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From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: 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: Wed, 21 Nov 2018 13:52:13 +0900	[thread overview]
Message-ID: <xmqqa7m3822q.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20181120094638.GA22742@sigill.intra.peff.net> (Jeff King's message of "Tue, 20 Nov 2018 04:46:38 -0500")

Jeff King <peff@peff.net> writes:

> 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.

Ouch.  I see counting and allocationg is hard (I think I spotted a
bug in another area that comes from the same "count while filtering
and then allocate" pattern during this cycle).  Thanks for spotting.


  parent reply	other threads:[~2018-11-21  4:52 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
2018-11-22 16:50     ` Jeff King
2018-11-21  4:52   ` Junio C Hamano [this message]
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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