mptcp: fix state tracking for fallback socket

We need to cope with some more state transition for
fallback sockets, or could still end-up moving to TCP_CLOSE
too early and avoid spooling some pending data

Fixes: e16163b ("mptcp: refactor shutdown and close")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/protocol.c

@@ -777,7 +777,9 @@ static void mptcp_check_for_eof(struct mptcp_sock *msk)
 		inet_sk_state_store(sk, TCP_CLOSE_WAIT);
 		break;
 	case TCP_FIN_WAIT1:
-		/* fallback sockets skip TCP_CLOSING - TCP will take care */
+		inet_sk_state_store(sk, TCP_CLOSING);
+		break;
+	case TCP_FIN_WAIT2:
 		inet_sk_state_store(sk, TCP_CLOSE);
 		break;
 	default:
@@ -2086,10 +2088,16 @@ static void __mptcp_check_send_data_fin(struct sock *sk)
 
 	WRITE_ONCE(msk->snd_nxt, msk->write_seq);
 
-	/* fallback socket will not get data_fin/ack, can move to close now */
-	if (__mptcp_check_fallback(msk) && sk->sk_state == TCP_LAST_ACK) {
-		inet_sk_state_store(sk, TCP_CLOSE);
-		mptcp_close_wake_up(sk);
+	/* fallback socket will not get data_fin/ack, can move to the next
+	 * state now
+	 */
+	if (__mptcp_check_fallback(msk)) {
+		if ((1 << sk->sk_state) & (TCPF_CLOSING | TCPF_LAST_ACK)) {
+			inet_sk_state_store(sk, TCP_CLOSE);
+			mptcp_close_wake_up(sk);
+		} else if (sk->sk_state == TCP_FIN_WAIT1) {
+			inet_sk_state_store(sk, TCP_FIN_WAIT2);
+		}
 	}
 
 	__mptcp_flush_join_list(msk);