From: Tom Lane <tgl@sss.pgh.pa.us>
To: Arseny Sher <a.sher@postgrespro.ru>
cc: pgsql-hackers <pgsql-hackers@postgresql.org>,
        Alvaro Herrera <alvherre@alvh.no-ip.org>
Subject: Re: Use-after-free in 12- EventTriggerAlterTableEnd
In-reply-to: <877drcyprb.fsf@ars-thinkpad>
References: <877drcyprb.fsf@ars-thinkpad>
Comments: In-reply-to Arseny Sher <a.sher@postgrespro.ru>
	message dated "Tue, 27 Oct 2020 12:36:24 +0300"
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Date: Tue, 27 Oct 2020 15:21:07 -0400
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Arseny Sher <a.sher@postgrespro.ru> writes:
> Valgrind on our internal buildfarm complained about use-after-free
> during currentEventTriggerState->commandList manipulations, e.g. lappend
> in EventTriggerCollectSimpleCommand. I've discovered that the source of
> problem is EventTriggerAlterTableEnd not bothering to switch into its
> own context before appending to the list. ced138e8cba fixed this in
> master and 13 but wasn't backpatched further, so I see the problem in
> 12-.

Yeah, that clearly should have been back-patched --- the fact that it
accidentally didn't fail in the most common case wasn't a good reason
for leaving the bug in place.  I'm not excited about the test case
ced138e8cba added though, so I think your proposed patch is fine.
Will push shortly.

			regards, tom lane