[PATCH 2/2] brd: Fix brd_direct_access with partitions

[Boaz Harrosh <boaz@plexistor.com>]

When brd_direct_access() is called on a partition-bdev
it would access the wrong sector. And caller would then
corrupt the device's data.

This is a preliminary fix, Matthew Wilcox has a patch
in his DAX patchset which will define a global wrapper
to bdev->bd_disk->fops->direct_access that will do the
proper checks and translations before calling a driver
global member. (The way it is done at the rest of the
block stack)

CC: Matthew Wilcox <matthew.r.wilcox@intel.com>
Signed-off-by: Boaz Harrosh <boaz@plexistor.com>
---
 drivers/block/brd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 92334f6..7506864 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -378,9 +378,10 @@ static int brd_direct_access(struct block_device *bdev, sector_t sector,
 
 	if (!brd)
 		return -ENODEV;
+	sector += get_start_sect(bdev);
 	if (sector & (PAGE_SECTORS-1))
 		return -EINVAL;
-	if (sector + PAGE_SECTORS > get_capacity(bdev->bd_disk))
+	if (unlikely(sector + PAGE_SECTORS > part_nr_sects_read(bdev->bd_part)))
 		return -ERANGE;
 	page = brd_insert_page(brd, sector);
 	if (!page)
-- 
1.9.3