net: tcp: Limit number of segment retransmissions

Defines a new tunable, CONFIG_NET_TCP_RETRY_COUNT, that determines the
number of segment retransmissions that the IP stack will attempt to
perform before resetting the connection.

The default value is 9 retransmissions, which amounts to 1:42 minutes,
as close as possible to the minimum recommended by RFC1122.

Jira: ZEP-1956, ZEP-1957

Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>

Author: lpereira

subsys/net/ip/Kconfig

@@ -139,6 +139,25 @@ config NET_TCP_ACK_TIMEOUT
 	various TCP states. The value is in milliseconds. Note that
 	having a very low value here could prevent connectivity.
 
+config NET_TCP_RETRY_COUNT
+	int "Maximum number of TCP segment retransmissions"
+	depends on NET_TCP
+	default 9
+	help
+	The following formula can be used to determine the time (in ms)
+	that a segment will be be buffered awaiting retransmission:
+	n=NET_TCP_RETRY_COUNT
+	∑((1<<n) * 200)
+	n=0
+	With the default value of 9, the IP stack will try to
+	retransmit for up to 1:42 minutes.  This is as close as possible
+	to the minimum value recommended by RFC1122 (1:40 minutes).
+	Only 5 bits are dedicated for the retransmission count, so accepted
+	values are in the 0-31 range.  It's highly recommended to not go
+	below 9, though.
+	Should a retransmission timeout occur, the receive callback is
+	called with -ECONNRESET error code and the context is dereferenced.
+
 config NET_UDP
 	bool "Enable UDP"
 	default y

subsys/net/ip/tcp.c

@@ -141,6 +141,20 @@ static inline void do_ref_if_needed(struct net_pkt *pkt)
 	}
 }
 
+static void abort_connection(struct net_tcp *tcp)
+{
+	struct net_context *ctx = tcp->context;
+
+	NET_DBG("Segment retransmission exceeds %d, resetting context %p",
+		CONFIG_NET_TCP_RETRY_COUNT, ctx);
+
+	if (ctx->recv_cb) {
+		ctx->recv_cb(ctx, NULL, -ECONNRESET, tcp->recv_user_data);
+	}
+
+	net_context_unref(ctx);
+}
+
 static void tcp_retry_expired(struct k_timer *timer)
 {
 	struct net_tcp *tcp = CONTAINER_OF(timer, struct net_tcp, retry_timer);
@@ -151,6 +165,12 @@ static void tcp_retry_expired(struct k_timer *timer)
 	 */
 	if (!sys_slist_is_empty(&tcp->sent_list)) {
 		tcp->retry_timeout_shift++;
+
+		if (tcp->retry_timeout_shift > CONFIG_NET_TCP_RETRY_COUNT) {
+			abort_connection(tcp);
+			return;
+		}
+
 		k_timer_start(&tcp->retry_timer, retry_timeout(tcp), 0);
 
 		pkt = CONTAINER_OF(sys_slist_peek_head(&tcp->sent_list),