//SPDX-License-Identifier: GPL-2.0
  /*
   * CFB: Cipher FeedBack mode
   *
   * Copyright (c) 2018 James.Bottomley@HansenPartnership.com
   *
   * CFB is a stream cipher mode which is layered on to a block
   * encryption scheme.  It works very much like a one time pad where
   * the pad is generated initially from the encrypted IV and then
   * subsequently from the encrypted previous block of ciphertext.  The
   * pad is XOR'd into the plain text to get the final ciphertext.
   *
   * The scheme of CFB is best described by wikipedia:
   *
   * https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB
   *
   * Note that since the pad for both encryption and decryption is
   * generated by an encryption operation, CFB never uses the block
   * decryption function.
   */
  
  #include <crypto/algapi.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>
  #include <linux/string.h>
  #include <linux/types.h>
  
  struct crypto_cfb_ctx {
  	struct crypto_cipher *child;
  };
  
  static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
  {
  	struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
  	struct crypto_cipher *child = ctx->child;
  
  	return crypto_cipher_blocksize(child);
  }
  
  static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm,
  					  const u8 *src, u8 *dst)
  {
  	struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
  
  	crypto_cipher_encrypt_one(ctx->child, dst, src);
  }
  
  /* final encrypt and decrypt is the same */
  static void crypto_cfb_final(struct skcipher_walk *walk,
  			     struct crypto_skcipher *tfm)
  {

  	const unsigned long alignmask = crypto_skcipher_alignmask(tfm);

  	u8 tmp[MAX_CIPHER_BLOCKSIZE + MAX_CIPHER_ALIGNMASK];

  	u8 *stream = PTR_ALIGN(tmp + 0, alignmask + 1);
  	u8 *src = walk->src.virt.addr;
  	u8 *dst = walk->dst.virt.addr;
  	u8 *iv = walk->iv;
  	unsigned int nbytes = walk->nbytes;
  
  	crypto_cfb_encrypt_one(tfm, iv, stream);
  	crypto_xor_cpy(dst, stream, src, nbytes);
  }
  
  static int crypto_cfb_encrypt_segment(struct skcipher_walk *walk,
  				      struct crypto_skcipher *tfm)
  {
  	const unsigned int bsize = crypto_cfb_bsize(tfm);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 *dst = walk->dst.virt.addr;
  	u8 *iv = walk->iv;
  
  	do {
  		crypto_cfb_encrypt_one(tfm, iv, dst);
  		crypto_xor(dst, src, bsize);

  		iv = dst;

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

  	memcpy(walk->iv, iv, bsize);

  	return nbytes;
  }
  
  static int crypto_cfb_encrypt_inplace(struct skcipher_walk *walk,
  				      struct crypto_skcipher *tfm)
  {
  	const unsigned int bsize = crypto_cfb_bsize(tfm);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 *iv = walk->iv;

  	u8 tmp[MAX_CIPHER_BLOCKSIZE];

  
  	do {
  		crypto_cfb_encrypt_one(tfm, iv, tmp);
  		crypto_xor(src, tmp, bsize);
  		iv = src;
  
  		src += bsize;
  	} while ((nbytes -= bsize) >= bsize);
  
  	memcpy(walk->iv, iv, bsize);
  
  	return nbytes;
  }
  
  static int crypto_cfb_encrypt(struct skcipher_request *req)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	struct skcipher_walk walk;
  	unsigned int bsize = crypto_cfb_bsize(tfm);
  	int err;
  
  	err = skcipher_walk_virt(&walk, req, false);
  
  	while (walk.nbytes >= bsize) {
  		if (walk.src.virt.addr == walk.dst.virt.addr)
  			err = crypto_cfb_encrypt_inplace(&walk, tfm);
  		else
  			err = crypto_cfb_encrypt_segment(&walk, tfm);
  		err = skcipher_walk_done(&walk, err);
  	}
  
  	if (walk.nbytes) {
  		crypto_cfb_final(&walk, tfm);
  		err = skcipher_walk_done(&walk, 0);
  	}
  
  	return err;
  }
  
  static int crypto_cfb_decrypt_segment(struct skcipher_walk *walk,
  				      struct crypto_skcipher *tfm)
  {
  	const unsigned int bsize = crypto_cfb_bsize(tfm);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;
  	u8 *dst = walk->dst.virt.addr;
  	u8 *iv = walk->iv;
  
  	do {
  		crypto_cfb_encrypt_one(tfm, iv, dst);

  		crypto_xor(dst, src, bsize);

  		iv = src;
  
  		src += bsize;
  		dst += bsize;
  	} while ((nbytes -= bsize) >= bsize);
  
  	memcpy(walk->iv, iv, bsize);
  
  	return nbytes;
  }
  
  static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk,
  				      struct crypto_skcipher *tfm)
  {
  	const unsigned int bsize = crypto_cfb_bsize(tfm);
  	unsigned int nbytes = walk->nbytes;
  	u8 *src = walk->src.virt.addr;

  	u8 * const iv = walk->iv;

  	u8 tmp[MAX_CIPHER_BLOCKSIZE];

  
  	do {
  		crypto_cfb_encrypt_one(tfm, iv, tmp);
  		memcpy(iv, src, bsize);
  		crypto_xor(src, tmp, bsize);
  		src += bsize;
  	} while ((nbytes -= bsize) >= bsize);

  	return nbytes;
  }
  
  static int crypto_cfb_decrypt_blocks(struct skcipher_walk *walk,
  				     struct crypto_skcipher *tfm)
  {
  	if (walk->src.virt.addr == walk->dst.virt.addr)
  		return crypto_cfb_decrypt_inplace(walk, tfm);
  	else
  		return crypto_cfb_decrypt_segment(walk, tfm);
  }
  
  static int crypto_cfb_setkey(struct crypto_skcipher *parent, const u8 *key,
  			     unsigned int keylen)
  {
  	struct crypto_cfb_ctx *ctx = crypto_skcipher_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_skcipher_get_flags(parent) &
  				       CRYPTO_TFM_REQ_MASK);
  	err = crypto_cipher_setkey(child, key, keylen);
  	crypto_skcipher_set_flags(parent, crypto_cipher_get_flags(child) &
  					  CRYPTO_TFM_RES_MASK);
  	return err;
  }
  
  static int crypto_cfb_decrypt(struct skcipher_request *req)
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	struct skcipher_walk walk;
  	const unsigned int bsize = crypto_cfb_bsize(tfm);
  	int err;
  
  	err = skcipher_walk_virt(&walk, req, false);
  
  	while (walk.nbytes >= bsize) {
  		err = crypto_cfb_decrypt_blocks(&walk, tfm);
  		err = skcipher_walk_done(&walk, err);
  	}
  
  	if (walk.nbytes) {
  		crypto_cfb_final(&walk, tfm);
  		err = skcipher_walk_done(&walk, 0);
  	}
  
  	return err;
  }
  
  static int crypto_cfb_init_tfm(struct crypto_skcipher *tfm)
  {
  	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
  	struct crypto_spawn *spawn = skcipher_instance_ctx(inst);
  	struct crypto_cfb_ctx *ctx = crypto_skcipher_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_cfb_exit_tfm(struct crypto_skcipher *tfm)
  {
  	struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
  
  	crypto_free_cipher(ctx->child);
  }
  
  static void crypto_cfb_free(struct skcipher_instance *inst)
  {
  	crypto_drop_skcipher(skcipher_instance_ctx(inst));
  	kfree(inst);
  }
  
  static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb)
  {
  	struct skcipher_instance *inst;
  	struct crypto_attr_type *algt;
  	struct crypto_spawn *spawn;
  	struct crypto_alg *alg;
  	u32 mask;
  	int err;
  
  	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER);
  	if (err)
  		return err;
  
  	inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
  	if (!inst)
  		return -ENOMEM;
  
  	algt = crypto_get_attr_type(tb);
  	err = PTR_ERR(algt);
  	if (IS_ERR(algt))
  		goto err_free_inst;
  
  	mask = CRYPTO_ALG_TYPE_MASK |
  		crypto_requires_off(algt->type, algt->mask,
  				    CRYPTO_ALG_NEED_FALLBACK);
  
  	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER, mask);
  	err = PTR_ERR(alg);
  	if (IS_ERR(alg))
  		goto err_free_inst;
  
  	spawn = skcipher_instance_ctx(inst);
  	err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst),
  				CRYPTO_ALG_TYPE_MASK);

  	if (err)

  		goto err_put_alg;

  
  	err = crypto_inst_setname(skcipher_crypto_instance(inst), "cfb", alg);
  	if (err)
  		goto err_drop_spawn;
  
  	inst->alg.base.cra_priority = alg->cra_priority;
  	/* we're a stream cipher independend of the crypto cra_blocksize */
  	inst->alg.base.cra_blocksize = 1;
  	inst->alg.base.cra_alignmask = alg->cra_alignmask;

  	/*
  	 * 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.ivsize = alg->cra_blocksize;
  	inst->alg.min_keysize = alg->cra_cipher.cia_min_keysize;
  	inst->alg.max_keysize = alg->cra_cipher.cia_max_keysize;
  
  	inst->alg.base.cra_ctxsize = sizeof(struct crypto_cfb_ctx);
  
  	inst->alg.init = crypto_cfb_init_tfm;
  	inst->alg.exit = crypto_cfb_exit_tfm;
  
  	inst->alg.setkey = crypto_cfb_setkey;
  	inst->alg.encrypt = crypto_cfb_encrypt;
  	inst->alg.decrypt = crypto_cfb_decrypt;
  
  	inst->free = crypto_cfb_free;
  
  	err = skcipher_register_instance(tmpl, inst);
  	if (err)
  		goto err_drop_spawn;

  	crypto_mod_put(alg);

  
  out:
  	return err;
  
  err_drop_spawn:
  	crypto_drop_spawn(spawn);

  err_put_alg:
  	crypto_mod_put(alg);

  err_free_inst:
  	kfree(inst);
  	goto out;
  }
  
  static struct crypto_template crypto_cfb_tmpl = {
  	.name = "cfb",
  	.create = crypto_cfb_create,
  	.module = THIS_MODULE,
  };
  
  static int __init crypto_cfb_module_init(void)
  {
  	return crypto_register_template(&crypto_cfb_tmpl);
  }
  
  static void __exit crypto_cfb_module_exit(void)
  {
  	crypto_unregister_template(&crypto_cfb_tmpl);
  }
  
  module_init(crypto_cfb_module_init);
  module_exit(crypto_cfb_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("CFB block cipher algorithm");
  MODULE_ALIAS_CRYPTO("cfb");