46fb0afb64
If overwrite, which is the option to control whether current rules are either overwritten or updated with new rules, was False, then policy files would be reloaded even if they had not changed and rules already existed. Closes-Bug: 1487661 Change-Id: I3c0d84ce3ba3d4b41cbb08b824cbdd4ee6dd664b
513 lines
19 KiB
Python
513 lines
19 KiB
Python
# -*- 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 are expressed as a target and an associated rule::
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"<target>": "<rule>"
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The `target` is specific to the service that is conducting policy
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enforcement. Typically, the target refers to an API call.
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A rule is made up of zero or more checks, where zero checks will always
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allow the action that is being enforced. A number of different check
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types are supported, which can be divided into generic checks and
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special checks.
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Generic Checks
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~~~~~~~~~~~~~~
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A :class:`generic check <oslo_policy.policy.GenericCheck>` is used
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to perform matching against attributes that are sent along with the API
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calls. These attributes can be used by the policy engine (on the right
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side of the expression), by using the following syntax::
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<some_attribute>:%(user.id)s
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The value on the right-hand side is either a string or resolves to a
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string using regular Python string substitution. The available attributes
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and values are dependent on the program that is using the common policy
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engine.
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All of these attributes (related to users, API calls, and context) can be
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checked against each other or against constants. It is important to note
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that these attributes are specific to the service that is conducting
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policy enforcement.
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Generic checks can be used to perform policy checks on the following user
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attributes obtained through a token:
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- user_id
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- domain_id or project_id (depending on the token scope)
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- list of roles held for the given token scope
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For example, a check on the user_id would be defined as::
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user_id:<some_value>
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Together with the previously shown example, a complete generic check
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would be::
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user_id:%(user.id)s
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It is also possible to perform checks against other attributes that
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represent the credentials. This is done by adding additional values to
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the ``creds`` dict that is passed to the
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:meth:`~oslo_policy.policy.Enforcer.enforce` method.
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Special Checks
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~~~~~~~~~~~~~~
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Special checks allow for more flexibility than is possible using generic
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checks. The built-in special check types are ``role``, ``rule``, and ``http``
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checks.
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Role Check
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^^^^^^^^^^
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A :class:`role check <oslo_policy.policy.RoleCheck>` is used to
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check if a specific role is present in the supplied credentials. A role
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check is expressed as::
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"role:<role_name>"
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Rule Check
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^^^^^^^^^^
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A :class:`rule check <oslo_policy.policy.RuleCheck>` is used to
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reference another defined rule by its name. This allows for common
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checks to be defined once as a reusable rule, which is then referenced
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within other rules. It also allows one to define a set of checks as a
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more descriptive name to aid in readabilty of policy. A rule check is
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expressed as::
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"rule:<rule_name>"
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The following example shows a role check that is defined as a rule,
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which is then used via a rule check::
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"admin_required": "role:admin"
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"<target>": "rule:admin_required"
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HTTP Check
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^^^^^^^^^^
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An :class:`http check <oslo_policy.policy.HttpCheck>` is used to
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make an HTTP request to a remote server to determine the results of the
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check. The target and credentials are passed to the remote server for
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evaluation. The action is authorized if the remote server returns a
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response of ``True``. An http check is expressed as::
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"http:<target URI>"
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It is expected that the target URI contains a string formatting keyword,
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where the keyword is a key from the target dictionary. An example of an
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http check where the `name` key from the target is used to construct the
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URL is would be defined as::
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"http://server.test/%(name)s"
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Registering New Special Checks
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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It is also possible for additional special check types to be registered
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using the :func:`~oslo_policy.policy.register` function.
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The following classes can be used as parents for custom special check types:
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* :class:`~oslo_policy.policy.AndCheck`
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* :class:`~oslo_policy.policy.NotCheck`
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* :class:`~oslo_policy.policy.OrCheck`
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* :class:`~oslo_policy.policy.RuleCheck`
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Policy Rule Expressions
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~~~~~~~~~~~~~~~~~~~~~~~
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Policy rules 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 URLs¹ | 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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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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Default Rule
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~~~~~~~~~~~~
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A default rule can be defined, which will be enforced when a rule does
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not exist for the target that is being checked. By default, the rule
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associated with the rule name of ``default`` will be used as the default
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rule. It is possible to use a different rule name as the default rule
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by setting the ``policy_default_rule`` configuration setting to the
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desired rule name.
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"""
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import logging
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import os
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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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from oslo_policy import _cache_handler
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from oslo_policy import _checks
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from oslo_policy._i18n import _
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from oslo_policy import _parser
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from oslo_policy import opts
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LOG = logging.getLogger(__name__)
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register = _checks.register
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Check = _checks.Check
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AndCheck = _checks.AndCheck
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NotCheck = _checks.NotCheck
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OrCheck = _checks.OrCheck
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RuleCheck = _checks.RuleCheck
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class PolicyNotAuthorized(Exception):
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"""Default exception raised for policy enforcement failure."""
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def __init__(self, rule, target, creds):
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msg = (_('%(rule)s on %(target)s by %(creds)s disallowed by policy') %
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{'rule': rule, 'target': target, 'creds': creds})
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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, _parser.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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@classmethod
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def from_dict(cls, rules_dict, default_rule=None):
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"""Allow loading of rule data from a dictionary."""
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# Parse the rules stored in the dictionary
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rules = dict((k, _parser.parse_rule(v)) for k, v in rules_dict.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, _checks.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, _checks.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 conf: A configuration object.
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:param policy_file: Custom policy file to use, if none is
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specified, ``conf.oslo_policy.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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:meth:`load_rules` with ``force_reload=True``,
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:meth:`clear` or :meth:`set_rules` with ``overwrite=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, conf, policy_file=None, rules=None,
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default_rule=None, use_conf=True, overwrite=True):
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self.conf = conf
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opts._register(conf)
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self.default_rule = (default_rule or
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self.conf.oslo_policy.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 self.conf.oslo_policy.policy_file
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self.use_conf = use_conf
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self.overwrite = overwrite
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self._loaded_files = []
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self._policy_dir_mtimes = {}
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self._file_cache = {}
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def set_rules(self, rules, overwrite=True, use_conf=False):
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"""Create a new :class:`Rules` based on the provided dict of rules.
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:param dict rules: New rules to use.
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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 :class:`Enforcer` contents.
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This will clear this instances rules, policy's cache, file cache
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and policy's path.
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"""
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self.set_rules({})
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self.default_rule = None
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self.policy_path = None
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self._loaded_files = []
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self._policy_dir_mtimes = {}
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self._file_cache.clear()
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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 self.conf.oslo_policy.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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continue
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if (force_reload or self._is_directory_updated(
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self._policy_dir_mtimes, path)):
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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 _is_directory_updated(cache, path):
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# Get the current modified time and compare it to what is in
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# the cache and check if the new mtime is greater than what
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# is in the cache
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mtime = 0
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if os.path.exists(path):
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# Make a list of all the files
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files = [path] + [os.path.join(path, file) for file in
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os.listdir(path)]
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# Pick the newest one, let's use its time.
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mtime = os.path.getmtime(max(files, key=os.path.getmtime))
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cache_info = cache.setdefault(path, {})
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if mtime > cache_info.get('mtime', 0):
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cache_info['mtime'] = mtime
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return True
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return 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 = _cache_handler.read_cached_file(
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self._file_cache, path, force_reload=force_reload)
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if reloaded or not self.rules:
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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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self._loaded_files.append(path)
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LOG.debug('Reloaded policy file: %(path)s', {'path': path})
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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 = self.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: The rule to evaluate.
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:type rule: string or :class:`BaseCheck`
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:param dict target: As much information about the object being operated
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on as possible.
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:param dict creds: As much information about the user performing the
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action as possible.
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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 :meth:`enforce` (both
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positional and keyword arguments) will be passed to
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the exception class. If not specified,
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:class:`PolicyNotAuthorized` will be used.
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:return: ``False`` if the policy does not allow the action and `exc` is
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not provided; otherwise, returns a value that evaluates to
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``True``. Note: for rules using the "case" expression, this
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``True`` value will be the specified string from the
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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, _checks.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] does not exist', rule)
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# If the rule doesn't exist, fail closed
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result = False
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# If it is False, raise the exception if requested
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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, target, creds)
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return result
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