linux-ext4 - Re: [PATCH v2] ext4: check for overlapping extents in ext4_valid_extent

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Message-ID: <20131021115954.GA2708@dhcp-13-216.nay.redhat.com>
Date:	Mon, 21 Oct 2013 19:59:54 +0800
From:	Eryu Guan <guaneryu@...il.com>
To:	linux-ext4@...r.kernel.org
Cc:	Theodore Ts'o <tytso@....edu>,
	Lukáš Czerner <lczerner@...hat.com>
Subject: Re: [PATCH v2] ext4: check for overlapping extents in
 ext4_valid_extent_entries()

On Sun, Oct 20, 2013 at 09:27:27PM +0800, Eryu Guan wrote:
> A corrupted ext4 may have out of order leaf extents, i.e.
> 
> extent: lblk 0--1023, len 1024, pblk 9217, flags: LEAF UNINIT
> extent: lblk 1000--2047, len 1024, pblk 10241, flags: LEAF UNINIT
>              ^^^^ overlap with previous extent
> 
> Reading such extent could hit BUG_ON() in ext4_es_cache_extent().
> 
> 	BUG_ON(end < lblk);
> 
> The problem is that __read_extent_tree_block() tries to cache holes as
> well but assumes 'lblk' is greater than 'prev' and passes underflowed
> length to ext4_es_cache_extent(). Fix it by checking for overlapping
> extents in ext4_valid_extent_entries().
> 
> I hit this when fuzz testing ext4, and am able to reproduce it by
> modifying the on-disk extent by hand.
> 
> Ran xfstests on patched ext4 and no regression.
> 
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: Lukáš Czerner <lczerner@...hat.com>
> Signed-off-by: Eryu Guan <guaneryu@...il.com>

Self NAK, I found problems in tests, will think about it more.

Thanks,
Eryu
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