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Date:	Mon, 10 Nov 2014 22:05:18 +0800
From:	Herbert Xu <>
To:	Stephan Mueller <>
Subject: Re: crypto: zeroization of sensitive data in af_alg

On Sun, Nov 09, 2014 at 11:33:52PM +0100, Stephan Mueller wrote:
> while working on the AF_ALG interface, I saw no active zeroizations of memory 
> that may hold sensitive data that is maintained outside the kernel crypto API 
> cipher handles. I think the following memory segments fall under that 
> category:

Are you talking about temporary data that we generate as part of
the processing? If so they should be zeroed by the entity that
generates them.
> However, I am failing to find the right spot to add a zeroization for the 
> latter one, i.e. the code that handles the pages send in by the user or the 
> pages that are returned by the crypto API. Initially I thought 
> skcipher_pull_sgl is a good spot for the symmetric ciphers as it evicts the 
> used pages out of the scope of the kernel crypto API. I added a 
> clear_page(sg_page(sg+1)) as well as memset(sg_page(sg+1), 0, plen) right 
> before the put_page call. All that I got in return was a BUG() from the memory 
> management layer.

I don't think I understand what exactly you're trying to zero.
Can you give an example?

Email: Herbert Xu <>
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