mptcp: free resources when the port number is mismatched

When the port number is mismatched with the announced ones, use
'goto dispose_child' to free the resources instead of using 'goto out'.

This patch also moves the port number checking code in
subflow_syn_recv_sock before mptcp_finish_join, otherwise subflow_drop_ctx
will fail in dispose_child.

Fixes: 5bc56388 ("mptcp: add port number check for MP_JOIN")
Reported-by: NPaolo Abeni <pabeni@redhat.com>
Signed-off-by: NGeliang Tang <geliangtang@gmail.com>
Signed-off-by: NMat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/mptcp/subflow.c

@@ -687,11 +687,6 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
 			/* move the msk reference ownership to the subflow */
 			subflow_req->msk = NULL;
 			ctx->conn = (struct sock *)owner;
-			if (!mptcp_finish_join(child))
-				goto dispose_child;
-
-			SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKRX);
-			tcp_rsk(req)->drop_req = true;
 
 			if (subflow_use_different_sport(owner, sk)) {
 				pr_debug("ack inet_sport=%d %d",
@@ -699,10 +694,16 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
 					 ntohs(inet_sk((struct sock *)owner)->inet_sport));
 				if (!mptcp_pm_sport_in_anno_list(owner, sk)) {
 					SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MISMATCHPORTACKRX);
-					goto out;
+					goto dispose_child;
 				}
 				SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINPORTACKRX);
 			}
+
+			if (!mptcp_finish_join(child))
+				goto dispose_child;
+
+			SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKRX);
+			tcp_rsk(req)->drop_req = true;
 		}
 	}