/*
   * eseqiv: Encrypted Sequence Number 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.
   *
   * Copyright (c) 2007 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/skcipher.h>
  #include <crypto/rng.h>
  #include <crypto/scatterwalk.h>
  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/module.h>
  #include <linux/scatterlist.h>
  #include <linux/spinlock.h>
  #include <linux/string.h>
  
  struct eseqiv_request_ctx {
  	struct scatterlist src[2];
  	struct scatterlist dst[2];
  	char tail[];
  };
  
  struct eseqiv_ctx {
  	spinlock_t lock;
  	unsigned int reqoff;
  	char salt[];
  };
  
  static void eseqiv_complete2(struct skcipher_givcrypt_request *req)
  {
  	struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
  	struct eseqiv_request_ctx *reqctx = skcipher_givcrypt_reqctx(req);
  
  	memcpy(req->giv, PTR_ALIGN((u8 *)reqctx->tail,
  			 crypto_ablkcipher_alignmask(geniv) + 1),
  	       crypto_ablkcipher_ivsize(geniv));
  }
  
  static void eseqiv_complete(struct crypto_async_request *base, int err)
  {
  	struct skcipher_givcrypt_request *req = base->data;
  
  	if (err)
  		goto out;
  
  	eseqiv_complete2(req);
  
  out:
  	skcipher_givcrypt_complete(req, err);
  }
  
  static int eseqiv_givencrypt(struct skcipher_givcrypt_request *req)
  {
  	struct crypto_ablkcipher *geniv = skcipher_givcrypt_reqtfm(req);
  	struct eseqiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
  	struct eseqiv_request_ctx *reqctx = skcipher_givcrypt_reqctx(req);
  	struct ablkcipher_request *subreq;
  	crypto_completion_t compl;
  	void *data;
  	struct scatterlist *osrc, *odst;
  	struct scatterlist *dst;
  	struct page *srcp;
  	struct page *dstp;
  	u8 *giv;
  	u8 *vsrc;
  	u8 *vdst;
  	__be64 seq;
  	unsigned int ivsize;
  	unsigned int len;
  	int err;
  
  	subreq = (void *)(reqctx->tail + ctx->reqoff);
  	ablkcipher_request_set_tfm(subreq, skcipher_geniv_cipher(geniv));
  
  	giv = req->giv;
  	compl = req->creq.base.complete;
  	data = req->creq.base.data;
  
  	osrc = req->creq.src;
  	odst = req->creq.dst;
  	srcp = sg_page(osrc);
  	dstp = sg_page(odst);
  	vsrc = PageHighMem(srcp) ? NULL : page_address(srcp) + osrc->offset;
  	vdst = PageHighMem(dstp) ? NULL : page_address(dstp) + odst->offset;
  
  	ivsize = crypto_ablkcipher_ivsize(geniv);
  
  	if (vsrc != giv + ivsize && vdst != giv + ivsize) {
  		giv = PTR_ALIGN((u8 *)reqctx->tail,
  				crypto_ablkcipher_alignmask(geniv) + 1);
  		compl = eseqiv_complete;
  		data = req;
  	}
  
  	ablkcipher_request_set_callback(subreq, req->creq.base.flags, compl,
  					data);
  
  	sg_init_table(reqctx->src, 2);
  	sg_set_buf(reqctx->src, giv, ivsize);
  	scatterwalk_crypto_chain(reqctx->src, osrc, vsrc == giv + ivsize, 2);
  
  	dst = reqctx->src;
  	if (osrc != odst) {
  		sg_init_table(reqctx->dst, 2);
  		sg_set_buf(reqctx->dst, giv, ivsize);
  		scatterwalk_crypto_chain(reqctx->dst, odst, vdst == giv + ivsize, 2);
  
  		dst = reqctx->dst;
  	}
  
  	ablkcipher_request_set_crypt(subreq, reqctx->src, dst,
  				     req->creq.nbytes + ivsize,
  				     req->creq.info);
  
  	memcpy(req->creq.info, ctx->salt, ivsize);
  
  	len = ivsize;
  	if (ivsize > sizeof(u64)) {
  		memset(req->giv, 0, ivsize - sizeof(u64));
  		len = sizeof(u64);
  	}
  	seq = cpu_to_be64(req->seq);
  	memcpy(req->giv + ivsize - len, &seq, len);
  
  	err = crypto_ablkcipher_encrypt(subreq);
  	if (err)
  		goto out;
  
  	if (giv != req->giv)
  		eseqiv_complete2(req);
  
  out:
  	return err;
  }
  
  static int eseqiv_init(struct crypto_tfm *tfm)
  {
  	struct crypto_ablkcipher *geniv = __crypto_ablkcipher_cast(tfm);
  	struct eseqiv_ctx *ctx = crypto_ablkcipher_ctx(geniv);
  	unsigned long alignmask;
  	unsigned int reqsize;
  	int err;
  
  	spin_lock_init(&ctx->lock);
  
  	alignmask = crypto_tfm_ctx_alignment() - 1;
  	reqsize = sizeof(struct eseqiv_request_ctx);
  
  	if (alignmask & reqsize) {
  		alignmask &= reqsize;
  		alignmask--;
  	}
  
  	alignmask = ~alignmask;
  	alignmask &= crypto_ablkcipher_alignmask(geniv);
  
  	reqsize += alignmask;
  	reqsize += crypto_ablkcipher_ivsize(geniv);
  	reqsize = ALIGN(reqsize, crypto_tfm_ctx_alignment());
  
  	ctx->reqoff = reqsize - sizeof(struct eseqiv_request_ctx);
  
  	tfm->crt_ablkcipher.reqsize = reqsize +
  				      sizeof(struct ablkcipher_request);
  
  	err = 0;
  	if (!crypto_get_default_rng()) {
  		crypto_ablkcipher_crt(geniv)->givencrypt = eseqiv_givencrypt;
  		err = crypto_rng_get_bytes(crypto_default_rng, ctx->salt,
  					   crypto_ablkcipher_ivsize(geniv));
  		crypto_put_default_rng();
  	}
  
  	return err ?: skcipher_geniv_init(tfm);
  }
  
  static struct crypto_template eseqiv_tmpl;
  
  static struct crypto_instance *eseqiv_alloc(struct rtattr **tb)
  {
  	struct crypto_instance *inst;
  	int err;
  
  	inst = skcipher_geniv_alloc(&eseqiv_tmpl, tb, 0, 0);
  	if (IS_ERR(inst))
  		goto out;
  
  	err = -EINVAL;
  	if (inst->alg.cra_ablkcipher.ivsize != inst->alg.cra_blocksize)
  		goto free_inst;
  
  	inst->alg.cra_init = eseqiv_init;
  	inst->alg.cra_exit = skcipher_geniv_exit;
  
  	inst->alg.cra_ctxsize = sizeof(struct eseqiv_ctx);
  	inst->alg.cra_ctxsize += inst->alg.cra_ablkcipher.ivsize;
  
  out:
  	return inst;
  
  free_inst:
  	skcipher_geniv_free(inst);
  	inst = ERR_PTR(err);
  	goto out;
  }
  
  static struct crypto_template eseqiv_tmpl = {
  	.name = "eseqiv",
  	.alloc = eseqiv_alloc,
  	.free = skcipher_geniv_free,
  	.module = THIS_MODULE,
  };
  
  static int __init eseqiv_module_init(void)
  {
  	return crypto_register_template(&eseqiv_tmpl);
  }
  
  static void __exit eseqiv_module_exit(void)
  {
  	crypto_unregister_template(&eseqiv_tmpl);
  }
  
  module_init(eseqiv_module_init);
  module_exit(eseqiv_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("Encrypted Sequence Number IV Generator");
  MODULE_ALIAS_CRYPTO("eseqiv");