openssh unix dev - May 2005 - forwarding stdin/out to remote socket

Hi!

Some vnc clients has '-via ssh_gateway' option to simplify the setup
of ssh port forwarding. Basically the option implements the following
3 steps:

1. Find local port available for listening.

2. Fork/exec ssh -L found_port:vnc_host:vnc_port ssh_gateway sleep some_delay

3. Connect to the found_port 

Although convenient the setup has its problems. First, it exposes the
remote vnc port for everybody on the localhost for the duration of
some_delay. Second it can cause connection at step 3 to fail if it
would take a long time for ssh to setup the forwarding.

Now all this can be avoided if vnc would simply use stdin/out from ssh
as a communication channel and make sure that ssh would forward the
remote port to it. Currently I did it using netpipes,
http://web.purplefrog.com/~thoth/netpipes/netpipes.html , but it does
not seem right to execute an additional process copying megabytes of
tcp trafic from vncserver to stdin/out just so ssh can forward it one
more time.

So it would be nice if ssh can forward a port to stdin/out on its own.
AFAICS for ssh2 it  would require to modify only ssh client, right?

Regards, Igor

Igor Bukanov wrote:
> Although convenient the setup has its problems. First, it exposes the
> remote vnc port for everybody on the localhost for the duration of
> some_delay. Second it can cause connection at step 3 to fail if it
> would take a long time for ssh to setup the forwarding.
> 
> Now all this can be avoided if vnc would simply use stdin/out from ssh
I believe you are working around a lack of feature in sshd: sshd should be 
able to choose a free port and forward that port, but, as for now, it isn't.

I've been working on a patch against 4.0p1 for a while (see thread 
http://www.mindrot.org/pipermail/openssh-unix-dev/2005-March/022829.html and 
relative follow-ups) that would implement said feature, but it has been 
rightly rejected.

Now I have to find the time to fix the bugs and recode the patch against 
latest CVS or against 4.1. I plan to work on it and have it approved within 
the end of june, but don't rely too much on that.

Lucio.

On 5/2/05, Lucio Crusca wrote:
>I believe you are working around a lack of feature in sshd: sshd should
> be able to choose a free port and forward that port, but, as for now, it 
> isn't.
I do not think so. What I would like to do is to replace the current
invocation (where hose is from
http://web.purplefrog.com/~thoth/netpipes/hose.html):

ssh remote_host hose localhost 5901 --netslave
by 
ssh -oForwardStdInAndOut=localhost/5901 remote_host 

In this way a process (hose) that simply copy megabytes of vnc traffic
would be eliminated decreasing latency. BTW, what would be a better
name then ForwardStdInAndOut ?

Regards, Igor