program to listen on TCP socket and start some program with I/O redirected to socket

leniviy · 08-09-2013, 06:56 AM

Hi. Is there a progam that does this? I need it to traverse ssh server with tunnels disabled.

gdejonge · 08-09-2013, 11:19 AM

Yes.
It is called xinetd

But could explain a little more what you try to do, so we can explain a little better how to do it.

Cheers

leniviy · 08-10-2013, 04:10 AM

There's a jumpstation to a closed network. I'm supposed to login to this JS with ssh and run another ssh command to connect to the target server. SSH tunnels on JS are disabled for security reasons.

I want to run a GUI database client.

The JS has modern bash which supports IO redirection to /dev/tcp/host/port.

On My workstation, when the database client connects to xinetd, it would launch ssh with remote command like this:

Code:

"exec 4<>/dev/tcp/serv1/1521 && cat >&4 <&0 & cat <&4"

leniviy · 08-12-2013, 05:47 AM

My Solution:

Code:

         localhost                               jumpstation                            srv
 ----------------------------           ----------------------------------        ----------------
|                            |         |                                  |      |                |
|   ----------------------   |         |                                  |      |                |
|  | Oracle SQL Developer |  |         |   ----------------------------   |      |                |
|   ----------------------   |         |  |  exec 4<>/dev/tcp/srv/1521 |  |      |                |
|            |               |         |  |                            |  |      |                |
|        ----------          |         |  |       ->-- "cat >&4"       |  |      |    --------    |
|       | wininetd |         |   |-----|--|------|                     |--|------|---| Oracle |   |
|        ----------          |   |     |  |       -<-- "cat <&4"       |  |      |    --------    |
|            |               |   |     |   ----------------------------   |      |                |
|         -------            |   |     |                                  |      |                |
|        | plink |-----------|---      |                                  |      |                |
|         -------            |         |                                  |      |                |
|                            |         |                                  |      |                |
 ----------------------------           ----------------------------------        ----------------

Wininetd was modified to work correctly with plink.
plink's stderr is redirected to nul.
Remote ssh command:

Code:

exec 4<>/dev/tcp/%host%/%port% || exit 1; cat <&4 & exec 1>&-; cat >&4 <&0; exec 0<&-; sleep 10; kill $!

leniviy · 08-12-2013, 05:51 AM

Since there's no way to call shutdown() on the socket opened by bash, I have to close all inherited fds of the socket. I do it by killing the receiving "cat".