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ssh.py
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ssh.py
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# Copyright 2012 Vaibhav Bajpai
# Copyright 2009 Shikhar Bhushan
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import base64
import getpass
import os
import re
import six
import sys
import socket
import threading
from binascii import hexlify
try:
import selectors
except ImportError:
import selectors2 as selectors
from ncclient.capabilities import Capabilities
from ncclient.logging_ import SessionLoggerAdapter
import paramiko
from ncclient.transport.errors import AuthenticationError, SSHError, SSHUnknownHostError
from ncclient.transport.session import Session
from ncclient.transport.parser import DefaultXMLParser
import logging
logger = logging.getLogger("ncclient.transport.ssh")
PORT_NETCONF_DEFAULT = 830
BUF_SIZE = 4096
#
# Define delimiters for chunks and messages for netconf 1.1 chunk enoding.
# When matched:
#
# * result.group(0) will contain whole matched string
# * result.group(1) will contain the digit string for a chunk
# * result.group(2) will be defined if '##' found
#
RE_NC11_DELIM = re.compile(br'\n(?:#([0-9]+)|(##))\n')
def default_unknown_host_cb(host, fingerprint):
"""An unknown host callback returns `True` if it finds the key acceptable, and `False` if not.
This default callback always returns `False`, which would lead to :meth:`connect` raising a :exc:`SSHUnknownHost` exception.
Supply another valid callback if you need to verify the host key programmatically.
*host* is the hostname that needs to be verified
*fingerprint* is a hex string representing the host key fingerprint, colon-delimited e.g. `"4b:69:6c:72:6f:79:20:77:61:73:20:68:65:72:65:21"`
"""
return False
def _colonify(fp):
fp = fp.decode('UTF-8')
finga = fp[:2]
for idx in range(2, len(fp), 2):
finga += ":" + fp[idx:idx+2]
return finga
if sys.version < '3':
from six import StringIO
else:
from io import BytesIO as StringIO
class SSHSession(Session):
"Implements a :rfc:`4742` NETCONF session over SSH."
def __init__(self, device_handler):
capabilities = Capabilities(device_handler.get_capabilities())
Session.__init__(self, capabilities)
self._host = None
self._host_keys = paramiko.HostKeys()
self._transport = None
self._connected = False
self._channel = None
self._channel_id = None
self._channel_name = None
self._buffer = StringIO()
self._device_handler = device_handler
self._message_list = []
self._closing = threading.Event()
self.parser = DefaultXMLParser(self) # SAX or DOM parser
self.logger = SessionLoggerAdapter(logger, {'session': self})
def _dispatch_message(self, raw):
# Provide basic response message
self.logger.info("Received message from host")
# Provide complete response from host at debug log level
self.logger.debug("Received:\n%s", raw)
return super(SSHSession, self)._dispatch_message(raw)
def _parse(self):
"Messages ae delimited by MSG_DELIM. The buffer could have grown by a maximum of BUF_SIZE bytes everytime this method is called. Retains state across method calls and if a byte has been read it will not be considered again."
return self.parser._parse10()
def load_known_hosts(self, filename=None):
"""Load host keys from an openssh :file:`known_hosts`-style file. Can
be called multiple times.
If *filename* is not specified, looks in the default locations i.e. :file:`~/.ssh/known_hosts` and :file:`~/ssh/known_hosts` for Windows.
"""
if filename is None:
filename = os.path.expanduser('~/.ssh/known_hosts')
try:
self._host_keys.load(filename)
except IOError:
# for windows
filename = os.path.expanduser('~/ssh/known_hosts')
try:
self._host_keys.load(filename)
except IOError:
pass
else:
self._host_keys.load(filename)
def close(self):
self._closing.set()
if self._transport.is_active():
self._transport.close()
# Wait for the transport thread to close.
while self.is_alive() and (self is not threading.current_thread()):
self.join(10)
if self._channel:
self._channel.close()
self._channel = None
self._connected = False
# REMEMBER to update transport.rst if sig. changes, since it is hardcoded there
def connect(
self,
host,
port = PORT_NETCONF_DEFAULT,
timeout = None,
unknown_host_cb = default_unknown_host_cb,
username = None,
password = None,
key_filename = None,
allow_agent = True,
hostkey_verify = True,
hostkey_b64 = None,
look_for_keys = True,
ssh_config = None,
sock_fd = None,
bind_addr = None,
sock = None,
keepalive = None,
environment = None):
"""Connect via SSH and initialize the NETCONF session. First attempts the publickey authentication method and then password authentication.
To disable attempting publickey authentication altogether, call with *allow_agent* and *look_for_keys* as `False`.
*host* is the hostname or IP address to connect to
*port* is by default 830 (PORT_NETCONF_DEFAULT), but some devices use the default SSH port of 22 so this may need to be specified
*timeout* is an optional timeout for socket connect
*unknown_host_cb* is called when the server host key is not recognized. It takes two arguments, the hostname and the fingerprint (see the signature of :func:`default_unknown_host_cb`)
*username* is the username to use for SSH authentication
*password* is the password used if using password authentication, or the passphrase to use for unlocking keys that require it
*key_filename* is a filename where a the private key to be used can be found
*allow_agent* enables querying SSH agent (if found) for keys
*hostkey_verify* enables hostkey verification from ~/.ssh/known_hosts
*hostkey_b64* only connect when server presents a public hostkey matching this (obtain from server /etc/ssh/ssh_host_*pub or ssh-keyscan)
*look_for_keys* enables looking in the usual locations for ssh keys (e.g. :file:`~/.ssh/id_*`)
*ssh_config* enables parsing of an OpenSSH configuration file, if set to its path, e.g. :file:`~/.ssh/config` or to True (in this case, use :file:`~/.ssh/config`).
*sock_fd* is an already open socket which shall be used for this connection. Useful for NETCONF outbound ssh. Use host=None together with a valid sock_fd number
*bind_addr* is a (local) source IP address to use, must be reachable from the remote device.
*sock* is an already open Python socket to be used for this connection.
*keepalive* Turn on/off keepalive packets (default is off). If this is set, after interval seconds without sending any data over the connection, a "keepalive" packet will be sent (and ignored by the remote host). This can be useful to keep connections alive over a NAT.
*environment* a dictionary containing the name and respective values to set
"""
if not (host or sock_fd or sock):
raise SSHError("Missing host, socket or socket fd")
self._host = host
# Optionally, parse .ssh/config
config = {}
if ssh_config is True:
ssh_config = "~/.ssh/config" if sys.platform != "win32" else "~/ssh/config"
if ssh_config is not None:
config = paramiko.SSHConfig()
with open(os.path.expanduser(ssh_config)) as ssh_config_file_obj:
config.parse(ssh_config_file_obj)
# Save default Paramiko SSH port so it can be reverted
paramiko_default_ssh_port = paramiko.config.SSH_PORT
# Change the default SSH port to the port specified by the user so expand_variables
# replaces %p with the passed in port rather than 22 (the defauld paramiko.config.SSH_PORT)
paramiko.config.SSH_PORT = port
config = config.lookup(host)
# paramiko.config.SSHconfig::expand_variables is called by lookup so we can set the SSH port
# back to the default
paramiko.config.SSH_PORT = paramiko_default_ssh_port
host = config.get("hostname", host)
if username is None:
username = config.get("user")
if key_filename is None:
key_filename = config.get("identityfile")
if timeout is None:
timeout = config.get("connecttimeout")
if timeout:
timeout = int(timeout)
if hostkey_verify:
userknownhostsfile = config.get("userknownhostsfile")
if userknownhostsfile:
self.load_known_hosts(os.path.expanduser(userknownhostsfile))
else:
self.load_known_hosts()
if username is None:
username = getpass.getuser()
if sock_fd is None and sock is None:
proxycommand = config.get("proxycommand")
if proxycommand:
self.logger.debug("Configuring Proxy. %s", proxycommand)
if not isinstance(proxycommand, six.string_types):
proxycommand = [os.path.expanduser(elem) for elem in proxycommand]
else:
proxycommand = os.path.expanduser(proxycommand)
sock = paramiko.proxy.ProxyCommand(proxycommand)
else:
for res in socket.getaddrinfo(host, port, socket.AF_UNSPEC, socket.SOCK_STREAM):
af, socktype, proto, canonname, sa = res
try:
sock = socket.socket(af, socktype, proto)
sock.settimeout(timeout)
except socket.error:
continue
try:
if bind_addr:
sock.bind((bind_addr, 0))
sock.connect(sa)
except socket.error:
sock.close()
continue
break
else:
raise SSHError("Could not open socket to %s:%s" % (host, port))
elif sock is None:
if sys.version_info[0] < 3:
s = socket.fromfd(int(sock_fd), socket.AF_INET, socket.SOCK_STREAM)
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, _sock=s)
else:
sock = socket.fromfd(int(sock_fd), socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(timeout)
self._transport = paramiko.Transport(sock)
self._transport.set_log_channel(logger.name)
if config.get("compression") == 'yes':
self._transport.use_compression()
if hostkey_b64:
# If we need to connect with a specific hostkey, negotiate for only its type
hostkey_obj = None
for key_cls in [paramiko.DSSKey, paramiko.Ed25519Key, paramiko.RSAKey, paramiko.ECDSAKey]:
try:
hostkey_obj = key_cls(data=base64.b64decode(hostkey_b64))
except paramiko.SSHException:
# Not a key of this type - try the next
pass
if not hostkey_obj:
# We've tried all known host key types and haven't found a suitable one to use - bail
raise SSHError("Couldn't find suitable paramiko key class for host key %s" % hostkey_b64)
self._transport._preferred_keys = [hostkey_obj.get_name()]
elif self._host_keys:
# Else set preferred host keys to those we possess for the host
# (avoids situation where known_hosts contains a valid key for the host, but that key type is not selected during negotiation)
known_host_keys_for_this_host = self._host_keys.lookup(host) or {}
host_port = '[%s]:%s' % (host, port)
known_host_keys_for_this_host.update(self._host_keys.lookup(host_port) or {})
if known_host_keys_for_this_host:
self._transport._preferred_keys = list(known_host_keys_for_this_host)
# Connect
try:
self._transport.start_client()
except paramiko.SSHException as e:
raise SSHError('Negotiation failed: %s' % e)
if hostkey_verify:
server_key_obj = self._transport.get_remote_server_key()
fingerprint = _colonify(hexlify(server_key_obj.get_fingerprint()))
is_known_host = False
# For looking up entries for nonstandard (22) ssh ports in known_hosts
# we enclose host in brackets and append port number
known_hosts_lookups = [host, '[%s]:%s' % (host, port)]
if hostkey_b64:
# If hostkey specified, remote host /must/ use that hostkey
if(hostkey_obj.get_name() == server_key_obj.get_name() and hostkey_obj.asbytes() == server_key_obj.asbytes()):
is_known_host = True
else:
# Check known_hosts
is_known_host = any(self._host_keys.check(lookup, server_key_obj) for lookup in known_hosts_lookups)
if not is_known_host and not unknown_host_cb(host, fingerprint):
raise SSHUnknownHostError(known_hosts_lookups[0], fingerprint)
# Authenticating with our private key/identity
if key_filename is None:
key_filenames = []
elif isinstance(key_filename, (str, bytes)):
key_filenames = [key_filename]
else:
key_filenames = key_filename
self._auth(username, password, key_filenames, allow_agent, look_for_keys)
self._connected = True # there was no error authenticating
self._closing.clear()
if keepalive:
self._transport.set_keepalive(keepalive)
# TODO: leopoul: Review, test, and if needed rewrite this part
subsystem_names = self._device_handler.get_ssh_subsystem_names()
for subname in subsystem_names:
self._channel = self._transport.open_session()
self._channel_id = self._channel.get_id()
channel_name = "%s-subsystem-%s" % (subname, str(self._channel_id))
self._channel.set_name(channel_name)
if environment:
try:
self._channel.update_environment(environment)
except paramiko.SSHException as e:
self.logger.info("%s (environment update rejected)", e)
handle_exception = self._device_handler.handle_connection_exceptions(self)
# Ignore the exception, since we continue to try the different
# subsystem names until we find one that can connect.
# have to handle exception for each vendor here
if not handle_exception:
continue
try:
self._channel.invoke_subsystem(subname)
except paramiko.SSHException as e:
self.logger.info("%s (subsystem request rejected)", e)
handle_exception = self._device_handler.handle_connection_exceptions(self)
# Ignore the exception, since we continue to try the different
# subsystem names until we find one that can connect.
# have to handle exception for each vendor here
if not handle_exception:
continue
self._channel_name = self._channel.get_name()
self._post_connect(timeout)
# for further upcoming RPC responses, vendor can chose their
# choice of parser. Say DOM or SAX
self.parser = self._device_handler.get_xml_parser(self)
return
raise SSHError("Could not open connection, possibly due to unacceptable"
" SSH subsystem name.")
def _auth(self, username, password, key_filenames, allow_agent,
look_for_keys):
saved_exception = None
for key_filename in key_filenames:
for cls in (paramiko.RSAKey, paramiko.DSSKey, paramiko.ECDSAKey, paramiko.Ed25519Key):
try:
key = cls.from_private_key_file(key_filename, password)
self.logger.debug("Trying key %s from %s",
hexlify(key.get_fingerprint()),
key_filename)
self._transport.auth_publickey(username, key)
return
except Exception as e:
saved_exception = e
self.logger.debug(e)
if allow_agent:
# resequence keys from agent using private key names
prepend_agent_keys=[]
append_agent_keys=list(paramiko.Agent().get_keys())
for key_filename in key_filenames:
pubkey_filename=key_filename.strip(".pub")+".pub"
try:
file_key=paramiko.PublicBlob.from_file(pubkey_filename).key_blob
except (FileNotFoundError, ValueError):
continue
for idx, agent_key in enumerate(append_agent_keys):
if agent_key.asbytes() == file_key:
self.logger.debug("Prioritising SSH agent key found in %s",key_filename )
prepend_agent_keys.append(append_agent_keys.pop(idx))
break
agent_keys=tuple(prepend_agent_keys+append_agent_keys)
for key in agent_keys:
try:
self.logger.debug("Trying SSH agent key %s",
hexlify(key.get_fingerprint()))
self._transport.auth_publickey(username, key)
return
except Exception as e:
saved_exception = e
self.logger.debug(e)
keyfiles = []
if look_for_keys:
rsa_key = os.path.expanduser("~/.ssh/id_rsa")
dsa_key = os.path.expanduser("~/.ssh/id_dsa")
ecdsa_key = os.path.expanduser("~/.ssh/id_ecdsa")
if os.path.isfile(rsa_key):
keyfiles.append((paramiko.RSAKey, rsa_key))
if os.path.isfile(dsa_key):
keyfiles.append((paramiko.DSSKey, dsa_key))
if os.path.isfile(ecdsa_key):
keyfiles.append((paramiko.ECDSAKey, ecdsa_key))
# look in ~/ssh/ for windows users:
rsa_key = os.path.expanduser("~/ssh/id_rsa")
dsa_key = os.path.expanduser("~/ssh/id_dsa")
ecdsa_key = os.path.expanduser("~/ssh/id_ecdsa")
if os.path.isfile(rsa_key):
keyfiles.append((paramiko.RSAKey, rsa_key))
if os.path.isfile(dsa_key):
keyfiles.append((paramiko.DSSKey, dsa_key))
if os.path.isfile(ecdsa_key):
keyfiles.append((paramiko.ECDSAKey, ecdsa_key))
for cls, filename in keyfiles:
try:
key = cls.from_private_key_file(filename, password)
self.logger.debug("Trying discovered key %s in %s",
hexlify(key.get_fingerprint()), filename)
self._transport.auth_publickey(username, key)
return
except Exception as e:
saved_exception = e
self.logger.debug(e)
if password is not None:
try:
self._transport.auth_password(username, password)
return
except Exception as e:
saved_exception = e
self.logger.debug(e)
if saved_exception is not None:
# need pep-3134 to do this right
raise AuthenticationError(repr(saved_exception))
raise AuthenticationError("No authentication methods available")
def _transport_read(self):
return self._channel.recv(BUF_SIZE)
def _transport_write(self, data):
return self._channel.send(data)
def _transport_register(self, selector, event):
selector.register(self._channel, event)
def _send_ready(self):
return self._channel.send_ready()
@property
def host(self):
"""Host this session is connected to, or None if not connected."""
if hasattr(self, '_host'):
return self._host
return None
@property
def transport(self):
"Underlying `paramiko.Transport <http://www.lag.net/paramiko/docs/paramiko.Transport-class.html>`_ object. This makes it possible to call methods like :meth:`~paramiko.Transport.set_keepalive` on it."
return self._transport