Hi Herbert,
I have a question about the crypto_cipher API in dm-crypt:
We are apparently trying to deprecate cryto_cipher API (see the ESSIV patchset),
but I am not sure what API now should be used instead.
See the patch below - all we need is to one block encryption for IV.
This algorithm makes sense only for FDE (old compatible Bitlocker devices),
I really do not want this to be shared in some crypto module...
What API should I use here? Sync skcipher? Is the crypto_cipher API
really a problem in this case?
Thanks,
Milan
On 04/07/2019 15:10, Milan Broz wrote:
> This IV is used in some BitLocker devices with CBC encryption mode.
>
> NOTE: maybe we need to use another crypto API if the bare cipher
> API is going to be deprecated.
>
> Signed-off-by: Milan Broz <gmazyland@xxxxxxxxx>
> ---
> drivers/md/dm-crypt.c | 82 ++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 81 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> index 96ead4492787..a5ffa1ac6a28 100644
> --- a/drivers/md/dm-crypt.c
> +++ b/drivers/md/dm-crypt.c
> @@ -120,6 +120,10 @@ struct iv_tcw_private {
> u8 *whitening;
> };
>
> +struct iv_eboiv_private {
> + struct crypto_cipher *tfm;
> +};
> +
> /*
> * Crypt: maps a linear range of a block device
> * and encrypts / decrypts at the same time.
> @@ -159,6 +163,7 @@ struct crypt_config {
> struct iv_benbi_private benbi;
> struct iv_lmk_private lmk;
> struct iv_tcw_private tcw;
> + struct iv_eboiv_private eboiv;
> } iv_gen_private;
> u64 iv_offset;
> unsigned int iv_size;
> @@ -290,6 +295,10 @@ static struct crypto_aead *any_tfm_aead(struct crypt_config *cc)
> * is calculated from initial key, sector number and mixed using CRC32.
> * Note that this encryption scheme is vulnerable to watermarking attacks
> * and should be used for old compatible containers access only.
> + *
> + * eboiv: Encrypted byte-offset IV (used in Bitlocker in CBC mode)
> + * The IV is encrypted little-endian byte-offset (with the same key
> + * and cipher as the volume).
> */
>
> static int crypt_iv_plain_gen(struct crypt_config *cc, u8 *iv,
> @@ -838,6 +847,67 @@ static int crypt_iv_random_gen(struct crypt_config *cc, u8 *iv,
> return 0;
> }
>
> +static void crypt_iv_eboiv_dtr(struct crypt_config *cc)
> +{
> + struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
> +
> + crypto_free_cipher(eboiv->tfm);
> + eboiv->tfm = NULL;
> +}
> +
> +static int crypt_iv_eboiv_ctr(struct crypt_config *cc, struct dm_target *ti,
> + const char *opts)
> +{
> + struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
> + struct crypto_cipher *tfm;
> +
> + tfm = crypto_alloc_cipher(cc->cipher, 0, 0);
> + if (IS_ERR(tfm)) {
> + ti->error = "Error allocating crypto tfm for EBOIV";
> + return PTR_ERR(tfm);
> + }
> +
> + if (crypto_cipher_blocksize(tfm) != cc->iv_size) {
> + ti->error = "Block size of EBOIV cipher does "
> + "not match IV size of block cipher";
> + crypto_free_cipher(tfm);
> + return -EINVAL;
> + }
> +
> + eboiv->tfm = tfm;
> + return 0;
> +}
> +
> +static int crypt_iv_eboiv_init(struct crypt_config *cc)
> +{
> + struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
> + int err;
> +
> + err = crypto_cipher_setkey(eboiv->tfm, cc->key, cc->key_size);
> + if (err)
> + return err;
> +
> + return 0;
> +}
> +
> +static int crypt_iv_eboiv_wipe(struct crypt_config *cc)
> +{
> + /* Called after cc->key is set to random key in crypt_wipe() */
> + return crypt_iv_eboiv_init(cc);
> +}
> +
> +static int crypt_iv_eboiv_gen(struct crypt_config *cc, u8 *iv,
> + struct dm_crypt_request *dmreq)
> +{
> + struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
> +
> + memset(iv, 0, cc->iv_size);
> + *(__le64 *)iv = cpu_to_le64(dmreq->iv_sector * cc->sector_size);
> + crypto_cipher_encrypt_one(eboiv->tfm, iv, iv);
> +
> + return 0;
> +}
> +
> static const struct crypt_iv_operations crypt_iv_plain_ops = {
> .generator = crypt_iv_plain_gen
> };
> @@ -890,6 +960,14 @@ static struct crypt_iv_operations crypt_iv_random_ops = {
> .generator = crypt_iv_random_gen
> };
>
> +static struct crypt_iv_operations crypt_iv_eboiv_ops = {
> + .ctr = crypt_iv_eboiv_ctr,
> + .dtr = crypt_iv_eboiv_dtr,
> + .init = crypt_iv_eboiv_init,
> + .wipe = crypt_iv_eboiv_wipe,
> + .generator = crypt_iv_eboiv_gen
> +};
> +
> /*
> * Integrity extensions
> */
> @@ -2293,6 +2371,8 @@ static int crypt_ctr_ivmode(struct dm_target *ti, const char *ivmode)
> cc->iv_gen_ops = &crypt_iv_benbi_ops;
> else if (strcmp(ivmode, "null") == 0)
> cc->iv_gen_ops = &crypt_iv_null_ops;
> + else if (strcmp(ivmode, "eboiv") == 0)
> + cc->iv_gen_ops = &crypt_iv_eboiv_ops;
> else if (strcmp(ivmode, "lmk") == 0) {
> cc->iv_gen_ops = &crypt_iv_lmk_ops;
> /*
> @@ -3093,7 +3173,7 @@ static void crypt_io_hints(struct dm_target *ti, struct queue_limits *limits)
>
> static struct target_type crypt_target = {
> .name = "crypt",
> - .version = {1, 18, 1},
> + .version = {1, 19, 0},
> .module = THIS_MODULE,
> .ctr = crypt_ctr,
> .dtr = crypt_dtr,
>
