bpf, unix: Check socket type in unix_bpf_update_proto()

As of now, only AF_UNIX datagram socket supports sockmap. But
unix_proto is shared for all kinds of AF_UNIX sockets, so we
have to check the socket type in unix_bpf_update_proto() to
explicitly reject other types, otherwise they could be added
into sockmap, too.

Fixes: c6382918 ("af_unix: Implement ->psock_update_sk_prot()")
Reported-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20210731195038.8084-1-xiyou.wangcong@gmail.com

net/unix/unix_bpf.c

@@ -105,6 +105,9 @@ static void unix_bpf_check_needs_rebuild(struct proto *ops)
 
 int unix_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)
 {
+	if (sk->sk_type != SOCK_DGRAM)
+		return -EOPNOTSUPP;
+
 	if (restore) {
 		sk->sk_write_space = psock->saved_write_space;
 		WRITE_ONCE(sk->sk_prot, psock->sk_proto);