bpf: Fix incorrect pruning due to atomic fetch precision tracking
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix incorrect pruning due to atomic fetch precision tracking When backtrack_insn encounters a BPF_STX instruction with BPF_ATOMIC and BPF_FETCH, the src register (or r0 for BPF_CMPXCHG) also acts as a destination, thus receiving the old value from the memory location. The current backtracking logic does not account for this. It treats atomic fetch operations the same as regular stores where the src register is only an input. This leads the backtrack_insn to fail to propagate precision to the stack location, which is then not marked as precise! Later, the verifier's p