CVE-2026-43271

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.

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel（修复补丁发布前的版本）

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

/*
 * Conceptual PoC for triggering the race condition in md-cluster.
 * This is a simplified representation of the vulnerable code path.
 */

#include <linux/module.h>
#include <linux/md.h>

// Simulating the vulnerable function logic
void vulnerable_process_metadata_update(struct mddev *mddev) {
    struct md_thread *thread;

    // Vulnerability: Acquiring pointer without checking if it's NULL
    // race window exists here between recv_daemon start and mddev->thread init
    thread = rcu_dereference_protected(mddev->thread, lockdep_is_held(&mddev->reconfig_mutex));

    // This line causes Kernel Panic if thread is NULL
    wait_event_interruptible(thread->wqueue, test_bit(THREAD_WAKEUP, &thread->flags));
}

// Fix implementation (for reference)
void fixed_process_metadata_update(struct mddev *mddev) {
    struct md_thread *thread;

    thread = rcu_dereference_protected(mddev->thread, lockdep_is_held(&mddev->reconfig_mutex));

    if (!thread) {
        // Release lock and return early if array is not ready
        return;
    }

    wait_event_interruptible(thread->wqueue, test_bit(THREAD_WAKEUP, &thread->flags));
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-43271
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-43271
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-43271/
[4] VulDB https://vuldb.com/cve/CVE-2026-43271
[5] https://git.kernel.org/stable/c/721599e837d3f4c0e6cc14da059612c017b6d3ec
[6] https://git.kernel.org/stable/c/a61c1bc84c4a0f1e7c2fe55b0f43d7d94af4adf1
[7] https://git.kernel.org/stable/c/dceb5a843910004cb118148e267036104fc3ee43
[8] https://git.kernel.org/stable/c/dec123825c1ed74d98fd5fc7571a851dea4f46ff
[9] https://git.kernel.org/stable/c/f150e753cb8dd756085f46e86f2c35ce472e0a3c

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-43271", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-06T12:16:48.313", "lastModified": "2026-05-08T20:00:00.693", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmd-cluster: fix NULL pointer dereference in process_metadata_update\n\nThe function process_metadata_update() blindly dereferences the 'thread'\npointer (acquired via rcu_dereference_protected) within the wait_event()\nmacro.\n\nWhile the code comment states \"daemon thread must exist\", there is a valid\nrace condition window during the MD array startup sequence (md_run):\n\n1. bitmap_load() is called, which invokes md_cluster_ops->join().\n2. join() starts the \"cluster_recv\" thread (recv_daemon).\n3. At this point, recv_daemon is active and processing messages.\n4. However, mddev->thread (the main MD thread) is not initialized until\n later in md_run().\n\nIf a METADATA_UPDATED message is received from a remote node during this\nspecific window, process_metadata_update() will be called while\nmddev->thread is still NULL, leading to a kernel panic.\n\nTo fix this, we must validate the 'thread' pointer. If it is NULL, we\nrelease the held lock (no_new_dev_lockres) and return early, safely\nignoring the update request as the array is not yet fully ready to\nprocess it."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-476"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.12", "versionEndExcluding": "6.6.128", "matchCriteriaId": "E90AEF03-C864-4508-AA5A-71B005F9732D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.75", "matchCriteriaId": "BCE16369-98ED-41CF-8995-DFDC10B288D2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.16", "matchCriteriaId": "B4B8CDA9-BADF-4CF5-8B3B-702DE8EEA40B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.6", "matchCriteriaId": "373EEEDA-FAA1-4FB4-B6ED-DB4DD99DBE67"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/721599e837d3f4c0e6cc14da059612c017b6d3ec", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/a61c1bc84c4a0f1e7c2fe55b0f43d7d94af4adf1", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/dceb5a843910004cb118148e267036104fc3ee43", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/dec123825c1ed74d98fd5fc7571a851dea4f46ff", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/f150e753cb8dd756085f46e86f2c35ce472e0a3c", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}