On 11/26/2014 09:52 AM, David Chadwick wrote:
I tend to agree with Morgan. There are resources and there are users.
And there is something in the middle that says which users can access
which resources. It might be an ACL, a RBAC role, or a set of ABAC
attributes, or something else (such as a MAC policy). So to my mind this
middle bit, whilst being connected to both resources and users, is
separate from both of them. So we should not artificially put it with
just one of them.
FYI, the roles in RBAC are part of the policy specification. You define
the roles, their hierarchical relationships, then assign both users and
resources (privileges actually) to them. So roles could be part of the
policy specification, except that the policy is distributed, so in which
part of the distributed policy would you put it? Would it be in the
specification of roles to actions, or in the attribute mappings, or in
the user to attribute assignments?
I'd say that for this split we leave roles in assignment, but that when
we get to the "store policy rules in a database" spec we move them to
policy.
https://review.openstack.org/#/c/133814
as using Hierarchical rules to generate policy implies that the whole
thing is in a unified, choherent structure.
https://review.openstack.org/#/c/125704/7
regards
David
On 25/11/2014 16:42, Morgan Fainberg wrote:
On Nov 25, 2014, at 4:25 AM, Henry Nash <[email protected]> wrote:
Hi
As most of you know, we have approved a spec (https://review.openstack.org/#/c/129397/) to
split the assignments component up into two pieces, and the code (divided up into a series of
patches) is currently in review (https://review.openstack.org/#/c/130954/). While most aspects
of the split appear to have agreement, there is one aspect that has been questioned - and that
is the whether "roles' should be in the "resource" component, as proposed?
First, let's recap the goals here:
1) The current "assignment" component is really what's left after we split off users/groups into
"identity" some releases ago. "Assignments" is pretty complicated and messy - and we
need a better structure (as an example, just doing the split allowed me to find 5 bugs in our current
implementation - and I wouldn't be surprised if there are more). This is made more urgent by the fact that
we are about to land some big new changes in this area, e.g. hierarchical projects and a re-implemntation
(for performance) of list_role_assignments.
2) While Keystone may have started off as a service where we "store all the users,
credentials & permissions" needed to access other OpenStack services, we more and
more see Keystone as a wrapper for existing corporate authentication and authorisation
mechanisms - and it's job is really to provided a common mechanism and language for these to
be consumed across OpenStack services. To do this well, we must make sure that the keystone
components are split along sensible lines...so that they can individually wrap these
corporate directories/services. The classic case of this was are previous split off of
Identity...and this new proposal takes this a step further.
3) As more and more broad OpenStack powered clouds are created, we must makes
sure that our Keystone implementation is as flexible as possible. We already
plan to support new abstractions for things like cloud providers enabling
resellers to do business within one OpenStack cloud (by providing hierarchical
multi-tenancy, domain-roles etc.). Our current assignments model is a) slightly
unusual in that all roles are global and every assignment has
actor-target-role, and b) cannot easily be substituted for alternate assignment
models (even for the whole of an OpenStack installation, let alone on a domain
by domain basis)
The proposal for splitting the assignment component is trying to provide a better basis for the above. It
separates the storing and CRUD operations of domain/projects/roles into a "resource" component,
while leaving the pure assignment model in "assignment". The rationale for this is that the
resource component defines the entities that the rest of the OpenStack services (and their policy engines)
understand...while assignment is a pure mapper between these entities. The details of these mappings are
never exposed outside of Keystone, except for the generation of contents of a token. This would allow new
assignment models to be introduced that, as long as they support the api to "list what role_ids are
mapped to project_id X for user_id Y", then the rest of OpenStack would never know anything had changed.
So to (finally) get the the point of this post...where should the role definitions live?
The proposal is that these live in "resource", because:
a) They represent the definition of how Keystone and the other services define
permission - and this should be independent of whatever assignment model we
choose
b) We may well chose (in the future) to morph what we currently means as a role...into what they really are,
which is a capability. Once we have domain-specifc roles (groups), which map to "global roles",
then we may well end up, more often than not, with a role representing a single API capability.
"Roles" might even be "created" simply by a service registering its capabilities with
Keystone. Again, this should be independent of any assignment model.
I think there is some dissonance in storing the roles in resource. The
assignment backend is what controls how the actor is connected with the scope.
If you’re keeping the role within the resource backend you’re now needing to
have yet another way of correlating the data from the resource side (2
elements) to the identity (user/group) side. The assignment backend is
connecting the role to the actor and scope (project/domain), it should in some
way be responsible for knowing what the role definition is. In the case of a
crazy ABAC system, a role would need to be a mapping of attributes on the actor
object, that now needs *another* layer of connection (similar to what we have
now) to the roles in resource. Logically the roles seem tightly coupled to the
assignment backend, not a loosely
coupled-and-theoretically-can-be-completly-ignored.
c) By placing roles in the resource component, we allow much greater
flexibility....for example we could have different domains having different
assignment models (e.g. one RABC, one ABAC, one HenrysWeirdAccessControl
(HWAC). Obviously this would be aimed at a different type of cloud than one
that has multiple layers of domain inheritance - but that's part of the goal of
OpenStack, to allow different models to be supported.
To point C, I am not convinced that each domain should have different
assignment model support. This is adding significant complexity to the whole
system and potentially breaking any form of consistency with the authorization
for users/groups to access the OpenStack services. I need to see a strong
use-case to see this as worthwhile, right now this feels like a “it would be
cool to have this functionality” but I don’t see a strong use-case. Please help
me to understand the use-case and how this benefits the system as a whole
without (essentially) making it significantly harder to ensure a consistent
answer to the question “what roles/actions can I perform in this deployment?”.
I am absolutely open to arguments that roles should remain with
"assignments"...but right now the above feels the better solution. I've put
this topic on the agenda for today's Keystone IRC meeting.
Let me add that I am for the split of resource and assignment from a purely
architectural standpoint. It opens the doors to allow for better/custom
implementations of assignments (whatever that may be) without needing to
implement all of the project/domain management logic as well.
Cheers,
Morgan
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