Date: Wed, 22 Jun 2022 09:25:50 -0700
From: Nathan Bossart <nathandbossart@gmail.com>
To: Noah Misch <noah@leadboat.com>
Cc: Michael Paquier <michael@paquier.xyz>, pgsql-bugs@lists.postgresql.org,
	=?iso-8859-1?Q?F=E4rber=2C_Franz-Josef_=28StMUK=29?=
 <Franz-Josef.Faerber@stmuk.bayern.de>,
	Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: Extension pg_trgm, permissions and pg_dump order
Message-ID: <20220622162550.GA95419@nathanxps13>
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On Tue, Jun 21, 2022 at 08:37:04PM -0700, Noah Misch wrote:
> On Tue, Jun 21, 2022 at 10:56:16AM -0700, Nathan Bossart wrote:
>> On Wed, Jun 15, 2022 at 10:42:18PM -0700, Noah Misch wrote:
>> > +		 * Identify the opclass to use.  Use of ddl_userid is necessary due to
>> > +		 * ACL checks therein.  This is safe despite opclasses containing
>> > +		 * opaque expressions (specifically, functions), because only
>> > +		 * superusers can define opclasses.
>> 
>> It's not clear to me why the fact that only superusers can define opclasses
>> makes this safe.
> 
> 		classOidP[attn] = ResolveOpClass(attribute->opclass,
> 										 atttype,
> 										 accessMethodName,
> 										 accessMethodId);
> 
> To write the comment, I pondered how those four arguments could conceivably
> lead ResolveOpClass() to locate Trojan code.  Since only superusers can define
> opclasses, we can assume the catalog entries of an opclass do not point to
> Trojan code.  (The superuser could just do the mischief directly, rather than
> going to extra trouble to set a trap for later.)  If you see a hole in that
> thinking, please do share.

Thanks for clarifying.  That makes sense to me.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com