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# -*- coding: utf-8 -*-
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#
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# Copyright (c) 2012 OpenStack Foundation.
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# All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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"""
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Common Policy Engine Implementation
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Policies can be expressed in one of two forms: A list of lists, or a
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string written in the new policy language.
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In the list-of-lists representation, each check inside the innermost
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list is combined as with an "and" conjunction--for that check to pass,
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all the specified checks must pass. These innermost lists are then
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combined as with an "or" conjunction. As an example, take the following
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rule, expressed in the list-of-lists representation::
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[["role:admin"], ["project_id:%(project_id)s", "role:projectadmin"]]
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This is the original way of expressing policies, but there now exists a
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new way: the policy language.
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In the policy language, each check is specified the same way as in the
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list-of-lists representation: a simple "a:b" pair that is matched to
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the correct class to perform that check::
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+===========================================================================+
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| TYPE | SYNTAX |
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+===========================================================================+
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|User's Role | role:admin |
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+---------------------------------------------------------------------------+
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|Rules already defined on policy | rule:admin_required |
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+---------------------------------------------------------------------------+
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|Against URL's¹ | http://my-url.org/check |
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+---------------------------------------------------------------------------+
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|User attributes² | project_id:%(target.project.id)s |
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+---------------------------------------------------------------------------+
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|Strings | <variable>:'xpto2035abc' |
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| | 'myproject':<variable> |
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+---------------------------------------------------------------------------+
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| | project_id:xpto2035abc |
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|Literals | domain_id:20 |
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| | True:%(user.enabled)s |
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+===========================================================================+
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¹URL checking must return 'True' to be valid
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²User attributes (obtained through the token): user_id, domain_id or project_id
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Conjunction operators are available, allowing for more expressiveness
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in crafting policies. So, in the policy language, the previous check in
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list-of-lists becomes::
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role:admin or (project_id:%(project_id)s and role:projectadmin)
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The policy language also has the "not" operator, allowing a richer
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policy rule::
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project_id:%(project_id)s and not role:dunce
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Attributes sent along with API calls can be used by the policy engine
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(on the right side of the expression), by using the following syntax::
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<some_value>:%(user.id)s
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Contextual attributes of objects identified by their IDs are loaded
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from the database. They are also available to the policy engine and
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can be checked through the `target` keyword::
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<some_value>:%(target.role.name)s
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Finally, two special policy checks should be mentioned; the policy
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check "@" will always accept an access, and the policy check "!" will
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always reject an access. (Note that if a rule is either the empty
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list ("[]") or the empty string, this is equivalent to the "@" policy
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check.) Of these, the "!" policy check is probably the most useful,
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as it allows particular rules to be explicitly disabled.
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"""
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import abc
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import ast
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import copy
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import os
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import re
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from oslo.config import cfg
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from oslo.serialization import jsonutils
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import six
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import six.moves.urllib.parse as urlparse
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import six.moves.urllib.request as urlrequest
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from castellan.openstack.common import fileutils
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from castellan.openstack.common._i18n import _, _LE, _LI
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from castellan.openstack.common import log as logging
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policy_opts = [
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cfg.StrOpt('policy_file',
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default='policy.json',
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help=_('The JSON file that defines policies.')),
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cfg.StrOpt('policy_default_rule',
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default='default',
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help=_('Default rule. Enforced when a requested rule is not '
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'found.')),
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cfg.MultiStrOpt('policy_dirs',
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default=['policy.d'],
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help=_('Directories where policy configuration files are '
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'stored. They can be relative to any directory '
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'in the search path defined by the config_dir '
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'option, or absolute paths. The file defined by '
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'policy_file must exist for these directories to '
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'be searched.')),
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]
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CONF = cfg.CONF
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CONF.register_opts(policy_opts)
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LOG = logging.getLogger(__name__)
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_checks = {}
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def list_opts():
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"""Entry point for oslo.config-generator."""
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return [(None, copy.deepcopy(policy_opts))]
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class PolicyNotAuthorized(Exception):
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def __init__(self, rule):
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msg = _("Policy doesn't allow %s to be performed.") % rule
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super(PolicyNotAuthorized, self).__init__(msg)
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class Rules(dict):
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"""A store for rules. Handles the default_rule setting directly."""
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@classmethod
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def load_json(cls, data, default_rule=None):
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"""Allow loading of JSON rule data."""
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# Suck in the JSON data and parse the rules
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rules = dict((k, parse_rule(v)) for k, v in
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jsonutils.loads(data).items())
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return cls(rules, default_rule)
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def __init__(self, rules=None, default_rule=None):
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"""Initialize the Rules store."""
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super(Rules, self).__init__(rules or {})
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self.default_rule = default_rule
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def __missing__(self, key):
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"""Implements the default rule handling."""
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if isinstance(self.default_rule, dict):
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raise KeyError(key)
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# If the default rule isn't actually defined, do something
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# reasonably intelligent
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if not self.default_rule:
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raise KeyError(key)
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if isinstance(self.default_rule, BaseCheck):
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return self.default_rule
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# We need to check this or we can get infinite recursion
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if self.default_rule not in self:
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raise KeyError(key)
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elif isinstance(self.default_rule, six.string_types):
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return self[self.default_rule]
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def __str__(self):
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"""Dumps a string representation of the rules."""
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# Start by building the canonical strings for the rules
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out_rules = {}
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for key, value in self.items():
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# Use empty string for singleton TrueCheck instances
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if isinstance(value, TrueCheck):
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out_rules[key] = ''
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else:
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out_rules[key] = str(value)
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# Dump a pretty-printed JSON representation
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return jsonutils.dumps(out_rules, indent=4)
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class Enforcer(object):
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"""Responsible for loading and enforcing rules.
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:param policy_file: Custom policy file to use, if none is
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specified, `CONF.policy_file` will be
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used.
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:param rules: Default dictionary / Rules to use. It will be
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considered just in the first instantiation. If
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`load_rules(True)`, `clear()` or `set_rules(True)`
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is called this will be overwritten.
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:param default_rule: Default rule to use, CONF.default_rule will
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be used if none is specified.
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:param use_conf: Whether to load rules from cache or config file.
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:param overwrite: Whether to overwrite existing rules when reload rules
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from config file.
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"""
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def __init__(self, policy_file=None, rules=None,
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default_rule=None, use_conf=True, overwrite=True):
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self.default_rule = default_rule or CONF.policy_default_rule
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self.rules = Rules(rules, self.default_rule)
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self.policy_path = None
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self.policy_file = policy_file or CONF.policy_file
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self.use_conf = use_conf
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self.overwrite = overwrite
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def set_rules(self, rules, overwrite=True, use_conf=False):
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"""Create a new Rules object based on the provided dict of rules.
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:param rules: New rules to use. It should be an instance of dict.
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:param overwrite: Whether to overwrite current rules or update them
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with the new rules.
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:param use_conf: Whether to reload rules from cache or config file.
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"""
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if not isinstance(rules, dict):
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raise TypeError(_("Rules must be an instance of dict or Rules, "
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"got %s instead") % type(rules))
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self.use_conf = use_conf
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if overwrite:
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self.rules = Rules(rules, self.default_rule)
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else:
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self.rules.update(rules)
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def clear(self):
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"""Clears Enforcer rules, policy's cache and policy's path."""
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self.set_rules({})
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fileutils.delete_cached_file(self.policy_path)
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self.default_rule = None
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self.policy_path = None
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def load_rules(self, force_reload=False):
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"""Loads policy_path's rules.
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Policy file is cached and will be reloaded if modified.
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:param force_reload: Whether to reload rules from config file.
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"""
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if force_reload:
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self.use_conf = force_reload
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if self.use_conf:
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if not self.policy_path:
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self.policy_path = self._get_policy_path(self.policy_file)
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self._load_policy_file(self.policy_path, force_reload,
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overwrite=self.overwrite)
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for path in CONF.policy_dirs:
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try:
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path = self._get_policy_path(path)
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except cfg.ConfigFilesNotFoundError:
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LOG.info(_LI("Can not find policy directory: %s"), path)
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continue
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self._walk_through_policy_directory(path,
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self._load_policy_file,
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force_reload, False)
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@staticmethod
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def _walk_through_policy_directory(path, func, *args):
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# We do not iterate over sub-directories.
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policy_files = next(os.walk(path))[2]
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policy_files.sort()
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for policy_file in [p for p in policy_files if not p.startswith('.')]:
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func(os.path.join(path, policy_file), *args)
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def _load_policy_file(self, path, force_reload, overwrite=True):
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reloaded, data = fileutils.read_cached_file(
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path, force_reload=force_reload)
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if reloaded or not self.rules or not overwrite:
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rules = Rules.load_json(data, self.default_rule)
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self.set_rules(rules, overwrite=overwrite, use_conf=True)
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LOG.debug("Rules successfully reloaded")
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def _get_policy_path(self, path):
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"""Locate the policy json data file/path.
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:param path: It's value can be a full path or related path. When
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full path specified, this function just returns the full
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path. When related path specified, this function will
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search configuration directories to find one that exists.
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:returns: The policy path
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:raises: ConfigFilesNotFoundError if the file/path couldn't
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be located.
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"""
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policy_path = CONF.find_file(path)
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if policy_path:
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return policy_path
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raise cfg.ConfigFilesNotFoundError((path,))
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def enforce(self, rule, target, creds, do_raise=False,
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exc=None, *args, **kwargs):
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"""Checks authorization of a rule against the target and credentials.
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:param rule: A string or BaseCheck instance specifying the rule
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to evaluate.
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:param target: As much information about the object being operated
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on as possible, as a dictionary.
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:param creds: As much information about the user performing the
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action as possible, as a dictionary.
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:param do_raise: Whether to raise an exception or not if check
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fails.
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:param exc: Class of the exception to raise if the check fails.
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Any remaining arguments passed to enforce() (both
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positional and keyword arguments) will be passed to
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the exception class. If not specified, PolicyNotAuthorized
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will be used.
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:return: Returns False if the policy does not allow the action and
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exc is not provided; otherwise, returns a value that
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evaluates to True. Note: for rules using the "case"
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expression, this True value will be the specified string
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from the expression.
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"""
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self.load_rules()
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# Allow the rule to be a Check tree
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if isinstance(rule, BaseCheck):
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result = rule(target, creds, self)
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elif not self.rules:
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# No rules to reference means we're going to fail closed
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result = False
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else:
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try:
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# Evaluate the rule
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result = self.rules[rule](target, creds, self)
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except KeyError:
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LOG.debug("Rule [%s] doesn't exist" % rule)
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# If the rule doesn't exist, fail closed
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result = False
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| 357 | |
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| 358 | |
# If it is False, raise the exception if requested
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| 359 | |
if do_raise and not result:
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if exc:
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raise exc(*args, **kwargs)
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raise PolicyNotAuthorized(rule)
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return result
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| 366 | |
|
| 367 | |
|
| 368 | |
@six.add_metaclass(abc.ABCMeta)
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class BaseCheck(object):
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| 370 | |
"""Abstract base class for Check classes."""
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| 371 | |
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@abc.abstractmethod
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| 373 | |
def __str__(self):
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| 374 | |
"""String representation of the Check tree rooted at this node."""
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| 375 | |
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| 376 | |
pass
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| 377 | |
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| 378 | |
@abc.abstractmethod
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| 379 | |
def __call__(self, target, cred, enforcer):
|
| 380 | |
"""Triggers if instance of the class is called.
|
| 381 | |
|
| 382 | |
Performs the check. Returns False to reject the access or a
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| 383 | |
true value (not necessary True) to accept the access.
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| 384 | |
"""
|
| 385 | |
|
| 386 | |
pass
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| 387 | |
|
| 388 | |
|
| 389 | |
class FalseCheck(BaseCheck):
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| 390 | |
"""A policy check that always returns False (disallow)."""
|
| 391 | |
|
| 392 | |
def __str__(self):
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| 393 | |
"""Return a string representation of this check."""
|
| 394 | |
|
| 395 | |
return "!"
|
| 396 | |
|
| 397 | |
def __call__(self, target, cred, enforcer):
|
| 398 | |
"""Check the policy."""
|
| 399 | |
|
| 400 | |
return False
|
| 401 | |
|
| 402 | |
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| 403 | |
class TrueCheck(BaseCheck):
|
| 404 | |
"""A policy check that always returns True (allow)."""
|
| 405 | |
|
| 406 | |
def __str__(self):
|
| 407 | |
"""Return a string representation of this check."""
|
| 408 | |
|
| 409 | |
return "@"
|
| 410 | |
|
| 411 | |
def __call__(self, target, cred, enforcer):
|
| 412 | |
"""Check the policy."""
|
| 413 | |
|
| 414 | |
return True
|
| 415 | |
|
| 416 | |
|
| 417 | |
class Check(BaseCheck):
|
| 418 | |
"""A base class to allow for user-defined policy checks."""
|
| 419 | |
|
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def __init__(self, kind, match):
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"""Initiates Check instance.
|
| 422 | |
|
| 423 | |
:param kind: The kind of the check, i.e., the field before the
|
| 424 | |
':'.
|
| 425 | |
:param match: The match of the check, i.e., the field after
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| 426 | |
the ':'.
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| 427 | |
"""
|
| 428 | |
|
| 429 | |
self.kind = kind
|
| 430 | |
self.match = match
|
| 431 | |
|
| 432 | |
def __str__(self):
|
| 433 | |
"""Return a string representation of this check."""
|
| 434 | |
|
| 435 | |
return "%s:%s" % (self.kind, self.match)
|
| 436 | |
|
| 437 | |
|
| 438 | |
class NotCheck(BaseCheck):
|
| 439 | |
"""Implements the "not" logical operator.
|
| 440 | |
|
| 441 | |
A policy check that inverts the result of another policy check.
|
| 442 | |
"""
|
| 443 | |
|
| 444 | |
def __init__(self, rule):
|
| 445 | |
"""Initialize the 'not' check.
|
| 446 | |
|
| 447 | |
:param rule: The rule to negate. Must be a Check.
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| 448 | |
"""
|
| 449 | |
|
| 450 | |
self.rule = rule
|
| 451 | |
|
| 452 | |
def __str__(self):
|
| 453 | |
"""Return a string representation of this check."""
|
| 454 | |
|
| 455 | |
return "not %s" % self.rule
|
| 456 | |
|
| 457 | |
def __call__(self, target, cred, enforcer):
|
| 458 | |
"""Check the policy.
|
| 459 | |
|
| 460 | |
Returns the logical inverse of the wrapped check.
|
| 461 | |
"""
|
| 462 | |
|
| 463 | |
return not self.rule(target, cred, enforcer)
|
| 464 | |
|
| 465 | |
|
| 466 | |
class AndCheck(BaseCheck):
|
| 467 | |
"""Implements the "and" logical operator.
|
| 468 | |
|
| 469 | |
A policy check that requires that a list of other checks all return True.
|
| 470 | |
"""
|
| 471 | |
|
| 472 | |
def __init__(self, rules):
|
| 473 | |
"""Initialize the 'and' check.
|
| 474 | |
|
| 475 | |
:param rules: A list of rules that will be tested.
|
| 476 | |
"""
|
| 477 | |
|
| 478 | |
self.rules = rules
|
| 479 | |
|
| 480 | |
def __str__(self):
|
| 481 | |
"""Return a string representation of this check."""
|
| 482 | |
|
| 483 | |
return "(%s)" % ' and '.join(str(r) for r in self.rules)
|
| 484 | |
|
| 485 | |
def __call__(self, target, cred, enforcer):
|
| 486 | |
"""Check the policy.
|
| 487 | |
|
| 488 | |
Requires that all rules accept in order to return True.
|
| 489 | |
"""
|
| 490 | |
|
| 491 | |
for rule in self.rules:
|
| 492 | |
if not rule(target, cred, enforcer):
|
| 493 | |
return False
|
| 494 | |
|
| 495 | |
return True
|
| 496 | |
|
| 497 | |
def add_check(self, rule):
|
| 498 | |
"""Adds rule to be tested.
|
| 499 | |
|
| 500 | |
Allows addition of another rule to the list of rules that will
|
| 501 | |
be tested. Returns the AndCheck object for convenience.
|
| 502 | |
"""
|
| 503 | |
|
| 504 | |
self.rules.append(rule)
|
| 505 | |
return self
|
| 506 | |
|
| 507 | |
|
| 508 | |
class OrCheck(BaseCheck):
|
| 509 | |
"""Implements the "or" operator.
|
| 510 | |
|
| 511 | |
A policy check that requires that at least one of a list of other
|
| 512 | |
checks returns True.
|
| 513 | |
"""
|
| 514 | |
|
| 515 | |
def __init__(self, rules):
|
| 516 | |
"""Initialize the 'or' check.
|
| 517 | |
|
| 518 | |
:param rules: A list of rules that will be tested.
|
| 519 | |
"""
|
| 520 | |
|
| 521 | |
self.rules = rules
|
| 522 | |
|
| 523 | |
def __str__(self):
|
| 524 | |
"""Return a string representation of this check."""
|
| 525 | |
|
| 526 | |
return "(%s)" % ' or '.join(str(r) for r in self.rules)
|
| 527 | |
|
| 528 | |
def __call__(self, target, cred, enforcer):
|
| 529 | |
"""Check the policy.
|
| 530 | |
|
| 531 | |
Requires that at least one rule accept in order to return True.
|
| 532 | |
"""
|
| 533 | |
|
| 534 | |
for rule in self.rules:
|
| 535 | |
if rule(target, cred, enforcer):
|
| 536 | |
return True
|
| 537 | |
return False
|
| 538 | |
|
| 539 | |
def add_check(self, rule):
|
| 540 | |
"""Adds rule to be tested.
|
| 541 | |
|
| 542 | |
Allows addition of another rule to the list of rules that will
|
| 543 | |
be tested. Returns the OrCheck object for convenience.
|
| 544 | |
"""
|
| 545 | |
|
| 546 | |
self.rules.append(rule)
|
| 547 | |
return self
|
| 548 | |
|
| 549 | |
|
| 550 | |
def _parse_check(rule):
|
| 551 | |
"""Parse a single base check rule into an appropriate Check object."""
|
| 552 | |
|
| 553 | |
# Handle the special checks
|
| 554 | |
if rule == '!':
|
| 555 | |
return FalseCheck()
|
| 556 | |
elif rule == '@':
|
| 557 | |
return TrueCheck()
|
| 558 | |
|
| 559 | |
try:
|
| 560 | |
kind, match = rule.split(':', 1)
|
| 561 | |
except Exception:
|
| 562 | |
LOG.exception(_LE("Failed to understand rule %s") % rule)
|
| 563 | |
# If the rule is invalid, we'll fail closed
|
| 564 | |
return FalseCheck()
|
| 565 | |
|
| 566 | |
# Find what implements the check
|
| 567 | |
if kind in _checks:
|
| 568 | |
return _checks[kind](kind, match)
|
| 569 | |
elif None in _checks:
|
| 570 | |
return _checks[None](kind, match)
|
| 571 | |
else:
|
| 572 | |
LOG.error(_LE("No handler for matches of kind %s") % kind)
|
| 573 | |
return FalseCheck()
|
| 574 | |
|
| 575 | |
|
| 576 | |
def _parse_list_rule(rule):
|
| 577 | |
"""Translates the old list-of-lists syntax into a tree of Check objects.
|
| 578 | |
|
| 579 | |
Provided for backwards compatibility.
|
| 580 | |
"""
|
| 581 | |
|
| 582 | |
# Empty rule defaults to True
|
| 583 | |
if not rule:
|
| 584 | |
return TrueCheck()
|
| 585 | |
|
| 586 | |
# Outer list is joined by "or"; inner list by "and"
|
| 587 | |
or_list = []
|
| 588 | |
for inner_rule in rule:
|
| 589 | |
# Elide empty inner lists
|
| 590 | |
if not inner_rule:
|
| 591 | |
continue
|
| 592 | |
|
| 593 | |
# Handle bare strings
|
| 594 | |
if isinstance(inner_rule, six.string_types):
|
| 595 | |
inner_rule = [inner_rule]
|
| 596 | |
|
| 597 | |
# Parse the inner rules into Check objects
|
| 598 | |
and_list = [_parse_check(r) for r in inner_rule]
|
| 599 | |
|
| 600 | |
# Append the appropriate check to the or_list
|
| 601 | |
if len(and_list) == 1:
|
| 602 | |
or_list.append(and_list[0])
|
| 603 | |
else:
|
| 604 | |
or_list.append(AndCheck(and_list))
|
| 605 | |
|
| 606 | |
# If we have only one check, omit the "or"
|
| 607 | |
if not or_list:
|
| 608 | |
return FalseCheck()
|
| 609 | |
elif len(or_list) == 1:
|
| 610 | |
return or_list[0]
|
| 611 | |
|
| 612 | |
return OrCheck(or_list)
|
| 613 | |
|
| 614 | |
|
| 615 | |
# Used for tokenizing the policy language
|
| 616 | |
_tokenize_re = re.compile(r'\s+')
|
| 617 | |
|
| 618 | |
|
| 619 | |
def _parse_tokenize(rule):
|
| 620 | |
"""Tokenizer for the policy language.
|
| 621 | |
|
| 622 | |
Most of the single-character tokens are specified in the
|
| 623 | |
_tokenize_re; however, parentheses need to be handled specially,
|
| 624 | |
because they can appear inside a check string. Thankfully, those
|
| 625 | |
parentheses that appear inside a check string can never occur at
|
| 626 | |
the very beginning or end ("%(variable)s" is the correct syntax).
|
| 627 | |
"""
|
| 628 | |
|
| 629 | |
for tok in _tokenize_re.split(rule):
|
| 630 | |
# Skip empty tokens
|
| 631 | |
if not tok or tok.isspace():
|
| 632 | |
continue
|
| 633 | |
|
| 634 | |
# Handle leading parens on the token
|
| 635 | |
clean = tok.lstrip('(')
|
| 636 | |
for i in range(len(tok) - len(clean)):
|
| 637 | |
yield '(', '('
|
| 638 | |
|
| 639 | |
# If it was only parentheses, continue
|
| 640 | |
if not clean:
|
| 641 | |
continue
|
| 642 | |
else:
|
| 643 | |
tok = clean
|
| 644 | |
|
| 645 | |
# Handle trailing parens on the token
|
| 646 | |
clean = tok.rstrip(')')
|
| 647 | |
trail = len(tok) - len(clean)
|
| 648 | |
|
| 649 | |
# Yield the cleaned token
|
| 650 | |
lowered = clean.lower()
|
| 651 | |
if lowered in ('and', 'or', 'not'):
|
| 652 | |
# Special tokens
|
| 653 | |
yield lowered, clean
|
| 654 | |
elif clean:
|
| 655 | |
# Not a special token, but not composed solely of ')'
|
| 656 | |
if len(tok) >= 2 and ((tok[0], tok[-1]) in
|
| 657 | |
[('"', '"'), ("'", "'")]):
|
| 658 | |
# It's a quoted string
|
| 659 | |
yield 'string', tok[1:-1]
|
| 660 | |
else:
|
| 661 | |
yield 'check', _parse_check(clean)
|
| 662 | |
|
| 663 | |
# Yield the trailing parens
|
| 664 | |
for i in range(trail):
|
| 665 | |
yield ')', ')'
|
| 666 | |
|
| 667 | |
|
| 668 | |
class ParseStateMeta(type):
|
| 669 | |
"""Metaclass for the ParseState class.
|
| 670 | |
|
| 671 | |
Facilitates identifying reduction methods.
|
| 672 | |
"""
|
| 673 | |
|
| 674 | |
def __new__(mcs, name, bases, cls_dict):
|
| 675 | |
"""Create the class.
|
| 676 | |
|
| 677 | |
Injects the 'reducers' list, a list of tuples matching token sequences
|
| 678 | |
to the names of the corresponding reduction methods.
|
| 679 | |
"""
|
| 680 | |
|
| 681 | |
reducers = []
|
| 682 | |
|
| 683 | |
for key, value in cls_dict.items():
|
| 684 | |
if not hasattr(value, 'reducers'):
|
| 685 | |
continue
|
| 686 | |
for reduction in value.reducers:
|
| 687 | |
reducers.append((reduction, key))
|
| 688 | |
|
| 689 | |
cls_dict['reducers'] = reducers
|
| 690 | |
|
| 691 | |
return super(ParseStateMeta, mcs).__new__(mcs, name, bases, cls_dict)
|
| 692 | |
|
| 693 | |
|
| 694 | |
def reducer(*tokens):
|
| 695 | |
"""Decorator for reduction methods.
|
| 696 | |
|
| 697 | |
Arguments are a sequence of tokens, in order, which should trigger running
|
| 698 | |
this reduction method.
|
| 699 | |
"""
|
| 700 | |
|
| 701 | |
def decorator(func):
|
| 702 | |
# Make sure we have a list of reducer sequences
|
| 703 | |
if not hasattr(func, 'reducers'):
|
| 704 | |
func.reducers = []
|
| 705 | |
|
| 706 | |
# Add the tokens to the list of reducer sequences
|
| 707 | |
func.reducers.append(list(tokens))
|
| 708 | |
|
| 709 | |
return func
|
| 710 | |
|
| 711 | |
return decorator
|
| 712 | |
|
| 713 | |
|
| 714 | |
@six.add_metaclass(ParseStateMeta)
|
| 715 | |
class ParseState(object):
|
| 716 | |
"""Implement the core of parsing the policy language.
|
| 717 | |
|
| 718 | |
Uses a greedy reduction algorithm to reduce a sequence of tokens into
|
| 719 | |
a single terminal, the value of which will be the root of the Check tree.
|
| 720 | |
|
| 721 | |
Note: error reporting is rather lacking. The best we can get with
|
| 722 | |
this parser formulation is an overall "parse failed" error.
|
| 723 | |
Fortunately, the policy language is simple enough that this
|
| 724 | |
shouldn't be that big a problem.
|
| 725 | |
"""
|
| 726 | |
|
| 727 | |
def __init__(self):
|
| 728 | |
"""Initialize the ParseState."""
|
| 729 | |
|
| 730 | |
self.tokens = []
|
| 731 | |
self.values = []
|
| 732 | |
|
| 733 | |
def reduce(self):
|
| 734 | |
"""Perform a greedy reduction of the token stream.
|
| 735 | |
|
| 736 | |
If a reducer method matches, it will be executed, then the
|
| 737 | |
reduce() method will be called recursively to search for any more
|
| 738 | |
possible reductions.
|
| 739 | |
"""
|
| 740 | |
|
| 741 | |
for reduction, methname in self.reducers:
|
| 742 | |
if (len(self.tokens) >= len(reduction) and
|
| 743 | |
self.tokens[-len(reduction):] == reduction):
|
| 744 | |
# Get the reduction method
|
| 745 | |
meth = getattr(self, methname)
|
| 746 | |
|
| 747 | |
# Reduce the token stream
|
| 748 | |
results = meth(*self.values[-len(reduction):])
|
| 749 | |
|
| 750 | |
# Update the tokens and values
|
| 751 | |
self.tokens[-len(reduction):] = [r[0] for r in results]
|
| 752 | |
self.values[-len(reduction):] = [r[1] for r in results]
|
| 753 | |
|
| 754 | |
# Check for any more reductions
|
| 755 | |
return self.reduce()
|
| 756 | |
|
| 757 | |
def shift(self, tok, value):
|
| 758 | |
"""Adds one more token to the state. Calls reduce()."""
|
| 759 | |
|
| 760 | |
self.tokens.append(tok)
|
| 761 | |
self.values.append(value)
|
| 762 | |
|
| 763 | |
# Do a greedy reduce...
|
| 764 | |
self.reduce()
|
| 765 | |
|
| 766 | |
@property
|
| 767 | |
def result(self):
|
| 768 | |
"""Obtain the final result of the parse.
|
| 769 | |
|
| 770 | |
Raises ValueError if the parse failed to reduce to a single result.
|
| 771 | |
"""
|
| 772 | |
|
| 773 | |
if len(self.values) != 1:
|
| 774 | |
raise ValueError("Could not parse rule")
|
| 775 | |
return self.values[0]
|
| 776 | |
|
| 777 | |
@reducer('(', 'check', ')')
|
| 778 | |
@reducer('(', 'and_expr', ')')
|
| 779 | |
@reducer('(', 'or_expr', ')')
|
| 780 | |
def _wrap_check(self, _p1, check, _p2):
|
| 781 | |
"""Turn parenthesized expressions into a 'check' token."""
|
| 782 | |
|
| 783 | |
return [('check', check)]
|
| 784 | |
|
| 785 | |
@reducer('check', 'and', 'check')
|
| 786 | |
def _make_and_expr(self, check1, _and, check2):
|
| 787 | |
"""Create an 'and_expr'.
|
| 788 | |
|
| 789 | |
Join two checks by the 'and' operator.
|
| 790 | |
"""
|
| 791 | |
|
| 792 | |
return [('and_expr', AndCheck([check1, check2]))]
|
| 793 | |
|
| 794 | |
@reducer('and_expr', 'and', 'check')
|
| 795 | |
def _extend_and_expr(self, and_expr, _and, check):
|
| 796 | |
"""Extend an 'and_expr' by adding one more check."""
|
| 797 | |
|
| 798 | |
return [('and_expr', and_expr.add_check(check))]
|
| 799 | |
|
| 800 | |
@reducer('check', 'or', 'check')
|
| 801 | |
def _make_or_expr(self, check1, _or, check2):
|
| 802 | |
"""Create an 'or_expr'.
|
| 803 | |
|
| 804 | |
Join two checks by the 'or' operator.
|
| 805 | |
"""
|
| 806 | |
|
| 807 | |
return [('or_expr', OrCheck([check1, check2]))]
|
| 808 | |
|
| 809 | |
@reducer('or_expr', 'or', 'check')
|
| 810 | |
def _extend_or_expr(self, or_expr, _or, check):
|
| 811 | |
"""Extend an 'or_expr' by adding one more check."""
|
| 812 | |
|
| 813 | |
return [('or_expr', or_expr.add_check(check))]
|
| 814 | |
|
| 815 | |
@reducer('not', 'check')
|
| 816 | |
def _make_not_expr(self, _not, check):
|
| 817 | |
"""Invert the result of another check."""
|
| 818 | |
|
| 819 | |
return [('check', NotCheck(check))]
|
| 820 | |
|
| 821 | |
|
| 822 | |
def _parse_text_rule(rule):
|
| 823 | |
"""Parses policy to the tree.
|
| 824 | |
|
| 825 | |
Translates a policy written in the policy language into a tree of
|
| 826 | |
Check objects.
|
| 827 | |
"""
|
| 828 | |
|
| 829 | |
# Empty rule means always accept
|
| 830 | |
if not rule:
|
| 831 | |
return TrueCheck()
|
| 832 | |
|
| 833 | |
# Parse the token stream
|
| 834 | |
state = ParseState()
|
| 835 | |
for tok, value in _parse_tokenize(rule):
|
| 836 | |
state.shift(tok, value)
|
| 837 | |
|
| 838 | |
try:
|
| 839 | |
return state.result
|
| 840 | |
except ValueError:
|
| 841 | |
# Couldn't parse the rule
|
| 842 | |
LOG.exception(_LE("Failed to understand rule %s") % rule)
|
| 843 | |
|
| 844 | |
# Fail closed
|
| 845 | |
return FalseCheck()
|
| 846 | |
|
| 847 | |
|
| 848 | |
def parse_rule(rule):
|
| 849 | |
"""Parses a policy rule into a tree of Check objects."""
|
| 850 | |
|
| 851 | |
# If the rule is a string, it's in the policy language
|
| 852 | |
if isinstance(rule, six.string_types):
|
| 853 | |
return _parse_text_rule(rule)
|
| 854 | |
return _parse_list_rule(rule)
|
| 855 | |
|
| 856 | |
|
| 857 | |
def register(name, func=None):
|
| 858 | |
"""Register a function or Check class as a policy check.
|
| 859 | |
|
| 860 | |
:param name: Gives the name of the check type, e.g., 'rule',
|
| 861 | |
'role', etc. If name is None, a default check type
|
| 862 | |
will be registered.
|
| 863 | |
:param func: If given, provides the function or class to register.
|
| 864 | |
If not given, returns a function taking one argument
|
| 865 | |
to specify the function or class to register,
|
| 866 | |
allowing use as a decorator.
|
| 867 | |
"""
|
| 868 | |
|
| 869 | |
# Perform the actual decoration by registering the function or
|
| 870 | |
# class. Returns the function or class for compliance with the
|
| 871 | |
# decorator interface.
|
| 872 | |
def decorator(func):
|
| 873 | |
_checks[name] = func
|
| 874 | |
return func
|
| 875 | |
|
| 876 | |
# If the function or class is given, do the registration
|
| 877 | |
if func:
|
| 878 | |
return decorator(func)
|
| 879 | |
|
| 880 | |
return decorator
|
| 881 | |
|
| 882 | |
|
| 883 | |
@register("rule")
|
| 884 | |
class RuleCheck(Check):
|
| 885 | |
def __call__(self, target, creds, enforcer):
|
| 886 | |
"""Recursively checks credentials based on the defined rules."""
|
| 887 | |
|
| 888 | |
try:
|
| 889 | |
return enforcer.rules[self.match](target, creds, enforcer)
|
| 890 | |
except KeyError:
|
| 891 | |
# We don't have any matching rule; fail closed
|
| 892 | |
return False
|
| 893 | |
|
| 894 | |
|
| 895 | |
@register("role")
|
| 896 | |
class RoleCheck(Check):
|
| 897 | |
def __call__(self, target, creds, enforcer):
|
| 898 | |
"""Check that there is a matching role in the cred dict."""
|
| 899 | |
|
| 900 | |
return self.match.lower() in [x.lower() for x in creds['roles']]
|
| 901 | |
|
| 902 | |
|
| 903 | |
@register('http')
|
| 904 | |
class HttpCheck(Check):
|
| 905 | |
def __call__(self, target, creds, enforcer):
|
| 906 | |
"""Check http: rules by calling to a remote server.
|
| 907 | |
|
| 908 | |
This example implementation simply verifies that the response
|
| 909 | |
is exactly 'True'.
|
| 910 | |
"""
|
| 911 | |
|
| 912 | |
url = ('http:' + self.match) % target
|
| 913 | |
|
| 914 | |
# Convert instances of object() in target temporarily to
|
| 915 | |
# empty dict to avoid circular reference detection
|
| 916 | |
# errors in jsonutils.dumps().
|
| 917 | |
temp_target = copy.deepcopy(target)
|
| 918 | |
for key in target.keys():
|
| 919 | |
element = target.get(key)
|
| 920 | |
if type(element) is object:
|
| 921 | |
temp_target[key] = {}
|
| 922 | |
|
| 923 | |
data = {'target': jsonutils.dumps(temp_target),
|
| 924 | |
'credentials': jsonutils.dumps(creds)}
|
| 925 | |
post_data = urlparse.urlencode(data)
|
| 926 | |
f = urlrequest.urlopen(url, post_data)
|
| 927 | |
return f.read() == "True"
|
| 928 | |
|
| 929 | |
|
| 930 | |
@register(None)
|
| 931 | |
class GenericCheck(Check):
|
| 932 | |
def __call__(self, target, creds, enforcer):
|
| 933 | |
"""Check an individual match.
|
| 934 | |
|
| 935 | |
Matches look like:
|
| 936 | |
|
| 937 | |
tenant:%(tenant_id)s
|
| 938 | |
role:compute:admin
|
| 939 | |
True:%(user.enabled)s
|
| 940 | |
'Member':%(role.name)s
|
| 941 | |
"""
|
| 942 | |
|
| 943 | |
try:
|
| 944 | |
match = self.match % target
|
| 945 | |
except KeyError:
|
| 946 | |
# While doing GenericCheck if key not
|
| 947 | |
# present in Target return false
|
| 948 | |
return False
|
| 949 | |
|
| 950 | |
try:
|
| 951 | |
# Try to interpret self.kind as a literal
|
| 952 | |
leftval = ast.literal_eval(self.kind)
|
| 953 | |
except ValueError:
|
| 954 | |
try:
|
| 955 | |
kind_parts = self.kind.split('.')
|
| 956 | |
leftval = creds
|
| 957 | |
for kind_part in kind_parts:
|
| 958 | |
leftval = leftval[kind_part]
|
| 959 | |
except KeyError:
|
| 960 | |
return False
|
| 961 | |
return match == six.text_type(leftval)
|