1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* Verify the signature on a PKCS#7 message.
3 *
4 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8 #define pr_fmt(fmt) "PKCS7: "fmt
9 #include <linux/kernel.h>
10 #include <linux/export.h>
11 #include <linux/slab.h>
12 #include <linux/err.h>
13 #include <linux/asn1.h>
14 #include <crypto/hash.h>
15 #include <crypto/hash_info.h>
16 #include <crypto/public_key.h>
17 #include "pkcs7_parser.h"
18
19 /*
20 * Digest the relevant parts of the PKCS#7 data
21 */
22 static int pkcs7_digest(struct pkcs7_message *pkcs7,
23 struct pkcs7_signed_info *sinfo)
24 {
25 struct public_key_signature *sig = sinfo->sig;
26 struct crypto_shash *tfm;
27 struct shash_desc *desc;
28 size_t desc_size;
29 int ret;
30
31 kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
32
33 /* The digest was calculated already. */
34 if (sig->digest)
35 return 0;
36
37 if (!sinfo->sig->hash_algo)
38 return -ENOPKG;
39
40 /* Allocate the hashing algorithm we're going to need and find out how
41 * big the hash operational data will be.
42 */
43 tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
44 if (IS_ERR(tfm))
45 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
46
47 desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
48 sig->digest_size = crypto_shash_digestsize(tfm);
49
50 ret = -ENOMEM;
51 sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
52 if (!sig->digest)
53 goto error_no_desc;
54
55 desc = kzalloc(desc_size, GFP_KERNEL);
56 if (!desc)
57 goto error_no_desc;
58
59 desc->tfm = tfm;
60
61 /* Digest the message [RFC2315 9.3] */
62 ret = crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len,
63 sig->digest);
64 if (ret < 0)
65 goto error;
66 pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
67
68 /* However, if there are authenticated attributes, there must be a
69 * message digest attribute amongst them which corresponds to the
70 * digest we just calculated.
71 */
72 if (sinfo->authattrs) {
73 u8 tag;
74
75 if (!sinfo->msgdigest) {
76 pr_warn("Sig %u: No messageDigest\n", sinfo->index);
77 ret = -EKEYREJECTED;
78 goto error;
79 }
80
81 if (sinfo->msgdigest_len != sig->digest_size) {
82 pr_debug("Sig %u: Invalid digest size (%u)\n",
83 sinfo->index, sinfo->msgdigest_len);
84 ret = -EBADMSG;
85 goto error;
86 }
87
88 if (memcmp(sig->digest, sinfo->msgdigest,
89 sinfo->msgdigest_len) != 0) {
90 pr_debug("Sig %u: Message digest doesn't match\n",
91 sinfo->index);
92 ret = -EKEYREJECTED;
93 goto error;
94 }
95
96 /* We then calculate anew, using the authenticated attributes
97 * as the contents of the digest instead. Note that we need to
98 * convert the attributes from a CONT.0 into a SET before we
99 * hash it.
100 */
101 memset(sig->digest, 0, sig->digest_size);
102
103 ret = crypto_shash_init(desc);
104 if (ret < 0)
105 goto error;
106 tag = ASN1_CONS_BIT | ASN1_SET;
107 ret = crypto_shash_update(desc, &tag, 1);
108 if (ret < 0)
109 goto error;
110 ret = crypto_shash_finup(desc, sinfo->authattrs,
111 sinfo->authattrs_len, sig->digest);
112 if (ret < 0)
113 goto error;
114 pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
115 }
116
117 error:
118 kfree(desc);
119 error_no_desc:
120 crypto_free_shash(tfm);
121 kleave(" = %d", ret);
122 return ret;
123 }
124
125 int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u32 *len,
126 enum hash_algo *hash_algo)
127 {
128 struct pkcs7_signed_info *sinfo = pkcs7->signed_infos;
129 int i, ret;
130
131 /*
132 * This function doesn't support messages with more than one signature.
133 */
134 if (sinfo == NULL || sinfo->next != NULL)
135 return -EBADMSG;
136
137 ret = pkcs7_digest(pkcs7, sinfo);
138 if (ret)
139 return ret;
140
141 *buf = sinfo->sig->digest;
142 *len = sinfo->sig->digest_size;
143
144 for (i = 0; i < HASH_ALGO__LAST; i++)
145 if (!strcmp(hash_algo_name[i], sinfo->sig->hash_algo)) {
146 *hash_algo = i;
147 break;
148 }
149
150 return 0;
151 }
152
153 /*
154 * Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7
155 * uses the issuer's name and the issuing certificate serial number for
156 * matching purposes. These must match the certificate issuer's name (not
157 * subject's name) and the certificate serial number [RFC 2315 6.7].
158 */
159 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
160 struct pkcs7_signed_info *sinfo)
161 {
162 struct x509_certificate *x509;
163 unsigned certix = 1;
164
165 kenter("%u", sinfo->index);
166
167 for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
168 /* I'm _assuming_ that the generator of the PKCS#7 message will
169 * encode the fields from the X.509 cert in the same way in the
170 * PKCS#7 message - but I can't be 100% sure of that. It's
171 * possible this will need element-by-element comparison.
172 */
173 if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
174 continue;
175 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
176 sinfo->index, certix);
177
178 if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
179 pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
180 sinfo->index);
181 continue;
182 }
183
184 sinfo->signer = x509;
185 return 0;
186 }
187
188 /* The relevant X.509 cert isn't found here, but it might be found in
189 * the trust keyring.
190 */
191 pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
192 sinfo->index,
193 sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
194 return 0;
195 }
196
197 /*
198 * Verify the internal certificate chain as best we can.
199 */
200 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
201 struct pkcs7_signed_info *sinfo)
202 {
203 struct public_key_signature *sig;
204 struct x509_certificate *x509 = sinfo->signer, *p;
205 struct asymmetric_key_id *auth;
206 int ret;
207
208 kenter("");
209
210 for (p = pkcs7->certs; p; p = p->next)
211 p->seen = false;
212
213 for (;;) {
214 pr_debug("verify %s: %*phN\n",
215 x509->subject,
216 x509->raw_serial_size, x509->raw_serial);
217 x509->seen = true;
218
219 if (x509->blacklisted) {
220 /* If this cert is blacklisted, then mark everything
221 * that depends on this as blacklisted too.
222 */
223 sinfo->blacklisted = true;
224 for (p = sinfo->signer; p != x509; p = p->signer)
225 p->blacklisted = true;
226 pr_debug("- blacklisted\n");
227 return 0;
228 }
229
230 if (x509->unsupported_key)
231 goto unsupported_crypto_in_x509;
232
233 pr_debug("- issuer %s\n", x509->issuer);
234 sig = x509->sig;
235 if (sig->auth_ids[0])
236 pr_debug("- authkeyid.id %*phN\n",
237 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
238 if (sig->auth_ids[1])
239 pr_debug("- authkeyid.skid %*phN\n",
240 sig->auth_ids[1]->len, sig->auth_ids[1]->data);
241
242 if (x509->self_signed) {
243 /* If there's no authority certificate specified, then
244 * the certificate must be self-signed and is the root
245 * of the chain. Likewise if the cert is its own
246 * authority.
247 */
248 if (x509->unsupported_sig)
249 goto unsupported_crypto_in_x509;
250 x509->signer = x509;
251 pr_debug("- self-signed\n");
252 return 0;
253 }
254
255 /* Look through the X.509 certificates in the PKCS#7 message's
256 * list to see if the next one is there.
257 */
258 auth = sig->auth_ids[0];
259 if (auth) {
260 pr_debug("- want %*phN\n", auth->len, auth->data);
261 for (p = pkcs7->certs; p; p = p->next) {
262 pr_debug("- cmp [%u] %*phN\n",
263 p->index, p->id->len, p->id->data);
264 if (asymmetric_key_id_same(p->id, auth))
265 goto found_issuer_check_skid;
266 }
267 } else if (sig->auth_ids[1]) {
268 auth = sig->auth_ids[1];
269 pr_debug("- want %*phN\n", auth->len, auth->data);
270 for (p = pkcs7->certs; p; p = p->next) {
271 if (!p->skid)
272 continue;
273 pr_debug("- cmp [%u] %*phN\n",
274 p->index, p->skid->len, p->skid->data);
275 if (asymmetric_key_id_same(p->skid, auth))
276 goto found_issuer;
277 }
278 }
279
280 /* We didn't find the root of this chain */
281 pr_debug("- top\n");
282 return 0;
283
284 found_issuer_check_skid:
285 /* We matched issuer + serialNumber, but if there's an
286 * authKeyId.keyId, that must match the CA subjKeyId also.
287 */
288 if (sig->auth_ids[1] &&
289 !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
290 pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
291 sinfo->index, x509->index, p->index);
292 return -EKEYREJECTED;
293 }
294 found_issuer:
295 pr_debug("- subject %s\n", p->subject);
296 if (p->seen) {
297 pr_warn("Sig %u: X.509 chain contains loop\n",
298 sinfo->index);
299 return 0;
300 }
301 ret = public_key_verify_signature(p->pub, x509->sig);
302 if (ret < 0)
303 return ret;
304 x509->signer = p;
305 if (x509 == p) {
306 pr_debug("- self-signed\n");
307 return 0;
308 }
309 x509 = p;
310 might_sleep();
311 }
312
313 unsupported_crypto_in_x509:
314 /* Just prune the certificate chain at this point if we lack some
315 * crypto module to go further. Note, however, we don't want to set
316 * sinfo->unsupported_crypto as the signed info block may still be
317 * validatable against an X.509 cert lower in the chain that we have a
318 * trusted copy of.
319 */
320 return 0;
321 }
322
323 /*
324 * Verify one signed information block from a PKCS#7 message.
325 */
326 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
327 struct pkcs7_signed_info *sinfo)
328 {
329 int ret;
330
331 kenter(",%u", sinfo->index);
332
333 /* First of all, digest the data in the PKCS#7 message and the
334 * signed information block
335 */
336 ret = pkcs7_digest(pkcs7, sinfo);
337 if (ret < 0)
338 return ret;
339
340 /* Find the key for the signature if there is one */
341 ret = pkcs7_find_key(pkcs7, sinfo);
342 if (ret < 0)
343 return ret;
344
345 if (!sinfo->signer)
346 return 0;
347
348 pr_devel("Using X.509[%u] for sig %u\n",
349 sinfo->signer->index, sinfo->index);
350
351 /* Check that the PKCS#7 signing time is valid according to the X.509
352 * certificate. We can't, however, check against the system clock
353 * since that may not have been set yet and may be wrong.
354 */
355 if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
356 if (sinfo->signing_time < sinfo->signer->valid_from ||
357 sinfo->signing_time > sinfo->signer->valid_to) {
358 pr_warn("Message signed outside of X.509 validity window\n");
359 return -EKEYREJECTED;
360 }
361 }
362
363 /* Verify the PKCS#7 binary against the key */
364 ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
365 if (ret < 0)
366 return ret;
367
368 pr_devel("Verified signature %u\n", sinfo->index);
369
370 /* Verify the internal certificate chain */
371 return pkcs7_verify_sig_chain(pkcs7, sinfo);
372 }
373
374 /**
375 * pkcs7_verify - Verify a PKCS#7 message
376 * @pkcs7: The PKCS#7 message to be verified
377 * @usage: The use to which the key is being put
378 *
379 * Verify a PKCS#7 message is internally consistent - that is, the data digest
380 * matches the digest in the AuthAttrs and any signature in the message or one
381 * of the X.509 certificates it carries that matches another X.509 cert in the
382 * message can be verified.
383 *
384 * This does not look to match the contents of the PKCS#7 message against any
385 * external public keys.
386 *
387 * Returns, in order of descending priority:
388 *
389 * (*) -EKEYREJECTED if a key was selected that had a usage restriction at
390 * odds with the specified usage, or:
391 *
392 * (*) -EKEYREJECTED if a signature failed to match for which we found an
393 * appropriate X.509 certificate, or:
394 *
395 * (*) -EBADMSG if some part of the message was invalid, or:
396 *
397 * (*) 0 if a signature chain passed verification, or:
398 *
399 * (*) -EKEYREJECTED if a blacklisted key was encountered, or:
400 *
401 * (*) -ENOPKG if none of the signature chains are verifiable because suitable
402 * crypto modules couldn't be found.
403 */
404 int pkcs7_verify(struct pkcs7_message *pkcs7,
405 enum key_being_used_for usage)
406 {
407 struct pkcs7_signed_info *sinfo;
408 int actual_ret = -ENOPKG;
409 int ret;
410
411 kenter("");
412
413 switch (usage) {
414 case VERIFYING_MODULE_SIGNATURE:
415 if (pkcs7->data_type != OID_data) {
416 pr_warn("Invalid module sig (not pkcs7-data)\n");
417 return -EKEYREJECTED;
418 }
419 if (pkcs7->have_authattrs) {
420 pr_warn("Invalid module sig (has authattrs)\n");
421 return -EKEYREJECTED;
422 }
423 break;
424 case VERIFYING_FIRMWARE_SIGNATURE:
425 if (pkcs7->data_type != OID_data) {
426 pr_warn("Invalid firmware sig (not pkcs7-data)\n");
427 return -EKEYREJECTED;
428 }
429 if (!pkcs7->have_authattrs) {
430 pr_warn("Invalid firmware sig (missing authattrs)\n");
431 return -EKEYREJECTED;
432 }
433 break;
434 case VERIFYING_KEXEC_PE_SIGNATURE:
435 if (pkcs7->data_type != OID_msIndirectData) {
436 pr_warn("Invalid kexec sig (not Authenticode)\n");
437 return -EKEYREJECTED;
438 }
439 /* Authattr presence checked in parser */
440 break;
441 case VERIFYING_UNSPECIFIED_SIGNATURE:
442 if (pkcs7->data_type != OID_data) {
443 pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
444 return -EKEYREJECTED;
445 }
446 break;
447 default:
448 return -EINVAL;
449 }
450
451 for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
452 ret = pkcs7_verify_one(pkcs7, sinfo);
453 if (sinfo->blacklisted) {
454 if (actual_ret == -ENOPKG)
455 actual_ret = -EKEYREJECTED;
456 continue;
457 }
458 if (ret < 0) {
459 if (ret == -ENOPKG) {
460 sinfo->unsupported_crypto = true;
461 continue;
462 }
463 kleave(" = %d", ret);
464 return ret;
465 }
466 actual_ret = 0;
467 }
468
469 kleave(" = %d", actual_ret);
470 return actual_ret;
471 }
472 EXPORT_SYMBOL_GPL(pkcs7_verify);
473
474 /**
475 * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
476 * @pkcs7: The PKCS#7 message
477 * @data: The data to be verified
478 * @datalen: The amount of data
479 *
480 * Supply the detached data needed to verify a PKCS#7 message. Note that no
481 * attempt to retain/pin the data is made. That is left to the caller. The
482 * data will not be modified by pkcs7_verify() and will not be freed when the
483 * PKCS#7 message is freed.
484 *
485 * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
486 */
487 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
488 const void *data, size_t datalen)
489 {
490 if (pkcs7->data) {
491 pr_debug("Data already supplied\n");
492 return -EINVAL;
493 }
494 pkcs7->data = data;
495 pkcs7->data_len = datalen;
496 return 0;
497 }