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 	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
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 /*
126  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
127  * uses the issuer's name and the issuing certificate serial number for
128  * matching purposes.  These must match the certificate issuer's name (not
129  * subject's name) and the certificate serial number [RFC 2315 6.7].
130  */
131 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
132 			  struct pkcs7_signed_info *sinfo)
133 {
134 	struct x509_certificate *x509;
135 	unsigned certix = 1;
136 
137 	kenter("%u", sinfo->index);
138 
139 	for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
140 		/* I'm _assuming_ that the generator of the PKCS#7 message will
141 		 * encode the fields from the X.509 cert in the same way in the
142 		 * PKCS#7 message - but I can't be 100% sure of that.  It's
143 		 * possible this will need element-by-element comparison.
144 		 */
145 		if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
146 			continue;
147 		pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
148 			 sinfo->index, certix);
149 
150 		if (strcmp(x509->pub->pkey_algo, sinfo->sig->pkey_algo) != 0) {
151 			pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
152 				sinfo->index);
153 			continue;
154 		}
155 
156 		sinfo->signer = x509;
157 		return 0;
158 	}
159 
160 	/* The relevant X.509 cert isn't found here, but it might be found in
161 	 * the trust keyring.
162 	 */
163 	pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
164 		 sinfo->index,
165 		 sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
166 	return 0;
167 }
168 
169 /*
170  * Verify the internal certificate chain as best we can.
171  */
172 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
173 				  struct pkcs7_signed_info *sinfo)
174 {
175 	struct public_key_signature *sig;
176 	struct x509_certificate *x509 = sinfo->signer, *p;
177 	struct asymmetric_key_id *auth;
178 	int ret;
179 
180 	kenter("");
181 
182 	for (p = pkcs7->certs; p; p = p->next)
183 		p->seen = false;
184 
185 	for (;;) {
186 		pr_debug("verify %s: %*phN\n",
187 			 x509->subject,
188 			 x509->raw_serial_size, x509->raw_serial);
189 		x509->seen = true;
190 
191 		if (x509->blacklisted) {
192 			/* If this cert is blacklisted, then mark everything
193 			 * that depends on this as blacklisted too.
194 			 */
195 			sinfo->blacklisted = true;
196 			for (p = sinfo->signer; p != x509; p = p->signer)
197 				p->blacklisted = true;
198 			pr_debug("- blacklisted\n");
199 			return 0;
200 		}
201 
202 		if (x509->unsupported_key)
203 			goto unsupported_crypto_in_x509;
204 
205 		pr_debug("- issuer %s\n", x509->issuer);
206 		sig = x509->sig;
207 		if (sig->auth_ids[0])
208 			pr_debug("- authkeyid.id %*phN\n",
209 				 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
210 		if (sig->auth_ids[1])
211 			pr_debug("- authkeyid.skid %*phN\n",
212 				 sig->auth_ids[1]->len, sig->auth_ids[1]->data);
213 
214 		if (x509->self_signed) {
215 			/* If there's no authority certificate specified, then
216 			 * the certificate must be self-signed and is the root
217 			 * of the chain.  Likewise if the cert is its own
218 			 * authority.
219 			 */
220 			if (x509->unsupported_sig)
221 				goto unsupported_crypto_in_x509;
222 			x509->signer = x509;
223 			pr_debug("- self-signed\n");
224 			return 0;
225 		}
226 
227 		/* Look through the X.509 certificates in the PKCS#7 message's
228 		 * list to see if the next one is there.
229 		 */
230 		auth = sig->auth_ids[0];
231 		if (auth) {
232 			pr_debug("- want %*phN\n", auth->len, auth->data);
233 			for (p = pkcs7->certs; p; p = p->next) {
234 				pr_debug("- cmp [%u] %*phN\n",
235 					 p->index, p->id->len, p->id->data);
236 				if (asymmetric_key_id_same(p->id, auth))
237 					goto found_issuer_check_skid;
238 			}
239 		} else if (sig->auth_ids[1]) {
240 			auth = sig->auth_ids[1];
241 			pr_debug("- want %*phN\n", auth->len, auth->data);
242 			for (p = pkcs7->certs; p; p = p->next) {
243 				if (!p->skid)
244 					continue;
245 				pr_debug("- cmp [%u] %*phN\n",
246 					 p->index, p->skid->len, p->skid->data);
247 				if (asymmetric_key_id_same(p->skid, auth))
248 					goto found_issuer;
249 			}
250 		}
251 
252 		/* We didn't find the root of this chain */
253 		pr_debug("- top\n");
254 		return 0;
255 
256 	found_issuer_check_skid:
257 		/* We matched issuer + serialNumber, but if there's an
258 		 * authKeyId.keyId, that must match the CA subjKeyId also.
259 		 */
260 		if (sig->auth_ids[1] &&
261 		    !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
262 			pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
263 				sinfo->index, x509->index, p->index);
264 			return -EKEYREJECTED;
265 		}
266 	found_issuer:
267 		pr_debug("- subject %s\n", p->subject);
268 		if (p->seen) {
269 			pr_warn("Sig %u: X.509 chain contains loop\n",
270 				sinfo->index);
271 			return 0;
272 		}
273 		ret = public_key_verify_signature(p->pub, x509->sig);
274 		if (ret < 0)
275 			return ret;
276 		x509->signer = p;
277 		if (x509 == p) {
278 			pr_debug("- self-signed\n");
279 			return 0;
280 		}
281 		x509 = p;
282 		might_sleep();
283 	}
284 
285 unsupported_crypto_in_x509:
286 	/* Just prune the certificate chain at this point if we lack some
287 	 * crypto module to go further.  Note, however, we don't want to set
288 	 * sinfo->unsupported_crypto as the signed info block may still be
289 	 * validatable against an X.509 cert lower in the chain that we have a
290 	 * trusted copy of.
291 	 */
292 	return 0;
293 }
294 
295 /*
296  * Verify one signed information block from a PKCS#7 message.
297  */
298 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
299 			    struct pkcs7_signed_info *sinfo)
300 {
301 	int ret;
302 
303 	kenter(",%u", sinfo->index);
304 
305 	/* First of all, digest the data in the PKCS#7 message and the
306 	 * signed information block
307 	 */
308 	ret = pkcs7_digest(pkcs7, sinfo);
309 	if (ret < 0)
310 		return ret;
311 
312 	/* Find the key for the signature if there is one */
313 	ret = pkcs7_find_key(pkcs7, sinfo);
314 	if (ret < 0)
315 		return ret;
316 
317 	if (!sinfo->signer)
318 		return 0;
319 
320 	pr_devel("Using X.509[%u] for sig %u\n",
321 		 sinfo->signer->index, sinfo->index);
322 
323 	/* Check that the PKCS#7 signing time is valid according to the X.509
324 	 * certificate.  We can't, however, check against the system clock
325 	 * since that may not have been set yet and may be wrong.
326 	 */
327 	if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
328 		if (sinfo->signing_time < sinfo->signer->valid_from ||
329 		    sinfo->signing_time > sinfo->signer->valid_to) {
330 			pr_warn("Message signed outside of X.509 validity window\n");
331 			return -EKEYREJECTED;
332 		}
333 	}
334 
335 	/* Verify the PKCS#7 binary against the key */
336 	ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
337 	if (ret < 0)
338 		return ret;
339 
340 	pr_devel("Verified signature %u\n", sinfo->index);
341 
342 	/* Verify the internal certificate chain */
343 	return pkcs7_verify_sig_chain(pkcs7, sinfo);
344 }
345 
346 /**
347  * pkcs7_verify - Verify a PKCS#7 message
348  * @pkcs7: The PKCS#7 message to be verified
349  * @usage: The use to which the key is being put
350  *
351  * Verify a PKCS#7 message is internally consistent - that is, the data digest
352  * matches the digest in the AuthAttrs and any signature in the message or one
353  * of the X.509 certificates it carries that matches another X.509 cert in the
354  * message can be verified.
355  *
356  * This does not look to match the contents of the PKCS#7 message against any
357  * external public keys.
358  *
359  * Returns, in order of descending priority:
360  *
361  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
362  *      odds with the specified usage, or:
363  *
364  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
365  *	appropriate X.509 certificate, or:
366  *
367  *  (*) -EBADMSG if some part of the message was invalid, or:
368  *
369  *  (*) 0 if a signature chain passed verification, or:
370  *
371  *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
372  *
373  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
374  *	crypto modules couldn't be found.
375  */
376 int pkcs7_verify(struct pkcs7_message *pkcs7,
377 		 enum key_being_used_for usage)
378 {
379 	struct pkcs7_signed_info *sinfo;
380 	int actual_ret = -ENOPKG;
381 	int ret;
382 
383 	kenter("");
384 
385 	switch (usage) {
386 	case VERIFYING_MODULE_SIGNATURE:
387 		if (pkcs7->data_type != OID_data) {
388 			pr_warn("Invalid module sig (not pkcs7-data)\n");
389 			return -EKEYREJECTED;
390 		}
391 		if (pkcs7->have_authattrs) {
392 			pr_warn("Invalid module sig (has authattrs)\n");
393 			return -EKEYREJECTED;
394 		}
395 		break;
396 	case VERIFYING_FIRMWARE_SIGNATURE:
397 		if (pkcs7->data_type != OID_data) {
398 			pr_warn("Invalid firmware sig (not pkcs7-data)\n");
399 			return -EKEYREJECTED;
400 		}
401 		if (!pkcs7->have_authattrs) {
402 			pr_warn("Invalid firmware sig (missing authattrs)\n");
403 			return -EKEYREJECTED;
404 		}
405 		break;
406 	case VERIFYING_KEXEC_PE_SIGNATURE:
407 		if (pkcs7->data_type != OID_msIndirectData) {
408 			pr_warn("Invalid kexec sig (not Authenticode)\n");
409 			return -EKEYREJECTED;
410 		}
411 		/* Authattr presence checked in parser */
412 		break;
413 	case VERIFYING_UNSPECIFIED_SIGNATURE:
414 		if (pkcs7->data_type != OID_data) {
415 			pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
416 			return -EKEYREJECTED;
417 		}
418 		break;
419 	default:
420 		return -EINVAL;
421 	}
422 
423 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
424 		ret = pkcs7_verify_one(pkcs7, sinfo);
425 		if (sinfo->blacklisted) {
426 			if (actual_ret == -ENOPKG)
427 				actual_ret = -EKEYREJECTED;
428 			continue;
429 		}
430 		if (ret < 0) {
431 			if (ret == -ENOPKG) {
432 				sinfo->unsupported_crypto = true;
433 				continue;
434 			}
435 			kleave(" = %d", ret);
436 			return ret;
437 		}
438 		actual_ret = 0;
439 	}
440 
441 	kleave(" = %d", actual_ret);
442 	return actual_ret;
443 }
444 EXPORT_SYMBOL_GPL(pkcs7_verify);
445 
446 /**
447  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
448  * @pkcs7: The PKCS#7 message
449  * @data: The data to be verified
450  * @datalen: The amount of data
451  *
452  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
453  * attempt to retain/pin the data is made.  That is left to the caller.  The
454  * data will not be modified by pkcs7_verify() and will not be freed when the
455  * PKCS#7 message is freed.
456  *
457  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
458  */
459 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
460 			       const void *data, size_t datalen)
461 {
462 	if (pkcs7->data) {
463 		pr_debug("Data already supplied\n");
464 		return -EINVAL;
465 	}
466 	pkcs7->data = data;
467 	pkcs7->data_len = datalen;
468 	return 0;
469 }
470