CVE-2026-31413bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR

Official description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR maybe_fork_scalars() is called for both BPF_AND and BPF_OR when the source operand is a constant. When dst has signed range [-1, 0], it forks the verifier state: the pushed path gets dst = 0, the current path gets dst = -1. For BPF_AND this is correct: 0 & K == 0. For BPF_OR this is wrong: 0 | K == K, not 0. The pushed path therefore tracks dst as 0 when the runtime value is K, producing an exploitable verifier/runtime divergence that allows out-of-bounds map access. Fix this by passing env->insn_idx (instead of env->insn_idx + 1) to push_stack(), so the pushed path re-executes the ALU instruction with dst = 0 and naturally computes the correct result for any opcode.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/342aa1ee995ef5bbf876096dc3a5e51218d76fa4
• https://git.kernel.org/stable/c/58bd87d0e69204dbd739e4387a1edb0c4b1644e7
• https://git.kernel.org/stable/c/d13281ae7ea8902b21d99d10a2c8caf0bdec0455
• https://git.kernel.org/stable/c/c845894ebd6fb43226b3118d6b017942550910c5