/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: "add_service", "remove_service",

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

# in "main".

# 

# Everything else is Copyright © 2007-2008 Teddy Hogeborn and 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 <https://www.fukt.bsnet.se/~belorn/> and

# <https://www.fukt.bsnet.se/~teddy/>.

# 

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 the connecting clients

# acts as a TLS "server".  The clients (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

# This variable is used to optionally bind to a specified interface.

# It is a global variable to fit in with the other variables from the

# Avahi example code.

serviceInterface = avahi.IF_UNSPEC

# From the Avahi example code:

serviceName = "Mandos"

serviceType = "_mandos._tcp" # http://www.dns-sd.org/ServiceTypes.html

servicePort = None                      # Not known at startup

serviceTXT = []                         # TXT record for the service

domain = ""                  # Domain to publish on, default to .local

host = ""          # Host to publish records for, default to localhost

group = None #our entry group

rename_count = 12       # Counter so we only rename after collisions a

                        # sensible number of times

# 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()

    last_seen: datetime.datetime() or None if not yet seen

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

                                   Is 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.  %()s 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 by 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, options=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

        # Uppercase and remove spaces from fingerprint

        # for later comparison purposes with return value of

        # the fingerprint() function

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

        if secret:

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

        elif secfile:

            sf = open(secfile)

            self.secret = sf.read()

            sf.close()

        else:

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

                               % self.name)

        self.fqdn = fqdn                # string

        self.created = datetime.datetime.now()

        self.last_seen = None

        if timeout is None:

            self.timeout = options.timeout

        else:

            self.timeout = string_to_delta(timeout)

        if interval == -1:

            self.interval = options.interval

        else:

            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 this 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 hasattr(self, "stop_initiator_tag") \

               and self.stop_initiator_tag:

            gobject.source_remove(self.stop_initiator_tag)

            self.stop_initiator_tag = None

        if hasattr(self, "checker_initiator_tag") \

               and self.checker_initiator_tag:

            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_seen = 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:

                command = self.check_command % self.fqdn

            except TypeError:

                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.critical(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 not hasattr(self, "checker") or self.checker 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:

                raise

        self.checker = None

    def still_valid(self, now=None):

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

        if now is None:

            now = datetime.datetime.now()

        if self.last_seen is None:

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

        else:

            return now < (self.last_seen + 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())

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

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

        #                "+DHE-DSS"))

        priority = "SECURE256"

        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

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

        # that the client timed out while establishing the GnuTLS

        # session.

        if (not client) or (not client.still_valid()):

            if client:

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

                             vars(client))

            else:

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

                             fpr)

            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:

        options:        Command line options

        clients:        Set() of Client objects

    """

    address_family = socket.AF_INET6

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

        if "options" in kwargs:

            self.options = kwargs["options"]

            del kwargs["options"]

        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.options.interface:

            if not hasattr(socket, "SO_BINDTODEVICE"):

                # From /usr/include/asm-i486/socket.h

                socket.SO_BINDTODEVICE = 25

            try:

                self.socket.setsockopt(socket.SOL_SOCKET,

                                       socket.SO_BINDTODEVICE,

                                       self.options.interface)

            except socket.error, error:

                if error[0] == errno.EPERM:

                    logger.warning(u"No permission to"

                                   u" bind to interface %s",

                                   self.options.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 add_service():

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

    global group, serviceName, serviceType, servicePort, serviceTXT, \

           domain, host

    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' ...",

                 serviceName, serviceType)

    group.AddService(

            serviceInterface,           # interface

            avahi.PROTO_INET6,          # protocol

            dbus.UInt32(0),             # flags

            serviceName, serviceType,

            domain, host,

            dbus.UInt16(servicePort),

            avahi.string_array_to_txt_array(serviceTXT))

    group.Commit()

def remove_service():

    """From the Avahi example code"""

    global group

    if not group is None:

        group.Reset()

def server_state_changed(state):

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

    if state == avahi.SERVER_COLLISION:

        logger.warning(u"Server name collision")

        remove_service()

    elif state == avahi.SERVER_RUNNING:

        add_service()

def entry_group_state_changed(state, error):

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

    global serviceName, server, rename_count

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

    if state == avahi.ENTRY_GROUP_ESTABLISHED:

        logger.debug(u"Service established.")

    elif state == avahi.ENTRY_GROUP_COLLISION:

        rename_count = rename_count - 1

        if rename_count > 0:

            name = server.GetAlternativeServiceName(name)

            logger.warning(u"Service name collision, "

                           u"changing name to '%s' ...", name)

            remove_service()

            add_service()

        else:

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

                         u" retries, exiting.", n_rename)

            killme(1)

    elif state == avahi.ENTRY_GROUP_FAILURE:

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

                     unicode(error))

        killme(1)

def if_nametoindex(interface):

    """Call the C function if_nametoindex()"""

    try:

        libc = ctypes.cdll.LoadLibrary("libc.so.6")

        return libc.if_nametoindex(interface)

    except (OSError, AttributeError):

        if "struct" not in sys.modules:

            import struct

        if "fcntl" not in sys.modules:

            import 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

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("/dev/null", 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 killme(status = 0):

    logger.debug("Stopping server with exit status %d", status)

    exitstatus = status

    if main_loop_started:

        main_loop.quit()

    else:

        sys.exit(status)

def main():

    global exitstatus

    exitstatus = 0

    global main_loop_started

    main_loop_started = False

    parser = OptionParser()

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

                      default=None, metavar="IF",

                      help="Bind to interface IF")

    parser.add_option("-a", "--address", type="string", default=None,

                      help="Address to listen for requests on")

    parser.add_option("-p", "--port", type="int", default=None,

                      help="Port number to receive requests on")

    parser.add_option("--timeout", type="string", # Parsed later

                      default="1h",

                      help="Amount of downtime allowed for clients")

    parser.add_option("--interval", type="string", # Parsed later

                      default="5m",

                      help="How often to check that a client is up")

    parser.add_option("--check", action="store_true", default=False,

                      help="Run self-test")

    parser.add_option("--debug", action="store_true", default=False,

                      help="Debug mode")

    (options, args) = parser.parse_args()

    if options.check:

        import doctest

        doctest.testmod()

        sys.exit()

    # Parse the time arguments

    try:

        options.timeout = string_to_delta(options.timeout)

    except ValueError:

        parser.error("option --timeout: Unparseable time")

    try:

        options.interval = string_to_delta(options.interval)

    except ValueError:

        parser.error("option --interval: Unparseable time")

    # Parse config file

    defaults = { "checker": "fping -q -- %%(fqdn)s" }

    client_config = ConfigParser.SafeConfigParser(defaults)

    #client_config.readfp(open("global.conf"), "global.conf")

    client_config.read("mandos-clients.conf")

    global main_loop