Re: [dm-devel] [PATCH 1/4] crypto: add eboiv as a crypto API template

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Oct 26, 2020 at 03:04:44PM +0200, Gilad Ben-Yossef wrote:
> diff --git a/crypto/eboiv.c b/crypto/eboiv.c
> new file mode 100644
> index 000000000000..467833e89139
> --- /dev/null
> +++ b/crypto/eboiv.c
> @@ -0,0 +1,295 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * EBOIV skcipher template for block encryption
> + *
> + * This template encapsulates the  Encrypted byte-offset IV generation algorithm
> + * used in Bitlocker in CBC mode by dm-crypt, which converts the initial vector
> + * for the skcipher used for block encryption, by encrypting it using the same
> + * skcipher key as encryption key. Usually, the input IV is a 64-bit sector
> + * offset (the byte offset of the start of the sector) in LE representation
> + * zero-padded to the size of the IV, but this * is not assumed by this driver.
> + *
> + * The typical use of this template is to instantiate the skcipher
> + * 'eboiv(cbc(aes))', which is the only instantiation used by
> + * dm-crypt for supporting BitLocker AES-CBC mode as specified in
> + * https://www.jedec.org/sites/default/files/docs/JESD223C.pdf
> + *
> + * Copyright (C) 2020 ARM Limited or its affiliates.
> + * Written by Gilad Ben-Yossef <gilad@benyossef.com>
> + *
> + * Heavily based on:
> + *
> + * ESSIV skcipher and aead template for block encryption
> + * Copyright (c) 2019 Linaro, Ltd. <ard.biesheuvel@linaro.org>
> + *
> + * and
> + *
> + * dm-crypt eboiv code
> + * by Milan Broz <gmazyland@gmail.com> and Ard Biesheuvel <ardb@kernel.org>
> + *
> + */
> +
> +#include <crypto/internal/skcipher.h>
> +#include <crypto/scatterwalk.h>
> +#include <linux/module.h>
> +
> +#include "internal.h"

internal.h shouldn't be included here.

> +
> +struct eboiv_instance_ctx {
> +	struct crypto_skcipher_spawn skcipher_spawn;
> +	char eboiv_cipher_name[CRYPTO_MAX_ALG_NAME];
> +};

The 'eboiv_cipher_name' field isn't used.

> +static void eboiv_skcipher_iv_done(struct crypto_async_request *areq, int err)
> +{
> +	struct eboiv_req_ctx *req_ctx = areq->data;
> +	struct skcipher_request *req = req_ctx->req;
> +	int ret;
> +
> +	if (!err) {
> +
> +		ret = eboiv_skcipher_do_crypt(req, req_ctx->enc);
> +
> +		if ((ret == -EINPROGRESS) || (ret == -EBUSY))
> +			return;
> +	}
> +
> +	skcipher_request_complete(req, err);
> +}

This looks wrong, because if eboiv_skcipher_do_crypt() fails,
skcipher_request_complete() will be called with err=0.

> +static int eboiv_create(struct crypto_template *tmpl, struct rtattr **tb)
> +{
> +	struct crypto_attr_type *algt;
> +	const char *inner_cipher_name;
> +	struct skcipher_instance *skcipher_inst = NULL;
> +	struct crypto_instance *inst;
> +	struct crypto_alg *base, *block_base;
> +	struct eboiv_instance_ctx *ictx;
> +	struct skcipher_alg *skcipher_alg = NULL;
> +	int ivsize;
> +	u32 mask;
> +	int err;
> +
> +	algt = crypto_get_attr_type(tb);
> +	if (IS_ERR(algt))
> +		return PTR_ERR(algt);

Need to check that the algorithm is being instantiated as skcipher.
crypto_check_attr_type() should be used.

> +
> +	inner_cipher_name = crypto_attr_alg_name(tb[1]);
> +	if (IS_ERR(inner_cipher_name))
> +		return PTR_ERR(inner_cipher_name);

The result of crypto_attr_alg_name() can be passed directly to
crypto_grab_skcipher().

> +	mask = crypto_algt_inherited_mask(algt);
> +
> +	skcipher_inst = kzalloc(sizeof(*skcipher_inst) + sizeof(*ictx), GFP_KERNEL);
> +	if (!skcipher_inst)
> +		return -ENOMEM;
> +
> +	inst = skcipher_crypto_instance(skcipher_inst);
> +	base = &skcipher_inst->alg.base;
> +	ictx = crypto_instance_ctx(inst);
> +
> +	/* Symmetric cipher, e.g., "cbc(aes)" */
> +	err = crypto_grab_skcipher(&ictx->skcipher_spawn, inst, inner_cipher_name, 0, mask);
> +	if (err)
> +		goto out_free_inst;
> +
> +	skcipher_alg = crypto_spawn_skcipher_alg(&ictx->skcipher_spawn);
> +	block_base = &skcipher_alg->base;
> +	ivsize = crypto_skcipher_alg_ivsize(skcipher_alg);
> +
> +	if (ivsize != block_base->cra_blocksize)
> +		goto out_drop_skcipher;

Shouldn't it be verified that the underlying algorithm is actually cbc?

> +	skcipher_inst->alg.chunksize	= crypto_skcipher_alg_chunksize(skcipher_alg);
> +	skcipher_inst->alg.walksize	= crypto_skcipher_alg_walksize(skcipher_alg);

Setting these isn't necessary.

> +
> +	skcipher_inst->free		= eboiv_skcipher_free_instance;
> +
> +	err = skcipher_register_instance(tmpl, skcipher_inst);
> +
> +	if (err)
> +		goto out_drop_skcipher;
> +
> +	return 0;
> +
> +out_drop_skcipher:
> +	crypto_drop_skcipher(&ictx->skcipher_spawn);
> +out_free_inst:
> +	kfree(skcipher_inst);
> +	return err;
> +}

eboiv_skcipher_free_instance() can be called on the error path.

> +/* eboiv(cipher_name) */
> +static struct crypto_template eboiv_tmpl = {
> +	.name	= "eboiv",
> +	.create	= eboiv_create,
> +	.module	= THIS_MODULE,
> +};

"cipher_name" => "cbc_cipher_name", since it wraps something like "cbc(aes)",
not "aes".

- Eric

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