Re: glibc qsort() vulnerability

On Fri, Feb 09, 2024 at 08:52:26AM +0100, Mats Kindahl wrote:
> Here is a new version introducing pg_cmp_s32 and friends and use them
> instead of the INT_CMP macro introduced before. It also moves the
> definitions to common/int.h and adds that as an include to all locations
> using these functions.

Thanks for the new version of the patch.

> Note that for integers with sizes less than sizeof(int), C standard
> conversions will convert the values to "int" before doing the arithmetic,
> so no casting is *necessary*. I did not force the 16-bit functions to
> return -1 or 1 and have updated the comment accordingly.

It might not be necessary, but this is one of those places where I would
add casting anyway to make it abundantly clear what we are expecting to
happen and why it is safe.

> The types "int" and "size_t" are treated as s32 and u32 respectively since
> that seems to be the case for most of the code, even if strictly not
> correct (size_t can be an unsigned long int for some architecture).

Why is it safe to do this?

> - return ((const SPLITCOST *) a)->cost - ((const SPLITCOST *) b)->cost;
> + return INT_CMP(((const SPLITCOST *) a)->cost, ((const SPLITCOST *) b)->cost);

The patch still contains several calls to INT_CMP.

> +/*------------------------------------------------------------------------
> + * Comparison routines for integers
> + *------------------------------------------------------------------------
> + */

I'd suggest separating this part out to a 0001 patch to make it easier to
review. The 0002 patch could take care of converting the existing qsort
comparators.

> +static inline int
> +pg_cmp_s16(int16 a, int16 b)
> +{
> + return a - b;
> +}
> +
> +static inline int
> +pg_cmp_u16(uint16 a, uint16 b)
> +{
> + return a - b;
> +}
> +
> +static inline int
> +pg_cmp_s32(int32 a, int32 b)
> +{
> + return (a > b) - (a < b);
> +}
> +
> +static inline int
> +pg_cmp_u32(uint32 a, uint32 b)
> +{
> + return (a > b) - (a < b);
> +}
> +
> +static inline int
> +pg_cmp_s64(int64 a, int64 b)
> +{
> + return (a > b) - (a < b);
> +}
> +
> +static inline int
> +pg_cmp_u64(uint64 a, uint64 b)
> +{
> + return (a > b) - (a < b);
> +}

As suggested above, IMHO we should be rather liberal with the casting to
ensure it is abundantly clear what is happening here.

--
Nathan Bossart
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