2017-09-13 13:18:01

by Mikulas Patocka

Subject: [PATCH] brd: fix overflow in __brd_direct_access

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.

Signed-off-by: Mikulas Patocka <[email protected]>
Fixes: 1647b9b959c7 ("brd: add dax_operations support")
Cc: [email protected] # 4.12+

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

Index: linux-4.13/drivers/block/brd.c
===================================================================
--- linux-4.13.orig/drivers/block/brd.c
+++ linux-4.13/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);

2017-09-13 16:22:29

by Dan Williams

Subject: Re: [PATCH] brd: fix overflow in __brd_direct_access

On Wed, Sep 13, 2017 at 6:17 AM, Mikulas Patocka <[email protected]> wrote:
> 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.
>
> Signed-off-by: Mikulas Patocka <[email protected]>
> Fixes: 1647b9b959c7 ("brd: add dax_operations support")
> Cc: [email protected] # 4.12+
>
> ---
> drivers/block/brd.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-4.13/drivers/block/brd.c
> ===================================================================
> --- linux-4.13.orig/drivers/block/brd.c
> +++ linux-4.13/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);

Looks good to me, you can add:

Reviewed-by: Dan Williams <[email protected]>

2017-09-13 17:18:24

by Jens Axboe

Subject: Re: [PATCH] brd: fix overflow in __brd_direct_access

On 09/13/2017 07:17 AM, Mikulas Patocka wrote:
> 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.

Thanks, applied with Dan's ack.

--
Jens Axboe