Re: glibc qsort() vulnerability

On Sat, Feb 10, 2024 at 9:53 PM Nathan Bossart <nathandbossart(at)gmail(dot)com>
wrote:

> On Sat, Feb 10, 2024 at 08:59:06AM +0100, Mats Kindahl wrote:
> > Split the code into two patches: one that just adds the functions
> > (including the new pg_cmp_size()) to common/int.h and one that starts
> using
> > them. I picked the name "pg_cmp_size" rather than "pg_cmp_size_t" since
> > "_t" is usually used as a suffix for types.
> >
> > I added a comment to the (a > b) - (a < b) return and have also added
> casts
> > to (int32) for the int16 and uint16 functions (we need a signed int for
> > uin16 since we need to be able to get a negative number).
> >
> > Changed the type of two instances that had an implicit cast from size_t
> to
> > int and used the new pg_,cmp_size() function.
> >
> > Also fixed the missed replacements in the "contrib" directory.
>
> Thanks for the new patches. I think the comparison in resowner.c is
> backwards,

Thanks for catching that.

> and I think we should expand on some of the commentary in int.h.
> For example, the comment at the top of int.h seems very tailored to the
> existing functions and should probably be adjusted.

I rewrote the beginning to the following, does that look good?

* int.h
* Routines to perform signed and unsigned integer arithmetics, including
* comparisons, in an overflow-safe way.

> And the "comparison
> routines for integers" comment might benefit from some additional details
> about the purpose and guarantees of the new functions.
>

I expanded that into the following. WDYT?

/*------------------------------------------------------------------------
* Comparison routines for integers.
*
* These routines are used to implement comparison functions for, e.g.,
* qsort(). They are designed to be efficient and not risk overflows in
* internal computations that could cause strange results, such as INT_MIN >
* INT_MAX if you just return "lhs - rhs".
*------------------------------------------------------------------------

Best wishes,
Mats Kindahl

> --
> Nathan Bossart
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