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From: Milan Broz <gmazyland@gmail.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>, linux-crypto@vger.kernel.org
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
	Eric Biggers <ebiggers@google.com>,
	dm-devel@redhat.com, linux-fscrypt@vger.kernel.org,
	Gilad Ben-Yossef <gilad@benyossef.com>
Subject: Re: [PATCH v9 3/7] md: dm-crypt: switch to ESSIV crypto API template
Date: Mon, 12 Aug 2019 08:33:32 +0200
Message-ID: <8679d2f5-b005-cd89-957e-d79440b78086@gmail.com> (raw)
In-Reply-To: <20190810094053.7423-4-ard.biesheuvel@linaro.org>

Hi,

On 10/08/2019 11:40, Ard Biesheuvel wrote:
> Replace the explicit ESSIV handling in the dm-crypt driver with calls
> into the crypto API, which now possesses the capability to perform
> this processing within the crypto subsystem.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  drivers/md/Kconfig    |   1 +
>  drivers/md/dm-crypt.c | 194 ++++----------------
>  2 files changed, 33 insertions(+), 162 deletions(-)
> 
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index 3834332f4963..b727e8f15264 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
...
> @@ -2493,6 +2339,20 @@ static int crypt_ctr_cipher_new(struct dm_target *ti, char *cipher_in, char *key
>  	if (*ivmode && !strcmp(*ivmode, "lmk"))
>  		cc->tfms_count = 64;
>  
> +	if (*ivmode && !strcmp(*ivmode, "essiv")) {
> +		if (!*ivopts) {
> +			ti->error = "Digest algorithm missing for ESSIV mode";
> +			return -EINVAL;
> +		}
> +		ret = snprintf(buf, CRYPTO_MAX_ALG_NAME, "essiv(%s,%s)",
> +			       cipher_api, *ivopts);

This is wrong. It works only in length-preserving modes, not in AEAD modes.

Try for example
# cryptsetup luksFormat /dev/sdc -c aes-cbc-essiv:sha256 --integrity hmac-sha256 -q -i1

It should produce Crypto API string
  authenc(hmac(sha256),essiv(cbc(aes),sha256))
while it produces
  essiv(authenc(hmac(sha256),cbc(aes)),sha256)
(and fails).

You can run "luks2-integrity-test" from cryptsetup test suite to detect it.

Just the test does not fail, it prints N/A for ESSIV use cases - we need to deal with older kernels...
I can probable change it to fail unconditionally though.

...
> @@ -2579,9 +2439,19 @@ static int crypt_ctr_cipher_old(struct dm_target *ti, char *cipher_in, char *key
>  	if (!cipher_api)
>  		goto bad_mem;
>  
> -	ret = snprintf(cipher_api, CRYPTO_MAX_ALG_NAME,
> -		       "%s(%s)", chainmode, cipher);
> -	if (ret < 0) {
> +	if (*ivmode && !strcmp(*ivmode, "essiv")) {
> +		if (!*ivopts) {
> +			ti->error = "Digest algorithm missing for ESSIV mode";
> +			kfree(cipher_api);
> +			return -EINVAL;
> +		}
> +		ret = snprintf(cipher_api, CRYPTO_MAX_ALG_NAME,
> +			       "essiv(%s(%s),%s)", chainmode, cipher, *ivopts);

I guess here it is ok, because old forma cannot use AEAD.

Thanks,
Milan

  reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-10  9:40 [PATCH v9 0/7] crypto: switch to crypto API for ESSIV generation Ard Biesheuvel
2019-08-10  9:40 ` [PATCH v9 1/7] crypto: essiv - create wrapper template " Ard Biesheuvel
2019-08-10  9:40 ` [PATCH v9 2/7] fs: crypto: invoke crypto API for ESSIV handling Ard Biesheuvel
2019-08-10  9:40 ` [PATCH v9 3/7] md: dm-crypt: switch to ESSIV crypto API template Ard Biesheuvel
2019-08-12  6:33   ` Milan Broz [this message]
2019-08-12  6:54     ` Ard Biesheuvel
2019-08-12  7:44       ` Milan Broz
2019-08-12  7:50         ` Ard Biesheuvel
2019-08-12 13:51           ` Milan Broz
2019-08-12 14:19             ` Ard Biesheuvel
2019-08-10  9:40 ` [PATCH v9 4/7] crypto: essiv - add tests for essiv in cbc(aes)+sha256 mode Ard Biesheuvel
2019-08-10  9:40 ` [PATCH v9 5/7] crypto: arm64/aes-cts-cbc - factor out CBC en/decryption of a walk Ard Biesheuvel
2019-08-10  9:40 ` [PATCH v9 6/7] crypto: arm64/aes - implement accelerated ESSIV/CBC mode Ard Biesheuvel
2019-08-10  9:40 ` [PATCH v9 7/7] md: dm-crypt: omit parsing of the encapsulated cipher Ard Biesheuvel

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