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 */
pkcs7_digest(struct pkcs7_message * pkcs7,struct pkcs7_signed_info * sinfo)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
pkcs7_get_digest(struct pkcs7_message * pkcs7,const u8 ** buf,u32 * len,enum hash_algo * hash_algo)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 i = match_string(hash_algo_name, HASH_ALGO__LAST,
145 sinfo->sig->hash_algo);
146 if (i >= 0)
147 *hash_algo = i;
148
149 return 0;
150 }
151
152 /*
153 * Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7
154 * uses the issuer's name and the issuing certificate serial number for
155 * matching purposes. These must match the certificate issuer's name (not
156 * subject's name) and the certificate serial number [RFC 2315 6.7].
157 */
pkcs7_find_key(struct pkcs7_message * pkcs7,struct pkcs7_signed_info * sinfo)158 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
159 struct pkcs7_signed_info *sinfo)
160 {
161 struct x509_certificate *x509;
162 unsigned certix = 1;
163
164 kenter("%u", sinfo->index);
165
166 for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
167 /* I'm _assuming_ that the generator of the PKCS#7 message will
168 * encode the fields from the X.509 cert in the same way in the
169 * PKCS#7 message - but I can't be 100% sure of that. It's
170 * possible this will need element-by-element comparison.
171 */
172 if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
173 continue;
174 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
175 sinfo->index, certix);
176
177 if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
178 pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
179 sinfo->index);
180 continue;
181 }
182
183 sinfo->signer = x509;
184 return 0;
185 }
186
187 /* The relevant X.509 cert isn't found here, but it might be found in
188 * the trust keyring.
189 */
190 pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
191 sinfo->index,
192 sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
193 return 0;
194 }
195
196 /*
197 * Verify the internal certificate chain as best we can.
198 */
pkcs7_verify_sig_chain(struct pkcs7_message * pkcs7,struct pkcs7_signed_info * sinfo)199 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
200 struct pkcs7_signed_info *sinfo)
201 {
202 struct public_key_signature *sig;
203 struct x509_certificate *x509 = sinfo->signer, *p;
204 struct asymmetric_key_id *auth;
205 int ret;
206
207 kenter("");
208
209 for (p = pkcs7->certs; p; p = p->next)
210 p->seen = false;
211
212 for (;;) {
213 pr_debug("verify %s: %*phN\n",
214 x509->subject,
215 x509->raw_serial_size, x509->raw_serial);
216 x509->seen = true;
217
218 if (x509->blacklisted) {
219 /* If this cert is blacklisted, then mark everything
220 * that depends on this as blacklisted too.
221 */
222 sinfo->blacklisted = true;
223 for (p = sinfo->signer; p != x509; p = p->signer)
224 p->blacklisted = true;
225 pr_debug("- blacklisted\n");
226 return 0;
227 }
228
229 if (x509->unsupported_key)
230 goto unsupported_crypto_in_x509;
231
232 pr_debug("- issuer %s\n", x509->issuer);
233 sig = x509->sig;
234 if (sig->auth_ids[0])
235 pr_debug("- authkeyid.id %*phN\n",
236 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
237 if (sig->auth_ids[1])
238 pr_debug("- authkeyid.skid %*phN\n",
239 sig->auth_ids[1]->len, sig->auth_ids[1]->data);
240
241 if (x509->self_signed) {
242 /* If there's no authority certificate specified, then
243 * the certificate must be self-signed and is the root
244 * of the chain. Likewise if the cert is its own
245 * authority.
246 */
247 if (x509->unsupported_sig)
248 goto unsupported_crypto_in_x509;
249 x509->signer = x509;
250 pr_debug("- self-signed\n");
251 return 0;
252 }
253
254 /* Look through the X.509 certificates in the PKCS#7 message's
255 * list to see if the next one is there.
256 */
257 auth = sig->auth_ids[0];
258 if (auth) {
259 pr_debug("- want %*phN\n", auth->len, auth->data);
260 for (p = pkcs7->certs; p; p = p->next) {
261 pr_debug("- cmp [%u] %*phN\n",
262 p->index, p->id->len, p->id->data);
263 if (asymmetric_key_id_same(p->id, auth))
264 goto found_issuer_check_skid;
265 }
266 } else if (sig->auth_ids[1]) {
267 auth = sig->auth_ids[1];
268 pr_debug("- want %*phN\n", auth->len, auth->data);
269 for (p = pkcs7->certs; p; p = p->next) {
270 if (!p->skid)
271 continue;
272 pr_debug("- cmp [%u] %*phN\n",
273 p->index, p->skid->len, p->skid->data);
274 if (asymmetric_key_id_same(p->skid, auth))
275 goto found_issuer;
276 }
277 }
278
279 /* We didn't find the root of this chain */
280 pr_debug("- top\n");
281 return 0;
282
283 found_issuer_check_skid:
284 /* We matched issuer + serialNumber, but if there's an
285 * authKeyId.keyId, that must match the CA subjKeyId also.
286 */
287 if (sig->auth_ids[1] &&
288 !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
289 pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
290 sinfo->index, x509->index, p->index);
291 return -EKEYREJECTED;
292 }
293 found_issuer:
294 pr_debug("- subject %s\n", p->subject);
295 if (p->seen) {
296 pr_warn("Sig %u: X.509 chain contains loop\n",
297 sinfo->index);
298 return 0;
299 }
300 ret = public_key_verify_signature(p->pub, x509->sig);
301 if (ret < 0)
302 return ret;
303 x509->signer = p;
304 if (x509 == p) {
305 pr_debug("- self-signed\n");
306 return 0;
307 }
308 x509 = p;
309 might_sleep();
310 }
311
312 unsupported_crypto_in_x509:
313 /* Just prune the certificate chain at this point if we lack some
314 * crypto module to go further. Note, however, we don't want to set
315 * sinfo->unsupported_crypto as the signed info block may still be
316 * validatable against an X.509 cert lower in the chain that we have a
317 * trusted copy of.
318 */
319 return 0;
320 }
321
322 /*
323 * Verify one signed information block from a PKCS#7 message.
324 */
pkcs7_verify_one(struct pkcs7_message * pkcs7,struct pkcs7_signed_info * sinfo)325 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
326 struct pkcs7_signed_info *sinfo)
327 {
328 int ret;
329
330 kenter(",%u", sinfo->index);
331
332 /* First of all, digest the data in the PKCS#7 message and the
333 * signed information block
334 */
335 ret = pkcs7_digest(pkcs7, sinfo);
336 if (ret < 0)
337 return ret;
338
339 /* Find the key for the signature if there is one */
340 ret = pkcs7_find_key(pkcs7, sinfo);
341 if (ret < 0)
342 return ret;
343
344 if (!sinfo->signer)
345 return 0;
346
347 pr_devel("Using X.509[%u] for sig %u\n",
348 sinfo->signer->index, sinfo->index);
349
350 /* Check that the PKCS#7 signing time is valid according to the X.509
351 * certificate. We can't, however, check against the system clock
352 * since that may not have been set yet and may be wrong.
353 */
354 if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
355 if (sinfo->signing_time < sinfo->signer->valid_from ||
356 sinfo->signing_time > sinfo->signer->valid_to) {
357 pr_warn("Message signed outside of X.509 validity window\n");
358 return -EKEYREJECTED;
359 }
360 }
361
362 /* Verify the PKCS#7 binary against the key */
363 ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
364 if (ret < 0)
365 return ret;
366
367 pr_devel("Verified signature %u\n", sinfo->index);
368
369 /* Verify the internal certificate chain */
370 return pkcs7_verify_sig_chain(pkcs7, sinfo);
371 }
372
373 /**
374 * pkcs7_verify - Verify a PKCS#7 message
375 * @pkcs7: The PKCS#7 message to be verified
376 * @usage: The use to which the key is being put
377 *
378 * Verify a PKCS#7 message is internally consistent - that is, the data digest
379 * matches the digest in the AuthAttrs and any signature in the message or one
380 * of the X.509 certificates it carries that matches another X.509 cert in the
381 * message can be verified.
382 *
383 * This does not look to match the contents of the PKCS#7 message against any
384 * external public keys.
385 *
386 * Returns, in order of descending priority:
387 *
388 * (*) -EKEYREJECTED if a key was selected that had a usage restriction at
389 * odds with the specified usage, or:
390 *
391 * (*) -EKEYREJECTED if a signature failed to match for which we found an
392 * appropriate X.509 certificate, or:
393 *
394 * (*) -EBADMSG if some part of the message was invalid, or:
395 *
396 * (*) 0 if a signature chain passed verification, or:
397 *
398 * (*) -EKEYREJECTED if a blacklisted key was encountered, or:
399 *
400 * (*) -ENOPKG if none of the signature chains are verifiable because suitable
401 * crypto modules couldn't be found.
402 */
pkcs7_verify(struct pkcs7_message * pkcs7,enum key_being_used_for usage)403 int pkcs7_verify(struct pkcs7_message *pkcs7,
404 enum key_being_used_for usage)
405 {
406 struct pkcs7_signed_info *sinfo;
407 int actual_ret = -ENOPKG;
408 int ret;
409
410 kenter("");
411
412 switch (usage) {
413 case VERIFYING_MODULE_SIGNATURE:
414 if (pkcs7->data_type != OID_data) {
415 pr_warn("Invalid module sig (not pkcs7-data)\n");
416 return -EKEYREJECTED;
417 }
418 if (pkcs7->have_authattrs) {
419 pr_warn("Invalid module sig (has authattrs)\n");
420 return -EKEYREJECTED;
421 }
422 break;
423 case VERIFYING_FIRMWARE_SIGNATURE:
424 if (pkcs7->data_type != OID_data) {
425 pr_warn("Invalid firmware sig (not pkcs7-data)\n");
426 return -EKEYREJECTED;
427 }
428 if (!pkcs7->have_authattrs) {
429 pr_warn("Invalid firmware sig (missing authattrs)\n");
430 return -EKEYREJECTED;
431 }
432 break;
433 case VERIFYING_KEXEC_PE_SIGNATURE:
434 if (pkcs7->data_type != OID_msIndirectData) {
435 pr_warn("Invalid kexec sig (not Authenticode)\n");
436 return -EKEYREJECTED;
437 }
438 /* Authattr presence checked in parser */
439 break;
440 case VERIFYING_UNSPECIFIED_SIGNATURE:
441 if (pkcs7->data_type != OID_data) {
442 pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
443 return -EKEYREJECTED;
444 }
445 break;
446 default:
447 return -EINVAL;
448 }
449
450 for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
451 ret = pkcs7_verify_one(pkcs7, sinfo);
452 if (sinfo->blacklisted) {
453 if (actual_ret == -ENOPKG)
454 actual_ret = -EKEYREJECTED;
455 continue;
456 }
457 if (ret < 0) {
458 if (ret == -ENOPKG) {
459 sinfo->unsupported_crypto = true;
460 continue;
461 }
462 kleave(" = %d", ret);
463 return ret;
464 }
465 actual_ret = 0;
466 }
467
468 kleave(" = %d", actual_ret);
469 return actual_ret;
470 }
471 EXPORT_SYMBOL_GPL(pkcs7_verify);
472
473 /**
474 * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
475 * @pkcs7: The PKCS#7 message
476 * @data: The data to be verified
477 * @datalen: The amount of data
478 *
479 * Supply the detached data needed to verify a PKCS#7 message. Note that no
480 * attempt to retain/pin the data is made. That is left to the caller. The
481 * data will not be modified by pkcs7_verify() and will not be freed when the
482 * PKCS#7 message is freed.
483 *
484 * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
485 */
pkcs7_supply_detached_data(struct pkcs7_message * pkcs7,const void * data,size_t datalen)486 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
487 const void *data, size_t datalen)
488 {
489 if (pkcs7->data) {
490 pr_debug("Data already supplied\n");
491 return -EINVAL;
492 }
493 pkcs7->data = data;
494 pkcs7->data_len = datalen;
495 return 0;
496 }
497