From: Srujith Poojary <poojarysrujith@gmail.com>
Date: Fri, 23 Oct 2026 16:56:13 GMT
Subject: Re: [PATCH] [Outreachy PATCH] diff-delta: use safe integer arithmetic
Message-ID: <CABh_KWgBzCXCSn4FUTSg+rXYj9vm6+AVZnDn3iR_4UJCsB8tjw@mail.gmail.com>
In-Reply-To: <xmqqtsmca0yy.fsf@gitster.g>

On Fri, Oct 23, 2026 at 9:00 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Srujith Poojary <poojarysrujith@gmail.com> writes:
>
> > Thank you for clarifying this. You are right—st_add() and st_mult()
> > call die() on overflow rather than returning NULL.
> > I will update the commit message to accurately reflect this behavior
> > and submit v2.
>
> Please don't, before making sure if it can overflow.  With the
> number of entries capped like this:
>
>         if (bufsize >= 0xffffffffUL)
>                 entries = 0xfffffffeU / RABIN_WINDOW;
>
> and then computed
>
>         hsize = entries / 4;
>         for (i = 4; (1u << i) < hsize; i++);
>         hsize = 1 << i;
>         /* allocate lookup index */
>         memsize = sizeof(*hash) * hsize +
>                   sizeof(*entry) * entries;
>
> it may not be possible to overflow size_t even on 32-bit platforms.
> I didn't have time to do math yet myself, though.
>

Hi Phillip and Junio,

Thank you for the detailed feedback.

I checked the bounds: since entries is capped by (0xffffffu /
RABIN_WINDOW), hsize remains small, making a size_t overflow
impossible even on 32-bit systems.

I ran git clang-format HEAD^ to fix the code alignment as suggested
and updated the patch.

Best regards,
Srujith