# Copyright (C) 2006-2007 Jeff Forcier # # This file is part of ssh. # # 'ssh' 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. # # 'ssh' is distrubuted 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 'ssh'; if not, write to the Free Software Foundation, Inc., # 51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA. """ L{SSHClient}. """ from binascii import hexlify import getpass import os import socket import warnings from ssh.agent import Agent from ssh.common import * from ssh.dsskey import DSSKey from ssh.hostkeys import HostKeys from ssh.resource import ResourceManager from ssh.rsakey import RSAKey from ssh.ssh_exception import SSHException, BadHostKeyException from ssh.transport import Transport SSH_PORT = 22 class MissingHostKeyPolicy (object): """ Interface for defining the policy that L{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 L{HostKeys} object (L{AutoAddPolicy}), and for automatically rejecting the key (L{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 L{SSHClient} receives a server key for a server that isn't in either the system or local L{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 L{HostKeys} object, and saving it. This is used by L{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 L{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('Unknown server %s' % hostname) class WarningPolicy (MissingHostKeyPolicy): """ Policy for logging a python-style warning for an unknown host key, but accepting it. This is used by L{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()))) class SSHClient (object): """ A high-level representation of a session with an SSH server. This class wraps L{Transport}, L{Channel}, and L{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). @since: 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 L{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 C{filename} is left as C{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 filename: the filename to read, or C{None} @type filename: str @raise 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 I{after} keys loaded via L{load_system_host_keys}, but will be saved back by L{save_host_keys} (so they can be modified). The missing host key policy L{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 filename: the filename to read @type filename: str @raise 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 L{load_host_keys} (plus any added directly) will be saved -- not any host keys loaded with L{load_system_host_keys}. @param filename: the filename to save to @type filename: str @raise IOError: if the file could not be written """ f = open(filename, 'w') f.write('# SSH host keys collected by ssh\n') for hostname, keys in self._host_keys.iteritems(): for keytype, key in keys.iteritems(): f.write('%s %s %s\n' % (hostname, keytype, key.get_base64())) f.close() def get_host_keys(self): """ Get the local L{HostKeys} object. This can be used to examine the local host keys or change them. @return: the local host keys @rtype: L{HostKeys} """ return self._host_keys def set_log_channel(self, name): """ Set the channel for logging. The default is C{"ssh.transport"} but it can be set to anything you want. @param name: new channel name for logging @type name: str """ self._log_channel = name def set_missing_host_key_policy(self, policy): """ Set the policy to use when connecting to a server that doesn't have a host key in either the system or local L{HostKeys} objects. The default policy is to reject all unknown servers (using L{RejectPolicy}). You may substitute L{AutoAddPolicy} or write your own policy class. @param policy: the policy to use when receiving a host key from a previously-unknown server @type policy: L{MissingHostKeyPolicy} """ self._policy = policy 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): """ Connect to an SSH server and authenticate to it. The server's host key is checked against the system host keys (see L{load_system_host_keys}) and any local host keys (L{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 L{set_missing_host_key_policy}). The default policy is to reject the key and raise an L{SSHException}. Authentication is attempted in the following order of priority: - The C{pkey} or C{key_filename} passed in (if any) - Any key we can find through an SSH agent - Any "id_rsa" or "id_dsa" key discoverable in C{~/.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 hostname: the server to connect to @type hostname: str @param port: the server port to connect to @type port: int @param username: the username to authenticate as (defaults to the current local username) @type username: str @param password: a password to use for authentication or for unlocking a private key @type password: str @param pkey: an optional private key to use for authentication @type pkey: L{PKey} @param key_filename: the filename, or list of filenames, of optional private key(s) to try for authentication @type key_filename: str or list(str) @param timeout: an optional timeout (in seconds) for the TCP connect @type timeout: float @param allow_agent: set to False to disable connecting to the SSH agent @type allow_agent: bool @param look_for_keys: set to False to disable searching for discoverable private key files in C{~/.ssh/} @type look_for_keys: bool @param compress: set to True to turn on compression @type compress: bool @raise BadHostKeyException: if the server's host key could not be verified @raise AuthenticationException: if authentication failed @raise SSHException: if there was any other error connecting or establishing an SSH session @raise socket.error: if a socket error occurred while connecting """ for (family, socktype, proto, canonname, sockaddr) in socket.getaddrinfo(hostname, port, socket.AF_UNSPEC, socket.SOCK_STREAM): if socktype == socket.SOCK_STREAM: af = family addr = sockaddr break else: # some OS like AIX don't indicate SOCK_STREAM support, so just guess. :( af, _, _, _, addr = socket.getaddrinfo(hostname, port, socket.AF_UNSPEC, socket.SOCK_STREAM) sock = socket.socket(af, socket.SOCK_STREAM) if timeout is not None: try: sock.settimeout(timeout) except: pass sock.connect(addr) t = self._transport = Transport(sock) t.use_compression(compress=compress) if self._log_channel is not None: t.set_log_channel(self._log_channel) t.start_client() 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) 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, (str, unicode)): key_filenames = [ key_filename ] else: key_filenames = key_filename self._auth(username, password, pkey, key_filenames, allow_agent, look_for_keys) def close(self): """ Close this SSHClient and its underlying L{Transport}. """ if self._transport is None: return self._transport.close() self._transport = None if self._agent != None: self._agent.close() self._agent = None def exec_command(self, command, bufsize=-1): """ Execute a command on the SSH server. A new L{Channel} is opened and the requested command is executed. The command's input and output streams are returned as python C{file}-like objects representing stdin, stdout, and stderr. @param command: the command to execute @type command: str @param bufsize: interpreted the same way as by the built-in C{file()} function in python @type bufsize: int @return: the stdin, stdout, and stderr of the executing command @rtype: tuple(L{ChannelFile}, L{ChannelFile}, L{ChannelFile}) @raise SSHException: if the server fails to execute the command """ chan = self._transport.open_session() chan.exec_command(command) stdin = chan.makefile('wb', bufsize) stdout = chan.makefile('rb', bufsize) stderr = chan.makefile_stderr('rb', bufsize) return stdin, stdout, stderr def invoke_shell(self, term='vt100', width=80, height=24): """ Start an interactive shell session on the SSH server. A new L{Channel} is opened and connected to a pseudo-terminal using the requested terminal type and size. @param term: the terminal type to emulate (for example, C{"vt100"}) @type term: str @param width: the width (in characters) of the terminal window @type width: int @param height: the height (in characters) of the terminal window @type height: int @return: a new channel connected to the remote shell @rtype: L{Channel} @raise SSHException: if the server fails to invoke a shell """ chan = self._transport.open_session() chan.get_pty(term, width, height) chan.invoke_shell() return chan def open_sftp(self): """ Open an SFTP session on the SSH server. @return: a new SFTP session object @rtype: L{SFTPClient} """ return self._transport.open_sftp_client() def get_transport(self): """ Return the underlying L{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 @rtype: L{Transport} """ return self._transport def _auth(self, username, password, pkey, key_filenames, allow_agent, look_for_keys): """ 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" or "id_dsa" 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.) """ saved_exception = None if pkey is not None: try: self._log(DEBUG, 'Trying SSH key %s' % hexlify(pkey.get_fingerprint())) self._transport.auth_publickey(username, pkey) return except SSHException, e: saved_exception = e for key_filename in key_filenames: for pkey_class in (RSAKey, DSSKey): 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)) self._transport.auth_publickey(username, key) return except SSHException, e: saved_exception = e if allow_agent: if self._agent == None: self._agent = Agent() for key in self._agent.get_keys(): try: self._log(DEBUG, 'Trying SSH agent key %s' % hexlify(key.get_fingerprint())) self._transport.auth_publickey(username, key) return except SSHException, e: saved_exception = e keyfiles = [] rsa_key = os.path.expanduser('~/.ssh/id_rsa') dsa_key = os.path.expanduser('~/.ssh/id_dsa') if os.path.isfile(rsa_key): keyfiles.append((RSAKey, rsa_key)) if os.path.isfile(dsa_key): keyfiles.append((DSSKey, dsa_key)) # look in ~/ssh/ for windows users: rsa_key = os.path.expanduser('~/ssh/id_rsa') dsa_key = os.path.expanduser('~/ssh/id_dsa') if os.path.isfile(rsa_key): keyfiles.append((RSAKey, rsa_key)) if os.path.isfile(dsa_key): keyfiles.append((DSSKey, dsa_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)) self._transport.auth_publickey(username, key) return except SSHException, e: saved_exception = e except IOError, e: saved_exception = e if password is not None: try: self._transport.auth_password(username, password) return except SSHException, 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)