c=80=static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
--
net/ceph/messenger_v1.c-99-
net/ceph/messenger_v1.c:100: bvec_set_page(&bvec, page, size, offset);
net/ceph/messenger_v1.c-101- iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
--
net/ceph/messenger_v2.c=142=static int do_try_sendpage(struct socket *sock, struct iov_iter *it)
--
net/ceph/messenger_v2.c-152- /* iov_iter_iovec() for ITER_BVEC */
net/ceph/messenger_v2.c:153: bvec_set_page(&bv, it->bvec->bv_page,
net/ceph/messenger_v2.c-154- min(iov_iter_count(it),
--
net/ceph/messenger_v2.c=284=static void set_out_bvec_zero(struct ceph_connection *con)
--
net/ceph/messenger_v2.c-288-
net/ceph/messenger_v2.c:289: bvec_set_page(&con->v2.out_bvec, ceph_zero_page,
net/ceph/messenger_v2.c-290- min(con->v2.out_zero, (int)PAGE_SIZE), 0);
--
net/ceph/messenger_v2.c=831=static void get_bvec_at(struct ceph_msg_data_cursor *cursor,
--
net/ceph/messenger_v2.c-844- page = ceph_msg_data_next(cursor, &off, &len);
net/ceph/messenger_v2.c:845: bvec_set_page(bv, page, len, off);
net/ceph/messenger_v2.c-846-}
--
net/ceph/messenger_v2.c=2049=static void prepare_read_enc_page(struct ceph_connection *con)
--
net/ceph/messenger_v2.c-2056-
net/ceph/messenger_v2.c:2057: bvec_set_page(&bv, con->v2.in_enc_pages[con->v2.in_enc_i],
net/ceph/messenger_v2.c-2058- min(con->v2.in_enc_resid, (int)PAGE_SIZE), 0);
--
net/ceph/messenger_v2.c=3206=static void queue_enc_page(struct ceph_connection *con)
--
net/ceph/messenger_v2.c-3213-
net/ceph/messenger_v2.c:3214: bvec_set_page(&bv, con->v2.out_enc_pages[con->v2.out_enc_i],
net/ceph/messenger_v2.c-3215- min(con->v2.out_enc_resid, (int)PAGE_SIZE), 0);
--
net/core/skbuff.c=3294=static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
--
net/core/skbuff.c-3358- msg.msg_flags |= more_hint;
net/core/skbuff.c:3359: bvec_set_page(&bvec, skb_frag_page(frag), slen,
net/core/skbuff.c-3360- skb_frag_off(frag) + offset);
--
net/ipv4/tcp_bpf.c=91=static int tcp_bpf_push(struct sock *sk, struct sk_msg *msg, u32 apply_bytes,
--
net/ipv4/tcp_bpf.c-120-
net/ipv4/tcp_bpf.c:121: bvec_set_page(&bvec, page, size, off);
net/ipv4/tcp_bpf.c-122- iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, size);
--
net/rds/tcp_send.c=70=int rds_tcp_xmit(struct rds_connection *conn, struct rds_message *rm,
--
net/rds/tcp_send.c-119-
net/rds/tcp_send.c:120: bvec_set_page(&bvec, sg_page(&rm->data.op_sg[sg]),
net/rds/tcp_send.c-121- rm->data.op_sg[sg].length - off,
--
net/rxrpc/output.c=925=void rxrpc_send_response(struct rxrpc_connection *conn, struct sk_buff *response)
--
net/rxrpc/output.c-947- for (int i = 0; i < nr_sg; i++)
net/rxrpc/output.c:948: bvec_set_page(&bvec[i], sg_page(&sg[i]), sg[i].length, sg[i].offset);
net/rxrpc/output.c-949-
--
net/rxrpc/rxgk.c=632=static int rxgk_issue_challenge(struct rxrpc_connection *conn)
--
net/rxrpc/rxgk.c-650-
net/rxrpc/rxgk.c:651: bvec_set_page(&bvec[0], page, len, 0);
net/rxrpc/rxgk.c-652- iov_iter_bvec(&msg.msg_iter, WRITE, bvec, 1, len);
--
net/rxrpc/rxperf.c=511=static int rxperf_process_call(struct rxperf_call *call)
--
net/rxrpc/rxperf.c-523- len = umin(reply_len, PAGE_SIZE);
net/rxrpc/rxperf.c:524: bvec_set_page(&bv, ZERO_PAGE(0), len, 0);
net/rxrpc/rxperf.c-525- iov_iter_bvec(&msg.msg_iter, WRITE, &bv, 1, len);
--
net/sunrpc/svcsock.c=339=static ssize_t svc_tcp_read_msg(struct svc_rqst *rqstp, size_t buflen,
--
net/sunrpc/svcsock.c-352- for (i = 0, t = 0; t < buflen; i++, t += PAGE_SIZE)
net/sunrpc/svcsock.c:353: bvec_set_page(&bvec[i], rqstp->rq_pages[i], PAGE_SIZE, 0);
net/sunrpc/svcsock.c-354- rqstp->rq_respages = &rqstp->rq_pages[i];
--
net/sunrpc/xdr.c=116=xdr_alloc_bvec(struct xdr_buf *buf, gfp_t gfp)
--
net/sunrpc/xdr.c-124- for (i = 0; i < n; i++) {
net/sunrpc/xdr.c:125: bvec_set_page(&buf->bvec[i], buf->pages[i], PAGE_SIZE,
net/sunrpc/xdr.c-126- 0);
--
net/sunrpc/xdr.c=147=unsigned int xdr_buf_to_bvec(struct bio_vec *bvec, unsigned int bvec_size,
--
net/sunrpc/xdr.c-167- PAGE_SIZE - offset);
net/sunrpc/xdr.c:168: bvec_set_page(bvec++, *pages++, len, offset);
net/sunrpc/xdr.c-169- remaining -= len;
--
net/sunrpc/xprtrdma/svc_rdma_rw.c=452=static void svc_rdma_pagelist_to_bvec(struct svc_rdma_write_info *info,
--
net/sunrpc/xprtrdma/svc_rdma_rw.c-468- PAGE_SIZE - page_off);
net/sunrpc/xprtrdma/svc_rdma_rw.c:469: bvec_set_page(&ctxt->rw_bvec[bvec_idx], *page, bvec_len,
net/sunrpc/xprtrdma/svc_rdma_rw.c-470- page_off);
--
net/sunrpc/xprtrdma/svc_rdma_rw.c=747=static int svc_rdma_build_read_segment(struct svc_rqst *rqstp,
--
net/sunrpc/xprtrdma/svc_rdma_rw.c-772-
net/sunrpc/xprtrdma/svc_rdma_rw.c:773: bvec_set_page(&ctxt->rw_bvec[bvec_idx],
net/sunrpc/xprtrdma/svc_rdma_rw.c-774- rqstp->rq_pages[head->rc_curpage],
--
net/tls/tls_main.c=170=int tls_push_sg(struct sock *sk,
--
net/tls/tls_main.c-193-retry:
net/tls/tls_main.c:194: bvec_set_page(&bvec, p, size, offset);
net/tls/tls_main.c-195- iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
--
net/xfrm/espintcp.c=209=static int espintcp_sendskmsg_locked(struct sock *sk,
--
net/xfrm/espintcp.c-234-retry:
net/xfrm/espintcp.c:235: bvec_set_page(&bvec, p, size, offset);
net/xfrm/espintcp.c-236- iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, size);
]
|
| 8/2 |
2026/05/23 07:15 |
llm |
expert |
0m
Model:
Tokens:
input: 26095
output: 43
thoughts: 42
Thoughts: Here's my analysis of the situation:
**Investigating a Kernel Crash**
Okay, so the crash dump points directly to `bvec_set_page`, specifically line 44 within `include/linux/bvec.h`. That's a clear starting point. Let me pull up the definition of `bvec_set_page` right away. Understanding the *implementation* of that function is key to diagnosing the issue. I need to refresh my memory on what it's supposed to be doing, the typical scenarios it's called in, and what the potential failure points might be in that specific context. Knowing the surrounding code, and the possible paths that could lead to this crash, will be crucial. I need to consider all possible reasons a page might cause a fault.
|
| 9/2 |
2026/05/23 07:16 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/bvec.h IncludeLines:true Name:bvec_set_page]
Results: map[SourceCode: 34: /**
35: * bvec_set_page - initialize a bvec based off a struct page
36: * @bv: bvec to initialize
37: * @page: page the bvec should point to
38: * @len: length of the bvec
39: * @offset: offset into the page
40: */
41: static inline void bvec_set_page(struct bio_vec *bv, struct page *page,
42: unsigned int len, unsigned int offset)
43: {
44: bv->bv_page = page;
45: bv->bv_len = len;
46: bv->bv_offset = offset;
47: }
SourceFile:include/linux/bvec.h]
|
| 10/2 |
2026/05/23 07:16 |
llm |
expert |
0m
Model:
Tokens:
input: 26575
output: 40
thoughts: 146
Thoughts: **Debugging a Null Pointer Dereference**
Okay, here's what's happening. I've got a crash, and it's pointing me right at line 44: `bv->bv_page = page;` in the code. The faulting address, `0xdffffc0000000000`, immediately flags a KASAN issue β it's a KASAN shadow address that translates to a NULL pointer dereference.
Looking at the KASAN report, it confirms my suspicion: `KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]`. That's crystal clear β `bv` is NULL.
Now, I need to understand why `bv` ended up as NULL. I should start investigating the `__bio_add_page` function in `block/bio.c`, because that's where this line of code is located. Time to trace back the call stack and figure out how `bv` is being initialized and where it could be failing.
|
| 11/2 |
2026/05/23 07:16 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:__bio_add_page]
Results: map[SourceCode: 973: /**
974: * __bio_add_page - add page(s) to a bio in a new segment
975: * @bio: destination bio
976: * @page: start page to add
977: * @len: length of the data to add, may cross pages
978: * @off: offset of the data relative to @page, may cross pages
979: *
980: * Add the data at @page + @off to @bio as a new bvec. The caller must ensure
981: * that @bio has space for another bvec.
982: */
983: void __bio_add_page(struct bio *bio, struct page *page,
984: unsigned int len, unsigned int off)
985: {
986: WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));
987: WARN_ON_ONCE(bio_full(bio, len));
988:
989: if (is_pci_p2pdma_page(page))
990: bio->bi_opf |= REQ_NOMERGE;
991:
992: bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], page, len, off);
993: bio->bi_iter.bi_size += len;
994: bio->bi_vcnt++;
995: }
SourceFile:block/bio.c]
|
| 12/2 |
2026/05/23 07:16 |
llm |
expert |
0m
Model:
Tokens:
input: 27446
output: 39
thoughts: 122
Thoughts: **Analyzing a Potential Null Pointer Dereference**
Okay, so I'm looking at this bit of code and something's bugging me. It's saying that if `&bio->bi_io_vec[bio->bi_vcnt]` is NULL, then either `bio->bi_io_vec` *must* be NULL, or the `bio` pointer itself is NULL. Seems straightforward enough, logically sound.
But hold on, this doesn't quite sit right. Both `bio_flagged(bio, BIO_CLONED)` and `bio_full(bio, len)` are used later and both are going to dereference `bio`. So, if `bio` were NULL, we would have already crashed long before this check. So then what's going on?
Ah, right... `bio->bi_io_vec` can be NULL, can't it? If the `bio` struct *doesn't* have a bvec array actually allocated, it could be null. That's a valid condition. I need to be sure though. Let's go check the `bio_add_page` function in `block/bio.c`. That's where all the vector allocation happens and will give me the answer.
|
| 13/2 |
2026/05/23 07:16 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_add_page]
Results: map[SourceCode:1014: /**
1015: * bio_add_page - attempt to add page(s) to bio
1016: * @bio: destination bio
1017: * @page: start page to add
1018: * @len: vec entry length, may cross pages
1019: * @offset: vec entry offset relative to @page, may cross pages
1020: *
1021: * Attempt to add page(s) to the bio_vec maplist. This will only fail
1022: * if either bio->bi_vcnt == bio->bi_max_vecs or it's a cloned bio.
1023: */
1024: int bio_add_page(struct bio *bio, struct page *page,
1025: unsigned int len, unsigned int offset)
1026: {
1027: if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
1028: return 0;
1029: if (WARN_ON_ONCE(len == 0))
1030: return 0;
1031: if (bio->bi_iter.bi_size > BIO_MAX_SIZE - len)
1032: return 0;
1033:
1034: if (bio->bi_vcnt > 0) {
1035: struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
1036:
1037: if (!zone_device_pages_have_same_pgmap(bv->bv_page, page))
1038: return 0;
1039:
1040: if (bvec_try_merge_page(bv, page, len, offset)) {
1041: bio->bi_iter.bi_size += len;
1042: return len;
1043: }
1044: }
1045:
1046: if (bio->bi_vcnt >= bio->bi_max_vecs)
1047: return 0;
1048: __bio_add_page(bio, page, len, offset);
1049: return len;
1050: }
SourceFile:block/bio.c]
|
| 14/2 |
2026/05/23 07:16 |
llm |
expert |
0m
Model:
Tokens:
input: 28514
output: 39
thoughts: 154
Thoughts: **Analyzing Potential Null Pointer Dereference in Block I/O Structure**
Okay, so I'm looking at this `bio` structure and immediately something jumps out at me. The `bio->bi_io_vec` field, that's a pointer, right? Which means it could be NULL. Now, if `bio->bi_vcnt` is zero, then intuitively, `bio->bi_io_vec` *could* be NULL. But here's the kicker: `bio->bi_max_vecs` should *also* be zero if `bio->bi_io_vec` is NULL, by design.
So, if the following check `bio->bi_vcnt >= bio->bi_max_vecs` evaluates to `false`, then we know that `bio->bi_max_vecs` has to be greater than zero. And if `bio->bi_max_vecs` *is* greater than zero, then `bio->bi_io_vec` *shouldn't* be NULL. Hmm, that feels like a potential inconsistency right there. I need to dig deeper to see if this is possible. Let's trace it back to `bio_add_folio` in `block/bio.c`, that's where I need to look. I'll check that routine for the logic that sets these values. That's probably where the condition could have a vulnerability.
|
| 15/2 |
2026/05/23 07:16 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_add_folio]
Results: map[SourceCode:1063: /**
1064: * bio_add_folio - Attempt to add part of a folio to a bio.
1065: * @bio: BIO to add to.
1066: * @folio: Folio to add.
1067: * @len: How many bytes from the folio to add.
1068: * @off: First byte in this folio to add.
1069: *
1070: * Filesystems that use folios can call this function instead of calling
1071: * bio_add_page() for each page in the folio. If @off is bigger than
1072: * PAGE_SIZE, this function can create a bio_vec that starts in a page
1073: * after the bv_page. BIOs do not support folios that are 4GiB or larger.
1074: *
1075: * Return: Whether the addition was successful.
1076: */
1077: bool bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
1078: size_t off)
1079: {
1080: unsigned long nr = off / PAGE_SIZE;
1081:
1082: if (len > BIO_MAX_SIZE)
1083: return false;
1084: return bio_add_page(bio, folio_page(folio, nr), len, off % PAGE_SIZE) > 0;
1085: }
SourceFile:block/bio.c]
|
| 16/2 |
2026/05/23 07:16 |
llm |
expert |
0m
Model:
Tokens:
input: 29432
output: 46
thoughts: 26
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Diving into the ext4 IO Submission Process**
Alright, let's pull up the source code for `io_submit_add_bh` β specifically, that function in `fs/ext4/page-io.c`. I need to refresh my understanding of how ext4 handles block I/O submission at the page level. What's the exact flow from a page being dirtied, through the scheduling of the I/O, and down to the device driver? This function is key. I'm guessing this is where the block header (bh) is added to the I/O request structure, possibly forming the basis of the submission. I need to see how the buffers are setup, how we deal with the different I/O types - synchronous versus asynchronous, and how the completion notification mechanisms are set up, if at all. It's important to keep track of any potential race conditions and to know how ext4 deals with them. This is likely the crucial building block to understanding the larger picture, like what happens when a writeback occurs. I hope I find a clean design in there.
|
| 17/2 |
2026/05/23 07:16 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/ext4/page-io.c IncludeLines:true Name:io_submit_add_bh]
Results: map[SourceCode: 453: static void io_submit_add_bh(struct ext4_io_submit *io,
454: struct inode *inode,
455: struct folio *folio,
456: struct folio *io_folio,
457: struct buffer_head *bh)
458: {
459: if (io->io_bio && io_submit_need_new_bio(io, inode, folio, bh)) {
460: submit_and_retry:
461: ext4_io_submit(io);
462: }
463: if (io->io_bio == NULL)
464: io_submit_init_bio(io, inode, folio, bh);
465: if (!bio_add_folio(io->io_bio, io_folio, bh->b_size, bh_offset(bh)))
466: goto submit_and_retry;
467: wbc_account_cgroup_owner(io->io_wbc, folio, bh->b_size);
468: io->io_next_block++;
469: }
SourceFile:fs/ext4/page-io.c]
|
| 18/2 |
2026/05/23 07:16 |
llm |
expert |
0m
Model:
Tokens:
input: 30096
output: 46
thoughts: 26
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into ext4's I/O Submission**
Alright, let's get down to it. I need to understand how ext4 handles the submission of I/O operations, particularly at the page level. My intuition says that `io_submit_init_bio` in `fs/ext4/page-io.c` is the key function I need to examine. It's the point where the details of a bio are initialized before being passed down. I'm hoping to understand what data is populated, what calculations are done, and how it interacts with the underlying block device layer. I need to figure out exactly how ext4 structures the requests to ensure efficient and correct I/O. I'm interested in the interplay between memory management, the block allocation strategies, and the overall performance implications. What locking is used during this initialization? Any clever optimizations or workarounds for specific hardware configurations? Let's see what's really happening.
|
| 19/2 |
2026/05/23 07:16 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/ext4/page-io.c IncludeLines:true Name:io_submit_init_bio]
Results: map[SourceCode: 417: static void io_submit_init_bio(struct ext4_io_submit *io,
418: struct inode *inode,
419: struct folio *folio,
420: struct buffer_head *bh)
421: {
422: struct bio *bio;
423:
424: /*
425: * bio_alloc will _always_ be able to allocate a bio if
426: * __GFP_DIRECT_RECLAIM is set, see comments for bio_alloc_bioset().
427: */
428: bio = bio_alloc(bh->b_bdev, BIO_MAX_VECS, REQ_OP_WRITE, GFP_NOIO);
429: fscrypt_set_bio_crypt_ctx(bio, inode, folio_pos(folio) + bh_offset(bh),
430: GFP_NOIO);
431: bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
432: bio->bi_end_io = ext4_end_bio;
433: bio->bi_private = ext4_get_io_end(io->io_end);
434: bio->bi_write_hint = inode->i_write_hint;
435: io->io_bio = bio;
436: io->io_next_block = bh->b_blocknr;
437: wbc_init_bio(io->io_wbc, bio);
438: }
SourceFile:fs/ext4/page-io.c]
|
| 20/2 |
2026/05/23 07:16 |
llm |
expert |
0m
Model:
Tokens:
input: 30842
output: 37
thoughts: 42
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person:
**Analyzing the BIO Allocation Path**
Right, `bio_alloc` is being called, and the caller is passing in `BIO_MAX_VECS`, which I know from memory is set to 256. My mental gears are already turning, considering potential implications of that. 256 vectors... that's a pretty hefty I/O request. I need to understand the allocation behavior when dealing with such a large vector count. My immediate instinct is to jump into `block/bio.c` and dive into the `bio_alloc` implementation. I want to see exactly how this function handles that `BIO_MAX_VECS` value. What's the allocation strategy? Is it statically allocating a large structure, or is it dynamically allocating based on this number? Are there any potential limitations or sanity checks within `bio_alloc` itself that might come into play with this size? Are there pre-defined thresholds for memory reservation or usage that could become a potential bottleneck? I'm particularly interested in how it interacts with the underlying memory management and if there are considerations for fragmentation or potential memory exhaustion. My prior experience tells me there's an interplay between performance, flexibility, and memory consumption when you're dealing with a large vector count like this, and I need to figure out how `bio_alloc` manages that balance. Let's see what's going on under the hood.
|
| 21/2 |
2026/05/23 07:16 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_alloc]
Results: map[SourceCode: 370: static inline struct bio *bio_alloc(struct block_device *bdev,
371: unsigned short nr_vecs, blk_opf_t opf, gfp_t gfp_mask)
372: {
373: return bio_alloc_bioset(bdev, nr_vecs, opf, gfp_mask, &fs_bio_set);
374: }
SourceFile:include/linux/bio.h]
|
| 22/2 |
2026/05/23 07:16 |
llm |
expert |
0m
Model:
Tokens:
input: 31376
output: 40
thoughts: 30
Thoughts: Here's my thought process, as if I were considering this code:
**Navigating the Bio Allocation Landscape**
Okay, so I'm diving into this `bio` stuff... I recall seeing `bio_alloc` floating around. Hmm, that rings a bell. Let me just quickly confirm where that's defined. Right, `include/linux/bio.h`. Standard spot, makes sense. Now, let's see, what was that other function? Ah, yes, `bio_alloc_bioset`. I think that might be the key to understanding how this whole allocation process works. Time to dive deeper and see what that function is up to. Let's trace where that's called, how it interacts with the bioset, and figure out the allocation strategy. This is likely the crucial building block in all of this.
|
| 23/2 |
2026/05/23 07:16 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_alloc_bioset]
Results: map[SourceCode: 492: /**
493: * bio_alloc_bioset - allocate a bio for I/O
494: * @bdev: block device to allocate the bio for (can be %NULL)
495: * @nr_vecs: number of bvecs to pre-allocate
496: * @opf: operation and flags for bio
497: * @gfp: the GFP_* mask given to the slab allocator
498: * @bs: the bio_set to allocate from.
499: *
500: * Allocate a bio from the mempools in @bs.
501: *
502: * If %__GFP_DIRECT_RECLAIM is set then bio_alloc will always be able to
503: * allocate a bio. This is due to the mempool guarantees. To make this work,
504: * callers must never allocate more than 1 bio at a time from the general pool.
505: * Callers that need to allocate more than 1 bio must always submit the
506: * previously allocated bio for IO before attempting to allocate a new one.
507: * Failure to do so can cause deadlocks under memory pressure.
508: *
509: * Note that when running under submit_bio_noacct() (i.e. any block driver),
510: * bios are not submitted until after you return - see the code in
511: * submit_bio_noacct() that converts recursion into iteration, to prevent
512: * stack overflows.
513: *
514: * This would normally mean allocating multiple bios under submit_bio_noacct()
515: * would be susceptible to deadlocks, but we have
516: * deadlock avoidance code that resubmits any blocked bios from a rescuer
517: * thread.
518: *
519: * However, we do not guarantee forward progress for allocations from other
520: * mempools. Doing multiple allocations from the same mempool under
521: * submit_bio_noacct() should be avoided - instead, use bio_set's front_pad
522: * for per bio allocations.
523: *
524: * Returns: Pointer to new bio on success, NULL on failure.
525: */
526: struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
527: blk_opf_t opf, gfp_t gfp, struct bio_set *bs)
528: {
529: struct bio_vec *bvecs = NULL;
530: struct bio *bio = NULL;
531: gfp_t saved_gfp = gfp;
532: void *p;
533:
534: /* should not use nobvec bioset for nr_vecs > 0 */
535: if (WARN_ON_ONCE(!mempool_initialized(&bs->bvec_pool) && nr_vecs > 0))
536: return NULL;
537:
538: gfp = try_alloc_gfp(gfp);
539: if (bs->cache && nr_vecs <= BIO_INLINE_VECS) {
540: /*
541: * Set REQ_ALLOC_CACHE even if no cached bio is available to
542: * return the allocated bio to the percpu cache when done.
543: */
544: opf |= REQ_ALLOC_CACHE;
545: bio = bio_alloc_percpu_cache(bs);
546: } else {
547: opf &= ~REQ_ALLOC_CACHE;
548: p = kmem_cache_alloc(bs->bio_slab, gfp);
549: if (p)
550: bio = p + bs->front_pad;
551: }
552:
553: if (bio && nr_vecs > BIO_INLINE_VECS) {
554: struct biovec_slab *bvs = biovec_slab(nr_vecs);
555:
556: /*
557: * Upgrade nr_vecs to take full advantage of the allocation.
558: * We also rely on this in bio_free().
559: */
560: nr_vecs = bvs->nr_vecs;
561: bvecs = kmem_cache_alloc(bvs->slab, gfp);
562: if (unlikely(!bvecs)) {
563: kmem_cache_free(bs->bio_slab, p);
564: bio = NULL;
565: }
566: }
567:
568: if (unlikely(!bio)) {
569: /*
570: * Give up if we are not allow to sleep as non-blocking mempool
571: * allocations just go back to the slab allocation.
572: */
573: if (!(saved_gfp & __GFP_DIRECT_RECLAIM))
574: return NULL;
575:
576: punt_bios_to_rescuer(bs);
577:
578: /*
579: * Don't rob the mempools by returning to the per-CPU cache if
580: * we're tight on memory.
581: */
582: opf &= ~REQ_ALLOC_CACHE;
583:
584: p = mempool_alloc(&bs->bio_pool, gfp);
585: bio = p + bs->front_pad;
586: if (nr_vecs > BIO_INLINE_VECS) {
587: nr_vecs = BIO_MAX_VECS;
588: bvecs = mempool_alloc(&bs->bvec_pool, gfp);
589: }
590: }
591:
592: if (nr_vecs && nr_vecs <= BIO_INLINE_VECS)
593: bio_init_inline(bio, bdev, nr_vecs, opf);
594: else
595: bio_init(bio, bdev, bvecs, nr_vecs, opf);
596: bio->bi_pool = bs;
597: return bio;
598: }
SourceFile:block/bio.c]
|
| 24/2 |
2026/05/23 07:16 |
llm |
expert |
0m
Model:
Tokens:
input: 33427
output: 39
thoughts: 228
Thoughts: **Analyzing Potential NULL Dereference in `io_submit_init_bio`**
Okay, so I'm digging into this `bio_alloc` call and something isn't quite right. My initial thought was, "Hang on, `bio_alloc` can actually return NULL if `__GFP_DIRECT_RECLAIM` isn't set, right?" But then I see that `io_submit_init_bio` calls `bio_alloc(bh->b_bdev, BIO_MAX_VECS, REQ_OP_WRITE, GFP_NOIO)`. And, I know that `GFP_NOIO` *should* include `__GFP_DIRECT_RECLAIM`! That seems odd.
Let me break this down... `GFP_NOIO` is defined as `(__GFP_RECLAIM | __GFP_IO) & ~__GFP_IO`, which effectively simplifies to just `__GFP_RECLAIM`. And since `__GFP_RECLAIM` certainly *does* include `__GFP_DIRECT_RECLAIM`, `bio_alloc` should *never* return NULL in this context. At least, that's what I'd expect.
But that nagging feeling won't go away. So, what *if* `bio_alloc` does return NULL despite the flags? This needs investigation. If `bio_alloc` fails, `io->io_bio` becomes NULL, obviously. But then the code calls `bio_add_folio(io->io_bio, ...)` on the following line. If `io->io_bio` is NULL, *that* is going to be a classic NULL dereference! I need to trace through the code. I need to confirm that this check for NULL is in place and that the code handles this condition. I need to understand what `bio_add_folio` does and if it correctly handles a potential NULL `bio` pointer. Let's see... I'm going to check the code for `bio_add_folio` right now.
|
| 25/2 |
2026/05/23 07:16 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_add_folio]
Results: map[SourceCode:1063: /**
1064: * bio_add_folio - Attempt to add part of a folio to a bio.
1065: * @bio: BIO to add to.
1066: * @folio: Folio to add.
1067: * @len: How many bytes from the folio to add.
1068: * @off: First byte in this folio to add.
1069: *
1070: * Filesystems that use folios can call this function instead of calling
1071: * bio_add_page() for each page in the folio. If @off is bigger than
1072: * PAGE_SIZE, this function can create a bio_vec that starts in a page
1073: * after the bv_page. BIOs do not support folios that are 4GiB or larger.
1074: *
1075: * Return: Whether the addition was successful.
1076: */
1077: bool bio_add_folio(struct bio *bio, struct folio *folio, size_t len,
1078: size_t off)
1079: {
1080: unsigned long nr = off / PAGE_SIZE;
1081:
1082: if (len > BIO_MAX_SIZE)
1083: return false;
1084: return bio_add_page(bio, folio_page(folio, nr), len, off % PAGE_SIZE) > 0;
1085: }
SourceFile:block/bio.c]
|
| 26/2 |
2026/05/23 07:16 |
llm |
expert |
0m
Model:
Tokens:
input: 34546
output: 37
thoughts: 590
Thoughts: **Debugging a Null Pointer Dereference in Block I/O**
Okay, so I'm tracking down this kernel crash and the stack trace is pointing me towards `bvec_set_page`, which is called within `__bio_add_page`, which is in turn called by `bio_add_page`. The initial assumption was `bio` being NULL, but after re-examining the trace, that's incorrect. I can see that `bio` *isn't* NULL, which throws my initial line of reasoning off course.
Now, if `bio` isn't NULL, then the problem *has* to be related to either `bio->bi_io_vec` being NULL or an out-of-bounds access on that array. Let's think this through. `bio->bi_io_vec` is a pointer, so if it's NULL, then addressing `&bio->bi_io_vec[bio->bi_vcnt]` becomes a calculation with NULL. Even if `bio->bi_vcnt` is zero, we're still effectively dereferencing NULL. That explains the crash, it seems the array pointer is NULL. The key problem here is the `bio->bi_io_vec` pointer is getting set to NULL.
So, the next step is to figure out why `bio->bi_io_vec` is NULL in the first place. I need to trace back how the `bio` is initialized to understand how `bi_io_vec` is potentially set to NULL. I'll need to look at `bio_init` in `block/bio.c` to see how the bio struct is being created and initialized.
|
| 27/2 |
2026/05/23 07:17 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_init]
Results: map[SourceCode: 206: /*
207: * Users of this function have their own bio allocation. Subsequently,
208: * they must remember to pair any call to bio_init() with bio_uninit()
209: * when IO has completed, or when the bio is released.
210: */
211: void bio_init(struct bio *bio, struct block_device *bdev, struct bio_vec *table,
212: unsigned short max_vecs, blk_opf_t opf)
213: {
214: bio->bi_next = NULL;
215: bio->bi_bdev = bdev;
216: bio->bi_opf = opf;
217: bio->bi_flags = 0;
218: bio->bi_ioprio = 0;
219: bio->bi_write_hint = 0;
220: bio->bi_write_stream = 0;
221: bio->bi_status = 0;
222: bio->bi_bvec_gap_bit = 0;
223: bio->bi_iter.bi_sector = 0;
224: bio->bi_iter.bi_size = 0;
225: bio->bi_iter.bi_idx = 0;
226: bio->bi_iter.bi_bvec_done = 0;
227: bio->bi_end_io = NULL;
228: bio->bi_private = NULL;
229: #ifdef CONFIG_BLK_CGROUP
230: bio->bi_blkg = NULL;
231: bio->issue_time_ns = 0;
232: if (bdev)
233: bio_associate_blkg(bio);
234: #ifdef CONFIG_BLK_CGROUP_IOCOST
235: bio->bi_iocost_cost = 0;
236: #endif
237: #endif
238: #ifdef CONFIG_BLK_INLINE_ENCRYPTION
239: bio->bi_crypt_context = NULL;
240: #endif
241: #ifdef CONFIG_BLK_DEV_INTEGRITY
242: bio->bi_integrity = NULL;
243: #endif
244: bio->bi_vcnt = 0;
245:
246: atomic_set(&bio->__bi_remaining, 1);
247: atomic_set(&bio->__bi_cnt, 1);
248: bio->bi_cookie = BLK_QC_T_NONE;
249:
250: bio->bi_max_vecs = max_vecs;
251: bio->bi_io_vec = table;
252: bio->bi_pool = NULL;
253: }
SourceFile:block/bio.c]
|
| 28/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 36349
output: 40
thoughts: 65
Thoughts: Okay, let's break this down.
**Analyzing Potential Memory Allocation Issues in the Bio Structure**
Right, so I'm looking at this `bio` structure and the conditions under which it's initialized. The critical scenario I'm focusing on is when `bio_init` gets called with a `NULL` table pointer but a positive `max_vecs` value. This triggers a specific condition, which implies that the `bi_io_vec` pointer within the `bio` structure will be null while its corresponding `bi_max_vecs` is still set to be greater than zero.
This raises an immediate flag. I need to revisit the `bio_alloc_bioset` function. This suggests a potential resource management conflict. Specifically, I need to understand whether this setup is intended, and if so how it is handled later in the process. My concern is whether we correctly allocate and deallocate the vector or if we're risking a double free or memory leak. The fact that `bi_max_vecs` is positive while `bi_io_vec` is NULL in this condition means something is potentially amiss. Time to dig in!
|
| 29/2 |
2026/05/23 07:17 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_alloc_bioset]
Results: map[SourceCode: 492: /**
493: * bio_alloc_bioset - allocate a bio for I/O
494: * @bdev: block device to allocate the bio for (can be %NULL)
495: * @nr_vecs: number of bvecs to pre-allocate
496: * @opf: operation and flags for bio
497: * @gfp: the GFP_* mask given to the slab allocator
498: * @bs: the bio_set to allocate from.
499: *
500: * Allocate a bio from the mempools in @bs.
501: *
502: * If %__GFP_DIRECT_RECLAIM is set then bio_alloc will always be able to
503: * allocate a bio. This is due to the mempool guarantees. To make this work,
504: * callers must never allocate more than 1 bio at a time from the general pool.
505: * Callers that need to allocate more than 1 bio must always submit the
506: * previously allocated bio for IO before attempting to allocate a new one.
507: * Failure to do so can cause deadlocks under memory pressure.
508: *
509: * Note that when running under submit_bio_noacct() (i.e. any block driver),
510: * bios are not submitted until after you return - see the code in
511: * submit_bio_noacct() that converts recursion into iteration, to prevent
512: * stack overflows.
513: *
514: * This would normally mean allocating multiple bios under submit_bio_noacct()
515: * would be susceptible to deadlocks, but we have
516: * deadlock avoidance code that resubmits any blocked bios from a rescuer
517: * thread.
518: *
519: * However, we do not guarantee forward progress for allocations from other
520: * mempools. Doing multiple allocations from the same mempool under
521: * submit_bio_noacct() should be avoided - instead, use bio_set's front_pad
522: * for per bio allocations.
523: *
524: * Returns: Pointer to new bio on success, NULL on failure.
525: */
526: struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
527: blk_opf_t opf, gfp_t gfp, struct bio_set *bs)
528: {
529: struct bio_vec *bvecs = NULL;
530: struct bio *bio = NULL;
531: gfp_t saved_gfp = gfp;
532: void *p;
533:
534: /* should not use nobvec bioset for nr_vecs > 0 */
535: if (WARN_ON_ONCE(!mempool_initialized(&bs->bvec_pool) && nr_vecs > 0))
536: return NULL;
537:
538: gfp = try_alloc_gfp(gfp);
539: if (bs->cache && nr_vecs <= BIO_INLINE_VECS) {
540: /*
541: * Set REQ_ALLOC_CACHE even if no cached bio is available to
542: * return the allocated bio to the percpu cache when done.
543: */
544: opf |= REQ_ALLOC_CACHE;
545: bio = bio_alloc_percpu_cache(bs);
546: } else {
547: opf &= ~REQ_ALLOC_CACHE;
548: p = kmem_cache_alloc(bs->bio_slab, gfp);
549: if (p)
550: bio = p + bs->front_pad;
551: }
552:
553: if (bio && nr_vecs > BIO_INLINE_VECS) {
554: struct biovec_slab *bvs = biovec_slab(nr_vecs);
555:
556: /*
557: * Upgrade nr_vecs to take full advantage of the allocation.
558: * We also rely on this in bio_free().
559: */
560: nr_vecs = bvs->nr_vecs;
561: bvecs = kmem_cache_alloc(bvs->slab, gfp);
562: if (unlikely(!bvecs)) {
563: kmem_cache_free(bs->bio_slab, p);
564: bio = NULL;
565: }
566: }
567:
568: if (unlikely(!bio)) {
569: /*
570: * Give up if we are not allow to sleep as non-blocking mempool
571: * allocations just go back to the slab allocation.
572: */
573: if (!(saved_gfp & __GFP_DIRECT_RECLAIM))
574: return NULL;
575:
576: punt_bios_to_rescuer(bs);
577:
578: /*
579: * Don't rob the mempools by returning to the per-CPU cache if
580: * we're tight on memory.
581: */
582: opf &= ~REQ_ALLOC_CACHE;
583:
584: p = mempool_alloc(&bs->bio_pool, gfp);
585: bio = p + bs->front_pad;
586: if (nr_vecs > BIO_INLINE_VECS) {
587: nr_vecs = BIO_MAX_VECS;
588: bvecs = mempool_alloc(&bs->bvec_pool, gfp);
589: }
590: }
591:
592: if (nr_vecs && nr_vecs <= BIO_INLINE_VECS)
593: bio_init_inline(bio, bdev, nr_vecs, opf);
594: else
595: bio_init(bio, bdev, bvecs, nr_vecs, opf);
596: bio->bi_pool = bs;
597: return bio;
598: }
SourceFile:block/bio.c]
|
| 30/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 38502
output: 40
thoughts: 313
Thoughts: **Analyzing Potential Null Pointer Dereference in Block Device Initialization**
Okay, let's break this down. My initial concern is whether `bvecs` could be a null pointer. The code seems to be implying it could be, but I need to be sure. I'm thinking about the potential for `mempool_alloc` failing. Now, I remember that if `mempool_alloc` is called with `__GFP_DIRECT_RECLAIM`, it *shouldn't* return NULL.
Hold on a second, what about the case where `nr_vecs` is zero? Let's trace it back. In `io_submit_init_bio`, `bio_alloc` is called. That uses `BIO_MAX_VECS`. Right, and `BIO_MAX_VECS` is 256. So, `nr_vecs` will be 256 then.
Back to the `bvecs` assignment: `bvecs = mempool_alloc(&bs->bvec_pool, gfp);`. Again, could `bvecs` be NULL? No, based on what I just said, with `mempool_alloc` and `__GFP_DIRECT_RECLAIM`, it *shouldn't* return NULL.
But wait, I need to check something... What if the `gfp` flags *don't* include `__GFP_DIRECT_RECLAIM`? Let's see... `gfp` is actually `GFP_NOIO`. Okay, and `GFP_NOIO` is defined as `(__GFP_RECLAIM | __GFP_IO) & ~__GFP_IO`. That makes sense. `__GFP_RECLAIM` expands to `___GFP_DIRECT_RECLAIM | ___GFP_KSWAPD_RECLAIM`. So, `GFP_NOIO` *does* have `__GFP_DIRECT_RECLAIM`. Good.
Aha, and then I see `gfp = try_alloc_gfp(gfp);`. Okay, that's where things get interesting. What does `try_alloc_gfp` actually *do*? I'll need to look into that function to understand any potential side effects.
|
| 31/2 |
2026/05/23 07:17 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:try_alloc_gfp]
Results: map[SourceCode: 164: /*
165: * Make the first allocation restricted and don't dump info on allocation
166: * failures, since we'll fall back to the mempool in case of failure.
167: */
168: static inline gfp_t try_alloc_gfp(gfp_t gfp)
169: {
170: return (gfp & ~(__GFP_DIRECT_RECLAIM | __GFP_IO)) |
171: __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
172: }
SourceFile:block/bio.c]
|
| 32/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 39518
output: 41
thoughts: 264
Thoughts: **Analyzing the GFP Flag Management**
Okay, so I'm looking at this code and something's immediately jumping out at me. The `try_alloc_gfp` function, it's clearing the `__GFP_DIRECT_RECLAIM` flag. But hang on, `saved_gfp` still holds the original value, including that flag. I see that here:
```c
gfp_t saved_gfp = gfp;
...
gfp = try_alloc_gfp(gfp);
...
```
Right, the interesting part is the `if` statement. If the `bio` allocation fails *and* if the *original* `saved_gfp` didn't have `__GFP_DIRECT_RECLAIM` set, then it returns NULL. Otherwise, it attempts to allocate from `mempool_alloc`. But wait, this is where it gets confusing... The `mempool_alloc` calls are made using `gfp`, which, as we established earlier, *now* has `__GFP_DIRECT_RECLAIM` cleared!
```c
if (!(saved_gfp & __GFP_DIRECT_RECLAIM))
return NULL;
p = mempool_alloc(&bs->bio_pool, gfp);
bio = p + bs->front_pad;
if (nr_vecs > BIO_INLINE_VECS) {
nr_vecs = BIO_MAX_VECS;
bvecs = mempool_alloc(&bs->bvec_pool, gfp);
}
```
So, here's where my expert instincts kick in. If `mempool_alloc` is called with `gfp`, that is `__GFP_DIRECT_RECLAIM` cleared and the pool is empty, what happens? Could `mempool_alloc` return NULL? I'd better double-check the `mempool_alloc` implementation to be certain of that behavior. Gotta confirm my understanding of the implications of that flag being cleared when it comes to mempool usage.
|
| 33/2 |
2026/05/23 07:17 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:mm/mempool.c IncludeLines:true Name:mempool_alloc]
Results: map[SourceCode: SourceFile:]
|
| 34/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 40296
output: 22
thoughts: 11
Thoughts: Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to a fellow expert:
**Locating `mempool_alloc`**
Right, let's get down to business. My immediate focus is to pinpoint the function `mempool_alloc`. This suggests we're dealing with memory pool allocation, which usually means managing pre-allocated memory blocks for efficiency, avoiding the overhead of frequent `malloc` and `free` calls. My initial thought process is geared toward *finding* this crucial function. The context isn't clear but my experience immediately triggers questions. Is it in the kernel? A userspace library? What architecture are we dealing with? Is there any available documentation? A quick `grep` might do the trick if the source code is readily available, but I'm mentally starting to formulate search strategies. I want to understand *how* this memory allocation is happening. What's the allocation strategy? Is there any metadata attached to the mempool? Are there any associated functions like `mempool_free` or pool initialization? Knowing this will help me understand its place in the grand scheme. I'm already anticipating the typical challenges: race conditions, fragmentation, and potential memory leaks. Let's see what we can find!
|
| 35/2 |
2026/05/23 07:17 |
tool |
grepper |
0m
Error:
Args: map[Expression:void \*mempool_alloc\(]
Results:
|
| 36/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 40611
output: 20
thoughts: 17
Thoughts: Here's a summary of my thought process:
**Potential `mempool_alloc` Dilemma**
Okay, so I'm thinking about this `mempool_alloc` function. The first thing that comes to mind is, I need to check whether this is an inline function, or if it's actually exported. If it's inline, that changes the whole game in terms of potential analysis, optimization, or interactions with other parts of the system. If it's exported, there are different considerations at play. I need to nail down that detail before I can make a solid assessment. Let's dig in and figure out which it is.
|
| 37/2 |
2026/05/23 07:17 |
tool |
grepper |
0m
Args: map[Expression:mempool_alloc\(]
Results: map[Output:
Full output is too long, showing 500 out of 1747 lines.
Use more precise expression if possible.
[arch/powerpc/platforms/pseries/rtas-work-area.c=81=struct rtas_work_area * __ref __rtas_work_area_alloc(size_t size)
--
arch/powerpc/platforms/pseries/rtas-work-area.c-106-
arch/powerpc/platforms/pseries/rtas-work-area.c:107: area = mempool_alloc(&rwa_state.descriptor_pool, GFP_KERNEL);
arch/powerpc/platforms/pseries/rtas-work-area.c-108- area->buf = (char *)addr;
--
arch/sh/kernel/dwarf.c=62=static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
--
arch/sh/kernel/dwarf.c-66-
arch/sh/kernel/dwarf.c:67: reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC);
arch/sh/kernel/dwarf.c-68- if (!reg) {
--
arch/sh/kernel/dwarf.c=574=struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
--
arch/sh/kernel/dwarf.c-622-
arch/sh/kernel/dwarf.c:623: frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
arch/sh/kernel/dwarf.c-624- if (!frame) {
--
block/bio-integrity-auto.c=89=void bio_integrity_prep(struct bio *bio, unsigned int action)
--
block/bio-integrity-auto.c-92-
block/bio-integrity-auto.c:93: bid = mempool_alloc(&bid_pool, GFP_NOIO);
block/bio-integrity-auto.c-94- bio_integrity_init(bio, &bid->bip, &bid->bvec, 1);
--
block/bio-integrity-fs.c=17=unsigned int fs_bio_integrity_alloc(struct bio *bio)
--
block/bio-integrity-fs.c-25-
block/bio-integrity-fs.c:26: iib = mempool_alloc(&fs_bio_integrity_pool, GFP_NOIO);
block/bio-integrity-fs.c-27- bio_integrity_init(bio, &iib->bip, &iib->bvec, 1);
--
block/bio-integrity.c=67=void bio_integrity_alloc_buf(struct bio *bio, bool zero_buffer)
--
block/bio-integrity.c-79-
block/bio-integrity.c:80: page = mempool_alloc(&integrity_buf_pool, GFP_NOFS);
block/bio-integrity.c-81- if (zero_buffer)
--
block/bio.c=526=struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
--
block/bio.c-583-
block/bio.c:584: p = mempool_alloc(&bs->bio_pool, gfp);
block/bio.c-585- bio = p + bs->front_pad;
--
block/bio.c-587- nr_vecs = BIO_MAX_VECS;
block/bio.c:588: bvecs = mempool_alloc(&bs->bvec_pool, gfp);
block/bio.c-589- }
--
block/blk-crypto-fallback.c=489=bool blk_crypto_fallback_bio_prep(struct bio *bio)
--
block/blk-crypto-fallback.c-515- */
block/blk-crypto-fallback.c:516: f_ctx = mempool_alloc(bio_fallback_crypt_ctx_pool, GFP_NOIO);
block/blk-crypto-fallback.c-517- f_ctx->crypt_ctx = *bc;
--
block/blk-crypto.c=101=void bio_crypt_set_ctx(struct bio *bio, const struct blk_crypto_key *key,
--
block/blk-crypto.c-107- * The caller must use a gfp_mask that contains __GFP_DIRECT_RECLAIM so
block/blk-crypto.c:108: * that the mempool_alloc() can't fail.
block/blk-crypto.c-109- */
--
block/blk-crypto.c-111-
block/blk-crypto.c:112: bc = mempool_alloc(bio_crypt_ctx_pool, gfp_mask);
block/blk-crypto.c-113-
--
block/blk-crypto.c=126=int __bio_crypt_clone(struct bio *dst, struct bio *src, gfp_t gfp_mask)
block/blk-crypto.c-127-{
block/blk-crypto.c:128: dst->bi_crypt_context = mempool_alloc(bio_crypt_ctx_pool, gfp_mask);
block/blk-crypto.c-129- if (!dst->bi_crypt_context)
--
block/blk-crypto.c=281=int __blk_crypto_rq_bio_prep(struct request *rq, struct bio *bio,
--
block/blk-crypto.c-284- if (!rq->crypt_ctx) {
block/blk-crypto.c:285: rq->crypt_ctx = mempool_alloc(bio_crypt_ctx_pool, gfp_mask);
block/blk-crypto.c-286- if (!rq->crypt_ctx)
--
block/blk-zoned.c=650=static struct blk_zone_wplug *disk_get_or_alloc_zone_wplug(struct gendisk *disk,
--
block/blk-zoned.c-665- */
block/blk-zoned.c:666: zwplug = mempool_alloc(disk->zone_wplugs_pool, gfp_mask);
block/blk-zoned.c-667- if (!zwplug)
--
drivers/block/aoe/aoecmd.c=843=nextbuf(struct aoedev *d)
--
drivers/block/aoe/aoecmd.c-871- }
drivers/block/aoe/aoecmd.c:872: buf = mempool_alloc(d->bufpool, GFP_ATOMIC);
drivers/block/aoe/aoecmd.c-873- if (buf == NULL) {
--
drivers/block/drbd/drbd_bitmap.c=1203=static void bm_page_io_async(struct drbd_bm_aio_ctx *ctx, int page_nr) __must_hold(local)
--
drivers/block/drbd/drbd_bitmap.c-1249- if (ctx->flags & BM_AIO_COPY_PAGES) {
drivers/block/drbd/drbd_bitmap.c:1250: page = mempool_alloc(&drbd_md_io_page_pool,
drivers/block/drbd/drbd_bitmap.c-1251- GFP_NOIO | __GFP_HIGHMEM);
--
drivers/block/drbd/drbd_receiver.c=310=static struct page *__drbd_alloc_pages(struct drbd_resource *resource, unsigned int number, gfp_t gfp_mask)
--
drivers/block/drbd/drbd_receiver.c-316- for (i = 0; i < number; i++) {
drivers/block/drbd/drbd_receiver.c:317: tmp = mempool_alloc(&drbd_buffer_page_pool, gfp_mask);
drivers/block/drbd/drbd_receiver.c-318- if (!tmp)
--
drivers/block/drbd/drbd_receiver.c=414=drbd_alloc_peer_req(struct drbd_peer_device *peer_device, gfp_t gfp_mask) __must_hold(local)
--
drivers/block/drbd/drbd_receiver.c-421-
drivers/block/drbd/drbd_receiver.c:422: peer_req = mempool_alloc(&drbd_ee_mempool, gfp_mask & ~__GFP_HIGHMEM);
drivers/block/drbd/drbd_receiver.c-423- if (!peer_req) {
--
drivers/block/drbd/drbd_req.c=23=static struct drbd_request *drbd_req_new(struct drbd_device *device, struct bio *bio_src)
--
drivers/block/drbd/drbd_req.c-26-
drivers/block/drbd/drbd_req.c:27: req = mempool_alloc(&drbd_request_mempool, GFP_NOIO);
drivers/block/drbd/drbd_req.c-28- if (!req)
--
drivers/dma/dmaengine.c=1458=dmaengine_get_unmap_data(struct device *dev, int nr, gfp_t flags)
--
drivers/dma/dmaengine.c-1461-
drivers/dma/dmaengine.c:1462: unmap = mempool_alloc(__get_unmap_pool(nr)->pool, flags);
drivers/dma/dmaengine.c-1463- if (!unmap)
--
drivers/gpu/drm/xe/xe_guc_relay.c=218=__relay_get_transaction(struct xe_guc_relay *relay, bool incoming, u32 remote, u32 rid,
--
drivers/gpu/drm/xe/xe_guc_relay.c-236- */
drivers/gpu/drm/xe/xe_guc_relay.c:237: txn = mempool_alloc(&relay->pool, incoming ? GFP_ATOMIC : GFP_NOWAIT);
drivers/gpu/drm/xe/xe_guc_relay.c-238- if (!txn)
--
drivers/infiniband/hw/mlx5/odp.c=1637=static void mlx5_ib_eq_pf_process(struct mlx5_ib_pf_eq *eq)
--
drivers/infiniband/hw/mlx5/odp.c-1644- while ((eqe = mlx5_eq_get_eqe(eq->core, cc))) {
drivers/infiniband/hw/mlx5/odp.c:1645: pfault = mempool_alloc(eq->pool, GFP_ATOMIC);
drivers/infiniband/hw/mlx5/odp.c-1646- if (!pfault) {
--
drivers/infiniband/hw/mlx5/odp.c=1782=static void mempool_refill(mempool_t *pool)
--
drivers/infiniband/hw/mlx5/odp.c-1784- while (pool->curr_nr < pool->min_nr)
drivers/infiniband/hw/mlx5/odp.c:1785: mempool_free(mempool_alloc(pool, GFP_KERNEL), pool);
drivers/infiniband/hw/mlx5/odp.c-1786-}
--
drivers/md/bcache/bset.c=1235=static void __btree_sort(struct btree_keys *b, struct btree_iter *iter,
--
drivers/md/bcache/bset.c-1247-
drivers/md/bcache/bset.c:1248: outp = mempool_alloc(&state->pool, GFP_NOIO);
drivers/md/bcache/bset.c-1249- out = page_address(outp);
--
drivers/md/bcache/btree.c=148=void bch_btree_node_read_done(struct btree *b)
--
drivers/md/bcache/btree.c-158- */
drivers/md/bcache/btree.c:159: iter = mempool_alloc(&b->c->fill_iter, GFP_NOIO);
drivers/md/bcache/btree.c-160- iter->size = b->c->cache->sb.bucket_size / b->c->cache->sb.block_size;
--
drivers/md/bcache/io.c=24=struct bio *bch_bbio_alloc(struct cache_set *c)
drivers/md/bcache/io.c-25-{
drivers/md/bcache/io.c:26: struct bbio *b = mempool_alloc(&c->bio_meta, GFP_NOIO);
drivers/md/bcache/io.c-27- struct bio *bio = &b->bio;
--
drivers/md/bcache/request.c=729=static inline struct search *search_alloc(struct bio *bio,
--
drivers/md/bcache/request.c-734-
drivers/md/bcache/request.c:735: s = mempool_alloc(&d->c->search, GFP_NOIO);
drivers/md/bcache/request.c-736-
--
drivers/md/dm-bio-prison-v1.c=74=struct dm_bio_prison_cell *dm_bio_prison_alloc_cell(struct dm_bio_prison *prison, gfp_t gfp)
drivers/md/dm-bio-prison-v1.c-75-{
drivers/md/dm-bio-prison-v1.c:76: return mempool_alloc(&prison->cell_pool, gfp);
drivers/md/dm-bio-prison-v1.c-77-}
--
drivers/md/dm-bio-prison-v1.h=61=void dm_bio_prison_destroy(struct dm_bio_prison *prison);
--
drivers/md/dm-bio-prison-v1.h-66- *
drivers/md/dm-bio-prison-v1.h:67: * Like mempool_alloc(), dm_bio_prison_alloc_cell() can only fail if called
drivers/md/dm-bio-prison-v1.h-68- * in interrupt context or passed GFP_NOWAIT.
--
drivers/md/dm-bio-prison-v2.c=67=struct dm_bio_prison_cell_v2 *dm_bio_prison_alloc_cell_v2(struct dm_bio_prison_v2 *prison, gfp_t gfp)
drivers/md/dm-bio-prison-v2.c-68-{
drivers/md/dm-bio-prison-v2.c:69: return mempool_alloc(&prison->cell_pool, gfp);
drivers/md/dm-bio-prison-v2.c-70-}
--
drivers/md/dm-bio-prison-v2.h=58=void dm_bio_prison_destroy_v2(struct dm_bio_prison_v2 *prison);
--
drivers/md/dm-bio-prison-v2.h-63- *
drivers/md/dm-bio-prison-v2.h:64: * Like mempool_alloc(), dm_bio_prison_alloc_cell_v2() can only fail if called
drivers/md/dm-bio-prison-v2.h-65- * in interrupt context or passed GFP_NOWAIT.
--
drivers/md/dm-cache-target.c=481=static struct dm_cache_migration *alloc_migration(struct cache *cache)
--
drivers/md/dm-cache-target.c-484-
drivers/md/dm-cache-target.c:485: mg = mempool_alloc(&cache->migration_pool, GFP_NOIO);
drivers/md/dm-cache-target.c-486-
--
drivers/md/dm-clone-target.c=662=static struct dm_clone_region_hydration *alloc_hydration(struct clone *clone)
--
drivers/md/dm-clone-target.c-669- */
drivers/md/dm-clone-target.c:670: hd = mempool_alloc(&clone->hydration_pool, GFP_NOIO);
drivers/md/dm-clone-target.c-671- hd->clone = clone;
--
drivers/md/dm-crypt.c=1466=static int crypt_alloc_req_skcipher(struct crypt_config *cc,
--
drivers/md/dm-crypt.c-1471- if (!ctx->r.req) {
drivers/md/dm-crypt.c:1472: ctx->r.req = mempool_alloc(&cc->req_pool, in_interrupt() ? GFP_ATOMIC : GFP_NOIO);
drivers/md/dm-crypt.c-1473- if (!ctx->r.req)
--
drivers/md/dm-crypt.c=1490=static int crypt_alloc_req_aead(struct crypt_config *cc,
--
drivers/md/dm-crypt.c-1493- if (!ctx->r.req_aead) {
drivers/md/dm-crypt.c:1494: ctx->r.req_aead = mempool_alloc(&cc->req_pool, in_interrupt() ? GFP_ATOMIC : GFP_NOIO);
drivers/md/dm-crypt.c-1495- if (!ctx->r.req_aead)
--
drivers/md/dm-crypt.c=1665=static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned int size)
--
drivers/md/dm-crypt.c-1707-
drivers/md/dm-crypt.c:1708: pages = mempool_alloc(&cc->page_pool, gfp_mask);
drivers/md/dm-crypt.c-1709- if (!pages) {
--
drivers/md/dm-crypt.c=3455=static int crypt_map(struct dm_target *ti, struct bio *bio)
--
drivers/md/dm-crypt.c-3516- dm_accept_partial_bio(bio, cc->tag_pool_max_sectors);
drivers/md/dm-crypt.c:3517: io->integrity_metadata = mempool_alloc(&cc->tag_pool, GFP_NOIO);
drivers/md/dm-crypt.c-3518- io->integrity_metadata_from_pool = true;
--
drivers/md/dm-integrity.c=1700=static void integrity_sector_checksum_ahash(struct dm_integrity_c *ic, struct ahash_request **ahash_req,
--
drivers/md/dm-integrity.c-1714- if (unlikely(!req)) {
drivers/md/dm-integrity.c:1715: req = mempool_alloc(&ic->ahash_req_pool, GFP_NOIO);
drivers/md/dm-integrity.c-1716- *ahash_req = req;
--
drivers/md/dm-integrity.c=1798=static noinline void integrity_recheck(struct dm_integrity_io *dio, char *checksum)
--
drivers/md/dm-integrity.c-1812-
drivers/md/dm-integrity.c:1813: page = mempool_alloc(&ic->recheck_pool, GFP_NOIO);
drivers/md/dm-integrity.c-1814-
--
drivers/md/dm-integrity.c=2508=static int dm_integrity_map_inline(struct dm_integrity_io *dio, bool from_map)
--
drivers/md/dm-integrity.c-2583- if (unlikely(!dio->integrity_payload)) {
drivers/md/dm-integrity.c:2584: dio->integrity_payload = page_to_virt((struct page *)mempool_alloc(&ic->recheck_pool, GFP_NOIO));
drivers/md/dm-integrity.c-2585- dio->integrity_payload_from_mempool = true;
--
drivers/md/dm-integrity.c=2639=static void dm_integrity_inline_recheck(struct work_struct *w)
--
drivers/md/dm-integrity.c-2646-
drivers/md/dm-integrity.c:2647: dio->integrity_payload = page_to_virt((struct page *)mempool_alloc(&ic->recheck_pool, GFP_NOIO));
drivers/md/dm-integrity.c-2648- dio->integrity_payload_from_mempool = true;
--
drivers/md/dm-integrity.c=2921=static void do_journal_write(struct dm_integrity_c *ic, unsigned int write_start,
--
drivers/md/dm-integrity.c-2980-
drivers/md/dm-integrity.c:2981: io = mempool_alloc(&ic->journal_io_mempool, GFP_NOIO);
drivers/md/dm-integrity.c-2982- io->comp = ∁
--
drivers/md/dm-io.c=412=static void async_io(struct dm_io_client *client, unsigned int num_regions,
--
drivers/md/dm-io.c-418-
drivers/md/dm-io.c:419: io = mempool_alloc(&client->pool, GFP_NOIO);
drivers/md/dm-io.c-420- io->error_bits = 0;
--
drivers/md/dm-kcopyd.c=778=void dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
--
drivers/md/dm-kcopyd.c-788- */
drivers/md/dm-kcopyd.c:789: job = mempool_alloc(&kc->job_pool, GFP_NOIO);
drivers/md/dm-kcopyd.c-790- mutex_init(&job->lock);
--
drivers/md/dm-kcopyd.c=866=void *dm_kcopyd_prepare_callback(struct dm_kcopyd_client *kc,
--
drivers/md/dm-kcopyd.c-870-
drivers/md/dm-kcopyd.c:871: job = mempool_alloc(&kc->job_pool, GFP_NOIO);
drivers/md/dm-kcopyd.c-872-
--
drivers/md/dm-log-userspace-base.c=648=static void userspace_mark_region(struct dm_dirty_log *log, region_t region)
--
drivers/md/dm-log-userspace-base.c-654- /* Wait for an allocation, but _never_ fail */
drivers/md/dm-log-userspace-base.c:655: fe = mempool_alloc(&lc->flush_entry_pool, GFP_NOIO);
drivers/md/dm-log-userspace-base.c-656- BUG_ON(!fe);
--
drivers/md/dm-log-userspace-base.c=675=static void userspace_clear_region(struct dm_dirty_log *log, region_t region)
--
drivers/md/dm-log-userspace-base.c-686- */
drivers/md/dm-log-userspace-base.c:687: fe = mempool_alloc(&lc->flush_entry_pool, GFP_ATOMIC);
drivers/md/dm-log-userspace-base.c-688- if (!fe) {
--
drivers/md/dm-pcache/backing_dev.c=201=static struct pcache_backing_dev_req *req_type_req_alloc(struct pcache_backing_dev *backing_dev,
--
drivers/md/dm-pcache/backing_dev.c-207-
drivers/md/dm-pcache/backing_dev.c:208: backing_req = mempool_alloc(&backing_dev->req_pool, opts->gfp_mask);
drivers/md/dm-pcache/backing_dev.c-209- if (!backing_req)
--
drivers/md/dm-pcache/backing_dev.c=223=static struct pcache_backing_dev_req *kmem_type_req_alloc(struct pcache_backing_dev *backing_dev,
--
drivers/md/dm-pcache/backing_dev.c-228-
drivers/md/dm-pcache/backing_dev.c:229: backing_req = mempool_alloc(&backing_dev->req_pool, opts->gfp_mask);
drivers/md/dm-pcache/backing_dev.c-230- if (!backing_req)
--
drivers/md/dm-pcache/backing_dev.c-235- if (n_vecs > BACKING_DEV_REQ_INLINE_BVECS) {
drivers/md/dm-pcache/backing_dev.c:236: backing_req->kmem.bvecs = mempool_alloc(&backing_dev->bvec_pool, opts->gfp_mask);
drivers/md/dm-pcache/backing_dev.c-237- if (!backing_req->kmem.bvecs)
--
drivers/md/dm-pcache/cache_key.c=17=struct pcache_cache_key *cache_key_alloc(struct pcache_cache_tree *cache_tree, gfp_t gfp_mask)
--
drivers/md/dm-pcache/cache_key.c-20-
drivers/md/dm-pcache/cache_key.c:21: key = mempool_alloc(&cache_tree->key_pool, gfp_mask);
drivers/md/dm-pcache/cache_key.c-22- if (!key)
--
drivers/md/dm-region-hash.c=291=static struct dm_region *__rh_alloc(struct dm_region_hash *rh, region_t region)
--
drivers/md/dm-region-hash.c-294-
drivers/md/dm-region-hash.c:295: nreg = mempool_alloc(&rh->region_pool, GFP_ATOMIC);
drivers/md/dm-region-hash.c-296- if (unlikely(!nreg))
--
drivers/md/dm-snap.c=745=static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
drivers/md/dm-snap.c-746-{
drivers/md/dm-snap.c:747: struct dm_snap_pending_exception *pe = mempool_alloc(&s->pending_pool,
drivers/md/dm-snap.c-748- GFP_NOIO);
--
drivers/md/dm-thin.c=1253=static int ensure_next_mapping(struct pool *pool)
--
drivers/md/dm-thin.c-1257-
drivers/md/dm-thin.c:1258: pool->next_mapping = mempool_alloc(&pool->mapping_pool, GFP_ATOMIC);
drivers/md/dm-thin.c-1259-
--
drivers/md/dm-vdo/flush.c=392=void vdo_launch_flush(struct vdo *vdo, struct bio *bio)
--
drivers/md/dm-vdo/flush.c-397- */
drivers/md/dm-vdo/flush.c:398: struct vdo_flush *flush = mempool_alloc(vdo->flusher->flush_pool, GFP_NOWAIT);
drivers/md/dm-vdo/flush.c-399- struct flusher *flusher = vdo->flusher;
--
drivers/md/dm-verity-fec.c=272=static struct dm_verity_fec_io *fec_alloc_and_init_io(struct dm_verity *v)
--
drivers/md/dm-verity-fec.c-278-
drivers/md/dm-verity-fec.c:279: fio = mempool_alloc(&f->fio_pool, GFP_NOIO);
drivers/md/dm-verity-fec.c:280: fio->rs = mempool_alloc(&f->rs_pool, GFP_NOIO);
drivers/md/dm-verity-fec.c-281-
drivers/md/dm-verity-fec.c:282: fio->bufs[0] = mempool_alloc(&f->prealloc_pool, GFP_NOIO);
drivers/md/dm-verity-fec.c-283-
--
drivers/md/dm-verity-fec.c-292-
drivers/md/dm-verity-fec.c:293: fio->output = mempool_alloc(&f->output_pool, GFP_NOIO);
drivers/md/dm-verity-fec.c-294- fio->level = 0;
--
drivers/md/dm-verity-target.c=375=static noinline int verity_recheck(struct dm_verity *v, struct dm_verity_io *io,
--
drivers/md/dm-verity-target.c-384-
drivers/md/dm-verity-target.c:385: page = mempool_alloc(&v->recheck_pool, GFP_NOIO);
drivers/md/dm-verity-target.c-386- buffer = page_to_virt(page);
--
drivers/md/dm-writecache.c=1892=static void __writecache_writeback_ssd(struct dm_writecache *wc, struct writeback_list *wbl)
--
drivers/md/dm-writecache.c-1913-
drivers/md/dm-writecache.c:1914: c = mempool_alloc(&wc->copy_pool, GFP_NOIO);
drivers/md/dm-writecache.c-1915- c->wc = wc;
--
drivers/md/raid1.c=82=static void wait_for_serialization(struct md_rdev *rdev, struct r1bio *r1_bio)
--
drivers/md/raid1.c-90- return;
drivers/md/raid1.c:91: si = mempool_alloc(mddev->serial_info_pool, GFP_NOIO);
drivers/md/raid1.c-92- wait_event(serial->serial_io_wait,
--
drivers/md/raid1.c=1301=alloc_r1bio(struct mddev *mddev, struct bio *bio)
--
drivers/md/raid1.c-1305-
drivers/md/raid1.c:1306: r1_bio = mempool_alloc(conf->r1bio_pool, GFP_NOIO);
drivers/md/raid1.c-1307- memset(r1_bio, 0, offsetof(struct r1bio, bios[conf->raid_disks * 2]));
--
drivers/md/raid1.c=2736=static struct r1bio *raid1_alloc_init_r1buf(struct r1conf *conf)
drivers/md/raid1.c-2737-{
drivers/md/raid1.c:2738: struct r1bio *r1bio = mempool_alloc(&conf->r1buf_pool, GFP_NOIO);
drivers/md/raid1.c-2739- struct resync_pages *rps;
--
drivers/md/raid10.c=1529=static void __make_request(struct mddev *mddev, struct bio *bio, int sectors)
--
drivers/md/raid10.c-1533-
drivers/md/raid10.c:1534: r10_bio = mempool_alloc(&conf->r10bio_pool, GFP_NOIO);
drivers/md/raid10.c-1535-
--
drivers/md/raid10.c=1602=static int raid10_handle_discard(struct mddev *mddev, struct bio *bio)
--
drivers/md/raid10.c-1725-retry_discard:
drivers/md/raid10.c:1726: r10_bio = mempool_alloc(&conf->r10bio_pool, GFP_NOIO);
drivers/md/raid10.c-1727- r10_bio->mddev = mddev;
--
drivers/md/raid10.c=3050=static struct r10bio *raid10_alloc_init_r10buf(struct r10conf *conf)
drivers/md/raid10.c-3051-{
drivers/md/raid10.c:3052: struct r10bio *r10bio = mempool_alloc(&conf->r10buf_pool, GFP_NOIO);
drivers/md/raid10.c-3053- struct rsync_pages *rp;
--
drivers/md/raid5-cache.c=762=static struct r5l_io_unit *r5l_new_meta(struct r5l_log *log)
--
drivers/md/raid5-cache.c-766-
drivers/md/raid5-cache.c:767: io = mempool_alloc(&log->io_pool, GFP_ATOMIC);
drivers/md/raid5-cache.c-768- if (!io)
--
drivers/md/raid5-cache.c-777-
drivers/md/raid5-cache.c:778: io->meta_page = mempool_alloc(&log->meta_pool, GFP_NOIO);
drivers/md/raid5-cache.c-779- block = page_address(io->meta_page);
--
drivers/md/raid5-ppl.c=232=static struct ppl_io_unit *ppl_new_iounit(struct ppl_log *log,
--
drivers/md/raid5-ppl.c-239-
drivers/md/raid5-ppl.c:240: io = mempool_alloc(&ppl_conf->io_pool, GFP_NOWAIT);
drivers/md/raid5-ppl.c-241- if (!io)
--
drivers/md/raid5.c=6084=static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
--
drivers/md/raid5.c-6128-
drivers/md/raid5.c:6129: ctx = mempool_alloc(conf->ctx_pool, GFP_NOIO);
drivers/md/raid5.c-6130- memset(ctx, 0, conf->ctx_size);
--
drivers/nvme/host/apple.c=538=static blk_status_t apple_nvme_map_data(struct apple_nvme *anv,
--
drivers/nvme/host/apple.c-554- iod->dma_len = 0;
drivers/nvme/host/apple.c:555: iod->sg = mempool_alloc(anv->iod_mempool, GFP_ATOMIC);
drivers/nvme/host/apple.c-556- if (!iod->sg)
--
drivers/nvme/host/auth.c=784=static void nvme_queue_auth_work(struct work_struct *work)
--
drivers/nvme/host/auth.c-795- */
drivers/nvme/host/auth.c:796: chap->buf = mempool_alloc(nvme_chap_buf_pool, GFP_KERNEL);
drivers/nvme/host/auth.c-797- if (!chap->buf) {
--
drivers/nvme/host/pci.c=963=static bool nvme_pci_prp_save_mapping(struct request *req,
--
drivers/nvme/host/pci.c-974-
drivers/nvme/host/pci.c:975: iod->dma_vecs = mempool_alloc(nvmeq->dev->dmavec_mempool,
drivers/nvme/host/pci.c-976- GFP_ATOMIC);
--
drivers/nvme/target/io-cmd-file.c=218=static void nvmet_file_execute_rw(struct nvmet_req *req)
--
drivers/nvme/target/io-cmd-file.c-236- /* fallback under memory pressure */
drivers/nvme/target/io-cmd-file.c:237: req->f.bvec = mempool_alloc(req->ns->bvec_pool, GFP_KERNEL);
drivers/nvme/target/io-cmd-file.c-238- req->f.mpool_alloc = true;
--
drivers/nvme/target/pci-epf.c=675=nvmet_pci_epf_alloc_iod(struct nvmet_pci_epf_queue *sq)
--
drivers/nvme/target/pci-epf.c-679-
drivers/nvme/target/pci-epf.c:680: iod = mempool_alloc(&ctrl->iod_pool, GFP_KERNEL);
drivers/nvme/target/pci-epf.c-681- if (unlikely(!iod))
--
drivers/s390/block/scm_blk.c=149=static inline struct aidaw *scm_aidaw_alloc(void)
drivers/s390/block/scm_blk.c-150-{
drivers/s390/block/scm_blk.c:151: struct page *page = mempool_alloc(aidaw_pool, GFP_ATOMIC);
drivers/s390/block/scm_blk.c-152-
--
drivers/s390/crypto/zcrypt_ccamisc.c=1121=int cca_clr2cipherkey(u16 card, u16 dom, u32 keybitsize, u32 keygenflags,
--
drivers/s390/crypto/zcrypt_ccamisc.c-1140- mempool_alloc_preallocated(cprb_mempool) :
drivers/s390/crypto/zcrypt_ccamisc.c:1141: mempool_alloc(cprb_mempool, GFP_KERNEL);
drivers/s390/crypto/zcrypt_ccamisc.c-1142- if (!mem)
--
drivers/s390/crypto/zcrypt_ccamisc.c=1632=int cca_get_info(u16 cardnr, u16 domain, struct cca_info *ci, u32 xflags)
--
drivers/s390/crypto/zcrypt_ccamisc.c-1655- mempool_alloc_preallocated(cprb_mempool) :
drivers/s390/crypto/zcrypt_ccamisc.c:1656: mempool_alloc(cprb_mempool, GFP_KERNEL);
drivers/s390/crypto/zcrypt_ccamisc.c-1657- if (!mem)
--
drivers/s390/crypto/zcrypt_ep11misc.c=641=int ep11_get_card_info(u16 card, struct ep11_card_info *info, u32 xflags)
--
drivers/s390/crypto/zcrypt_ep11misc.c-673- mempool_alloc_preallocated(cprb_mempool) :
drivers/s390/crypto/zcrypt_ep11misc.c:674: mempool_alloc(cprb_mempool, GFP_KERNEL);
drivers/s390/crypto/zcrypt_ep11misc.c-675- if (!pmqi)
--
drivers/s390/crypto/zcrypt_ep11misc.c=1354=int ep11_clr2keyblob(u16 card, u16 domain, u32 keybitsize, u32 keygenflags,
--
drivers/s390/crypto/zcrypt_ep11misc.c-1378- mempool_alloc_preallocated(cprb_mempool) :
drivers/s390/crypto/zcrypt_ep11misc.c:1379: mempool_alloc(cprb_mempool, GFP_KERNEL);
drivers/s390/crypto/zcrypt_ep11misc.c-1380- if (!mem)
--
drivers/s390/crypto/zcrypt_ep11misc.c=1422=int ep11_kblob2protkey(u16 card, u16 dom,
--
drivers/s390/crypto/zcrypt_ep11misc.c-1462- mempool_alloc_preallocated(cprb_mempool) :
drivers/s390/crypto/zcrypt_ep11misc.c:1463: mempool_alloc(cprb_mempool, GFP_ATOMIC);
drivers/s390/crypto/zcrypt_ep11misc.c-1464- if (!wkbuf) {
--
drivers/s390/scsi/zfcp_fc.c=420=static int zfcp_fc_ns_gid_pn(struct zfcp_port *port)
--
drivers/s390/scsi/zfcp_fc.c-425-
drivers/s390/scsi/zfcp_fc.c:426: fc_req = mempool_alloc(adapter->pool.gid_pn, GFP_ATOMIC);
drivers/s390/scsi/zfcp_fc.c-427- if (!fc_req)
--
drivers/s390/scsi/zfcp_fsf.c=802=static struct zfcp_fsf_req *zfcp_fsf_alloc(mempool_t *pool)
--
drivers/s390/scsi/zfcp_fsf.c-806- if (likely(pool))
drivers/s390/scsi/zfcp_fsf.c:807: req = mempool_alloc(pool, GFP_ATOMIC);
drivers/s390/scsi/zfcp_fsf.c-808- else
--
drivers/s390/scsi/zfcp_fsf.c=819=static struct fsf_qtcb *zfcp_fsf_qtcb_alloc(mempool_t *pool)
--
drivers/s390/scsi/zfcp_fsf.c-823- if (likely(pool))
drivers/s390/scsi/zfcp_fsf.c:824: qtcb = mempool_alloc(pool, GFP_ATOMIC);
drivers/s390/scsi/zfcp_fsf.c-825- else
--
drivers/s390/scsi/zfcp_fsf.c=928=int zfcp_fsf_status_read(struct zfcp_qdio *qdio)
--
drivers/s390/scsi/zfcp_fsf.c-947-
drivers/s390/scsi/zfcp_fsf.c:948: page = mempool_alloc(adapter->pool.sr_data, GFP_ATOMIC);
drivers/s390/scsi/zfcp_fsf.c-949- if (!page) {
--
drivers/scsi/csiostor/csio_attr.c=417=csio_fcoe_alloc_vnp(struct csio_hw *hw, struct csio_lnode *ln)
--
drivers/scsi/csiostor/csio_attr.c-427- spin_lock_irq(&hw->lock);
drivers/scsi/csiostor/csio_attr.c:428: mbp = mempool_alloc(hw->mb_mempool, GFP_ATOMIC);
drivers/scsi/csiostor/csio_attr.c-429- if (!mbp) {
--
drivers/scsi/csiostor/csio_attr.c=498=csio_fcoe_free_vnp(struct csio_hw *hw, struct csio_lnode *ln)
--
drivers/scsi/csiostor/csio_attr.c-508- spin_lock_irq(&hw->lock);
drivers/scsi/csiostor/csio_attr.c:509: mbp = mempool_alloc(hw->mb_mempool, GFP_ATOMIC);
drivers/scsi/csiostor/csio_attr.c-510- if (!mbp) {
]
]
|
| 38/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 52212
output: 41
thoughts: 21
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into `mempool_alloc`**
Okay, time to get my hands dirty and dig into the guts of the `mempool` allocation mechanism. Specifically, I need to check out the `mempool_alloc` function. I know it resides in `mm/mempool.c`, so I'll jump right into that file. My aim is to understand the core logic of how memory is pulled from the pool. I want to pay particularly close attention to potential contention issues, error handling, and the fallback strategies if the pool is exhausted. I'm also curious about the interaction with the underlying slab or page allocator; are there any subtle performance implications related to the choice of the memory backing the pool? I'll probably be looking for any spinlocks or mutexes involved, and how they are used to protect access to the pool's data structures. Specifically, I wonder if it includes any fairness considerations and how it implements any such guarantees. Let's see what the code reveals!
|
| 39/2 |
2026/05/23 07:17 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:mm/mempool.c IncludeLines:true Name:mempool_alloc]
Results: map[SourceCode: SourceFile:]
|
| 40/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 52524
output: 43
thoughts: 46
Thoughts: Okay, let's see... Where did I last see that mempool function? I'm pretty sure it was in the kernel's memory management code. Right, *mempool*. Could it be that the relevant function is in `mm/mempool.c` but maybe hasn't been exported properly? It's always a possibility in a big codebase. Alternatively, maybe `mempool_alloc` is defined as a macro, which would explain why I'm having trouble finding a direct definition.
Alright, to figure this out, the next step is definitely to check the header file that defines the mempool interface. Let me take a look at `include/linux/mempool.h` and see what it reveals. That should tell me whether I'm looking for a function declaration or if it's indeed a macro. Time to dig in!
|
| 41/2 |
2026/05/23 07:17 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:include/linux/mempool.h IncludeLines:true Name:mempool_alloc]
Results: map[SourceCode: SourceFile:]
|
| 42/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 52819
output: 21
thoughts: 22
Thoughts: Here's my summary, as though I'm thinking through this process:
**Diving into the Mempool Code**
Okay, so I need to understand how the memory pool allocation works. I'm going to start with a grep. Let's get right down to it, specifically `mempool_alloc`. I'll focus on `mm/mempool.c`, because that's where I expect the core implementation to reside. This should quickly pinpoint the key functions involved in the allocation process and where to start digging deeper into the details. Time to pull up the terminal... let's see what we uncover.
|
| 43/2 |
2026/05/23 07:17 |
tool |
grepper |
0m
Args: map[Expression:void \*mempool_alloc]
Results: map[Output:include/linux/mempool.h=63=void mempool_destroy(struct mempool *pool);
include/linux/mempool.h-64-
include/linux/mempool.h:65:void *mempool_alloc_noprof(struct mempool *pool, gfp_t gfp_mask) __malloc;
include/linux/mempool.h-66-#define mempool_alloc(...) \
--
include/linux/mempool.h=68=int mempool_alloc_bulk_noprof(struct mempool *pool, void **elem,
--
include/linux/mempool.h-72-
include/linux/mempool.h:73:void *mempool_alloc_preallocated(struct mempool *pool) __malloc;
include/linux/mempool.h-74-void mempool_free(void *element, struct mempool *pool);
include/linux/mempool.h=75=unsigned int mempool_free_bulk(struct mempool *pool, void **elem,
--
include/linux/mempool.h-82- */
include/linux/mempool.h:83:void *mempool_alloc_slab(gfp_t gfp_mask, void *pool_data);
include/linux/mempool.h-84-void mempool_free_slab(void *element, void *pool_data);
--
include/linux/mempool.h=96=void mempool_kfree(void *element, void *pool_data);
--
include/linux/mempool.h-108- */
include/linux/mempool.h:109:void *mempool_alloc_pages(gfp_t gfp_mask, void *pool_data);
include/linux/mempool.h-110-void mempool_free_pages(void *element, void *pool_data);
--
mm/mempool.c=534=EXPORT_SYMBOL_GPL(mempool_alloc_bulk_noprof);
--
mm/mempool.c-551- */
mm/mempool.c:552:void *mempool_alloc_noprof(struct mempool *pool, gfp_t gfp_mask)
mm/mempool.c-553-{
--
mm/mempool.c=590=EXPORT_SYMBOL(mempool_alloc_noprof);
--
mm/mempool.c-603- */
mm/mempool.c:604:void *mempool_alloc_preallocated(struct mempool *pool)
mm/mempool.c-605-{
--
mm/mempool.c=713=EXPORT_SYMBOL(mempool_free);
--
mm/mempool.c-717- */
mm/mempool.c:718:void *mempool_alloc_slab(gfp_t gfp_mask, void *pool_data)
mm/mempool.c-719-{
--
mm/mempool.c=748=EXPORT_SYMBOL(mempool_kfree);
--
mm/mempool.c-753- */
mm/mempool.c:754:void *mempool_alloc_pages(gfp_t gfp_mask, void *pool_data)
mm/mempool.c-755-{
]
|
| 44/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 53852
output: 45
thoughts: 50
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm already familiar with memory management concepts.
**Diving into the Mempool Allocation Macro**
Hmm, so `mempool_alloc` is just a macro, and a quick glance tells me it expands to `mempool_alloc_noprof`. Right, no surprises there, just a convenience wrapper. I've seen that pattern before, usually for avoiding profiling overhead in the common allocation path. Now, let's get down to brass tacks. I need to understand the underlying implementation, so I'll jump straight into `mm/mempool.c` and check out the `mempool_alloc_noprof` function. That's where the real magic happens, I bet. I'm especially interested in how it handles the pool's internal data structures and what happens when the pool is either full or has available entries. I need to refresh my understanding of the exact allocation logic in this particular mempool implementation, so I'll be looking for details regarding locking, error handling, and perhaps some optimization considerations, such as how it interacts with the underlying page allocator, and how it avoids contention when multiple tasks are using the same mempool.
|
| 45/2 |
2026/05/23 07:17 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/mempool.c IncludeLines:true Name:mempool_alloc_noprof]
Results: map[SourceCode: 536: /**
537: * mempool_alloc - allocate an element from a memory pool
538: * @pool: pointer to the memory pool
539: * @gfp_mask: GFP_* flags. %__GFP_ZERO is not supported.
540: *
541: * Allocate an element from @pool. This is done by first calling into the
542: * alloc_fn supplied at pool initialization time, and dipping into the reserved
543: * pool when alloc_fn fails to allocate an element.
544: *
545: * This function only sleeps if the alloc_fn callback sleeps, or when waiting
546: * for elements to become available in the pool.
547: *
548: * Return: pointer to the allocated element or %NULL when failing to allocate
549: * an element. Allocation failure can only happen when @gfp_mask does not
550: * include %__GFP_DIRECT_RECLAIM.
551: */
552: void *mempool_alloc_noprof(struct mempool *pool, gfp_t gfp_mask)
553: {
554: gfp_t gfp_temp = mempool_adjust_gfp(&gfp_mask);
555: void *element;
556:
557: VM_WARN_ON_ONCE(gfp_mask & __GFP_ZERO);
558: might_alloc(gfp_mask);
559:
560: repeat_alloc:
561: if (should_fail_ex(&fail_mempool_alloc, 1, FAULT_NOWARN)) {
562: pr_info("forcing mempool usage for %pS\n",
563: (void *)_RET_IP_);
564: element = NULL;
565: } else {
566: element = pool->alloc(gfp_temp, pool->pool_data);
567: }
568:
569: if (unlikely(!element)) {
570: /*
571: * Try to allocate an element from the pool.
572: *
573: * The first pass won't have __GFP_DIRECT_RECLAIM and won't
574: * sleep in mempool_alloc_from_pool. Retry the allocation
575: * with all flags set in that case.
576: */
577: if (!mempool_alloc_from_pool(pool, &element, 1, 0, gfp_temp)) {
578: if (gfp_temp != gfp_mask) {
579: gfp_temp = gfp_mask;
580: goto repeat_alloc;
581: }
582: if (gfp_mask & __GFP_DIRECT_RECLAIM) {
583: goto repeat_alloc;
584: }
585: }
586: }
587:
588: return element;
589: }
SourceFile:mm/mempool.c]
|
| 46/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 55090
output: 40
thoughts: 106
Thoughts: **Analyzing Potential Null Pointer Dereference in `bio_alloc_bioset`**
Okay, hold on a second. I think I see a potential issue here with `mempool_alloc` and the `__GFP_DIRECT_RECLAIM` flag. If `__GFP_DIRECT_RECLAIM` is *cleared* β and I believe it is in this instance β `mempool_alloc` will return NULL when `mempool_alloc_from_pool` fails, right? Let me confirm... yes, that's the expected behavior. Now, let's look at `gfp_mask` as it is passed to `mempool_alloc` within `bio_alloc_bioset`. This is set to `gfp`, and if I remember correctly, the `try_alloc_gfp` function *clears* the `__GFP_DIRECT_RECLAIM` flag from the `gfp` mask! That's concerning. We could be dealing with a NULL return here in a potentially sensitive area. Okay, time to go back to `bio_alloc_bioset` and meticulously trace the execution path again. We need to be absolutely sure about this.
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2026/05/23 07:17 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_alloc_bioset]
Results: map[SourceCode: 492: /**
493: * bio_alloc_bioset - allocate a bio for I/O
494: * @bdev: block device to allocate the bio for (can be %NULL)
495: * @nr_vecs: number of bvecs to pre-allocate
496: * @opf: operation and flags for bio
497: * @gfp: the GFP_* mask given to the slab allocator
498: * @bs: the bio_set to allocate from.
499: *
500: * Allocate a bio from the mempools in @bs.
501: *
502: * If %__GFP_DIRECT_RECLAIM is set then bio_alloc will always be able to
503: * allocate a bio. This is due to the mempool guarantees. To make this work,
504: * callers must never allocate more than 1 bio at a time from the general pool.
505: * Callers that need to allocate more than 1 bio must always submit the
506: * previously allocated bio for IO before attempting to allocate a new one.
507: * Failure to do so can cause deadlocks under memory pressure.
508: *
509: * Note that when running under submit_bio_noacct() (i.e. any block driver),
510: * bios are not submitted until after you return - see the code in
511: * submit_bio_noacct() that converts recursion into iteration, to prevent
512: * stack overflows.
513: *
514: * This would normally mean allocating multiple bios under submit_bio_noacct()
515: * would be susceptible to deadlocks, but we have
516: * deadlock avoidance code that resubmits any blocked bios from a rescuer
517: * thread.
518: *
519: * However, we do not guarantee forward progress for allocations from other
520: * mempools. Doing multiple allocations from the same mempool under
521: * submit_bio_noacct() should be avoided - instead, use bio_set's front_pad
522: * for per bio allocations.
523: *
524: * Returns: Pointer to new bio on success, NULL on failure.
525: */
526: struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
527: blk_opf_t opf, gfp_t gfp, struct bio_set *bs)
528: {
529: struct bio_vec *bvecs = NULL;
530: struct bio *bio = NULL;
531: gfp_t saved_gfp = gfp;
532: void *p;
533:
534: /* should not use nobvec bioset for nr_vecs > 0 */
535: if (WARN_ON_ONCE(!mempool_initialized(&bs->bvec_pool) && nr_vecs > 0))
536: return NULL;
537:
538: gfp = try_alloc_gfp(gfp);
539: if (bs->cache && nr_vecs <= BIO_INLINE_VECS) {
540: /*
541: * Set REQ_ALLOC_CACHE even if no cached bio is available to
542: * return the allocated bio to the percpu cache when done.
543: */
544: opf |= REQ_ALLOC_CACHE;
545: bio = bio_alloc_percpu_cache(bs);
546: } else {
547: opf &= ~REQ_ALLOC_CACHE;
548: p = kmem_cache_alloc(bs->bio_slab, gfp);
549: if (p)
550: bio = p + bs->front_pad;
551: }
552:
553: if (bio && nr_vecs > BIO_INLINE_VECS) {
554: struct biovec_slab *bvs = biovec_slab(nr_vecs);
555:
556: /*
557: * Upgrade nr_vecs to take full advantage of the allocation.
558: * We also rely on this in bio_free().
559: */
560: nr_vecs = bvs->nr_vecs;
561: bvecs = kmem_cache_alloc(bvs->slab, gfp);
562: if (unlikely(!bvecs)) {
563: kmem_cache_free(bs->bio_slab, p);
564: bio = NULL;
565: }
566: }
567:
568: if (unlikely(!bio)) {
569: /*
570: * Give up if we are not allow to sleep as non-blocking mempool
571: * allocations just go back to the slab allocation.
572: */
573: if (!(saved_gfp & __GFP_DIRECT_RECLAIM))
574: return NULL;
575:
576: punt_bios_to_rescuer(bs);
577:
578: /*
579: * Don't rob the mempools by returning to the per-CPU cache if
580: * we're tight on memory.
581: */
582: opf &= ~REQ_ALLOC_CACHE;
583:
584: p = mempool_alloc(&bs->bio_pool, gfp);
585: bio = p + bs->front_pad;
586: if (nr_vecs > BIO_INLINE_VECS) {
587: nr_vecs = BIO_MAX_VECS;
588: bvecs = mempool_alloc(&bs->bvec_pool, gfp);
589: }
590: }
591:
592: if (nr_vecs && nr_vecs <= BIO_INLINE_VECS)
593: bio_init_inline(bio, bdev, nr_vecs, opf);
594: else
595: bio_init(bio, bdev, bvecs, nr_vecs, opf);
596: bio->bi_pool = bs;
597: return bio;
598: }
SourceFile:block/bio.c]
|
| 48/2 |
2026/05/23 07:17 |
llm |
expert |
0m
Model:
Tokens:
input: 57292
output: 47
thoughts: 140
Thoughts: **Analyzing Potential Memory Allocation Issues in the Kernel**
Okay, hold on a second. I'm seeing something here with `mempool_alloc`. The fact that it's being called with `gfp` and, crucially, that `__GFP_DIRECT_RECLAIM` is *cleared* in that `gfp` mask is a red flag. If `__GFP_DIRECT_RECLAIM` is not set, then the mempool allocation has a higher chance of failing because the system won't immediately try to reclaim memory if it's running low.
Aha, and then I recall that `mempool_alloc` specifically uses that `gfp_mask` value that's passed to it. So, if `gfp_mask` *doesn't* include `__GFP_DIRECT_RECLAIM`, then we *could* get a `NULL` return from `mempool_alloc`. This is something I need to keep in mind, because `NULL` returns from mempool allocations can be a source of problems, and the lack of reclaim can exacerbate the issue.
But wait, I need to take a step back and think, wasn't there something about how it handled `saved_gfp` in older kernels with respect to this? Maybe I am mixing this up. The safest approach is to go back and check the code. Let's quickly check the git log for the `block/bio.c` file around the calls to `mempool_alloc(&bs->bio_pool, gfp)` to see what might have changed with that. That should give me a good history to understand how the memory allocation strategy evolved.
|
| 49/2 |
2026/05/23 07:18 |
tool |
git-log |
0m
Args: map[CodeRegexp:mempool_alloc.*bs->bio_pool.*gfp Count:10 PathPrefix:block/bio.c]
Results: map[Output:b520c4eef83d block: split bio_alloc_bioset more clearly into a fast and slowpath
3175199ab0ac block: split bio_kmalloc from bio_alloc_bioset
8aa6ba2f6e3d block: Convert bio_set to mempool_init()
f9c78b2be2ca block: move bio.c and bio-integrity.c from fs/ to block/
]
|
| 50/2 |
2026/05/23 07:18 |
llm |
expert |
0m
Model:
Tokens:
input: 57952
output: 26
thoughts: 18
Thoughts: Okay, let's dive into this. Here's my perspective on that thought process:
**Diving into Commit b520c4eef83d**
Right, let's take a look at commit `b520c4eef83d`. I need to understand what changed, how it affects the codebase, and whether it introduces any potential issues. Immediately, I'm thinking about the context. What was the purpose of this commit? Was it a bug fix, a new feature, a refactor, or something else entirely? I'll probably start by looking at the commit message and any related pull requests to get a high-level understanding. From there, I'll need to dig into the diff itself. I'll focus on the specific files that were modified and the nature of those changes. Are we talking about code modifications, configuration updates, documentation improvements, or something else? I will then assess the potential impact of this commit. Does it introduce any new dependencies? Does it alter any existing API contracts? Does it change any behavior, and if so, how? I'll be particularly vigilant for potential regressions or performance bottlenecks. I'll be forming hypotheses about the design decisions that led to these changes, and I'll use my deep understanding of the system's architecture to evaluate them.
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| 51/2 |
2026/05/23 07:18 |
tool |
git-show |
0m
Args:
Results: map[Output:commit b520c4eef83dd406591431f936de0908c3ed7fb9
Author: Christoph Hellwig <hch@lst.de>
Date: Mon Mar 16 17:11:30 2026 +0100
block: split bio_alloc_bioset more clearly into a fast and slowpath
bio_alloc_bioset tries non-waiting slab allocations first for the bio and
bvec array, but does so in a somewhat convoluted way.
Restructure the function so that it first open codes these slab
allocations, and then falls back to the mempools with the original
gfp mask.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com> -ck
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://patch.msgid.link/20260316161144.1607877-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/bio.c b/block/bio.c
index 6131ccb7284a..5982bf069cef 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -176,43 +176,12 @@ static void bvec_free(struct mempool *pool, struct bio_vec *bv,
* Make the first allocation restricted and don't dump info on allocation
* failures, since we'll fall back to the mempool in case of failure.
*/
-static inline gfp_t bvec_alloc_gfp(gfp_t gfp)
+static inline gfp_t try_alloc_gfp(gfp_t gfp)
{
return (gfp & ~(__GFP_DIRECT_RECLAIM | __GFP_IO)) |
__GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
}
-static struct bio_vec *bvec_alloc(struct mempool *pool, unsigned short *nr_vecs,
- gfp_t gfp_mask)
-{
- struct biovec_slab *bvs = biovec_slab(*nr_vecs);
-
- if (WARN_ON_ONCE(!bvs))
- return NULL;
-
- /*
- * Upgrade the nr_vecs request to take full advantage of the allocation.
- * We also rely on this in the bvec_free path.
- */
- *nr_vecs = bvs->nr_vecs;
-
- /*
- * Try a slab allocation first for all smaller allocations. If that
- * fails and __GFP_DIRECT_RECLAIM is set retry with the mempool.
- * The mempool is sized to handle up to BIO_MAX_VECS entries.
- */
- if (*nr_vecs < BIO_MAX_VECS) {
- struct bio_vec *bvl;
-
- bvl = kmem_cache_alloc(bvs->slab, bvec_alloc_gfp(gfp_mask));
- if (likely(bvl) || !(gfp_mask & __GFP_DIRECT_RECLAIM))
- return bvl;
- *nr_vecs = BIO_MAX_VECS;
- }
-
- return mempool_alloc(pool, gfp_mask);
-}
-
void bio_uninit(struct bio *bio)
{
#ifdef CONFIG_BLK_CGROUP
@@ -433,13 +402,31 @@ static void bio_alloc_rescue(struct work_struct *work)
}
}
+/*
+ * submit_bio_noacct() converts recursion to iteration; this means if we're
+ * running beneath it, any bios we allocate and submit will not be submitted
+ * (and thus freed) until after we return.
+ *
+ * This exposes us to a potential deadlock if we allocate multiple bios from the
+ * same bio_set while running underneath submit_bio_noacct(). If we were to
+ * allocate multiple bios (say a stacking block driver that was splitting bios),
+ * we would deadlock if we exhausted the mempool's reserve.
+ *
+ * We solve this, and guarantee forward progress by punting the bios on
+ * current->bio_list to a per bio_set rescuer workqueue before blocking to wait
+ * for elements being returned to the mempool.
+ */
static void punt_bios_to_rescuer(struct bio_set *bs)
{
struct bio_list punt, nopunt;
struct bio *bio;
- if (WARN_ON_ONCE(!bs->rescue_workqueue))
+ if (!current->bio_list || !bs->rescue_workqueue)
return;
+ if (bio_list_empty(¤t->bio_list[0]) &&
+ bio_list_empty(¤t->bio_list[1]))
+ return;
+
/*
* In order to guarantee forward progress we must punt only bios that
* were allocated from this bio_set; otherwise, if there was a bio on
@@ -486,9 +473,7 @@ static void bio_alloc_irq_cache_splice(struct bio_alloc_cache *cache)
local_irq_restore(flags);
}
-static struct bio *bio_alloc_percpu_cache(struct block_device *bdev,
- unsigned short nr_vecs, blk_opf_t opf, gfp_t gfp,
- struct bio_set *bs)
+static struct bio *bio_alloc_percpu_cache(struct bio_set *bs)
{
struct bio_alloc_cache *cache;
struct bio *bio;
@@ -506,11 +491,6 @@ static struct bio *bio_alloc_percpu_cache(struct block_device *bdev,
cache->free_list = bio->bi_next;
cache->nr--;
put_cpu();
-
- if (nr_vecs)
- bio_init_inline(bio, bdev, nr_vecs, opf);
- else
- bio_init(bio, bdev, NULL, nr_vecs, opf);
bio->bi_pool = bs;
return bio;
}
@@ -520,7 +500,7 @@ static struct bio *bio_alloc_percpu_cache(struct block_device *bdev,
* @bdev: block device to allocate the bio for (can be %NULL)
* @nr_vecs: number of bvecs to pre-allocate
* @opf: operation and flags for bio
- * @gfp_mask: the GFP_* mask given to the slab allocator
+ * @gfp: the GFP_* mask given to the slab allocator
* @bs: the bio_set to allocate from.
*
* Allocate a bio from the mempools in @bs.
@@ -550,91 +530,77 @@ static struct bio *bio_alloc_percpu_cache(struct block_device *bdev,
* Returns: Pointer to new bio on success, NULL on failure.
*/
struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
- blk_opf_t opf, gfp_t gfp_mask,
- struct bio_set *bs)
+ blk_opf_t opf, gfp_t gfp, struct bio_set *bs)
{
- gfp_t saved_gfp = gfp_mask;
- struct bio *bio;
+ struct bio_vec *bvecs = NULL;
+ struct bio *bio = NULL;
+ gfp_t saved_gfp = gfp;
void *p;
/* should not use nobvec bioset for nr_vecs > 0 */
if (WARN_ON_ONCE(!mempool_initialized(&bs->bvec_pool) && nr_vecs > 0))
return NULL;
+ gfp = try_alloc_gfp(gfp);
if (bs->cache && nr_vecs <= BIO_INLINE_VECS) {
- opf |= REQ_ALLOC_CACHE;
- bio = bio_alloc_percpu_cache(bdev, nr_vecs, opf,
- gfp_mask, bs);
- if (bio)
- return bio;
/*
- * No cached bio available, bio returned below marked with
- * REQ_ALLOC_CACHE to participate in per-cpu alloc cache.
+ * Set REQ_ALLOC_CACHE even if no cached bio is available to
+ * return the allocated bio to the percpu cache when done.
*/
- } else
+ opf |= REQ_ALLOC_CACHE;
+ bio = bio_alloc_percpu_cache(bs);
+ } else {
opf &= ~REQ_ALLOC_CACHE;
-
- /*
- * submit_bio_noacct() converts recursion to iteration; this means if
- * we're running beneath it, any bios we allocate and submit will not be
- * submitted (and thus freed) until after we return.
- *
- * This exposes us to a potential deadlock if we allocate multiple bios
- * from the same bio_set() while running underneath submit_bio_noacct().
- * If we were to allocate multiple bios (say a stacking block driver
- * that was splitting bios), we would deadlock if we exhausted the
- * mempool's reserve.
- *
- * We solve this, and guarantee forward progress, with a rescuer
- * workqueue per bio_set. If we go to allocate and there are bios on
- * current->bio_list, we first try the allocation without
- * __GFP_DIRECT_RECLAIM; if that fails, we punt those bios we would be
- * blocking to the rescuer workqueue before we retry with the original
- * gfp_flags.
- */
- if (current->bio_list &&
- (!bio_list_empty(¤t->bio_list[0]) ||
- !bio_list_empty(¤t->bio_list[1])) &&
- bs->rescue_workqueue)
- gfp_mask &= ~__GFP_DIRECT_RECLAIM;
-
- p = mempool_alloc(&bs->bio_pool, gfp_mask);
- if (!p && gfp_mask != saved_gfp) {
- punt_bios_to_rescuer(bs);
- gfp_mask = saved_gfp;
- p = mempool_alloc(&bs->bio_pool, gfp_mask);
+ p = kmem_cache_alloc(bs->bio_slab, gfp);
+ if (p)
+ bio = p + bs->front_pad;
}
- if (unlikely(!p))
- return NULL;
- if (!mempool_is_saturated(&bs->bio_pool))
- opf &= ~REQ_ALLOC_CACHE;
- bio = p + bs->front_pad;
- if (nr_vecs > BIO_INLINE_VECS) {
- struct bio_vec *bvl = NULL;
+ if (bio && nr_vecs > BIO_INLINE_VECS) {
+ struct biovec_slab *bvs = biovec_slab(nr_vecs);
- bvl = bvec_alloc(&bs->bvec_pool, &nr_vecs, gfp_mask);
- if (!bvl && gfp_mask != saved_gfp) {
- punt_bios_to_rescuer(bs);
- gfp_mask = saved_gfp;
- bvl = bvec_alloc(&bs->bvec_pool, &nr_vecs, gfp_mask);
+ /*
+ * Upgrade nr_vecs to take full advantage of the allocation.
+ * We also rely on this in bvec_free().
+ */
+ nr_vecs = bvs->nr_vecs;
+ bvecs = kmem_cache_alloc(bvs->slab, gfp);
+ if (unlikely(!bvecs)) {
+ kmem_cache_free(bs->bio_slab, p);
+ bio = NULL;
}
- if (unlikely(!bvl))
- goto err_free;
+ }
- bio_init(bio, bdev, bvl, nr_vecs, opf);
- } else if (nr_vecs) {
- bio_init_inline(bio, bdev, BIO_INLINE_VECS, opf);
- } else {
- bio_init(bio, bdev, NULL, 0, opf);
+ if (unlikely(!bio)) {
+ /*
+ * Give up if we are not allow to sleep as non-blocking mempool
+ * allocations just go back to the slab allocation.
+ */
+ if (!(saved_gfp & __GFP_DIRECT_RECLAIM))
+ return NULL;
+
+ punt_bios_to_rescuer(bs);
+
+ /*
+ * Don't rob the mempools by returning to the per-CPU cache if
+ * we're tight on memory.
+ */
+ opf &= ~REQ_ALLOC_CACHE;
+
+ p = mempool_alloc(&bs->bio_pool, gfp);
+ bio = p + bs->front_pad;
+ if (nr_vecs > BIO_INLINE_VECS) {
+ nr_vecs = BIO_MAX_VECS;
+ bvecs = mempool_alloc(&bs->bvec_pool, gfp);
+ }
}
+ if (nr_vecs && nr_vecs <= BIO_INLINE_VECS)
+ bio_init_inline(bio, bdev, nr_vecs, opf);
+ else
+ bio_init(bio, bdev, bvecs, nr_vecs, opf);
bio->bi_pool = bs;
return bio;
-
-err_free:
- mempool_free(p, &bs->bio_pool);
- return NULL;
}
EXPORT_SYMBOL(bio_alloc_bioset);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 9693a0d6fefe..984844d2870b 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -350,8 +350,7 @@ extern void bioset_exit(struct bio_set *);
extern int biovec_init_pool(mempool_t *pool, int pool_entries);
struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs,
- blk_opf_t opf, gfp_t gfp_mask,
- struct bio_set *bs);
+ blk_opf_t opf, gfp_t gfp, struct bio_set *bs);
struct bio *bio_kmalloc(unsigned short nr_vecs, gfp_t gfp_mask);
extern void bio_put(struct bio *);
]
|
| 52/2 |
2026/05/23 07:18 |
llm |
expert |
0m
Model:
Tokens:
input: 62142
output: 23
thoughts: 1311
Thoughts: **Root Cause Analysis of the bio_alloc_bioset Crash**
Okay, let's break this down. I'm looking at `bio_alloc_bioset` and something's clearly not right. First, the `gfp` flag is crucial here. It gets passed to `mempool_alloc`, but it *specifically* has `__GFP_DIRECT_RECLAIM` *cleared*. That's the first red flag. This means `mempool_alloc` *cannot* sleep; it's a non-blocking allocation. If the memory pool is empty, it returns NULL.
Now, follow the code flow. `p = mempool_alloc(&bs->bio_pool, gfp);` and `bio = p + bs->front_pad;`. If `p` is NULL, then `bio` becomes `NULL + bs->front_pad`. I initially thought this would immediately lead to a crash in the `bio_init` call but the crash is reported inside of `__bio_add_page`.
I went back and checked the call chain from the reported backtrace which is `bvec_set_page` to verify how the null pointer arises. The problem must have arisen *later* in the call chain.
I see the logic flow to allocate `bvecs`:
```c
if (nr_vecs > BIO_INLINE_VECS) {
nr_vecs = BIO_MAX_VECS;
bvecs = mempool_alloc(&bs->bvec_pool, gfp);
}
```
If `nr_vecs > BIO_INLINE_VECS`, `bvecs` will be `mempool_alloc` to a `bvec_pool`. If this mempool returns NULL because the `gfp` flags are missing the `__GFP_DIRECT_RECLAIM` then `bvecs` becomes NULL.
Then it proceeds to call `bio_init`:
```c
else
bio_init(bio, bdev, bvecs, nr_vecs, opf);
```
If `bvecs` is NULL, then `bio->bi_io_vec` becomes NULL in the call to `bio_init`. The maximum number of vector is set here.
Now, looking at the subsequent calls, `io_submit_init_bio` gets this `bio`. Then, when `bio_add_folio` is called, because `bio->bi_vcnt` is 0, and `bio->bi_max_vecs` is `BIO_MAX_VECS`, it's going to call `__bio_add_page`. The problem here is in `__bio_add_page`:
```c
bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], page, len, off);
```
Since `bio->bi_io_vec` is NULL, `&bio->bi_io_vec[0]` is NULL! And `bvec_set_page` is dereferencing NULL. *That's* the crash! This perfectly matches the reported crash.
I've got to confirm this. The key is `mempool_alloc` returning NULL because of `gfp` lacking `__GFP_DIRECT_RECLAIM`. I see that `try_alloc_gfp` clears `__GFP_DIRECT_RECLAIM`, and the code *specifically* uses this modified `gfp`. Now let's double-check the logic in `mempool_alloc`.
I need to confirm that `mempool_alloc` can return NULL *without* sleeping. Looking at `mempool_alloc_noprof`, if `gfp_mask` does *not* have `__GFP_DIRECT_RECLAIM`, it will just return the `element` (which will be NULL). The problem is that neither `p` nor `bvecs` are ever checked for NULL.
Aha! If `p` is NULL, `bio` is `bs->front_pad`, but is `front_pad` zero? If it is zero, then this wouldn't cause a crash as `bio` would be NULL. It must be a small offset that would trigger the crash in `bio_init` when dereferenced. Let me check the initialization of `fs_bio_set` to be certain. I am going to have to check what `bs->front_pad` actually is.
|
| 53/2 |
2026/05/23 07:18 |
tool |
codesearch-find-references |
0m
Error:
Args:
Results: map[References:<nil> TruncatedOutput:false]
|
| 54/2 |
2026/05/23 07:18 |
llm |
expert |
0m
Model:
Tokens:
input: 64480
output: 19
thoughts: 12
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Grep Hunt for `fs_bio_set`**
Okay, so I'm thinking about digging into the file system code, and the first thing that pops into my head is to leverage `grep`. Specifically, I want to find where `fs_bio_set` is used. This is likely a structure or function related to BIO (Block I/O) sets, which are fundamental for understanding how the kernel manages block device interactions, especially when dealing with asynchronous I/O. Using `grep`, or its equivalent in the shell I'm working in, is my go-to for quickly locating all instances of a symbol, macro, or function. This search will give me a roadmap to understand how that structure is used across the codebase, which would be essential if I were, for example, debugging a performance issue involving the block layer, or perhaps contributing a patch. I'll need to remember to specify any necessary flags for `grep` such as `-r` for recursive search, and maybe `-n` for line numbers to make it easy to see context. I'll likely also filter for the specific files using `-path` to narrow down the search space to a specific directory in the kernel sources. It's a quick way to get a bird's-eye view.
|
| 55/2 |
2026/05/23 07:18 |
tool |
grepper |
0m
Args: map[Expression:fs_bio_set]
Results: map[Output:block/bio.c=50=static struct biovec_slab *biovec_slab(unsigned short nr_vecs)
--
block/bio.c-68-/*
block/bio.c:69: * fs_bio_set is the bio_set containing bio and iovec memory pools used by
block/bio.c-70- * IO code that does not need private memory pools.
block/bio.c-71- */
block/bio.c:72:struct bio_set fs_bio_set;
block/bio.c:73:EXPORT_SYMBOL(fs_bio_set);
block/bio.c-74-
--
block/bio.c=1944=static int __init init_bio(void)
--
block/bio.c-1960-
block/bio.c:1961: if (bioset_init(&fs_bio_set, BIO_POOL_SIZE, 0,
block/bio.c-1962- BIOSET_NEED_BVECS | BIOSET_PERCPU_CACHE))
--
block/blk-map.c=45=static struct bio *blk_rq_map_bio_alloc(struct request *rq,
--
block/blk-map.c-51- bio = bio_alloc_bioset(bdev, nr_vecs, rq->cmd_flags, gfp_mask,
block/blk-map.c:52: &fs_bio_set);
block/blk-map.c-53- if (!bio)
--
block/blk-mq.c=3368=int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
--
block/blk-mq.c-3375- if (!bs)
block/blk-mq.c:3376: bs = &fs_bio_set;
block/blk-mq.c-3377-
--
fs/iomap/bio.c=47=static struct bio_set *iomap_read_bio_set(struct iomap_read_folio_ctx *ctx)
--
fs/iomap/bio.c-50- return ctx->ops->bio_set;
fs/iomap/bio.c:51: return &fs_bio_set;
fs/iomap/bio.c-52-}
--
fs/squashfs/block.c=79=static int squashfs_bio_read_cached(struct bio *fullbio,
--
fs/squashfs/block.c-123- struct bio *new = bio_alloc_clone(bdev, fullbio,
fs/squashfs/block.c:124: GFP_NOIO, &fs_bio_set);
fs/squashfs/block.c-125-
--
fs/xfs/xfs_buf.c=1330=xfs_buf_submit_bio(
--
fs/xfs/xfs_buf.c-1357- split = bio_split(bio, bp->b_maps[map].bm_len, GFP_NOFS,
fs/xfs/xfs_buf.c:1358: &fs_bio_set);
fs/xfs/xfs_buf.c-1359- split->bi_iter.bi_sector = bp->b_maps[map].bm_bn;
--
fs/xfs/xfs_log.c=1542=xlog_write_iclog(
--
fs/xfs/xfs_log.c-1620- split = bio_split(&iclog->ic_bio, log->l_logBBsize - bno,
fs/xfs/xfs_log.c:1621: GFP_NOIO, &fs_bio_set);
fs/xfs/xfs_log.c-1622- bio_chain(split, &iclog->ic_bio);
--
include/linux/bio.h=365=int bio_init_clone(struct block_device *bdev, struct bio *bio,
--
include/linux/bio.h-367-
include/linux/bio.h:368:extern struct bio_set fs_bio_set;
include/linux/bio.h-369-
include/linux/bio.h=370=static inline struct bio *bio_alloc(struct block_device *bdev,
--
include/linux/bio.h-372-{
include/linux/bio.h:373: return bio_alloc_bioset(bdev, nr_vecs, opf, gfp_mask, &fs_bio_set);
include/linux/bio.h-374-}
]
|
| 56/2 |
2026/05/23 07:18 |
llm |
expert |
0m
Model:
Tokens:
input: 65963
output: 49
thoughts: 808
Thoughts: **Debugging a `bio_alloc_bioset` Bug**
Okay, so I'm looking at this `fs_bio_set` initialization, and right away I see `front_pad = 0`. This makes `p` and `bio` NULL to start. But if `bio` *is* NULL, the code calls `bio_init`, and that's going to dereference NULL! Hold on...
The code branches between `bio_init_inline` and `bio_init`. The second looks most likely in this case. In `bio_init`, the very first thing it does is `bio->bi_next = NULL`. And that's a NULL pointer dereference. But, the crash happens later in `bvec_set_page`, meaning `bio` is *not* NULL.
So, *why* isn't `bio` NULL, but `bvecs` *is* NULL? Let me go back to `bio_alloc_bioset`. Ah, here it is:
```c
if (unlikely(!bio)) {
/* ... */
p = mempool_alloc(&bs->bio_pool, gfp);
bio = p + bs->front_pad;
if (nr_vecs > BIO_INLINE_VECS) {
nr_vecs = BIO_MAX_VECS;
bvecs = mempool_alloc(&bs->bvec_pool, gfp);
}
}
```
Okay, I see. If `p` is *not* NULL, but `bvecs` *is* NULL, then `bs->bio_pool` must have had elements to allocate, but `bs->bvec_pool` was empty. Which means `mempool_alloc` returned NULL for the `bvecs` allocation.
So, when `bvecs` *is* NULL, the code calls `bio_init(bio, bdev, bvecs, nr_vecs, opf);`. `bio_init` sets `bio->bi_io_vec = bvecs` (which is NULL). The function returns a valid `bio`, but its `bi_io_vec` member is NULL. Then `io_submit_init_bio` assigns `bio` to `io->io_bio`. After that, `bio_add_folio` will call `__bio_add_page`, which dereferences the NULL pointer at `bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], page, len, off);`. BINGO! That's the crash.
So, here's the root cause: `bio_alloc_bioset` is using `gfp` in the `mempool_alloc` for the *second* allocation where it should have used the saved `saved_gfp` (which has `__GFP_DIRECT_RECLAIM` set). This means that it can fail to allocate a page vector when it should have allocated it using direct reclaim! That's a definite bug. It would cause a failure in page vector allocation when we were in a low-memory situation, even though we had specified to allow direct memory reclaim.
I wonder if this has been fixed.
|
| 57/2 |
2026/05/23 07:18 |
tool |
git-log |
0m
Args: map[CodeRegexp:mempool_alloc.*bs->bio_pool.*saved_gfp Count:10 PathPrefix:block/bio.c]
Results:
|
| 58/2 |
2026/05/23 07:18 |
llm |
expert |
0m
Model:
Tokens:
input: 67540
output: 42
thoughts: 13
Thoughts: Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to a fellow expert:
**Investigating a Potential Bug Fix**
Alright, I'm encountering a potential issue here, and the first thing that pops into my head is, "Hasn't someone already addressed this?" I mean, we're a team, and odds are someone has either seen this before or already put in a fix. So, my initial thought process begins with a quick search, a dive into the commit history. I need to see if a recent commit, or perhaps even a more obscure one, has tackled this head-on. The goal is efficiency - avoid redundant work and leverage existing solutions if possible. Let's dig in and see what we can find!
|
| 59/2 |
2026/05/23 07:19 |
tool |
git-log |
0m
Args: map[MessageRegexps:[bio_alloc_bioset mempool_alloc] PathPrefix:block/bio.c]
Results: map[Output:9c24c10a2c1e Revert "block: Add warning for bi_next not NULL in bio_endio()"
]
|
| 60/2 |
2026/05/23 07:19 |
llm |
expert |
0m
Model:
Tokens:
input: 67802
output: 39
thoughts: 24
Thoughts: Okay, let's get this done. Here's how I'd approach summarizing those thoughts, speaking as an expert:
**Investigating Memory Allocation Issues in the Kernel**
Alright, I'm diving into this memory allocation issue. Before I jump into the specifics of the current problem report, my gut tells me to take a step back and consider potential prior causes. Instead of starting with the current context, I need to check for known issues. I should search for past fixes related to `bio_alloc_bioset` and `mempool_alloc`. These are the key functions. If there's a problem, itβs most likely stemming from errors introduced into these functions. This quick investigation could save me a ton of time. It's an efficient way to check if someone's already trod this path before me and if a fix is already in place that might be relevant to the issue at hand. If I find something, it's a lead, and if I donβt, I still have a good starting point for a deeper dive. The results of the search will inform whether the issue is a regression, a new manifestation of an old problem, or a completely novel one.
|
| 61/2 |
2026/05/23 07:19 |
tool |
git-log |
0m
Args: map[MessageRegexps:[bio_alloc_bioset gfp] PathPrefix:block/bio.c]
Results: map[Output:b520c4eef83d block: split bio_alloc_bioset more clearly into a fast and slowpath
609be1066731 block: pass a block_device and opf to bio_alloc_bioset
]
|
| 62/2 |
2026/05/23 07:19 |
llm |
expert |
0m
Model:
Tokens:
input: 68186
output: 40
thoughts: 18
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Analyzing `bio_alloc_bioset`**
Okay, let's dive into `bio_alloc_bioset` and see what's what in the current kernel tree. I'm primarily interested in how the bioset allocation works, especially any recent changes or novel approaches to performance or resource management. I'll need to check for any interaction with newer memory management features or potential lock contention issues. I'll be looking for nuances in how it handles various `bio` sizes and alignment requirements, and how it deals with the common cases as well as edge conditions. I expect it's going to be a key part of I/O performance. Let's start digging.
|
| 63/2 |
2026/05/23 07:19 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_alloc_bioset]
|
| 64/2 |
2026/05/23 07:19 |
llm |
expert |
0m
Model:
Tokens:
input: 68446
output: 44
thoughts: 968
Thoughts: **Analyzing a Kernel Denial of Service Vulnerability**
Okay, I've seen this code snippet before, it's that `mempool_alloc` call. Bingo, I've got it! The core issue lies in the interaction between `mempool_alloc` and `gfp`. Specifically, `mempool_alloc` is called with `gfp` where `__GFP_DIRECT_RECLAIM` is cleared.
If the `bvec_pool` is empty, which can happen, `mempool_alloc` returns NULL. This is the critical point. Subsequently, `bio` is populated, but `bio->bi_io_vec` ends up as NULL and `bio->bi_max_vecs` becomes 256. Then, `bio_add_page` tries to dereference this NULL pointer, and that's the crash.
Now, the question is, how exploitable is this? The write happens to `NULL->bv_page`. On modern systems, SMAP and `mmap_min_addr` *should* prevent privilege escalation via mapping page 0, making this a Denial of Service (DoS) bug. Good.
Can an unprivileged user trigger this? Let's trace it. The problem occurs when `mempool_alloc(&bs->bvec_pool, gfp)` returns NULL. This specifically happens when the pool is empty AND `gfp` has `__GFP_DIRECT_RECLAIM` cleared. I already see that `try_alloc_gfp` clears this flag. Since the fallback path is using `mempool_alloc` with this flag cleared. This will always happen.
So, how can the pool be empty? The pool empties when all pre-allocated elements are consumed. This `fs_bio_set` is used by many filesystems, which means a user can create many concurrent I/O requests that consume all `bvecs` in `fs_bio_set.bvec_pool`, and empty the pool. If the pool is empty, and there is memory pressure or fragmentation, the slab allocation can fail. It goes to the fallback `mempool_alloc` call, and the NULL is returned. That means, with an unprivileged user that can cause memory pressure and high I/O concurrency, this crash can be triggered!
Okay, wait, let's double check that NULL return path. `mempool_alloc_noprof` and specifically, the `mempool_alloc_from_pool` call is the key. The code then checks `gfp_temp != gfp_mask`. Where is `gfp_temp` coming from? And what does `mempool_adjust_gfp` do?
|
| 65/2 |
2026/05/23 07:19 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/mempool.c IncludeLines:true Name:mempool_adjust_gfp]
Results: map[SourceCode: 464: /*
465: * Adjust the gfp flags for mempool allocations, as we never want to dip into
466: * the global emergency reserves or retry in the page allocator.
467: *
468: * The first pass also doesn't want to go reclaim, but the next passes do, so
469: * return a separate subset for that first iteration.
470: */
471: static inline gfp_t mempool_adjust_gfp(gfp_t *gfp_mask)
472: {
473: *gfp_mask |= __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
474: return *gfp_mask & ~(__GFP_DIRECT_RECLAIM | __GFP_IO);
475: }
SourceFile:mm/mempool.c]
|
| 66/2 |
2026/05/23 07:19 |
llm |
expert |
0m
Model:
Tokens:
input: 70297
output: 43
thoughts: 6355
Thoughts: **Bug Analysis: bio_alloc_bioset Memory Allocation Vulnerability**
Okay, so here's the deal. I've been dissecting this code in `bio_alloc_bioset` and I've zeroed in on a critical memory allocation vulnerability introduced in commit `b520c4eef83d`. Basically, the function uses a flawed approach when allocating memory for block I/O operations under memory pressure. Let's break it down:
The primary issue stems from how `mempool_alloc` is called within the fallback path. The code, in essence, removes the `__GFP_DIRECT_RECLAIM` flag from the `gfp` mask passed to `mempool_alloc` through `try_alloc_gfp`, which is not what's intended. In cases where the initial allocation fails (mempool is empty, and the slab allocator has no elements and cannot directly reclaim), the code attempts a retry, but *it uses the modified gfp value*, and so, could still fail because it lacks `__GFP_DIRECT_RECLAIM`, and so, is unable to attempt to sleep and reclaim memory directly. This modified `gfp` may not be appropriate for the second allocation, as it can cause `mempool_alloc` to return NULL when the original allocation *should* have succeeded with direct reclaim capabilities. The fix would be to pass `saved_gfp` to mempool_alloc in the retry.
If `mempool_alloc` fails and it returns NULL, the resulting `bio` structure will have `bi_io_vec` set to NULL. This means the `bio` structure might be invalid. The caller in `io_submit_init_bio` receives this broken `bio`.
Later, when trying to add a page to this `bio` with `bio_add_page`, a call to `bvec_set_page` occurs. In the `bvec_set_page` function, the code dereferences a `NULL` pointer (or near-NULL if `front_pad` is not zero). This is a textbook NULL pointer dereference, a critical bug. This leads to an immediate kernel crash.
Now, as an expert in this, I need to address the exploitability. Could this bug be used to gain unauthorized access? No. This specific bug, while severe, is not exploitable for privilege escalation. Any attempt to write to address 0 causes an immediate kernel crash. It's strictly a Denial-of-Service (DoS) vulnerability.
What about how it can be triggered. Can an unprivileged user trigger this vulnerability? Yes. This bug can be triggered by memory pressure, which is something any unprivileged user can induce through normal I/O operations (reading, writing, etc.). This, in turn, can be triggered from user namespaces, by a VM guest performing disk I/O, but is not directly related to a VM host, or a network, or a malicious filesystem image, or peripheral.
|
| 67/2 |
2026/05/23 07:20 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_iov_iter_get_pages]
Results: map[SourceCode:1208: /**
1209: * bio_iov_iter_get_pages - add user or kernel pages to a bio
1210: * @bio: bio to add pages to
1211: * @iter: iov iterator describing the region to be added
1212: * @len_align_mask: the mask to align the total size to, 0 for any length
1213: *
1214: * This takes either an iterator pointing to user memory, or one pointing to
1215: * kernel pages (BVEC iterator). If we're adding user pages, we pin them and
1216: * map them into the kernel. On IO completion, the caller should put those
1217: * pages. For bvec based iterators bio_iov_iter_get_pages() uses the provided
1218: * bvecs rather than copying them. Hence anyone issuing kiocb based IO needs
1219: * to ensure the bvecs and pages stay referenced until the submitted I/O is
1220: * completed by a call to ->ki_complete() or returns with an error other than
1221: * -EIOCBQUEUED. The caller needs to check if the bio is flagged BIO_NO_PAGE_REF
1222: * on IO completion. If it isn't, then pages should be released.
1223: *
1224: * The function tries, but does not guarantee, to pin as many pages as
1225: * fit into the bio, or are requested in @iter, whatever is smaller. If
1226: * MM encounters an error pinning the requested pages, it stops. Error
1227: * is returned only if 0 pages could be pinned.
1228: */
1229: int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter,
1230: unsigned len_align_mask)
1231: {
1232: iov_iter_extraction_t flags = 0;
1233:
1234: if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
1235: return -EIO;
1236:
1237: if (iov_iter_is_bvec(iter)) {
1238: bio_iov_bvec_set(bio, iter);
1239: iov_iter_advance(iter, bio->bi_iter.bi_size);
1240: return 0;
1241: }
1242:
1243: if (iov_iter_extract_will_pin(iter))
1244: bio_set_flag(bio, BIO_PAGE_PINNED);
1245: if (bio->bi_bdev && blk_queue_pci_p2pdma(bio->bi_bdev->bd_disk->queue))
1246: flags |= ITER_ALLOW_P2PDMA;
1247:
1248: do {
1249: ssize_t ret;
1250:
1251: ret = iov_iter_extract_bvecs(iter, bio->bi_io_vec,
1252: BIO_MAX_SIZE - bio->bi_iter.bi_size,
1253: &bio->bi_vcnt, bio->bi_max_vecs, flags);
1254: if (ret <= 0) {
1255: if (!bio->bi_vcnt)
1256: return ret;
1257: break;
1258: }
1259: bio->bi_iter.bi_size += ret;
1260: } while (iov_iter_count(iter) && !bio_full(bio, 0));
1261:
1262: if (is_pci_p2pdma_page(bio->bi_io_vec->bv_page))
1263: bio->bi_opf |= REQ_NOMERGE;
1264: return bio_iov_iter_align_down(bio, iter, len_align_mask);
1265: }
SourceFile:block/bio.c]
|
| 68/2 |
2026/05/23 07:20 |
llm |
expert |
0m
Model:
Tokens:
input: 78440
output: 42
thoughts: 206
Thoughts: **Analyzing a Potential NULL Pointer Dereference**
Okay, so I'm looking at this `bio_iov_iter_get_pages` function, and something's bugging me. Specifically, I'm concerned about the case where `bio->bi_io_vec` is `NULL`. The code path directs me to `iov_iter_extract_bvecs`, and I see that it's being called with `bv = NULL`. That's where things get interesting.
Now, inside `iov_iter_extract_bvecs`:
```c
ssize_t iov_iter_extract_bvecs(struct iov_iter *iter, struct bio_vec *bv,
size_t maxsize, unsigned int *nr_vecs,
unsigned int max_vecs, iov_iter_extraction_t flags)
```
The issue seems to be that if `bv` is indeed `NULL`, it appears the code attempts to write to `bv[*nr_vecs]`. Since `*nr_vecs` is initialized to 0, that's equivalent to writing to `NULL[0]`. Bingo! That's a classic NULL pointer dereference, and it will predictably crash the system. We're attempting to write to address 0, which is never a valid memory location.
I'm making a mental note of this potential vulnerability. We need to be absolutely certain that `bio->bi_io_vec` isn't `NULL` when calling this function, or implement null checks.
Now, I'm thinking, what about `bio_iov_bvec_set`? I need to check that as well.
|
| 69/2 |
2026/05/23 07:20 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:block/bio.c IncludeLines:true Name:bio_iov_bvec_set]
Results: map[SourceCode:1162: void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter)
1163: {
1164: WARN_ON_ONCE(bio->bi_max_vecs);
1165:
1166: bio->bi_io_vec = (struct bio_vec *)iter->bvec;
1167: bio->bi_iter.bi_idx = 0;
1168: bio->bi_iter.bi_bvec_done = iter->iov_offset;
1169: bio->bi_iter.bi_size = iov_iter_count(iter);
1170: bio_set_flag(bio, BIO_CLONED);
1171: }
SourceFile:block/bio.c]
|
| 70/2 |
2026/05/23 07:20 |
llm |
expert |
0m
Model:
Tokens:
input: 79277
output: 66
thoughts: 470
Thoughts: **Analysis of `bio_iov_bvec_set` and Memory Allocation**
Okay, let's break this down. First, `bio_iov_bvec_set` seems a bit odd. It assigns `iter->bvec` to `bio->bi_io_vec`, but the `WARN_ON_ONCE(bio->bi_max_vecs)` suggests a potential issue when `bio->bi_max_vecs` is 256. My initial thought was, "Uh oh, a possible overwrite!". But, wait, it *does* overwrite it, which prevents a crash. The warning is just informational.
Then, I remember that `bio_iov_bvec_set` is only called if `iov_iter_is_bvec(iter)` is true. And it's supposed to be only called if `bio->bi_max_vecs` is expected to be 0, like when a `bio` is allocated without pre-allocated bvecs. So, the warning only occurs when `bio` was allocated with bvecs in the first place! In that case, `bio->bi_max_vecs` is > 0, and the warning is triggered. However, no crash.
Consequently, in every scenario where `bio->bi_io_vec` is used, it's either overwritten without a crash, or it's dereferenced at index 0, which could lead to a NULL pointer dereference. The conclusion here is that it's not exploitable.
Now, let's shift gears and consider the memory allocation side. I needed to double-check if `mempool_alloc` with `__GFP_DIRECT_RECLAIM` cleared could potentially sleep. The answer is no, because `__GFP_DIRECT_RECLAIM` is the flag that allows it to sleep and reclaim memory directly. Without that flag, the allocator will use the free lists and maybe some non-sleeping reclaim like `__GFP_KSWAPD_RECLAIM`. It won't sleep, and if that fails, it will return NULL.
Finally, I confirmed that `mempool_alloc` *can* return NULL. `mempool_alloc_noprof` does return NULL if `mempool_alloc_from_pool` fails and the `gfp_mask` doesn't include `__GFP_DIRECT_RECLAIM`.
So, from all of this, I believe the analysis is sound. I'm satisfied. Now, time to call `set-results` and provide this reasoning.
|
| 71/2 |
2026/05/23 07:20 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:true VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:true VMHostTrigger:false]
|
| 72/2 |
2026/05/23 07:20 |
llm |
expert |
0m
Model:
Tokens:
input: 80426
output: 869
thoughts: 526
Thoughts: **My Analysis of the Kernel Bug**
Okay, the results are in. Time to solidify my findings into a concise explanation.
So, the issue is pinpointed within `bio_alloc_bioset` in `block/bio.c`. The problem arises when allocating both a `bio` and its associated `bvec` array. The initial attempt to allocate uses slab allocators. If that fails, it falls back to mempools. The crucial detail is that the `gfp` mask passed to `mempool_alloc` for this fallback is altered via `try_alloc_gfp(gfp)`, which *removes* the `__GFP_DIRECT_RECLAIM` flag.
The scenario unfolds like this: The `bio_pool` allocation succeeds, but the `bvec_pool` allocation fails. This can happen, especially if the `bvec_pool` is empty and memory is tight. The cleared flag (`__GFP_DIRECT_RECLAIM`) is the culprit here, as it prevents the allocator from sleeping to reclaim memory. Consequently, `mempool_alloc` returns `NULL` for the `bvecs` array.
The critical oversight is that `bio_alloc_bioset` fails to check if `bvecs` is `NULL` in this fallback path. It continues, calling `bio_init` with `bvecs` as `NULL`. This leads to a `bio` structure where `bi_io_vec` is `NULL` but `bi_max_vecs` is incorrectly initialized to 256.
The crash occurs later when a caller, such as `io_submit_init_bio` in ext4 writeback, attempts to add a page to this faulty `bio` using `bio_add_page`. Inside the function, it calls `bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], ...)`. Since `bio->bi_vcnt` is initially 0, this translates to an attempt to write to `NULL[0]`. Bingo β a null pointer dereference and a kernel crash.
The good news (relatively speaking) is that the crash *always* happens on the first `bio_add_page` call, when `bi_vcnt` is 0, making it a straightforward null pointer dereference, writing to address 0. On modern systems with `mmap_min_addr`, this is not exploitable for privilege escalation or arbitrary code execution. It's essentially a Denial of Service, nothing more.
Finally, the trigger: Any unprivileged user can trigger this bug by generating a substantial amount of concurrent block I/O (think file writes, loop devices) under memory pressure. This exhausts the `bvec_pool` and forces the allocation failure. This can also be triggered from within a VM guest, leading to a guest kernel crash.
|
| 73/1 |
2026/05/23 07:21 |
action |
format-explanation |
0m
Results: map[Explanation:**Bug Analysis**
The crash is a NULL pointer dereference in `bvec_set_page()` called from
`__bio_add_page()`. It occurs because a `bio` structure is created with a `NULL`
`bi_io_vec` array but a non-zero `bi_max_vecs` count.
This is caused by a bug in `bio_alloc_bioset()` in `block/bio.c`. When
allocating a bio and its associated `bvec` array, the function first attempts a
fast-path slab allocation. If that fails, it falls back to allocating from the
`bio_set`'s mempools:
```c
gfp = try_alloc_gfp(gfp);
// ...
if (unlikely(!bio)) {
if (!(saved_gfp & __GFP_DIRECT_RECLAIM))
return NULL;
// ...
p = mempool_alloc(&bs->bio_pool, gfp);
bio = p + bs->front_pad;
if (nr_vecs > BIO_INLINE_VECS) {
nr_vecs = BIO_MAX_VECS;
bvecs = mempool_alloc(&bs->bvec_pool, gfp);
}
}
```
The issue is that `try_alloc_gfp(gfp)` strips the `__GFP_DIRECT_RECLAIM` flag
from the `gfp` mask. In the fallback path, `mempool_alloc()` is called with this
modified `gfp` mask instead of the original `saved_gfp`.
Because `__GFP_DIRECT_RECLAIM` is cleared, `mempool_alloc()` is not allowed to
sleep and wait for memory reclaim. If the `bvec_pool` is currently empty (due to
high concurrent I/O) and the underlying slab allocation fails (due to memory
pressure), `mempool_alloc()` will return `NULL`.
If `mempool_alloc` succeeds for the `bio_pool` but fails for the `bvec_pool`,
`bvecs` becomes `NULL`. `bio_alloc_bioset()` does not check for this failure and
proceeds to initialize the bio with `bvecs = NULL` and `nr_vecs = 256`.
When the caller (e.g., ext4 writeback) subsequently tries to add a page to this
bio via `bio_add_page()`, it executes
`bvec_set_page(&bio->bi_io_vec[bio->bi_vcnt], ...)`. Since `bi_vcnt` is `0`, it
attempts to write to index 0 of a `NULL` pointer, resulting in a direct write to
memory address `0x0` and an immediate kernel crash.
**Security Impact**
* **Exploitable:** **False**. The crash always occurs on the very first page
addition when `bi_vcnt` is `0`. It is impossible to advance the index to write
to an arbitrary memory offset. The bug strictly results in a NULL pointer
dereference (writing to address `0x0`), which is mitigated by `mmap_min_addr` on
modern systems and cannot be exploited for privilege escalation or arbitrary
code execution.
* **Denial of Service:** **True**. Triggering the bug causes a kernel
oops/panic, leading to a system crash.
* **Accessible From Unprivileged Processes:** **True**. Any unprivileged user
can trigger this by generating a massive amount of concurrent block I/O (e.g.,
writing to files, using `pipe2`, `epoll`, or loop devices) while inducing memory
pressure to exhaust the `bvec_pool` and force the allocation failure.
* **Accessible From User Namespaces:** **True**. Unprivileged users inside user
namespaces can perform the same I/O operations.
* **VM Guest Trigger:** **True**. A typical KVM guest can trigger this bug
within its own guest kernel by issuing heavy block I/O.]
|