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