GHSA-RG97-JHP7-4449
Vulnerability from github – Published: 2025-12-04 18:30 – Updated: 2025-12-23 18:30In 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)
[ 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.
{
"affected": [],
"aliases": [
"CVE-2025-40237"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-12-04T16:16:16Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs/notify: call exportfs_encode_fid with s_umount\n\nCalling intotify_show_fdinfo() on fd watching an overlayfs inode, while\nthe overlayfs is being unmounted, can lead to dereferencing NULL ptr.\n\nThis issue was found by syzkaller.\n\nRace Condition Diagram:\n\nThread 1 Thread 2\n-------- --------\n\ngeneric_shutdown_super()\n shrink_dcache_for_umount\n sb-\u003es_root = NULL\n\n |\n | vfs_read()\n | inotify_fdinfo()\n | * inode get from mark *\n | show_mark_fhandle(m, inode)\n | exportfs_encode_fid(inode, ..)\n | ovl_encode_fh(inode, ..)\n | ovl_check_encode_origin(inode)\n | * deref i_sb-\u003es_root *\n |\n |\n v\n fsnotify_sb_delete(sb)\n\nWhich then leads to:\n\n[ 32.133461] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI\n[ 32.134438] KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]\n[ 32.135032] CPU: 1 UID: 0 PID: 4468 Comm: systemd-coredum Not tainted 6.17.0-rc6 #22 PREEMPT(none)\n\n\u003csnip registers, unreliable trace\u003e\n\n[ 32.143353] Call Trace:\n[ 32.143732] ovl_encode_fh+0xd5/0x170\n[ 32.144031] exportfs_encode_inode_fh+0x12f/0x300\n[ 32.144425] show_mark_fhandle+0xbe/0x1f0\n[ 32.145805] inotify_fdinfo+0x226/0x2d0\n[ 32.146442] inotify_show_fdinfo+0x1c5/0x350\n[ 32.147168] seq_show+0x530/0x6f0\n[ 32.147449] seq_read_iter+0x503/0x12a0\n[ 32.148419] seq_read+0x31f/0x410\n[ 32.150714] vfs_read+0x1f0/0x9e0\n[ 32.152297] ksys_read+0x125/0x240\n\nIOW ovl_check_encode_origin derefs inode-\u003ei_sb-\u003es_root, after it was set\nto NULL in the unmount path.\n\nFix it by protecting calling exportfs_encode_fid() from\nshow_mark_fhandle() with s_umount lock.\n\nThis form of fix was suggested by Amir in [1].\n\n[1]: https://lore.kernel.org/all/CAOQ4uxhbDwhb+2Brs1UdkoF0a3NSdBAOQPNfEHjahrgoKJpLEw@mail.gmail.com/",
"id": "GHSA-rg97-jhp7-4449",
"modified": "2025-12-23T18:30:22Z",
"published": "2025-12-04T18:30:52Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-40237"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3f307a9f7a7a2822e38ac451b73e2244e7279496"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/950b604384fd75d62e860bec7135b2b62eb4d508"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a7c4bb43bfdc2b9f06ee9d036028ed13a83df42a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/bc1c6b803e14ea2b8f7e33b7164013f666ceb656"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d1894bc542becb0fda61e7e513b09523cab44030"
}
],
"schema_version": "1.4.0",
"severity": []
}
Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
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- Confirmed: The vulnerability has been validated from an analyst's perspective.
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- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
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- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.