---
id: CVE-2026-43271
title: 'md-cluster: fix NULL pointer dereference in process_metadata_update'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  md-cluster: fix NULL pointer dereference in process_metadata_update

  The function process_metadata_update() blindly dereferences the 'thread'
  pointer (acquired via rcu_…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 0ba959774e93911caff596de6391f085fb640ac4 <
    b65ea893290056bee380d0c8eeb47797c2bcb311
  - >-
    Linux >= 0ba959774e93911caff596de6391f085fb640ac4 <
    a61c1bc84c4a0f1e7c2fe55b0f43d7d94af4adf1
  - >-
    Linux >= 0ba959774e93911caff596de6391f085fb640ac4 <
    dec123825c1ed74d98fd5fc7571a851dea4f46ff
  - >-
    Linux >= 0ba959774e93911caff596de6391f085fb640ac4 <
    721599e837d3f4c0e6cc14da059612c017b6d3ec
  - >-
    Linux >= 0ba959774e93911caff596de6391f085fb640ac4 <
    dceb5a843910004cb118148e267036104fc3ee43
  - >-
    Linux >= 0ba959774e93911caff596de6391f085fb640ac4 <
    f150e753cb8dd756085f46e86f2c35ce472e0a3c
  - Linux 4.12
published: '2026-05-06'
updated: '2026-10-30'
sourceUpdated: '2026-10-30T12:25:21.976Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-43271'
references:
  - url: 'https://git.kernel.org/stable/c/b65ea893290056bee380d0c8eeb47797c2bcb311'
  - url: 'https://git.kernel.org/stable/c/a61c1bc84c4a0f1e7c2fe55b0f43d7d94af4adf1'
  - url: 'https://git.kernel.org/stable/c/dec123825c1ed74d98fd5fc7571a851dea4f46ff'
  - url: 'https://git.kernel.org/stable/c/721599e837d3f4c0e6cc14da059612c017b6d3ec'
  - url: 'https://git.kernel.org/stable/c/dceb5a843910004cb118148e267036104fc3ee43'
  - url: 'https://git.kernel.org/stable/c/f150e753cb8dd756085f46e86f2c35ce472e0a3c'
tags:
  - cve.org
epss: 0.00117
epssPercentile: 0.01652
ingestedAt: '2026-11-05T15:02:32.283Z'
---

## Overview

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

md-cluster: fix NULL pointer dereference in process_metadata_update

The function process_metadata_update() blindly dereferences the 'thread'
pointer (acquired via rcu_dereference_protected) within the wait_event()
macro.

While the code comment states "daemon thread must exist", there is a valid
race condition window during the MD array startup sequence (md_run):

1. bitmap_load() is called, which invokes md_cluster_ops->join().
2. join() starts the "cluster_recv" thread (recv_daemon).
3. At this point, recv_daemon is active and processing messages.
4. However, mddev->thread (the main MD thread) is not initialized until
   later in md_run().

If a METADATA_UPDATED message is received from a remote node during this
specific window, process_metadata_update() will be called while
mddev->thread is still NULL, leading to a kernel panic.

To fix this, we must validate the 'thread' pointer. If it is NULL, we
release the held lock (no_new_dev_lockres) and return early, safely
ignoring the update request as the array is not yet fully ready to
process it.

## Affected

- `Linux >= 0ba959774e93911caff596de6391f085fb640ac4 < b65ea893290056bee380d0c8eeb47797c2bcb311`
- `Linux >= 0ba959774e93911caff596de6391f085fb640ac4 < a61c1bc84c4a0f1e7c2fe55b0f43d7d94af4adf1`
- `Linux >= 0ba959774e93911caff596de6391f085fb640ac4 < dec123825c1ed74d98fd5fc7571a851dea4f46ff`
- `Linux >= 0ba959774e93911caff596de6391f085fb640ac4 < 721599e837d3f4c0e6cc14da059612c017b6d3ec`
- `Linux >= 0ba959774e93911caff596de6391f085fb640ac4 < dceb5a843910004cb118148e267036104fc3ee43`
- `Linux >= 0ba959774e93911caff596de6391f085fb640ac4 < f150e753cb8dd756085f46e86f2c35ce472e0a3c`
- `Linux 4.12`

## Remediation

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