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@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);
--
1.8.3.1
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