upstream: don't start the ObscureKeystrokeTiming mitigations if

there has been traffic on a X11 forwarding channel recently.

Should fix X11 forwarding performance problems when this setting is
enabled. Patch from Antonio Larrosa via bz3655

OpenBSD-Commit-ID: 820284a92eb4592fcd3d181a62c1b86b08a4a7ab

Author: djmdjm

channels.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.c,v 1.439 2024/07/25 22:40:08 djm Exp $ */
+/* $OpenBSD: channels.c,v 1.440 2024/10/13 22:20:06 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -5336,3 +5336,22 @@ x11_request_forwarding_with_spoofing(struct ssh *ssh, int client_session_id,
 		fatal_fr(r, "send x11-req");
 	free(new_data);
 }
+
+/*
+ * Returns whether an x11 channel was used recently (less than a second ago)
+ */
+int
+x11_channel_used_recently(struct ssh *ssh) {
+	u_int i;
+	Channel *c;
+	time_t lastused = 0;
+
+	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
+		c = ssh->chanctxt->channels[i];
+		if (c == NULL || c->ctype == NULL || c->lastused == 0 ||
+		    strcmp(c->ctype, "x11-connection") != 0)
+			continue;
+		lastused = c->lastused;
+	}
+	return lastused != 0 && monotime() > lastused + 1;
+}

channels.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.h,v 1.157 2024/07/25 22:40:08 djm Exp $ */
+/* $OpenBSD: channels.h,v 1.158 2024/10/13 22:20:06 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -382,6 +382,7 @@ int	 x11_connect_display(struct ssh *);
 int	 x11_create_display_inet(struct ssh *, int, int, int, u_int *, int **);
 void	 x11_request_forwarding_with_spoofing(struct ssh *, int,
 	    const char *, const char *, const char *, int);
+int      x11_channel_used_recently(struct ssh *ssh);
 
 /* channel close */
 

clientloop.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.c,v 1.408 2024/07/01 04:31:17 djm Exp $ */
+/* $OpenBSD: clientloop.c,v 1.409 2024/10/13 22:20:06 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -659,9 +659,10 @@ obfuscate_keystroke_timing(struct ssh *ssh, struct timespec *timeout,
 	if (just_started)
 		return 1;
 
-	/* Don't arm output fd for poll until the timing interval has elapsed */
+	/* Don't arm output fd for poll until the timing interval has elapsed... */
 	if (timespeccmp(&now, &next_interval, <))
-		return 0;
+		/* ...unless there's x11 communicattion happening */
+		return x11_channel_used_recently(ssh);
 
 	/* Calculate number of intervals missed since the last check */
 	n = (now.tv_sec - next_interval.tv_sec) * 1000LL * 1000 * 1000;