loopdev: ignore negative offset when calculate loop device size
Negative offset may cause loop device size larger than backing file
size.
$ fallocate -l 1M a
$ losetup --offset 0xffffffffffff0000 /dev/loop0 a
$ blockdev --getsize64 /dev/loop0
1114112
$ ls -l a
-rw-r--r-- 1 root root 1048576 Jan 23 12:46 a
$ cat /dev/loop0
cat: /dev/loop0: Input/output error
It makes no sense to do that. Only apply offset when it's positive.
Fix a typo in the comment by the way.
Signed-off-by: Guo Chao <yan@linux.vnet.ibm.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Guo Chao <yan@linux.vnet.ibm.com>
Cc: M. Hindess <hindessm@uk.ibm.com>
Cc: Nikanth Karthikesan <knikanth@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1b1b0c9..bef9d63 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -162,12 +162,13 @@
static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
{
- loff_t size, loopsize;
+ loff_t loopsize;
/* Compute loopsize in bytes */
- size = i_size_read(file->f_mapping->host);
- loopsize = size - offset;
- /* offset is beyond i_size, wierd but possible */
+ loopsize = i_size_read(file->f_mapping->host);
+ if (offset > 0)
+ loopsize -= offset;
+ /* offset is beyond i_size, weird but possible */
if (loopsize < 0)
return 0;
