From: Tom Lane <tgl@sss.pgh.pa.us>
To: anisimow.d@gmail.com
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17816: Invalid memory access in translate function
In-reply-to: <17816-70f3d2764e88a108@postgresql.org>
References: <17816-70f3d2764e88a108@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Wed, 01 Mar 2023 08:17:56 +0000"
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Date: Wed, 01 Mar 2023 10:46:10 -0500
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PG Bug reporting form <noreply@postgresql.org> writes:
> When running this query in psql with valgrind-enabled server:
> select translate('(123)', '()', '');

> I get:
> ==00:00:00:05.576 29520== Invalid read of size 1
> ==00:00:00:05.576 29520==    at 0x7605BE: pg_utf_mblen (wchar.c:553)
> ==00:00:00:05.576 29520==    by 0x71CEDE: pg_mblen (mbutils.c:968)
> ==00:00:00:05.576 29520==    by 0x67B1E3: translate (oracle_compat.c:864)

Thanks for the report!

> These changes fix the issue:
> for (i = 0; i < from_index; i++)
> {
>     if (p >= (to_ptr + tolen))
>         break;
>     p += pg_mblen(p);
> }

Yeah, I agree, we need to switch the order of those two statements.
Will fix.

(Might be worth pulling out the common subexpression here?
I wonder if all compilers are smart enough to evaluate to_ptr + to_len
just once.)

			regards, tom lane