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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 <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>
This commit is contained in:
Guo Chao 2013-02-21 15:16:50 -08:00 committed by Jens Axboe
parent b1a6650406
commit b7a1da695f
1 changed files with 5 additions and 4 deletions
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9
drivers/block/loop.c
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@ -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) 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 */ /* Compute loopsize in bytes */
size = i_size_read(file->f_mapping->host); loopsize = i_size_read(file->f_mapping->host);
loopsize = size - offset; if (offset > 0)
/* offset is beyond i_size, wierd but possible */ loopsize -= offset;
/* offset is beyond i_size, weird but possible */
if (loopsize < 0) if (loopsize < 0)
return 0; return 0;