[PATCH v2] ext4: check for overlapping extents in ext4_valid_extent_entries()

[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(). 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@mit.edu>
Cc: Lukáš Czerner <lczerner@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
---
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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