Re: DROP OWNED BY fails to clean out pg_init_privs grants

Attached is a minimal patch to allow missing roles in REVOKE command

This should fix the pg_upgrade issue and also a case where somebody
has dropped a role you are trying to revoke privileges from :

smalltest=# create table revoketest();
CREATE TABLE
smalltest=# revoke select on revoketest from bob;
WARNING: ignoring REVOKE FROM a missing role "bob"
REVOKE
smalltest=# create user bob;
CREATE ROLE
smalltest=# grant select on revoketest to bob;
GRANT
smalltest=# \du
List of roles
Role name | Attributes
-----------+------------------------------------------------------------
bob |
hannuk | Superuser, Create role, Create DB, Replication, Bypass RLS

smalltest=# \dp
Access privileges
Schema | Name | Type | Access privileges | Column
privileges | Policies
--------+------------+-------+------------------------+-------------------+----------
public | revoketest | table | hannuk=arwdDxtm/hannuk+| |
| | | bob=r/hannuk | |
public | vacwatch | table | | |
(2 rows)

smalltest=# revoke select on revoketest from bob, joe;
WARNING: ignoring REVOKE FROM a missing role "joe"
REVOKE
smalltest=# \dp
Access privileges
Schema | Name | Type | Access privileges | Column
privileges | Policies
--------+------------+-------+------------------------+-------------------+----------
public | revoketest | table | hannuk=arwdDxtm/hannuk | |
public | vacwatch | table | | |
(2 rows)

On Sun, May 26, 2024 at 12:05 AM Hannu Krosing <hannuk(at)google(dot)com> wrote:
>
> On Sat, May 25, 2024 at 4:48 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >
> > Hannu Krosing <hannuk(at)google(dot)com> writes:
> > > Having an pg_init_privs entry referencing a non-existing user is
> > > certainly of no practical use.
> >
> > Sure, that's not up for debate. What I think we're discussing
> > right now is
> >
> > 1. What other cases are badly handled by the pg_init_privs
> > mechanisms.
> >
> > 2. How much of that is practical to fix in v17, seeing that
> > it's all long-standing bugs and we're already past beta1.
> >
> > I kind of doubt that the answer to #2 is "all of it".
> > But perhaps we can do better than "none of it".
>
> Putting the fix either in pg_dump or making REVOKE tolerate
> non-existing users would definitely be most practical / useful fixes,
> as these would actually allow pg_upgrade to v17 to work without
> changing anything in older versions.
>
> Currently one already can revoke a privilege that is not there in the
> first place, with the end state being that the privilege (still) does
> not exist.
> This does not even generate a warning.
>
> Extending this to revoking from users that do not exist does not seem
> any different on conceptual level, though I understand that
> implementation would be very different as it needs catching the user
> lookup error from a very different part of the code.
>
> That said, it would be better if we can have something that would be
> easy to backport something that would make pg_upgrade work for all
> supported versions.
> Making REVOKE silently ignore revoking from non-existing users would
> improve general robustness but could conceivably change behaviour if
> somebody relies on it in their workflows.
>
> Regards,
> Hannu