CVE-2026-98049
UnknownSummary
In the Linux kernel's BPF subsystem, is_cmpxchg_insn() matches only BPF_MODE == BPF_ATOMIC, so an arena cmpxchg misses the required zero extension for a 32-bit operation. This can lead to incorrect values in the destination register on architectures requiring explicit zero extension.
Risk Assessment
Incorrect zero extension of a 32-bit cmpxchg result in BPF programs can lead to faulty eBPF program behavior, potentially causing logic errors or bypassing security mechanisms.
Recommendation
Update the Linux kernel to a version with the fix that modifies is_cmpxchg_insn() to match BPF_PROBE_ATOMIC alongside BPF_ATOMIC.
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Original NVD description (English source)
In 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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS