[nrf fromtree] net: tcp: Fix FIN with data handling

In case FIN packet included data bytes, Zephyr would ignore the
data. It wasn't passed to the application, and it wasn't considered
when bumping the ACK counter. This ended out in connection timing out,
instead of being properly terminated.

Fix this, by refactoring FIN processing in TCP_ESTABLISHED state.
Instead of handling FIN/FIN,ACK/FIN,ACK,PSH cases separately, have a
common handler when FIN flag is present, and when ACK flag is present
along with FIN. When FIN is present, take any potentially incoming data
into account.

Signed-off-by: Robert Lubos <[email protected]>
(cherry picked from commit a0f0e55)

Author: rlubos

subsys/net/ip/tcp.c

@@ -2719,28 +2719,9 @@ static enum net_verdict tcp_in(struct tcp *conn, struct net_pkt *pkt)
 		break;
 	case TCP_ESTABLISHED:
 		/* full-close */
-		if (th && FL(&fl, ==, (FIN | ACK), th_seq(th) == conn->ack)) {
-			if (net_tcp_seq_cmp(th_ack(th), conn->seq) > 0) {
-				uint32_t len_acked = th_ack(th) - conn->seq;
+		if (th && FL(&fl, &, FIN, th_seq(th) == conn->ack)) {
+			bool acked = false;
 
-				conn_seq(conn, + len_acked);
-			}
-
-			conn_ack(conn, + 1);
-			tcp_out(conn, FIN | ACK);
-			conn_seq(conn, + 1);
-			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);
-			tcp_out(conn, ACK);
-			next = TCP_CLOSE_WAIT;
-			verdict = NET_OK;
-			break;
-		} else if (th && FL(&fl, ==, (FIN | ACK | PSH),
-				    th_seq(th) == conn->ack)) {
 			if (len) {
 				verdict = tcp_data_get(conn, pkt, &len);
 				if (verdict == NET_OK) {
@@ -2752,10 +2733,27 @@ static enum net_verdict tcp_in(struct tcp *conn, struct net_pkt *pkt)
 			}
 
 			conn_ack(conn, + len + 1);
-			tcp_out(conn, FIN | ACK);
-			conn_seq(conn, + 1);
-			next = TCP_LAST_ACK;
-			tcp_setup_last_ack_timer(conn);
+
+			if (FL(&fl, &, ACK)) {
+				acked = true;
+
+				if (net_tcp_seq_cmp(th_ack(th), conn->seq) > 0) {
+					uint32_t len_acked = th_ack(th) - conn->seq;
+
+					conn_seq(conn, + len_acked);
+				}
+			}
+
+			if (acked) {
+				tcp_out(conn, FIN | ACK);
+				conn_seq(conn, + 1);
+				tcp_setup_last_ack_timer(conn);
+				next = TCP_LAST_ACK;
+			} else {
+				tcp_out(conn, ACK);
+				next = TCP_CLOSE_WAIT;
+			}
+
 			break;
 		}