OpenSSH with "resumable" functionality

[Andreas Gunnarsson]

> On Sun, Apr 18, 2010 at 05:26:06PM -0500, Misha Koshelev wrote:
> > I was wondering if it might at all be possible to have the following functionality in OpenSSH:
> > (i) upon "timeout" of connection (say 2-5 seconds) disconnect
> > (ii) keep trying to reconnect
> > (iii) upon reconnection, resume session exactly where started

On Mon, Apr 19, 2010 at 01:08:36PM +0200, Markus Friedl wrote:
> this is a work-in-progress, some parts are already commited to
> the released versions. other parts need to be reviewed.
> 
> Andreas can provide details, I think -- and yes, I should 
> look into reviewing the remaining patches.......

I've made the patch available here:

   http://www.zzlevo.net/ssh-roaming.diff

This is a diff against OpenBSD-current which adds "roaming" to allow an
ssh session to be suspended (i.e. terminate the TCP session) and then
resumed over a new TCP session. The client may resume from the same or a
new IP address.

A solution which just sets up a new ssh session would tear down open
port forwarded TCP sessions. This patch keeps the client and server
processes running, and applications that use port forwards will not
notice that the ssh session has been suspended and resumed.

The session is not resumed automatically (the user has to press return)
but that could be a possible enhancement once this is committed. The
patch is based on code written by Martin Forssén and donated by my
previous employer, AppGate. I haven't made a version for portable
OpenSSH but anyone who wants to will probably be able to do that with
minimal effort.

As Markus said, this hasn't been fully audited yet. It does touch the
preauth and privsep parts of the code so use on your own risk. :)

   Andreas