/*
   * echainiv: Encrypted Chain IV Generator
   *
   * This generator generates an IV based on a sequence number by xoring it
   * with a salt and then encrypting it with the same key as used to encrypt
   * the plain text.  This algorithm requires that the block size be equal
   * to the IV size.  It is mainly useful for CBC.
   *
   * This generator can only be used by algorithms where authentication
   * is performed after encryption (i.e., authenc).
   *
   * Copyright (c) 2015 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/internal/geniv.h>

  #include <crypto/scatterwalk.h>

  #include <crypto/skcipher.h>

  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/module.h>
  #include <linux/percpu.h>
  #include <linux/spinlock.h>
  #include <linux/string.h>
  
  #define MAX_IV_SIZE 16

  static DEFINE_PER_CPU(u32 [MAX_IV_SIZE / sizeof(u32)], echainiv_iv);

  /* We don't care if we get preempted and read/write IVs from the next CPU. */

  static void echainiv_read_iv(u8 *dst, unsigned size)

  {
  	u32 *a = (u32 *)dst;
  	u32 __percpu *b = echainiv_iv;
  
  	for (; size >= 4; size -= 4) {
  		*a++ = this_cpu_read(*b);
  		b++;
  	}
  }

  static void echainiv_write_iv(const u8 *src, unsigned size)

  {
  	const u32 *a = (const u32 *)src;
  	u32 __percpu *b = echainiv_iv;
  
  	for (; size >= 4; size -= 4) {
  		this_cpu_write(*b, *a);
  		a++;
  		b++;
  	}
  }

  static void echainiv_encrypt_complete2(struct aead_request *req, int err)
  {
  	struct aead_request *subreq = aead_request_ctx(req);
  	struct crypto_aead *geniv;
  	unsigned int ivsize;
  
  	if (err == -EINPROGRESS)
  		return;
  
  	if (err)
  		goto out;
  
  	geniv = crypto_aead_reqtfm(req);
  	ivsize = crypto_aead_ivsize(geniv);
  
  	echainiv_write_iv(subreq->iv, ivsize);
  
  	if (req->iv != subreq->iv)
  		memcpy(req->iv, subreq->iv, ivsize);
  
  out:
  	if (req->iv != subreq->iv)
  		kzfree(subreq->iv);
  }
  
  static void echainiv_encrypt_complete(struct crypto_async_request *base,
  					 int err)
  {
  	struct aead_request *req = base->data;
  
  	echainiv_encrypt_complete2(req, err);
  	aead_request_complete(req, err);
  }

  static int echainiv_encrypt(struct aead_request *req)
  {
  	struct crypto_aead *geniv = crypto_aead_reqtfm(req);

  	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);

  	struct aead_request *subreq = aead_request_ctx(req);
  	crypto_completion_t compl;
  	void *data;
  	u8 *info;

  	unsigned int ivsize = crypto_aead_ivsize(geniv);

  	int err;

  	if (req->cryptlen < ivsize)
  		return -EINVAL;

  	aead_request_set_tfm(subreq, ctx->child);

  
  	compl = echainiv_encrypt_complete;
  	data = req;
  	info = req->iv;

  	if (req->src != req->dst) {

  		SKCIPHER_REQUEST_ON_STACK(nreq, ctx->sknull);

  		skcipher_request_set_tfm(nreq, ctx->sknull);
  		skcipher_request_set_callback(nreq, req->base.flags,
  					      NULL, NULL);
  		skcipher_request_set_crypt(nreq, req->src, req->dst,
  					   req->assoclen + req->cryptlen,
  					   NULL);
  
  		err = crypto_skcipher_encrypt(nreq);

  		if (err)
  			return err;
  	}
  
  	if (unlikely(!IS_ALIGNED((unsigned long)info,
  				 crypto_aead_alignmask(geniv) + 1))) {
  		info = kmalloc(ivsize, req->base.flags &
  				       CRYPTO_TFM_REQ_MAY_SLEEP ? GFP_KERNEL:
  								  GFP_ATOMIC);
  		if (!info)
  			return -ENOMEM;
  
  		memcpy(info, req->iv, ivsize);
  	}
  
  	aead_request_set_callback(subreq, req->base.flags, compl, data);
  	aead_request_set_crypt(subreq, req->dst, req->dst,

  			       req->cryptlen, info);
  	aead_request_set_ad(subreq, req->assoclen);

  
  	crypto_xor(info, ctx->salt, ivsize);
  	scatterwalk_map_and_copy(info, req->dst, req->assoclen, ivsize, 1);
  	echainiv_read_iv(info, ivsize);
  
  	err = crypto_aead_encrypt(subreq);
  	echainiv_encrypt_complete2(req, err);
  	return err;
  }

  static int echainiv_decrypt(struct aead_request *req)
  {
  	struct crypto_aead *geniv = crypto_aead_reqtfm(req);

  	struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);

  	struct aead_request *subreq = aead_request_ctx(req);
  	crypto_completion_t compl;
  	void *data;

  	unsigned int ivsize = crypto_aead_ivsize(geniv);

  	if (req->cryptlen < ivsize)

  		return -EINVAL;

  	aead_request_set_tfm(subreq, ctx->child);

  
  	compl = req->base.complete;
  	data = req->base.data;

  	aead_request_set_callback(subreq, req->base.flags, compl, data);
  	aead_request_set_crypt(subreq, req->src, req->dst,
  			       req->cryptlen - ivsize, req->iv);

  	aead_request_set_ad(subreq, req->assoclen + ivsize);

  
  	scatterwalk_map_and_copy(req->iv, req->src, req->assoclen, ivsize, 0);

  
  	return crypto_aead_decrypt(subreq);
  }

  static int echainiv_aead_create(struct crypto_template *tmpl,
  				struct rtattr **tb)

  {
  	struct aead_instance *inst;
  	struct crypto_aead_spawn *spawn;
  	struct aead_alg *alg;

  	int err;

  	inst = aead_geniv_alloc(tmpl, tb, 0, 0);

  
  	if (IS_ERR(inst))

  		return PTR_ERR(inst);

  	spawn = aead_instance_ctx(inst);
  	alg = crypto_spawn_aead_alg(spawn);

  	err = -EINVAL;

  	if (inst->alg.ivsize & (sizeof(u32) - 1) ||

  	    inst->alg.ivsize > MAX_IV_SIZE)
  		goto free_inst;

  	inst->alg.encrypt = echainiv_encrypt;

  	inst->alg.decrypt = echainiv_decrypt;

  	inst->alg.init = aead_init_geniv;
  	inst->alg.exit = aead_exit_geniv;

  
  	inst->alg.base.cra_alignmask |= __alignof__(u32) - 1;

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

  	inst->alg.base.cra_ctxsize += inst->alg.ivsize;

  	inst->free = aead_geniv_free;

  	err = aead_register_instance(tmpl, inst);
  	if (err)
  		goto free_inst;

  out:

  	return err;
  
  free_inst:
  	aead_geniv_free(inst);
  	goto out;

  }

  static void echainiv_free(struct crypto_instance *inst)
  {
  	aead_geniv_free(aead_instance(inst));

  }
  
  static struct crypto_template echainiv_tmpl = {
  	.name = "echainiv",

  	.create = echainiv_aead_create,

  	.free = echainiv_free,
  	.module = THIS_MODULE,
  };
  
  static int __init echainiv_module_init(void)
  {
  	return crypto_register_template(&echainiv_tmpl);
  }
  
  static void __exit echainiv_module_exit(void)
  {
  	crypto_unregister_template(&echainiv_tmpl);
  }
  
  module_init(echainiv_module_init);
  module_exit(echainiv_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("Encrypted Chain IV Generator");
  MODULE_ALIAS_CRYPTO("echainiv");