---
id: CVE-2026-89835
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  f2fs: avoid NULL checkpoint thread access in sysfs

  checkpoint_merge can be enabled even when no checkpoint merge thread is
  running
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  f2fs: avoid NULL checkpoint thread access in sysfs

  checkpoint_merge can be enabled even when no checkpoint merge thread is
  running. A read-only mount is one case: f2fs…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= e65920661708b7c0f3db45c9cd5d0095034ee37f <
    a6573f3ffc19542de9ebc1a2b1f930fd48ba538c
  - >-
    Linux >= e65920661708b7c0f3db45c9cd5d0095034ee37f <
    aefcec3bebdeed2bff444378122300763325ba23
  - >-
    Linux >= e65920661708b7c0f3db45c9cd5d0095034ee37f <
    8f3b99c50dd0da1777994ce7c7e60d39b9f60f4b
  - >-
    Linux >= e65920661708b7c0f3db45c9cd5d0095034ee37f <
    5cb33b00c8fbb6e8f1fa3d281c3036d5f7c7c41f
  - Linux 5.12
published: '2026-09-16'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T11:16:50.290'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89835'
references:
  - url: 'https://git.kernel.org/stable/c/5cb33b00c8fbb6e8f1fa3d281c3036d5f7c7c41f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8f3b99c50dd0da1777994ce7c7e60d39b9f60f4b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a6573f3ffc19542de9ebc1a2b1f930fd48ba538c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/aefcec3bebdeed2bff444378122300763325ba23'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-16T10:53:53.998Z'
epss: 0.00209
epssPercentile: 0.09773
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

f2fs: avoid NULL checkpoint thread access in sysfs

checkpoint_merge can be enabled even when no checkpoint merge thread is
running. A read-only mount is one case: f2fs does not start
f2fs_issue_ckpt there, but ckpt_thread_ioprio is still writable through
sysfs.

The ckpt_thread_ioprio store path updates the saved ioprio value and,
when checkpoint_merge is enabled, calls set_task_ioprio() for the
checkpoint thread. If cprc->f2fs_issue_ckpt is NULL, that dereferences a
NULL task pointer.

Protect ckpt_thread_ioprio sysfs writes with s_umount as well, so the
checkpoint thread cannot disappear under the store path while updating
its ioprio.

## Remediation

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