From: Duy Nguyen <pclouds@gmail.com>
To: Jeff King <peff@peff.net>
Cc: Git Mailing List <git@vger.kernel.org>,
Christian Couder <chriscool@tuxfamily.org>,
Derrick Stolee <dstolee@microsoft.com>
Subject: Re: [PATCH 1/3] pack-objects: fix tree_depth and layer invariants
Date: Tue, 20 Nov 2018 17:37:18 +0100 [thread overview]
Message-ID: <CACsJy8AETNxNnEq-8ROrQTkjy-_9mtoprmc=BQ554f7QECajPw@mail.gmail.com> (raw)
In-Reply-To: <20181120094638.GA22742@sigill.intra.peff.net>
On Tue, Nov 20, 2018 at 11:04 AM Jeff King <peff@peff.net> 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
next prev parent reply other threads:[~2018-11-20 16:37 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-20 9:44 [PATCH 0/3] delta-island fixes Jeff King
2018-11-20 9:46 ` [PATCH 1/3] pack-objects: fix tree_depth and layer invariants Jeff King
2018-11-20 16:37 ` Duy Nguyen [this message]
2018-11-22 16:50 ` Jeff King
2018-11-21 4:52 ` Junio C Hamano
2018-11-20 9:48 ` [PATCH 2/3] pack-objects: zero-initialize tree_depth/layer arrays Jeff King
2018-11-20 9:50 ` [PATCH 3/3] pack-objects: fix off-by-one in delta-island tree-depth computation Jeff King
2018-11-20 15:06 ` [PATCH 0/3] delta-island fixes Derrick Stolee
2018-11-22 16:43 ` Jeff King
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