CVE-2026-31446 (GCVE-0-2026-31446)
Vulnerability from cvelistv5
Published
2026-04-22 13:53
Modified
2026-04-27 14:03
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
ext4: fix use-after-free in update_super_work when racing with umount
Commit b98535d09179 ("ext4: fix bug_on in start_this_handle during umount
filesystem") moved ext4_unregister_sysfs() before flushing s_sb_upd_work
to prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups
reads during unmount. However, this introduced a use-after-free because
update_super_work calls ext4_notify_error_sysfs() -> sysfs_notify() which
accesses the kobject's kernfs_node after it has been freed by kobject_del()
in ext4_unregister_sysfs():
update_super_work ext4_put_super
----------------- --------------
ext4_unregister_sysfs(sb)
kobject_del(&sbi->s_kobj)
__kobject_del()
sysfs_remove_dir()
kobj->sd = NULL
sysfs_put(sd)
kernfs_put() // RCU free
ext4_notify_error_sysfs(sbi)
sysfs_notify(&sbi->s_kobj)
kn = kobj->sd // stale pointer
kernfs_get(kn) // UAF on freed kernfs_node
ext4_journal_destroy()
flush_work(&sbi->s_sb_upd_work)
Instead of reordering the teardown sequence, fix this by making
ext4_notify_error_sysfs() detect that sysfs has already been torn down
by checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call
in that case. A dedicated mutex (s_error_notify_mutex) serializes
ext4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs()
to prevent TOCTOU races where the kobject could be deleted between the
state_in_sysfs check and the sysfs_notify() call.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 Version: b98535d091795a79336f520b0708457aacf55c67 Version: b98535d091795a79336f520b0708457aacf55c67 Version: b98535d091795a79336f520b0708457aacf55c67 Version: b98535d091795a79336f520b0708457aacf55c67 Version: b98535d091795a79336f520b0708457aacf55c67 Version: b98535d091795a79336f520b0708457aacf55c67 Version: 585ef03c9e79672781f954daae730dfe24bf3a46 Version: afe490e48d47df1b3f64012835c1bc2f075a8c8b |
||
{
"containers": {
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"programFiles": [
"fs/ext4/ext4.h",
"fs/ext4/super.c",
"fs/ext4/sysfs.c"
],
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],
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"vendor": "Linux",
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},
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"version": "0",
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},
{
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"status": "unaffected",
"version": "5.15.203",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "6.1.168",
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},
{
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"status": "unaffected",
"version": "6.6.131",
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},
{
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},
{
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"version": "6.18.21",
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},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.0",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
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"nodes": [
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],
"negate": false,
"operator": "OR"
}
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],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: fix use-after-free in update_super_work when racing with umount\n\nCommit b98535d09179 (\"ext4: fix bug_on in start_this_handle during umount\nfilesystem\") moved ext4_unregister_sysfs() before flushing s_sb_upd_work\nto prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups\nreads during unmount. However, this introduced a use-after-free because\nupdate_super_work calls ext4_notify_error_sysfs() -\u003e sysfs_notify() which\naccesses the kobject\u0027s kernfs_node after it has been freed by kobject_del()\nin ext4_unregister_sysfs():\n\n update_super_work ext4_put_super\n ----------------- --------------\n ext4_unregister_sysfs(sb)\n kobject_del(\u0026sbi-\u003es_kobj)\n __kobject_del()\n sysfs_remove_dir()\n kobj-\u003esd = NULL\n sysfs_put(sd)\n kernfs_put() // RCU free\n ext4_notify_error_sysfs(sbi)\n sysfs_notify(\u0026sbi-\u003es_kobj)\n kn = kobj-\u003esd // stale pointer\n kernfs_get(kn) // UAF on freed kernfs_node\n ext4_journal_destroy()\n flush_work(\u0026sbi-\u003es_sb_upd_work)\n\nInstead of reordering the teardown sequence, fix this by making\next4_notify_error_sysfs() detect that sysfs has already been torn down\nby checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call\nin that case. A dedicated mutex (s_error_notify_mutex) serializes\next4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs()\nto prevent TOCTOU races where the kobject could be deleted between the\nstate_in_sysfs check and the sysfs_notify() call."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
"version": "3.1"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-04-27T14:03:11.293Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/c8fe17a1b308c3d8c703ebfb049b325f844342c3"
},
{
"url": "https://git.kernel.org/stable/c/c4d829737329f2290dd41e290b7d75effdb2a7ff"
},
{
"url": "https://git.kernel.org/stable/c/9449f99ba04f5dd1c8423ad8a90b3651d7240d1d"
},
{
"url": "https://git.kernel.org/stable/c/034053378dd81837fd6c7a43b37ee2e58d4f0b4e"
},
{
"url": "https://git.kernel.org/stable/c/c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe"
},
{
"url": "https://git.kernel.org/stable/c/08b10e6f37fc533a759e9833af0692242e8b3f93"
},
{
"url": "https://git.kernel.org/stable/c/d15e4b0a418537aafa56b2cb80d44add83e83697"
}
],
"title": "ext4: fix use-after-free in update_super_work when racing with umount",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-31446",
"datePublished": "2026-04-22T13:53:42.751Z",
"dateReserved": "2026-03-09T15:48:24.091Z",
"dateUpdated": "2026-04-27T14:03:11.293Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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