brd: fix overflow in __brd_direct_access

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>

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 104b71c0490dd0cf377c0bc7d138c0c226fc02c9..b7dce4e3f5ff8e834b95cd83258746275fd5d93f 100644 (file)
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -339,7 +339,7 @@ static long __brd_direct_access(struct brd_device *brd, pgoff_t pgoff,
 
        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);