From: Tom Lane <tgl@sss.pgh.pa.us>
To: PetSerAl <petseral@gmail.com>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: Server crash when selecting from pg_cursors
Date: Sun, 06 Oct 2024 14:08:25 -0400
Message-ID: <1375463.1728238105@sss.pgh.pa.us> (raw)
In-Reply-To: <CAKygsHTBXLXjwV43kpZa+Cs+XTiaeeJiZdL4cPBm9f4MTdw7wg@mail.gmail.com>
References: <CAKygsHTBXLXjwV43kpZa+Cs+XTiaeeJiZdL4cPBm9f4MTdw7wg@mail.gmail.com>
PetSerAl <petseral@gmail.com> writes:
> postgres=# CREATE TABLE t (a integer, b integer);
> CREATE TABLE
> postgres=# CREATE FUNCTION f() RETURNS integer
> postgres-# STABLE STRICT LANGUAGE plpgsql
> postgres-# AS $$
> postgres$# BEGIN
> postgres$# PERFORM FROM pg_cursors;
> postgres$# RETURN null;
> postgres$# END
> postgres$# $$;
> CREATE FUNCTION
> postgres=# DO $$
> postgres$# DECLARE
> postgres$# a integer;
> postgres$# BEGIN
> postgres$# FOR a IN SELECT t.a FROM t WHERE t.b = f() LOOP
> postgres$# END LOOP;
> postgres$# END
> postgres$# $$;
> server closed the connection unexpectedly
Huh, nice one. It's not new in v17 though --- it seems quite ancient.
The proximate cause is that pg_cursor() is assuming portal->sourceText
can't be NULL:
values[1] = CStringGetTextDatum(portal->sourceText);
which is not unreasonable considering that portal.h quoth
const char *sourceText; /* text of query (as of 8.4, never NULL) */
But there's a problem: we may be examining a portal that has been
added to the portal hashtable, but for which PortalDefineQuery
hasn't been called yet.
There are a few ways we might try to deal with this, but I think
the most reasonable one is to make pg_cursor() ignore portals
that haven't been defined yet, as attached.
regards, tom lane
Attachments:harden-pg_cursor-against-null-sourceText.patch (text/x-diff, 548B) downloaddiff --git a/src/backend/utils/mmgr/portalmem.c b/src/backend/utils/mmgr/portalmem.cindex 4a24613537..93137820ac 100644--- a/src/backend/utils/mmgr/portalmem.c+++ b/src/backend/utils/mmgr/portalmem.c@@ -1150,6 +1150,9 @@ pg_cursor(PG_FUNCTION_ARGS)
/* report only "visible" entries */
if (!portal->visible)
continue;
+ /* also ignore it if PortalDefineQuery hasn't been called yet */+ if (!portal->sourceText)+ continue;
values[0] = CStringGetTextDatum(portal->name);
values[1] = CStringGetTextDatum(portal->sourceText);
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, petseral@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: Server crash when selecting from pg_cursors
In-Reply-To: <1375463.1728238105@sss.pgh.pa.us>
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