Subject: Re: pg_maintain and USAGE privilege on schema

From: Nathan Bossart <[email-masked]>
Date: Sun, 7 Jul 2024 21:13:44 -0500

On Mon, Jul 08, 2024 at 01:03:42AM +0900, Fujii Masao wrote:
> I've noticed an issue with non-superusers who have the pg_maintain role.
> When they run VACUUM on a specific table within a specific schema,
> like "VACUUM mynsp.mytbl", it fails if they don't have the USAGE privilege
> on the schema. For example, the error message logged is
> "ERROR: permission denied for schema mynsp". However, running VACUUM
> without specifying the table name, such as "VACUUM",
> completes successfully and vacuums all tables, including those in schemas
> where the user lacks the USAGE privilege.
> 
> Is this behavior intentional?

I'd consider it intentional because it matches the database owner behavior.
If the database owner does not have USAGE on a schema, they'll similarly be
unable to VACUUM a specific table in that schema while being able to VACUUM
it via a database-wide command.  That's admittedly a little weird, but IMHO
any changes in this area should apply to both pg_maintain and the database
owner.

> I assumed that a pg_maintain user could run VACUUM on specific tables
> in any schema without needing additional privileges. So, shouldn't
> pg_maintain users be able to perform maintenance commands as if they have
> USAGE rights on all schemas?

It might be reasonable to give implicit USAGE privileges on all schemas
during maintenance commands to pg_maintain roles.  I would be a little
hesitant to consider this v17 material, though.

There are some other inconsistencies that predate MAINTAIN that I think we
ought to clear up at some point.  For example, the privilege checks for
REINDEX work a bit differently than VACUUM, ANALYZE, and CLUSTER.  I doubt
that's causing anyone too much trouble in the field, but since we're
grouping these commands together as "maintenance commands" now, it'd be
nice to make them as consistent as possible.

-- 
nathan

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From: Fujii Masao <[email-masked]>
Date: Wed, 10 Jul 2024 17:13:58 +0900

On 2024/07/08 11:13, Nathan Bossart wrote:
> it via a database-wide command. 

Yes, you're right.

> That's admittedly a little weird, but IMHO

However, unlike the database owner, pg_maintain by definition should
have *all* the rights needed for maintenance tasks, including MAINTAIN
rights on tables and USAGE rights on schemas? ISTM that both
pg_read_all_data and pg_write_all_data roles are defined similarly,
with USAGE rights on all schemas. So, granting USAGE rights to
pg_maintain, but not the database owner, doesn't seem so odd to me.

> hesitant to consider this v17 material, though.

That's a valid concern. I'd like hear more opinions about this.

> nice to make them as consistent as possible.

+1

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION

---

From: Jeff Davis <[email-masked]>
Date: Wed, 10 Jul 2024 12:29:00 -0700

On Wed, 2024-07-10 at 17:13 +0900, Fujii Masao wrote:
> ISTM that both
> with USAGE rights on all schemas.

I'm not so sure that was a great idea to begin with. If you create a
private schema with a SECURITY DEFINER function in it, it's a bit odd
to allow someone with pg_read_all_data to execute it. Granted, that's
documented behavior, but I'm not sure the privileges should be bundled
in that fashion.

> > during maintenance commands to pg_maintain roles.

That's an even more specific exception: having USAGE only in the
context of a maintenance command. I think that's a new concept, right?

Regards,
	Jeff Davis

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From: Nathan Bossart <[email-masked]>
Date: Wed, 10 Jul 2024 14:32:06 -0500

> context of a maintenance command. I think that's a new concept, right?

AFAIK yes.

-- 
nathan