Edit File: client.py
# Copyright (C) 2006-2007 Robey Pointer <robeypointer@gmail.com> # # This file is part of paramiko. # # Paramiko is free software; you can redistribute it and/or modify it under the # terms of the GNU Lesser General Public License as published by the Free # Software Foundation; either version 2.1 of the License, or (at your option) # any later version. # # Paramiko is distributed in the hope that it will be useful, but WITHOUT ANY # WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR # A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more # details. # # You should have received a copy of the GNU Lesser General Public License # along with Paramiko; if not, write to the Free Software Foundation, Inc., # 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. """ SSH client & key policies """ from binascii import hexlify import getpass import os import socket import warnings from errno import ECONNREFUSED, EHOSTUNREACH from paramiko.agent import Agent from paramiko.common import DEBUG from paramiko.config import SSH_PORT from paramiko.dsskey import DSSKey from paramiko.ecdsakey import ECDSAKey from paramiko.hostkeys import HostKeys from paramiko.py3compat import string_types from paramiko.resource import ResourceManager from paramiko.rsakey import RSAKey from paramiko.ssh_exception import ( SSHException, BadHostKeyException, NoValidConnectionsError ) from paramiko.transport import Transport from paramiko.util import retry_on_signal, ClosingContextManager class SSHClient (ClosingContextManager): """ A high-level representation of a session with an SSH server. This class wraps `.Transport`, `.Channel`, and `.SFTPClient` to take care of most aspects of authenticating and opening channels. A typical use case is:: client = SSHClient() client.load_system_host_keys() client.connect('ssh.example.com') stdin, stdout, stderr = client.exec_command('ls -l') You may pass in explicit overrides for authentication and server host key checking. The default mechanism is to try to use local key files or an SSH agent (if one is running). Instances of this class may be used as context managers. .. versionadded:: 1.6 """ def __init__(self): """ Create a new SSHClient. """ self._system_host_keys = HostKeys() self._host_keys = HostKeys() self._host_keys_filename = None self._log_channel = None self._policy = RejectPolicy() self._transport = None self._agent = None def load_system_host_keys(self, filename=None): """ Load host keys from a system (read-only) file. Host keys read with this method will not be saved back by `save_host_keys`. This method can be called multiple times. Each new set of host keys will be merged with the existing set (new replacing old if there are conflicts). If ``filename`` is left as ``None``, an attempt will be made to read keys from the user's local "known hosts" file, as used by OpenSSH, and no exception will be raised if the file can't be read. This is probably only useful on posix. :param str filename: the filename to read, or ``None`` :raises IOError: if a filename was provided and the file could not be read """ if filename is None: # try the user's .ssh key file, and mask exceptions filename = os.path.expanduser('~/.ssh/known_hosts') try: self._system_host_keys.load(filename) except IOError: pass return self._system_host_keys.load(filename) def load_host_keys(self, filename): """ Load host keys from a local host-key file. Host keys read with this method will be checked after keys loaded via `load_system_host_keys`, but will be saved back by `save_host_keys` (so they can be modified). The missing host key policy `.AutoAddPolicy` adds keys to this set and saves them, when connecting to a previously-unknown server. This method can be called multiple times. Each new set of host keys will be merged with the existing set (new replacing old if there are conflicts). When automatically saving, the last hostname is used. :param str filename: the filename to read :raises IOError: if the filename could not be read """ self._host_keys_filename = filename self._host_keys.load(filename) def save_host_keys(self, filename): """ Save the host keys back to a file. Only the host keys loaded with `load_host_keys` (plus any added directly) will be saved -- not any host keys loaded with `load_system_host_keys`. :param str filename: the filename to save to :raises IOError: if the file could not be written """ # update local host keys from file (in case other SSH clients # have written to the known_hosts file meanwhile. if self._host_keys_filename is not None: self.load_host_keys(self._host_keys_filename) with open(filename, 'w') as f: for hostname, keys in self._host_keys.items(): for keytype, key in keys.items(): f.write('%s %s %s\n' % (hostname, keytype, key.get_base64())) def get_host_keys(self): """ Get the local `.HostKeys` object. This can be used to examine the local host keys or change them. :return: the local host keys as a `.HostKeys` object. """ return self._host_keys def set_log_channel(self, name): """ Set the channel for logging. The default is ``"paramiko.transport"`` but it can be set to anything you want. :param str name: new channel name for logging """ self._log_channel = name def set_missing_host_key_policy(self, policy): """ Set policy to use when connecting to servers without a known host key. Specifically: * A **policy** is an instance of a "policy class", namely some subclass of `.MissingHostKeyPolicy` such as `.RejectPolicy` (the default), `.AutoAddPolicy`, `.WarningPolicy`, or a user-created subclass. .. note:: This method takes class **instances**, not **classes** themselves. Thus it must be called as e.g. ``.set_missing_host_key_policy(WarningPolicy())`` and *not* ``.set_missing_host_key_policy(WarningPolicy)``. * A host key is **known** when it appears in the client object's cached host keys structures (those manipulated by `load_system_host_keys` and/or `load_host_keys`). :param .MissingHostKeyPolicy policy: the policy to use when receiving a host key from a previously-unknown server """ self._policy = policy def _families_and_addresses(self, hostname, port): """ Yield pairs of address families and addresses to try for connecting. :param str hostname: the server to connect to :param int port: the server port to connect to :returns: Yields an iterable of ``(family, address)`` tuples """ guess = True addrinfos = socket.getaddrinfo(hostname, port, socket.AF_UNSPEC, socket.SOCK_STREAM) for (family, socktype, proto, canonname, sockaddr) in addrinfos: if socktype == socket.SOCK_STREAM: yield family, sockaddr guess = False # some OS like AIX don't indicate SOCK_STREAM support, so just guess. :( # We only do this if we did not get a single result marked as socktype == SOCK_STREAM. if guess: for family, _, _, _, sockaddr in addrinfos: yield family, sockaddr def connect( self, hostname, port=SSH_PORT, username=None, password=None, pkey=None, key_filename=None, timeout=None, allow_agent=True, look_for_keys=True, compress=False, sock=None, gss_auth=False, gss_kex=False, gss_deleg_creds=True, gss_host=None, banner_timeout=None ): """ Connect to an SSH server and authenticate to it. The server's host key is checked against the system host keys (see `load_system_host_keys`) and any local host keys (`load_host_keys`). If the server's hostname is not found in either set of host keys, the missing host key policy is used (see `set_missing_host_key_policy`). The default policy is to reject the key and raise an `.SSHException`. Authentication is attempted in the following order of priority: - The ``pkey`` or ``key_filename`` passed in (if any) - Any key we can find through an SSH agent - Any "id_rsa", "id_dsa" or "id_ecdsa" key discoverable in ``~/.ssh/`` - Plain username/password auth, if a password was given If a private key requires a password to unlock it, and a password is passed in, that password will be used to attempt to unlock the key. :param str hostname: the server to connect to :param int port: the server port to connect to :param str username: the username to authenticate as (defaults to the current local username) :param str password: a password to use for authentication or for unlocking a private key :param .PKey pkey: an optional private key to use for authentication :param str key_filename: the filename, or list of filenames, of optional private key(s) to try for authentication :param float timeout: an optional timeout (in seconds) for the TCP connect :param bool allow_agent: set to False to disable connecting to the SSH agent :param bool look_for_keys: set to False to disable searching for discoverable private key files in ``~/.ssh/`` :param bool compress: set to True to turn on compression :param socket sock: an open socket or socket-like object (such as a `.Channel`) to use for communication to the target host :param bool gss_auth: ``True`` if you want to use GSS-API authentication :param bool gss_kex: Perform GSS-API Key Exchange and user authentication :param bool gss_deleg_creds: Delegate GSS-API client credentials or not :param str gss_host: The targets name in the kerberos database. default: hostname :param float banner_timeout: an optional timeout (in seconds) to wait for the SSH banner to be presented. :raises BadHostKeyException: if the server's host key could not be verified :raises AuthenticationException: if authentication failed :raises SSHException: if there was any other error connecting or establishing an SSH session :raises socket.error: if a socket error occurred while connecting .. versionchanged:: 1.15 Added the ``banner_timeout``, ``gss_auth``, ``gss_kex``, ``gss_deleg_creds`` and ``gss_host`` arguments. """ if not sock: errors = {} # Try multiple possible address families (e.g. IPv4 vs IPv6) to_try = list(self._families_and_addresses(hostname, port)) for af, addr in to_try: try: sock = socket.socket(af, socket.SOCK_STREAM) if timeout is not None: try: sock.settimeout(timeout) except: pass retry_on_signal(lambda: sock.connect(addr)) # Break out of the loop on success break except socket.error as e: # Raise anything that isn't a straight up connection error # (such as a resolution error) if e.errno not in (ECONNREFUSED, EHOSTUNREACH): raise # Capture anything else so we know how the run looks once # iteration is complete. Retain info about which attempt # this was. errors[addr] = e # Make sure we explode usefully if no address family attempts # succeeded. We've no way of knowing which error is the "right" # one, so we construct a hybrid exception containing all the real # ones, of a subclass that client code should still be watching for # (socket.error) if len(errors) == len(to_try): raise NoValidConnectionsError(errors) t = self._transport = Transport(sock, gss_kex=gss_kex, gss_deleg_creds=gss_deleg_creds) t.use_compression(compress=compress) if gss_kex and gss_host is None: t.set_gss_host(hostname) elif gss_kex and gss_host is not None: t.set_gss_host(gss_host) else: pass if self._log_channel is not None: t.set_log_channel(self._log_channel) if banner_timeout is not None: t.banner_timeout = banner_timeout t.start_client(timeout=timeout) ResourceManager.register(self, t) server_key = t.get_remote_server_key() keytype = server_key.get_name() if port == SSH_PORT: server_hostkey_name = hostname else: server_hostkey_name = "[%s]:%d" % (hostname, port) # If GSS-API Key Exchange is performed we are not required to check the # host key, because the host is authenticated via GSS-API / SSPI as # well as our client. if not self._transport.use_gss_kex: our_server_key = self._system_host_keys.get(server_hostkey_name, {}).get(keytype, None) if our_server_key is None: our_server_key = self._host_keys.get(server_hostkey_name, {}).get(keytype, None) if our_server_key is None: # will raise exception if the key is rejected; let that fall out self._policy.missing_host_key(self, server_hostkey_name, server_key) # if the callback returns, assume the key is ok our_server_key = server_key if server_key != our_server_key: raise BadHostKeyException(hostname, server_key, our_server_key) if username is None: username = getpass.getuser() if key_filename is None: key_filenames = [] elif isinstance(key_filename, string_types): key_filenames = [key_filename] else: key_filenames = key_filename if gss_host is None: gss_host = hostname self._auth(username, password, pkey, key_filenames, allow_agent, look_for_keys, gss_auth, gss_kex, gss_deleg_creds, gss_host) def close(self): """ Close this SSHClient and its underlying `.Transport`. .. warning:: Failure to do this may, in some situations, cause your Python interpreter to hang at shutdown (often due to race conditions). It's good practice to `close` your client objects anytime you're done using them, instead of relying on garbage collection. """ if self._transport is None: return self._transport.close() self._transport = None if self._agent is not None: self._agent.close() self._agent = None def exec_command( self, command, bufsize=-1, timeout=None, get_pty=False, environment=None, ): """ Execute a command on the SSH server. A new `.Channel` is opened and the requested command is executed. The command's input and output streams are returned as Python ``file``-like objects representing stdin, stdout, and stderr. :param str command: the command to execute :param int bufsize: interpreted the same way as by the built-in ``file()`` function in Python :param int timeout: set command's channel timeout. See `Channel.settimeout`.settimeout :param dict environment: a dict of shell environment variables, to be merged into the default environment that the remote command executes within. .. warning:: Servers may silently reject some environment variables; see the warning in `.Channel.set_environment_variable` for details. :return: the stdin, stdout, and stderr of the executing command, as a 3-tuple :raises SSHException: if the server fails to execute the command """ chan = self._transport.open_session(timeout=timeout) if get_pty: chan.get_pty() chan.settimeout(timeout) if environment: chan.update_environment(environment) chan.exec_command(command) stdin = chan.makefile('wb', bufsize) stdout = chan.makefile('r', bufsize) stderr = chan.makefile_stderr('r', bufsize) return stdin, stdout, stderr def invoke_shell(self, term='vt100', width=80, height=24, width_pixels=0, height_pixels=0, environment=None): """ Start an interactive shell session on the SSH server. A new `.Channel` is opened and connected to a pseudo-terminal using the requested terminal type and size. :param str term: the terminal type to emulate (for example, ``"vt100"``) :param int width: the width (in characters) of the terminal window :param int height: the height (in characters) of the terminal window :param int width_pixels: the width (in pixels) of the terminal window :param int height_pixels: the height (in pixels) of the terminal window :param dict environment: the command's environment :return: a new `.Channel` connected to the remote shell :raises SSHException: if the server fails to invoke a shell """ chan = self._transport.open_session() chan.get_pty(term, width, height, width_pixels, height_pixels) chan.invoke_shell() return chan def open_sftp(self): """ Open an SFTP session on the SSH server. :return: a new `.SFTPClient` session object """ return self._transport.open_sftp_client() def get_transport(self): """ Return the underlying `.Transport` object for this SSH connection. This can be used to perform lower-level tasks, like opening specific kinds of channels. :return: the `.Transport` for this connection """ return self._transport def _auth(self, username, password, pkey, key_filenames, allow_agent, look_for_keys, gss_auth, gss_kex, gss_deleg_creds, gss_host): """ Try, in order: - The key passed in, if one was passed in. - Any key we can find through an SSH agent (if allowed). - Any "id_rsa", "id_dsa" or "id_ecdsa" key discoverable in ~/.ssh/ (if allowed). - Plain username/password auth, if a password was given. (The password might be needed to unlock a private key, or for two-factor authentication [for which it is required].) """ saved_exception = None two_factor = False allowed_types = set() two_factor_types = set(['keyboard-interactive','password']) # If GSS-API support and GSS-PI Key Exchange was performed, we attempt # authentication with gssapi-keyex. if gss_kex and self._transport.gss_kex_used: try: self._transport.auth_gssapi_keyex(username) return except Exception as e: saved_exception = e # Try GSS-API authentication (gssapi-with-mic) only if GSS-API Key # Exchange is not performed, because if we use GSS-API for the key # exchange, there is already a fully established GSS-API context, so # why should we do that again? if gss_auth: try: self._transport.auth_gssapi_with_mic(username, gss_host, gss_deleg_creds) return except Exception as e: saved_exception = e if pkey is not None: try: self._log(DEBUG, 'Trying SSH key %s' % hexlify(pkey.get_fingerprint())) allowed_types = set(self._transport.auth_publickey(username, pkey)) two_factor = (allowed_types & two_factor_types) if not two_factor: return except SSHException as e: saved_exception = e if not two_factor: for key_filename in key_filenames: for pkey_class in (RSAKey, DSSKey, ECDSAKey): try: key = pkey_class.from_private_key_file(key_filename, password) self._log(DEBUG, 'Trying key %s from %s' % (hexlify(key.get_fingerprint()), key_filename)) allowed_types = set(self._transport.auth_publickey(username, key)) two_factor = (allowed_types & two_factor_types) if not two_factor: return break except SSHException as e: saved_exception = e if not two_factor and allow_agent: if self._agent is None: self._agent = Agent() for key in self._agent.get_keys(): try: self._log(DEBUG, 'Trying SSH agent key %s' % hexlify(key.get_fingerprint())) # for 2-factor auth a successfully auth'd key password will return an allowed 2fac auth method allowed_types = set(self._transport.auth_publickey(username, key)) two_factor = (allowed_types & two_factor_types) if not two_factor: return break except SSHException as e: saved_exception = e if not two_factor: keyfiles = [] 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((RSAKey, rsa_key)) if os.path.isfile(dsa_key): keyfiles.append((DSSKey, dsa_key)) if os.path.isfile(ecdsa_key): keyfiles.append((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((RSAKey, rsa_key)) if os.path.isfile(dsa_key): keyfiles.append((DSSKey, dsa_key)) if os.path.isfile(ecdsa_key): keyfiles.append((ECDSAKey, ecdsa_key)) if not look_for_keys: keyfiles = [] for pkey_class, filename in keyfiles: try: key = pkey_class.from_private_key_file(filename, password) self._log(DEBUG, 'Trying discovered key %s in %s' % (hexlify(key.get_fingerprint()), filename)) # for 2-factor auth a successfully auth'd key will result in ['password'] allowed_types = set(self._transport.auth_publickey(username, key)) two_factor = (allowed_types & two_factor_types) if not two_factor: return break except (SSHException, IOError) as e: saved_exception = e if password is not None: try: self._transport.auth_password(username, password) return except SSHException as e: saved_exception = e elif two_factor: try: self._transport.auth_interactive_dumb(username) return except SSHException as e: saved_exception = e # if we got an auth-failed exception earlier, re-raise it if saved_exception is not None: raise saved_exception raise SSHException('No authentication methods available') def _log(self, level, msg): self._transport._log(level, msg) class MissingHostKeyPolicy (object): """ Interface for defining the policy that `.SSHClient` should use when the SSH server's hostname is not in either the system host keys or the application's keys. Pre-made classes implement policies for automatically adding the key to the application's `.HostKeys` object (`.AutoAddPolicy`), and for automatically rejecting the key (`.RejectPolicy`). This function may be used to ask the user to verify the key, for example. """ def missing_host_key(self, client, hostname, key): """ Called when an `.SSHClient` receives a server key for a server that isn't in either the system or local `.HostKeys` object. To accept the key, simply return. To reject, raised an exception (which will be passed to the calling application). """ pass class AutoAddPolicy (MissingHostKeyPolicy): """ Policy for automatically adding the hostname and new host key to the local `.HostKeys` object, and saving it. This is used by `.SSHClient`. """ def missing_host_key(self, client, hostname, key): client._host_keys.add(hostname, key.get_name(), key) if client._host_keys_filename is not None: client.save_host_keys(client._host_keys_filename) client._log(DEBUG, 'Adding %s host key for %s: %s' % (key.get_name(), hostname, hexlify(key.get_fingerprint()))) class RejectPolicy (MissingHostKeyPolicy): """ Policy for automatically rejecting the unknown hostname & key. This is used by `.SSHClient`. """ def missing_host_key(self, client, hostname, key): client._log(DEBUG, 'Rejecting %s host key for %s: %s' % (key.get_name(), hostname, hexlify(key.get_fingerprint()))) raise SSHException('Server %r not found in known_hosts' % hostname) class WarningPolicy (MissingHostKeyPolicy): """ Policy for logging a Python-style warning for an unknown host key, but accepting it. This is used by `.SSHClient`. """ def missing_host_key(self, client, hostname, key): warnings.warn('Unknown %s host key for %s: %s' % (key.get_name(), hostname, hexlify(key.get_fingerprint())))