use st_add and st_mult for allocation size computation

If our size computation overflows size_t, we may allocate a
much smaller buffer than we expected and overflow it. It's
probably impossible to trigger an overflow in most of these
sites in practice, but it is easy enough convert their
additions and multiplications into overflow-checking
variants. This may be fixing real bugs, and it makes
auditing the code easier.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/refs.c b/refs.c
index 2d86445231..b0e6ece6f4 100644
--- a/refs.c
+++ b/refs.c
@@ -906,7 +906,7 @@ char *shorten_unambiguous_ref(const char *refname, int strict)
 			/* -2 for strlen("%.*s") - strlen("%s"); +1 for NUL */
 			total_len += strlen(ref_rev_parse_rules[nr_rules]) - 2 + 1;
 
-		scanf_fmts = xmalloc(nr_rules * sizeof(char *) + total_len);
+		scanf_fmts = xmalloc(st_add(st_mult(nr_rules, sizeof(char *)), total_len));
 
 		offset = 0;
 		for (i = 0; i < nr_rules; i++) {