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