openssh unix dev - Apr 2015 - Tera Term, Unexpected SSH2 message(80) on current stage(6) [was Re: SAP-2015-3-1 issues]

On Thu, Apr 9, 2015 at 12:28 PM, Bryan Drewery <bryan at shatow.net>
wrote:
>
> It seems that Tera Term has fixed this but not yet released a build with
> it.
>
> http://en.sourceforge.jp/ticket/browse.php?group_id=1412&tid=35010
> http://en.sourceforge.jp/projects/ttssh2/scm/svn/commits/5829

Reading that change it looks like Tera Term before that change would also
crash when ClientAliveInterval is enabled on the server?

This patch fixes it in OpenSSH for me:
> https://people.freebsd.org/~bdrewery/patches/ttssh-host-keys.diff
>
-- 
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.

On 4/8/2015 9:56 PM, Darren Tucker wrote:
> On Thu, Apr 9, 2015 at 12:28 PM, Bryan Drewery <bryan at shatow.net
> <mailto:bryan at shatow.net>> wrote:
> 
>     It seems that Tera Term has fixed this but not yet released a build
>     with it.
> 
>     http://en.sourceforge.jp/ticket/browse.php?group_id=1412&tid=35010
>     http://en.sourceforge.jp/projects/ttssh2/scm/svn/commits/5829
> 
> 
> Reading that change it looks like Tera Term before that change would
> also crash when ClientAliveInterval is enabled on the server?
I see what you're saying but I am unable to create any error by enabling
ClientAliveInterval. I set it to 1 and get no errors on the client. sshd
debugging:

debug2: channel 0: request keepalive at openssh.com confirm 1
debug2: tcpwinsz: 65700 for connection: 3
debug2: tcpwinsz: 65700 for connection: 3
debug1: Got 100/16 for keepalive
debug2: tcpwinsz: 65700 for connection: 3
debug2: channel 0: request keepalive at openssh.com confirm 1
debug2: tcpwinsz: 65700 for connection: 3
debug2: tcpwinsz: 65700 for connection: 3
debug1: Got 100/17 for keepalive
debug2: tcpwinsz: 65700 for connection: 3
debug2: channel 0: request keepalive at openssh.com confirm 1
debug2: tcpwinsz: 65700 for connection: 3
debug2: tcpwinsz: 65700 for connection: 3
debug1: Got 100/18 for keepalive
debug2: tcpwinsz: 65700 for connection: 3
debug2: channel 0: request keepalive at openssh.com confirm 1
debug2: tcpwinsz: 65700 for connection: 3
debug2: tcpwinsz: 65700 for connection: 3
debug1: Got 100/19 for keepalive
debug2: tcpwinsz: 65700 for connection: 3

I think it just ignores the SSH2_MSG_GLOBAL_REQUEST packets once it is
fully connected. Seeing them before the full connection is unexpected to
it as the error seems to imply (Unexpected... on current stage). I don't
see anything in ssh.c handling keepalive messages.
> 
>     This patch fixes it in OpenSSH for me:
>     https://people.freebsd.org/~bdrewery/patches/ttssh-host-keys.diff
> 
>

On Thu, Apr 9, 2015 at 1:07 PM, Bryan Drewery <bryan at shatow.net> wrote:
> On 4/8/2015 9:56 PM, Darren Tucker wrote:ading that change it looks like
> Tera Term before that change would
> > also crash when ClientAliveInterval is enabled on the server?
>
> I see what you're saying but I am unable to create any error by
enabling
> ClientAliveInterval. I set it to 1 and get no errors on the client. sshd
> debugging:
>
> debug2: channel 0: request keepalive at openssh.com confirm 1
>
Those are channel requests not global requests.  sshd does this in
serverloop.c:

         if ((channel_id = channel_find_open()) == -1) {
                packet_start(SSH2_MSG_GLOBAL_REQUEST);
                packet_put_cstring("keepalive at openssh.com");
                packet_put_char(1);     /* boolean: want reply */
        } else {
                channel_request_start(channel_id, "keepalive at
openssh.com",
1);
        }

and Tera Term seems to handle the channel requests just fine.  Presumably
if you could get a connection with no active channels (ie the equivalent of
ssh -N) then perhaps it'd have a problem, or perhaps that's not even
possible with that client.

-- 
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.