{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-43121","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-05-01T14:12:55.987Z","datePublished":"2026-05-06T11:27:08.216Z","dateUpdated":"2026-05-11T22:18:09.791Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-05-11T22:18:09.791Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/zcrx: fix user_ref race between scrub and refill paths\n\nThe io_zcrx_put_niov_uref() function uses a non-atomic\ncheck-then-decrement pattern (atomic_read followed by separate\natomic_dec) to manipulate user_refs. This is serialized against other\ncallers by rq_lock, but io_zcrx_scrub() modifies the same counter with\natomic_xchg() WITHOUT holding rq_lock.\n\nOn SMP systems, the following race exists:\n\n  CPU0 (refill, holds rq_lock)          CPU1 (scrub, no rq_lock)\n  put_niov_uref:\n    atomic_read(uref) - 1\n    // window opens\n                                        atomic_xchg(uref, 0) - 1\n                                        return_niov_freelist(niov) [PUSH #1]\n    // window closes\n    atomic_dec(uref) - wraps to -1\n    returns true\n    return_niov(niov)\n    return_niov_freelist(niov)           [PUSH #2: DOUBLE-FREE]\n\nThe same niov is pushed to the freelist twice, causing free_count to\nexceed nr_iovs. Subsequent freelist pushes then perform an out-of-bounds\nwrite (a u32 value) past the kvmalloc'd freelist array into the adjacent\nslab object.\n\nFix this by replacing the non-atomic read-then-dec in\nio_zcrx_put_niov_uref() with an atomic_try_cmpxchg loop that atomically\ntests and decrements user_refs. This makes the operation safe against\nconcurrent atomic_xchg from scrub without requiring scrub to acquire\nrq_lock.\n\n[pavel: removed a warning and a comment]"}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["io_uring/zcrx.c"],"versions":[{"version":"34a3e60821ab9f335a58d43a88cccdbefdebdec3","lessThan":"a94f096e28bfc7975163a6b80f1c8f323efe317a","status":"affected","versionType":"git"},{"version":"34a3e60821ab9f335a58d43a88cccdbefdebdec3","lessThan":"485dc691257b96e6d3bdc25b0eff2daadcc5c46c","status":"affected","versionType":"git"},{"version":"34a3e60821ab9f335a58d43a88cccdbefdebdec3","lessThan":"003049b1c4fb8aabb93febb7d1e49004f6ad653b","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["io_uring/zcrx.c"],"versions":[{"version":"6.15","status":"affected"},{"version":"0","lessThan":"6.15","status":"unaffected","versionType":"semver"},{"version":"6.18.16","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"6.19.6","lessThanOrEqual":"6.19.*","status":"unaffected","versionType":"semver"},{"version":"7.0","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"6.18.16"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"6.19.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.15","versionEndExcluding":"7.0"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/a94f096e28bfc7975163a6b80f1c8f323efe317a"},{"url":"https://git.kernel.org/stable/c/485dc691257b96e6d3bdc25b0eff2daadcc5c46c"},{"url":"https://git.kernel.org/stable/c/003049b1c4fb8aabb93febb7d1e49004f6ad653b"}],"title":"io_uring/zcrx: fix user_ref race between scrub and refill paths","x_generator":{"engine":"bippy-1.2.0"}}}}