linux-kernel - Re: [PATCH 1/2] crypto: af_alg - Add nokey compatibility path

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Date:	Fri, 8 Jan 2016 19:21:12 +0100
From:	Milan Broz <gmazyland@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Stephan Mueller <smueller@...onox.de>,
	Dmitry Vyukov <dvyukov@...gle.com>, syzkaller@...glegroups.com,
	davem@...emloft.net, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, kcc@...gle.com, glider@...gle.com,
	edumazet@...gle.com, sasha.levin@...cle.com, keescook@...gle.com,
	Ondrej Kozina <okozina@...hat.com>
Subject: Re: [PATCH 1/2] crypto: af_alg - Add nokey compatibility path

On 01/08/2016 01:48 PM, Herbert Xu wrote:
> On Mon, Jan 04, 2016 at 01:33:54PM +0100, Milan Broz wrote:
>>
>> - hmac() is now failing the same way (SETKEY after accept())
>> (I initially tested without two patches above, these are not in linux-next yet.)
>> This breaks all cryptsetup TrueCrypt support (and moreover all systems if
>> kernel crypto API is set as a default vcrypto backend - but that's not default).
> 
> Yes algif_hash would need the same compatibility patch and I'm
> working on that.

Ok, I fixed this already.

> 
>> - cipher_null before worked without setkey, now it requires to set key
>> (either before or after accept().
>> This was actually probably bad workaround in cryptsetup, anyway it will now cause
>> old cryptsetup-reencrypt tool failing with your patches.
>> (Try "cryptsetup benchmark -c cipher_null-ecb". I am not sure what to do here,
>> but not requiring setkey for "cipher" that has no key internally seems ok for me...)
> 
> Is cipher_null actually used in production or is this just a
> benchmark? Using the kernel crypto API to perform no encryption
> sounds crazy.

Except benchmarks (I do not care about this) we use cipher_null in cryptsetup-reencrypt
when adding encryption in-place (plaintext-only device is converted
to LUKS, cipher_null is used during conversion for original plainext device,
then offline converted to some real cipher with key).
(It reuses the same logic as re-encryption, IOW volume key change.)

So it is used in production but just for this specific case.

Thanks,
Milan