Give the policy vision document a facelift
This document had a bunch of great content, but some of it has been addressed and other initiatives have changed the content or approach. This commit attempts to refresh this documentation so that developers can continue to use it to improve policy enforcement. Change-Id: Iac7a2157d625524932b94a5564723b440efd7344
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Lance Bragstad
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@ -28,13 +28,13 @@ Problems with current system
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The following is a list of issues with the existing policy enforcement system:
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* Default policies lack exhaustive testing
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* Mismatch between authoritative scope and resources
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* Policies are inconsistently named
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* Current defaults do not use default roles provided from keystone
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* Policy enforcement is spread across multiple levels and components
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* Some policies use hard-coded check strings
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* Some APIs do not use granular rules
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* `Testing default policies`_
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* `Mismatched authorization`_
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* `Inconsistent naming`_
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* `Incorporating default roles`_
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* `Compartmentalized policy enforcement`_
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* `Refactoring hard-coded permission checks`_
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* `Granular policy checks`_
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Addressing the list above helps operators by:
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@ -55,89 +55,124 @@ Additionally, the following is a list of benefits to contributors:
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3. Increased confidence in RBAC refactoring through exhaustive testing that
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prevents regressions before they merge
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Future of policy enforcement
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----------------------------
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Testing default policies
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------------------------
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The generic rule for all the improvement is keep V2 API back-compatible.
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Because V2 API may be deprecated after V2.1 parity with V2. This can reduce
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the risk we take. The improvement just for EC2 and V2.1 API. There isn't
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any user for V2.1, as it isn't ready yet. We have to do change for EC2 API.
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EC2 API won't be removed like v2 API. If we keep back-compatible for EC2 API
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also, the old compute api layer checks won't be removed forever. EC2 API is
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really small than Nova API. It's about 29 APIs without volume and image
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related(those policy check done by cinder and glance). So it will affect user
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less.
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Testing default policies is important in protecting against authoritative
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regression. Authoritative regression is when a change accidentally allows
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someone to do something or see something they shouldn't. It can also be when a
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change accidentally restricts a user from doing something they used to have the
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authorization to perform. This testing is especially useful prior to
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refactoring large parts of the policy system. For example, this level of
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testing would be invaluable prior to pulling policy enforcement logic from the
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database layer up to the API layer.
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Enforcement policy at REST API layer
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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`Testing documentation`_ exists that describes the process for developing these
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types of tests.
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The policy should be only enforced at REST API layer. This is clear for user
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to know where the policy will be enforced. If the policy spread into multiple
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layer of nova code, user won't know when and where the policy will be enforced
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if they didn't have knowledge about nova code.
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.. _Testing documentation: https://docs.openstack.org/keystone/latest/contributor/services.html#ruthless-testing
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Remove all the permission checking under REST API layer. Policy will only be
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enforced at REST API layer.
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Mismatched authorization
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------------------------
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This will affect the EC2 API and V2.1 API, there are some API just have policy
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enforcement at Compute/Network API layer, those policy will be move to API
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layer and renamed.
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The compute API is rich in functionality and has grown to manage both physical
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and virtual hardware. Some APIs were meant to assist operators while others
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were specific to end users. Historically, nova used project-scoped tokens to
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protect almost every API, regardless of the intended user. Using project-scoped
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tokens to authorize requests for system-level APIs makes for undesirable
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user-experience and is prone to overloading roles. For example, to prevent
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every user from accessing hardware level APIs that would otherwise violate
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tenancy requires operators to create a ``system-admin`` or ``super-admin``
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role, then rewrite those system-level policies to incorporate that role. This
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means users with that special role on a project could access system-level
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resources that aren't even tracked against projects (hypervisor information is
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an example of system-specific information.)
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Removes hard-code permission checks
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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As of the Queens release, keystone supports a scope type dedicated to easing
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this problem, called system scope. Consuming system scope across the compute
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API results in fewer overloaded roles, less specialized authorization logic in
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code, and simpler policies that expose more functionality to users without
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violating tenancy. Please refer to keystone's `authorization scopes
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documentation`_ to learn more about scopes and how to use them effectively.
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Hard-coded permission checks make it impossible to supply a configurable
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policy. They should be removed in order to make nova auth completely
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configurable.
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.. _authorization scopes documentation: https://docs.openstack.org/keystone/latest/contributor/services.html#authorization-scopes
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This will affect EC2 API and Nova V2.1 API. User need update their policy
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rule to match the old hard-code permission.
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Inconsistent naming
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-------------------
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For Nova V2 API, the hard-code permission checks will be moved to REST API
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layer to guarantee it won't break the back-compatibility. That may ugly
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some hard-code permission check in API layer, but V2 API will be removed
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once V2.1 API ready, so our choice will reduce the risk.
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Inconsistent conventions for policy names are scattered across most OpenStack
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services, nova included. Recently, there was an effort that introduced a
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convention that factored in service names, resources, and use cases. This new
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convention is applicable to nova policy names. The convention is formally
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`documented`_ in oslo.policy and we can use policy `deprecation tooling`_ to
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gracefully rename policies.
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Use different prefix in policy rule name for EC2/V2/V2.1 API
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. _documented: https://docs.openstack.org/oslo.policy/latest/user/usage.html#naming-policies
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.. _deprecation tooling: https://docs.openstack.org/oslo.policy/latest/reference/api/oslo_policy.policy.html#oslo_policy.policy.DeprecatedRule
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Currently all the APIs(Nova v2/v2.1 API, EC2 API) use same set of policy
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rules. Especially there isn't obvious mapping between those policy rules
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and EC2 API. User can know clearly which policy should be configured for
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specific API.
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Incorporating default roles
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---------------------------
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Nova should provide different prefix for policy rule name that used to
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group them, and put them in different policy configure file in policy.d
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Up until the Rocky release, keystone only ensured a single role called
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``admin``
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was available to the deployment upon installation. In Rocky, this support was
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expanded to include ``member`` and ``reader`` roles as first-class citizens during
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keystone's installation. This allows service developers to rely on these roles
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and include them in their default policy definitions. Standardizing on a set of
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role names for default policies increases interoperability between deployments
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and decreases operator overhead.
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* EC2 API: Use prefix "ec2_api". The rule looks like "ec2_api:[action]"
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You can find more information on default roles in the keystone `specification`_
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or `developer documentation`_.
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* Nova V2 API: After we move to V2.1, we needn't spend time to change V2
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api rule, and needn't to bother deployer upgrade their policy config. So
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just keep V2 API policy rule named as before.
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.. _specification: http://specs.openstack.org/openstack/keystone-specs/specs/keystone/rocky/define-default-roles.html
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.. _developer documentation: https://docs.openstack.org/keystone/latest/contributor/services.html#reusable-default-roles
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* Nova V2.1 API: We name the policy rule as
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"os_compute_api:[extension]:[action]". The core API may be changed in
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the future, so we needn't name them as "compute" or "compute_extension"
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to distinguish the core or extension API.
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Compartmentalized policy enforcement
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------------------------------------
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This will affect EC2 API and V2.1 API. For EC2 API, it need deployer update
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their policy config. For V2.1 API, there isn't any user yet, so there won't
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any effect.
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Policy logic and processing is inherently sensitive and often complicated. It
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is sensitive in that coding mistakes can lead to security vulnerabilities. It
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is complicated in the resources and APIs it needs to protect and the vast
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number of use cases it needs to support. These reasons make a case for
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isolating policy enforcement and processing into a compartmentalized space, as
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opposed to policy logic bleeding through to different layers of nova. Not
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having all policy logic in a single place makes evolving the policy enforcement
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system arduous and makes the policy system itself fragile.
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Existed Nova API being restricted
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---------------------------------
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Currently, the database and API components of nova contain policy logic. At
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some point, we should refactor these systems into a single component that is
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easier to maintain. Before we do this, we should consider approaches for
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bolstering testing coverage, which ensures we are aware of or prevent policy
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regressions. There are examples and documentation in API protection `testing
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guides`_.
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Nova provide default policy rules for all the APIs. Operator should only make
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the policy rule more permissive. If the Operator make the API to be restricted
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that make break the existed API user or application. That's kind of
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back-incompatible. SO Operator can free to add additional permission to the
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existed API.
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.. _testing guides: https://docs.openstack.org/keystone/latest/contributor/services.html#ruthless-testing
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Policy Enforcement by user_id
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-----------------------------
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Refactoring hard-coded permission checks
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----------------------------------------
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In the legacy v2 API, the policy enforces with target object, and some operators
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implement user-based authorization based on that. Actually only project-based
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authorization is well tested, the user based authorization is untested and
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isn't supported by Nova. In the future, the nova will remove all the supports
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for user-based authorization.
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The policy system in nova is designed to be configurable. Despite this design,
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there are some APIs that have hard-coded checks for specific roles. This makes
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configuration impossible, misleading, and frustrating for operators. Instead,
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we can remove hard-coded policies and ensure a configuration-driven approach,
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which reduces technical debt, increases consistency, and provides better
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user-experience for operators. Additionally, moving hard-coded checks into
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first-class policy rules let us use existing policy tooling to deprecate,
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document, and evolve policies.
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Granular policy checks
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----------------------
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Policies should be as granular as possible to ensure consistency and reasonable
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defaults. Using a single policy to protect CRUD for an entire API is
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restrictive because it prevents us from using default roles to make delegation
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to that API flexible. For example, a policy for ``compute:foobar`` could be
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broken into ``compute:foobar:create``, ``compute:foobar:update``,
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``compute:foobar:list``, ``compute:foobar:get``, and ``compute:foobar:delete``.
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Breaking policies down this way allows us to set read-only policies for
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readable operations or use another default role for creation and management of
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`foobar` resources. The oslo.policy library has `examples`_ that show how to do
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this using deprecated policy rules.
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.. _examples: https://docs.openstack.org/oslo.policy/latest/reference/api/oslo_policy.policy.html#oslo_policy.policy.DeprecatedRule
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