Re: [Libssh] X11 forwarding and Forward listening

[Vic Lee <llyzs@xxxxxxx>]

Hi,

After finish reading RFC4254, I realized that X11 forwarding works a
little different from forward listening:

1. forward listening is to ask the SSH server to listen on a port by
sending "tcpip-forward" global request; when a connection comes in, the
server allocates a channel and inform the client.

2. X11 forwarding is a channel request "x11-req" over an existing
interactive session channel; when an x11 connection comes in, the server
allocates a channel and inform the client.

Both x11 forwarding and forward listening require the channel to be
opened on the server side; so both need callbacks to pass the allocated
channels to the client app.

Vic

On Mon, 2009-07-13 at 18:06 +0800, Vic Lee wrote:
> Hi Aris,
> 
> I am raising this discussion again because you now got one demand from
> my project grdc :)
> 
> Basically, I am going to support XDMCP in grdc next release and I have
> everything ready to work, except to secure the X11 connection using
> libssh. Forward listening seems is the only way to secure X11
> connection.
> 
> I can work on this feature and submit a patch if you'd like.
> 
> My idea is to implement a general forward listening API; then X11
> forwarding can be implemented using forward listening on port 6000+n.
> 
> Thanks,
> 
> Vic
> 
> On Tue, 2009-06-09 at 11:35 +0200, Aris Adamantiadis wrote:
> > Hello,
> > 
> > I am happy our project serve to yours. The X11 forwarding and Forward
> > listening features are not currently implemented. They are in the todo
> > list. The reason for this is that we got no demand yet for X11
> > forwarding, and that forward listening needs to adapt the architecture
> > of libssh to handle callback handlers. But stay in tune !
> > 
> > Aris
> > 
> > Vic Lee a crit :
> > > Hi guys,
> > >
> > > First of all thanks for this great project!
> > >
> > > Acually I am using almost all SSH client features (port forwarding,
> > > shell, sftp) in my project (grdc) so I really appreciate it.
> > >
> > > Recently I am seeking the possibility to use X11 forwarding. This is
> > > the the feature in openssh -X option.
> > >
> > > Another feature is forward listening: ask the SSH server to listen on
> > > a port, and if a connection is made, create a tunnel to the SSH client.
> > >
> > > And I think X11 forwarding can be implemented through forward
> > > listening (by asking the SSH server to listen on a dummy x11 display
> > > and tunnel back to the local X server) but I need some more time to
> > > look at the openssh source code to understand exactly how it works.
> > >
> > > Are these two features already planned in the future?
> > >
> > > Thanks again!
> > >
> > > Vic
> > >
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