CVE-2026-80738 bpf: Check sk_state before sk_protocol in bpf_tcp_*_syncookie

CVE-2026-80738 affects the Linux kernel BPF TCP SYN cookie helpers bpf_tcp_gen_syncookie and bpf_tcp_check_syncookie . These functions accept a socket pointer typed as ARG_PTR_TO_BTF_ID_SOCK_COMMON but dereference sk->sk_protocol —a field specific to full sockets—without first confirming the s...