CVE-2026-43121 (GCVE-0-2026-43121)

Vulnerability from cvelistv5 – Published: 2026-05-06 11:27 – Updated: 2026-05-11 22:18
VLAI?
Title
io_uring/zcrx: fix user_ref race between scrub and refill paths
Summary
In the Linux kernel, the following vulnerability has been resolved: io_uring/zcrx: fix user_ref race between scrub and refill paths The io_zcrx_put_niov_uref() function uses a non-atomic check-then-decrement pattern (atomic_read followed by separate atomic_dec) to manipulate user_refs. This is serialized against other callers by rq_lock, but io_zcrx_scrub() modifies the same counter with atomic_xchg() WITHOUT holding rq_lock. On SMP systems, the following race exists: CPU0 (refill, holds rq_lock) CPU1 (scrub, no rq_lock) put_niov_uref: atomic_read(uref) - 1 // window opens atomic_xchg(uref, 0) - 1 return_niov_freelist(niov) [PUSH #1] // window closes atomic_dec(uref) - wraps to -1 returns true return_niov(niov) return_niov_freelist(niov) [PUSH #2: DOUBLE-FREE] The same niov is pushed to the freelist twice, causing free_count to exceed nr_iovs. Subsequent freelist pushes then perform an out-of-bounds write (a u32 value) past the kvmalloc'd freelist array into the adjacent slab object. Fix this by replacing the non-atomic read-then-dec in io_zcrx_put_niov_uref() with an atomic_try_cmpxchg loop that atomically tests and decrements user_refs. This makes the operation safe against concurrent atomic_xchg from scrub without requiring scrub to acquire rq_lock. [pavel: removed a warning and a comment]
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 34a3e60821ab9f335a58d43a88cccdbefdebdec3 , < a94f096e28bfc7975163a6b80f1c8f323efe317a (git)
Affected: 34a3e60821ab9f335a58d43a88cccdbefdebdec3 , < 485dc691257b96e6d3bdc25b0eff2daadcc5c46c (git)
Affected: 34a3e60821ab9f335a58d43a88cccdbefdebdec3 , < 003049b1c4fb8aabb93febb7d1e49004f6ad653b (git)
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Linux Linux Affected: 6.15
Unaffected: 0 , < 6.15 (semver)
Unaffected: 6.18.16 , ≤ 6.18.* (semver)
Unaffected: 6.19.6 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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          "programFiles": [
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    "dateReserved": "2026-05-01T14:12:55.987Z",
    "dateUpdated": "2026-05-11T22:18:09.791Z",
    "state": "PUBLISHED"
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