Re: Proposal: allow database-specific role memberships

Hi Antonin,

First of all, thank you so much for taking the time to review my patch.
I'll answer your questions in reverse order:

The "unsafe_tests" directory is where the pre-existing role tests were
located. According to the readme of the "unsafe_tests" directory, the tests
contained within are not run during "make installcheck" because they could
have side-effects that seem undesirable for a production installation. This
seemed like a reasonable location as the new tests that this patch
introduces also modifies the "state" of the database cluster by adding,
modifying, and removing roles & databases (including template1).

Regarding roles_is_member_of(), the nuance is that role "A" in your example
would only be considered a member of role "B" (and by extension role "C")
when connected to the database in which "A" was granted database-specific
membership to "B". Conversely, when connected to any other database, "A"
would not be considered to be a member of "B".

This patch is designed to solve the scenarios in which one may want to
grant constrained access to a broader set of privileges. For example,
membership in "pg_read_all_data" effectively grants SELECT and USAGE rights
on everything (implicitly cluster-wide in today's implementation). By
granting a role membership to "pg_read_all_data" within the context of a
specific database, the grantee's read-everything privilege is effectively
constrained to just that specific database (as membership within
"pg_read_all_data" would not otherwise be held).

A rebased version is attached.

Thanks again!

- Kenaniah

On Wed, Jun 29, 2022 at 6:45 AM Antonin Houska <ah(at)cybertec(dot)at> wrote:

> Kenaniah Cerny <kenaniah(at)gmail(dot)com> wrote:
>
> > Attached is a newly-rebased patch -- would love to get a review from
> someone whenever possible.
>
> I've picked this patch for a review. The patch currently does not apply to
> the
> master branch, so I could only read the diff. Following are my comments:
>
> * I think that roles_is_member_of() deserves a comment explaining why the
> code
> that you moved into append_role_memberships() needs to be called twice,
> i.e. once for global memberships and once for the database-specific ones.
>
> I think the reason is that if, for example, role "A" is a
> database-specific
> member of role "B" and "B" is a "global" member of role "C", then "A"
> should
> not be considered a member of "C", unless "A" is granted "C" explicitly.
> Is
> this behavior intended?
>
> Note that in this example, the "C" members are a superset of "B" members,
> and thus "C" should have weaker permissions on database objects than
> "B". What's then the reason to not consider "A" a member of "C"? If "C"
> gives its members some permissions of "B" (e.g. "pg_write_all_data"),
> then I
> think the roles hierarchy is poorly designed.
>
> A counter-example might help me to understand.
>
> * Why do you think that "unsafe_tests" is the appropriate name for the
> directory that contains regression tests?
>
> I can spend more time on the review if the patch gets rebased.
>
> --
> Antonin Houska
> Web: https://www.cybertec-postgresql.com
>