CVE-2026-98049

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.