Horton

Re: glibc qsort() vulnerability

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>, Mats Kindahl <mats@timescale.com>, Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@lists.postgresql.org
Date: 2024-02-08T00:42:07Z
Lists: pgsql-hackers

Commits

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

Hi,

On 2024-02-07 16:21:24 -0600, Nathan Bossart wrote:
> On Wed, Feb 07, 2024 at 01:48:57PM -0800, Andres Freund wrote:
> > Now, in most cases this won't matter, the sorting isn't performance
> > critical. But I don't think it's a good idea to standardize on a generally
> > slower pattern.
> > 
> > Not that that's a good test, but I did quickly benchmark [1] this with
> > intarray. There's about a 10% difference in performance between using the
> > existing compASC() and one using
> > 	return (int64) *(const int32 *) a - (int64) *(const int32 *) b;
> > 
> > 
> > Perhaps we could have a central helper for this somewhere?
> 
> Maybe said helper could use __builtin_sub_overflow() and fall back to the
> slow "if" version only if absolutely necessary.

I suspect that'll be worse code in the common case, given the cmov generated
by gcc & clang for the typical branch-y formulation. But it's worth testing.


> The assembly for that looks encouraging, but I still need to actually test
> it...

Possible. For 16bit upcasting to 32bit is clearly the best way. For 32 bit
that doesn't work, given the 32bit return, so we need something more.

Greetings,

Andres Freund