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Subject[PATCH 7/7] loopdev: ignore negative offset when calculate loop device size
Date
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>
---
drivers/block/loop.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 9190a82..7a235db 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -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;

--
1.7.9.5


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