Introduce a transport-level ping facility

This adds a pair of SSH transport protocol messages SSH2_MSG_PING/PONG
to implement a ping capability. These messages use numbers in the "local
extensions" number space and are advertised using a "ping@openssh.com"
ext-info message with a string version number of "0".

ok markus@

1 files changed, 21 insertions, 2 deletions

diff --git a/usr.bin/ssh/packet.c b/usr.bin/ssh/packet.c
index b9a5343bf7b..600d51080fa 100644
--- a/usr.bin/ssh/packet.c
+++ b/usr.bin/ssh/packet.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: packet.c,v 1.310 2023/04/06 03:21:31 djm Exp $ */
+/* $OpenBSD: packet.c,v 1.311 2023/08/28 03:28:43 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1034,6 +1034,8 @@ int
 ssh_packet_log_type(u_char type)
 {
 	switch (type) {
+	case SSH2_MSG_PING:
+	case SSH2_MSG_PONG:
 	case SSH2_MSG_CHANNEL_DATA:
 	case SSH2_MSG_CHANNEL_EXTENDED_DATA:
 	case SSH2_MSG_CHANNEL_WINDOW_ADJUST:
@@ -1654,7 +1656,7 @@ ssh_packet_read_poll2(struct ssh *ssh, u_char *typep, u_int32_t *seqnr_p)
 		goto out;
 	if (ssh_packet_log_type(*typep))
 		debug3("receive packet: type %u", *typep);
-	if (*typep < SSH2_MSG_MIN || *typep >= SSH2_MSG_LOCAL_MIN) {
+	if (*typep < SSH2_MSG_MIN) {
 		if ((r = sshpkt_disconnect(ssh,
 		    "Invalid ssh2 packet type: %d", *typep)) != 0 ||
 		    (r = ssh_packet_write_wait(ssh)) != 0)
@@ -1689,6 +1691,8 @@ ssh_packet_read_poll_seqnr(struct ssh *ssh, u_char *typep, u_int32_t *seqnr_p)
 	u_int reason, seqnr;
 	int r;
 	u_char *msg;
+	const u_char *d;
+	size_t len;
 
 	for (;;) {
 		msg = NULL;
@@ -1732,6 +1736,21 @@ ssh_packet_read_poll_seqnr(struct ssh *ssh, u_char *typep, u_int32_t *seqnr_p)
 			debug("Received SSH2_MSG_UNIMPLEMENTED for %u",
 			    seqnr);
 			break;
+		case SSH2_MSG_PING:
+			if ((r = sshpkt_get_string_direct(ssh, &d, &len)) != 0)
+				return r;
+			DBG(debug("Received SSH2_MSG_PING len %zu", len));
+			if ((r = sshpkt_start(ssh, SSH2_MSG_PONG)) != 0 ||
+			    (r = sshpkt_put_string(ssh, d, len)) != 0 ||
+			    (r = sshpkt_send(ssh)) != 0)
+				return r;
+			break;
+		case SSH2_MSG_PONG:
+			if ((r = sshpkt_get_string_direct(ssh,
+			    NULL, &len)) != 0)
+				return r;
+			DBG(debug("Received SSH2_MSG_PONG len %zu", len));
+			break;
 		default:
 			return 0;
 		}