On Tue, Nov 20, 2018 at 11:04 AM Jeff King <peff@xxxxxxxx> wrote: > > 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" > array > > 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. Do you think if this splitting data to packing_data is too fragile that we should just scrape the whole thing and move all data back to object_entry[]? We would use more memory of course but higher memory usage is still better than more bugs (if these are likely to show up again). -- Duy
