Re: BUG #19523: psql tab-completion shadows pg_db_role_setting

Hi Kirill,

Thanks, and sorry for the two threads — the second was an accidental
resend that didn't thread properly on my end , so let's keep it here.

You're right that it's not a vulnerability, and the "attacker" framing
was overblown — the docs are clear that removing publicly-writable
schemas from search_path is the real safeguard. The intent is just
consistency and robustness: the same query already qualifies
unnest()/split_part() with pg_catalog, and the analogous
subscription-variable completion query qualifies its catalogs, so this
only brings pg_db_role_setting/pg_database in line. As a side benefit
it avoids a surprising tab-completion result for anyone who happens to
have a same-named table earlier in search_path, misconfigured or not.

Thanks for the +1.

Regards,
Vismay

On Fri, Jul 10, 2026 at 10:19 AM Kirill Reshke <reshkekirill(at)gmail(dot)com> wrote:
>
>
> Hi! You seem to create two threads on the issue, so I don't quite understand where to respond. anyway:
>
> On Thu, 9 Jul 2026, 15:14 Vismay Tiwari, <vismay(dot)t(at)gmail(dot)com> wrote:
>>
>> Hi,
>>
>> Reproduced on current master. The tab-completion query for
>> "ALTER DATABASE ... RESET" (Query_for_list_of_database_vars) references
>> pg_db_role_setting and pg_database without a pg_catalog qualification, so a
>> same-named table earlier in search_path shadows the catalog:
>>
>> CREATE SCHEMA attacker;
>> CREATE TABLE attacker.pg_db_role_setting (setdatabase oid, setrole
>> oid, setconfig text[]);
>> INSERT INTO attacker.pg_db_role_setting
>> SELECT oid, 0, ARRAY['evil_var=x'] FROM pg_database WHERE
>> datname = 'postgres';
>> SET search_path = attacker, pg_catalog;
>> -- "ALTER DATABASE postgres RESET <TAB>" then offers evil_var
>>
>
> Preventing this makes sense in case somebody accidentally misconfigured their server. Which is not very probable for a table with `pg_db_role_setting` name.
> Also note that this is not a vulnerability: from https://www.postgresql.org/docs/current/app-psql.html says:
>
> If untrusted users have access to a database that has not adopted a secure
> schema usage pattern, begin your session by removing publicly-writable
> schemas from search_path.
>
> Anyway +1 on fixing
>
>