Re: Fix unqualified catalog references in psql describe queries - Mailing list pgsql-hackers

在 2026/6/8 16:46, Chao Li 写道:
> Hi,
>
> While testing "[aecc55866] psql: Show comments in \dRp+, \dRs+, and \dX+", I noticed a small issue that was actually
introducedby "[8185bb534] CREATE SUBSCRIPTION … SERVER”.
 
>
> The problem is that, when querying pg_foreign_server, it misses the "pg_catalog" schema qualification:
> ```
>             appendPQExpBuffer(&buf,
>                               ", (select srvname from pg_foreign_server where oid=subserver) AS \"%s\"\n",
>                               gettext_noop("Server"));
> ```
>
> This is not a big problem, but it provides a way to pollute the result of \dRs+ by adding a fake pg_foreign_server
earlierin search_path. See this repro:
 
>
> 1. Setup: create a server and a sub
> ```
> evantest=# create extension postgres_fdw;
> CREATE EXTENSION
> evantest=# create publication pub;
> CREATE PUBLICATION
> evantest=# create server s foreign data wrapper postgres_fdw options (dbname 'postgres');
> CREATE SERVER
> evantest=# create user mapping for current_user server s;
> CREATE USER MAPPING
> evantest=# create subscription sub server s publication pub with (connect=false, slot_name=none);
> WARNING:  subscription was created, but is not connected
> HINT:  To initiate replication, you must manually create the replication slot, enable the subscription, and alter the
subscriptionto refresh publications.
 
> CREATE SUBSCRIPTION
> evantest=# \dRs+ sub;
>
                        List of subscriptions
 
>   Name | Owner | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password
required| Run as owner? | Failover | Server | Retain dead tuples | Max retention duration | Retention active |
Synchronouscommit | Conninfo | Receiver timeout |  Skip LSN  | Description
 
>
------+-------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------+--------------------+------------------------+------------------+--------------------+----------+------------------+------------+-------------
>   sub  | chaol | f       | {pub}       | f      | parallel  | d                | f                | any    | t
        | f             | f        | s      | f                  |                      0 | f                | off
         |          | -1               | 0/00000000 |
 
> (1 row)
> ```
>
> As shown above, “Server” column shows the correct server name “s”.
>
> 2. Now, pollute the result
> ```
> evantest=# create temp table pg_foreign_server (oid oid, srvname name);
> CREATE TABLE
> evantest=# insert into pg_foreign_server select oid, 'fake_s'::name from pg_catalog.pg_foreign_server where
srvname='s';
> INSERT 0 1
> evantest=# \dRs+ sub;
>
                        List of subscriptions
 
>   Name | Owner | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password
required| Run as owner? | Failover | Server | Retain dead tuples | Max retention duration | Retention active |
Synchronouscommit | Conninfo | Receiver timeout |  Skip LSN  | Description
 
>
------+-------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------+--------------------+------------------------+------------------+--------------------+----------+------------------+------------+-------------
>   sub  | chaol | f       | {pub}       | f      | parallel  | d                | f                | any    | t
        | f             | f        | fake_s | f                  |                      0 | f                | off
         |          | -1               | 0/00000000 |
 
> (1 row)
> ```
>
> Now, the "Server" column shows the fake server name that I supplied.

I just tried the repro. I never knew a way to make \dRs+ to output wrong data like this, this is interesting.

> The fix is to add the schema qualification, using "pg_catalog.pg_foreign_server". In describe.c, catalog objects are
generallyreferenced by qualified names. I found 3 other occurrences that missed schema qualification, so I fixed them
aswell.
 
>
> There are 4 spots in total. Two are v19-new, oversights of 8185bb53476378443240d57f7d844347d5fae1bf and
2f094e7ac691abc9d2fe0f4dcf0feac4a6ce1d9c.The other two are older and might be worth back-patching. So I split the fix
into2 commits: 0001 is v19-new, and 0002 is a back-patch candidate.
 
>
> Best regards,
> --
> Chao Li (Evan)
> HighGo Software Co., Ltd.
> https://www.highgo.com/
>
>
>

The patch looks good to me. I applied the patch locally and verified it with “make check-world”.

Regards,
Tingchuan Sun