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cbc.c

/*
 * 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/module.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>

struct crypto_cbc_ctx {
      struct crypto_cipher *child;
      void (*xor)(u8 *dst, const u8 *src, unsigned int bs);
};

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 (*xor)(u8 *, const u8 *,
                                      unsigned int))
{
      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 {
            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 (*xor)(u8 *, const u8 *,
                                      unsigned int))
{
      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 {
            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;
      void (*xor)(u8 *, const u8 *, unsigned int bs) = ctx->xor;
      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,
                                              xor);
            else
                  nbytes = crypto_cbc_encrypt_segment(desc, &walk, child,
                                              xor);
            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 (*xor)(u8 *, const u8 *,
                                      unsigned int))
{
      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);
            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 (*xor)(u8 *, const u8 *,
                                      unsigned int))
{
      void (*fn)(struct crypto_tfm *, u8 *, const u8 *) =
            crypto_cipher_alg(tfm)->cia_decrypt;
      int bsize = crypto_cipher_blocksize(tfm);
      unsigned long alignmask = crypto_cipher_alignmask(tfm);
      unsigned int nbytes = walk->nbytes;
      u8 *src = walk->src.virt.addr;
      u8 stack[bsize + alignmask];
      u8 *first_iv = (u8 *)ALIGN((unsigned long)stack, alignmask + 1);

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

      /* Start of the last block. */
      src += nbytes - nbytes % bsize - bsize;
      memcpy(walk->iv, src, bsize);

      for (;;) {
            fn(crypto_cipher_tfm(tfm), src, src);
            if ((nbytes -= bsize) < bsize)
                  break;
            xor(src, src - bsize, bsize);
            src -= bsize;
      }

      xor(src, first_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;
      void (*xor)(u8 *, const u8 *, unsigned int bs) = ctx->xor;
      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,
                                              xor);
            else
                  nbytes = crypto_cbc_decrypt_segment(desc, &walk, child,
                                              xor);
            err = blkcipher_walk_done(desc, &walk, nbytes);
      }

      return err;
}

static void xor_byte(u8 *a, const u8 *b, unsigned int bs)
{
      do {
            *a++ ^= *b++;
      } while (--bs);
}

static void xor_quad(u8 *dst, const u8 *src, unsigned int bs)
{
      u32 *a = (u32 *)dst;
      u32 *b = (u32 *)src;

      do {
            *a++ ^= *b++;
      } while ((bs -= 4));
}

static void xor_64(u8 *a, const u8 *b, unsigned int bs)
{
      ((u32 *)a)[0] ^= ((u32 *)b)[0];
      ((u32 *)a)[1] ^= ((u32 *)b)[1];
}

static void xor_128(u8 *a, const u8 *b, unsigned int bs)
{
      ((u32 *)a)[0] ^= ((u32 *)b)[0];
      ((u32 *)a)[1] ^= ((u32 *)b)[1];
      ((u32 *)a)[2] ^= ((u32 *)b)[2];
      ((u32 *)a)[3] ^= ((u32 *)b)[3];
}

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;

      switch (crypto_tfm_alg_blocksize(tfm)) {
      case 8:
            ctx->xor = xor_64;
            break;

      case 16:
            ctx->xor = xor_128;
            break;

      default:
            if (crypto_tfm_alg_blocksize(tfm) % 4)
                  ctx->xor = xor_byte;
            else
                  ctx->xor = xor_quad;
      }

      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_PTR(PTR_ERR(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;

      if (!(alg->cra_blocksize % 4))
            inst->alg.cra_alignmask |= 3;
      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");

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