Bug 2467074 (CVE-2026-43271)

Summary: CVE-2026-43271 kernel: md-cluster: fix NULL pointer dereference in process_metadata_update
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's md-cluster module. During the startup of a multi-device (MD) array, a race condition can occur where a remote node sends a metadata update message before the system is fully ready to process it. This premature processing leads to a null pointer dereference, causing the kernel to panic. A successful exploit could result in a Denial of Service (DoS) for the affected system.
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Description OSIDB Bzimport 2026-05-06 13:02:52 UTC 
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.
Comment 1 Keith Grant 2026-05-07 00:03:10 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050610-CVE-2026-43271-0404@gregkh/T