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Subject: Re: dm-crypt error when CONFIG_CRYPTO_AUTHENC is disabled
To:     Mike Snitzer <snitzer@redhat.com>,
        Thibaut Sautereau <thibaut.sautereau@clip-os.org>
Cc:     dm-devel@redhat.com, Alasdair Kergon <agk@redhat.com>,
        linux-kernel@vger.kernel.org
References: <20190920154434.GA923@gandi.net>
 <20190920173707.GA21143@redhat.com>
From:   Milan Broz <gmazyland@gmail.com>
Openpgp: preference=signencrypt
Message-ID: <13e25b01-f344-ea1d-8f6c-9d0a60eb1e0f@gmail.com>
Date:   Fri, 20 Sep 2019 21:21:33 +0200
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On 20/09/2019 19:37, Mike Snitzer wrote:
> On Fri, Sep 20 2019 at 11:44am -0400,
> Thibaut Sautereau <thibaut.sautereau@clip-os.org> wrote:
> 
>> Hi,
>>
>> I just got a dm-crypt "crypt: Error allocating crypto tfm" error when
>> trying to "cryptsetup open" a volume. I found out that it was only
>> happening when I disabled CONFIG_CRYPTO_AUTHENC.
>>
>> drivers/md/dm-crypt.c includes the crypto/authenc.h header and seems to
>> use some CRYPTO_AUTHENC-related stuff. Therefore, shouldn't
>> CONFIG_DM_CRYPT select CONFIG_CRYPTO_AUTHENC?
> 
> Yes, it looks like commit ef43aa38063a6 ("dm crypt: add cryptographic
> data integrity protection (authenticated encryption)") should've added
> 'select CRYPTO_AUTHENC' to dm-crypt's Kconfig.  I'll let Milan weigh-in
> but that seems like the right way forward.

No, I don't this so. It is like you use some algorithm that is just not compiled-in,
or it is disabled in the current state (because of FIPS mode od so) - it fails
to initialize it.

I think we should not force dm-crypt to depend on AEAD - most users
do not use authenticated encryption, it is perfectly ok to keep this compiled out.

I do not see any principal difference from disabling any other crypto
(if you disable XTS mode, it fails to open device that uses it).

IMO the current config dependence is ok.

Milan