mptcp: Add handling of outgoing MP_JOIN requests

Subflow creation may be initiated by the path manager when
the primary connection is fully established and a remote
address has been received via ADD_ADDR.

Create an in-kernel sock and use kernel_connect() to
initiate connection.

Passive sockets can't acquire the mptcp socket lock at
subflow creation time, so an additional list protected by
a new spinlock is used to track the MPJ subflows.

Such list is spliced into conn_list tail every time the msk
socket lock is acquired, so that it will not interfere
with data flow on the original connection.

Data flow and connection failover not addressed by this commit.

Co-developed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Co-developed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Co-developed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Peter Krystad <peter.krystad@linux.intel.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 94 insertions, 14 deletions

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 8e2b2dbadf6d..20ba00865c55 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -328,6 +328,16 @@ bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
 		opts->sndr_key = subflow->local_key;
 		*size = TCPOLEN_MPTCP_MPC_SYN;
 		return true;
+	} else if (subflow->request_join) {
+		pr_debug("remote_token=%u, nonce=%u", subflow->remote_token,
+			 subflow->local_nonce);
+		opts->suboptions = OPTION_MPTCP_MPJ_SYN;
+		opts->join_id = subflow->local_id;
+		opts->token = subflow->remote_token;
+		opts->nonce = subflow->local_nonce;
+		opts->backup = subflow->request_bkup;
+		*size = TCPOLEN_MPTCP_MPJ_SYN;
+		return true;
 	}
 	return false;
 }
@@ -337,16 +347,55 @@ void mptcp_rcv_synsent(struct sock *sk)
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	pr_debug("subflow=%p", subflow);
 	if (subflow->request_mptcp && tp->rx_opt.mptcp.mp_capable) {
 		subflow->mp_capable = 1;
 		subflow->can_ack = 1;
 		subflow->remote_key = tp->rx_opt.mptcp.sndr_key;
-	} else {
+		pr_debug("subflow=%p, remote_key=%llu", subflow,
+			 subflow->remote_key);
+	} else if (subflow->request_join && tp->rx_opt.mptcp.mp_join) {
+		subflow->mp_join = 1;
+		subflow->thmac = tp->rx_opt.mptcp.thmac;
+		subflow->remote_nonce = tp->rx_opt.mptcp.nonce;
+		pr_debug("subflow=%p, thmac=%llu, remote_nonce=%u", subflow,
+			 subflow->thmac, subflow->remote_nonce);
+	} else if (subflow->request_mptcp) {
 		tcp_sk(sk)->is_mptcp = 0;
 	}
 }
 
+/* MP_JOIN client subflow must wait for 4th ack before sending any data:
+ * TCP can't schedule delack timer before the subflow is fully established.
+ * MPTCP uses the delack timer to do 3rd ack retransmissions
+ */
+static void schedule_3rdack_retransmission(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+	unsigned long timeout;
+
+	/* reschedule with a timeout above RTT, as we must look only for drop */
+	if (tp->srtt_us)
+		timeout = tp->srtt_us << 1;
+	else
+		timeout = TCP_TIMEOUT_INIT;
+
+	WARN_ON_ONCE(icsk->icsk_ack.pending & ICSK_ACK_TIMER);
+	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
+	icsk->icsk_ack.timeout = timeout;
+	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
+}
+
+static void clear_3rdack_retransmission(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	sk_stop_timer(sk, &icsk->icsk_delack_timer);
+	icsk->icsk_ack.timeout = 0;
+	icsk->icsk_ack.ato = 0;
+	icsk->icsk_ack.pending &= ~(ICSK_ACK_SCHED | ICSK_ACK_TIMER);
+}
+
 static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
 					 unsigned int *size,
 					 unsigned int remaining,
@@ -356,17 +405,21 @@ static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
 	struct mptcp_ext *mpext;
 	unsigned int data_len;
 
-	pr_debug("subflow=%p fully established=%d seq=%x:%x remaining=%d",
-		 subflow, subflow->fully_established, subflow->snd_isn,
-		 skb ? TCP_SKB_CB(skb)->seq : 0, remaining);
+	/* When skb is not available, we better over-estimate the emitted
+	 * options len. A full DSS option (28 bytes) is longer than
+	 * TCPOLEN_MPTCP_MPC_ACK_DATA(22) or TCPOLEN_MPTCP_MPJ_ACK(24), so
+	 * tell the caller to defer the estimate to
+	 * mptcp_established_options_dss(), which will reserve enough space.
+	 */
+	if (!skb)
+		return false;
 
-	if (subflow->mp_capable && !subflow->fully_established && skb &&
-	    subflow->snd_isn == TCP_SKB_CB(skb)->seq) {
-		/* When skb is not available, we better over-estimate the
-		 * emitted options len. A full DSS option is longer than
-		 * TCPOLEN_MPTCP_MPC_ACK_DATA, so let's the caller try to fit
-		 * that.
-		 */
+	/* MPC/MPJ needed only on 3rd ack packet */
+	if (subflow->fully_established ||
+	    subflow->snd_isn != TCP_SKB_CB(skb)->seq)
+		return false;
+
+	if (subflow->mp_capable) {
 		mpext = mptcp_get_ext(skb);
 		data_len = mpext ? mpext->data_len : 0;
 
@@ -394,6 +447,14 @@ static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
 			 data_len);
 
 		return true;
+	} else if (subflow->mp_join) {
+		opts->suboptions = OPTION_MPTCP_MPJ_ACK;
+		memcpy(opts->hmac, subflow->hmac, MPTCPOPT_HMAC_LEN);
+		*size = TCPOLEN_MPTCP_MPJ_ACK;
+		pr_debug("subflow=%p", subflow);
+
+		schedule_3rdack_retransmission(sk);
+		return true;
 	}
 	return false;
 }
@@ -674,10 +735,12 @@ fully_established:
 		return true;
 
 	subflow->pm_notified = 1;
-	if (subflow->mp_join)
+	if (subflow->mp_join) {
+		clear_3rdack_retransmission(sk);
 		mptcp_pm_subflow_established(msk, subflow);
-	else
+	} else {
 		mptcp_pm_fully_established(msk);
+	}
 	return true;
 }
 
@@ -860,6 +923,16 @@ mp_capable_done:
 				      0, opts->rm_id);
 	}
 
+	if (OPTION_MPTCP_MPJ_SYN & opts->suboptions) {
+		*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
+				      TCPOLEN_MPTCP_MPJ_SYN,
+				      opts->backup, opts->join_id);
+		put_unaligned_be32(opts->token, ptr);
+		ptr += 1;
+		put_unaligned_be32(opts->nonce, ptr);
+		ptr += 1;
+	}
+
 	if (OPTION_MPTCP_MPJ_SYNACK & opts->suboptions) {
 		*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
 				      TCPOLEN_MPTCP_MPJ_SYNACK,
@@ -870,6 +943,13 @@ mp_capable_done:
 		ptr += 1;
 	}
 
+	if (OPTION_MPTCP_MPJ_ACK & opts->suboptions) {
+		*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
+				      TCPOLEN_MPTCP_MPJ_ACK, 0, 0);
+		memcpy(ptr, opts->hmac, MPTCPOPT_HMAC_LEN);
+		ptr += 5;
+	}
+
 	if (opts->ext_copy.use_ack || opts->ext_copy.use_map) {
 		struct mptcp_ext *mpext = &opts->ext_copy;
 		u8 len = TCPOLEN_MPTCP_DSS_BASE;