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

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Date:	Sat, 29 Jan 2011 10:49:24 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Robert Jennings <rcj@...ux.vnet.ibm.com>
Cc:	Nitin Gupta <ngupta@...are.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] zram: Return zero'd pages on new reads

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@...ux.vnet.ibm.com>

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

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