Re: [PATCH v2] diff-delta: use safe integer arithmetic

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Srujith

On 23/10/2026 06:56, Srujith A Poojary via GitGitGadget wrote:
> 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.

Sounds like a good idea

> 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));

The alignment is off here, see 
https://github.com/gitgitgadget/git/actions/runs/39906906057/job/120260845179?pr=2276 
for a suggested fix from clang-format. I think you should be able to use 
"git clang-format HEAD^" to fix it.
  >   	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),

What are the bounds of hsize? Can adding one to it overflow? The 
alignment is off here as well, all the arguments to st_add3() should be 
aligned.

Thanks

Phillip

> +			st_mult(sizeof(*packed_entry), entries));
>   	mem = malloc(memsize);
>   	if (!mem) {
>   		free(hash);
> 
> base-commit: 47fdf2208c5b94c8cc01c106b8f7c85efb91c926