ssh.py

# (c) 2012, Michael DeHaan <michael.dehaan@gmail.com>
# Copyright 2015 Abhijit Menon-Sen <ams@2ndQuadrant.com>
#
# This file is part of Ansible
#
# Ansible is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Ansible 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
#
from __future__ import (absolute_import, division, print_function)
__metaclass__ = type

import errno
import fcntl
import os
import pipes
import pty
import select
import subprocess
import time

from ansible import constants as C
from ansible.errors import AnsibleError, AnsibleConnectionFailure, AnsibleFileNotFound
from ansible.plugins.connection import ConnectionBase
from ansible.utils.path import unfrackpath, makedirs_safe
from ansible.utils.unicode import to_bytes, to_unicode, to_str
from ansible.compat.six import text_type, binary_type

try:
    from __main__ import display
except ImportError:
    from ansible.utils.display import Display
    display = Display()

SSHPASS_AVAILABLE = None


class Connection(ConnectionBase):
    ''' ssh based connections '''

    transport = 'ssh'
    has_pipelining = True
    become_methods = frozenset(C.BECOME_METHODS).difference(['runas'])

    def __init__(self, *args, **kwargs):
        super(Connection, self).__init__(*args, **kwargs)

        self.host = self._play_context.remote_addr

    # The connection is created by running ssh/scp/sftp from the exec_command,
    # put_file, and fetch_file methods, so we don't need to do any connection
    # management here.

    def _connect(self):
        return self

    @staticmethod
    def _sshpass_available():
        global SSHPASS_AVAILABLE

        # We test once if sshpass is available, and remember the result. It
        # would be nice to use distutils.spawn.find_executable for this, but
        # distutils isn't always available; shutils.which() is Python3-only.

        if SSHPASS_AVAILABLE is None:
            try:
                p = subprocess.Popen(["sshpass"], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
                p.communicate()
                SSHPASS_AVAILABLE = True
            except OSError:
                SSHPASS_AVAILABLE = False

        return SSHPASS_AVAILABLE

    @staticmethod
    def _persistence_controls(command):
        '''
        Takes a command array and scans it for ControlPersist and ControlPath
        settings and returns two booleans indicating whether either was found.
        This could be smarter, e.g. returning false if ControlPersist is 'no',
        but for now we do it simple way.
        '''

        controlpersist = False
        controlpath = False

        for arg in command:
            if 'controlpersist' in arg.lower():
                controlpersist = True
            elif 'controlpath' in arg.lower():
                controlpath = True

        return controlpersist, controlpath

    def _add_args(self, explanation, args):
        """
        Adds the given args to self._command and displays a caller-supplied
        explanation of why they were added.
        """
        self._command += args
        display.vvvvv('SSH: ' + explanation + ': (%s)' % ')('.join(args), host=self._play_context.remote_addr)

    def _build_command(self, binary, *other_args):
        '''
        Takes a binary (ssh, scp, sftp) and optional extra arguments and returns
        a command line as an array that can be passed to subprocess.Popen.
        '''

        self._command = []

        ## First, the command name.

        # If we want to use password authentication, we have to set up a pipe to
        # write the password to sshpass.

        if self._play_context.password:
            if not self._sshpass_available():
                raise AnsibleError("to use the 'ssh' connection type with passwords, you must install the sshpass program")

            self.sshpass_pipe = os.pipe()
            self._command += ['sshpass', '-d{0}'.format(self.sshpass_pipe[0])]

        self._command += [binary]

        ## Next, additional arguments based on the configuration.

        # sftp batch mode allows us to correctly catch failed transfers, but can
        # be disabled if the client side doesn't support the option. However,
        # sftp batch mode does not prompt for passwords so it must be disabled
        # if not using controlpersist and using sshpass
        if binary == 'sftp' and C.DEFAULT_SFTP_BATCH_MODE:
            if self._play_context.password:
                self._add_args('disable batch mode for sshpass', ['-o', 'BatchMode=no'])
            self._command += ['-b', '-']

        if self._play_context.verbosity > 3:
            self._command += ['-vvv']
        elif binary == 'ssh':
            # Older versions of ssh (e.g. in RHEL 6) don't accept sftp -q.
            self._command += ['-q']

        # Next, we add [ssh_connection]ssh_args from ansible.cfg.

        if self._play_context.ssh_args:
            args = self._split_ssh_args(self._play_context.ssh_args)
            self._add_args("ansible.cfg set ssh_args", args)

        # Now we add various arguments controlled by configuration file settings
        # (e.g. host_key_checking) or inventory variables (ansible_ssh_port) or
        # a combination thereof.

        if not C.HOST_KEY_CHECKING:
            self._add_args(
                "ANSIBLE_HOST_KEY_CHECKING/host_key_checking disabled",
                ("-o", "StrictHostKeyChecking=no")
            )

        if self._play_context.port is not None:
            self._add_args(
                "ANSIBLE_REMOTE_PORT/remote_port/ansible_port set",
                ("-o", "Port={0}".format(self._play_context.port))
            )

        key = self._play_context.private_key_file
        if key:
            self._add_args(
                "ANSIBLE_PRIVATE_KEY_FILE/private_key_file/ansible_ssh_private_key_file set",
                ("-o", "IdentityFile=\"{0}\"".format(os.path.expanduser(key)))
            )

        if not self._play_context.password:
            self._add_args(
                "ansible_password/ansible_ssh_pass not set", (
                    "-o", "KbdInteractiveAuthentication=no",
                    "-o", "PreferredAuthentications=gssapi-with-mic,gssapi-keyex,hostbased,publickey",
                    "-o", "PasswordAuthentication=no"
                )
            )

        user = self._play_context.remote_user
        if user:
            self._add_args(
                "ANSIBLE_REMOTE_USER/remote_user/ansible_user/user/-u set",
                ("-o", "User={0}".format(to_bytes(self._play_context.remote_user)))
            )

        self._add_args(
            "ANSIBLE_TIMEOUT/timeout set",
            ("-o", "ConnectTimeout={0}".format(self._play_context.timeout))
        )

        # Add in any common or binary-specific arguments from the PlayContext
        # (i.e. inventory or task settings or overrides on the command line).

        for opt in ['ssh_common_args', binary + '_extra_args']:
            attr = getattr(self._play_context, opt, None)
            if attr is not None:
                args = self._split_ssh_args(attr)
                self._add_args("PlayContext set %s" % opt, args)

        # Check if ControlPersist is enabled and add a ControlPath if one hasn't
        # already been set.

        controlpersist, controlpath = self._persistence_controls(self._command)

        if controlpersist:
            self._persistent = True

            if not controlpath:
                cpdir = unfrackpath('$HOME/.ansible/cp')

                # The directory must exist and be writable.
                makedirs_safe(cpdir, 0o700)
                if not os.access(cpdir, os.W_OK):
                    raise AnsibleError("Cannot write to ControlPath %s" % cpdir)

                args = ("-o", "ControlPath={0}".format(
                    to_bytes(C.ANSIBLE_SSH_CONTROL_PATH % dict(directory=cpdir)))
                )
                self._add_args("found only ControlPersist; added ControlPath", args)

        ## Finally, we add any caller-supplied extras.

        if other_args:
            self._command += other_args

        return self._command

    def _send_initial_data(self, fh, in_data):
        '''
        Writes initial data to the stdin filehandle of the subprocess and closes
        it. (The handle must be closed; otherwise, for example, "sftp -b -" will
        just hang forever waiting for more commands.)
        '''

        display.debug('Sending initial data')

        try:
            fh.write(in_data)
            fh.close()
        except (OSError, IOError):
            raise AnsibleConnectionFailure('SSH Error: data could not be sent to the remote host. Make sure this host can be reached over ssh')

        display.debug('Sent initial data (%d bytes)' % len(in_data))

    # Used by _run() to kill processes on failures
    @staticmethod
    def _terminate_process(p):
        """ Terminate a process, ignoring errors """
        try:
            p.terminate()
        except (OSError, IOError):
            pass

    # This is separate from _run() because we need to do the same thing for stdout
    # and stderr.
    def _examine_output(self, source, state, chunk, sudoable):
        '''
        Takes a string, extracts complete lines from it, tests to see if they
        are a prompt, error message, etc., and sets appropriate flags in self.
        Prompt and success lines are removed.

        Returns the processed (i.e. possibly-edited) output and the unprocessed
        remainder (to be processed with the next chunk) as strings.
        '''

        output = []
        for l in chunk.splitlines(True):
            suppress_output = False

            #display.debug("Examining line (source=%s, state=%s): '%s'" % (source, state, l.rstrip('\r\n')))
            if self._play_context.prompt and self.check_password_prompt(l):
                display.debug("become_prompt: (source=%s, state=%s): '%s'" % (source, state, l.rstrip('\r\n')))
                self._flags['become_prompt'] = True
                suppress_output = True
            elif self._play_context.success_key and self.check_become_success(l):
                display.debug("become_success: (source=%s, state=%s): '%s'" % (source, state, l.rstrip('\r\n')))
                self._flags['become_success'] = True
                suppress_output = True
            elif sudoable and self.check_incorrect_password(l):
                display.debug("become_error: (source=%s, state=%s): '%s'" % (source, state, l.rstrip('\r\n')))
                self._flags['become_error'] = True
            elif sudoable and self.check_missing_password(l):
                display.debug("become_nopasswd_error: (source=%s, state=%s): '%s'" % (source, state, l.rstrip('\r\n')))
                self._flags['become_nopasswd_error'] = True

            if not suppress_output:
                output.append(l)

        # The chunk we read was most likely a series of complete lines, but just
        # in case the last line was incomplete (and not a prompt, which we would
        # have removed from the output), we retain it to be processed with the
        # next chunk.

        remainder = ''
        if output and not output[-1].endswith('\n'):
            remainder = output[-1]
            output = output[:-1]

        return ''.join(output), remainder

    def _run(self, cmd, in_data, sudoable=True):
        '''
        Starts the command and communicates with it until it ends.
        '''

        display_cmd = map(to_unicode, map(pipes.quote, cmd))
        display.vvv(u'SSH: EXEC {0}'.format(u' '.join(display_cmd)), host=self.host)

        # Start the given command. If we don't need to pipeline data, we can try
        # to use a pseudo-tty (ssh will have been invoked with -tt). If we are
        # pipelining data, or can't create a pty, we fall back to using plain
        # old pipes.

        p = None

        if isinstance(cmd, (text_type, binary_type)):
            cmd = to_bytes(cmd)
        else:
            cmd = list(map(to_bytes, cmd))

        if not in_data:
            try:
                # Make sure stdin is a proper pty to avoid tcgetattr errors
                master, slave = pty.openpty()
                p = subprocess.Popen(cmd, stdin=slave, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
                stdin = os.fdopen(master, 'w', 0)
                os.close(slave)
            except (OSError, IOError):
                p = None

        if not p:
            p = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
            stdin = p.stdin

        # If we are using SSH password authentication, write the password into
        # the pipe we opened in _build_command.

        if self._play_context.password:
            os.close(self.sshpass_pipe[0])
            try:
                os.write(self.sshpass_pipe[1], "{0}\n".format(to_bytes(self._play_context.password)))
            except OSError as e:
                # Ignore broken pipe errors if the sshpass process has exited.
                if e.errno != errno.EPIPE or p.poll() is None:
                    raise
            os.close(self.sshpass_pipe[1])

        ## SSH state machine
        #
        # Now we read and accumulate output from the running process until it
        # exits. Depending on the circumstances, we may also need to write an
        # escalation password and/or pipelined input to the process.

        states = [
            'awaiting_prompt', 'awaiting_escalation', 'ready_to_send', 'awaiting_exit'
        ]

        # Are we requesting privilege escalation? Right now, we may be invoked
        # to execute sftp/scp with sudoable=True, but we can request escalation
        # only when using ssh. Otherwise we can send initial data straightaway.

        state = states.index('ready_to_send')
        if b'ssh' in cmd:
            if self._play_context.prompt:
                # We're requesting escalation with a password, so we have to
                # wait for a password prompt.
                state = states.index('awaiting_prompt')
                display.debug('Initial state: %s: %s' % (states[state], self._play_context.prompt))
            elif self._play_context.become and self._play_context.success_key:
                # We're requesting escalation without a password, so we have to
                # detect success/failure before sending any initial data.
                state = states.index('awaiting_escalation')
                display.debug('Initial state: %s: %s' % (states[state], self._play_context.success_key))

        # We store accumulated stdout and stderr output from the process here,
        # but strip any privilege escalation prompt/confirmation lines first.
        # Output is accumulated into tmp_*, complete lines are extracted into
        # an array, then checked and removed or copied to stdout or stderr. We
        # set any flags based on examining the output in self._flags.

        stdout = stderr = ''
        tmp_stdout = tmp_stderr = ''

        self._flags = dict(
            become_prompt=False, become_success=False,
            become_error=False, become_nopasswd_error=False
        )

        # select timeout should be longer than the connect timeout, otherwise
        # they will race each other when we can't connect, and the connect
        # timeout usually fails
        timeout = 2 + self._play_context.timeout
        rpipes = [p.stdout, p.stderr]
        for fd in rpipes:
            fcntl.fcntl(fd, fcntl.F_SETFL, fcntl.fcntl(fd, fcntl.F_GETFL) | os.O_NONBLOCK)

        # If we can send initial data without waiting for anything, we do so
        # before we call select.

        if states[state] == 'ready_to_send' and in_data:
            self._send_initial_data(stdin, in_data)
            state += 1

        while True:
            rfd, wfd, efd = select.select(rpipes, [], [], timeout)

            # We pay attention to timeouts only while negotiating a prompt.

            if not rfd:
                if state <= states.index('awaiting_escalation'):
                    # If the process has already exited, then it's not really a
                    # timeout; we'll let the normal error handling deal with it.
                    if p.poll() is not None:
                        break
                    self._terminate_process(p)
                    raise AnsibleError('Timeout (%ds) waiting for privilege escalation prompt: %s' % (timeout, stdout))

            # Read whatever output is available on stdout and stderr, and stop
            # listening to the pipe if it's been closed.

            if p.stdout in rfd:
                chunk = p.stdout.read()
                if chunk == '':
                    rpipes.remove(p.stdout)
                tmp_stdout += chunk
                display.debug("stdout chunk (state=%s):\n>>>%s<<<\n" % (state, chunk))

            if p.stderr in rfd:
                chunk = p.stderr.read()
                if chunk == '':
                    rpipes.remove(p.stderr)
                tmp_stderr += chunk
                display.debug("stderr chunk (state=%s):\n>>>%s<<<\n" % (state, chunk))

            # We examine the output line-by-line until we have negotiated any
            # privilege escalation prompt and subsequent success/error message.
            # Afterwards, we can accumulate output without looking at it.

            if state < states.index('ready_to_send'):
                if tmp_stdout:
                    output, unprocessed = self._examine_output('stdout', states[state], tmp_stdout, sudoable)
                    stdout += output
                    tmp_stdout = unprocessed

                if tmp_stderr:
                    output, unprocessed = self._examine_output('stderr', states[state], tmp_stderr, sudoable)
                    stderr += output
                    tmp_stderr = unprocessed
            else:
                stdout += tmp_stdout
                stderr += tmp_stderr
                tmp_stdout = tmp_stderr = ''

            # If we see a privilege escalation prompt, we send the password.
            # (If we're expecting a prompt but the escalation succeeds, we
            # didn't need the password and can carry on regardless.)

            if states[state] == 'awaiting_prompt':
                if self._flags['become_prompt']:
                    display.debug('Sending become_pass in response to prompt')
                    stdin.write('{0}\n'.format(to_bytes(self._play_context.become_pass )))
                    self._flags['become_prompt'] = False
                    state += 1
                elif self._flags['become_success']:
                    state += 1

            # We've requested escalation (with or without a password), now we
            # wait for an error message or a successful escalation.

            if states[state] == 'awaiting_escalation':
                if self._flags['become_success']:
                    display.debug('Escalation succeeded')
                    self._flags['become_success'] = False
                    state += 1
                elif self._flags['become_error']:
                    display.debug('Escalation failed')
                    self._terminate_process(p)
                    self._flags['become_error'] = False
                    raise AnsibleError('Incorrect %s password' % self._play_context.become_method)
                elif self._flags['become_nopasswd_error']:
                    display.debug('Escalation requires password')
                    self._terminate_process(p)
                    self._flags['become_nopasswd_error'] = False
                    raise AnsibleError('Missing %s password' % self._play_context.become_method)
                elif self._flags['become_prompt']:
                    # This shouldn't happen, because we should see the "Sorry,
                    # try again" message first.
                    display.debug('Escalation prompt repeated')
                    self._terminate_process(p)
                    self._flags['become_prompt'] = False
                    raise AnsibleError('Incorrect %s password' % self._play_context.become_method)

            # Once we're sure that the privilege escalation prompt, if any, has
            # been dealt with, we can send any initial data and start waiting
            # for output.

            if states[state] == 'ready_to_send':
                if in_data:
                    self._send_initial_data(stdin, in_data)
                state += 1

            # Now we're awaiting_exit: has the child process exited? If it has,
            # and we've read all available output from it, we're done.

            if p.poll() is not None:
                if not rpipes or not rfd:
                    break

                # When ssh has ControlMaster (+ControlPath/Persist) enabled, the
                # first connection goes into the background and we never see EOF
                # on stderr. If we see EOF on stdout and the process has exited,
                # we're probably done. We call select again with a zero timeout,
                # just to make certain we don't miss anything that may have been
                # written to stderr between the time we called select() and when
                # we learned that the process had finished.

                if p.stdout not in rpipes:
                    timeout = 0
                    continue

            # If the process has not yet exited, but we've already read EOF from
            # its stdout and stderr (and thus removed both from rpipes), we can
            # just wait for it to exit.

            elif not rpipes:
                p.wait()
                break

            # Otherwise there may still be outstanding data to read.

        # close stdin after process is terminated and stdout/stderr are read
        # completely (see also issue #848)
        stdin.close()

        if C.HOST_KEY_CHECKING:
            if cmd[0] == b"sshpass" and p.returncode == 6:
                raise AnsibleError('Using a SSH password instead of a key is not possible because Host Key checking is enabled and sshpass does not support this.  Please add this host\'s fingerprint to your known_hosts file to manage this host.')

        controlpersisterror = 'Bad configuration option: ControlPersist' in stderr or 'unknown configuration option: ControlPersist' in stderr
        if p.returncode != 0 and controlpersisterror:
            raise AnsibleError('using -c ssh on certain older ssh versions may not support ControlPersist, set ANSIBLE_SSH_ARGS="" (or ssh_args in [ssh_connection] section of the config file) before running again')

        if p.returncode == 255 and in_data:
            raise AnsibleConnectionFailure('SSH Error: data could not be sent to the remote host. Make sure this host can be reached over ssh')

        return (p.returncode, stdout, stderr)

    def _exec_command(self, cmd, in_data=None, sudoable=True):
        ''' run a command on the remote host '''

        super(Connection, self).exec_command(cmd, in_data=in_data, sudoable=sudoable)

        display.vvv(u"ESTABLISH SSH CONNECTION FOR USER: {0}".format(self._play_context.remote_user), host=self._play_context.remote_addr)

        # we can only use tty when we are not pipelining the modules. piping
        # data into /usr/bin/python inside a tty automatically invokes the
        # python interactive-mode but the modules are not compatible with the
        # interactive-mode ("unexpected indent" mainly because of empty lines)

        if not in_data and sudoable:
            args = ('ssh', '-tt', self.host, cmd)
        else:
            args = ('ssh', self.host, cmd)

        cmd = self._build_command(*args)
        (returncode, stdout, stderr) = self._run(cmd, in_data, sudoable=sudoable)

        return (returncode, stdout, stderr)

    #
    # Main public methods
    #
    def exec_command(self, *args, **kwargs):
        """
        Wrapper around _exec_command to retry in the case of an ssh failure

        Will retry if:
        * an exception is caught
        * ssh returns 255
        Will not retry if
        * remaining_tries is <2
        * retries limit reached
        """

        remaining_tries = int(C.ANSIBLE_SSH_RETRIES) + 1
        cmd_summary = "%s..." % args[0]
        for attempt in range(remaining_tries):
            try:
                return_tuple = self._exec_command(*args, **kwargs)
                # 0 = success
                # 1-254 = remote command return code
                # 255 = failure from the ssh command itself
                if return_tuple[0] != 255:
                    break
                else:
                    raise AnsibleConnectionFailure("Failed to connect to the host via ssh.")
            except (AnsibleConnectionFailure, Exception) as e:
                if attempt == remaining_tries - 1:
                    raise
                else:
                    pause = 2 ** attempt - 1
                    if pause > 30:
                        pause = 30

                    if isinstance(e, AnsibleConnectionFailure):
                        msg = "ssh_retry: attempt: %d, ssh return code is 255. cmd (%s), pausing for %d seconds" % (attempt, cmd_summary, pause)
                    else:
                        msg = "ssh_retry: attempt: %d, caught exception(%s) from cmd (%s), pausing for %d seconds" % (attempt, e, cmd_summary, pause)

                    display.vv(msg, host=self.host)

                    time.sleep(pause)
                    continue

        return return_tuple

    def put_file(self, in_path, out_path):
        ''' transfer a file from local to remote '''

        super(Connection, self).put_file(in_path, out_path)

        display.vvv(u"PUT {0} TO {1}".format(in_path, out_path), host=self.host)
        if not os.path.exists(to_bytes(in_path, errors='strict')):
            raise AnsibleFileNotFound("file or module does not exist: {0}".format(to_str(in_path)))

        # scp and sftp require square brackets for IPv6 addresses, but
        # accept them for hostnames and IPv4 addresses too.
        host = '[%s]' % self.host

        if C.DEFAULT_SCP_IF_SSH:
            cmd = self._build_command('scp', in_path, u'{0}:{1}'.format(host, pipes.quote(out_path)))
            in_data = None
        else:
            cmd = self._build_command('sftp', to_bytes(host))
            in_data = u"put {0} {1}\n".format(pipes.quote(in_path), pipes.quote(out_path))

        in_data = to_bytes(in_data, nonstring='passthru')
        (returncode, stdout, stderr) = self._run(cmd, in_data)

        if returncode != 0:
            raise AnsibleError("failed to transfer file to {0}:\n{1}\n{2}".format(to_str(out_path), to_str(stdout), to_str(stderr)))

    def fetch_file(self, in_path, out_path):
        ''' fetch a file from remote to local '''

        super(Connection, self).fetch_file(in_path, out_path)

        display.vvv(u"FETCH {0} TO {1}".format(in_path, out_path), host=self.host)

        # scp and sftp require square brackets for IPv6 addresses, but
        # accept them for hostnames and IPv4 addresses too.
        host = '[%s]' % self.host

        if C.DEFAULT_SCP_IF_SSH:
            cmd = self._build_command('scp', u'{0}:{1}'.format(host, pipes.quote(in_path)), out_path)
            in_data = None
        else:
            cmd = self._build_command('sftp', host)
            in_data = u"get {0} {1}\n".format(pipes.quote(in_path), pipes.quote(out_path))

        in_data = to_bytes(in_data, nonstring='passthru')
        (returncode, stdout, stderr) = self._run(cmd, in_data)

        if returncode != 0:
            raise AnsibleError("failed to transfer file from {0}:\n{1}\n{2}".format(in_path, stdout, stderr))

    def close(self):
        # If we have a persistent ssh connection (ControlPersist), we can ask it
        # to stop listening. Otherwise, there's nothing to do here.

        # TODO: reenable once winrm issues are fixed
        # temporarily disabled as we are forced to currently close connections after every task because of winrm
        # if self._connected and self._persistent:
        #     cmd = self._build_command('ssh', '-O', 'stop', self.host)
        #
        #     cmd = map(to_bytes, cmd)
        #     p = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        #     stdout, stderr = p.communicate()

        self._connected = False