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 		sinfo->signer = x509;
178 		return 0;
179 	}
180 
181 	/* The relevant X.509 cert isn't found here, but it might be found in
182 	 * the trust keyring.
183 	 */
184 	pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
185 		 sinfo->index,
186 		 sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
187 	return 0;
188 }
189 
190 /*
191  * Verify the internal certificate chain as best we can.
192  */
pkcs7_verify_sig_chain(struct pkcs7_message * pkcs7,struct pkcs7_signed_info * sinfo)193 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
194 				  struct pkcs7_signed_info *sinfo)
195 {
196 	struct public_key_signature *sig;
197 	struct x509_certificate *x509 = sinfo->signer, *p;
198 	struct asymmetric_key_id *auth;
199 	int ret;
200 
201 	kenter("");
202 
203 	for (p = pkcs7->certs; p; p = p->next)
204 		p->seen = false;
205 
206 	for (;;) {
207 		pr_debug("verify %s: %*phN\n",
208 			 x509->subject,
209 			 x509->raw_serial_size, x509->raw_serial);
210 		x509->seen = true;
211 
212 		if (x509->blacklisted) {
213 			/* If this cert is blacklisted, then mark everything
214 			 * that depends on this as blacklisted too.
215 			 */
216 			sinfo->blacklisted = true;
217 			for (p = sinfo->signer; p != x509; p = p->signer)
218 				p->blacklisted = true;
219 			pr_debug("- blacklisted\n");
220 			return 0;
221 		}
222 
223 		pr_debug("- issuer %s\n", x509->issuer);
224 		sig = x509->sig;
225 		if (sig->auth_ids[0])
226 			pr_debug("- authkeyid.id %*phN\n",
227 				 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
228 		if (sig->auth_ids[1])
229 			pr_debug("- authkeyid.skid %*phN\n",
230 				 sig->auth_ids[1]->len, sig->auth_ids[1]->data);
231 
232 		if (x509->self_signed) {
233 			/* If there's no authority certificate specified, then
234 			 * the certificate must be self-signed and is the root
235 			 * of the chain.  Likewise if the cert is its own
236 			 * authority.
237 			 */
238 			if (x509->unsupported_sig)
239 				goto unsupported_sig_in_x509;
240 			x509->signer = x509;
241 			pr_debug("- self-signed\n");
242 			return 0;
243 		}
244 
245 		/* Look through the X.509 certificates in the PKCS#7 message's
246 		 * list to see if the next one is there.
247 		 */
248 		auth = sig->auth_ids[0];
249 		if (auth) {
250 			pr_debug("- want %*phN\n", auth->len, auth->data);
251 			for (p = pkcs7->certs; p; p = p->next) {
252 				pr_debug("- cmp [%u] %*phN\n",
253 					 p->index, p->id->len, p->id->data);
254 				if (asymmetric_key_id_same(p->id, auth))
255 					goto found_issuer_check_skid;
256 			}
257 		} else if (sig->auth_ids[1]) {
258 			auth = sig->auth_ids[1];
259 			pr_debug("- want %*phN\n", auth->len, auth->data);
260 			for (p = pkcs7->certs; p; p = p->next) {
261 				if (!p->skid)
262 					continue;
263 				pr_debug("- cmp [%u] %*phN\n",
264 					 p->index, p->skid->len, p->skid->data);
265 				if (asymmetric_key_id_same(p->skid, auth))
266 					goto found_issuer;
267 			}
268 		}
269 
270 		/* We didn't find the root of this chain */
271 		pr_debug("- top\n");
272 		return 0;
273 
274 	found_issuer_check_skid:
275 		/* We matched issuer + serialNumber, but if there's an
276 		 * authKeyId.keyId, that must match the CA subjKeyId also.
277 		 */
278 		if (sig->auth_ids[1] &&
279 		    !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
280 			pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
281 				sinfo->index, x509->index, p->index);
282 			return -EKEYREJECTED;
283 		}
284 	found_issuer:
285 		pr_debug("- subject %s\n", p->subject);
286 		if (p->seen) {
287 			pr_warn("Sig %u: X.509 chain contains loop\n",
288 				sinfo->index);
289 			return 0;
290 		}
291 		ret = public_key_verify_signature(p->pub, x509->sig);
292 		if (ret < 0)
293 			return ret;
294 		x509->signer = p;
295 		if (x509 == p) {
296 			pr_debug("- self-signed\n");
297 			return 0;
298 		}
299 		x509 = p;
300 		might_sleep();
301 	}
302 
303 unsupported_sig_in_x509:
304 	/* Just prune the certificate chain at this point if we lack some
305 	 * crypto module to go further.  Note, however, we don't want to set
306 	 * sinfo->unsupported_crypto as the signed info block may still be
307 	 * validatable against an X.509 cert lower in the chain that we have a
308 	 * trusted copy of.
309 	 */
310 	return 0;
311 }
312 
313 /*
314  * Verify one signed information block from a PKCS#7 message.
315  */
pkcs7_verify_one(struct pkcs7_message * pkcs7,struct pkcs7_signed_info * sinfo)316 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
317 			    struct pkcs7_signed_info *sinfo)
318 {
319 	int ret;
320 
321 	kenter(",%u", sinfo->index);
322 
323 	/* First of all, digest the data in the PKCS#7 message and the
324 	 * signed information block
325 	 */
326 	ret = pkcs7_digest(pkcs7, sinfo);
327 	if (ret < 0)
328 		return ret;
329 
330 	/* Find the key for the signature if there is one */
331 	ret = pkcs7_find_key(pkcs7, sinfo);
332 	if (ret < 0)
333 		return ret;
334 
335 	if (!sinfo->signer)
336 		return 0;
337 
338 	pr_devel("Using X.509[%u] for sig %u\n",
339 		 sinfo->signer->index, sinfo->index);
340 
341 	/* Check that the PKCS#7 signing time is valid according to the X.509
342 	 * certificate.  We can't, however, check against the system clock
343 	 * since that may not have been set yet and may be wrong.
344 	 */
345 	if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
346 		if (sinfo->signing_time < sinfo->signer->valid_from ||
347 		    sinfo->signing_time > sinfo->signer->valid_to) {
348 			pr_warn("Message signed outside of X.509 validity window\n");
349 			return -EKEYREJECTED;
350 		}
351 	}
352 
353 	/* Verify the PKCS#7 binary against the key */
354 	ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
355 	if (ret < 0)
356 		return ret;
357 
358 	pr_devel("Verified signature %u\n", sinfo->index);
359 
360 	/* Verify the internal certificate chain */
361 	return pkcs7_verify_sig_chain(pkcs7, sinfo);
362 }
363 
364 /**
365  * pkcs7_verify - Verify a PKCS#7 message
366  * @pkcs7: The PKCS#7 message to be verified
367  * @usage: The use to which the key is being put
368  *
369  * Verify a PKCS#7 message is internally consistent - that is, the data digest
370  * matches the digest in the AuthAttrs and any signature in the message or one
371  * of the X.509 certificates it carries that matches another X.509 cert in the
372  * message can be verified.
373  *
374  * This does not look to match the contents of the PKCS#7 message against any
375  * external public keys.
376  *
377  * Returns, in order of descending priority:
378  *
379  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
380  *      odds with the specified usage, or:
381  *
382  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
383  *	appropriate X.509 certificate, or:
384  *
385  *  (*) -EBADMSG if some part of the message was invalid, or:
386  *
387  *  (*) 0 if a signature chain passed verification, or:
388  *
389  *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
390  *
391  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
392  *	crypto modules couldn't be found.
393  */
pkcs7_verify(struct pkcs7_message * pkcs7,enum key_being_used_for usage)394 int pkcs7_verify(struct pkcs7_message *pkcs7,
395 		 enum key_being_used_for usage)
396 {
397 	struct pkcs7_signed_info *sinfo;
398 	int actual_ret = -ENOPKG;
399 	int ret;
400 
401 	kenter("");
402 
403 	switch (usage) {
404 	case VERIFYING_MODULE_SIGNATURE:
405 		if (pkcs7->data_type != OID_data) {
406 			pr_warn("Invalid module sig (not pkcs7-data)\n");
407 			return -EKEYREJECTED;
408 		}
409 		if (pkcs7->have_authattrs) {
410 			pr_warn("Invalid module sig (has authattrs)\n");
411 			return -EKEYREJECTED;
412 		}
413 		break;
414 	case VERIFYING_FIRMWARE_SIGNATURE:
415 		if (pkcs7->data_type != OID_data) {
416 			pr_warn("Invalid firmware sig (not pkcs7-data)\n");
417 			return -EKEYREJECTED;
418 		}
419 		if (!pkcs7->have_authattrs) {
420 			pr_warn("Invalid firmware sig (missing authattrs)\n");
421 			return -EKEYREJECTED;
422 		}
423 		break;
424 	case VERIFYING_KEXEC_PE_SIGNATURE:
425 		if (pkcs7->data_type != OID_msIndirectData) {
426 			pr_warn("Invalid kexec sig (not Authenticode)\n");
427 			return -EKEYREJECTED;
428 		}
429 		/* Authattr presence checked in parser */
430 		break;
431 	case VERIFYING_UNSPECIFIED_SIGNATURE:
432 		if (pkcs7->data_type != OID_data) {
433 			pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
434 			return -EKEYREJECTED;
435 		}
436 		break;
437 	default:
438 		return -EINVAL;
439 	}
440 
441 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
442 		ret = pkcs7_verify_one(pkcs7, sinfo);
443 		if (sinfo->blacklisted) {
444 			if (actual_ret == -ENOPKG)
445 				actual_ret = -EKEYREJECTED;
446 			continue;
447 		}
448 		if (ret < 0) {
449 			if (ret == -ENOPKG) {
450 				sinfo->unsupported_crypto = true;
451 				continue;
452 			}
453 			kleave(" = %d", ret);
454 			return ret;
455 		}
456 		actual_ret = 0;
457 	}
458 
459 	kleave(" = %d", actual_ret);
460 	return actual_ret;
461 }
462 EXPORT_SYMBOL_GPL(pkcs7_verify);
463 
464 /**
465  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
466  * @pkcs7: The PKCS#7 message
467  * @data: The data to be verified
468  * @datalen: The amount of data
469  *
470  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
471  * attempt to retain/pin the data is made.  That is left to the caller.  The
472  * data will not be modified by pkcs7_verify() and will not be freed when the
473  * PKCS#7 message is freed.
474  *
475  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
476  */
pkcs7_supply_detached_data(struct pkcs7_message * pkcs7,const void * data,size_t datalen)477 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
478 			       const void *data, size_t datalen)
479 {
480 	if (pkcs7->data) {
481 		pr_debug("Data already supplied\n");
482 		return -EINVAL;
483 	}
484 	pkcs7->data = data;
485 	pkcs7->data_len = datalen;
486 	return 0;
487 }
488