prevent users from SELECT-ing from pg_roles/pg_database

Greetings,

To prevent a user or role from selecting data from certain system tables in
PostgreSQL, you can revoke the default select permissions on those tables.
Here’s how you can do it:

1. Revoke SELECT permission on the system tables from the public role.
2. Grant SELECT permission only to specific roles that need it.

Here’s a step-by-step guide on how to achieve this:

Salahuddin.

On Fri, 24 May 2024, 20:52 Andreas Joseph Krogh, <andreas@visena.com> wrote:

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

Greetings,

Yes, you are correct. And

For applications/systems/scripts relying on this information may require
sgnificent modifications to handle the restricted access.

Alternative approches can be.

Auditing and monitoring.
You can use pgaudit extension for auditing and minitoring.

Use SE-PostgeSQL extension that give fine grained access control other than
PG standard permissions.

Try RLS row level security. May involve careful planning and may not cover
all use cases.

Regards,
Salahuddin.

On Fri, 24 May 2024, 22:02 Tom Lane, <tgl@sss.pgh.pa.us> wrote:

På fredag 24. mai 2024 kl. 19:02:13, skrev Tom Lane <tgl@sss.pgh.pa.us
<mailto:tgl@sss.pgh.pa.us>>:
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

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…

--
Andreas Joseph Krogh
CTO / Partner - Visena AS
Mobile: +47 909 56 963
andreas@visena.com <mailto:andreas@visena.com>
www.visena.com <https://www.visena.com&gt;
<https://www.visena.com&gt;

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

På mandag 27. mai 2024 kl. 11:10:10, skrev Laurenz Albe <
laurenz.albe@cybertec.at <mailto: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".

Yours,
Laurenz Albe

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

Any hints welcome.

--
Andreas Joseph Krogh
CTO / Partner - Visena AS
Mobile: +47 909 56 963
andreas@visena.com <mailto:andreas@visena.com>
www.visena.com <https://www.visena.com&gt;
<https://www.visena.com&gt;

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

På tirsdag 28. mai 2024 kl. 01:48:17, skrev Tom Lane <tgl@sss.pgh.pa.us
<mailto:tgl@sss.pgh.pa.us>>:
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

Ah, that's what I was missing. Thanks for pointing that out, it's working as
expected now.

--
Andreas Joseph Krogh
CTO / Partner - Visena AS
Mobile: +47 909 56 963
andreas@visena.com <mailto:andreas@visena.com>
www.visena.com <https://www.visena.com&gt;
<https://www.visena.com&gt;