Delay in starting programs on FreeBSD via ssh after upgrade OpenBSD from 7.3 to 7.4

[Damien Miller]

On Wed, 8 Nov 2023, Roger Marsh wrote:

> Damien,
> 
> Sorry about distributed context.
>
> Those discussions told me about the new ObscureKeystrokeTiming
> argument to the ssh command. One reply suggested I try that because it
> is easy to test.
>
> Most of my xterm ssh command combinations in fvwm configuration file
> are expressed 'Exec exec xterm -title ... -e ssh <user>@<host>' and do
> not have a noticable delay.
>
> One is expressed 'Exec exec ssh -Y opendev xterm -title
> roger at opendev', which you mention, and does have a noticable delay. It
> seemed far easier to find out what was going on by asking about this
> command rather than the formally identical 'ssh -Y <hostname> idle3.n'
> command: xterm is in OpenBSD base so asking a Python question on
> ports@ was probably too wide.
>
> It is the 'ssh -Y <hostname> idle3.n' command that worries me, and
> two scripts with 'ssh -vvv -Y ...' traces follow. The first is for
> starting idle, and the second is for invoking the open file dialogue.
>
> Adding '-o "ObscureKeystokeTiming no"' into the command gets rid
> of the delay: but I count this as a workaround unless told this is
> how the command is supposed to be done at OpenSSH 9.5 compared with
> OpenSSH 9.3.

It's possible the timing attack mitigation interacts badly with
X11 forwarding. Could you try this patch? If you still have problems,
then please post another -vvv debug trace.

diff --git a/channels.c b/channels.c
index 1b310e3..111c808 100644
--- a/channels.c
+++ b/channels.c
@@ -886,6 +886,23 @@ channel_still_open(struct ssh *ssh)
 	return 0;
 }
 
+/* Returns true if a channel with a TTY is open. */
+int
+channel_tty_open(struct ssh *ssh)
+{
+	u_int i;
+	Channel *c;
+
+	for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
+		c = ssh->chanctxt->channels[i];
+		if (c == NULL || c->type != SSH_CHANNEL_OPEN)
+			continue;
+		if (c->client_tty)
+			return 1;
+	}
+	return 0;
+}
+
 /* Returns the id of an open channel suitable for keepaliving */
 int
 channel_find_open(struct ssh *ssh)
diff --git a/channels.h b/channels.h
index 7cfba92..c31733f 100644
--- a/channels.h
+++ b/channels.h
@@ -337,6 +337,7 @@ int	 channel_output_poll(struct ssh *);
 int      channel_not_very_much_buffered_data(struct ssh *);
 void     channel_close_all(struct ssh *);
 int      channel_still_open(struct ssh *);
+int	 channel_tty_open(struct ssh *);
 const char *channel_format_extended_usage(const Channel *);
 char	*channel_open_message(struct ssh *);
 int	 channel_find_open(struct ssh *);
diff --git a/clientloop.c b/clientloop.c
index deebbba..cb69c72 100644
--- a/clientloop.c
+++ b/clientloop.c
@@ -580,7 +580,7 @@ obfuscate_keystroke_timing(struct ssh *ssh, struct timespec *timeout,
 	if (options.obscure_keystroke_timing_interval <= 0)
 		return 1;	/* disabled in config */
 
-	if (!channel_still_open(ssh) || quit_pending) {
+	if (!channel_tty_open(ssh) || quit_pending) {
 		/* Stop if no channels left of we're waiting for one to close */
 		stop_reason = "no active channels";
 	} else if (ssh_packet_is_rekeying(ssh)) {