CVE-2026-68438 (GCVE-0-2026-68438)

Vulnerability from cvelistv5 – Published: 2026-08-12 00:07 – Updated: 2026-08-17 05:05
VLAI
Title
smp: Make CSD lock acquisition atomic for debug mode
Summary
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.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: b0473dcd4b1d7e2e44947e7ac1820c73a268821a , < 282d220bae5fbfc90cf0e3d5b5e42c00ad79f989 (git)
Affected: b0473dcd4b1d7e2e44947e7ac1820c73a268821a , < 35551efb155e3b83445a6c3f66cb498d5efc182c (git)
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Linux Linux Affected: 7.1
Unaffected: 0 , < 7.1 (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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    "datePublished": "2026-08-12T00:07:27.105Z",
    "dateReserved": "2026-07-30T09:28:09.394Z",
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmp: Make CSD lock acquisition atomic for debug mode\n\nCommit b0473dcd4b1d (\"smp: Improve smp_call_function_single()\nCSD-lock diagnostics\") changed smp_call_function_single() so that,\nwhen CSD lock debugging is enabled, async !wait calls use the\ndestination CPU csd_data. That improves diagnostics, but it also removes\nthe single-writer property that made the old csd_lock() safe: multiple\nCPUs can now prepare the same destination CPU CSD concurrently.\n\ncsd_lock() currently waits for CSD_FLAG_LOCK to clear and then sets the\nbit with a non-atomic read-modify-write. Two senders can both see an\nunlocked CSD, set the bit, overwrite the callback fields, and enqueue\nthe same llist node. Re-adding a node that is already the queue head can\nmake node-\u003enext point to itself, leaving the target CPU stuck walking\ncall_single_queue. Later synchronous work, such as a TLB shootdown, can\nthen remain queued and trigger soft-lockup warnings or panics.\n\nKeep the single csd_lock() implementation, but when CSD lock debugging is\nenabled, acquire CSD_FLAG_LOCK with try_cmpxchg_acquire(). This makes the\ndestination CPU CSD a real atomic lock in the only configuration where it\ncan be shared by multiple remote senders, while preserving the existing\nnon-debug fast path."
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        "metrics": {},
        "published": "2026-08-12T00:17:44.013",
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}



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