Subject: Re: Fix overflow in pg_size_pretty

From: Joseph Koshakow <[email-masked]>
Date: Sat, 27 Jul 2024 19:06:30 -0400

On Sat, Jul 27, 2024 at 6:28 PM David Rowley <[email-masked]> wrote:
>
> On Sun, 28 Jul 2024 at 07:18, Joseph Koshakow <[email-masked]> wrote:
>> Attached is a patch that resolves an overflow in pg_size_pretty() that
>> resulted in unexpected behavior when PG_INT64_MIN was passed in as an
>> argument.
>
> Could we just fix this more simply by assigning the absolute value of
> the signed variable into an unsigned type?

I might be misunderstanding, but my previous patch does assign the
absolute value of the signed variable into an unsigned type.

> It's a bit less code and
> gets rid of the explicit test for PG_INT64_MIN.

> + uint64 usize = size < 0 ? (uint64) (-size) : (uint64) size;

I think that the explicit test for PG_INT64_MIN is still required. If
`size` is equal to PG_INT64_MIN then `-size` will overflow. You end up
with the correct behavior if `size` wraps around, but that's only
guaranteed on platforms that support the `-fwrapv` flag.

Thanks,
Joseph Koshakow