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

CVE-2026-31446
HIGH 7.8

At a glance

Source
NVD
EPSS
EPSS 0.14 % · percentile 3 ()
State
PUBLISHED
Published
Updated
Assigner
Linux
NVD status
Modified

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Description

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.

Weaknesses (CWE)

References

Scores

VersionScoreVectorScored by
CVSS 3.1HIGH 7.8CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HLinux
CVSS 3.1HIGH 7.8CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HNVD · 416baaa9-dc9f-4396-8d5f-8c081fb06d67 (Secondary)

European references

CERT-FR advisories

Affected configurations (NVD CPE)

Affected products

ProductVersions
Linux · Linuxaffected 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 < c8fe17a1b308c3d8c703ebfb049b325f844342c3 ; affected b98535d091795a79336f520b0708457aacf55c67 < c4d829737329f2290dd41e290b7d75effdb2a7ff ; affected b98535d091795a79336f520b0708457aacf55c67 < 9449f99ba04f5dd1c8423ad8a90b3651d7240d1d ; affected b98535d091795a79336f520b0708457aacf55c67 < 034053378dd81837fd6c7a43b37ee2e58d4f0b4e ; affected b98535d091795a79336f520b0708457aacf55c67 < c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe ; affected b98535d091795a79336f520b0708457aacf55c67 < 08b10e6f37fc533a759e9833af0692242e8b3f93
Linux · Linuxaffected 5.18 ; unaffected 0 < 5.18 ; unaffected 5.15.203 ≤ 5.15.* ; unaffected 6.1.168 ≤ 6.1.* ; unaffected 6.6.131 ≤ 6.6.* ; unaffected 6.12.80 ≤ 6.12.*

Sources

SourceLicence
CVE List (CVEProject cvelistV5)CVE Program Terms of Use
EPSS (FIRST.org)FIRST — attribution requested
ENISA EUVDENISA — reproduction authorised, source acknowledged
CERT-FR (ANSSI)Licence Ouverte / Etalab 2.0
NVD (NIST) via fkie-cad/nvd-json-data-feedsPublic domain — this product uses data from the NVD API but is not endorsed or certified by the NVD