logical replication worker accesses catalogs in error context callback

[Andres Freund]

Hi,

Due to a debug ereport I just noticed that worker.c's
slot_store_error_callback is doing something quite dangerous:

static void
slot_store_error_callback(void *arg)
{
        SlotErrCallbackArg *errarg = (SlotErrCallbackArg *) arg;
        LogicalRepRelMapEntry *rel;
        char       *remotetypname;
        Oid                     remotetypoid,
                                localtypoid;

        /* Nothing to do if remote attribute number is not set */
        if (errarg->remote_attnum < 0)
                return;

        rel = errarg->rel;
        remotetypoid = rel->remoterel.atttyps[errarg->remote_attnum];

        /* Fetch remote type name from the LogicalRepTypMap cache */
        remotetypname = logicalrep_typmap_gettypname(remotetypoid);

        /* Fetch local type OID from the local sys cache */
        localtypoid = get_atttype(rel->localreloid, errarg->local_attnum + 1);

        errcontext("processing remote data for replication target relation 
\"%s.%s\" column \"%s\", "
                           "remote type %s, local type %s",
                           rel->remoterel.nspname, rel->remoterel.relname,
                           rel->remoterel.attnames[errarg->remote_attnum],
                           remotetypname,
                           format_type_be(localtypoid));
}


that's not code that can run in an error context callback. It's
theoretically possible (but unlikely) that
logicalrep_typmap_gettypname() is safe to run in an error context
callback. But get_atttype() definitely isn't.

get_attype() may do catalog accesses. That definitely can't happen
inside an error context callback - the entire transaction might be
borked at this point!


I think this was basically broken from the start in

commit 665d1fad99e7b11678b0d5fa24d2898424243cd6
Author: Peter Eisentraut <pete...@gmx.net>
Date:   2017-01-19 12:00:00 -0500

    Logical replication

but then got a lot worse in

commit 24c0a6c649768f428929e76dd7f5012ec9b93ce1
Author: Alvaro Herrera <alvhe...@alvh.no-ip.org>
Date:   2018-03-14 21:34:26 -0300

    logical replication: fix OID type mapping mechanism

Greetings,

Andres Freund