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builtin/repack.c: be more conservative with unsigned overflows

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There are a number of places in the geometric repack code where we
multiply the number of objects in a pack by another unsigned value. We
trust that the number of objects in a pack is always representable by a
uint32_t, but we don't necessarily trust that that number can be
multiplied without overflow.

Sprinkle some unsigned_add_overflows() and unsigned_mult_overflows() in
split_pack_geometry() to check that we never overflow any unsigned types
when adding or multiplying them.

Arguably these checks are a little too conservative, and certainly they
do not help the readability of this function. But they are serving a
useful purpose, so I think they are worthwhile overall.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Taylor Blau 2021-03-05 10:21:56 -05:00 committed by Junio C Hamano
parent 13d746a303
commit 2a15964128
1 changed files with 22 additions and 2 deletions
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24
builtin/repack.c
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@ -363,6 +363,12 @@ static void split_pack_geometry(struct pack_geometry *geometry, int factor)
for (i = geometry->pack_nr - 1; i > 0; i--) {
struct packed_git *ours = geometry->pack[i];
struct packed_git *prev = geometry->pack[i - 1];
if (unsigned_mult_overflows(factor, geometry_pack_weight(prev)))
die(_("pack %s too large to consider in geometric "
"progression"),
prev->pack_name);
if (geometry_pack_weight(ours) < factor * geometry_pack_weight(prev))
break;
}
@ -388,11 +394,25 @@ static void split_pack_geometry(struct pack_geometry *geometry, int factor)
* packs in the heavy half need to be joined into it (if any) to restore
* the geometric progression.
*/
for (i = 0; i < split; i++)
total_size += geometry_pack_weight(geometry->pack[i]);
for (i = 0; i < split; i++) {
struct packed_git *p = geometry->pack[i];
if (unsigned_add_overflows(total_size, geometry_pack_weight(p)))
die(_("pack %s too large to roll up"), p->pack_name);
total_size += geometry_pack_weight(p);
}
for (i = split; i < geometry->pack_nr; i++) {
struct packed_git *ours = geometry->pack[i];
if (unsigned_mult_overflows(factor, total_size))
die(_("pack %s too large to roll up"), ours->pack_name);
if (geometry_pack_weight(ours) < factor * total_size) {
if (unsigned_add_overflows(total_size,
geometry_pack_weight(ours)))
die(_("pack %s too large to roll up"),
ours->pack_name);
split++;
total_size += geometry_pack_weight(ours);
} else