From: Srujith A Poojary via GitGitGadget Date: Sat, 24 Oct 2026 03:48:17 GMT Subject: [PATCH v3] diff-delta: use safe integer arithmetic Message-ID: In-Reply-To: From: Srujith A Poojary 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 --- [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 @@ 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(-) diff --git a/diff-delta.c b/diff-delta.c index 7cbedeb507..efebce3aca 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 -- gitgitgadget