crypto/ctr.c - fs/xfs/xfs-linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * CTR: Counter mode
  *
  * (C) Copyright IBM Corp. 2007 - Joy Latten <latten@us.ibm.com>
  */

 #include <crypto/algapi.h>
 #include <crypto/ctr.h>
 #include <crypto/internal/skcipher.h>
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/slab.h>

 struct crypto_rfc3686_ctx {
 	struct crypto_skcipher *child;
 	u8 nonce[CTR_RFC3686_NONCE_SIZE];
 };

 struct crypto_rfc3686_req_ctx {
 	u8 iv[CTR_RFC3686_BLOCK_SIZE];
 	struct skcipher_request subreq CRYPTO_MINALIGN_ATTR;
 };

 static void crypto_ctr_crypt_final(struct skcipher_walk *walk,
 				   struct crypto_cipher *tfm)
 {
 	unsigned int bsize = crypto_cipher_blocksize(tfm);
 	unsigned long alignmask = crypto_cipher_alignmask(tfm);
 	u8 *ctrblk = walk->iv;
 	u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
 	u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1);
 	u8 *src = walk->src.virt.addr;
 	u8 *dst = walk->dst.virt.addr;
 	unsigned int nbytes = walk->nbytes;

 	crypto_cipher_encrypt_one(tfm, keystream, ctrblk);
 	crypto_xor_cpy(dst, keystream, src, nbytes);

 	crypto_inc(ctrblk, bsize);
 }

 static int crypto_ctr_crypt_segment(struct skcipher_walk *walk,
 				    struct crypto_cipher *tfm)
 {
 	void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
 		   crypto_cipher_alg(tfm)->cia_encrypt;
 	unsigned int bsize = crypto_cipher_blocksize(tfm);
 	u8 *ctrblk = walk->iv;
 	u8 *src = walk->src.virt.addr;
 	u8 *dst = walk->dst.virt.addr;
 	unsigned int nbytes = walk->nbytes;

 	do {
 		/* create keystream */
 		fn(crypto_cipher_tfm(tfm), dst, ctrblk);
 		crypto_xor(dst, src, bsize);

 		/* increment counter in counterblock */
 		crypto_inc(ctrblk, bsize);

 		src += bsize;
 		dst += bsize;
 	} while ((nbytes -= bsize) >= bsize);

 	return nbytes;
 }

 static int crypto_ctr_crypt_inplace(struct skcipher_walk *walk,
 				    struct crypto_cipher *tfm)
 {
 	void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
 		   crypto_cipher_alg(tfm)->cia_encrypt;
 	unsigned int bsize = crypto_cipher_blocksize(tfm);
 	unsigned long alignmask = crypto_cipher_alignmask(tfm);
 	unsigned int nbytes = walk->nbytes;
 	u8 *ctrblk = walk->iv;
 	u8 *src = walk->src.virt.addr;
 	u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
 	u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1);

 	do {
 		/* create keystream */
 		fn(crypto_cipher_tfm(tfm), keystream, ctrblk);
 		crypto_xor(src, keystream, bsize);

 		/* increment counter in counterblock */
 		crypto_inc(ctrblk, bsize);

 		src += bsize;
 	} while ((nbytes -= bsize) >= bsize);

 	return nbytes;
 }

 static int crypto_ctr_crypt(struct skcipher_request *req)
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
 	const unsigned int bsize = crypto_cipher_blocksize(cipher);
 	struct skcipher_walk walk;
 	unsigned int nbytes;
 	int err;

 	err = skcipher_walk_virt(&walk, req, false);

 	while (walk.nbytes >= bsize) {
 		if (walk.src.virt.addr == walk.dst.virt.addr)
 			nbytes = crypto_ctr_crypt_inplace(&walk, cipher);
 		else
 			nbytes = crypto_ctr_crypt_segment(&walk, cipher);

 		err = skcipher_walk_done(&walk, nbytes);
 	}

 	if (walk.nbytes) {
 		crypto_ctr_crypt_final(&walk, cipher);
 		err = skcipher_walk_done(&walk, 0);
 	}

 	return err;
 }

 static int crypto_ctr_create(struct crypto_template *tmpl, struct rtattr **tb)
 {
 	struct skcipher_instance *inst;
 	struct crypto_alg *alg;
 	int err;

 	inst = skcipher_alloc_instance_simple(tmpl, tb, &alg);
 	if (IS_ERR(inst))
 		return PTR_ERR(inst);

 	/* Block size must be >= 4 bytes. */
 	err = -EINVAL;
 	if (alg->cra_blocksize < 4)
 		goto out_free_inst;

 	/* If this is false we'd fail the alignment of crypto_inc. */
 	if (alg->cra_blocksize % 4)
 		goto out_free_inst;

 	/* CTR mode is a stream cipher. */
 	inst->alg.base.cra_blocksize = 1;

 	/*
 	 * To simplify the implementation, configure the skcipher walk to only
 	 * give a partial block at the very end, never earlier.
 	 */
 	inst->alg.chunksize = alg->cra_blocksize;

 	inst->alg.encrypt = crypto_ctr_crypt;
 	inst->alg.decrypt = crypto_ctr_crypt;

 	err = skcipher_register_instance(tmpl, inst);
 	if (err)
 		goto out_free_inst;
 	goto out_put_alg;

 out_free_inst:
 	inst->free(inst);
 out_put_alg:
 	crypto_mod_put(alg);
 	return err;
 }

 static int crypto_rfc3686_setkey(struct crypto_skcipher *parent,
 				 const u8 *key, unsigned int keylen)
 {
 	struct crypto_rfc3686_ctx *ctx = crypto_skcipher_ctx(parent);
 	struct crypto_skcipher *child = ctx->child;
 	int err;

 	/* the nonce is stored in bytes at end of key */
 	if (keylen < CTR_RFC3686_NONCE_SIZE)
 		return -EINVAL;

 	memcpy(ctx->nonce, key + (keylen - CTR_RFC3686_NONCE_SIZE),
 	       CTR_RFC3686_NONCE_SIZE);

 	keylen -= CTR_RFC3686_NONCE_SIZE;

 	crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
 	crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
 					 CRYPTO_TFM_REQ_MASK);
 	err = crypto_skcipher_setkey(child, key, keylen);
 	crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
 					  CRYPTO_TFM_RES_MASK);

 	return err;
 }

 static int crypto_rfc3686_crypt(struct skcipher_request *req)
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 	struct crypto_rfc3686_ctx *ctx = crypto_skcipher_ctx(tfm);
 	struct crypto_skcipher *child = ctx->child;
 	unsigned long align = crypto_skcipher_alignmask(tfm);
 	struct crypto_rfc3686_req_ctx *rctx =
 		(void *)PTR_ALIGN((u8 *)skcipher_request_ctx(req), align + 1);
 	struct skcipher_request *subreq = &rctx->subreq;
 	u8 *iv = rctx->iv;

 	/* set up counter block */
 	memcpy(iv, ctx->nonce, CTR_RFC3686_NONCE_SIZE);
 	memcpy(iv + CTR_RFC3686_NONCE_SIZE, req->iv, CTR_RFC3686_IV_SIZE);

 	/* initialize counter portion of counter block */
 	*(__be32 *)(iv + CTR_RFC3686_NONCE_SIZE + CTR_RFC3686_IV_SIZE) =
 		cpu_to_be32(1);

 	skcipher_request_set_tfm(subreq, child);
 	skcipher_request_set_callback(subreq, req->base.flags,
 				      req->base.complete, req->base.data);
 	skcipher_request_set_crypt(subreq, req->src, req->dst,
 				   req->cryptlen, iv);

 	return crypto_skcipher_encrypt(subreq);
 }

 static int crypto_rfc3686_init_tfm(struct crypto_skcipher *tfm)
 {
 	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
 	struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
 	struct crypto_rfc3686_ctx *ctx = crypto_skcipher_ctx(tfm);
 	struct crypto_skcipher *cipher;
 	unsigned long align;
 	unsigned int reqsize;

 	cipher = crypto_spawn_skcipher(spawn);
 	if (IS_ERR(cipher))
 		return PTR_ERR(cipher);

 	ctx->child = cipher;

 	align = crypto_skcipher_alignmask(tfm);
 	align &= ~(crypto_tfm_ctx_alignment() - 1);
 	reqsize = align + sizeof(struct crypto_rfc3686_req_ctx) +
 		  crypto_skcipher_reqsize(cipher);
 	crypto_skcipher_set_reqsize(tfm, reqsize);

 	return 0;
 }

 static void crypto_rfc3686_exit_tfm(struct crypto_skcipher *tfm)
 {
 	struct crypto_rfc3686_ctx *ctx = crypto_skcipher_ctx(tfm);

 	crypto_free_skcipher(ctx->child);
 }

 static void crypto_rfc3686_free(struct skcipher_instance *inst)
 {
 	struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);

 	crypto_drop_skcipher(spawn);
 	kfree(inst);
 }

 static int crypto_rfc3686_create(struct crypto_template *tmpl,
 				 struct rtattr **tb)
 {
 	struct crypto_attr_type *algt;
 	struct skcipher_instance *inst;
 	struct skcipher_alg *alg;
 	struct crypto_skcipher_spawn *spawn;
 	const char *cipher_name;
 	u32 mask;

 	int err;

 	algt = crypto_get_attr_type(tb);
 	if (IS_ERR(algt))
 		return PTR_ERR(algt);

 	if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
 		return -EINVAL;

 	cipher_name = crypto_attr_alg_name(tb[1]);
 	if (IS_ERR(cipher_name))
 		return PTR_ERR(cipher_name);

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

 	mask = crypto_requires_sync(algt->type, algt->mask) |
 		crypto_requires_off(algt->type, algt->mask,
 				    CRYPTO_ALG_NEED_FALLBACK);

 	spawn = skcipher_instance_ctx(inst);

 	crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
 	err = crypto_grab_skcipher(spawn, cipher_name, 0, mask);
 	if (err)
 		goto err_free_inst;

 	alg = crypto_spawn_skcipher_alg(spawn);

 	/* We only support 16-byte blocks. */
 	err = -EINVAL;
 	if (crypto_skcipher_alg_ivsize(alg) != CTR_RFC3686_BLOCK_SIZE)
 		goto err_drop_spawn;

 	/* Not a stream cipher? */
 	if (alg->base.cra_blocksize != 1)
 		goto err_drop_spawn;

 	err = -ENAMETOOLONG;
 	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
 		     "rfc3686(%s)", alg->base.cra_name) >= CRYPTO_MAX_ALG_NAME)
 		goto err_drop_spawn;
 	if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
 		     "rfc3686(%s)", alg->base.cra_driver_name) >=
 	    CRYPTO_MAX_ALG_NAME)
 		goto err_drop_spawn;

 	inst->alg.base.cra_priority = alg->base.cra_priority;
 	inst->alg.base.cra_blocksize = 1;
 	inst->alg.base.cra_alignmask = alg->base.cra_alignmask;

 	inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;

 	inst->alg.ivsize = CTR_RFC3686_IV_SIZE;
 	inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
 	inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg) +
 				CTR_RFC3686_NONCE_SIZE;
 	inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg) +
 				CTR_RFC3686_NONCE_SIZE;

 	inst->alg.setkey = crypto_rfc3686_setkey;
 	inst->alg.encrypt = crypto_rfc3686_crypt;
 	inst->alg.decrypt = crypto_rfc3686_crypt;

 	inst->alg.base.cra_ctxsize = sizeof(struct crypto_rfc3686_ctx);

 	inst->alg.init = crypto_rfc3686_init_tfm;
 	inst->alg.exit = crypto_rfc3686_exit_tfm;

 	inst->free = crypto_rfc3686_free;

 	err = skcipher_register_instance(tmpl, inst);
 	if (err)
 		goto err_drop_spawn;

 out:
 	return err;

 err_drop_spawn:
 	crypto_drop_skcipher(spawn);
 err_free_inst:
 	kfree(inst);
 	goto out;
 }

 static struct crypto_template crypto_ctr_tmpls[] = {
 	{
 		.name = "ctr",
 		.create = crypto_ctr_create,
 		.module = THIS_MODULE,
 	}, {
 		.name = "rfc3686",
 		.create = crypto_rfc3686_create,
 		.module = THIS_MODULE,
 	},
 };

 static int __init crypto_ctr_module_init(void)
 {
 	return crypto_register_templates(crypto_ctr_tmpls,
 					 ARRAY_SIZE(crypto_ctr_tmpls));
 }

 static void __exit crypto_ctr_module_exit(void)
 {
 	crypto_unregister_templates(crypto_ctr_tmpls,
 				    ARRAY_SIZE(crypto_ctr_tmpls));
 }

 subsys_initcall(crypto_ctr_module_init);
 module_exit(crypto_ctr_module_exit);

 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("CTR block cipher mode of operation");
 MODULE_ALIAS_CRYPTO("rfc3686");
 MODULE_ALIAS_CRYPTO("ctr");
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* CTR: Counter mode
	*
	* (C) Copyright IBM Corp. 2007 - Joy Latten <latten@us.ibm.com>
	*/

	#include <crypto/algapi.h>
	#include <crypto/ctr.h>
	#include <crypto/internal/skcipher.h>
	#include <linux/err.h>
	#include <linux/init.h>
	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/slab.h>

	struct crypto_rfc3686_ctx {
	struct crypto_skcipher *child;
	u8 nonce[CTR_RFC3686_NONCE_SIZE];
	};

	struct crypto_rfc3686_req_ctx {
	u8 iv[CTR_RFC3686_BLOCK_SIZE];
	struct skcipher_request subreq CRYPTO_MINALIGN_ATTR;
	};

	static void crypto_ctr_crypt_final(struct skcipher_walk *walk,
	struct crypto_cipher *tfm)
	{
	unsigned int bsize = crypto_cipher_blocksize(tfm);
	unsigned long alignmask = crypto_cipher_alignmask(tfm);
	u8 *ctrblk = walk->iv;
	u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
	u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1);
	u8 *src = walk->src.virt.addr;
	u8 *dst = walk->dst.virt.addr;
	unsigned int nbytes = walk->nbytes;

	crypto_cipher_encrypt_one(tfm, keystream, ctrblk);
	crypto_xor_cpy(dst, keystream, src, nbytes);

	crypto_inc(ctrblk, bsize);
	}

	static int crypto_ctr_crypt_segment(struct skcipher_walk *walk,
	struct crypto_cipher *tfm)
	{
	void (fn)(struct crypto_tfm , u8 , const u8 ) =
	crypto_cipher_alg(tfm)->cia_encrypt;
	unsigned int bsize = crypto_cipher_blocksize(tfm);
	u8 *ctrblk = walk->iv;
	u8 *src = walk->src.virt.addr;
	u8 *dst = walk->dst.virt.addr;
	unsigned int nbytes = walk->nbytes;

	do {
	/* create keystream */
	fn(crypto_cipher_tfm(tfm), dst, ctrblk);
	crypto_xor(dst, src, bsize);

	/* increment counter in counterblock */
	crypto_inc(ctrblk, bsize);

	src += bsize;
	dst += bsize;
	} while ((nbytes -= bsize) >= bsize);

	return nbytes;
	}

	static int crypto_ctr_crypt_inplace(struct skcipher_walk *walk,
	struct crypto_cipher *tfm)
	{
	void (fn)(struct crypto_tfm , u8 , const u8 ) =
	crypto_cipher_alg(tfm)->cia_encrypt;
	unsigned int bsize = crypto_cipher_blocksize(tfm);
	unsigned long alignmask = crypto_cipher_alignmask(tfm);
	unsigned int nbytes = walk->nbytes;
	u8 *ctrblk = walk->iv;
	u8 *src = walk->src.virt.addr;
	u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];
	u8 *keystream = PTR_ALIGN(tmp + 0, alignmask + 1);

	do {
	/* create keystream */
	fn(crypto_cipher_tfm(tfm), keystream, ctrblk);
	crypto_xor(src, keystream, bsize);

	/* increment counter in counterblock */
	crypto_inc(ctrblk, bsize);

	src += bsize;
	} while ((nbytes -= bsize) >= bsize);

	return nbytes;
	}

	static int crypto_ctr_crypt(struct skcipher_request *req)
	{
	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
	struct crypto_cipher *cipher = skcipher_cipher_simple(tfm);
	const unsigned int bsize = crypto_cipher_blocksize(cipher);
	struct skcipher_walk walk;
	unsigned int nbytes;
	int err;

	err = skcipher_walk_virt(&walk, req, false);

	while (walk.nbytes >= bsize) {
	if (walk.src.virt.addr == walk.dst.virt.addr)
	nbytes = crypto_ctr_crypt_inplace(&walk, cipher);
	else
	nbytes = crypto_ctr_crypt_segment(&walk, cipher);

	err = skcipher_walk_done(&walk, nbytes);
	}

	if (walk.nbytes) {
	crypto_ctr_crypt_final(&walk, cipher);
	err = skcipher_walk_done(&walk, 0);
	}

	return err;
	}

	static int crypto_ctr_create(struct crypto_template tmpl, struct rtattr *tb)
	{
	struct skcipher_instance *inst;
	struct crypto_alg *alg;
	int err;

	inst = skcipher_alloc_instance_simple(tmpl, tb, &alg);
	if (IS_ERR(inst))
	return PTR_ERR(inst);

	/* Block size must be >= 4 bytes. */
	err = -EINVAL;
	if (alg->cra_blocksize < 4)
	goto out_free_inst;

	/* If this is false we'd fail the alignment of crypto_inc. */
	if (alg->cra_blocksize % 4)
	goto out_free_inst;

	/* CTR mode is a stream cipher. */
	inst->alg.base.cra_blocksize = 1;

	/*
	* To simplify the implementation, configure the skcipher walk to only
	* give a partial block at the very end, never earlier.
	*/
	inst->alg.chunksize = alg->cra_blocksize;

	inst->alg.encrypt = crypto_ctr_crypt;
	inst->alg.decrypt = crypto_ctr_crypt;

	err = skcipher_register_instance(tmpl, inst);
	if (err)
	goto out_free_inst;
	goto out_put_alg;

	out_free_inst:
	inst->free(inst);
	out_put_alg:
	crypto_mod_put(alg);
	return err;
	}

	static int crypto_rfc3686_setkey(struct crypto_skcipher *parent,
	const u8 *key, unsigned int keylen)
	{
	struct crypto_rfc3686_ctx *ctx = crypto_skcipher_ctx(parent);
	struct crypto_skcipher *child = ctx->child;
	int err;

	/* the nonce is stored in bytes at end of key */
	if (keylen < CTR_RFC3686_NONCE_SIZE)
	return -EINVAL;

	memcpy(ctx->nonce, key + (keylen - CTR_RFC3686_NONCE_SIZE),
	CTR_RFC3686_NONCE_SIZE);

	keylen -= CTR_RFC3686_NONCE_SIZE;

	crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
	crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
	CRYPTO_TFM_REQ_MASK);
	err = crypto_skcipher_setkey(child, key, keylen);
	crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
	CRYPTO_TFM_RES_MASK);

	return err;
	}

	static int crypto_rfc3686_crypt(struct skcipher_request *req)
	{
	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
	struct crypto_rfc3686_ctx *ctx = crypto_skcipher_ctx(tfm);
	struct crypto_skcipher *child = ctx->child;
	unsigned long align = crypto_skcipher_alignmask(tfm);
	struct crypto_rfc3686_req_ctx *rctx =
	(void )PTR_ALIGN((u8 )skcipher_request_ctx(req), align + 1);
	struct skcipher_request *subreq = &rctx->subreq;
	u8 *iv = rctx->iv;

	/* set up counter block */
	memcpy(iv, ctx->nonce, CTR_RFC3686_NONCE_SIZE);
	memcpy(iv + CTR_RFC3686_NONCE_SIZE, req->iv, CTR_RFC3686_IV_SIZE);

	/* initialize counter portion of counter block */
	(__be32 )(iv + CTR_RFC3686_NONCE_SIZE + CTR_RFC3686_IV_SIZE) =
	cpu_to_be32(1);

	skcipher_request_set_tfm(subreq, child);
	skcipher_request_set_callback(subreq, req->base.flags,
	req->base.complete, req->base.data);
	skcipher_request_set_crypt(subreq, req->src, req->dst,
	req->cryptlen, iv);

	return crypto_skcipher_encrypt(subreq);
	}

	static int crypto_rfc3686_init_tfm(struct crypto_skcipher *tfm)
	{
	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
	struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
	struct crypto_rfc3686_ctx *ctx = crypto_skcipher_ctx(tfm);
	struct crypto_skcipher *cipher;
	unsigned long align;
	unsigned int reqsize;

	cipher = crypto_spawn_skcipher(spawn);
	if (IS_ERR(cipher))
	return PTR_ERR(cipher);

	ctx->child = cipher;

	align = crypto_skcipher_alignmask(tfm);
	align &= ~(crypto_tfm_ctx_alignment() - 1);
	reqsize = align + sizeof(struct crypto_rfc3686_req_ctx) +
	crypto_skcipher_reqsize(cipher);
	crypto_skcipher_set_reqsize(tfm, reqsize);

	return 0;
	}

	static void crypto_rfc3686_exit_tfm(struct crypto_skcipher *tfm)
	{
	struct crypto_rfc3686_ctx *ctx = crypto_skcipher_ctx(tfm);

	crypto_free_skcipher(ctx->child);
	}

	static void crypto_rfc3686_free(struct skcipher_instance *inst)
	{
	struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);

	crypto_drop_skcipher(spawn);
	kfree(inst);
	}

	static int crypto_rfc3686_create(struct crypto_template *tmpl,
	struct rtattr **tb)
	{
	struct crypto_attr_type *algt;
	struct skcipher_instance *inst;
	struct skcipher_alg *alg;
	struct crypto_skcipher_spawn *spawn;
	const char *cipher_name;
	u32 mask;

	int err;

	algt = crypto_get_attr_type(tb);
	if (IS_ERR(algt))
	return PTR_ERR(algt);

	if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
	return -EINVAL;

	cipher_name = crypto_attr_alg_name(tb[1]);
	if (IS_ERR(cipher_name))
	return PTR_ERR(cipher_name);

	inst = kzalloc(sizeof(inst) + sizeof(spawn), GFP_KERNEL);
	if (!inst)
	return -ENOMEM;

	mask = crypto_requires_sync(algt->type, algt->mask) \|
	crypto_requires_off(algt->type, algt->mask,
	CRYPTO_ALG_NEED_FALLBACK);

	spawn = skcipher_instance_ctx(inst);

	crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
	err = crypto_grab_skcipher(spawn, cipher_name, 0, mask);
	if (err)
	goto err_free_inst;

	alg = crypto_spawn_skcipher_alg(spawn);

	/* We only support 16-byte blocks. */
	err = -EINVAL;
	if (crypto_skcipher_alg_ivsize(alg) != CTR_RFC3686_BLOCK_SIZE)
	goto err_drop_spawn;

	/* Not a stream cipher? */
	if (alg->base.cra_blocksize != 1)
	goto err_drop_spawn;

	err = -ENAMETOOLONG;
	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
	"rfc3686(%s)", alg->base.cra_name) >= CRYPTO_MAX_ALG_NAME)
	goto err_drop_spawn;
	if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
	"rfc3686(%s)", alg->base.cra_driver_name) >=
	CRYPTO_MAX_ALG_NAME)
	goto err_drop_spawn;

	inst->alg.base.cra_priority = alg->base.cra_priority;
	inst->alg.base.cra_blocksize = 1;
	inst->alg.base.cra_alignmask = alg->base.cra_alignmask;

	inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;

	inst->alg.ivsize = CTR_RFC3686_IV_SIZE;
	inst->alg.chunksize = crypto_skcipher_alg_chunksize(alg);
	inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg) +
	CTR_RFC3686_NONCE_SIZE;
	inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg) +
	CTR_RFC3686_NONCE_SIZE;

	inst->alg.setkey = crypto_rfc3686_setkey;
	inst->alg.encrypt = crypto_rfc3686_crypt;
	inst->alg.decrypt = crypto_rfc3686_crypt;

	inst->alg.base.cra_ctxsize = sizeof(struct crypto_rfc3686_ctx);

	inst->alg.init = crypto_rfc3686_init_tfm;
	inst->alg.exit = crypto_rfc3686_exit_tfm;

	inst->free = crypto_rfc3686_free;

	err = skcipher_register_instance(tmpl, inst);
	if (err)
	goto err_drop_spawn;

	out:
	return err;

	err_drop_spawn:
	crypto_drop_skcipher(spawn);
	err_free_inst:
	kfree(inst);
	goto out;
	}

	static struct crypto_template crypto_ctr_tmpls[] = {
	{
	.name = "ctr",
	.create = crypto_ctr_create,
	.module = THIS_MODULE,
	}, {
	.name = "rfc3686",
	.create = crypto_rfc3686_create,
	.module = THIS_MODULE,
	},
	};

	static int __init crypto_ctr_module_init(void)
	{
	return crypto_register_templates(crypto_ctr_tmpls,
	ARRAY_SIZE(crypto_ctr_tmpls));
	}

	static void __exit crypto_ctr_module_exit(void)
	{
	crypto_unregister_templates(crypto_ctr_tmpls,
	ARRAY_SIZE(crypto_ctr_tmpls));
	}

	subsys_initcall(crypto_ctr_module_init);
	module_exit(crypto_ctr_module_exit);

	MODULE_LICENSE("GPL");
	MODULE_DESCRIPTION("CTR block cipher mode of operation");
	MODULE_ALIAS_CRYPTO("rfc3686");
	MODULE_ALIAS_CRYPTO("ctr");