Re: glibc qsort() vulnerability

On Tue, Feb 6, 2024 at 9:56 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Nathan Bossart <nathandbossart(at)gmail(dot)com> writes:
> > Even if the glibc issue doesn't apply to Postgres, I'm tempted to suggest
> > that we make it project policy that comparison functions must be
> > transitive. There might be no real issues today, but if we write all
> > comparison functions the way Mats is suggesting, it should be easier to
> > reason about overflow risks.
>
> A comparison routine that is not is probably broken, agreed.
> I didn't look through the details of the patch --- I was more
> curious whether we had a version of the qsort bug, because
> if we do, we should fix that too.
>

The patch basically removes the risk of overflow in three routines and just
returns -1, 0, or 1, and adds a comment in one.

The routines modified do a subtraction of int:s and return that, which can
cause an overflow. This method is used for some int16 as well but since
standard conversions in C will perform the arithmetics in "int" precision,
this cannot overflow, so added a comment there. It might still be a good
idea to follow the same pattern for the int16 routines, but since there is
no bug there, I did not add them to the patch.

Best wishes,
Mats Kindahl

>
> regards, tom lane
>