[nrf fromtree] net: tcp: Install a last ack timer in passive close

If we are in a passive close state, then it is possible that
the ack we are waiting is lost or we do not accept the one peer
sent to us because of some earlier out of memory issue.
So install a timer (using by default the FIN timer value) to
close the connection if the last ack is not received on time.

Signed-off-by: Jukka Rissanen <[email protected]>
(cherry picked from commit 40215e0)
Signed-off-by: Robert Lubos <[email protected]>

Author: jukkar

subsys/net/ip/tcp.c

@@ -28,6 +28,8 @@ LOG_MODULE_REGISTER(net_tcp, CONFIG_NET_TCP_LOG_LEVEL);
 
 #define ACK_TIMEOUT_MS CONFIG_NET_TCP_ACK_TIMEOUT
 #define ACK_TIMEOUT K_MSEC(ACK_TIMEOUT_MS)
+#define LAST_ACK_TIMEOUT_MS tcp_fin_timeout_ms
+#define LAST_ACK_TIMEOUT K_MSEC(LAST_ACK_TIMEOUT_MS)
 #define FIN_TIMEOUT K_MSEC(tcp_fin_timeout_ms)
 #define ACK_DELAY K_MSEC(100)
 #define ZWP_MAX_DELAY_MS 120000
@@ -1593,9 +1595,9 @@ static void tcp_resend_data(struct k_work *work)
 	conn->send_data_retries++;
 	if (ret == 0) {
 		if (conn->in_close && conn->send_data_total == 0) {
-			NET_DBG("TCP connection in active close, "
+			NET_DBG("TCP connection in %s close, "
 				"not disposing yet (waiting %dms)",
-				tcp_fin_timeout_ms);
+				"active", tcp_fin_timeout_ms);
 			k_work_reschedule_for_queue(&tcp_work_q,
 						    &conn->fin_timer,
 						    FIN_TIMEOUT);
@@ -1675,6 +1677,40 @@ static void tcp_fin_timeout(struct k_work *work)
 	(void)tcp_conn_close(conn, -ETIMEDOUT);
 }
 
+static void tcp_last_ack_timeout(struct k_work *work)
+{
+	struct k_work_delayable *dwork = k_work_delayable_from_work(work);
+	struct tcp *conn = CONTAINER_OF(dwork, struct tcp, fin_timer);
+
+	NET_DBG("Did not receive %s in %dms", "last ACK", LAST_ACK_TIMEOUT_MS);
+	NET_DBG("conn: %p %s", conn, tcp_conn_state(conn, NULL));
+
+	(void)tcp_conn_close(conn, -ETIMEDOUT);
+}
+
+static void tcp_setup_last_ack_timer(struct tcp *conn)
+{
+	/* Just in case the last ack is lost, install a timer that will
+	 * close the connection in that case. Use the fin_timer for that
+	 * as the fin handling cannot be done in this passive close state.
+	 * Instead of default tcp_fin_timeout() function, have a separate
+	 * function to catch this last ack case.
+	 */
+	k_work_init_delayable(&conn->fin_timer, tcp_last_ack_timeout);
+
+	NET_DBG("TCP connection in %s close, "
+		"not disposing yet (waiting %dms)",
+		"passive", LAST_ACK_TIMEOUT_MS);
+	k_work_reschedule_for_queue(&tcp_work_q,
+				    &conn->fin_timer,
+				    LAST_ACK_TIMEOUT);
+}
+
+static void tcp_cancel_last_ack_timer(struct tcp *conn)
+{
+	k_work_cancel_delayable(&conn->fin_timer);
+}
+
 static void tcp_send_zwp(struct k_work *work)
 {
 	struct k_work_delayable *dwork = k_work_delayable_from_work(work);
@@ -2694,6 +2730,7 @@ static enum net_verdict tcp_in(struct tcp *conn, struct net_pkt *pkt)
 			tcp_out(conn, FIN | ACK);
 			next = TCP_LAST_ACK;
 			verdict = NET_OK;
+			tcp_setup_last_ack_timer(conn);
 			break;
 		} else if (th && FL(&fl, ==, FIN, th_seq(th) == conn->ack)) {
 			conn_ack(conn, + 1);
@@ -2716,6 +2753,7 @@ static enum net_verdict tcp_in(struct tcp *conn, struct net_pkt *pkt)
 			conn_ack(conn, + len + 1);
 			tcp_out(conn, FIN | ACK);
 			next = TCP_LAST_ACK;
+			tcp_setup_last_ack_timer(conn);
 			break;
 		}
 
@@ -2890,13 +2928,17 @@ static enum net_verdict tcp_in(struct tcp *conn, struct net_pkt *pkt)
 	case TCP_CLOSE_WAIT:
 		tcp_out(conn, FIN);
 		next = TCP_LAST_ACK;
+		tcp_setup_last_ack_timer(conn);
 		break;
 	case TCP_LAST_ACK:
 		if (th && FL(&fl, ==, ACK, th_seq(th) == conn->ack)) {
 			tcp_send_timer_cancel(conn);
 			do_close = true;
 			verdict = NET_OK;
 			close_status = 0;
+
+			/* Remove the last ack timer if we received it in time */
+			tcp_cancel_last_ack_timer(conn);
 		}
 		break;
 	case TCP_CLOSED:
@@ -3222,8 +3264,9 @@ int net_tcp_put(struct net_context *context)
 		} else {
 			int ret;
 
-			NET_DBG("TCP connection in active close, not "
-				"disposing yet (waiting %dms)", tcp_fin_timeout_ms);
+			NET_DBG("TCP connection in %s close, "
+				"not disposing yet (waiting %dms)",
+				"active", tcp_fin_timeout_ms);
 			k_work_reschedule_for_queue(&tcp_work_q,
 						    &conn->fin_timer,
 						    FIN_TIMEOUT);