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

[Eric Biggers]

On Mon, Oct 26, 2020 at 11:24:50AM -0700, Eric Biggers wrote:
> > +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.

Here's the version of eboiv_create() I recommend (untested):

static int eboiv_create(struct crypto_template *tmpl, struct rtattr **tb)
{
	struct skcipher_instance *inst;
	struct eboiv_instance_ctx *ictx;
	struct skcipher_alg *alg;
	u32 mask;
	int err;

	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER, &mask);
	if (err)
		return err;

	inst = kzalloc(sizeof(*inst) + sizeof(*ictx), GFP_KERNEL);
	if (!inst)
		return -ENOMEM;
	ictx = skcipher_instance_ctx(inst);

	err = crypto_grab_skcipher(&ictx->skcipher_spawn,
				   skcipher_crypto_instance(inst),
				   crypto_attr_alg_name(tb[1]), 0, mask);
	if (err)
		goto err_free_inst;
	alg = crypto_spawn_skcipher_alg(&ictx->skcipher_spawn);

	err = -EINVAL;
	if (strncmp(alg->base.cra_name, "cbc(", 4) ||
	    crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
		goto err_free_inst;

	err = -ENAMETOOLONG;
	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME, "eboiv(%s)",
		     alg->base.cra_name) >= CRYPTO_MAX_ALG_NAME)
		goto err_free_inst;

	if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
		     "eboiv(%s)", alg->base.cra_driver_name) >=
	    CRYPTO_MAX_ALG_NAME)
		goto err_free_inst;

	inst->alg.base.cra_blocksize	= alg->base.cra_blocksize;
	inst->alg.base.cra_ctxsize	= sizeof(struct eboiv_tfm_ctx);
	inst->alg.base.cra_alignmask	= alg->base.cra_alignmask;
	inst->alg.base.cra_priority	= alg->base.cra_priority;

	inst->alg.setkey	= eboiv_skcipher_setkey;
	inst->alg.encrypt	= eboiv_skcipher_encrypt;
	inst->alg.decrypt	= eboiv_skcipher_decrypt;
	inst->alg.init		= eboiv_skcipher_init_tfm;
	inst->alg.exit		= eboiv_skcipher_exit_tfm;

	inst->alg.min_keysize	= crypto_skcipher_alg_min_keysize(alg);
	inst->alg.max_keysize	= crypto_skcipher_alg_max_keysize(alg);
	inst->alg.ivsize	= crypto_skcipher_alg_ivsize(alg);

	inst->free		= eboiv_skcipher_free_instance;

	err = skcipher_register_instance(tmpl, inst);
	if (err) {
err_free_inst:
		eboiv_skcipher_free_instance(inst);
	}
	return err;
}