[Gnumed-devel] remote help

[Ian Haywood]

This is a little script to help people who for various reasons are unwilling or 
unable
to open ports and hand out root passwords on their boxes but still need help in 
setting things up or fixing problems.

It connects to the helper's machine (who must open the SSH port and have an 
ordinary user account available.)
The helper can then access a shell via this incoming connection (so it's the 
reverse of a
normal SSH connection)
The session is replayed live on the local console, so the helpee can see what 
is going on
(and check the helper isn't doing anything untoward)

The helper must have 'netcat' installed, and listen for connections using

stty raw -echo; nc -l -p 8883; stty sane

the port number 8883 is of course arbitrary.


Ian

import select, pty, popen2, os, signal, sys
if len (sys.argv) != 3:
    print """
remote_help.py user host

host is a remote host where someone who can help you is logged in.
user is the name of a low-priviledge account on that system.
ssh is used to connect to that system, then the connection is
run 'backwards': the remote host has access to a shell on the local
machine, as the current user.
Obviusly a certain amount of trust in the remote user is required,
but not that much: the session is replayed live on the terminal, so you
can see what they are doing in real-time.

The remote user needs to run
stty raw -echo; nc -l -p 8883; stty sane

in a terminal and wait for the shell prompt to appear.
"""
    sys.exit (0)
ssh = popen2.Popen4 ("/usr/bin/ssh -l %s %s nc 127.0.0.1 8883" % (sys.argv[1], 
sys.argv[2]))
ssh_stdout = ssh.fromchild.fileno ()
ssh_stdin = ssh.tochild.fileno ()
bash_pid, bash = pty.fork ()
bashbuf = ''
sshbuf = ''
if bash_pid == 0:
    os.execl ('/bin/bash', '-l')
else:
    try:
        while 1:
            wfds = []
            if sshbuf:
                wfds.append (bash)
            if bashbuf:
                wfds.append (ssh_stdin)
            rfds, wfds, efds = select.select ([bash, ssh_stdout], wfds, [bash, 
ssh_stdout, ssh_stdin])
            if bash in rfds:
                bashbuf += os.read (bash, 1024)
            if ssh_stdout in rfds:
                sshbuf += os.read (ssh_stdout, 1024)
            if bash in wfds:
                n = os.write (bash, sshbuf)
                sshbuf = sshbuf[n:]
            if ssh_stdin in wfds:
                n = os.write (ssh_stdin, bashbuf)
                os.write (1, bashbuf[:n])
                bashbuf = bashbuf[n:]
    except OSError, e:
        os.kill (bash_pid, signal.SIGKILL)
        os.kill (ssh.pid, signal.SIGKILL)