mptcp: Properly reset sockets in tcp_disconnect

It is possible that we end up in tcp_disconnect after a failed call to
connect(). In that case tp->request_mptcp is set. We correctly remove
the socket from the token hash-table but leave request_mptcp set. This
can lead to inconsistent states later on if for some reason we end up
disabling MPTCP on that disconnected socket.

Fixes: Zero-day bug
Signed-off-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
(cherry picked from commit f4596c1)
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
(cherry picked from commit 7700fc3)
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>

net/ipv4/tcp.c

@@ -2683,6 +2683,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	if (is_meta_sk(sk)) {
 		mptcp_disconnect(sk);
 	} else {
+		tp->request_mptcp = 0;
 		if (tp->inside_tk_table)
 			mptcp_hash_remove_bh(tp);
 	}