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CVE PROGRAM SOURCE RECORD7.8 High

CVE-2026-31446

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

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Status
Published
Published
Updated
Assigning organization
Linux

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.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Linux Linux

Default version status: unaffected

  • 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 to < c8fe17a1b308c3d8c703ebfb049b325f844342c3affected
  • b98535d091795a79336f520b0708457aacf55c67 to < c4d829737329f2290dd41e290b7d75effdb2a7ffaffected
  • b98535d091795a79336f520b0708457aacf55c67 to < 9449f99ba04f5dd1c8423ad8a90b3651d7240d1daffected
  • b98535d091795a79336f520b0708457aacf55c67 to < 034053378dd81837fd6c7a43b37ee2e58d4f0b4eaffected
  • b98535d091795a79336f520b0708457aacf55c67 to < c97e282f7bfd0c3554c63d289964a5ca6a1d2ffeaffected
  • b98535d091795a79336f520b0708457aacf55c67 to < 08b10e6f37fc533a759e9833af0692242e8b3f93affected
  • b98535d091795a79336f520b0708457aacf55c67 to < d15e4b0a418537aafa56b2cb80d44add83e83697affected
  • 585ef03c9e79672781f954daae730dfe24bf3a46affected
  • afe490e48d47df1b3f64012835c1bc2f075a8c8baffected
  • 5.15.38 to < 5.15.203affected
  • 5.10.114 to < 5.11affected
  • 5.17.6 to < 5.18affected

Linux Linux

Default version status: affected

  • 5.18affected
  • 0 to < 5.18unaffected
  • 5.15.203 to ≤ 5.15.*unaffected
  • 6.1.168 to ≤ 6.1.*unaffected
  • 6.6.131 to ≤ 6.6.*unaffected
  • 6.12.80 to ≤ 6.12.*unaffected
  • 6.18.21 to ≤ 6.18.*unaffected
  • 6.19.11 to ≤ 6.19.*unaffected
  • 7.0 to ≤ *unaffected

References