Horton

Re: glibc qsort() vulnerability

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: "Andrey M. Borodin" <x4mmm@yandex-team.ru>
Cc: Andres Freund <andres@anarazel.de>, Heikki Linnakangas <hlinnaka@iki.fi>, Mats Kindahl <mats@timescale.com>, Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@lists.postgresql.org
Date: 2024-02-09T16:32:45Z
Lists: pgsql-hackers

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Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Use new overflow-safe integer comparison functions.

  2. Introduce overflow-safe integer comparison functions.

  3. Replace calls to pg_qsort() with the qsort() macro.

  4. Switch over to using our own qsort() all the time, as has been proposed

On Fri, Feb 09, 2024 at 01:19:49PM +0500, Andrey M. Borodin wrote:
> If we care about branch prediction in comparison function, maybe we could
> produce sorting that inlines comparator, thus eliminating function call
> to comparator? We convert comparison logic to int, to extract comparison
> back then.
> 
> I bet “call" is more expensive than “if".

It might make sense to have a couple of built-in qsort implementations for
pointers to integers, pointers to unsigned integers, etc.  However, a lot
of current use-cases require inspecting specific fields of structs, so
(assuming I understand your proposal correctly), we'd end up with many
qsort implementations.  If that can be made simple and elegant and
demonstrates substantial improvements, then it might be worth considering,
but I'm somewhat skeptical that the current uses are performance-sensitive
enough to be worth the effort.

-- 
Nathan Bossart
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