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@xxxxxxx>
Cc: Lukáš Czerner <lczerner@xxxxxxxxxx>
Signed-off-by: Eryu Guan <guaneryu@xxxxxxxxx>
---
Hi,
My second try to find and report the corruption instead of hiding it,
how about this one?
Thanks!
Eryu
fs/ext4/extents.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c9ebcb9..855b11d 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -387,11 +387,21 @@ static int ext4_valid_extent_entries(struct inode *inode,
if (depth == 0) {
/* leaf entries */
struct ext4_extent *ext = EXT_FIRST_EXTENT(eh);
+ ext4_lblk_t block = 0;
+ ext4_lblk_t prev = 0;
+ int len = 0;
while (entries) {
if (!ext4_valid_extent(inode, ext))
return 0;
+
+ /* Check for overlapping extents */
+ block = le32_to_cpu(ext->ee_block);
+ len = ext4_ext_get_actual_len(ext);
+ if ((block <= prev) && prev)
+ return 0;
ext++;
entries--;
+ prev = block + len - 1;
}
} else {
struct ext4_extent_idx *ext_idx = EXT_FIRST_INDEX(eh);
--
1.8.3.1
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