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1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * This file is part of UBIFS.
4  *
5  * Copyright (C) 2018 Pengutronix, Sascha Hauer <s.hauer@pengutronix.de>
6  */
7 
8 /*
9  * This file implements various helper functions for UBIFS authentication support
10  */
11 
12 #include <linux/crypto.h>
13 #include <linux/verification.h>
14 #include <crypto/hash.h>
15 #include <crypto/algapi.h>
16 #include <keys/user-type.h>
17 #include <keys/asymmetric-type.h>
18 
19 #include "ubifs.h"
20 
21 /**
22  * ubifs_node_calc_hash - calculate the hash of a UBIFS node
23  * @c: UBIFS file-system description object
24  * @node: the node to calculate a hash for
25  * @hash: the returned hash
26  *
27  * Returns 0 for success or a negative error code otherwise.
28  */
__ubifs_node_calc_hash(const struct ubifs_info * c,const void * node,u8 * hash)29 int __ubifs_node_calc_hash(const struct ubifs_info *c, const void *node,
30 			    u8 *hash)
31 {
32 	const struct ubifs_ch *ch = node;
33 
34 	return crypto_shash_tfm_digest(c->hash_tfm, node, le32_to_cpu(ch->len),
35 				       hash);
36 }
37 
38 /**
39  * ubifs_hash_calc_hmac - calculate a HMAC from a hash
40  * @c: UBIFS file-system description object
41  * @hash: the node to calculate a HMAC for
42  * @hmac: the returned HMAC
43  *
44  * Returns 0 for success or a negative error code otherwise.
45  */
ubifs_hash_calc_hmac(const struct ubifs_info * c,const u8 * hash,u8 * hmac)46 static int ubifs_hash_calc_hmac(const struct ubifs_info *c, const u8 *hash,
47 				 u8 *hmac)
48 {
49 	return crypto_shash_tfm_digest(c->hmac_tfm, hash, c->hash_len, hmac);
50 }
51 
52 /**
53  * ubifs_prepare_auth_node - Prepare an authentication node
54  * @c: UBIFS file-system description object
55  * @node: the node to calculate a hash for
56  * @inhash: input hash of previous nodes
57  *
58  * This function prepares an authentication node for writing onto flash.
59  * It creates a HMAC from the given input hash and writes it to the node.
60  *
61  * Returns 0 for success or a negative error code otherwise.
62  */
ubifs_prepare_auth_node(struct ubifs_info * c,void * node,struct shash_desc * inhash)63 int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
64 			     struct shash_desc *inhash)
65 {
66 	struct ubifs_auth_node *auth = node;
67 	u8 hash[UBIFS_HASH_ARR_SZ];
68 	int err;
69 
70 	{
71 		SHASH_DESC_ON_STACK(hash_desc, c->hash_tfm);
72 
73 		hash_desc->tfm = c->hash_tfm;
74 		ubifs_shash_copy_state(c, inhash, hash_desc);
75 
76 		err = crypto_shash_final(hash_desc, hash);
77 		if (err)
78 			return err;
79 	}
80 
81 	err = ubifs_hash_calc_hmac(c, hash, auth->hmac);
82 	if (err)
83 		return err;
84 
85 	auth->ch.node_type = UBIFS_AUTH_NODE;
86 	ubifs_prepare_node(c, auth, ubifs_auth_node_sz(c), 0);
87 	return 0;
88 }
89 
ubifs_get_desc(const struct ubifs_info * c,struct crypto_shash * tfm)90 static struct shash_desc *ubifs_get_desc(const struct ubifs_info *c,
91 					 struct crypto_shash *tfm)
92 {
93 	struct shash_desc *desc;
94 	int err;
95 
96 	if (!ubifs_authenticated(c))
97 		return NULL;
98 
99 	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(tfm), GFP_KERNEL);
100 	if (!desc)
101 		return ERR_PTR(-ENOMEM);
102 
103 	desc->tfm = tfm;
104 
105 	err = crypto_shash_init(desc);
106 	if (err) {
107 		kfree(desc);
108 		return ERR_PTR(err);
109 	}
110 
111 	return desc;
112 }
113 
114 /**
115  * __ubifs_hash_get_desc - get a descriptor suitable for hashing a node
116  * @c: UBIFS file-system description object
117  *
118  * This function returns a descriptor suitable for hashing a node. Free after use
119  * with kfree.
120  */
__ubifs_hash_get_desc(const struct ubifs_info * c)121 struct shash_desc *__ubifs_hash_get_desc(const struct ubifs_info *c)
122 {
123 	return ubifs_get_desc(c, c->hash_tfm);
124 }
125 
126 /**
127  * ubifs_bad_hash - Report hash mismatches
128  * @c: UBIFS file-system description object
129  * @node: the node
130  * @hash: the expected hash
131  * @lnum: the LEB @node was read from
132  * @offs: offset in LEB @node was read from
133  *
134  * This function reports a hash mismatch when a node has a different hash than
135  * expected.
136  */
ubifs_bad_hash(const struct ubifs_info * c,const void * node,const u8 * hash,int lnum,int offs)137 void ubifs_bad_hash(const struct ubifs_info *c, const void *node, const u8 *hash,
138 		    int lnum, int offs)
139 {
140 	int len = min(c->hash_len, 20);
141 	int cropped = len != c->hash_len;
142 	const char *cont = cropped ? "..." : "";
143 
144 	u8 calc[UBIFS_HASH_ARR_SZ];
145 
146 	__ubifs_node_calc_hash(c, node, calc);
147 
148 	ubifs_err(c, "hash mismatch on node at LEB %d:%d", lnum, offs);
149 	ubifs_err(c, "hash expected:   %*ph%s", len, hash, cont);
150 	ubifs_err(c, "hash calculated: %*ph%s", len, calc, cont);
151 }
152 
153 /**
154  * __ubifs_node_check_hash - check the hash of a node against given hash
155  * @c: UBIFS file-system description object
156  * @node: the node
157  * @expected: the expected hash
158  *
159  * This function calculates a hash over a node and compares it to the given hash.
160  * Returns 0 if both hashes are equal or authentication is disabled, otherwise a
161  * negative error code is returned.
162  */
__ubifs_node_check_hash(const struct ubifs_info * c,const void * node,const u8 * expected)163 int __ubifs_node_check_hash(const struct ubifs_info *c, const void *node,
164 			    const u8 *expected)
165 {
166 	u8 calc[UBIFS_HASH_ARR_SZ];
167 	int err;
168 
169 	err = __ubifs_node_calc_hash(c, node, calc);
170 	if (err)
171 		return err;
172 
173 	if (ubifs_check_hash(c, expected, calc))
174 		return -EPERM;
175 
176 	return 0;
177 }
178 
179 /**
180  * ubifs_sb_verify_signature - verify the signature of a superblock
181  * @c: UBIFS file-system description object
182  * @sup: The superblock node
183  *
184  * To support offline signed images the superblock can be signed with a
185  * PKCS#7 signature. The signature is placed directly behind the superblock
186  * node in an ubifs_sig_node.
187  *
188  * Returns 0 when the signature can be successfully verified or a negative
189  * error code if not.
190  */
ubifs_sb_verify_signature(struct ubifs_info * c,const struct ubifs_sb_node * sup)191 int ubifs_sb_verify_signature(struct ubifs_info *c,
192 			      const struct ubifs_sb_node *sup)
193 {
194 	int err;
195 	struct ubifs_scan_leb *sleb;
196 	struct ubifs_scan_node *snod;
197 	const struct ubifs_sig_node *signode;
198 
199 	sleb = ubifs_scan(c, UBIFS_SB_LNUM, UBIFS_SB_NODE_SZ, c->sbuf, 0);
200 	if (IS_ERR(sleb)) {
201 		err = PTR_ERR(sleb);
202 		return err;
203 	}
204 
205 	if (sleb->nodes_cnt == 0) {
206 		ubifs_err(c, "Unable to find signature node");
207 		err = -EINVAL;
208 		goto out_destroy;
209 	}
210 
211 	snod = list_first_entry(&sleb->nodes, struct ubifs_scan_node, list);
212 
213 	if (snod->type != UBIFS_SIG_NODE) {
214 		ubifs_err(c, "Signature node is of wrong type");
215 		err = -EINVAL;
216 		goto out_destroy;
217 	}
218 
219 	signode = snod->node;
220 
221 	if (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node)) {
222 		ubifs_err(c, "invalid signature len %d", le32_to_cpu(signode->len));
223 		err = -EINVAL;
224 		goto out_destroy;
225 	}
226 
227 	if (le32_to_cpu(signode->type) != UBIFS_SIGNATURE_TYPE_PKCS7) {
228 		ubifs_err(c, "Signature type %d is not supported\n",
229 			  le32_to_cpu(signode->type));
230 		err = -EINVAL;
231 		goto out_destroy;
232 	}
233 
234 	err = verify_pkcs7_signature(sup, sizeof(struct ubifs_sb_node),
235 				     signode->sig, le32_to_cpu(signode->len),
236 				     NULL, VERIFYING_UNSPECIFIED_SIGNATURE,
237 				     NULL, NULL);
238 
239 	if (err)
240 		ubifs_err(c, "Failed to verify signature");
241 	else
242 		ubifs_msg(c, "Successfully verified super block signature");
243 
244 out_destroy:
245 	ubifs_scan_destroy(sleb);
246 
247 	return err;
248 }
249 
250 /**
251  * ubifs_init_authentication - initialize UBIFS authentication support
252  * @c: UBIFS file-system description object
253  *
254  * This function returns 0 for success or a negative error code otherwise.
255  */
ubifs_init_authentication(struct ubifs_info * c)256 int ubifs_init_authentication(struct ubifs_info *c)
257 {
258 	struct key *keyring_key;
259 	const struct user_key_payload *ukp;
260 	int err;
261 	char hmac_name[CRYPTO_MAX_ALG_NAME];
262 
263 	if (!c->auth_hash_name) {
264 		ubifs_err(c, "authentication hash name needed with authentication");
265 		return -EINVAL;
266 	}
267 
268 	c->auth_hash_algo = match_string(hash_algo_name, HASH_ALGO__LAST,
269 					 c->auth_hash_name);
270 	if ((int)c->auth_hash_algo < 0) {
271 		ubifs_err(c, "Unknown hash algo %s specified",
272 			  c->auth_hash_name);
273 		return -EINVAL;
274 	}
275 
276 	snprintf(hmac_name, CRYPTO_MAX_ALG_NAME, "hmac(%s)",
277 		 c->auth_hash_name);
278 
279 	keyring_key = request_key(&key_type_logon, c->auth_key_name, NULL);
280 
281 	if (IS_ERR(keyring_key)) {
282 		ubifs_err(c, "Failed to request key: %ld",
283 			  PTR_ERR(keyring_key));
284 		return PTR_ERR(keyring_key);
285 	}
286 
287 	down_read(&keyring_key->sem);
288 
289 	if (keyring_key->type != &key_type_logon) {
290 		ubifs_err(c, "key type must be logon");
291 		err = -ENOKEY;
292 		goto out;
293 	}
294 
295 	ukp = user_key_payload_locked(keyring_key);
296 	if (!ukp) {
297 		/* key was revoked before we acquired its semaphore */
298 		err = -EKEYREVOKED;
299 		goto out;
300 	}
301 
302 	c->hash_tfm = crypto_alloc_shash(c->auth_hash_name, 0, 0);
303 	if (IS_ERR(c->hash_tfm)) {
304 		err = PTR_ERR(c->hash_tfm);
305 		ubifs_err(c, "Can not allocate %s: %d",
306 			  c->auth_hash_name, err);
307 		goto out;
308 	}
309 
310 	c->hash_len = crypto_shash_digestsize(c->hash_tfm);
311 	if (c->hash_len > UBIFS_HASH_ARR_SZ) {
312 		ubifs_err(c, "hash %s is bigger than maximum allowed hash size (%d > %d)",
313 			  c->auth_hash_name, c->hash_len, UBIFS_HASH_ARR_SZ);
314 		err = -EINVAL;
315 		goto out_free_hash;
316 	}
317 
318 	c->hmac_tfm = crypto_alloc_shash(hmac_name, 0, 0);
319 	if (IS_ERR(c->hmac_tfm)) {
320 		err = PTR_ERR(c->hmac_tfm);
321 		ubifs_err(c, "Can not allocate %s: %d", hmac_name, err);
322 		goto out_free_hash;
323 	}
324 
325 	c->hmac_desc_len = crypto_shash_digestsize(c->hmac_tfm);
326 	if (c->hmac_desc_len > UBIFS_HMAC_ARR_SZ) {
327 		ubifs_err(c, "hmac %s is bigger than maximum allowed hmac size (%d > %d)",
328 			  hmac_name, c->hmac_desc_len, UBIFS_HMAC_ARR_SZ);
329 		err = -EINVAL;
330 		goto out_free_hmac;
331 	}
332 
333 	err = crypto_shash_setkey(c->hmac_tfm, ukp->data, ukp->datalen);
334 	if (err)
335 		goto out_free_hmac;
336 
337 	c->authenticated = true;
338 
339 	c->log_hash = ubifs_hash_get_desc(c);
340 	if (IS_ERR(c->log_hash)) {
341 		err = PTR_ERR(c->log_hash);
342 		goto out_free_hmac;
343 	}
344 
345 	err = 0;
346 
347 out_free_hmac:
348 	if (err)
349 		crypto_free_shash(c->hmac_tfm);
350 out_free_hash:
351 	if (err)
352 		crypto_free_shash(c->hash_tfm);
353 out:
354 	up_read(&keyring_key->sem);
355 	key_put(keyring_key);
356 
357 	return err;
358 }
359 
360 /**
361  * __ubifs_exit_authentication - release resource
362  * @c: UBIFS file-system description object
363  *
364  * This function releases the authentication related resources.
365  */
__ubifs_exit_authentication(struct ubifs_info * c)366 void __ubifs_exit_authentication(struct ubifs_info *c)
367 {
368 	if (!ubifs_authenticated(c))
369 		return;
370 
371 	crypto_free_shash(c->hmac_tfm);
372 	crypto_free_shash(c->hash_tfm);
373 	kfree(c->log_hash);
374 }
375 
376 /**
377  * ubifs_node_calc_hmac - calculate the HMAC of a UBIFS node
378  * @c: UBIFS file-system description object
379  * @node: the node to insert a HMAC into.
380  * @len: the length of the node
381  * @ofs_hmac: the offset in the node where the HMAC is inserted
382  * @hmac: returned HMAC
383  *
384  * This function calculates a HMAC of a UBIFS node. The HMAC is expected to be
385  * embedded into the node, so this area is not covered by the HMAC. Also not
386  * covered is the UBIFS_NODE_MAGIC and the CRC of the node.
387  */
ubifs_node_calc_hmac(const struct ubifs_info * c,const void * node,int len,int ofs_hmac,void * hmac)388 static int ubifs_node_calc_hmac(const struct ubifs_info *c, const void *node,
389 				int len, int ofs_hmac, void *hmac)
390 {
391 	SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
392 	int hmac_len = c->hmac_desc_len;
393 	int err;
394 
395 	ubifs_assert(c, ofs_hmac > 8);
396 	ubifs_assert(c, ofs_hmac + hmac_len < len);
397 
398 	shash->tfm = c->hmac_tfm;
399 
400 	err = crypto_shash_init(shash);
401 	if (err)
402 		return err;
403 
404 	/* behind common node header CRC up to HMAC begin */
405 	err = crypto_shash_update(shash, node + 8, ofs_hmac - 8);
406 	if (err < 0)
407 		return err;
408 
409 	/* behind HMAC, if any */
410 	if (len - ofs_hmac - hmac_len > 0) {
411 		err = crypto_shash_update(shash, node + ofs_hmac + hmac_len,
412 			    len - ofs_hmac - hmac_len);
413 		if (err < 0)
414 			return err;
415 	}
416 
417 	return crypto_shash_final(shash, hmac);
418 }
419 
420 /**
421  * __ubifs_node_insert_hmac - insert a HMAC into a UBIFS node
422  * @c: UBIFS file-system description object
423  * @node: the node to insert a HMAC into.
424  * @len: the length of the node
425  * @ofs_hmac: the offset in the node where the HMAC is inserted
426  *
427  * This function inserts a HMAC at offset @ofs_hmac into the node given in
428  * @node.
429  *
430  * This function returns 0 for success or a negative error code otherwise.
431  */
__ubifs_node_insert_hmac(const struct ubifs_info * c,void * node,int len,int ofs_hmac)432 int __ubifs_node_insert_hmac(const struct ubifs_info *c, void *node, int len,
433 			    int ofs_hmac)
434 {
435 	return ubifs_node_calc_hmac(c, node, len, ofs_hmac, node + ofs_hmac);
436 }
437 
438 /**
439  * __ubifs_node_verify_hmac - verify the HMAC of UBIFS node
440  * @c: UBIFS file-system description object
441  * @node: the node to insert a HMAC into.
442  * @len: the length of the node
443  * @ofs_hmac: the offset in the node where the HMAC is inserted
444  *
445  * This function verifies the HMAC at offset @ofs_hmac of the node given in
446  * @node. Returns 0 if successful or a negative error code otherwise.
447  */
__ubifs_node_verify_hmac(const struct ubifs_info * c,const void * node,int len,int ofs_hmac)448 int __ubifs_node_verify_hmac(const struct ubifs_info *c, const void *node,
449 			     int len, int ofs_hmac)
450 {
451 	int hmac_len = c->hmac_desc_len;
452 	u8 *hmac;
453 	int err;
454 
455 	hmac = kmalloc(hmac_len, GFP_NOFS);
456 	if (!hmac)
457 		return -ENOMEM;
458 
459 	err = ubifs_node_calc_hmac(c, node, len, ofs_hmac, hmac);
460 	if (err) {
461 		kfree(hmac);
462 		return err;
463 	}
464 
465 	err = crypto_memneq(hmac, node + ofs_hmac, hmac_len);
466 
467 	kfree(hmac);
468 
469 	if (!err)
470 		return 0;
471 
472 	return -EPERM;
473 }
474 
__ubifs_shash_copy_state(const struct ubifs_info * c,struct shash_desc * src,struct shash_desc * target)475 int __ubifs_shash_copy_state(const struct ubifs_info *c, struct shash_desc *src,
476 			     struct shash_desc *target)
477 {
478 	u8 *state;
479 	int err;
480 
481 	state = kmalloc(crypto_shash_descsize(src->tfm), GFP_NOFS);
482 	if (!state)
483 		return -ENOMEM;
484 
485 	err = crypto_shash_export(src, state);
486 	if (err)
487 		goto out;
488 
489 	err = crypto_shash_import(target, state);
490 
491 out:
492 	kfree(state);
493 
494 	return err;
495 }
496 
497 /**
498  * ubifs_hmac_wkm - Create a HMAC of the well known message
499  * @c: UBIFS file-system description object
500  * @hmac: The HMAC of the well known message
501  *
502  * This function creates a HMAC of a well known message. This is used
503  * to check if the provided key is suitable to authenticate a UBIFS
504  * image. This is only a convenience to the user to provide a better
505  * error message when the wrong key is provided.
506  *
507  * This function returns 0 for success or a negative error code otherwise.
508  */
ubifs_hmac_wkm(struct ubifs_info * c,u8 * hmac)509 int ubifs_hmac_wkm(struct ubifs_info *c, u8 *hmac)
510 {
511 	SHASH_DESC_ON_STACK(shash, c->hmac_tfm);
512 	int err;
513 	const char well_known_message[] = "UBIFS";
514 
515 	if (!ubifs_authenticated(c))
516 		return 0;
517 
518 	shash->tfm = c->hmac_tfm;
519 
520 	err = crypto_shash_init(shash);
521 	if (err)
522 		return err;
523 
524 	err = crypto_shash_update(shash, well_known_message,
525 				  sizeof(well_known_message) - 1);
526 	if (err < 0)
527 		return err;
528 
529 	err = crypto_shash_final(shash, hmac);
530 	if (err)
531 		return err;
532 	return 0;
533 }
534 
535 /*
536  * ubifs_hmac_zero - test if a HMAC is zero
537  * @c: UBIFS file-system description object
538  * @hmac: the HMAC to test
539  *
540  * This function tests if a HMAC is zero and returns true if it is
541  * and false otherwise.
542  */
ubifs_hmac_zero(struct ubifs_info * c,const u8 * hmac)543 bool ubifs_hmac_zero(struct ubifs_info *c, const u8 *hmac)
544 {
545 	return !memchr_inv(hmac, 0, c->hmac_desc_len);
546 }
547