On Thu, 17 Oct 2013, Eryu Guan wrote: > Date: Thu, 17 Oct 2013 17:27:53 +0800 > From: Eryu Guan <guaneryu@xxxxxxxxx> > To: linux-ext4@xxxxxxxxxxxxxxx > Cc: Eryu Guan <guaneryu@xxxxxxxxx>, Theodore Ts'o <tytso@xxxxxxx> > 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. Thanks! -Lukas > > Cc: "Theodore Ts'o" <tytso@xxxxxxx> > Signed-off-by: Eryu Guan <guaneryu@xxxxxxxxx> > --- > fs/ext4/extents.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > index 54d52af..c9ebcb9 100644 > --- a/fs/ext4/extents.c > +++ b/fs/ext4/extents.c > @@ -503,7 +503,7 @@ __read_extent_tree_block(const char *function, unsigned int line, > ext4_lblk_t lblk = le32_to_cpu(ex->ee_block); > int len = ext4_ext_get_actual_len(ex); > > - if (prev && (prev != lblk)) > + if (prev && (prev < lblk)) > ext4_es_cache_extent(inode, prev, > lblk - prev, ~0, > EXTENT_STATUS_HOLE); > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
