From: Tom Lane <tgl@sss.pgh.pa.us>
To: Daniel Gustafsson <daniel@yesql.se>
cc: 13952878799@163.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #19092: scram_free() will free on address which was not
 malloc()-ed in pg_scram_mech
In-reply-to: <64F1394B-E765-4291-91CF-E6CFE019D195@yesql.se>
References: <19092-b06adfd70ddcd2ab@postgresql.org>
 <64F1394B-E765-4291-91CF-E6CFE019D195@yesql.se>
Comments: In-reply-to Daniel Gustafsson <daniel@yesql.se>
	message dated "Tue, 21 Oct 2025 15:14:08 +0200"
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Date: Tue, 21 Oct 2025 11:06:19 -0400
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Daniel Gustafsson <daniel@yesql.se> writes:
>> On 21 Oct 2025, at 09:43, PG Bug reporting form <noreply@postgresql.org=
> wrote:
>> The issue is about the only implementation of pg_fe_sasl_mech interface=
:
>> pg_scram_mech. In the init func of pg_scram_mech, the variable
>> state->password is assigned by variable prep_password, which is prepare=
d in
>> function pg_saslprep(). However, pg_saslprep() will use palloc/pfree or
>> malloc/free determined by FRONTEND

> Mixing frontend and backend code like that seems to register somewhere o=
n the
> "break it and you get to keep both pieces" scale.

We'd really need to see a concrete example to decide whether this is
a PG bug or user error.  I think the SASL stuff is sufficiently poorly
tested that it could be a previously-unknown PG bug, but it's not clear.
So: test case, please.

>> This issue occurred when I was attempting to make a connection to Backe=
nd
>> via libpq interfaces in Backend itself.

> You tried to open a new database connection from a backend by embedding =
a libpq
> client into the backend?

postgres_fdw and dblink both do that.  The operation is ticklish
enough that we've developed some common infrastructure, which
maybe you should be using: see src/include/libpq/libpq-be-fe.h
and src/include/libpq/libpq-be-fe-helpers.h.

			regards, tom lane