[openstack-dev] [all][policy][keystone] Better Policy Model and Representing Capabilites

Morgan Fainberg morgan.fainberg at gmail.com
Mon Oct 13 20:17:44 UTC 2014

Description of the problem: Without attempting an action on an endpoint with a current scoped token, it is impossible to know what actions are available to a user.

Horizon makes some attempts to solve this issue by sourcing all of the policy files from all of the services to determine what a user can accomplish with a given role. This is highly inefficient as it requires processing the various policy.json files for each request in multiple places and presents a mechanism that is not really scalable to understand what a user can do with the current authorization. Horizon may not be the only service that (in the long term) would want to know what actions a token can take.

I would like to start a discussion on how we should improve our policy implementation (OpenStack wide) to help make it easier to know what is possible with a current authorization context (Keystone token). The key feature should be that whatever the implementation is, it doesn’t require another round-trip to a third party service to “enforce” the policy which avoids another scaling point like UUID Keystone token validation.

Here are a couple of ideas that we’ve discussed over the last few development cycles (and none of this changes the requirements to manage scope of authorization, e.g. project, domain, trust, ...):

1. Keystone is the holder of all policy files. Each service gets it’s policy file from Keystone and it is possible to validate the policy (by any other service) against a token provided they get the relevant policy file from the authoritative source (Keystone).

Pros: This is nearly completely compatible with the current policy system. The biggest change is that policy files are published to Keystone instead of to a local file on disk. This also could open the door to having keystone build “stacked” policies (user/project/domain/endpoint/service specific) where the deployer could layer policy definitions (layering would allow for stricter enforcement at more specific levels, e.g. users from project X can’t terminate any VMs).

Cons: This doesn’t ease up the processing requirement or the need to hold (potentially) a significant number of policy files for each service that wants to evaluate what actions a token can do.

2. Each enforcement point in a service is turned into an attribute/role, and the token contains all of the information on what a user can do (effectively shipping the entire policy information with the token).

Pros: It is trivial to know what a token provides access to: the token would contain something like `{“nova”: [“terminate”, “boot”], “keystone”: [“create_user”, “update_user”], ...}`. It would be easily possible to allow glance “get image” nova “boot” capability instead of needing to know the roles for policy.json for both glance and nova work for booting a new VM.

Cons: This would likely require a central registry of all the actions that could be taken (something akin to an IANA port list). Without a grouping to apply these authorizations to a user (e.g. keystone_admin would convey “create_project, delete_project, update_project, create_user, delete_user, update_user, ...”) this becomes unwieldy. The “roles” or “attribute” that convey capabilities are also relatively static instead of highly dynamic as they are today. This could also contribute to token-bloat.

I’m sure there are more ways to approach this problem, so please don’t hesitate to add to the conversation and expand on the options. The above options are by no mean exhaustive  nor fully explored. This change may not even be something to be expected within the current development cycle (Kilo) or even the next, but this is a conversation that needs to be started as it will help make OpenStack better.


Morgan Fainberg

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