There is a situation in SSH -> HPN connection the advertised

window will 16MB and then it will cause some odd behaviour
on the part of the ssh client. Basically it looks like it's
doing a lot of expensive drains and fills on a buffer
that significantly impacts throughput. This is a fix that
annoys me because *any* SSH to HPN connection is now limited
to a maximum recieve window of 15MB. Which is not
optimal in anyway. Still, it's better than the through
put of the pathological state which significantly slower.

Author: rapier1

channels.c

@@ -1250,10 +1250,12 @@ channel_tcpwinsz(struct ssh *ssh)
 		tcpwinsz = SSHBUF_SIZE_MAX;
 	/* if the remote side is OpenSSH after version 8.8 we need to restrict
 	 * the size of the advertised window. Now this means that any HPN to non-HPN
-	 * connection will be window limited but thats okay. This bug shows up when
-	 * sending data to an hpn */
-	//if ((ssh->compat & SSH_RESTRICT_WINDOW) && (tcpwinsz > NON_HPN_WINDOW_MAX))
-	//	tcpwinsz = NON_HPN_WINDOW_MAX;
+	 * connection will be window limited to 15MB of receive space. This is a
+	 * non-optimal solution.
+	 */
+
+	if ((ssh->compat & SSH_RESTRICT_WINDOW) && (tcpwinsz > NON_HPN_WINDOW_MAX))
+		tcpwinsz = NON_HPN_WINDOW_MAX;
 	return (tcpwinsz);
 }
 
@@ -2368,10 +2370,6 @@ channel_check_window(struct ssh *ssh, Channel *c)
 	    c->local_consumed > 0) {
 		u_int addition = 0;
 		u_int32_t tcpwinsz = channel_tcpwinsz(ssh);
-		if ((ssh->compat & SSH_RESTRICT_WINDOW) &&
-		    (tcpwinsz > NON_HPN_WINDOW_MAX))
-			tcpwinsz = NON_HPN_WINDOW_MAX;
-		
 		/* adjust max window size if we are in a dynamic environment
 		 * and the tcp receive buffer is larger than the ssh window */
 		if (c->dynamic_window && (tcpwinsz > c->local_window_max)) {
@@ -2390,8 +2388,10 @@ channel_check_window(struct ssh *ssh, Channel *c)
 				addition = tcpwinsz - c->local_window_max;
 			}
 			c->local_window_max += addition;
-			//sshbuf_set_window_max(c->output, c->local_window_max);
-			//sshbuf_set_window_max(c->input, c->local_window_max);
+			/* doesn't look like we need these
+			 * sshbuf_set_window_max(c->output, c->local_window_max);
+			 * sshbuf_set_window_max(c->input, c->local_window_max);
+			 */
 			debug("Channel %d: Window growth to %d by %d bytes",c->self,
 			      c->local_window_max, addition);
 		}

compat.c

@@ -124,11 +124,9 @@ compat_banner(struct ssh *ssh, const char *version)
 		{ NULL,			0 }
 	};
 
-	debug ("------------------------ VERSION IS %s", version);
 	/* process table, return first match */
 	ssh->compat = 0;
 	for (i = 0; check[i].pat; i++) {
-		debug_f("PATTERN IS %d for %s\n", i, check[i].pat);
 		if (match_pattern_list(version, check[i].pat, 0) == 1) {
 			debug_f("match: %s pat %s compat 0x%08x",
 			    version, check[i].pat, check[i].bugs);
@@ -155,13 +153,15 @@ compat_banner(struct ssh *ssh, const char *version)
 					debug("Remote uses HPNSSH prefixes.");
 					break;
 				}
+				/* if it's openssh and not hpn */
 				if ((strstr(version, "OpenSSH_8.9") != NULL) ||
 				    (strstr(version, "OpenSSH_9") != NULL)) {
 					ssh->compat |= SSH_RESTRICT_WINDOW;
 					debug("Restricting adverstised window size.");
 				}
 			}
 			debug("ssh->compat is %u", ssh->compat);
+			return;
 		}
 	}
 	debug_f("no match: %s", version);

kex.c

@@ -1753,8 +1753,8 @@ kex_exchange_identification(struct ssh *ssh, int timeout_ms,
 		debug("Non-HPN to HPN Connection.");
 
 	if(ssh->compat & SSH_RESTRICT_WINDOW)
-		debug ("---------------------- RESTRICT");
-	
+		debug ("Window size restricted.");
+
 	mismatch = 0;
 	switch (remote_major) {
 	case 2:

ssh.c

@@ -2194,14 +2194,6 @@ ssh_session2_setup(struct ssh *ssh, int id, int success, void *arg)
 static void
 hpn_options_init(struct ssh *ssh)
 {
-	if (ssh->compat & SSH_HPNSSH)
-		debug("HPN to HPN Connection.");
-	else
-		debug("Non-HPN to HPN Connection.");
-
-	if(ssh->compat & SSH_RESTRICT_WINDOW)
-		debug ("---------------------- RESTRICT");
-
 	channel_set_hpn_disabled(options.hpn_disabled);
 	debug_f("HPN disabled: %d", options.hpn_disabled);
 }

sshbuf.c

@@ -371,7 +371,7 @@ sshbuf_check_reserve(const struct sshbuf *buf, size_t len)
 void
 sshbuf_set_window_max(struct sshbuf *buf, size_t len)
 {
-	//buf->window_max = len;
+	buf->window_max = len;
 }
 
 int