core-admin/qubes/ext/admin.py

# -*- encoding: utf8 -*-
#
# The Qubes OS Project, http://www.qubes-os.org
#
# Copyright (C) 2017 Wojtek Porczyk <woju@invisiblethingslab.com>
#
# This library 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.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, see <https://www.gnu.org/licenses/>.

import qubes.api
import qubes.api.internal
import qubes.ext
import qubes.vm.adminvm
from qrexec.policy import utils, parser


class JustEvaluateAskResolution(parser.AskResolution):
    def execute(self, caller_ident):
        pass


class JustEvaluateAllowResolution(parser.AllowResolution):
    def execute(self, caller_ident):
        pass


class AdminExtension(qubes.ext.Extension):
    def __init__(self):
        super(AdminExtension, self).__init__()
        # during tests, __init__() of the extension can be called multiple
        # times, because there are multiple Qubes() object instances
        if not hasattr(self, 'policy_cache'):
            self.policy_cache = utils.PolicyCache(lazy_load=True)
            self.policy_cache.initialize_watcher()

    # pylint: disable=too-few-public-methods
    @qubes.ext.handler(
        'admin-permission:admin.vm.tag.Set',
        'admin-permission:admin.vm.tag.Remove')
    def on_tag_set_or_remove(self, vm, event, arg, **kwargs):
        '''Forbid changing specific tags'''
        # pylint: disable=no-self-use,unused-argument
        if arg.startswith('created-by-') and \
                not isinstance(vm, qubes.vm.adminvm.AdminVM):
            raise qubes.api.PermissionDenied(
                'changing this tag is prohibited by {}.{}'.format(
                    __name__, type(self).__name__))

    # TODO create that tag here (need to figure out how to pass mgmtvm name)

    @qubes.ext.handler('admin-permission:admin.vm.List')
    def admin_vm_list(self, vm, event, arg, **kwargs):
        '''When called with target 'dom0' (aka "get full list"), exclude domains
           that the caller don't have permission to list
        '''
        # pylint: disable=unused-argument

        if vm.klass == 'AdminVM':
            # dom0 can always list everything
            return None

        policy = self.policy_cache.get_policy()
        system_info = qubes.api.internal.get_system_info(vm.app)

        def filter_vms(dest_vm):
            request = parser.Request(
                'admin.vm.List',
                '+' + arg,
                vm.name,
                dest_vm.name,
                system_info=system_info,
                ask_resolution_type=JustEvaluateAskResolution,
                allow_resolution_type=JustEvaluateAllowResolution)
            try:
                resolution = policy.evaluate(request)
                # do not consider 'ask' as allow here,
                # this needs to be not interactive
                return isinstance(resolution, parser.AllowResolution)
            except parser.AccessDenied:
                return False

        return (filter_vms,)

    @qubes.ext.handler('admin-permission:admin.Events')
    def admin_events(self, vm, event, arg, **kwargs):
        '''When called with target 'dom0' (aka "get all events"),
           exclude domains that the caller don't have permission to receive
           events about
        '''
        # pylint: disable=unused-argument

        if vm.klass == 'AdminVM':
            # dom0 can always list everything
            return None

        def filter_events(event):
            subject, event, kwargs = event
            try:
                dest = subject.name
            except AttributeError:
                # domain-add and similar events fired on the Qubes() object
                if 'vm' in kwargs:
                    dest = kwargs['vm'].name
                else:
                    dest = '@adminvm'

            policy = self.policy_cache.get_policy()
            # TODO: cache system_info (based on last qubes.xml write time?)
            system_info = qubes.api.internal.get_system_info(vm.app)
            request = parser.Request(
                'admin.Events',
                '+' + event.replace(':', '_'),
                vm.name,
                dest,
                system_info=system_info,
                ask_resolution_type=JustEvaluateAskResolution,
                allow_resolution_type=JustEvaluateAllowResolution)
            try:
                resolution = policy.evaluate(request)
                # do not consider 'ask' as allow here,
                # this needs to be not interactive
                return isinstance(resolution, parser.AllowResolution)
            except parser.AccessDenied:
                return False

        return (filter_events,)

    @qubes.ext.handler('qubes-close', system=True)
    def on_qubes_close(self, app, event, **kwargs):
        """Unregister policy file watches on app.close()."""
        # pylint: disable=unused-argument
        if hasattr(self, 'policy_cache'):
            self.policy_cache.cleanup()
            del self.policy_cache