/mandos/release

#!/usr/bin/python

# -*- mode: python; coding: utf-8 -*-

# 

# Mandos server - give out binary blobs to connecting clients.

# 

# This program is partly derived from an example program for an Avahi

# service publisher, downloaded from

# <http://avahi.org/wiki/PythonPublishExample>.  This includes the

# following functions: "AvahiService.add", "AvahiService.remove",

# "server_state_changed", "entry_group_state_changed", and some lines

# in "main".

# 

# Everything else is

# Copyright © 2007-2008 Teddy Hogeborn & Björn Påhlsson

# 

# This program 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.

#

#     This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

# 

# Contact the authors at <mandos@fukt.bsnet.se>.

# 

from __future__ import division

import SocketServer

import socket

import select

from optparse import OptionParser

import datetime

import errno

import gnutls.crypto

import gnutls.connection

import gnutls.errors

import gnutls.library.functions

import gnutls.library.constants

import gnutls.library.types

import ConfigParser

import sys

import re

import os

import signal

from sets import Set

import subprocess

import atexit

import stat

import logging

import logging.handlers

import dbus

import gobject

import avahi

from dbus.mainloop.glib import DBusGMainLoop

import ctypes

# Brief description of the operation of this program:

# 

# This server announces itself as a Zeroconf service.  Connecting

# clients use the TLS protocol, with the unusual quirk that this

# server program acts as a TLS "client" while a connecting client acts

# as a TLS "server".  The client (acting as a TLS "server") must

# supply an OpenPGP certificate, and the fingerprint of this

# certificate is used by this server to look up (in a list read from a

# file at start time) which binary blob to give the client.  No other

# authentication or authorization is done by this server.

logger = logging.Logger('mandos')

syslogger = logging.handlers.SysLogHandler\

            (facility = logging.handlers.SysLogHandler.LOG_DAEMON)

syslogger.setFormatter(logging.Formatter\

                        ('%(levelname)s: %(message)s'))

logger.addHandler(syslogger)

del syslogger

class AvahiError(Exception):

    def __init__(self, value):

        self.value = value

    def __str__(self):

        return repr(self.value)

class AvahiServiceError(AvahiError):

    pass

class AvahiGroupError(AvahiError):

    pass

class AvahiService(object):

    """

    interface: integer; avahi.IF_UNSPEC or an interface index.

               Used to optionally bind to the specified interface.

    name = string; Example: "Mandos"

    type = string; Example: "_mandos._tcp".

                   See <http://www.dns-sd.org/ServiceTypes.html>

    port = integer; what port to announce

    TXT = list of strings; TXT record for the service

    domain = string; Domain to publish on, default to .local if empty.

    host = string; Host to publish records for, default to localhost

                   if empty.

    max_renames = integer; maximum number of renames

    rename_count = integer; counter so we only rename after collisions

                   a sensible number of times

    """

    def __init__(self, interface = avahi.IF_UNSPEC, name = None,

                 type = None, port = None, TXT = None, domain = "",

                 host = "", max_renames = 12):

        """An Avahi (Zeroconf) service. """

        self.interface = interface

        self.name = name

        self.type = type

        self.port = port

        if TXT is None:

            self.TXT = []

        else:

            self.TXT = TXT

        self.domain = domain

        self.host = host

        self.rename_count = 0

    def rename(self):

        """Derived from the Avahi example code"""

        if self.rename_count >= self.max_renames:

            logger.critical(u"No suitable service name found after %i"

                            u" retries, exiting.", rename_count)

            raise AvahiServiceError("Too many renames")

        name = server.GetAlternativeServiceName(name)

        logger.notice(u"Changing name to %r ...", name)

        self.remove()

        self.add()

        self.rename_count += 1

    def remove(self):

        """Derived from the Avahi example code"""

        if group is not None:

            group.Reset()

    def add(self):

        """Derived from the Avahi example code"""

        global group

        if group is None:

            group = dbus.Interface\

                    (bus.get_object(avahi.DBUS_NAME,

                                    server.EntryGroupNew()),

                     avahi.DBUS_INTERFACE_ENTRY_GROUP)

            group.connect_to_signal('StateChanged',

                                    entry_group_state_changed)

        logger.debug(u"Adding service '%s' of type '%s' ...",

                     service.name, service.type)

        group.AddService(

                self.interface,         # interface

                avahi.PROTO_INET6,      # protocol

                dbus.UInt32(0),         # flags

                self.name, self.type,

                self.domain, self.host,

                dbus.UInt16(self.port),

                avahi.string_array_to_txt_array(self.TXT))

        group.Commit()

# From the Avahi example code:

group = None                            # our entry group

# End of Avahi example code

class Client(object):

    """A representation of a client host served by this server.

    Attributes:

    name:      string; from the config file, used in log messages

    fingerprint: string (40 or 32 hexadecimal digits); used to

                 uniquely identify the client

    secret:    bytestring; sent verbatim (over TLS) to client

    fqdn:      string (FQDN); available for use by the checker command

    created:   datetime.datetime(); object creation, not client host

    last_checked_ok: datetime.datetime() or None if not yet checked OK

    timeout:   datetime.timedelta(); How long from last_checked_ok

                                     until this client is invalid

    interval:  datetime.timedelta(); How often to start a new checker

    stop_hook: If set, called by stop() as stop_hook(self)

    checker:   subprocess.Popen(); a running checker process used

                                   to see if the client lives.

                                   'None' if no process is running.

    checker_initiator_tag: a gobject event source tag, or None

    stop_initiator_tag:    - '' -

    checker_callback_tag:  - '' -

    checker_command: string; External command which is run to check if

                     client lives.  %() expansions are done at

                     runtime with vars(self) as dict, so that for

                     instance %(name)s can be used in the command.

    Private attibutes:

    _timeout: Real variable for 'timeout'

    _interval: Real variable for 'interval'

    _timeout_milliseconds: Used when calling gobject.timeout_add()

    _interval_milliseconds: - '' -

    """

    def _set_timeout(self, timeout):

        "Setter function for 'timeout' attribute"

        self._timeout = timeout

        self._timeout_milliseconds = ((self.timeout.days

                                       * 24 * 60 * 60 * 1000)

                                      + (self.timeout.seconds * 1000)

                                      + (self.timeout.microseconds

                                         // 1000))

    timeout = property(lambda self: self._timeout,

                       _set_timeout)

    del _set_timeout

    def _set_interval(self, interval):

        "Setter function for 'interval' attribute"

        self._interval = interval

        self._interval_milliseconds = ((self.interval.days

                                        * 24 * 60 * 60 * 1000)

                                       + (self.interval.seconds

                                          * 1000)

                                       + (self.interval.microseconds

                                          // 1000))

    interval = property(lambda self: self._interval,

                        _set_interval)

    del _set_interval

    def __init__(self, name=None, stop_hook=None, fingerprint=None,

                 secret=None, secfile=None, fqdn=None, timeout=None,

                 interval=-1, checker=None):

        """Note: the 'checker' argument sets the 'checker_command'

        attribute and not the 'checker' attribute.."""

        self.name = name

        logger.debug(u"Creating client %r", self.name)

        # Uppercase and remove spaces from fingerprint

        # for later comparison purposes with return value of

        # the fingerprint() function

        self.fingerprint = fingerprint.upper().replace(u" ", u"")

        logger.debug(u"  Fingerprint: %s", self.fingerprint)

        if secret:

            self.secret = secret.decode(u"base64")

        elif secfile:

            sf = open(secfile)

            self.secret = sf.read()

            sf.close()

        else:

            raise TypeError(u"No secret or secfile for client %s"

                            % self.name)

        self.fqdn = fqdn

        self.created = datetime.datetime.now()

        self.last_checked_ok = None

        self.timeout = string_to_delta(timeout)

        self.interval = string_to_delta(interval)

        self.stop_hook = stop_hook

        self.checker = None

        self.checker_initiator_tag = None

        self.stop_initiator_tag = None

        self.checker_callback_tag = None

        self.check_command = checker

    def start(self):

        """Start this client's checker and timeout hooks"""

        # Schedule a new checker to be started an 'interval' from now,

        # and every interval from then on.

        self.checker_initiator_tag = gobject.timeout_add\

                                     (self._interval_milliseconds,

                                      self.start_checker)

        # Also start a new checker *right now*.

        self.start_checker()

        # Schedule a stop() when 'timeout' has passed

        self.stop_initiator_tag = gobject.timeout_add\

                                  (self._timeout_milliseconds,

                                   self.stop)

    def stop(self):

        """Stop this client.

        The possibility that a client might be restarted is left open,

        but not currently used."""

        # If this client doesn't have a secret, it is already stopped.

        if self.secret:

            logger.debug(u"Stopping client %s", self.name)

            self.secret = None

        else:

            return False

        if getattr(self, "stop_initiator_tag", False):

            gobject.source_remove(self.stop_initiator_tag)

            self.stop_initiator_tag = None

        if getattr(self, "checker_initiator_tag", False):

            gobject.source_remove(self.checker_initiator_tag)

            self.checker_initiator_tag = None

        self.stop_checker()

        if self.stop_hook:

            self.stop_hook(self)

        # Do not run this again if called by a gobject.timeout_add

        return False

    def __del__(self):

        self.stop_hook = None

        self.stop()

    def checker_callback(self, pid, condition):

        """The checker has completed, so take appropriate actions."""

        now = datetime.datetime.now()

        self.checker_callback_tag = None

        self.checker = None

        if os.WIFEXITED(condition) \

               and (os.WEXITSTATUS(condition) == 0):

            logger.debug(u"Checker for %(name)s succeeded",

                         vars(self))

            self.last_checked_ok = now

            gobject.source_remove(self.stop_initiator_tag)

            self.stop_initiator_tag = gobject.timeout_add\

                                      (self._timeout_milliseconds,

                                       self.stop)

        elif not os.WIFEXITED(condition):

            logger.warning(u"Checker for %(name)s crashed?",

                           vars(self))

        else:

            logger.debug(u"Checker for %(name)s failed",

                         vars(self))

    def start_checker(self):

        """Start a new checker subprocess if one is not running.

        If a checker already exists, leave it running and do

        nothing."""

        # The reason for not killing a running checker is that if we

        # did that, then if a checker (for some reason) started

        # running slowly and taking more than 'interval' time, the

        # client would inevitably timeout, since no checker would get

        # a chance to run to completion.  If we instead leave running

        # checkers alone, the checker would have to take more time

        # than 'timeout' for the client to be declared invalid, which

        # is as it should be.

        if self.checker is None:

            try:

                # In case check_command has exactly one % operator

                command = self.check_command % self.fqdn

            except TypeError:

                # Escape attributes for the shell

                escaped_attrs = dict((key, re.escape(str(val)))

                                     for key, val in

                                     vars(self).iteritems())

                try:

                    command = self.check_command % escaped_attrs

                except TypeError, error:

                    logger.error(u'Could not format string "%s":'

                                 u' %s', self.check_command, error)

                    return True # Try again later

            try:

                logger.debug(u"Starting checker %r for %s",

                             command, self.name)

                self.checker = subprocess.Popen(command,

                                                close_fds=True,

                                                shell=True, cwd="/")

                self.checker_callback_tag = gobject.child_watch_add\

                                            (self.checker.pid,

                                             self.checker_callback)

            except subprocess.OSError, error:

                logger.error(u"Failed to start subprocess: %s",

                             error)

        # Re-run this periodically if run by gobject.timeout_add

        return True

    def stop_checker(self):

        """Force the checker process, if any, to stop."""

        if self.checker_callback_tag:

            gobject.source_remove(self.checker_callback_tag)

            self.checker_callback_tag = None

        if getattr(self, "checker", None) is None:

            return

        logger.debug("Stopping checker for %(name)s", vars(self))

        try:

            os.kill(self.checker.pid, signal.SIGTERM)

            #os.sleep(0.5)

            #if self.checker.poll() is None:

            #    os.kill(self.checker.pid, signal.SIGKILL)

        except OSError, error:

            if error.errno != errno.ESRCH: # No such process

                raise

        self.checker = None

    def still_valid(self):

        """Has the timeout not yet passed for this client?"""

        now = datetime.datetime.now()

        if self.last_checked_ok is None:

            return now < (self.created + self.timeout)

        else:

            return now < (self.last_checked_ok + self.timeout)

def peer_certificate(session):

    "Return the peer's OpenPGP certificate as a bytestring"

    # If not an OpenPGP certificate...

    if gnutls.library.functions.gnutls_certificate_type_get\

            (session._c_object) \

           != gnutls.library.constants.GNUTLS_CRT_OPENPGP:

        # ...do the normal thing

        return session.peer_certificate

    list_size = ctypes.c_uint()

    cert_list = gnutls.library.functions.gnutls_certificate_get_peers\

        (session._c_object, ctypes.byref(list_size))

    if list_size.value == 0:

        return None

    cert = cert_list[0]

    return ctypes.string_at(cert.data, cert.size)

def fingerprint(openpgp):

    "Convert an OpenPGP bytestring to a hexdigit fingerprint string"

    # New empty GnuTLS certificate

    crt = gnutls.library.types.gnutls_openpgp_crt_t()

    gnutls.library.functions.gnutls_openpgp_crt_init\

        (ctypes.byref(crt))

    # New GnuTLS "datum" with the OpenPGP public key

    datum = gnutls.library.types.gnutls_datum_t\

        (ctypes.cast(ctypes.c_char_p(openpgp),

                     ctypes.POINTER(ctypes.c_ubyte)),

         ctypes.c_uint(len(openpgp)))

    # Import the OpenPGP public key into the certificate

    ret = gnutls.library.functions.gnutls_openpgp_crt_import\

        (crt,

         ctypes.byref(datum),

         gnutls.library.constants.GNUTLS_OPENPGP_FMT_RAW)

    # New buffer for the fingerprint

    buffer = ctypes.create_string_buffer(20)

    buffer_length = ctypes.c_size_t()

    # Get the fingerprint from the certificate into the buffer

    gnutls.library.functions.gnutls_openpgp_crt_get_fingerprint\

        (crt, ctypes.byref(buffer), ctypes.byref(buffer_length))

    # Deinit the certificate

    gnutls.library.functions.gnutls_openpgp_crt_deinit(crt)

    # Convert the buffer to a Python bytestring

    fpr = ctypes.string_at(buffer, buffer_length.value)

    # Convert the bytestring to hexadecimal notation

    hex_fpr = u''.join(u"%02X" % ord(char) for char in fpr)

    return hex_fpr

class tcp_handler(SocketServer.BaseRequestHandler, object):

    """A TCP request handler class.

    Instantiated by IPv6_TCPServer for each request to handle it.

    Note: This will run in its own forked process."""

    def handle(self):

        logger.debug(u"TCP connection from: %s",

                     unicode(self.client_address))

        session = gnutls.connection.ClientSession\

                  (self.request, gnutls.connection.X509Credentials())

        # Note: gnutls.connection.X509Credentials is really a generic

        # GnuTLS certificate credentials object so long as no X.509

        # keys are added to it.  Therefore, we can use it here despite

        # using OpenPGP certificates.

        #priority = ':'.join(("NONE", "+VERS-TLS1.1", "+AES-256-CBC",

        #                "+SHA1", "+COMP-NULL", "+CTYPE-OPENPGP",

        #                "+DHE-DSS"))

        priority = "NORMAL"             # Fallback default, since this

                                        # MUST be set.

        if self.server.settings["priority"]:

            priority = self.server.settings["priority"]

        gnutls.library.functions.gnutls_priority_set_direct\

            (session._c_object, priority, None);

        try:

            session.handshake()

        except gnutls.errors.GNUTLSError, error:

            logger.debug(u"Handshake failed: %s", error)

            # Do not run session.bye() here: the session is not

            # established.  Just abandon the request.

            return

        try:

            fpr = fingerprint(peer_certificate(session))

        except (TypeError, gnutls.errors.GNUTLSError), error:

            logger.debug(u"Bad certificate: %s", error)

            session.bye()

            return

        logger.debug(u"Fingerprint: %s", fpr)

        client = None

        for c in self.server.clients:

            if c.fingerprint == fpr:

                client = c

                break

        if not client:

            logger.debug(u"Client not found for fingerprint: %s", fpr)

            session.bye()

            return

        # Have to check if client.still_valid(), since it is possible

        # that the client timed out while establishing the GnuTLS

        # session.

        if not client.still_valid():

            logger.debug(u"Client %(name)s is invalid", vars(client))

            session.bye()

            return

        sent_size = 0

        while sent_size < len(client.secret):

            sent = session.send(client.secret[sent_size:])

            logger.debug(u"Sent: %d, remaining: %d",

                         sent, len(client.secret)

                         - (sent_size + sent))

            sent_size += sent

        session.bye()

class IPv6_TCPServer(SocketServer.ForkingTCPServer, object):

    """IPv6 TCP server.  Accepts 'None' as address and/or port.

    Attributes:

        settings:       Server settings

        clients:        Set() of Client objects

    """

    address_family = socket.AF_INET6

    def __init__(self, *args, **kwargs):

        if "settings" in kwargs:

            self.settings = kwargs["settings"]

            del kwargs["settings"]

        if "clients" in kwargs:

            self.clients = kwargs["clients"]

            del kwargs["clients"]

        return super(type(self), self).__init__(*args, **kwargs)

    def server_bind(self):

        """This overrides the normal server_bind() function

        to bind to an interface if one was specified, and also NOT to

        bind to an address or port if they were not specified."""

        if self.settings["interface"]:

            # 25 is from /usr/include/asm-i486/socket.h

            SO_BINDTODEVICE = getattr(socket, "SO_BINDTODEVICE", 25)

            try:

                self.socket.setsockopt(socket.SOL_SOCKET,

                                       SO_BINDTODEVICE,

                                       self.settings["interface"])

            except socket.error, error:

                if error[0] == errno.EPERM:

                    logger.warning(u"No permission to"

                                   u" bind to interface %s",

                                   self.settings["interface"])

                else:

                    raise error

        # Only bind(2) the socket if we really need to.

        if self.server_address[0] or self.server_address[1]:

            if not self.server_address[0]:

                in6addr_any = "::"

                self.server_address = (in6addr_any,

                                       self.server_address[1])

            elif self.server_address[1] is None:

                self.server_address = (self.server_address[0],

                                       0)

            return super(type(self), self).server_bind()

def string_to_delta(interval):

    """Parse a string and return a datetime.timedelta

    >>> string_to_delta('7d')

    datetime.timedelta(7)

    >>> string_to_delta('60s')

    datetime.timedelta(0, 60)

    >>> string_to_delta('60m')

    datetime.timedelta(0, 3600)

    >>> string_to_delta('24h')

    datetime.timedelta(1)

    >>> string_to_delta(u'1w')

    datetime.timedelta(7)

    """

    try:

        suffix=unicode(interval[-1])

        value=int(interval[:-1])

        if suffix == u"d":

            delta = datetime.timedelta(value)

        elif suffix == u"s":

            delta = datetime.timedelta(0, value)

        elif suffix == u"m":

            delta = datetime.timedelta(0, 0, 0, 0, value)

        elif suffix == u"h":

            delta = datetime.timedelta(0, 0, 0, 0, 0, value)

        elif suffix == u"w":

            delta = datetime.timedelta(0, 0, 0, 0, 0, 0, value)

        else:

            raise ValueError

    except (ValueError, IndexError):

        raise ValueError

    return delta

def server_state_changed(state):

    """Derived from the Avahi example code"""

    if state == avahi.SERVER_COLLISION:

        logger.warning(u"Server name collision")

        service.remove()

    elif state == avahi.SERVER_RUNNING:

        service.add()

def entry_group_state_changed(state, error):

    """Derived from the Avahi example code"""

    logger.debug(u"state change: %i", state)

    if state == avahi.ENTRY_GROUP_ESTABLISHED:

        logger.debug(u"Service established.")

    elif state == avahi.ENTRY_GROUP_COLLISION:

        logger.warning(u"Service name collision.")

        service.rename()

    elif state == avahi.ENTRY_GROUP_FAILURE:

        logger.critical(u"Error in group state changed %s",

                        unicode(error))

        raise AvahiGroupError("State changed: %s", str(error))

def if_nametoindex(interface, _func=[None]):

    """Call the C function if_nametoindex(), or equivalent"""

    if _func[0] is not None:

        return _func[0](interface)

    try:

        if "ctypes.util" not in sys.modules:

            import ctypes.util

        while True:

            try:

                libc = ctypes.cdll.LoadLibrary\

                       (ctypes.util.find_library("c"))

                _func[0] = libc.if_nametoindex

                return _func[0](interface)

            except IOError, e:

                if e != errno.EINTR:

                    raise

    except (OSError, AttributeError):

        if "struct" not in sys.modules:

            import struct

        if "fcntl" not in sys.modules:

            import fcntl

        def the_hard_way(interface):

            "Get an interface index the hard way, i.e. using fcntl()"

            SIOCGIFINDEX = 0x8933  # From /usr/include/linux/sockios.h

            s = socket.socket()

            ifreq = fcntl.ioctl(s, SIOCGIFINDEX,

                                struct.pack("16s16x", interface))

            s.close()

            interface_index = struct.unpack("I", ifreq[16:20])[0]

            return interface_index

        _func[0] = the_hard_way

        return _func[0](interface)

def daemon(nochdir, noclose):

    """See daemon(3).  Standard BSD Unix function.

    This should really exist as os.daemon, but it doesn't (yet)."""

    if os.fork():

        sys.exit()

    os.setsid()

    if not nochdir:

        os.chdir("/")

    if not noclose:

        # Close all standard open file descriptors

        null = os.open(os.path.devnull, os.O_NOCTTY | os.O_RDWR)

        if not stat.S_ISCHR(os.fstat(null).st_mode):

            raise OSError(errno.ENODEV,

                          "/dev/null not a character device")

        os.dup2(null, sys.stdin.fileno())

        os.dup2(null, sys.stdout.fileno())

        os.dup2(null, sys.stderr.fileno())

        if null > 2:

            os.close(null)

def main():

    global main_loop_started

    main_loop_started = False

    parser = OptionParser()

    parser.add_option("-i", "--interface", type="string",

                      metavar="IF", help="Bind to interface IF")

    parser.add_option("-a", "--address", type="string",

                      help="Address to listen for requests on")

    parser.add_option("-p", "--port", type="int",

                      help="Port number to receive requests on")