[PATCH 1/3] pack-objects: fix tree_depth and layer invariants
- Date: Tue, 20 Nov 2018 04:46:38 -0500
- From: Jeff King <peff@xxxxxxxx>
- Subject: [PATCH 1/3] pack-objects: fix tree_depth and layer invariants
Commit 108f530385 (pack-objects: move tree_depth into 'struct
packing_data', 2018-08-16) dynamically manages a tree_depth array in
packing_data that maintains one of these invariants:
1. tree_depth is NULL (i.e., the requested options don't require us to
track tree depths)
2. tree_depth is non-NULL and has as many entries as the "objects"
We maintain (2) by:
a. When the objects array grows, grow tree_depth to the same size
(unless it's NULL, in which case we can leave it).
b. When a caller asks to set a depth via oe_set_tree_depth(), if
tree_depth is NULL we allocate it.
But in (b), we use the number of stored objects, _not_ the allocated
size of the objects array. So we can run into a situation like this:
1. packlist_alloc() needs to store the Nth object, so it grows the
objects array to M, where M > N.
2. oe_set_tree_depth() wants to store a depth, so it allocates an
array of length N. Now we've violated our invariant.
3. packlist_alloc() needs to store the N+1th object. But it _doesn't_
grow the objects array, since N <= M still holds. We try to assign
to tree_depth[N+1], which is out of bounds.
That doesn't happen in our test scripts, because the repositories they
use are so small, but it's easy to trigger by running:
echo HEAD | git pack-objects --revs --delta-islands --stdout >/dev/null
in any reasonably-sized repo (like git.git).
We can fix it by always growing the array to match pack->nr_alloc, not
pack->nr_objects. Likewise for the "layer" array from fe0ac2fb7f
(pack-objects: move 'layer' into 'struct packing_data', 2018-08-16),
which has the same bug.
Signed-off-by: Jeff King <peff@xxxxxxxx>
pack-objects.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/pack-objects.h b/pack-objects.h
index feb6a6a05e..f31ac1c81c 100644
@@ -412,7 +412,7 @@ static inline void oe_set_tree_depth(struct packing_data *pack,
unsigned int tree_depth)
- ALLOC_ARRAY(pack->tree_depth, pack->nr_objects);
+ ALLOC_ARRAY(pack->tree_depth, pack->nr_alloc);
pack->tree_depth[e - pack->objects] = tree_depth;
@@ -429,7 +429,7 @@ static inline void oe_set_layer(struct packing_data *pack,
unsigned char layer)
- ALLOC_ARRAY(pack->layer, pack->nr_objects);
+ ALLOC_ARRAY(pack->layer, pack->nr_alloc);
pack->layer[e - pack->objects] = layer;