ext4: fix use-after-free in update_super_work when racing with umount

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Summary

CVECVE-2026-31446
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-22 14:16:38 UTC
Updated2026-07-14 13:18:41 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS: 0.000240000 probability, percentile 0.067850000 (date 2026-04-27)

Problem Types: CWE-416

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 c8fe17a1b308c3d8c703ebfb049b325f844342c3 git Not specified
CNA Linux Linux affected b98535d091795a79336f520b0708457aacf55c67 c4d829737329f2290dd41e290b7d75effdb2a7ff git Not specified
CNA Linux Linux affected b98535d091795a79336f520b0708457aacf55c67 9449f99ba04f5dd1c8423ad8a90b3651d7240d1d git Not specified
CNA Linux Linux affected b98535d091795a79336f520b0708457aacf55c67 034053378dd81837fd6c7a43b37ee2e58d4f0b4e git Not specified
CNA Linux Linux affected b98535d091795a79336f520b0708457aacf55c67 c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe git Not specified
CNA Linux Linux affected b98535d091795a79336f520b0708457aacf55c67 08b10e6f37fc533a759e9833af0692242e8b3f93 git Not specified
CNA Linux Linux affected b98535d091795a79336f520b0708457aacf55c67 d15e4b0a418537aafa56b2cb80d44add83e83697 git Not specified
CNA Linux Linux affected 585ef03c9e79672781f954daae730dfe24bf3a46 git Not specified
CNA Linux Linux affected afe490e48d47df1b3f64012835c1bc2f075a8c8b git Not specified
CNA Linux Linux affected 5.15.38 5.15.203 semver Not specified
CNA Linux Linux affected 5.10.114 5.11 semver Not specified
CNA Linux Linux affected 5.17.6 5.18 semver Not specified
CNA Linux Linux affected 5.18 Not specified
CNA Linux Linux unaffected 5.18 semver Not specified
CNA Linux Linux unaffected 5.15.203 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.168 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.131 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.80 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.21 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.11 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.5 * custom Not specified
ADP Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.5 * custom Not specified

References

ReferenceSourceLinkTags
cert-portal.siemens.com/productcert/html/ssa-082556.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/034053378dd81837fd6c7a43b37ee2e58d4f0b4e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/08b10e6f37fc533a759e9833af0692242e8b3f93 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/c8fe17a1b308c3d8c703ebfb049b325f844342c3 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-019113.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/c4d829737329f2290dd41e290b7d75effdb2a7ff 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/9449f99ba04f5dd1c8423ad8a90b3651d7240d1d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/d15e4b0a418537aafa56b2cb80d44add83e83697 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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