From 1be2ccdf1937b8f11fe1a375ab4766ad96ffa80b Mon Sep 17 00:00:00 2001 From: Srujith A Poojary Date: Thu, 22 Oct 2026 12:00:32 +0000 Subject: [PATCH] diff-delta: use safe integer arithmetic MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 --- diff-delta.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/diff-delta.c b/diff-delta.c index 7cbedeb5071bcc..efebce3aca49a1 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);