[X2go-dev] ENHANCEMENT-REQUEST: x2goclient -- option for reverse SSH port

[Mike Gabriel]

Hi there,

in the current x2goclient package (3.01-5, Debian, Qt version) there  
is need for an option to configure the reverse SSH port number (i.e.  
the SSH daemon's port on the client side). This option should be a  
client wide config option (not a per-session option).

Printing and file sharing (sshfs/fuse) build up a reverse port  
forwarding tunnel from the x2goserver back to the client. This feature  
is used for x2goprint and x2gomountdirs (if I understand the perl code  
correctly) and could also be used for any other feature that could be  
evoked by a reverse SSH connection...

The linux x2goclient, however, pre-requisites a running ssh daemon on  
the client system. Its standard port is 22. The x2goclient will only  
work if the client's SSH daemon runs on the default port 22. It will  
fail if the port has been set to a custom (high) port.

Consider a client, whose system administrator has set the SSH port to  
a high --- to potential intruders unknown --- port number (e.g.  
20222). With such an SSH setup, sshfs/fuse will fail...

Reproduce:

   o modify /etc/ssh/sshd_config
   o set ,,Port 20222'' (or something else)
   o /etc/init.d/ssh restart
   o start x2goclient as some user and login to a remote x2goserver
   o start a shell within the x2go session on the server
   o type ,,mount | grep sshfs''

Suggestions:

(a)
add a global SSH port number option to the x2goclient (linux-only).

(b)
Another way for the x2goclient could be some autodetect code:
lsof -ni  | egrep "^sshd.*root.*IPv4" | awk '{ print $8 }'

(c)
Another way, similar to the windows client, could be to run a separate  
ssh instance that binds to a random port on the localhost lo-device  
only. That's where the reverse SSH tunnel (server -> client) has its  
endpoint.

sshd -o ListenAddress 127.0.0.1:<someport> -o <someOtherOption>


Hope to be of help,
Mike

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