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 	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  */
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  */
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  */
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  */
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  */
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