From: Srujith Poojary <poojarysrujith@gmail.com>
Date: Fri, 23 Oct 2026 05:29:45 GMT
Subject: Re: [PATCH] [Outreachy PATCH] diff-delta: use safe integer arithmetic
Message-ID: <CABh_KWiKmXP4KTgF=k2gGdSvcZXkRipD61AVn+AS7ZgvhcjHWw@mail.gmail.com>
In-Reply-To: <xmqqld7paty9.fsf@gitster.g>

On Fri, Oct 23, 2026 at 10:34 AM Junio C Hamano <gitster@pobox.com> wrote:
>
> "Srujith A Poojary via GitGitGadget" <gitgitgadget@gmail.com>
> writes:
>
> > From: Srujith A Poojary <poojarysrujith@gmail.com>
> >
> > Replace manual multiplication and addition in create_delta_index()
> > with safe integer helpers (st_mult, st_add, st_add3) to prevent
> > overflows while preserving NULL returns on failure.
>
> I do not quite understand what the last part of this explanation
> wants to say, i.e., "while preserving NULL returns on failure".  It
> makes it sound as if the function would return NULL if the integer
> helpers detect integer overflow, but I do not think that is what
> actually the updated code does at all.  st_add() and friends will
> simply die() when overflow happens, so you will not even reach
> malloc(), let alone return NULL when the malloc fails.
>
> And if you reply to this review message, please do not top-post.
>
> Thanks.
>
> >
> > Signed-off-by: Srujith A Poojary <poojarysrujith@gmail.com>
> > ---
> >     [Outreachy PATCH] diff-delta: use safe integer arithmetic
> >
> > Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2276%2Fpoojarysrujith%2Fc-refactor-target-name-v1
> > Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2276/poojarysrujith/c-refactor-target-name-v1
> > Pull-Request: https://github.com/gitgitgadget/git/pull/2276
> >
> >  diff-delta.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/diff-delta.c b/diff-delta.c
> > index 7cbedeb507..45df070ab9 100644
> > --- a/diff-delta.c
> > +++ b/diff-delta.c
> > @@ -162,8 +162,8 @@ struct delta_index * create_delta_index(const void *buf, size_t bufsize)
> >       hmask = hsize - 1;
> >
> >       /* allocate lookup index */
> > -     memsize = sizeof(*hash) * hsize +
> > -               sizeof(*entry) * entries;
> > +     memsize = st_add(st_mult(sizeof(*hash), hsize),
> > +                             st_mult(sizeof(*entry), entries));
> >       mem = malloc(memsize);
> >       if (!mem)
> >               return NULL;
> > @@ -258,9 +258,9 @@ struct delta_index * create_delta_index(const void *buf, size_t bufsize)
> >        * Now create the packed index in array form
> >        * rather than linked lists.
> >        */
> > -     memsize = sizeof(*index)
> > -             + sizeof(*packed_hash) * (hsize+1)
> > -             + sizeof(*packed_entry) * entries;
> > +     memsize = st_add3(sizeof(*index),
> > +                     st_mult(sizeof(*packed_hash), hsize + 1),
> > +                     st_mult(sizeof(*packed_entry), entries));
> >       mem = malloc(memsize);
> >       if (!mem) {
> >               free(hash);
> >
> > base-commit: 47fdf2208c5b94c8cc01c106b8f7c85efb91c926

Hi Junio,

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.

Best regards,
Srujith