{"id":"CVE-2026-68438","summary":"smp: Make CSD lock acquisition atomic for debug mode","details":"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.","modified":"2026-08-18T03:30:50.585770761Z","published":"2026-08-12T00:07:27.105Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/68xxx/CVE-2026-68438.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/282d220bae5fbfc90cf0e3d5b5e42c00ad79f989"},{"type":"WEB","url":"https://git.kernel.org/stable/c/35551efb155e3b83445a6c3f66cb498d5efc182c"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/68xxx/CVE-2026-68438.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-68438"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"b0473dcd4b1d7e2e44947e7ac1820c73a268821a"},{"fixed":"282d220bae5fbfc90cf0e3d5b5e42c00ad79f989"},{"fixed":"35551efb155e3b83445a6c3f66cb498d5efc182c"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-68438.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"7.1.0"},{"fixed":"7.1.6"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-68438.json"}}],"schema_version":"1.9.0"}