Re: [PATCH 6/7] zram: Return zero'd pages on new reads

[Pekka Enberg <penberg@cs.helsinki.fi>]

On Fri, 2011-01-28 at 09:00 -0600, Robert Jennings wrote:
> Currently zram will do nothing to the page in the bvec when that page
> has not been previously written.  This allows random data to leak to
> user space.  That can be seen by doing the following:
> 
>  ## Load the module and create a 256Mb zram device called /dev/zram0
>  # modprobe zram
>  # echo $((256*1024*1024)) > /sys/class/block/zram0/disksize
> 
>  ## Initialize the device by writing zero to the first block
>  # dd if=/dev/zero of=/dev/zram0 bs=512 count=1
> 
>  ## Read ~256Mb of memory into a file and hope for something interesting
>  # dd if=/dev/zram0 of=file
> 
> This patch will treat an unwritten page as a zero-filled page.  If a
> page is read before a write has occurred the data returned is all 0's.
> 
> Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com>

Reviewed-by: Pekka Enberg <penberg@kernel.org>