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
 32struct crypto_cfb_ctx {
 33	struct crypto_cipher *child;
 34};
 35
 36static 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
 44static 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 */
 53static 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
 69static 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
 90static 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
112static 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
137static 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
160static 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
181static 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
190static 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
206static 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
228static 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
243static 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
250static void crypto_cfb_free(struct skcipher_instance *inst)
251{
252	crypto_drop_skcipher(skcipher_instance_ctx(inst));
253	kfree(inst);
254}
255
256static 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
322out:
323	return err;
324
325err_drop_spawn:
326	crypto_drop_spawn(spawn);
327err_free_inst:
328	kfree(inst);
329	goto out;
330}
331
332static struct crypto_template crypto_cfb_tmpl = {
333	.name = "cfb",
334	.create = crypto_cfb_create,
335	.module = THIS_MODULE,
336};
337
338static int __init crypto_cfb_module_init(void)
339{
340	return crypto_register_template(&crypto_cfb_tmpl);
341}
342
343static void __exit crypto_cfb_module_exit(void)
344{
345	crypto_unregister_template(&crypto_cfb_tmpl);
346}
347
348module_init(crypto_cfb_module_init);
349module_exit(crypto_cfb_module_exit);
350
351MODULE_LICENSE("GPL");
352MODULE_DESCRIPTION("CFB block cipher algorithm");
353MODULE_ALIAS_CRYPTO("cfb");