krb5enc.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * AEAD wrapper for Kerberos 5 RFC3961 simplified profile.
  4 *
  5 * Copyright (C) 2025 Red Hat, Inc. All Rights Reserved.
  6 * Written by David Howells (dhowells@redhat.com)
  7 *
  8 * Derived from authenc:
  9 * Copyright (c) 2007-2015 Herbert Xu <herbert@gondor.apana.org.au>
 10 */
 11
 12#include <crypto/internal/aead.h>
 13#include <crypto/internal/hash.h>
 14#include <crypto/internal/skcipher.h>
 15#include <crypto/authenc.h>
 16#include <crypto/scatterwalk.h>
 17#include <linux/err.h>
 18#include <linux/init.h>
 19#include <linux/kernel.h>
 20#include <linux/module.h>
 21#include <linux/rtnetlink.h>
 22#include <linux/slab.h>
 23#include <linux/spinlock.h>
 24
 25struct krb5enc_instance_ctx {
 26	struct crypto_ahash_spawn auth;
 27	struct crypto_skcipher_spawn enc;
 28	unsigned int reqoff;
 29};
 30
 31struct krb5enc_ctx {
 32	struct crypto_ahash *auth;
 33	struct crypto_skcipher *enc;
 34};
 35
 36struct krb5enc_request_ctx {
 37	struct scatterlist src[2];
 38	struct scatterlist dst[2];
 39	char tail[];
 40};
 41
 42static void krb5enc_request_complete(struct aead_request *req, int err)
 43{
 44	if (err != -EINPROGRESS)
 45		aead_request_complete(req, err);
 46}
 47
 48/**
 49 * crypto_krb5enc_extractkeys - Extract Ke and Ki keys from the key blob.
 50 * @keys: Where to put the key sizes and pointers
 51 * @key: Encoded key material
 52 * @keylen: Amount of key material
 53 *
 54 * Decode the key blob we're given.  It starts with an rtattr that indicates
 55 * the format and the length.  Format CRYPTO_AUTHENC_KEYA_PARAM is:
 56 *
 57 *	rtattr || __be32 enckeylen || authkey || enckey
 58 *
 59 * Note that the rtattr is in cpu-endian form, unlike enckeylen.  This must be
 60 * handled correctly in static testmgr data.
 61 */
 62int crypto_krb5enc_extractkeys(struct crypto_authenc_keys *keys, const u8 *key,
 63			       unsigned int keylen)
 64{
 65	struct rtattr *rta = (struct rtattr *)key;
 66	struct crypto_authenc_key_param *param;
 67
 68	if (!RTA_OK(rta, keylen))
 69		return -EINVAL;
 70	if (rta->rta_type != CRYPTO_AUTHENC_KEYA_PARAM)
 71		return -EINVAL;
 72
 73	/*
 74	 * RTA_OK() didn't align the rtattr's payload when validating that it
 75	 * fits in the buffer.  Yet, the keys should start on the next 4-byte
 76	 * aligned boundary.  To avoid confusion, require that the rtattr
 77	 * payload be exactly the param struct, which has a 4-byte aligned size.
 78	 */
 79	if (RTA_PAYLOAD(rta) != sizeof(*param))
 80		return -EINVAL;
 81	BUILD_BUG_ON(sizeof(*param) % RTA_ALIGNTO);
 82
 83	param = RTA_DATA(rta);
 84	keys->enckeylen = be32_to_cpu(param->enckeylen);
 85
 86	key += rta->rta_len;
 87	keylen -= rta->rta_len;
 88
 89	if (keylen < keys->enckeylen)
 90		return -EINVAL;
 91
 92	keys->authkeylen = keylen - keys->enckeylen;
 93	keys->authkey = key;
 94	keys->enckey = key + keys->authkeylen;
 95	return 0;
 96}
 97EXPORT_SYMBOL(crypto_krb5enc_extractkeys);
 98
 99static int krb5enc_setkey(struct crypto_aead *krb5enc, const u8 *key,
100			  unsigned int keylen)
101{
102	struct crypto_authenc_keys keys;
103	struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
104	struct crypto_skcipher *enc = ctx->enc;
105	struct crypto_ahash *auth = ctx->auth;
106	unsigned int flags = crypto_aead_get_flags(krb5enc);
107	int err = -EINVAL;
108
109	if (crypto_krb5enc_extractkeys(&keys, key, keylen) != 0)
110		goto out;
111
112	crypto_ahash_clear_flags(auth, CRYPTO_TFM_REQ_MASK);
113	crypto_ahash_set_flags(auth, flags & CRYPTO_TFM_REQ_MASK);
114	err = crypto_ahash_setkey(auth, keys.authkey, keys.authkeylen);
115	if (err)
116		goto out;
117
118	crypto_skcipher_clear_flags(enc, CRYPTO_TFM_REQ_MASK);
119	crypto_skcipher_set_flags(enc, flags & CRYPTO_TFM_REQ_MASK);
120	err = crypto_skcipher_setkey(enc, keys.enckey, keys.enckeylen);
121out:
122	memzero_explicit(&keys, sizeof(keys));
123	return err;
124}
125
126static void krb5enc_encrypt_done(void *data, int err)
127{
128	struct aead_request *req = data;
129
130	krb5enc_request_complete(req, err);
131}
132
133/*
134 * Start the encryption of the plaintext.  We skip over the associated data as
135 * that only gets included in the hash.
136 */
137static int krb5enc_dispatch_encrypt(struct aead_request *req,
138				    unsigned int flags)
139{
140	struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
141	struct aead_instance *inst = aead_alg_instance(krb5enc);
142	struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
143	struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
144	struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
145	struct crypto_skcipher *enc = ctx->enc;
146	struct skcipher_request *skreq = (void *)(areq_ctx->tail +
147						  ictx->reqoff);
148	struct scatterlist *src, *dst;
149
150	src = scatterwalk_ffwd(areq_ctx->src, req->src, req->assoclen);
151	if (req->src == req->dst)
152		dst = src;
153	else
154		dst = scatterwalk_ffwd(areq_ctx->dst, req->dst, req->assoclen);
155
156	skcipher_request_set_tfm(skreq, enc);
157	skcipher_request_set_callback(skreq, aead_request_flags(req),
158				      krb5enc_encrypt_done, req);
159	skcipher_request_set_crypt(skreq, src, dst, req->cryptlen, req->iv);
160
161	return crypto_skcipher_encrypt(skreq);
162}
163
164/*
165 * Insert the hash into the checksum field in the destination buffer directly
166 * after the encrypted region.
167 */
168static void krb5enc_insert_checksum(struct aead_request *req, u8 *hash)
169{
170	struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
171
172	scatterwalk_map_and_copy(hash, req->dst,
173				 req->assoclen + req->cryptlen,
174				 crypto_aead_authsize(krb5enc), 1);
175}
176
177/*
178 * Upon completion of an asynchronous digest, transfer the hash to the checksum
179 * field.
180 */
181static void krb5enc_encrypt_ahash_done(void *data, int err)
182{
183	struct aead_request *req = data;
184	struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
185	struct aead_instance *inst = aead_alg_instance(krb5enc);
186	struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
187	struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
188	struct ahash_request *ahreq = (void *)(areq_ctx->tail + ictx->reqoff);
189
190	if (err)
191		return krb5enc_request_complete(req, err);
192
193	krb5enc_insert_checksum(req, ahreq->result);
194
195	err = krb5enc_dispatch_encrypt(req, 0);
196	if (err != -EINPROGRESS)
197		aead_request_complete(req, err);
198}
199
200/*
201 * Start the digest of the plaintext for encryption.  In theory, this could be
202 * run in parallel with the encryption, provided the src and dst buffers don't
203 * overlap.
204 */
205static int krb5enc_dispatch_encrypt_hash(struct aead_request *req)
206{
207	struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
208	struct aead_instance *inst = aead_alg_instance(krb5enc);
209	struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
210	struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
211	struct crypto_ahash *auth = ctx->auth;
212	struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
213	struct ahash_request *ahreq = (void *)(areq_ctx->tail + ictx->reqoff);
214	u8 *hash = areq_ctx->tail;
215	int err;
216
217	ahash_request_set_callback(ahreq, aead_request_flags(req),
218				   krb5enc_encrypt_ahash_done, req);
219	ahash_request_set_tfm(ahreq, auth);
220	ahash_request_set_crypt(ahreq, req->src, hash, req->assoclen + req->cryptlen);
221
222	err = crypto_ahash_digest(ahreq);
223	if (err)
224		return err;
225
226	krb5enc_insert_checksum(req, hash);
227	return 0;
228}
229
230/*
231 * Process an encryption operation.  We can perform the cipher and the hash in
232 * parallel, provided the src and dst buffers are separate.
233 */
234static int krb5enc_encrypt(struct aead_request *req)
235{
236	int err;
237
238	err = krb5enc_dispatch_encrypt_hash(req);
239	if (err < 0)
240		return err;
241
242	return krb5enc_dispatch_encrypt(req, aead_request_flags(req));
243}
244
245static int krb5enc_verify_hash(struct aead_request *req)
246{
247	struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
248	struct aead_instance *inst = aead_alg_instance(krb5enc);
249	struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
250	struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
251	struct ahash_request *ahreq = (void *)(areq_ctx->tail + ictx->reqoff);
252	unsigned int authsize = crypto_aead_authsize(krb5enc);
253	u8 *calc_hash = areq_ctx->tail;
254	u8 *msg_hash  = areq_ctx->tail + authsize;
255
256	scatterwalk_map_and_copy(msg_hash, req->src, ahreq->nbytes, authsize, 0);
257
258	if (crypto_memneq(msg_hash, calc_hash, authsize))
259		return -EBADMSG;
260	return 0;
261}
262
263static void krb5enc_decrypt_hash_done(void *data, int err)
264{
265	struct aead_request *req = data;
266
267	if (err)
268		return krb5enc_request_complete(req, err);
269
270	err = krb5enc_verify_hash(req);
271	krb5enc_request_complete(req, err);
272}
273
274/*
275 * Dispatch the hashing of the plaintext after we've done the decryption.
276 */
277static int krb5enc_dispatch_decrypt_hash(struct aead_request *req)
278{
279	struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
280	struct aead_instance *inst = aead_alg_instance(krb5enc);
281	struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
282	struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
283	struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
284	struct ahash_request *ahreq = (void *)(areq_ctx->tail + ictx->reqoff);
285	struct crypto_ahash *auth = ctx->auth;
286	unsigned int authsize = crypto_aead_authsize(krb5enc);
287	u8 *hash = areq_ctx->tail;
288	int err;
289
290	ahash_request_set_tfm(ahreq, auth);
291	ahash_request_set_crypt(ahreq, req->dst, hash,
292				req->assoclen + req->cryptlen - authsize);
293	ahash_request_set_callback(ahreq, aead_request_flags(req),
294				   krb5enc_decrypt_hash_done, req);
295
296	err = crypto_ahash_digest(ahreq);
297	if (err < 0)
298		return err;
299
300	return krb5enc_verify_hash(req);
301}
302
303/*
304 * Dispatch the decryption of the ciphertext.
305 */
306static int krb5enc_dispatch_decrypt(struct aead_request *req)
307{
308	struct crypto_aead *krb5enc = crypto_aead_reqtfm(req);
309	struct aead_instance *inst = aead_alg_instance(krb5enc);
310	struct krb5enc_ctx *ctx = crypto_aead_ctx(krb5enc);
311	struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
312	struct krb5enc_request_ctx *areq_ctx = aead_request_ctx(req);
313	struct skcipher_request *skreq = (void *)(areq_ctx->tail +
314						  ictx->reqoff);
315	unsigned int authsize = crypto_aead_authsize(krb5enc);
316	struct scatterlist *src, *dst;
317
318	src = scatterwalk_ffwd(areq_ctx->src, req->src, req->assoclen);
319	dst = src;
320
321	if (req->src != req->dst)
322		dst = scatterwalk_ffwd(areq_ctx->dst, req->dst, req->assoclen);
323
324	skcipher_request_set_tfm(skreq, ctx->enc);
325	skcipher_request_set_callback(skreq, aead_request_flags(req),
326				      req->base.complete, req->base.data);
327	skcipher_request_set_crypt(skreq, src, dst,
328				   req->cryptlen - authsize, req->iv);
329
330	return crypto_skcipher_decrypt(skreq);
331}
332
333static int krb5enc_decrypt(struct aead_request *req)
334{
335	int err;
336
337	err = krb5enc_dispatch_decrypt(req);
338	if (err < 0)
339		return err;
340
341	return krb5enc_dispatch_decrypt_hash(req);
342}
343
344static int krb5enc_init_tfm(struct crypto_aead *tfm)
345{
346	struct aead_instance *inst = aead_alg_instance(tfm);
347	struct krb5enc_instance_ctx *ictx = aead_instance_ctx(inst);
348	struct krb5enc_ctx *ctx = crypto_aead_ctx(tfm);
349	struct crypto_ahash *auth;
350	struct crypto_skcipher *enc;
351	int err;
352
353	auth = crypto_spawn_ahash(&ictx->auth);
354	if (IS_ERR(auth))
355		return PTR_ERR(auth);
356
357	enc = crypto_spawn_skcipher(&ictx->enc);
358	err = PTR_ERR(enc);
359	if (IS_ERR(enc))
360		goto err_free_ahash;
361
362	ctx->auth = auth;
363	ctx->enc = enc;
364
365	crypto_aead_set_reqsize(
366		tfm,
367		sizeof(struct krb5enc_request_ctx) +
368		ictx->reqoff + /* Space for two checksums */
369		umax(sizeof(struct ahash_request) + crypto_ahash_reqsize(auth),
370		     sizeof(struct skcipher_request) + crypto_skcipher_reqsize(enc)));
371
372	return 0;
373
374err_free_ahash:
375	crypto_free_ahash(auth);
376	return err;
377}
378
379static void krb5enc_exit_tfm(struct crypto_aead *tfm)
380{
381	struct krb5enc_ctx *ctx = crypto_aead_ctx(tfm);
382
383	crypto_free_ahash(ctx->auth);
384	crypto_free_skcipher(ctx->enc);
385}
386
387static void krb5enc_free(struct aead_instance *inst)
388{
389	struct krb5enc_instance_ctx *ctx = aead_instance_ctx(inst);
390
391	crypto_drop_skcipher(&ctx->enc);
392	crypto_drop_ahash(&ctx->auth);
393	kfree(inst);
394}
395
396/*
397 * Create an instance of a template for a specific hash and cipher pair.
398 */
399static int krb5enc_create(struct crypto_template *tmpl, struct rtattr **tb)
400{
401	struct krb5enc_instance_ctx *ictx;
402	struct skcipher_alg_common *enc;
403	struct hash_alg_common *auth;
404	struct aead_instance *inst;
405	struct crypto_alg *auth_base;
406	u32 mask;
407	int err;
408
409	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_AEAD, &mask);
410	if (err) {
411		pr_err("attr_type failed\n");
412		return err;
413	}
414
415	inst = kzalloc(sizeof(*inst) + sizeof(*ictx), GFP_KERNEL);
416	if (!inst)
417		return -ENOMEM;
418	ictx = aead_instance_ctx(inst);
419
420	err = crypto_grab_ahash(&ictx->auth, aead_crypto_instance(inst),
421				crypto_attr_alg_name(tb[1]), 0, mask);
422	if (err) {
423		pr_err("grab ahash failed\n");
424		goto err_free_inst;
425	}
426	auth = crypto_spawn_ahash_alg(&ictx->auth);
427	auth_base = &auth->base;
428
429	err = crypto_grab_skcipher(&ictx->enc, aead_crypto_instance(inst),
430				   crypto_attr_alg_name(tb[2]), 0, mask);
431	if (err) {
432		pr_err("grab skcipher failed\n");
433		goto err_free_inst;
434	}
435	enc = crypto_spawn_skcipher_alg_common(&ictx->enc);
436
437	ictx->reqoff = 2 * auth->digestsize;
438
439	err = -ENAMETOOLONG;
440	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
441		     "krb5enc(%s,%s)", auth_base->cra_name,
442		     enc->base.cra_name) >=
443	    CRYPTO_MAX_ALG_NAME)
444		goto err_free_inst;
445
446	if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
447		     "krb5enc(%s,%s)", auth_base->cra_driver_name,
448		     enc->base.cra_driver_name) >= CRYPTO_MAX_ALG_NAME)
449		goto err_free_inst;
450
451	inst->alg.base.cra_priority = enc->base.cra_priority * 10 +
452				      auth_base->cra_priority;
453	inst->alg.base.cra_blocksize = enc->base.cra_blocksize;
454	inst->alg.base.cra_alignmask = enc->base.cra_alignmask;
455	inst->alg.base.cra_ctxsize = sizeof(struct krb5enc_ctx);
456
457	inst->alg.ivsize = enc->ivsize;
458	inst->alg.chunksize = enc->chunksize;
459	inst->alg.maxauthsize = auth->digestsize;
460
461	inst->alg.init = krb5enc_init_tfm;
462	inst->alg.exit = krb5enc_exit_tfm;
463
464	inst->alg.setkey = krb5enc_setkey;
465	inst->alg.encrypt = krb5enc_encrypt;
466	inst->alg.decrypt = krb5enc_decrypt;
467
468	inst->free = krb5enc_free;
469
470	err = aead_register_instance(tmpl, inst);
471	if (err) {
472		pr_err("ref failed\n");
473		goto err_free_inst;
474	}
475
476	return 0;
477
478err_free_inst:
479	krb5enc_free(inst);
480	return err;
481}
482
483static struct crypto_template crypto_krb5enc_tmpl = {
484	.name = "krb5enc",
485	.create = krb5enc_create,
486	.module = THIS_MODULE,
487};
488
489static int __init crypto_krb5enc_module_init(void)
490{
491	return crypto_register_template(&crypto_krb5enc_tmpl);
492}
493
494static void __exit crypto_krb5enc_module_exit(void)
495{
496	crypto_unregister_template(&crypto_krb5enc_tmpl);
497}
498
499module_init(crypto_krb5enc_module_init);
500module_exit(crypto_krb5enc_module_exit);
501
502MODULE_LICENSE("GPL");
503MODULE_DESCRIPTION("Simple AEAD wrapper for Kerberos 5 RFC3961");
504MODULE_ALIAS_CRYPTO("krb5enc");