crypto/cfb.c

   1 //SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * CFB: Cipher FeedBack mode
   4  *
   5  * Copyright (c) 2018 James.Bottomley@HansenPartnership.com
   6  *
   7  * CFB is a stream cipher mode which is layered on to a block
   8  * encryption scheme.  It works very much like a one time pad where
   9  * the pad is generated initially from the encrypted IV and then
  10  * subsequently from the encrypted previous block of ciphertext.  The
  11  * pad is XOR'd into the plain text to get the final ciphertext.
  12  *
  13  * The scheme of CFB is best described by wikipedia:
  14  *
  15  * https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#CFB
  16  *
  17  * Note that since the pad for both encryption and decryption is
  18  * generated by an encryption operation, CFB never uses the block
  19  * decryption function.
  20  */
  21
  22 #include <crypto/algapi.h>
  23 #include <crypto/internal/skcipher.h>
  24 #include <linux/err.h>
  25 #include <linux/init.h>
  26 #include <linux/kernel.h>
  27 #include <linux/module.h>
  28 #include <linux/slab.h>
  29 #include <linux/string.h>
  30 #include <linux/types.h>
  31
  32 struct crypto_cfb_ctx {
  33         struct crypto_cipher *child;
  34 };
  35
  36 static unsigned int crypto_cfb_bsize(struct crypto_skcipher *tfm)
  37 {
  38         struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
  39         struct crypto_cipher *child = ctx->child;
  40
  41         return crypto_cipher_blocksize(child);
  42 }
  43
  44 static void crypto_cfb_encrypt_one(struct crypto_skcipher *tfm,
  45                                           const u8 *src, u8 *dst)
  46 {
  47         struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
  48
  49         crypto_cipher_encrypt_one(ctx->child, dst, src);
  50 }
  51
  52 /* final encrypt and decrypt is the same */
  53 static void crypto_cfb_final(struct skcipher_walk *walk,
  54                              struct crypto_skcipher *tfm)
  55 {
  56         const unsigned int bsize = crypto_cfb_bsize(tfm);
  57         const unsigned long alignmask = crypto_skcipher_alignmask(tfm);
  58         u8 tmp[bsize + alignmask];
  59         u8 *stream = PTR_ALIGN(tmp + 0, alignmask + 1);
  60         u8 *src = walk->src.virt.addr;
  61         u8 *dst = walk->dst.virt.addr;
  62         u8 *iv = walk->iv;
  63         unsigned int nbytes = walk->nbytes;
  64
  65         crypto_cfb_encrypt_one(tfm, iv, stream);
  66         crypto_xor_cpy(dst, stream, src, nbytes);
  67 }
  68
  69 static int crypto_cfb_encrypt_segment(struct skcipher_walk *walk,
  70                                       struct crypto_skcipher *tfm)
  71 {
  72         const unsigned int bsize = crypto_cfb_bsize(tfm);
  73         unsigned int nbytes = walk->nbytes;
  74         u8 *src = walk->src.virt.addr;
  75         u8 *dst = walk->dst.virt.addr;
  76         u8 *iv = walk->iv;
  77
  78         do {
  79                 crypto_cfb_encrypt_one(tfm, iv, dst);
  80                 crypto_xor(dst, src, bsize);
  81                 memcpy(iv, dst, bsize);
  82
  83                 src += bsize;
  84                 dst += bsize;
  85         } while ((nbytes -= bsize) >= bsize);
  86
  87         return nbytes;
  88 }
  89
  90 static int crypto_cfb_encrypt_inplace(struct skcipher_walk *walk,
  91                                       struct crypto_skcipher *tfm)
  92 {
  93         const unsigned int bsize = crypto_cfb_bsize(tfm);
  94         unsigned int nbytes = walk->nbytes;
  95         u8 *src = walk->src.virt.addr;
  96         u8 *iv = walk->iv;
  97         u8 tmp[bsize];
  98
  99         do {
 100                 crypto_cfb_encrypt_one(tfm, iv, tmp);
 101                 crypto_xor(src, tmp, bsize);
 102                 iv = src;
 103
 104                 src += bsize;
 105         } while ((nbytes -= bsize) >= bsize);
 106
 107         memcpy(walk->iv, iv, bsize);
 108
 109         return nbytes;
 110 }
 111
 112 static int crypto_cfb_encrypt(struct skcipher_request *req)
 113 {
 114         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 115         struct skcipher_walk walk;
 116         unsigned int bsize = crypto_cfb_bsize(tfm);
 117         int err;
 118
 119         err = skcipher_walk_virt(&walk, req, false);
 120
 121         while (walk.nbytes >= bsize) {
 122                 if (walk.src.virt.addr == walk.dst.virt.addr)
 123                         err = crypto_cfb_encrypt_inplace(&walk, tfm);
 124                 else
 125                         err = crypto_cfb_encrypt_segment(&walk, tfm);
 126                 err = skcipher_walk_done(&walk, err);
 127         }
 128
 129         if (walk.nbytes) {
 130                 crypto_cfb_final(&walk, tfm);
 131                 err = skcipher_walk_done(&walk, 0);
 132         }
 133
 134         return err;
 135 }
 136
 137 static int crypto_cfb_decrypt_segment(struct skcipher_walk *walk,
 138                                       struct crypto_skcipher *tfm)
 139 {
 140         const unsigned int bsize = crypto_cfb_bsize(tfm);
 141         unsigned int nbytes = walk->nbytes;
 142         u8 *src = walk->src.virt.addr;
 143         u8 *dst = walk->dst.virt.addr;
 144         u8 *iv = walk->iv;
 145
 146         do {
 147                 crypto_cfb_encrypt_one(tfm, iv, dst);
 148                 crypto_xor(dst, iv, bsize);
 149                 iv = src;
 150
 151                 src += bsize;
 152                 dst += bsize;
 153         } while ((nbytes -= bsize) >= bsize);
 154
 155         memcpy(walk->iv, iv, bsize);
 156
 157         return nbytes;
 158 }
 159
 160 static int crypto_cfb_decrypt_inplace(struct skcipher_walk *walk,
 161                                       struct crypto_skcipher *tfm)
 162 {
 163         const unsigned int bsize = crypto_cfb_bsize(tfm);
 164         unsigned int nbytes = walk->nbytes;
 165         u8 *src = walk->src.virt.addr;
 166         u8 *iv = walk->iv;
 167         u8 tmp[bsize];
 168
 169         do {
 170                 crypto_cfb_encrypt_one(tfm, iv, tmp);
 171                 memcpy(iv, src, bsize);
 172                 crypto_xor(src, tmp, bsize);
 173                 src += bsize;
 174         } while ((nbytes -= bsize) >= bsize);
 175
 176         memcpy(walk->iv, iv, bsize);
 177
 178         return nbytes;
 179 }
 180
 181 static int crypto_cfb_decrypt_blocks(struct skcipher_walk *walk,
 182                                      struct crypto_skcipher *tfm)
 183 {
 184         if (walk->src.virt.addr == walk->dst.virt.addr)
 185                 return crypto_cfb_decrypt_inplace(walk, tfm);
 186         else
 187                 return crypto_cfb_decrypt_segment(walk, tfm);
 188 }
 189
 190 static int crypto_cfb_setkey(struct crypto_skcipher *parent, const u8 *key,
 191                              unsigned int keylen)
 192 {
 193         struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(parent);
 194         struct crypto_cipher *child = ctx->child;
 195         int err;
 196
 197         crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
 198         crypto_cipher_set_flags(child, crypto_skcipher_get_flags(parent) &
 199                                        CRYPTO_TFM_REQ_MASK);
 200         err = crypto_cipher_setkey(child, key, keylen);
 201         crypto_skcipher_set_flags(parent, crypto_cipher_get_flags(child) &
 202                                           CRYPTO_TFM_RES_MASK);
 203         return err;
 204 }
 205
 206 static int crypto_cfb_decrypt(struct skcipher_request *req)
 207 {
 208         struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 209         struct skcipher_walk walk;
 210         const unsigned int bsize = crypto_cfb_bsize(tfm);
 211         int err;
 212
 213         err = skcipher_walk_virt(&walk, req, false);
 214
 215         while (walk.nbytes >= bsize) {
 216                 err = crypto_cfb_decrypt_blocks(&walk, tfm);
 217                 err = skcipher_walk_done(&walk, err);
 218         }
 219
 220         if (walk.nbytes) {
 221                 crypto_cfb_final(&walk, tfm);
 222                 err = skcipher_walk_done(&walk, 0);
 223         }
 224
 225         return err;
 226 }
 227
 228 static int crypto_cfb_init_tfm(struct crypto_skcipher *tfm)
 229 {
 230         struct skcipher_instance *inst = skcipher_alg_instance(tfm);
 231         struct crypto_spawn *spawn = skcipher_instance_ctx(inst);
 232         struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
 233         struct crypto_cipher *cipher;
 234
 235         cipher = crypto_spawn_cipher(spawn);
 236         if (IS_ERR(cipher))
 237                 return PTR_ERR(cipher);
 238
 239         ctx->child = cipher;
 240         return 0;
 241 }
 242
 243 static void crypto_cfb_exit_tfm(struct crypto_skcipher *tfm)
 244 {
 245         struct crypto_cfb_ctx *ctx = crypto_skcipher_ctx(tfm);
 246
 247         crypto_free_cipher(ctx->child);
 248 }
 249
 250 static void crypto_cfb_free(struct skcipher_instance *inst)
 251 {
 252         crypto_drop_skcipher(skcipher_instance_ctx(inst));
 253         kfree(inst);
 254 }
 255
 256 static int crypto_cfb_create(struct crypto_template *tmpl, struct rtattr **tb)
 257 {
 258         struct skcipher_instance *inst;
 259         struct crypto_attr_type *algt;
 260         struct crypto_spawn *spawn;
 261         struct crypto_alg *alg;
 262         u32 mask;
 263         int err;
 264
 265         err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER);
 266         if (err)
 267                 return err;
 268
 269         inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
 270         if (!inst)
 271                 return -ENOMEM;
 272
 273         algt = crypto_get_attr_type(tb);
 274         err = PTR_ERR(algt);
 275         if (IS_ERR(algt))
 276                 goto err_free_inst;
 277
 278         mask = CRYPTO_ALG_TYPE_MASK |
 279                 crypto_requires_off(algt->type, algt->mask,
 280                                     CRYPTO_ALG_NEED_FALLBACK);
 281
 282         alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER, mask);
 283         err = PTR_ERR(alg);
 284         if (IS_ERR(alg))
 285                 goto err_free_inst;
 286
 287         spawn = skcipher_instance_ctx(inst);
 288         err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst),
 289                                 CRYPTO_ALG_TYPE_MASK);
 290         crypto_mod_put(alg);
 291         if (err)
 292                 goto err_free_inst;
 293
 294         err = crypto_inst_setname(skcipher_crypto_instance(inst), "cfb", alg);
 295         if (err)
 296                 goto err_drop_spawn;
 297
 298         inst->alg.base.cra_priority = alg->cra_priority;
 299         /* we're a stream cipher independend of the crypto cra_blocksize */
 300         inst->alg.base.cra_blocksize = 1;
 301         inst->alg.base.cra_alignmask = alg->cra_alignmask;
 302
 303         inst->alg.ivsize = alg->cra_blocksize;
 304         inst->alg.min_keysize = alg->cra_cipher.cia_min_keysize;
 305         inst->alg.max_keysize = alg->cra_cipher.cia_max_keysize;
 306
 307         inst->alg.base.cra_ctxsize = sizeof(struct crypto_cfb_ctx);
 308
 309         inst->alg.init = crypto_cfb_init_tfm;
 310         inst->alg.exit = crypto_cfb_exit_tfm;
 311
 312         inst->alg.setkey = crypto_cfb_setkey;
 313         inst->alg.encrypt = crypto_cfb_encrypt;
 314         inst->alg.decrypt = crypto_cfb_decrypt;
 315
 316         inst->free = crypto_cfb_free;
 317
 318         err = skcipher_register_instance(tmpl, inst);
 319         if (err)
 320                 goto err_drop_spawn;
 321
 322 out:
 323         return err;
 324
 325 err_drop_spawn:
 326         crypto_drop_spawn(spawn);
 327 err_free_inst:
 328         kfree(inst);
 329         goto out;
 330 }
 331
 332 static struct crypto_template crypto_cfb_tmpl = {
 333         .name = "cfb",
 334         .create = crypto_cfb_create,
 335         .module = THIS_MODULE,
 336 };
 337
 338 static int __init crypto_cfb_module_init(void)
 339 {
 340         return crypto_register_template(&crypto_cfb_tmpl);
 341 }
 342
 343 static void __exit crypto_cfb_module_exit(void)
 344 {
 345         crypto_unregister_template(&crypto_cfb_tmpl);
 346 }
 347
 348 module_init(crypto_cfb_module_init);
 349 module_exit(crypto_cfb_module_exit);
 350
 351 MODULE_LICENSE("GPL");
 352 MODULE_DESCRIPTION("CFB block cipher algorithm");
 353 MODULE_ALIAS_CRYPTO("cfb");