/*
   * CBC: Cipher Block Chaining mode
   *
   * Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License as published by the Free
   * Software Foundation; either version 2 of the License, or (at your option)
   * any later version.
   *
   */
  
  #include <crypto/algapi.h>
  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/log2.h>
  #include <linux/module.h>
  #include <linux/scatterlist.h>
  #include <linux/slab.h>
  
  struct crypto_cbc_ctx {
  	struct crypto_cipher *child;
  };
  
  static int crypto_cbc_setkey(struct crypto_tfm *parent, const u8 *key,
  			     unsigned int keylen)
  {
  	struct crypto_cbc_ctx *ctx = crypto_tfm_ctx(parent);
  	struct crypto_cipher *child = ctx->child;
  	int err;
  
  	crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
  	crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
  				       CRYPTO_TFM_REQ_MASK);
  	err = crypto_cipher_setkey(child, key, keylen);
  	crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
  				     CRYPTO_TFM_RES_MASK);
  	return err;
  }
  
  static int crypto_cbc_encrypt_segment(struct blkcipher_desc *desc,
  				      struct blkcipher_walk *walk,
  				      struct crypto_cipher *tfm)
  {
  	void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
  		crypto_cipher_alg(tfm)->cia_encrypt;
  	int bsize = crypto_cipher_blocksize(tfm);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 *dst = walk->dst.virt.addr;
  	u8 *iv = walk->iv;
  
  	do {
  		crypto_xor(iv, src, bsize);
  		fn(crypto_cipher_tfm(tfm), dst, iv);
  		memcpy(iv, dst, bsize);
  
  		src += bsize;
  		dst += bsize;
  	} while ((nbytes -= bsize) >= bsize);
  
  	return nbytes;
  }
  
  static int crypto_cbc_encrypt_inplace(struct blkcipher_desc *desc,
  				      struct blkcipher_walk *walk,
  				      struct crypto_cipher *tfm)
  {
  	void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
  		crypto_cipher_alg(tfm)->cia_encrypt;
  	int bsize = crypto_cipher_blocksize(tfm);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 *iv = walk->iv;
  
  	do {
  		crypto_xor(src, iv, bsize);
  		fn(crypto_cipher_tfm(tfm), src, src);
  		iv = src;
  
  		src += bsize;
  	} while ((nbytes -= bsize) >= bsize);
  
  	memcpy(walk->iv, iv, bsize);
  
  	return nbytes;
  }
  
  static int crypto_cbc_encrypt(struct blkcipher_desc *desc,
  			      struct scatterlist *dst, struct scatterlist *src,
  			      unsigned int nbytes)
  {
  	struct blkcipher_walk walk;
  	struct crypto_blkcipher *tfm = desc->tfm;
  	struct crypto_cbc_ctx *ctx = crypto_blkcipher_ctx(tfm);
  	struct crypto_cipher *child = ctx->child;
  	int err;
  
  	blkcipher_walk_init(&walk, dst, src, nbytes);
  	err = blkcipher_walk_virt(desc, &walk);
  
  	while ((nbytes = walk.nbytes)) {
  		if (walk.src.virt.addr == walk.dst.virt.addr)
  			nbytes = crypto_cbc_encrypt_inplace(desc, &walk, child);
  		else
  			nbytes = crypto_cbc_encrypt_segment(desc, &walk, child);
  		err = blkcipher_walk_done(desc, &walk, nbytes);
  	}
  
  	return err;
  }
  
  static int crypto_cbc_decrypt_segment(struct blkcipher_desc *desc,
  				      struct blkcipher_walk *walk,
  				      struct crypto_cipher *tfm)
  {
  	void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
  		crypto_cipher_alg(tfm)->cia_decrypt;
  	int bsize = crypto_cipher_blocksize(tfm);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 *dst = walk->dst.virt.addr;
  	u8 *iv = walk->iv;
  
  	do {
  		fn(crypto_cipher_tfm(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 blkcipher_desc *desc,
  				      struct blkcipher_walk *walk,
  				      struct crypto_cipher *tfm)
  {
  	void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
  		crypto_cipher_alg(tfm)->cia_decrypt;
  	int bsize = crypto_cipher_blocksize(tfm);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 last_iv[bsize];
  
  	/* Start of the last block. */
  	src += nbytes - (nbytes & (bsize - 1)) - bsize;
  	memcpy(last_iv, src, bsize);
  
  	for (;;) {
  		fn(crypto_cipher_tfm(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 blkcipher_desc *desc,
  			      struct scatterlist *dst, struct scatterlist *src,
  			      unsigned int nbytes)
  {
  	struct blkcipher_walk walk;
  	struct crypto_blkcipher *tfm = desc->tfm;
  	struct crypto_cbc_ctx *ctx = crypto_blkcipher_ctx(tfm);
  	struct crypto_cipher *child = ctx->child;
  	int err;
  
  	blkcipher_walk_init(&walk, dst, src, nbytes);
  	err = blkcipher_walk_virt(desc, &walk);
  
  	while ((nbytes = walk.nbytes)) {
  		if (walk.src.virt.addr == walk.dst.virt.addr)
  			nbytes = crypto_cbc_decrypt_inplace(desc, &walk, child);
  		else
  			nbytes = crypto_cbc_decrypt_segment(desc, &walk, child);
  		err = blkcipher_walk_done(desc, &walk, nbytes);
  	}
  
  	return err;
  }
  
  static int crypto_cbc_init_tfm(struct crypto_tfm *tfm)
  {
  	struct crypto_instance *inst = (void *)tfm->__crt_alg;
  	struct crypto_spawn *spawn = crypto_instance_ctx(inst);
  	struct crypto_cbc_ctx *ctx = crypto_tfm_ctx(tfm);
  	struct crypto_cipher *cipher;
  
  	cipher = crypto_spawn_cipher(spawn);
  	if (IS_ERR(cipher))
  		return PTR_ERR(cipher);
  
  	ctx->child = cipher;
  	return 0;
  }
  
  static void crypto_cbc_exit_tfm(struct crypto_tfm *tfm)
  {
  	struct crypto_cbc_ctx *ctx = crypto_tfm_ctx(tfm);
  	crypto_free_cipher(ctx->child);
  }
  
  static struct crypto_instance *crypto_cbc_alloc(struct rtattr **tb)
  {
  	struct crypto_instance *inst;
  	struct crypto_alg *alg;
  	int err;
  
  	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_BLKCIPHER);
  	if (err)
  		return ERR_PTR(err);
  
  	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
  				  CRYPTO_ALG_TYPE_MASK);
  	if (IS_ERR(alg))
  		return ERR_CAST(alg);
  
  	inst = ERR_PTR(-EINVAL);
  	if (!is_power_of_2(alg->cra_blocksize))
  		goto out_put_alg;
  
  	inst = crypto_alloc_instance("cbc", alg);
  	if (IS_ERR(inst))
  		goto out_put_alg;
  
  	inst->alg.cra_flags = CRYPTO_ALG_TYPE_BLKCIPHER;
  	inst->alg.cra_priority = alg->cra_priority;
  	inst->alg.cra_blocksize = alg->cra_blocksize;
  	inst->alg.cra_alignmask = alg->cra_alignmask;
  	inst->alg.cra_type = &crypto_blkcipher_type;
  
  	/* We access the data as u32s when xoring. */
  	inst->alg.cra_alignmask |= __alignof__(u32) - 1;
  
  	inst->alg.cra_blkcipher.ivsize = alg->cra_blocksize;
  	inst->alg.cra_blkcipher.min_keysize = alg->cra_cipher.cia_min_keysize;
  	inst->alg.cra_blkcipher.max_keysize = alg->cra_cipher.cia_max_keysize;
  
  	inst->alg.cra_ctxsize = sizeof(struct crypto_cbc_ctx);
  
  	inst->alg.cra_init = crypto_cbc_init_tfm;
  	inst->alg.cra_exit = crypto_cbc_exit_tfm;
  
  	inst->alg.cra_blkcipher.setkey = crypto_cbc_setkey;
  	inst->alg.cra_blkcipher.encrypt = crypto_cbc_encrypt;
  	inst->alg.cra_blkcipher.decrypt = crypto_cbc_decrypt;
  
  out_put_alg:
  	crypto_mod_put(alg);
  	return inst;
  }
  
  static void crypto_cbc_free(struct crypto_instance *inst)
  {
  	crypto_drop_spawn(crypto_instance_ctx(inst));
  	kfree(inst);
  }
  
  static struct crypto_template crypto_cbc_tmpl = {
  	.name = "cbc",
  	.alloc = crypto_cbc_alloc,
  	.free = crypto_cbc_free,
  	.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);
  }
  
  module_init(crypto_cbc_module_init);
  module_exit(crypto_cbc_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("CBC block cipher algorithm");
  MODULE_ALIAS_CRYPTO("cbc");