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

From: Pekka Enberg
Date: Sat Jan 29 2011 - 03:49:29 EST

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@xxxxxxxxxxxxxxxxxx>

Reviewed-by: Pekka Enberg <penberg@xxxxxxxxxx>

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