openssh unix dev - Aug 2008 - Hanging ssh sessions with openssh-5.1p1 and Solaris 8 & 10

Since we upgraded OpenSSH from 5.0p1 to 5.1p1 on our Solaris 8 boxes
(I know, I know, we should upgrade or retire them...), we've started
experiencing problems with slogin'ing into these boxes, running vi,
and pasting text into the vi session.

As long as we are pasting in less that 1024 characters it's fine.
With >= 1024 characters, the session hangs.

If you run "/usr/ucb/lptest 72 23 | cat -n" in one window, and
then cut paste up to the "V" on line 13, things work as expected.
If you include the "W" on the line 13, the vi session will hang
with none of characters that are being pasted showing up.

We've been building OpenSSH with Sun Studio 11 -- I tried building
it with GNU-CC 3.4.4 with the same results.  We also link against
a locally built zlib, since Solaris 8 doesn't have zlib 1.2.3.
And we've used OpenSSL 0.9.8g and 0.9.8h with the same results.

We also tried building OpenSSH 5.1p1 on our Solaris 10 boxes using
Sun Studio 12, and we also get the hangs there.  The client doesn't
seem to matter -- we've seen it OpenSSH 5.1p1 from both Solaris
and Slackware Linux, and also from SecureCRT.

I have not been able to get anything useful from running sshd in
debug mode (at least, not that I recognize as useful :-) ).
-- 
           Jeff Wieland            |         Purdue University
    Network Systems Administrator  |        ITN&S Data Networks
        Voice: (765)496-8234       |        501 Harrison Street
         FAX: (765)494-6620        |   West Lafayette, IN 47907-2025

On Mon, Aug 04, 2008 at 02:34:23PM -0400, Jeff Wieland
wrote:
> Since we upgraded OpenSSH from 5.0p1 to 5.1p1 on our Solaris 8 boxes
> (I know, I know, we should upgrade or retire them...), we've started
> experiencing problems with slogin'ing into these boxes, running vi,
> and pasting text into the vi session.
> 
> As long as we are pasting in less that 1024 characters it's fine.
> With >= 1024 characters, the session hangs.
Do you know if the problem occurs on the client or server side?  ie if
you use an older client with a newer server (and vice versa) does the
problem occur?
> If you run "/usr/ucb/lptest 72 23 | cat -n" in one window, and
> then cut paste up to the "V" on line 13, things work as expected.
> If you include the "W" on the line 13, the vi session will hang
> with none of characters that are being pasted showing up.
> 
> We've been building OpenSSH with Sun Studio 11 -- I tried building
> it with GNU-CC 3.4.4 with the same results.  We also link against
> a locally built zlib, since Solaris 8 doesn't have zlib 1.2.3.
> And we've used OpenSSL 0.9.8g and 0.9.8h with the same results.
> 
> We also tried building OpenSSH 5.1p1 on our Solaris 10 boxes using
> Sun Studio 12, and we also get the hangs there.  The client doesn't
> seem to matter -- we've seen it OpenSSH 5.1p1 from both Solaris
> and Slackware Linux, and also from SecureCRT.
> 
> I have not been able to get anything useful from running sshd in
> debug mode (at least, not that I recognize as useful :-) ).
Well you could post it, someone else might recognise someting :-)

Some versions of AIX have bugs in the tty drivers that prevent largish
writes from working correctly.  Pehaps Solaris has something similar
(although I can't imagine why it's only started recently).

You could try the patch below to test this theory.

Index: channels.c
==================================================================RCS file:
/usr/local/src/security/openssh/cvs/openssh/channels.c,v
retrieving revision 1.273
diff -u -p -r1.273 channels.c
--- channels.c	16 Jul 2008 12:42:06 -0000	1.273
+++ channels.c	5 Aug 2008 01:08:22 -0000
@@ -1578,11 +1578,10 @@ channel_handle_wfd(Channel *c, fd_set *r
 			}
 			return 1;
 		}
-#ifdef _AIX
+
 		/* XXX: Later AIX versions can't push as much data to tty */
 		if (compat20 && c->wfd_isatty)
-			dlen = MIN(dlen, 8*1024);
-#endif
+			dlen = MIN(dlen, 1024);
 
 		len = write(c->wfd, buf, dlen);
 		if (len < 0 &&

-- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.