[PATCH v3] diff-delta: use safe integer arithmetic

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 potential overflows when computing memory allocation sizes.

On 32-bit platforms, struct alignment padding could cause the total allocation size calculation to exceed 2^32, making safe integer arithmetic necessary. Note that hsize + 1 inside st_add3() is safe from overflow because hsize is capped at 2^26 early in the function.

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-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2276/poojarysrujith/c-refactor-target-name-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/2276

Range-diff vs v2:

 1:  14ffd630ca ! 1:  d288bfe9e3 diff-delta: use safe integer arithmetic
     @@ Commit message
          diff-delta: use safe integer arithmetic
      
          Replace manual multiplication and addition in create_delta_index()
     -    with safe integer helpers (st_mult, st_add, st_add3) to prevent
     -    overflows.
     +    with safe integer helpers (st_mult, st_add, st_add3) to prevent potential
     +    overflows when computing memory allocation sizes.
     +
     +    On 32-bit platforms, struct alignment padding could cause the total
     +    allocation size calculation to exceed 2^32, making safe integer arithmetic
     +    necessary. Note that hsize + 1 inside st_add3() is safe from overflow
     +    because hsize is capped at 2^26 early in the function.
      
          Signed-off-by: Srujith A Poojary <poojarysrujith@gmail.com>
      
     @@ diff-delta.c: struct delta_index * create_delta_index(const void *buf, size_t bu
      -	memsize = sizeof(*hash) * hsize +
      -		  sizeof(*entry) * entries;
      +	memsize = st_add(st_mult(sizeof(*hash), hsize),
     -+				st_mult(sizeof(*entry), entries));
     ++			 st_mult(sizeof(*entry), entries));
       	mem = malloc(memsize);
       	if (!mem)
       		return NULL;
     @@ diff-delta.c: struct delta_index * create_delta_index(const void *buf, size_t bu
      -		+ 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));
     ++			  st_mult(sizeof(*packed_hash), hsize + 1),
     ++			  st_mult(sizeof(*packed_entry), entries));
       	mem = malloc(memsize);
       	if (!mem) {
       		free(hash);

 diff-delta.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)