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 }
498