Обсуждение: prevent users from SELECT-ing from pg_roles/pg_database

Andreas Joseph Krogh <andreas@visena.com> writes:
> Hi, is there a way to prevent a user/role from SELECT-ing from certain 
> system-tables?
> I'd like the contents of pg_{user,roles,database} to not be visible to all 
> users.

As noted, you can in principle revoke the public SELECT grant from
those views/catalogs.  However, the system is not designed to hide
such information, which means you'll have (at least) two kinds of
issues to worry about:

1. Queries or tools breaking that you didn't expect to break.
It's hardly uncommon for instance for queries on pg_class to
join to pg_roles to get the owner names for tables.

2. Information leaks.  For example, mapping role OID to role name
is trivial with either regrole or pg_get_userbyid(), so it
wouldn't take long to scan the plausible range of role OIDs and
get all their names, even without SQL access to the underlying
catalog.

            regards, tom lane

On Mon, 2024-05-27 at 09:33 +0200, Andreas Joseph Krogh wrote:
> I tried:
>
>   REVOKE SELECT ON pg_catalog.pg_database FROM public;
>
> But that doesn't prevent a normal user from querying pg_database it seems…

It works here.

Perhaps the "normal" user is a member of "pg_read_all_data".

Yours,
Laurenz Albe

On Mon, 2024-05-27 at 11:33 +0200, Andreas Joseph Krogh wrote:
> På mandag 27. mai 2024 kl. 11:10:10, skrev Laurenz Albe <laurenz.albe@cybertec.at>:
> > On Mon, 2024-05-27 at 09:33 +0200, Andreas Joseph Krogh wrote:
> > > I tried:
> > >
> > >    REVOKE SELECT ON pg_catalog.pg_database FROM public;
> > >
> > > But that doesn't prevent a normal user from querying pg_database it seems…
> >
> > It works here.
> >
> > Perhaps the "normal" user is a member of "pg_read_all_data".
>  
> Don't think so:
> andreak@[local]:5432 16.3 andreak=# REVOKE pg_read_all_data from nisse;
> WARNING:  role "nisse" has not been granted membership in role "pg_read_all_data" by role "postgres"
> REVOKE ROLE

Possibilities:

- you are running a modified version of PostgreSQL
- you are actually a superuser, perhaps by inheritance

Yours,
Laurenz Albe

Laurenz Albe <laurenz.albe@cybertec.at> writes:
> On Mon, 2024-05-27 at 09:33 +0200, Andreas Joseph Krogh wrote:
>> I tried:
>>    REVOKE SELECT ON pg_catalog.pg_database FROM public;
>> But that doesn't prevent a normal user from querying pg_database it seems…

> It works here.

Works for me too, although you'd have to do it over in each
database where you want it to be effective.  (Although
pg_database is a shared catalog, the metadata about it
is not shared.)

            regards, tom lane