CVE-2026-31446 (GCVE-0-2026-31446)

Vulnerability from cvelistv5 – Published: 2026-04-22 13:53 – Updated: 2026-04-22 13:53
VLAI?
Title
ext4: fix use-after-free in update_super_work when racing with umount
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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 , < c8fe17a1b308c3d8c703ebfb049b325f844342c3 (git)
Affected: b98535d091795a79336f520b0708457aacf55c67 , < c4d829737329f2290dd41e290b7d75effdb2a7ff (git)
Affected: b98535d091795a79336f520b0708457aacf55c67 , < 9449f99ba04f5dd1c8423ad8a90b3651d7240d1d (git)
Affected: b98535d091795a79336f520b0708457aacf55c67 , < 034053378dd81837fd6c7a43b37ee2e58d4f0b4e (git)
Affected: b98535d091795a79336f520b0708457aacf55c67 , < c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe (git)
Affected: b98535d091795a79336f520b0708457aacf55c67 , < 08b10e6f37fc533a759e9833af0692242e8b3f93 (git)
Affected: b98535d091795a79336f520b0708457aacf55c67 , < d15e4b0a418537aafa56b2cb80d44add83e83697 (git)
Affected: 585ef03c9e79672781f954daae730dfe24bf3a46 (git)
Affected: afe490e48d47df1b3f64012835c1bc2f075a8c8b (git)
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    Linux Linux Affected: 5.18
Unaffected: 0 , < 5.18 (semver)
Unaffected: 5.15.203 , ≤ 5.15.* (semver)
Unaffected: 6.1.168 , ≤ 6.1.* (semver)
Unaffected: 6.6.131 , ≤ 6.6.* (semver)
Unaffected: 6.12.80 , ≤ 6.12.* (semver)
Unaffected: 6.18.21 , ≤ 6.18.* (semver)
Unaffected: 6.19.11 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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          "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."
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      "providerMetadata": {
        "dateUpdated": "2026-04-22T13:53:42.751Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/c4d829737329f2290dd41e290b7d75effdb2a7ff"
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          "url": "https://git.kernel.org/stable/c/08b10e6f37fc533a759e9833af0692242e8b3f93"
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        {
          "url": "https://git.kernel.org/stable/c/d15e4b0a418537aafa56b2cb80d44add83e83697"
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      ],
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    "datePublished": "2026-04-22T13:53:42.751Z",
    "dateReserved": "2026-03-09T15:48:24.091Z",
    "dateUpdated": "2026-04-22T13:53:42.751Z",
    "state": "PUBLISHED"
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  }
}


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