From: Srujith A Poojary via GitGitGadget Date: Tue, 27 Oct 2026 16:56:00 GMT Subject: [PATCH v9] diff-delta: use safe integer arithmetic Message-ID: In-Reply-To: From: Srujith A Poojary In create_delta_index(), buffer sizes for allocating the delta index are calculated using arithmetic operations on entries and hsize: memsize = sizeof(*hash) * hsize + sizeof(*entry) * entries To prevent potential size_t wrap-around when computing allocation sizes on 32-bit systems, replace manual arithmetic with overflow-checked helpers (st_mult, st_add, st_add3). Struct sizes and alignment rules (such as padding for struct unpacked_index_entry) are implementation-defined and can vary across compilers and platforms. While current bounds on entries and hsize limit allocation sizes (with entries capped by 0xfffffffeU / RABIN_WINDOW and hsize capped at 2^26 with a minimum of 16), using st_mult() and st_add() provides robust defensive programming—ensuring that any future layout changes, compiler padding differences, or boundary adjustments will safely die() on size_t overflow instead of wrapping around. For the packed index allocation: - (hsize + 1) is passed to st_mult(), which is evaluated as an argument inside st_add3(), and is safe from overflow because hsize is capped 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-v9 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2276/poojarysrujith/c-refactor-target-name-v9 Pull-Request: https://github.com/gitgitgadget/git/pull/2276 Range-diff vs v8: 1: 0b88f5a10b ! 1: 1be2ccdf19 diff-delta: use safe integer arithmetic @@ Commit message on 32-bit systems, replace manual arithmetic with overflow-checked helpers (st_mult, st_add, st_add3). - For the unpacked index allocation: - - sizeof(struct unpacked_index_entry) is 16 bytes on 32-bit systems - (4 bytes for ptr, 4 bytes for val, and 4 bytes for the next pointer, - where "inner entry" consists of ptr + val). - - sizeof(struct index_entry *) is 4 bytes. - - entries is capped by 0xfffffffeU / RABIN_WINDOW, limiting entries. - - hsize is the smallest power of 2 >= (entries / 4), capped at 2^26 - (with a minimum of 16). - - Using st_mult() and st_add() guarantees that any allocation calculations - will safely die() on size_t overflow instead of wrapping around. + Struct sizes and alignment rules (such as padding for + struct unpacked_index_entry) are implementation-defined and can vary + across compilers and platforms. While current bounds on entries and + hsize limit allocation sizes (with entries capped by 0xfffffffeU / + RABIN_WINDOW and hsize capped at 2^26 with a minimum of 16), using + st_mult() and st_add() provides robust defensive programming—ensuring + that any future layout changes, compiler padding differences, or boundary + adjustments will safely die() on size_t overflow instead of wrapping around. For the packed index allocation: - (hsize + 1) is passed to st_mult(), which is evaluated as an argument 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