bpf: zero extend the result of an arena 32-bit cmpxchg

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Summary

CVECVE-2026-98049
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-25 11:17:33 UTC
Updated2026-09-30 14:10:59 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: bpf: zero extend the result of an arena 32-bit cmpxchg bpf_convert_ctx_accesses() rewrites an atomic on an arena pointer from BPF_STX | BPF_ATOMIC to BPF_STX | BPF_PROBE_ATOMIC, and it runs before bpf_opt_subreg_zext_lo32_rnd_hi32(). That pass emits an explicit zero extension for a 32-bit cmpxchg even when bpf_jit_needs_zext() is false. This is done because on some architectures 32-bit cmpxchg requires explicit zero extension for the dst register. E.g. on x86-64 'lock cmpxchg' does not change the %eax if comparison is successful, while BPF semantics declare that each operation on a 32-bit register zero extends it's upper half. is_cmpxchg_insn() matches BPF_MODE == BPF_ATOMIC only, so an arena cmpxchg misses said zero extension adjustment. This patch adjusts is_cmpxchg_insn() to match BPF_PROBE_ATOMIC alongside BPF_ATOMIC.

Risk And Classification

EPSS: 0.001550000 probability, percentile 0.039790000 (date 2026-09-27)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected d503a04f8bc0c75dc9db9452d8cc79d748afb752 1c1b476d43a8b6c9bc04600369dd8cc39950d98e git Not specified
CNA Linux Linux affected d503a04f8bc0c75dc9db9452d8cc79d748afb752 4814ed6406f3493bd554ad046da5f7fc04833571 git Not specified
CNA Linux Linux affected 6.10 Not specified
CNA Linux Linux unaffected 6.10 semver Not specified
CNA Linux Linux unaffected 7.2.7 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/1c1b476d43a8b6c9bc04600369dd8cc39950d98e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/4814ed6406f3493bd554ad046da5f7fc04833571 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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