// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   * CBC: Cipher Block Chaining mode
   *

   * Copyright (c) 2006-2016 Herbert Xu <herbert@gondor.apana.org.au>

   */

  #include <crypto/algapi.h>

  #include <crypto/internal/skcipher.h>

  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/kernel.h>

  #include <linux/log2.h>

  #include <linux/module.h>

  static int crypto_cbc_encrypt_segment(struct skcipher_walk *walk,
  				      struct crypto_skcipher *skcipher)

  {

  	unsigned int bsize = crypto_skcipher_blocksize(skcipher);
  	void (*fn)(struct crypto_tfm *, u8 *, const u8 *);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 *dst = walk->dst.virt.addr;
  	struct crypto_cipher *cipher;
  	struct crypto_tfm *tfm;
  	u8 *iv = walk->iv;
  
  	cipher = skcipher_cipher_simple(skcipher);
  	tfm = crypto_cipher_tfm(cipher);
  	fn = crypto_cipher_alg(cipher)->cia_encrypt;
  
  	do {
  		crypto_xor(iv, src, bsize);
  		fn(tfm, dst, iv);
  		memcpy(iv, dst, bsize);
  
  		src += bsize;
  		dst += bsize;
  	} while ((nbytes -= bsize) >= bsize);
  
  	return nbytes;
  }
  
  static int crypto_cbc_encrypt_inplace(struct skcipher_walk *walk,
  				      struct crypto_skcipher *skcipher)
  {
  	unsigned int bsize = crypto_skcipher_blocksize(skcipher);
  	void (*fn)(struct crypto_tfm *, u8 *, const u8 *);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	struct crypto_cipher *cipher;
  	struct crypto_tfm *tfm;
  	u8 *iv = walk->iv;
  
  	cipher = skcipher_cipher_simple(skcipher);
  	tfm = crypto_cipher_tfm(cipher);
  	fn = crypto_cipher_alg(cipher)->cia_encrypt;
  
  	do {
  		crypto_xor(src, iv, bsize);
  		fn(tfm, src, src);
  		iv = src;
  
  		src += bsize;
  	} while ((nbytes -= bsize) >= bsize);
  
  	memcpy(walk->iv, iv, bsize);
  
  	return nbytes;

  }
  
  static int crypto_cbc_encrypt(struct skcipher_request *req)

  {

  	struct crypto_skcipher *skcipher = crypto_skcipher_reqtfm(req);
  	struct skcipher_walk walk;
  	int err;
  
  	err = skcipher_walk_virt(&walk, req, false);
  
  	while (walk.nbytes) {
  		if (walk.src.virt.addr == walk.dst.virt.addr)
  			err = crypto_cbc_encrypt_inplace(&walk, skcipher);
  		else
  			err = crypto_cbc_encrypt_segment(&walk, skcipher);
  		err = skcipher_walk_done(&walk, err);
  	}
  
  	return err;
  }
  
  static int crypto_cbc_decrypt_segment(struct skcipher_walk *walk,
  				      struct crypto_skcipher *skcipher)
  {
  	unsigned int bsize = crypto_skcipher_blocksize(skcipher);
  	void (*fn)(struct crypto_tfm *, u8 *, const u8 *);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 *dst = walk->dst.virt.addr;
  	struct crypto_cipher *cipher;
  	struct crypto_tfm *tfm;
  	u8 *iv = walk->iv;
  
  	cipher = skcipher_cipher_simple(skcipher);
  	tfm = crypto_cipher_tfm(cipher);
  	fn = crypto_cipher_alg(cipher)->cia_decrypt;
  
  	do {
  		fn(tfm, dst, src);
  		crypto_xor(dst, iv, bsize);
  		iv = src;
  
  		src += bsize;
  		dst += bsize;
  	} while ((nbytes -= bsize) >= bsize);
  
  	memcpy(walk->iv, iv, bsize);
  
  	return nbytes;

  }

  static int crypto_cbc_decrypt_inplace(struct skcipher_walk *walk,
  				      struct crypto_skcipher *skcipher)

  {

  	unsigned int bsize = crypto_skcipher_blocksize(skcipher);
  	void (*fn)(struct crypto_tfm *, u8 *, const u8 *);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 last_iv[MAX_CIPHER_BLOCKSIZE];
  	struct crypto_cipher *cipher;
  	struct crypto_tfm *tfm;
  
  	cipher = skcipher_cipher_simple(skcipher);
  	tfm = crypto_cipher_tfm(cipher);
  	fn = crypto_cipher_alg(cipher)->cia_decrypt;
  
  	/* Start of the last block. */
  	src += nbytes - (nbytes & (bsize - 1)) - bsize;
  	memcpy(last_iv, src, bsize);
  
  	for (;;) {
  		fn(tfm, src, src);
  		if ((nbytes -= bsize) < bsize)
  			break;
  		crypto_xor(src, src - bsize, bsize);
  		src -= bsize;
  	}
  
  	crypto_xor(src, walk->iv, bsize);
  	memcpy(walk->iv, last_iv, bsize);
  
  	return nbytes;

  }
  
  static int crypto_cbc_decrypt(struct skcipher_request *req)
  {

  	struct crypto_skcipher *skcipher = crypto_skcipher_reqtfm(req);

  	struct skcipher_walk walk;

  	int err;

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

  	while (walk.nbytes) {

  		if (walk.src.virt.addr == walk.dst.virt.addr)
  			err = crypto_cbc_decrypt_inplace(&walk, skcipher);
  		else
  			err = crypto_cbc_decrypt_segment(&walk, skcipher);

  		err = skcipher_walk_done(&walk, err);

  	}
  
  	return err;
  }

  static int crypto_cbc_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);

  	if (IS_ERR(inst))
  		return PTR_ERR(inst);

  	alg = skcipher_ialg_simple(inst);

  	err = -EINVAL;
  	if (!is_power_of_2(alg->cra_blocksize))

  		goto out_free_inst;

  	inst->alg.encrypt = crypto_cbc_encrypt;
  	inst->alg.decrypt = crypto_cbc_decrypt;

  	err = skcipher_register_instance(tmpl, inst);

  	if (err) {

  out_free_inst:

  		inst->free(inst);
  	}

  	return err;

  }
  
  static struct crypto_template crypto_cbc_tmpl = {
  	.name = "cbc",

  	.create = crypto_cbc_create,

  	.module = THIS_MODULE,
  };
  
  static int __init crypto_cbc_module_init(void)
  {
  	return crypto_register_template(&crypto_cbc_tmpl);
  }
  
  static void __exit crypto_cbc_module_exit(void)
  {
  	crypto_unregister_template(&crypto_cbc_tmpl);
  }

  subsys_initcall(crypto_cbc_module_init);

  module_exit(crypto_cbc_module_exit);
  
  MODULE_LICENSE("GPL");

  MODULE_DESCRIPTION("CBC block cipher mode of operation");

  MODULE_ALIAS_CRYPTO("cbc");