🛡️ CVE-2025-40237 — kernel

⚪ Unknown ✅ No Known Exploit NVD
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

fs/notify: call exportfs_encode_fid with s_umount

In the Linux kernel, the following vulnerability has been resolved:

fs/notify: call exportfs_encode_fid with s_umount

Calling intotify_show_fdinfo() on fd watching an overlayfs inode, while

the overlayfs is being unmounted, can lead to dereferencing NULL ptr.

This issue was found by syzkaller.

Race Condition Diagram:

Thread 1 Thread 2

-------- --------

generic_shutdown_super()

shrink_dcache_for_umount

sb->s_root = NULL

|

| vfs_read()

| inotify_fdinfo()

| * inode get from mark *

| show_mark_fhandle(m, inode)

| exportfs_encode_fid(inode, ..)

| ovl_encode_fh(inode, ..)

| ovl_check_encode_origin(inode)

| * deref i_sb->s_root *

|

|

v

fsnotify_sb_delete(sb)

Which then leads to:

[ 32.133461] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI

[ 32.134438] KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]

[ 32.135032] CPU: 1 UID: 0 PID: 4468 Comm: systemd-coredum Not tainted 6.17.0-rc6 #22 PREEMPT(none)

<snip registers, unreliable trace>

[ 32.143353] Call Trace:

[ 32.143732] ovl_encode_fh+0xd5/0x170

[ 32.144031] exportfs_encode_inode_fh+0x12f/0x300

[ 32.144425] show_mark_fhandle+0xbe/0x1f0

[ 32.145805] inotify_fdinfo+0x226/0x2d0

[ 32.146442] inotify_show_fdinfo+0x1c5/0x350

[ 32.147168] seq_show+0x530/0x6f0

[ 32.147449] seq_read_iter+0x503/0x12a0

[ 32.148419] seq_read+0x31f/0x410

[ 32.150714] vfs_read+0x1f0/0x9e0

[ 32.152297] ksys_read+0x125/0x240

IOW ovl_check_encode_origin derefs inode->i_sb->s_root, after it was set

to NULL in the unmount path.

Fix it by protecting calling exportfs_encode_fid() from

show_mark_fhandle() with s_umount lock.

This form of fix was suggested by Amir in [1].

[1]: https://lore.kernel.org/all/CAOQ4uxhbDwhb+2Brs1UdkoF0a3NSdBAOQPNfEHjahrgoKJpLEw@mail.gmail.com/

Affected software

CVE-2025-40237 is recorded against 2 packages.

  • kernel (from 6.13.0 up to 6.17.6)
  • unknown

Timeline and source

Published on 4 December 2025 and last revised on 31 July 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
github.com (Advisory)
nvd.nist.gov (Advisory)
git.kernel.org (Package)

CVE-2025-40237 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity Unknown
CVSS Score N/A
CVSS Vector N/A
CWE N/A
Public Exploit ✅ No
Source NVD
Published 2025-12-04
Updated 2026-08-12
Modified 2026-07-31
Fix URL N/A

Affected Packages

Software From version Fixed in
kernel 6.13.0 6.17.6
unknown — —

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