Re: BUG #19097: System catalog modifications are allowed by alter

On Wed, 29 Oct 2025 at 16:02, PG Bug reporting form
<noreply@postgresql.org> wrote:
>
> The following bug has been logged on the website:
>
> Bug reference:      19097
> Logged by:          RekGRpth
> Email address:      rekgrpth@gmail.com
> PostgreSQL version: 18.0
> Operating system:   docker alpine
> Description:
>
> ```sql
> create table pg_catalog.t (i int);
> ERROR:  permission denied to create "pg_catalog.t"
> DETAIL:  System catalog modifications are currently disallowed.
>
> create table t (i int);
> CREATE TABLE
>
> alter table t set schema pg_catalog;
> ALTER TABLE
>
> \dS+ t
>                                           Table "pg_catalog.t"
>  Column |  Type   | Collation | Nullable | Default | Storage | Compression |
> Stats target | Description
> --------+---------+-----------+----------+---------+---------+-------------+--------------+-------------
>  i      | integer |           |          |         | plain   |             |
> |
> Replica Identity: NOTHING
> Access method: heap
>
> drop table pg_catalog.t;
> DROP TABLE
> ```
>

reproduced here on v13, v16, v18 and HEAD. Looks like we need to teach
ExecAlterObjectSchemaStmt to respect allow_system_table_mods GUC.
PFA doing this by adding checks to CheckSetNamespace

-- 
Best regards,
Kirill Reshke