tcp: Restrict SO_TXREHASH to TCP socket.

sk->sk_txrehash is only used for TCP.

Let's restrict SO_TXREHASH to TCP to reflect this.

Later, we will make sk_txrehash a part of the union for other
protocol families.

Note that we need to modify BPF selftest not to get/set
SO_TEREHASH for non-TCP sockets.

Signed-off-by: Kuniyuki Iwashima <[e-mail]>
Reviewed-by: Willem de Bruijn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/core/sock.c

···
 		return 0;
 		}
 	case SO_TXREHASH:
+		if (!sk_is_tcp(sk))
+			return -EOPNOTSUPP;
 		if (val < -1 || val > 1)
 			return -EINVAL;
 		if ((u8)val == SOCK_TXREHASH_DEFAULT)
···
 		break;
 
 	case SO_TXREHASH:
+		if (!sk_is_tcp(sk))
+			return -EOPNOTSUPP;
+
 		/* Paired with WRITE_ONCE() in sk_setsockopt() */
 		v.val = READ_ONCE(sk->sk_txrehash);
 		break;

tools/testing/selftests/bpf/progs/setget_sockopt.c

···
 	struct sock *sk;
 };
 
+static bool sk_is_tcp(struct sock *sk)
+{
+	return (sk->__sk_common.skc_family == AF_INET ||
+		sk->__sk_common.skc_family == AF_INET6) &&
+		sk->sk_type == SOCK_STREAM &&
+		sk->sk_protocol == IPPROTO_TCP;
+}
+
 static int bpf_test_sockopt_flip(void *ctx, struct sock *sk,
 				 const struct sockopt_test *t,
 				 int level)
···
 	int old, tmp, new, opt = t->opt;
 
 	opt = t->opt;
+
+	if (opt == SO_TXREHASH && !sk_is_tcp(sk))
+		return 0;
 
 	if (bpf_getsockopt(ctx, level, opt, &old, sizeof(old)))
 		return 1;