packfile.c: use checked arithmetic in `nth_packed_object_offset()`
In a similar spirit as the previous commits, ensure that we use `st_add()` or `st_mult()` when computing values that may overflow the 32-bit unsigned limit. Note that in each of these instances, we prevent 32-bit overflow already since we have explicit casts to `size_t`. So this code is OK as-is, but let's clarify it by using the `st_xyz()` helpers to make it obvious that we are performing the relevant computations using 64 bits. Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Taylor Blau committed
Jul 12, 2023 at 19:37 UTC
a519abca02eeca7dce864717b9664c62a124e1c0
1 file changed
+5
-4
packfile.c
+5
-4
@@ -1948,14 +1948,15 @@ off_t nth_packed_object_offset(const struct packed_git *p, uint32_t n)
1948
const unsigned int hashsz = the_hash_algo->rawsz;
1949
index += 4 * 256;
1950
if (p->index_version == 1) {
1951
- return ntohl(*((uint32_t *)(index + (hashsz + 4) * (size_t)n)));
1951
+ return ntohl(*((uint32_t *)(index + st_mult(hashsz + 4, n))));
1952
} else {
1953
uint32_t off;
1954
- index += 8 + (size_t)p->num_objects * (hashsz + 4);
1955
- off = ntohl(*((uint32_t *)(index + 4 * n)));
1954
+ index += st_add(8, st_mult(p->num_objects, hashsz + 4));
1955
+ off = ntohl(*((uint32_t *)(index + st_mult(4, n))));
1956
if (!(off & 0x80000000))
1957
return off;
1958
- index += (size_t)p->num_objects * 4 + (off & 0x7fffffff) * 8;
1958
+ index += st_add(st_mult(p->num_objects, 4),
1959
+ st_mult(off & 0x7fffffff, 8));
1960
check_pack_index_ptr(p, index);
1961
return get_be64(index);
1962
}