Linux Kernel SMP CSD Lock csd_lock race condition

Summaryinfo

A vulnerability classified as problematic was found in Linux Kernel. The affected element is the function csd_lock of the component SMP CSD Lock. The manipulation results in race condition. This vulnerability was named CVE-2026-68438. The attack needs to be approached locally. There is no available exploit.

Detailsinfo

A vulnerability was found in Linux Kernel (version unknown). It has been classified as problematic. Affected is the function csd_lock of the component SMP CSD Lock. The manipulation with an unknown input leads to a race condition vulnerability. CWE is classifying the issue as CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. This is going to have an impact on integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: smp: Make CSD lock acquisition atomic for debug mode Commit b0473dcd4b1d ("smp: Improve smp_call_function_single() CSD-lock diagnostics") changed smp_call_function_single() so that, when CSD lock debugging is enabled, async !wait calls use the destination CPU csd_data. That improves diagnostics, but it also removes the single-writer property that made the old csd_lock() safe: multiple CPUs can now prepare the same destination CPU CSD concurrently. csd_lock() currently waits for CSD_FLAG_LOCK to clear and then sets the bit with a non-atomic read-modify-write. Two senders can both see an unlocked CSD, set the bit, overwrite the callback fields, and enqueue the same llist node. Re-adding a node that is already the queue head can make node->next point to itself, leaving the target CPU stuck walking call_single_queue. Later synchronous work, such as a TLB shootdown, can then remain queued and trigger soft-lockup warnings or panics. Keep the single csd_lock() implementation, but when CSD lock debugging is enabled, acquire CSD_FLAG_LOCK with try_cmpxchg_acquire(). This makes the destination CPU CSD a real atomic lock in the only configuration where it can be shared by multiple remote senders, while preserving the existing non-debug fast path.

The advisory is available at git.kernel.org. This vulnerability is traded as CVE-2026-68438 since 07/30/2026. The exploitability is told to be easy. Local access is required to approach this attack. Technical details are known, but there is no available exploit.

Applying the patch 282d220bae5fbfc90cf0e3d5b5e42c00ad79f989 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

License

• open-source

Website

• Vendor: https://www.kernel.org/

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