CVE-2026-93138bpf: Fix vmlinux BTF prep race in bpf_get_btf_vmlinux

Official description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix vmlinux BTF prep race in bpf_get_btf_vmlinux bpf_get_btf_vmlinux() lazily parses the vmlinux BTF under the bpf_verifier_lock, but publishes the result through a plain store and re-checks it through a plain lockless load. Nothing orders the stores initializing the struct btf inside btf_parse_vmlinux() against the store publishing the pointer: On a weakly ordered arch, a concurrent first-time caller taking the lockless fast path could in principle observe the pointer before the parsed contents are visible. The mutex_unlock() does not help such a reader given it only synchronizes with a later acquisition of the same lock. Thus, publish the pointer with smp_store_release() and read it on the fast path with smp_load_acquire(). Acquire semantics are needed rather than a dependency-ordered READ_ONCE(): btf_parse_vmlinux() also populates globals outside the returned object (e.g. bpf_ctx_convert.t). An address dependency would only order accesses performed through the pointer and not cover other globals.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/f32a4a40bc635be25d6816da4bd91e9e58c31bf3
• https://git.kernel.org/stable/c/a7fe72d780122eb934536f1719abad445f6afdf7
• https://git.kernel.org/stable/c/e18a10b39c994f04e1ebd7f8fc042bb1ca8ad053
• https://git.kernel.org/stable/c/978524ecfc1c539282df5858de1eec20748c6f74
• https://git.kernel.org/stable/c/eaf302628a78806f66d8224d6ba03fb4d5025de4
• https://git.kernel.org/stable/c/2892f3f44bf865c8fb6b6c0960edec4cc91806ee
• https://git.kernel.org/stable/c/86d11c594d60b255b526fa5260f669463fb1a063
• https://git.kernel.org/stable/c/92863e678070f57c17c868e4bfa2441a5c61ad2b