[PATCH 3.8 101/166] ext4: check for overlapping extents in ext4_valid_extent_entries()

Kamal Mostafa
2014-01-15T21:51:55Z

From: Eryu Guan <guaneryu@gmail.com>

commit 5946d089379a35dda0e531710b48fca05446a196 upstream.

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.

Also add the check for (ee_block + len - 1) in ext4_valid_extent() to
make sure the value is not overflow.

Ran xfstests on patched ext4 and no regression.

Cc: Lukáš Czerner <lczerner@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
fs/ext4/extents.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c3db941..8b5c264 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -363,8 +363,10 @@ static int ext4_valid_extent(struct inode *inode, struct ext4_extent *ext)
{
ext4_fsblk_t block = ext4_ext_pblock(ext);
int len = ext4_ext_get_actual_len(ext);
+ ext4_lblk_t lblock = le32_to_cpu(ext->ee_block);
+ ext4_lblk_t last = lblock + len - 1;

- if (len == 0)
+ if (lblock > last)
return 0;
return ext4_data_block_valid(EXT4_SB(inode->i_sb), block, len);
}
@@ -390,11 +392,26 @@ static int ext4_valid_extent_entries(struct inode *inode,
if (depth == 0) {
/* leaf entries */
struct ext4_extent *ext = EXT_FIRST_EXTENT(eh);
+ struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
+ ext4_fsblk_t pblock = 0;
+ ext4_lblk_t lblock = 0;
+ ext4_lblk_t prev = 0;
+ int len = 0;
while (entries) {
if (!ext4_valid_extent(inode, ext))
return 0;
+
+ /* Check for overlapping extents */
+ lblock = le32_to_cpu(ext->ee_block);
+ len = ext4_ext_get_actual_len(ext);
+ if ((lblock <= prev) && prev) {
+ pblock = ext4_ext_pblock(ext);
+ es->s_last_error_block = cpu_to_le64(pblock);
+ return 0;
+ }
ext++;
entries--;
+ prev = lblock + len - 1;
}
} else {
struct ext4_extent_idx *ext_idx = EXT_FIRST_INDEX(eh);
--
1.8.3.2