[PATCH] ext4: don't cache out of order extents

[Eryu Guan <guaneryu@gmail.com>]

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.

Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
---
 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);
-- 
1.8.3.1