CVE-2026-43271: md-cluster: fix NULL pointer dereference in process_metadata_update

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-06 · updated 2026-10-30
Weakness: CWE-476

Description

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 products

Linux kernel: from 4.12 before 6.6.128; from 6.7 before 6.12.75; from 6.13 before 6.18.16; from 6.19 before 6.19.6 — fixed in 6.6.128, 6.12.75, 6.18.16, 6.19.6
Linux: 4.12 — fixed in 7.0

How to fix

Upgrade to a fixed version: Linux kernel 6.6.128, 6.12.75, 6.18.16, 6.19.6; Linux 7.0. Check the vendor advisory for mitigations.

References

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