From: Eryu Guan <guaneryu@gmail.com>
To: "Lukáš Czerner" <lczerner@redhat.com>
Cc: linux-ext4@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH] ext4: don't cache out of order extents
Date: Thu, 17 Oct 2013 23:06:30 +0800 [thread overview]
Message-ID: <20131017150630.GC11404@dhcp-13-216.nay.redhat.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1310171534440.3212@localhost.localdomain>
On Thu, Oct 17, 2013 at 03:44:35PM +0200, Lukáš Czerner wrote:
> On Thu, 17 Oct 2013, Eryu Guan wrote:
>
> > Date: Thu, 17 Oct 2013 17:27:53 +0800
> > From: Eryu Guan <guaneryu@gmail.com>
> > To: linux-ext4@vger.kernel.org
> > Cc: Eryu Guan <guaneryu@gmail.com>, Theodore Ts'o <tytso@mit.edu>
> > Subject: [PATCH] ext4: don't cache out of order extents
> >
> > 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().
> >
> > 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.
>
> So what will happen with the file system with this patch when
> presented with such corruption ?
>
> It seems to me that ext4_es_cache_extent() will happily skip this
> extent because it will find that this particular offset is already
> in the tree. Hence we'll have a gap in the status tree which really
> should not be there and I suspect that something bad will happen.
>
> I think that we should deal with this corruption immediately when we
> spot it there, not just hide it.
Yes, agreed, we should validate the extent not cover the corruption as
Ted pointed out. Don't know why I didn't think about it more in the
first place..
Thanks!
Eryu Guan
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next prev parent reply other threads:[~2013-10-17 15:06 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-17 9:27 [PATCH] ext4: don't cache out of order extents Eryu Guan
2013-10-17 13:44 ` Lukáš Czerner
2013-10-17 14:40 ` Theodore Ts'o
2013-10-17 15:22 ` Lukáš Czerner
2013-10-17 15:58 ` Theodore Ts'o
2013-10-17 15:06 ` Eryu Guan [this message]
2013-10-20 13:27 ` [PATCH v2] ext4: check for overlapping extents in ext4_valid_extent_entries() Eryu Guan
2013-10-21 11:59 ` Eryu Guan
2013-10-21 12:47 ` Eryu Guan
2013-10-21 16:06 ` Lukáš Czerner
2013-10-22 18:40 ` Eryu Guan
2013-12-04 2:36 ` [PATCH v3] " Theodore Ts'o
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