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Subject[PATCH 4.13 064/110] brd: fix overflow in __brd_direct_access
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4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@redhat.com>

commit 02a4843618fb35f847cf8c31cd3893873aa0edde upstream.

The code in __brd_direct_access multiplies the pgoff variable by page size
and divides it by 512. It can cause overflow on 32-bit architectures. The
overflow happens if we create ramdisk larger than 4G and use it as a
sparse device.

This patch replaces multiplication and division with multiplication by the
number of sectors per page.

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: 1647b9b959c7 ("brd: add dax_operations support")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/brd.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -339,7 +339,7 @@ static long __brd_direct_access(struct b

if (!brd)
return -ENODEV;
- page = brd_insert_page(brd, PFN_PHYS(pgoff) / 512);
+ page = brd_insert_page(brd, (sector_t)pgoff << PAGE_SECTORS_SHIFT);
if (!page)
return -ENOSPC;
*kaddr = page_address(page);

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