---
id: CVE-2026-31446
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…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 <
    c8fe17a1b308c3d8c703ebfb049b325f844342c3
  - >-
    Linux >= b98535d091795a79336f520b0708457aacf55c67 <
    c4d829737329f2290dd41e290b7d75effdb2a7ff
  - >-
    Linux >= b98535d091795a79336f520b0708457aacf55c67 <
    9449f99ba04f5dd1c8423ad8a90b3651d7240d1d
  - >-
    Linux >= b98535d091795a79336f520b0708457aacf55c67 <
    034053378dd81837fd6c7a43b37ee2e58d4f0b4e
  - >-
    Linux >= b98535d091795a79336f520b0708457aacf55c67 <
    c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe
  - >-
    Linux >= b98535d091795a79336f520b0708457aacf55c67 <
    08b10e6f37fc533a759e9833af0692242e8b3f93
  - >-
    Linux >= b98535d091795a79336f520b0708457aacf55c67 <
    d15e4b0a418537aafa56b2cb80d44add83e83697
  - Linux 585ef03c9e79672781f954daae730dfe24bf3a46
  - Linux afe490e48d47df1b3f64012835c1bc2f075a8c8b
  - Linux >= 5.15.38 < 5.15.203
  - Linux >= 5.10.114 < 5.11
  - Linux >= 5.17.6 < 5.18
  - Linux 5.18
published: '2026-04-22'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:47:09.923Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-31446'
references:
  - url: 'https://git.kernel.org/stable/c/c8fe17a1b308c3d8c703ebfb049b325f844342c3'
  - url: 'https://git.kernel.org/stable/c/c4d829737329f2290dd41e290b7d75effdb2a7ff'
  - url: 'https://git.kernel.org/stable/c/9449f99ba04f5dd1c8423ad8a90b3651d7240d1d'
  - url: 'https://git.kernel.org/stable/c/034053378dd81837fd6c7a43b37ee2e58d4f0b4e'
  - url: 'https://git.kernel.org/stable/c/c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe'
  - url: 'https://git.kernel.org/stable/c/08b10e6f37fc533a759e9833af0692242e8b3f93'
  - url: 'https://git.kernel.org/stable/c/d15e4b0a418537aafa56b2cb80d44add83e83697'
tags:
  - cve.org
epss: 0.00135
epssPercentile: 0.03335
ingestedAt: '2026-09-08T15:33:26.990Z'
---

## Overview

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

- `Linux >= 52c3a04f9ec2a16a4204d6274db338cb8d5b2d74 < c8fe17a1b308c3d8c703ebfb049b325f844342c3`
- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < c4d829737329f2290dd41e290b7d75effdb2a7ff`
- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < 9449f99ba04f5dd1c8423ad8a90b3651d7240d1d`
- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < 034053378dd81837fd6c7a43b37ee2e58d4f0b4e`
- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe`
- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < 08b10e6f37fc533a759e9833af0692242e8b3f93`
- `Linux >= b98535d091795a79336f520b0708457aacf55c67 < d15e4b0a418537aafa56b2cb80d44add83e83697`
- `Linux 585ef03c9e79672781f954daae730dfe24bf3a46`
- `Linux afe490e48d47df1b3f64012835c1bc2f075a8c8b`
- `Linux >= 5.15.38 < 5.15.203`
- `Linux >= 5.10.114 < 5.11`
- `Linux >= 5.17.6 < 5.18`
- `Linux 5.18`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.