[PATCH] ext4: check for zero length extent explicitly

[PATCH] ext4: check for zero length extent explicitly

[Eryu Guan]

The following commit introduced a bug when checking for zero length extent

5946d08 ext4: check for overlapping extents in ext4_valid_extent_entries()

Zero length extent could pass the check if lblock is zero.

Adding the explicit check for zero length back.

Signed-off-by: Eryu Guan <guaneryu@gmail.com>
---

This is uncovered by recent updates for encryption, catting a file with zero
length extent results in infinite loop ext4_mpage_readpages(), and process
cannot be killed either.

Tested with corrupted ext4 image in e2fsprogs sources, cat returned EIO
correctly

tests/f_ext_zero_len/image.gz

 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 d74e0802..451b92a 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -377,7 +377,7 @@ static int ext4_valid_extent(struct inode *inode, struct ext4_extent *ext)
 	ext4_lblk_t lblock = le32_to_cpu(ext->ee_block);
 	ext4_lblk_t last = lblock + len - 1;
 
-	if (lblock > last)
+	if (len == 0 || lblock > last)
 		return 0;
 	return ext4_data_block_valid(EXT4_SB(inode->i_sb), block, len);
 }
-- 
1.8.3.1

Re: [PATCH] ext4: check for zero length extent explicitly

[Theodore Ts'o]

On Mon, May 04, 2015 at 06:14:28PM +0800, Eryu Guan wrote:
> The following commit introduced a bug when checking for zero length extent
> 
> 5946d08 ext4: check for overlapping extents in ext4_valid_extent_entries()
> 
> Zero length extent could pass the check if lblock is zero.
> 
> Adding the explicit check for zero length back.
> 
> Signed-off-by: Eryu Guan <guaneryu@gmail.com>

Thanks, applied.

					- Ted