selinux: do not report error on connect(AF_UNSPEC)

calling connect(AF_UNSPEC) on an already connected TCP socket is an
established way to disconnect() such socket. After commit 68741a8a
("selinux: Fix ltp test connect-syscall failure") it no longer works
and, in the above scenario connect() fails with EAFNOSUPPORT.

Fix the above explicitly early checking for AF_UNSPEC family, and
returning success in that case.
Reported-by: Tom Deseyn <tdeseyn@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 68741a8a ("selinux: Fix ltp test connect-syscall failure")
Suggested-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/hooks.c

@@ -4637,6 +4637,14 @@ static int selinux_socket_connect_helper(struct socket *sock,
 	err = sock_has_perm(sk, SOCKET__CONNECT);
 	if (err)
 		return err;
+	if (addrlen < offsetofend(struct sockaddr, sa_family))
+		return -EINVAL;
+
+	/* connect(AF_UNSPEC) has special handling, as it is a documented
+	 * way to disconnect the socket
+	 */
+	if (address->sa_family == AF_UNSPEC)
+		return 0;
 
 	/*
 	 * If a TCP, DCCP or SCTP socket, check name_connect permission
@@ -4657,8 +4665,6 @@ static int selinux_socket_connect_helper(struct socket *sock,
 		 * need to check address->sa_family as it is possible to have
 		 * sk->sk_family = PF_INET6 with addr->sa_family = AF_INET.
 		 */
-		if (addrlen < offsetofend(struct sockaddr, sa_family))
-			return -EINVAL;
 		switch (address->sa_family) {
 		case AF_INET:
 			addr4 = (struct sockaddr_in *)address;