{"id":"CVE-2026-68438","state":"PUBLISHED","title":"smp: Make CSD lock acquisition atomic for debug mode","description":"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->next 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.","publishedAt":"2026-08-12T00:07:27.105Z","updatedAt":"2026-08-17T05:05:35.262Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b0473dcd4b1d7e2e44947e7ac1820c73a268821a","status":"affected","lessThan":"282d220bae5fbfc90cf0e3d5b5e42c00ad79f989","versionType":"git"},{"version":"b0473dcd4b1d7e2e44947e7ac1820c73a268821a","status":"affected","lessThan":"35551efb155e3b83445a6c3f66cb498d5efc182c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/smp.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.1","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.1","versionType":"semver"},{"version":"7.1.6","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/smp.c"]}],"references":["https://git.kernel.org/stable/c/282d220bae5fbfc90cf0e3d5b5e42c00ad79f989","https://git.kernel.org/stable/c/35551efb155e3b83445a6c3f66cb498d5efc182c"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:49.727Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/68xxx/CVE-2026-68438.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-68438","state":"PUBLISHED","datePublished":"2026-08-12T00:07:27.105Z","dateUpdated":"2026-08-17T05:05:35.262Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-30T09:28:09.394Z"},"containers":{"cna":{"title":"smp: Make CSD lock acquisition atomic for debug mode","descriptions":[{"lang":"en","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->next 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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b0473dcd4b1d7e2e44947e7ac1820c73a268821a","status":"affected","lessThan":"282d220bae5fbfc90cf0e3d5b5e42c00ad79f989","versionType":"git"},{"version":"b0473dcd4b1d7e2e44947e7ac1820c73a268821a","status":"affected","lessThan":"35551efb155e3b83445a6c3f66cb498d5efc182c","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/smp.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"7.1","status":"affected"},{"version":"0","status":"unaffected","lessThan":"7.1","versionType":"semver"},{"version":"7.1.6","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/smp.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/282d220bae5fbfc90cf0e3d5b5e42c00ad79f989"},{"url":"https://git.kernel.org/stable/c/35551efb155e3b83445a6c3f66cb498d5efc182c"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-17T05:05:35.262Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.1","versionEndExcluding":"7.1.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"7.1","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}