1 /* Verify the signature on a PKCS#7 message.
2  *
3  * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
4  * Written by David Howells (dhowells@redhat.com)
5  *
6  * This program is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public Licence
8  * as published by the Free Software Foundation; either version
9  * 2 of the Licence, or (at your option) any later version.
10  */
11 
12 #define pr_fmt(fmt) "PKCS7: "fmt
13 #include <linux/kernel.h>
14 #include <linux/export.h>
15 #include <linux/slab.h>
16 #include <linux/err.h>
17 #include <linux/asn1.h>
18 #include <crypto/hash.h>
19 #include <crypto/public_key.h>
20 #include "pkcs7_parser.h"
21 
22 /*
23  * Digest the relevant parts of the PKCS#7 data
24  */
25 static int pkcs7_digest(struct pkcs7_message *pkcs7,
26 			struct pkcs7_signed_info *sinfo)
27 {
28 	struct public_key_signature *sig = sinfo->sig;
29 	struct crypto_shash *tfm;
30 	struct shash_desc *desc;
31 	size_t desc_size;
32 	int ret;
33 
34 	kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
35 
36 	if (!sinfo->sig->hash_algo)
37 		return -ENOPKG;
38 
39 	/* Allocate the hashing algorithm we're going to need and find out how
40 	 * big the hash operational data will be.
41 	 */
42 	tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
43 	if (IS_ERR(tfm))
44 		return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
45 
46 	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
47 	sig->digest_size = crypto_shash_digestsize(tfm);
48 
49 	ret = -ENOMEM;
50 	sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
51 	if (!sig->digest)
52 		goto error_no_desc;
53 
54 	desc = kzalloc(desc_size, GFP_KERNEL);
55 	if (!desc)
56 		goto error_no_desc;
57 
58 	desc->tfm   = tfm;
59 
60 	/* Digest the message [RFC2315 9.3] */
61 	ret = crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len,
62 				  sig->digest);
63 	if (ret < 0)
64 		goto error;
65 	pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
66 
67 	/* However, if there are authenticated attributes, there must be a
68 	 * message digest attribute amongst them which corresponds to the
69 	 * digest we just calculated.
70 	 */
71 	if (sinfo->authattrs) {
72 		u8 tag;
73 
74 		if (!sinfo->msgdigest) {
75 			pr_warn("Sig %u: No messageDigest\n", sinfo->index);
76 			ret = -EKEYREJECTED;
77 			goto error;
78 		}
79 
80 		if (sinfo->msgdigest_len != sig->digest_size) {
81 			pr_debug("Sig %u: Invalid digest size (%u)\n",
82 				 sinfo->index, sinfo->msgdigest_len);
83 			ret = -EBADMSG;
84 			goto error;
85 		}
86 
87 		if (memcmp(sig->digest, sinfo->msgdigest,
88 			   sinfo->msgdigest_len) != 0) {
89 			pr_debug("Sig %u: Message digest doesn't match\n",
90 				 sinfo->index);
91 			ret = -EKEYREJECTED;
92 			goto error;
93 		}
94 
95 		/* We then calculate anew, using the authenticated attributes
96 		 * as the contents of the digest instead.  Note that we need to
97 		 * convert the attributes from a CONT.0 into a SET before we
98 		 * hash it.
99 		 */
100 		memset(sig->digest, 0, sig->digest_size);
101 
102 		ret = crypto_shash_init(desc);
103 		if (ret < 0)
104 			goto error;
105 		tag = ASN1_CONS_BIT | ASN1_SET;
106 		ret = crypto_shash_update(desc, &tag, 1);
107 		if (ret < 0)
108 			goto error;
109 		ret = crypto_shash_finup(desc, sinfo->authattrs,
110 					 sinfo->authattrs_len, sig->digest);
111 		if (ret < 0)
112 			goto error;
113 		pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
114 	}
115 
116 error:
117 	kfree(desc);
118 error_no_desc:
119 	crypto_free_shash(tfm);
120 	kleave(" = %d", ret);
121 	return ret;
122 }
123 
124 /*
125  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
126  * uses the issuer's name and the issuing certificate serial number for
127  * matching purposes.  These must match the certificate issuer's name (not
128  * subject's name) and the certificate serial number [RFC 2315 6.7].
129  */
130 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
131 			  struct pkcs7_signed_info *sinfo)
132 {
133 	struct x509_certificate *x509;
134 	unsigned certix = 1;
135 
136 	kenter("%u", sinfo->index);
137 
138 	for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
139 		/* I'm _assuming_ that the generator of the PKCS#7 message will
140 		 * encode the fields from the X.509 cert in the same way in the
141 		 * PKCS#7 message - but I can't be 100% sure of that.  It's
142 		 * possible this will need element-by-element comparison.
143 		 */
144 		if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
145 			continue;
146 		pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
147 			 sinfo->index, certix);
148 
149 		if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
150 			pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
151 				sinfo->index);
152 			continue;
153 		}
154 
155 		sinfo->signer = x509;
156 		return 0;
157 	}
158 
159 	/* The relevant X.509 cert isn't found here, but it might be found in
160 	 * the trust keyring.
161 	 */
162 	pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
163 		 sinfo->index,
164 		 sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
165 	return 0;
166 }
167 
168 /*
169  * Verify the internal certificate chain as best we can.
170  */
171 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
172 				  struct pkcs7_signed_info *sinfo)
173 {
174 	struct public_key_signature *sig;
175 	struct x509_certificate *x509 = sinfo->signer, *p;
176 	struct asymmetric_key_id *auth;
177 	int ret;
178 
179 	kenter("");
180 
181 	for (p = pkcs7->certs; p; p = p->next)
182 		p->seen = false;
183 
184 	for (;;) {
185 		pr_debug("verify %s: %*phN\n",
186 			 x509->subject,
187 			 x509->raw_serial_size, x509->raw_serial);
188 		x509->seen = true;
189 
190 		if (x509->blacklisted) {
191 			/* If this cert is blacklisted, then mark everything
192 			 * that depends on this as blacklisted too.
193 			 */
194 			sinfo->blacklisted = true;
195 			for (p = sinfo->signer; p != x509; p = p->signer)
196 				p->blacklisted = true;
197 			pr_debug("- blacklisted\n");
198 			return 0;
199 		}
200 
201 		if (x509->unsupported_key)
202 			goto unsupported_crypto_in_x509;
203 
204 		pr_debug("- issuer %s\n", x509->issuer);
205 		sig = x509->sig;
206 		if (sig->auth_ids[0])
207 			pr_debug("- authkeyid.id %*phN\n",
208 				 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
209 		if (sig->auth_ids[1])
210 			pr_debug("- authkeyid.skid %*phN\n",
211 				 sig->auth_ids[1]->len, sig->auth_ids[1]->data);
212 
213 		if (x509->self_signed) {
214 			/* If there's no authority certificate specified, then
215 			 * the certificate must be self-signed and is the root
216 			 * of the chain.  Likewise if the cert is its own
217 			 * authority.
218 			 */
219 			if (x509->unsupported_sig)
220 				goto unsupported_crypto_in_x509;
221 			x509->signer = x509;
222 			pr_debug("- self-signed\n");
223 			return 0;
224 		}
225 
226 		/* Look through the X.509 certificates in the PKCS#7 message's
227 		 * list to see if the next one is there.
228 		 */
229 		auth = sig->auth_ids[0];
230 		if (auth) {
231 			pr_debug("- want %*phN\n", auth->len, auth->data);
232 			for (p = pkcs7->certs; p; p = p->next) {
233 				pr_debug("- cmp [%u] %*phN\n",
234 					 p->index, p->id->len, p->id->data);
235 				if (asymmetric_key_id_same(p->id, auth))
236 					goto found_issuer_check_skid;
237 			}
238 		} else if (sig->auth_ids[1]) {
239 			auth = sig->auth_ids[1];
240 			pr_debug("- want %*phN\n", auth->len, auth->data);
241 			for (p = pkcs7->certs; p; p = p->next) {
242 				if (!p->skid)
243 					continue;
244 				pr_debug("- cmp [%u] %*phN\n",
245 					 p->index, p->skid->len, p->skid->data);
246 				if (asymmetric_key_id_same(p->skid, auth))
247 					goto found_issuer;
248 			}
249 		}
250 
251 		/* We didn't find the root of this chain */
252 		pr_debug("- top\n");
253 		return 0;
254 
255 	found_issuer_check_skid:
256 		/* We matched issuer + serialNumber, but if there's an
257 		 * authKeyId.keyId, that must match the CA subjKeyId also.
258 		 */
259 		if (sig->auth_ids[1] &&
260 		    !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
261 			pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
262 				sinfo->index, x509->index, p->index);
263 			return -EKEYREJECTED;
264 		}
265 	found_issuer:
266 		pr_debug("- subject %s\n", p->subject);
267 		if (p->seen) {
268 			pr_warn("Sig %u: X.509 chain contains loop\n",
269 				sinfo->index);
270 			return 0;
271 		}
272 		ret = public_key_verify_signature(p->pub, x509->sig);
273 		if (ret < 0)
274 			return ret;
275 		x509->signer = p;
276 		if (x509 == p) {
277 			pr_debug("- self-signed\n");
278 			return 0;
279 		}
280 		x509 = p;
281 		might_sleep();
282 	}
283 
284 unsupported_crypto_in_x509:
285 	/* Just prune the certificate chain at this point if we lack some
286 	 * crypto module to go further.  Note, however, we don't want to set
287 	 * sinfo->unsupported_crypto as the signed info block may still be
288 	 * validatable against an X.509 cert lower in the chain that we have a
289 	 * trusted copy of.
290 	 */
291 	return 0;
292 }
293 
294 /*
295  * Verify one signed information block from a PKCS#7 message.
296  */
297 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
298 			    struct pkcs7_signed_info *sinfo)
299 {
300 	int ret;
301 
302 	kenter(",%u", sinfo->index);
303 
304 	/* First of all, digest the data in the PKCS#7 message and the
305 	 * signed information block
306 	 */
307 	ret = pkcs7_digest(pkcs7, sinfo);
308 	if (ret < 0)
309 		return ret;
310 
311 	/* Find the key for the signature if there is one */
312 	ret = pkcs7_find_key(pkcs7, sinfo);
313 	if (ret < 0)
314 		return ret;
315 
316 	if (!sinfo->signer)
317 		return 0;
318 
319 	pr_devel("Using X.509[%u] for sig %u\n",
320 		 sinfo->signer->index, sinfo->index);
321 
322 	/* Check that the PKCS#7 signing time is valid according to the X.509
323 	 * certificate.  We can't, however, check against the system clock
324 	 * since that may not have been set yet and may be wrong.
325 	 */
326 	if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
327 		if (sinfo->signing_time < sinfo->signer->valid_from ||
328 		    sinfo->signing_time > sinfo->signer->valid_to) {
329 			pr_warn("Message signed outside of X.509 validity window\n");
330 			return -EKEYREJECTED;
331 		}
332 	}
333 
334 	/* Verify the PKCS#7 binary against the key */
335 	ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
336 	if (ret < 0)
337 		return ret;
338 
339 	pr_devel("Verified signature %u\n", sinfo->index);
340 
341 	/* Verify the internal certificate chain */
342 	return pkcs7_verify_sig_chain(pkcs7, sinfo);
343 }
344 
345 /**
346  * pkcs7_verify - Verify a PKCS#7 message
347  * @pkcs7: The PKCS#7 message to be verified
348  * @usage: The use to which the key is being put
349  *
350  * Verify a PKCS#7 message is internally consistent - that is, the data digest
351  * matches the digest in the AuthAttrs and any signature in the message or one
352  * of the X.509 certificates it carries that matches another X.509 cert in the
353  * message can be verified.
354  *
355  * This does not look to match the contents of the PKCS#7 message against any
356  * external public keys.
357  *
358  * Returns, in order of descending priority:
359  *
360  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
361  *      odds with the specified usage, or:
362  *
363  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
364  *	appropriate X.509 certificate, or:
365  *
366  *  (*) -EBADMSG if some part of the message was invalid, or:
367  *
368  *  (*) 0 if a signature chain passed verification, or:
369  *
370  *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
371  *
372  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
373  *	crypto modules couldn't be found.
374  */
375 int pkcs7_verify(struct pkcs7_message *pkcs7,
376 		 enum key_being_used_for usage)
377 {
378 	struct pkcs7_signed_info *sinfo;
379 	int actual_ret = -ENOPKG;
380 	int ret;
381 
382 	kenter("");
383 
384 	switch (usage) {
385 	case VERIFYING_MODULE_SIGNATURE:
386 		if (pkcs7->data_type != OID_data) {
387 			pr_warn("Invalid module sig (not pkcs7-data)\n");
388 			return -EKEYREJECTED;
389 		}
390 		if (pkcs7->have_authattrs) {
391 			pr_warn("Invalid module sig (has authattrs)\n");
392 			return -EKEYREJECTED;
393 		}
394 		break;
395 	case VERIFYING_FIRMWARE_SIGNATURE:
396 		if (pkcs7->data_type != OID_data) {
397 			pr_warn("Invalid firmware sig (not pkcs7-data)\n");
398 			return -EKEYREJECTED;
399 		}
400 		if (!pkcs7->have_authattrs) {
401 			pr_warn("Invalid firmware sig (missing authattrs)\n");
402 			return -EKEYREJECTED;
403 		}
404 		break;
405 	case VERIFYING_KEXEC_PE_SIGNATURE:
406 		if (pkcs7->data_type != OID_msIndirectData) {
407 			pr_warn("Invalid kexec sig (not Authenticode)\n");
408 			return -EKEYREJECTED;
409 		}
410 		/* Authattr presence checked in parser */
411 		break;
412 	case VERIFYING_UNSPECIFIED_SIGNATURE:
413 		if (pkcs7->data_type != OID_data) {
414 			pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
415 			return -EKEYREJECTED;
416 		}
417 		break;
418 	default:
419 		return -EINVAL;
420 	}
421 
422 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
423 		ret = pkcs7_verify_one(pkcs7, sinfo);
424 		if (sinfo->blacklisted) {
425 			if (actual_ret == -ENOPKG)
426 				actual_ret = -EKEYREJECTED;
427 			continue;
428 		}
429 		if (ret < 0) {
430 			if (ret == -ENOPKG) {
431 				sinfo->unsupported_crypto = true;
432 				continue;
433 			}
434 			kleave(" = %d", ret);
435 			return ret;
436 		}
437 		actual_ret = 0;
438 	}
439 
440 	kleave(" = %d", actual_ret);
441 	return actual_ret;
442 }
443 EXPORT_SYMBOL_GPL(pkcs7_verify);
444 
445 /**
446  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
447  * @pkcs7: The PKCS#7 message
448  * @data: The data to be verified
449  * @datalen: The amount of data
450  *
451  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
452  * attempt to retain/pin the data is made.  That is left to the caller.  The
453  * data will not be modified by pkcs7_verify() and will not be freed when the
454  * PKCS#7 message is freed.
455  *
456  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
457  */
458 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
459 			       const void *data, size_t datalen)
460 {
461 	if (pkcs7->data) {
462 		pr_debug("Data already supplied\n");
463 		return -EINVAL;
464 	}
465 	pkcs7->data = data;
466 	pkcs7->data_len = datalen;
467 	return 0;
468 }
469