net: mptcp: don't hang in mptcp_sendmsg() after TCP fallback

it's still possible for packetdrill to hang in mptcp_sendmsg(), when the
MPTCP socket falls back to regular TCP (e.g. after receiving unsupported
flags/version during the three-way handshake). Adjust MPTCP socket state
earlier, to ensure correct functionality of mptcp_sendmsg() even in case
of TCP fallback.

Fixes: 767d3ded5f ("net: mptcp: don't hang before sending 'MP capable with data'")
Fixes: 1954b86016 ("mptcp: Check connection state before attempting send")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/protocol.c

@@ -1055,10 +1055,6 @@ void mptcp_finish_connect(struct sock *ssk)
 	WRITE_ONCE(msk->write_seq, subflow->idsn + 1);
 	WRITE_ONCE(msk->ack_seq, ack_seq);
 	WRITE_ONCE(msk->can_ack, 1);
-	if (inet_sk_state_load(sk) != TCP_ESTABLISHED) {
-		inet_sk_state_store(sk, TCP_ESTABLISHED);
-		sk->sk_state_change(sk);
-	}
 }
 
 static void mptcp_sock_graft(struct sock *sk, struct socket *parent)

net/mptcp/subflow.c

@@ -109,9 +109,15 @@ static void subflow_v6_init_req(struct request_sock *req,
 static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct sock *parent = subflow->conn;
 
 	subflow->icsk_af_ops->sk_rx_dst_set(sk, skb);
 
+	if (inet_sk_state_load(parent) != TCP_ESTABLISHED) {
+		inet_sk_state_store(parent, TCP_ESTABLISHED);
+		parent->sk_state_change(parent);
+	}
+
 	if (!subflow->conn_finished) {
 		pr_debug("subflow=%p, remote_key=%llu", mptcp_subflow_ctx(sk),
 			 subflow->remote_key);