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