"""
This module handles SSH Connections
"""
import subprocess
class SshAgentException(Exception):
"""
Raised if an SSH Agent isn't running (Normally the SPA client should invoke the agent
before trying to execute anythign or create any tunnels)
"""
pass
class SshValidationException(Exception):
"""
Raised if any parameters passed to SSH don't look valid,
eg hostnames are not hostnames, ports are not numbers, usernames are
not the correct format
"""
pass
class SshCtrlException(Exception):
"""
Raised if the ssh control socket is not valid.
"""
pass
class Ssh:
"""
Ssh class can execute or create tunnelstat
"""
@staticmethod
def validate_port(port):
"validate that the port we're being asked to connect to is an integer"
try:
port = int(port)
except:
raise SshValidationException("port number {} was not an integer".format(port))
@staticmethod
def validate_username(user):
"""
ensure that the username conforms to posix standards
Some systems do not conform to this standard, and linux still works
but for the moment, lets assume they do conform.
"""
import re
username_re = re.compile(r'^[a-z_]([a-z0-9_-]{0,31}|[a-z0-9_\.-]{0,30}\$)$')
if not username_re.match(user):
raise SshValidationException("username {} is not valid according to " \
"posix standards".format(user))
@staticmethod
def validate_hostname(host):
"ensure that the hostname at least conforms to naming standards"
import re
hostname_re = re.compile(r'^[a-z0-9_\.-]+$')
if not hostname_re.match(host):
raise SshValidationException("hostname {} is not valid".format(host))
@staticmethod
def validate_command(cmd):
"""So in theory, due the the format of the Popen command
we can take any input as a commnand to execute on the login host, including
; and other forms of injection,
and the worst that can happen is the user screws up their own account
"""
pass
@staticmethod
def get_ctrl_master_socket(sess, host, user):
"""
Returns the socket for the control master process
Opens it if needed.
"""
import os
import stat
ctrlsocket = "/tmp/cm-{}-{}".format(user,host)
try:
mode = os.stat(ctrlsocket).st_mode
except FileNotFoundError:
mode = None
if mode is None:
ctrlsocket = "/tmp/cm-{}-{}".format(user,host)
sshcmd = ["ssh", '-o', 'StrictHostKeyChecking=no',
"-S", ctrlsocket,
"-M", '-o', 'ControlPersist=10m',
'-l', user, host]
env = os.environ.copy()
if sess.socket is None:
raise SshAgentException("No ssh-agent yet")
env['SSH_AUTH_SOCK'] = sess.socket
ctrl_p = subprocess.Popen(sshcmd,
stdout=subprocess.PIPE, stderr=subprocess.PIPE,
stdin=subprocess.PIPE, env=env)
sess.pids.append(ctrl_p.pid)
try:
mode = os.stat(ctrlsocket).st_mode
except FileNotFoundError:
mode = None
if not stat.S_ISSOCK(mode):
raise SshCtrlException()
return ctrlsocket
@staticmethod
def execute(sess, host, user, cmd, stdin=None):
"""
execute the command cmd on the host via ssh
# assume the environment is already setup with an
# SSH_AUTH_SOCK that allows login
"""
import os
if cmd is None and stdin is None:
return {'stdout': b'', 'stderr': b'No command given to execute'}
env = os.environ.copy()
if sess.socket is None:
raise SshAgentException("No ssh-agent yet")
env['SSH_AUTH_SOCK'] = sess.socket
Ssh.validate_username(user)
Ssh.validate_hostname(host)
Ssh.validate_command(cmd)
ctrlsocket = Ssh.get_ctrl_master_socket(sess, host, user)
exec_p = subprocess.Popen(['ssh', '-A', '-o', 'Stricthostkeychecking=no',
'-S', ctrlsocket,
'-l', user, host, cmd],
stdout=subprocess.PIPE, stderr=subprocess.PIPE,
stdin=subprocess.PIPE, env=env)
if stdin is not None:
(stdout, stderr) = exec_p.communicate(stdin.encode())
else:
(stdout, stderr) = exec_p.communicate()
return {'stdout':stdout, 'stderr':stderr}
@staticmethod
def tunnel(sess, port, batchhost, user, host, internalfirewall = True, localbind = True, authtok = None):
"""
the ProxyCommand is used if the server we run on the batch host is only
addressable on localhost
e.g. jupyter in its default config runs on localhost:8888 so a web
browser on the login node can not connect to it
If the server port is directly accessible from the login host (eg the
ssh server port is directly accessible) or the batchhost IS the login host
(i.e. batchhost = localhost) we can use -O forward -S <control socket>
"""
import os
import logging
logger = logging.getLogger()
logger.debug('entering Ssh.tunnel')
env = os.environ.copy()
env['SSH_AUTH_SOCK'] = sess.socket
Ssh.validate_port(port)
Ssh.validate_hostname(batchhost)
Ssh.validate_username(user)
Ssh.validate_hostname(host)
ctrlsocket = Ssh.get_ctrl_master_socket(sess, host, user)
logger.debug('Ssh.tunnel, got ctrlsocket')
localport = Ssh.get_free_port()
if port == 22 or (not internalfirewall and not localbind):
# Can we use the existing control master connection and just add a
# port forward to the batch node
sshcmd = ['ssh', '-o', 'Stricthostkeychecking=no', '-N',
'-L', '{localport}:{batchhost}:{port}'.
format(port=port, localport=localport, batchhost=batchhost),
'-O', 'forward', '-S', ctrlsocket,
'-l', user, host]
else:
# Create an ssh tunnel to the batch node using a proxycommand.
# The proxy command should utilise
# the existing control master connection
proxycmd = "ssh -o Stricthostkeychecking=no {user}@{host} -W {batchhost}:22 -S {ctrlsocket}".format(
user=user, host=host,
ctrlsocket=ctrlsocket,
batchhost=batchhost)
sshcmd = ['ssh', '-o', 'Stricthostkeychecking=no', '-N',
'-L', '{localport}:localhost:{port}'.
format(port=port, localport=localport),
'-o', "ProxyCommand={}".format(proxycmd),
'-l', user, batchhost]
logger.debug('Ssh.tunnel: attempting command {}'.format(sshcmd))
tunnel_p = subprocess.Popen(sshcmd, env=env)
logger.debug('Ssh.tunnel: waiting for the tunnel to connect before returning')
Ssh.wait_for_tunnel(localport)
if sess.port is None:
sess.port = {}
sess.port.update({authtok: localport})
sess.pids.append(tunnel_p.pid)
logger.debug('Ssh.tunnel: tunnel established, returning')
return localport, [tunnel_p.pid]
# @staticmethod
# def addkey(sess, key, cert):
# ""
# pass
@staticmethod
def wait_for_tunnel(localport):
"""
# In order to avoid a race condition, we wait for the tunnel to be established
"""
import socket
notopen = True
while notopen:
ssock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
ssock.setblocking(True)
try:
ssock.connect(('127.0.0.1', localport))
notopen = False
ssock.close()
except socket.error:
ssock.close()
@staticmethod
def get_free_port():
"""
# Finds a port which the local server can listen on.
"""
import socket
serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
for testport in range(1025, 65500):
try:
serversocket.bind(('127.0.0.1', testport))
port = testport
serversocket.close()
return port
except OSError:
pass