669 lines
24 KiB
Python
Executable File
669 lines
24 KiB
Python
Executable File
# coding=utf-8
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# The Qubes OS Project, https://www.qubes-os.org/
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#
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# Copyright (C) 2013-2015 Joanna Rutkowska <joanna@invisiblethingslab.com>
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# Copyright (C) 2013-2017 Marek Marczykowski-Górecki
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# <marmarek@invisiblethingslab.com>
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License along
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# with this program; if not, write to the Free Software Foundation, Inc.,
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# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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''' Qrexec policy parser and evaluator '''
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import enum
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import itertools
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import json
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import os
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import os.path
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import socket
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import subprocess
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# don't import 'qubes.config' please, it takes 0.3s
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QREXEC_CLIENT = '/usr/lib/qubes/qrexec-client'
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QUBES_RPC_MULTIPLEXER_PATH = '/usr/lib/qubes/qubes-rpc-multiplexer'
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POLICY_DIR = '/etc/qubes-rpc/policy'
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QUBESD_INTERNAL_SOCK = '/var/run/qubesd.internal.sock'
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class AccessDenied(Exception):
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''' Raised when qrexec policy denied access '''
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pass
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class PolicySyntaxError(AccessDenied):
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''' Syntax error in qrexec policy, abort parsing '''
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def __init__(self, filename, lineno, msg):
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super(PolicySyntaxError, self).__init__(
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'{}:{}: {}'.format(filename, lineno, msg))
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class Action(enum.Enum):
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''' Action as defined by policy '''
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allow = 1
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deny = 2
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ask = 3
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def verify_target_value(system_info, value):
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''' Check if given value names valid target
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This function check if given value is not only syntactically correct,
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but also if names valid service call target (existing domain,
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or valid $dispvm like keyword)
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:param system_info: information about the system
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:param value: value to be checked
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'''
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if value == '$dispvm':
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return True
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elif value == '$adminvm':
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return True
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elif value.startswith('$dispvm:'):
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dispvm_base = value.split(':', 1)[1]
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if dispvm_base not in system_info['domains']:
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return False
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dispvm_base_info = system_info['domains'][dispvm_base]
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return bool(dispvm_base_info['dispvm_allowed'])
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else:
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return value in system_info['domains']
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def verify_special_value(value, for_target=True):
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'''
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Verify if given special VM-specifier ('$...') is valid
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:param value: value to verify
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:param for_target: should classify target-only values as valid (
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'$default', '$dispvm')
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:return: True or False
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'''
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# pylint: disable=too-many-return-statements
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if value.startswith('$tag:') and len(value) > len('$tag:'):
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return True
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elif value.startswith('$type:') and len(value) > len('$type:'):
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return True
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elif value == '$anyvm':
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return True
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elif value == '$adminvm':
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return True
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elif value.startswith('$dispvm:') and for_target:
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return True
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elif value == '$dispvm' and for_target:
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return True
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elif value == '$default' and for_target:
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return True
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return False
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class PolicyRule(object):
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''' A single line of policy file '''
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def __init__(self, line, filename=None, lineno=None):
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'''
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Load a single line of qrexec policy and check its syntax.
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Do not verify existence of named objects.
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:raise PolicySyntaxError: when syntax error is found
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:param line: a single line of actual qrexec policy (not a comment,
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empty line or $include)
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:param filename: name of the file from which this line is loaded
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:param lineno: line number from which this line is loaded
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'''
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self.lineno = lineno
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self.filename = filename
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try:
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self.source, self.target, self.full_action = line.split(maxsplit=2)
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except ValueError:
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raise PolicySyntaxError(filename, lineno, 'wrong number of fields')
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(action, *params) = self.full_action.replace(' ', '').split(',')
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try:
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self.action = Action[action]
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except KeyError:
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raise PolicySyntaxError(filename, lineno,
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'invalid action: {}'.format(action))
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#: alternative target, used instead of the one specified by the caller
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self.override_target = None
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#: alternative user, used instead of vm.default_user
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self.override_user = None
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#: default target when asking the user for confirmation
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self.default_target = None
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for param in params:
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try:
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param_name, value = param.split('=')
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except ValueError:
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raise PolicySyntaxError(filename, lineno,
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'invalid action parameter syntax: {}'.format(param))
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if param_name == 'target':
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if self.action == Action.deny:
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raise PolicySyntaxError(filename, lineno,
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'target= option not allowed for deny action')
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self.override_target = value
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elif param_name == 'user':
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if self.action == Action.deny:
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raise PolicySyntaxError(filename, lineno,
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'user= option not allowed for deny action')
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self.override_user = value
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elif param_name == 'default_target':
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if self.action != Action.ask:
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raise PolicySyntaxError(filename, lineno,
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'default_target= option allowed only for ask action')
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self.default_target = value
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else:
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raise PolicySyntaxError(filename, lineno,
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'invalid option {} for {} action'.format(param, action))
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# verify special values
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if self.source.startswith('$'):
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if not verify_special_value(self.source, False):
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raise PolicySyntaxError(filename, lineno,
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'invalid source specification: {}'.format(self.source))
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if self.target.startswith('$'):
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if not verify_special_value(self.target, True):
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raise PolicySyntaxError(filename, lineno,
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'invalid target specification: {}'.format(self.target))
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if self.target == '$default' \
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and self.action == Action.allow \
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and self.override_target is None:
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raise PolicySyntaxError(filename, lineno,
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'allow action for $default rule must specify target= option')
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if self.override_target is not None:
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if self.override_target.startswith('$') and \
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not self.override_target.startswith('$dispvm') and \
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self.override_target != '$adminvm':
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raise PolicySyntaxError(filename, lineno,
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'target= option needs to name specific target')
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@staticmethod
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def is_match_single(system_info, policy_value, value):
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'''
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Evaluate if a single value (VM name or '$default') matches policy
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specification
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:param system_info: information about the system
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:param policy_value: value from qrexec policy (either self.source or
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self.target)
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:param value: value to be compared (source or target)
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:return: True or False
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'''
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# pylint: disable=too-many-return-statements
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# not specified target matches only with $default and $anyvm policy
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# entry
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if value == '$default' or value == '':
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return policy_value in ('$default', '$anyvm')
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# if specific target used, check if it's valid
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# this function (is_match_single) is also used for checking call source
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# values, but this isn't a problem, because it will always be a
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# domain name (not $dispvm or such) - this is guaranteed by a nature
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# of qrexec call
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if not verify_target_value(system_info, value):
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return False
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# handle $adminvm keyword
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if policy_value == 'dom0':
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# TODO: log a warning in Qubes 4.1
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policy_value = '$adminvm'
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if value == 'dom0':
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value = '$adminvm'
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# allow any _valid_, non-dom0 target
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if policy_value == '$anyvm':
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return value != '$adminvm'
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# exact match, including $dispvm* and $adminvm
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if value == policy_value:
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return True
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# if $dispvm* not matched above, reject it; missing ':' is
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# intentional - handle both '$dispvm' and '$dispvm:xxx'
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if value.startswith('$dispvm'):
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return False
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# require $adminvm to be matched explicitly (not through $tag or $type)
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# - if not matched already, reject it
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if value == '$adminvm':
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return False
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# at this point, value name a specific target
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domain_info = system_info['domains'][value]
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if policy_value.startswith('$tag:'):
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tag = policy_value.split(':', 1)[1]
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return tag in domain_info['tags']
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if policy_value.startswith('$type:'):
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type_ = policy_value.split(':', 1)[1]
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return type_ == domain_info['type']
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return False
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def is_match(self, system_info, source, target):
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'''
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Check if given (source, target) matches this policy line.
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:param system_info: information about the system - available VMs,
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their types, labels, tags etc. as returned by
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:py:func:`app_to_system_info`
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:param source: name of the source VM
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:param target: name of the target VM, or None if not specified
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:return: True or False
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'''
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if not self.is_match_single(system_info, self.source, source):
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return False
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if not self.is_match_single(system_info, self.target, target):
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return False
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return True
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def expand_target(self, system_info):
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'''
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Return domains matching target of this policy line
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:param system_info: information about the system
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:return: matching domains
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'''
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if self.target.startswith('$tag:'):
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tag = self.target.split(':', 1)[1]
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for name, domain in system_info['domains'].items():
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if tag in domain['tags']:
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yield name
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elif self.target.startswith('$type:'):
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type_ = self.target.split(':', 1)[1]
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for name, domain in system_info['domains'].items():
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if type_ == domain['type']:
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yield name
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elif self.target == '$anyvm':
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for name, domain in system_info['domains'].items():
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if name != 'dom0':
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yield name
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if domain['dispvm_allowed']:
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yield '$dispvm:' + name
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yield '$dispvm'
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elif self.target.startswith('$dispvm:'):
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dispvm_base = self.target.split(':', 1)[1]
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try:
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if system_info['domains'][dispvm_base]['dispvm_allowed']:
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yield self.target
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except KeyError:
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# TODO log a warning?
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pass
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elif self.target == '$adminvm':
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yield self.target
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elif self.target == '$dispvm':
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yield self.target
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else:
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if self.target in system_info['domains']:
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yield self.target
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def expand_override_target(self, system_info, source):
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'''
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Replace '$dispvm' with specific '$dispvm:...' value, based on qrexec
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call source.
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:param system_info: System information
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:param source: Source domain name
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:return: :py:attr:`override_target` with '$dispvm' substituted
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'''
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if self.override_target == '$dispvm':
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if system_info['domains'][source]['default_dispvm'] is None:
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return None
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return '$dispvm:' + system_info['domains'][source]['default_dispvm']
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else:
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return self.override_target
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class PolicyAction(object):
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''' Object representing positive policy evaluation result -
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either ask or allow action '''
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def __init__(self, service, source, target, rule, original_target,
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targets_for_ask=None):
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#: service name
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self.service = service
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#: calling domain
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self.source = source
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#: target domain the service should be connected to, None if
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# not chosen yet
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if targets_for_ask is None or target in targets_for_ask:
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self.target = target
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else:
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# TODO: log a warning?
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self.target = None
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#: original target specified by the caller
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self.original_target = original_target
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#: targets for the user to choose from
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self.targets_for_ask = targets_for_ask
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#: policy rule from which this action is derived
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self.rule = rule
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if rule.action == Action.deny:
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# this should be really rejected by Policy.eval()
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raise AccessDenied(
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'denied by policy {}:{}'.format(rule.filename, rule.lineno))
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elif rule.action == Action.ask:
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assert targets_for_ask is not None
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elif rule.action == Action.allow:
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assert targets_for_ask is None
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assert target is not None
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self.action = rule.action
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def handle_user_response(self, response, target=None):
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'''
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Handle user response for the 'ask' action
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:param response: whether the call was allowed or denied (bool)
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:param target: target chosen by the user (if reponse==True)
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:return: None
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'''
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assert self.action == Action.ask
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assert self.target is None
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if response:
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assert target in self.targets_for_ask
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self.target = target
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self.action = Action.allow
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else:
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self.action = Action.deny
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raise AccessDenied(
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'denied by the user {}:{}'.format(self.rule.filename,
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self.rule.lineno))
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def execute(self, caller_ident):
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''' Execute allowed service call
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:param caller_ident: Service caller ident (`process_ident,source_name,
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source_id`)
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'''
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assert self.action == Action.allow
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assert self.target is not None
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if self.target == '$adminvm':
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self.target = 'dom0'
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if self.target == 'dom0':
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cmd = '{multiplexer} {service} {source} {original_target}'.format(
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multiplexer=QUBES_RPC_MULTIPLEXER_PATH,
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service=self.service,
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source=self.source,
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original_target=self.original_target)
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else:
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cmd = '{user}:QUBESRPC {service} {source}'.format(
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user=(self.rule.override_user or 'DEFAULT'),
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service=self.service,
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source=self.source)
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if self.target.startswith('$dispvm:'):
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target = self.spawn_dispvm()
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dispvm = True
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else:
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target = self.target
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dispvm = False
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self.ensure_target_running()
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qrexec_opts = ['-d', target, '-c', caller_ident]
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if dispvm:
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qrexec_opts.append('-W')
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try:
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subprocess.call([QREXEC_CLIENT] + qrexec_opts + [cmd])
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finally:
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if dispvm:
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self.cleanup_dispvm(target)
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def spawn_dispvm(self):
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'''
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Create and start Disposable VM based on AppVM specified in
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:py:attr:`target`
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:return: name of new Disposable VM
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'''
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base_appvm = self.target.split(':', 1)[1]
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dispvm_name = qubesd_call(base_appvm, 'internal.vm.Create.DispVM')
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dispvm_name = dispvm_name.decode('ascii')
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qubesd_call(dispvm_name, 'internal.vm.Start')
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return dispvm_name
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def ensure_target_running(self):
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'''
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Start domain if not running already
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:return: None
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'''
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try:
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qubesd_call(self.target, 'internal.vm.Start')
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except QubesMgmtException as e:
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if e.exc_type == 'QubesVMNotHaltedError':
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pass
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else:
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raise
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@staticmethod
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def cleanup_dispvm(dispvm):
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'''
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Kill and remove Disposable VM
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:param dispvm: name of Disposable VM
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:return: None
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'''
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qubesd_call(dispvm, 'internal.vm.CleanupDispVM')
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class Policy(object):
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''' Full policy for a given service
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Usage:
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>>> system_info = get_system_info()
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>>> policy = Policy('some-service')
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>>> action = policy.evaluate(system_info, 'source-name', 'target-name')
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>>> if action.action == Action.ask:
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(... ask the user, see action.targets_for_ask ...)
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>>> action.handle_user_response(response, target_chosen_by_user)
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>>> action.execute('process-ident')
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'''
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def __init__(self, service):
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policy_file = os.path.join(POLICY_DIR, service)
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if not os.path.exists(policy_file):
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# fallback to policy without specific argument set (if any)
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policy_file = os.path.join(POLICY_DIR, service.split('+')[0])
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#: service name
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self.service = service
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#: list of PolicyLine objects
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self.policy_rules = []
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try:
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self.load_policy_file(policy_file)
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except OSError as e:
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raise AccessDenied(
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'failed to load {} file: {!s}'.format(e.filename, e))
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def load_policy_file(self, path):
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''' Load policy file and append rules to :py:attr:`policy_rules`
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:param path: file to load
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'''
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with open(path) as policy_file:
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for lineno, line in zip(itertools.count(start=1),
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policy_file.readlines()):
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line = line.strip()
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if not line:
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# skip empty lines
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continue
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if line[0] == '#':
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# skip comments
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continue
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if line.startswith('$include:'):
|
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include_path = line.split(':', 1)[1]
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# os.path.join will leave include_path unchanged if it's
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# already absolute
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include_path = os.path.join(POLICY_DIR, include_path)
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self.load_policy_file(include_path)
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else:
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self.policy_rules.append(PolicyRule(line, path, lineno))
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|
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def find_matching_rule(self, system_info, source, target):
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''' Find the first rule matching given arguments '''
|
|
|
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for rule in self.policy_rules:
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if rule.is_match(system_info, source, target):
|
|
return rule
|
|
raise AccessDenied('no matching rule found')
|
|
|
|
|
|
def collect_targets_for_ask(self, system_info, source):
|
|
''' Collect targets the user can choose from in 'ask' action
|
|
|
|
Word 'targets' is used intentionally instead of 'domains', because it
|
|
can also contains $dispvm like keywords.
|
|
'''
|
|
targets = set()
|
|
|
|
# iterate over rules in reversed order to easier handle 'deny'
|
|
# actions - simply remove matching domains from allowed set
|
|
for rule in reversed(self.policy_rules):
|
|
if rule.is_match_single(system_info, rule.source, source):
|
|
if rule.action == Action.deny:
|
|
targets -= set(rule.expand_target(system_info))
|
|
else:
|
|
if rule.override_target is not None:
|
|
override_target = rule.expand_override_target(
|
|
system_info, source)
|
|
if verify_target_value(system_info, override_target):
|
|
targets.add(rule.override_target)
|
|
else:
|
|
targets.update(rule.expand_target(system_info))
|
|
|
|
# expand default DispVM
|
|
if '$dispvm' in targets:
|
|
targets.remove('$dispvm')
|
|
if system_info['domains'][source]['default_dispvm'] is not None:
|
|
dispvm = '$dispvm:' + \
|
|
system_info['domains'][source]['default_dispvm']
|
|
if verify_target_value(system_info, dispvm):
|
|
targets.add(dispvm)
|
|
|
|
return targets
|
|
|
|
def evaluate(self, system_info, source, target):
|
|
''' Evaluate policy
|
|
|
|
:raise AccessDenied: when action should be denied unconditionally
|
|
|
|
:return tuple(rule, considered_targets) - where considered targets is a
|
|
list of possible targets for 'ask' action (rule.action == Action.ask)
|
|
'''
|
|
rule = self.find_matching_rule(system_info, source, target)
|
|
if rule.action == Action.deny:
|
|
raise AccessDenied(
|
|
'denied by policy {}:{}'.format(rule.filename, rule.lineno))
|
|
|
|
if rule.override_target is not None:
|
|
override_target = rule.expand_override_target(system_info, source)
|
|
if not verify_target_value(system_info, override_target):
|
|
raise AccessDenied('invalid target= value in {}:{}'.format(
|
|
rule.filename, rule.lineno))
|
|
actual_target = override_target
|
|
else:
|
|
actual_target = target
|
|
|
|
if rule.action == Action.ask:
|
|
if rule.override_target is not None:
|
|
targets = [actual_target]
|
|
else:
|
|
targets = list(
|
|
self.collect_targets_for_ask(system_info, source))
|
|
if not targets:
|
|
raise AccessDenied(
|
|
'policy define \'ask\' action at {}:{} but no target is '
|
|
'available to choose from'.format(
|
|
rule.filename, rule.lineno))
|
|
return PolicyAction(self.service, source, rule.default_target,
|
|
rule, target, targets)
|
|
elif rule.action == Action.allow:
|
|
if actual_target == '$default':
|
|
raise AccessDenied(
|
|
'policy define \'allow\' action at {}:{} but no target is '
|
|
'specified by caller or policy'.format(
|
|
rule.filename, rule.lineno))
|
|
return PolicyAction(self.service, source,
|
|
actual_target, rule, target)
|
|
else:
|
|
# should be unreachable
|
|
raise AccessDenied(
|
|
'invalid action?! {}:{}'.format(rule.filename, rule.lineno))
|
|
|
|
|
|
class QubesMgmtException(Exception):
|
|
''' Exception returned by qubesd '''
|
|
def __init__(self, exc_type):
|
|
super(QubesMgmtException, self).__init__()
|
|
self.exc_type = exc_type
|
|
|
|
|
|
def qubesd_call(dest, method, arg=None, payload=None):
|
|
try:
|
|
client_socket = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
|
|
client_socket.connect(QUBESD_INTERNAL_SOCK)
|
|
except IOError:
|
|
# TODO:
|
|
raise
|
|
|
|
# src, method, dest, arg
|
|
for call_arg in ('dom0', method, dest, arg):
|
|
if call_arg is not None:
|
|
client_socket.sendall(call_arg.encode('ascii'))
|
|
client_socket.sendall(b'\0')
|
|
if payload is not None:
|
|
client_socket.sendall(payload)
|
|
|
|
client_socket.shutdown(socket.SHUT_WR)
|
|
|
|
return_data = client_socket.makefile('rb').read()
|
|
if return_data.startswith(b'0\x00'):
|
|
return return_data[2:]
|
|
elif return_data.startswith(b'2\x00'):
|
|
(_, exc_type, _traceback, _format_string, _args) = \
|
|
return_data.split(b'\x00', 4)
|
|
raise QubesMgmtException(exc_type.decode('ascii'))
|
|
else:
|
|
raise AssertionError(
|
|
'invalid qubesd response: {!r}'.format(return_data))
|
|
|
|
|
|
def get_system_info():
|
|
''' Get system information
|
|
|
|
This retrieve information necessary to process qrexec policy. Returned
|
|
data is nested dict structure with this structure:
|
|
|
|
- domains:
|
|
- <domain name>:
|
|
- tags: list of tags
|
|
- type: domain type
|
|
- dispvm_allowed: should DispVM based on this VM be allowed
|
|
- default_dispvm: name of default AppVM for DispVMs started from here
|
|
|
|
'''
|
|
|
|
system_info = qubesd_call('dom0', 'internal.GetSystemInfo')
|
|
return json.loads(system_info.decode('utf-8'))
|