RE: Global Request for tcpip reverse forward

[Martín Fernández <fmartin91@xxxxxxxxx>]

Meng,

Thank you very much for your response!

Actually, I have tried that before. After sending the global response, calling `ssh_channel_open_reverse_forward`. Problem is that after calling the function, client and server get blocked. I’m sending a snippet of what I changed. Also, just for providing more information, this is the log from the server and client.

Server:
[2018/03/29 13:41:32.810991, 2] ssh_packet_global_request:  Calling callback for SSH_MSG_GLOBAL_REQUEST tcpip-forward 1 0.0.0.0:2000
[2018/03/29 13:41:32.811025, 3] ssh_socket_unbuffered_write:  Enabling POLLOUT for socket
[2018/03/29 13:41:32.811036, 3] packet_send2:  packet: wrote [len=12,padding=10,comp=1,payload=1]
[2018/03/29 13:41:32.811077, 2] channel_open:  Creating a channel 43 with 64000 window and 32768 max packet
[2018/03/29 13:41:32.811104, 3] packet_send2:  packet: wrote [len=76,padding=9,comp=66,payload=66]
[2018/03/29 13:41:32.811114, 3] channel_open:  Sent a SSH_MSG_CHANNEL_OPEN type forwarded-tcpip for channel 43

Client:
[2018/03/29 13:41:32.810891, 3] global_request:  Sent a SSH_MSG_GLOBAL_REQUEST tcpip-forward
[2018/03/29 13:41:32.811106, 3] ssh_packet_socket_callback:  packet: read type 81 [len=12,padding=10,comp=1,payload=1]
[2018/03/29 13:41:32.811121, 3] ssh_packet_process:  Dispatching handler for packet type 81
[2018/03/29 13:41:32.811130, 3] ssh_request_success:  Received SSH_REQUEST_SUCCESS
[2018/03/29 13:41:32.811139, 2] global_request:  Global request tcpip-forward success

/**
* @brief Global request callback
*
* @param session
* @param message
* @param userdata
*/
static void handle_global_request (ssh_session session, ssh_message message, void *userdata) {
ssh_message_global_request_reply_success (message, 8080 );

ssh_channel channel = ssh_channel_new (session);
int result = ssh_channel_open_reverse_forward (channel, "localhost" , 8080 , "localhost" , 8080 );

printf ( "RESULT %d \n " , result);
}

Thanks before hand!

Martín

On Thu, Mar 29, 2018 at 7:22 AM Meng Hourk Tan < Meng Hourk Tan ( Meng Hourk Tan <mtan@xxxxxxxxxx> ) > wrote:

> 
> 
> 
> Hi Martin,
> 
> 
> 
> 
> 
> 
> 
> 
> 
> I think your code lacks one step on server side:
> 
> 
> 
> After the Server handles the request using callback global_request_function
> and responds with ssh_message_global_request_reply_success,
> 
> 
> 
> You need to create a new channel and call
> ssh_channel_open_reverse_forward() on this channel.
> 
> 
> 
> 
> Then the client will receive the opening request of the reverse port
> forwarding channel.
> 
> 
> Hope it helps,
> 
> Regards,
> 
> 
> 
> 
> 
> 
> 
> 
> Meng
> 
> 
> 
> *De :* Martín Fernández <fmartin91@xxxxxxxxx>
> *Envoyé :* lundi 26 mars 2018 08:20:23
> *À :* libssh@xxxxxxxxxx
> *Objet :* Global Request for tcpip reverse forward
>  
> 
> Hello!
> 
> 
> This is my first time writing in the mailing list, I’m really new to
> libssh.
> 
> 
> I’m trying to get a server and client implementation for reverse port
> forwarding. 
> 
> 
> My understanding it that client requests the server for reverse port
> forwarding in a given port, server handles the petition and is responsible
> for managing the socket and redirecting data from socket to ssh channel.
> Client is responsible for reading ssh channel and sending data to the
> local server.
> 
> 
> I have successfully managed to get authentication between client and
> server work correctly.
> 
> 
> The part I’m probably missing something is on how to handle the global
> request from client and how to pull for data in the client.
> 
> 
> Basic pseudo code that I’m doing.
> 
> 
> - Client send global request to server using `ssh_channel_listen_forward`.
> 
> - Server handles the request using callback global_request_function and
> responds with ssh_message_global_request_reply_success
> - Client calls ssh_channel_accept_forward to get a new channel
> 
> 
> My problem is that `ssh_channel_accept_forward` never returns. I’m not
> sure If I’m missing something on the server side to initiate the channel.
> I know that I then need to redirect data between socket and channel but
> first I think I need to get a valid channel for forwarding right ?
> 
> 
> My complete code can be found here:
> https://gist.github.com/bilby91/22d5cc5db0e6118f06d6d35051c32cc6
> 
> 
> Thanks before hand!
> 
> 
> Martín
>