Commit b7a1da69 authored Feb 21, 2013 by Guo Chao Committed by Jens Axboe Feb 22, 2013

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>

parent b1a66504

drivers/block/loop.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -162,12 +162,13 @@ static struct loop_func_table *xfer_funcs[MAX_LO_CRYPT] = {

		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;