Re: SSH Tunnels

[Loïc Michaux <lmichaux@xxxxxxxxxx>]

Hi Andreas,

Thanks you for your answer and your server example.

I pretty well understood the libssh callbacks implementation. My question is about callbacks catching tunneling/port forwarding/... requests, libssh doesn't seem to meet this need yet.

If you take a look at src/messages.c, in ssh_execute_server_request(), you will find :

case SSH_REQUEST_CHANNEL_OPEN:
  if (msg->channel_request_open.type == SSH_CHANNEL_SESSION &&
      ssh_callbacks_exists(session->server_callbacks, channel_open_request_session_function)) {
    [...]
  }

But no "if (msg->channel_request_open.type == SSH_CHANNEL_DIRECT_TCPIP [...]" or something like that.

You will find a short example of code about what I want to do attached to this message. The patch I attached on my previous message do the job.

--
Loïc Michaux

----- Original Message -----
From: "Andreas Schneider" <asn@xxxxxxxxxxxxxx>
To: libssh@xxxxxxxxxx
Sent: Wednesday, March 12, 2014 4:17:03 PM
Subject: Re: SSH Tunnels

On Wednesday 12 February 2014 13:27:46 Loïc Michaux wrote:
> Hi,

Hey,

> I am currently trying to implement tunnels via ssh forwardings and libssh
> callbacks system.
> 
> Some questions where posted here about this kind of problem but I couldn't
> find any detailed answer.
> 
> When trying to open tunnels with `ssh -p <port> -ND <lport>
> <user>@<server_addr>` (or any other set of options which asks for tunnels),
> no callback is triggered in order to handle this.
> 
> I supposed at least channel_open_request_session_function() or
> global_request_function() had to be called with a SSH_REQUEST_GLOBAL
> request type or a SSH_CHANNEL_FORWARDED_TCPIP channel type, but this is not
> what actually happens.
> 
> Did I miss something ? A callback specially created for this use ?
> Or do I have to patch the lib to create one or more callbacks which will be
> triggered by ssh_execute_server_request() in src/messages.c ?

this is not the callback way how libssh server should be implemented. See

http://git.libssh.org/projects/libssh.git/tree/examples/ssh_server_fork.c


	-- andreas

-- 
Andreas Schneider                   GPG-ID: CC014E3D
www.cryptomilk.org                asn@xxxxxxxxxxxxxx


#include <libssh/libssh.h>
#include <libssh/server.h>
#include <libssh/callbacks.h>
#include <stdlib.h>

static ssh_channel
channel_open_request_session(ssh_session session, void *userdata) {
    (void) session;
    (void) userdata;
    ssh_channel chan = NULL;

    return chan;
}

static ssh_channel
channel_open_direct_tcpip(ssh_session session,
                          const char *dest, uint16_t dest_port,
                          const char *orig, uint16_t orig_port,
                          void *userdata) {
    (void) userdata;
    ssh_channel chan = NULL;

/* XXX Do someting ... */

    return chan;
}

int
main(void) {
    ssh_session session;
    ssh_bind ssh_bind;
    ssh_event e;

    struct ssh_server_callbacks_struct srv_cb = {
        .userdata = NULL,
        .channel_open_request_session_function = channel_open_request_session,
        .channel_open_request_direct_tcpip_function = channel_open_direct_tcpip,
    };

    /* [...] */

    ssh_callbacks_init(&srv_cb);
    ssh_set_server_callbacks(session, &srv_cb);

    /* [...] */

    e = ssh_event_new();
    ssh_event_add_session(e, session);

    while (1) {
        /* [...] */
        ssh_event_dopoll(e, 100);
        /* [...] */
    }
    return EXIT_SUCCESS;
}