mptcp + TFO: Only send ADD_ADDR after receiving the third ACK

When TFO is being used, we create the full-fledged MPTCP-socket right at
the reception of the SYN. At this point, we also call
mptcp_update_metasocket(), which ends up calling the path-manager to
check for addresses,...

This also means that the server will send ADD_ADDR-options. These
ADD_ADDR-options will actually be sent before the SYN/ACK, in
full_mesh_new_session(). These ACKs with ADD_ADDR-option will actually
be discarded by the client, because the client is still waiting for a
SYN/ACK.

This patch changes this so that ADD_ADDR will only be sent after the
reception of the third ACK.

Fixes: 8d66361 (mptcp: fastopen server support)
Signed-off-by: Christoph Paasch <[email protected]>
Signed-off-by: Matthieu Baerts <[email protected]>
(cherry picked from commit c642642)
Signed-off-by: Matthieu Baerts <[email protected]>

include/net/mptcp.h

@@ -781,7 +781,7 @@ void mptcp_cleanup_rbuf(struct sock *meta_sk, int copied);
 int mptcp_add_sock(struct sock *meta_sk, struct sock *sk, u8 loc_id, u8 rem_id,
 		   gfp_t flags);
 void mptcp_del_sock(struct sock *sk);
-void mptcp_update_metasocket(struct sock *sock, const struct sock *meta_sk);
+void mptcp_update_metasocket(const struct sock *meta_sk);
 void mptcp_reinject_data(struct sock *orig_sk, int clone_it);
 void mptcp_update_sndbuf(const struct tcp_sock *tp);
 void mptcp_send_fin(struct sock *meta_sk);
@@ -1366,7 +1366,7 @@ static inline int is_master_tp(const struct tcp_sock *tp)
 }
 static inline void mptcp_purge_ofo_queue(struct tcp_sock *meta_tp) {}
 static inline void mptcp_del_sock(const struct sock *sk) {}
-static inline void mptcp_update_metasocket(struct sock *sock, const struct sock *meta_sk) {}
+static inline void mptcp_update_metasocket(const struct sock *meta_sk) {}
 static inline void mptcp_reinject_data(struct sock *orig_sk, int clone_it) {}
 static inline void mptcp_update_sndbuf(const struct tcp_sock *tp) {}
 static inline void mptcp_clean_rtx_infinite(const struct sk_buff *skb,

net/ipv4/tcp_input.c

@@ -5954,7 +5954,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 			 * addresses, which can only be done after the third ack
 			 * of the 3-way handshake.
 			 */
-			mptcp_update_metasocket(sk, tp->meta_sk);
+			mptcp_update_metasocket(tp->meta_sk);
 		}
 		if (queued >= 0)
 			return queued;
@@ -6050,12 +6050,16 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
 
 		tcp_initialize_rcv_mss(sk);
 		tcp_fast_path_on(tp);
-		/* Send an ACK when establishing a new
-		 * MPTCP subflow, i.e. using an MP_JOIN
-		 * subtype.
+
+		/* Send an ACK when establishing a new  MPTCP subflow, i.e.
+		 * using an MP_JOIN subtype.
 		 */
-		if (mptcp(tp) && !is_master_tp(tp))
-			tcp_send_ack(sk);
+		if (mptcp(tp)) {
+			if (is_master_tp(tp))
+				mptcp_update_metasocket(mptcp_meta_sk(sk));
+			else
+				tcp_send_ack(sk);
+		}
 		break;
 
 	case TCP_FIN_WAIT1: {

net/mptcp/mptcp_ctrl.c

@@ -1404,10 +1404,10 @@ void mptcp_del_sock(struct sock *sk)
 /* Updates the MPTCP-session based on path-manager information (e.g., addresses,
  * low-prio flows,...).
  */
-void mptcp_update_metasocket(struct sock *sk, const struct sock *meta_sk)
+void mptcp_update_metasocket(const struct sock *meta_sk)
 {
-	if (tcp_sk(sk)->mpcb->pm_ops->new_session)
-		tcp_sk(sk)->mpcb->pm_ops->new_session(meta_sk);
+	if (tcp_sk(meta_sk)->mpcb->pm_ops->new_session)
+		tcp_sk(meta_sk)->mpcb->pm_ops->new_session(meta_sk);
 }
 
 /* Clean up the receive buffer for full frames taken by the user,
@@ -1984,9 +1984,6 @@ static int __mptcp_check_req_master(struct sock *child,
 	mpcb->dss_csum = mtreq->dss_csum;
 	mpcb->server_side = 1;
 
-	/* Will be moved to ESTABLISHED by  tcp_rcv_state_process() */
-	mptcp_update_metasocket(child, meta_sk);
-
 	/* Needs to be done here additionally, because when accepting a
 	 * new connection we pass by __reqsk_free and not reqsk_free.
 	 */