Skip to main content
cve.nowby Sazabi
← All vulnerabilities
CVE-2026-31446

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

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.15.203, 5.11, 5.18, 6.1.168, 6.6.131, and 3 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 · fixed in c8fe17a1b308c3d8c703ebfb049b325f844342c3; From b98535d091795a79336f520b0708457aacf55c67 · fixed in c4d829737329f2290dd41e290b7d75effdb2a7ff; From b98535d091795a79336f520b0708457aacf55c67 · fixed in 9449f99ba04f5dd1c8423ad8a90b3651d7240d1d; From b98535d091795a79336f520b0708457aacf55c67 · fixed in 034053378dd81837fd6c7a43b37ee2e58d4f0b4e; From b98535d091795a79336f520b0708457aacf55c67 · fixed in c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe; From b98535d091795a79336f520b0708457aacf55c67 · fixed in 08b10e6f37fc533a759e9833af0692242e8b3f93; From b98535d091795a79336f520b0708457aacf55c67 · fixed in d15e4b0a418537aafa56b2cb80d44add83e83697; From 5.15.38 · fixed in 5.15.203; From 5.10.114 · fixed in 5.11; From 5.17.6 · fixed in 5.18

  • Linux Linux

    5.18

  • KernelLinux

    fixed in 5.15.203; From 5.16.0 · fixed in 6.1.168; From 5.18.0 · fixed in 6.6.131; From 6.2.0 · fixed in 6.12.80; From 6.7.0 · fixed in 6.18.21; From 6.13.0 · fixed in 6.19.11

References 7

git.kernel.org