[Twisted-Python] How to switch users in SSH session.

27 Sep 2007

      After much wrangling and a small miracle I have managed to write an object 
that fetches the output of three commands in the order given through an 
SSH connection. How come I cannot switch users? Some of the information I 
need can only be fetched through a root account and security is such that 
I cannot log in remotely from a root account but must switch once logged 
in from an account with less than root privileges.

Here's the line that instaniates my SSH object (also repeated at the end 
of my code):

myssh = SSH("my.host.com", "myusername", "mypasswd", ["id; su - root; 
myrootpasswd; id", "pwd", "ls -l"])

The last argument above is a  list of three commands. Inside one command 
";" separates the piece parts.
I am not even able to su to accounts that don't require a password.

###========= CODE STARTS ================###
from twisted.conch import error
from twisted.conch.ssh import transport, connection, keys, userauth, 
channel, common
from twisted.internet import defer, protocol, reactor
import sys, getpass, os, string

class ClientCommandTransport(transport.SSHClientTransport):
    def __init__(self, username, password, cmds, caller):
        self.username = username
        self.password = password
        self.cmds = cmds
        self.caller = caller

    def verifyHostKey(self, pubKey, fingerprint):
        # in a real app, you should verify that the fingerprint matches
        # the one you expected to get from this server
        return defer.succeed(True)

    def connectionSecure(self):
        self.requestService(PasswordAuth(self.username, self.password, 
ClientConnection(self.cmds, self.caller)))

class PasswordAuth(userauth.SSHUserAuthClient):
    def __init__(self, user, password, connection):
        userauth.SSHUserAuthClient.__init__(self, user, connection)
        self.password = password

    def getPassword(self, prompt=None):
        return defer.succeed(self.password)

class ClientConnection(connection.SSHConnection):
    def __init__(self, cmds, caller, *args, **kwargs):
        connection.SSHConnection.__init__(self)
        self.cmds = cmds
        self.caller = caller

    #======================
    def serviceStarted(self):
        self.d = defer.Deferred()
        self.d.addCallback(self._cbFirst)
        self.d.addErrback(self._ebFirst)
        self.openChannel(CommandChannel(self.cmds[0], lastcmd=0, 
conn=self))

    def _cbFirst(self, result):
        #print 'CALLBACK Result 1:', result
        self.caller.responses.append(result.rstrip())
        self.d = defer.Deferred()
        self.d.addCallback(self._cbSecond)
        self.d.addErrback(self._ebSecond)
        self.openChannel(CommandChannel(self.cmds[1], lastcmd=0, 
conn=self))

    def _ebFirst(self, f):
        self.caller.responses.append(None)
        print "Error 1"
        self.d = defer.Deferred()
        self.d.addCallback(self._cbSecond)
        self.d.addErrback(self._ebSecond)
        self.openChannel(CommandChannel(self.cmds[1], lastcmd=0, 
conn=self))
        #log.err()

    def _cbSecond(self, result):
        #print 'CALLBACK Result 2:', result
        self.caller.responses.append(result.rstrip())
        self.d = defer.Deferred()
        self.d.addCallback(self._cbThird)
        self.d.addErrback(self._ebThird)
        self.openChannel(CommandChannel(self.cmds[2], lastcmd=1, 
conn=self))

    def _ebSecond(self, f):
        self.caller.responses.append(None)
        self.d = defer.Deferred()
        self.d.addCallback(self._cbThird)
        self.d.addErrback(self._ebThird)
        self.openChannel(CommandChannel(self.cmds[2], lastcmd=1, 
conn=self))
        #log.err()

    def _cbThird(self, result):
        self.caller.responses.append(result.rstrip())
        #print 'CALLBACK Result 3:', result
        reactor.stop()

    def _ebThird(self, f):
        self.caller.responses.append(None)
        log.err()
        reactor.stop()
    #======================

class CommandChannel(channel.SSHChannel):
    name = 'session'

    def __init__(self, command, lastcmd, *args, **kwargs):
        channel.SSHChannel.__init__(self, *args, **kwargs)
        self.command = command
        self.lastcmd = lastcmd
        self.data = ""

    def channelOpen(self, data):
        self.conn.sendRequest(self, 'exec', common.NS(self.command), 
wantReply=True).addCallback(self._gotResponse)

    def _gotResponse(self, _):
        #print "RESPONSE"
        self.conn.sendEOF(self)

    def dataReceived(self, data):
        #print "Data Received:", data
        self.data += data

    def closed(self):
        self.conn.d.callback(self.data)
        self.loseConnection()
        ##        if self.lastcmd:
        ##            print "closing reactor."
        ##            reactor.stop()

class ClientCommandFactory(protocol.ClientFactory):
    def __init__(self, username, password, cmds, caller):
        self.username = username
        self.password = password
        self.cmds = cmds
        self.caller = caller

    def buildProtocol(self, addr):
        protocol = ClientCommandTransport(self.username, self.password, 
self.cmds, self.caller)
        return protocol

class SSH():
    """ Contains a SSH connection, runs commands, and stores results. """
    def __init__(self, host, username, password, cmds):
        self.host = host
        self.username = username
        self.password = password
        self.cmds = cmds
        self.responses = []
        self.run_commands()

    def run_commands(self):
        factory = ClientCommandFactory(self.username, self.password, 
self.cmds, self)
        reactor.connectTCP(self.host, 22, factory)
        reactor.run()

myssh = SSH("my.host.com", "myacct", "mypasswd", ["id; su - root; 
myrootpasswd; id", "pwd", "ls -l"])

print "=" * 25
for i, response in enumerate(myssh.responses):
    print i, response
    print "=" * 25

print "\nDone."

[Twisted-Python] How to switch users in SSH session.

Paul_S_Johnson＠mnb.uscourts.gov