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loopdev: ignore negative offset when calculate loop device size

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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 <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Guo Chao <[email protected]>
Cc: M. Hindess <[email protected]>
Cc: Nikanth Karthikesan <[email protected]>
Cc: Jens Axboe <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Guo Chao 2013-02-21 15:16:50 -08:00 • committed by Jens Axboe
commit b7a1da695f
1 changed files with 5 additions and 4 deletions
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9
drivers/block/loop.c
View file

@ -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;