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@cybertec.at> wrote:

Kenaniah Cerny <kenaniah@gmail.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