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 "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 crypto_shash *tfm;
29 	struct shash_desc *desc;
30 	size_t digest_size, desc_size;
31 	void *digest;
32 	int ret;
33 
34 	kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo);
35 
36 	if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
37 	    !hash_algo_name[sinfo->sig.pkey_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(hash_algo_name[sinfo->sig.pkey_hash_algo],
44 				 0, 0);
45 	if (IS_ERR(tfm))
46 		return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
47 
48 	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
49 	sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm);
50 
51 	ret = -ENOMEM;
52 	digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
53 	if (!digest)
54 		goto error_no_desc;
55 
56 	desc = digest + digest_size;
57 	desc->tfm   = tfm;
58 	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
59 
60 	/* Digest the message [RFC2315 9.3] */
61 	ret = crypto_shash_init(desc);
62 	if (ret < 0)
63 		goto error;
64 	ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest);
65 	if (ret < 0)
66 		goto error;
67 	pr_devel("MsgDigest = [%*ph]\n", 8, digest);
68 
69 	/* However, if there are authenticated attributes, there must be a
70 	 * message digest attribute amongst them which corresponds to the
71 	 * digest we just calculated.
72 	 */
73 	if (sinfo->authattrs) {
74 		u8 tag;
75 
76 		if (!sinfo->msgdigest) {
77 			pr_warn("Sig %u: No messageDigest\n", sinfo->index);
78 			ret = -EKEYREJECTED;
79 			goto error;
80 		}
81 
82 		if (sinfo->msgdigest_len != sinfo->sig.digest_size) {
83 			pr_debug("Sig %u: Invalid digest size (%u)\n",
84 				 sinfo->index, sinfo->msgdigest_len);
85 			ret = -EBADMSG;
86 			goto error;
87 		}
88 
89 		if (memcmp(digest, sinfo->msgdigest, 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(digest, 0, sinfo->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, digest);
112 		if (ret < 0)
113 			goto error;
114 		pr_devel("AADigest = [%*ph]\n", 8, digest);
115 	}
116 
117 	sinfo->sig.digest = digest;
118 	digest = NULL;
119 
120 error:
121 	kfree(digest);
122 error_no_desc:
123 	crypto_free_shash(tfm);
124 	kleave(" = %d", ret);
125 	return ret;
126 }
127 
128 /*
129  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
130  * uses the issuer's name and the issuing certificate serial number for
131  * matching purposes.  These must match the certificate issuer's name (not
132  * subject's name) and the certificate serial number [RFC 2315 6.7].
133  */
134 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
135 			  struct pkcs7_signed_info *sinfo)
136 {
137 	struct x509_certificate *x509;
138 	unsigned certix = 1;
139 
140 	kenter("%u", sinfo->index);
141 
142 	for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
143 		/* I'm _assuming_ that the generator of the PKCS#7 message will
144 		 * encode the fields from the X.509 cert in the same way in the
145 		 * PKCS#7 message - but I can't be 100% sure of that.  It's
146 		 * possible this will need element-by-element comparison.
147 		 */
148 		if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id))
149 			continue;
150 		pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
151 			 sinfo->index, certix);
152 
153 		if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
154 			pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
155 				sinfo->index);
156 			continue;
157 		}
158 
159 		sinfo->signer = x509;
160 		return 0;
161 	}
162 
163 	/* The relevant X.509 cert isn't found here, but it might be found in
164 	 * the trust keyring.
165 	 */
166 	pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
167 		 sinfo->index,
168 		 sinfo->signing_cert_id->len, sinfo->signing_cert_id->data);
169 	return 0;
170 }
171 
172 /*
173  * Verify the internal certificate chain as best we can.
174  */
175 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
176 				  struct pkcs7_signed_info *sinfo)
177 {
178 	struct x509_certificate *x509 = sinfo->signer, *p;
179 	struct asymmetric_key_id *auth;
180 	int ret;
181 
182 	kenter("");
183 
184 	for (p = pkcs7->certs; p; p = p->next)
185 		p->seen = false;
186 
187 	for (;;) {
188 		pr_debug("verify %s: %*phN\n",
189 			 x509->subject,
190 			 x509->raw_serial_size, x509->raw_serial);
191 		x509->seen = true;
192 		ret = x509_get_sig_params(x509);
193 		if (ret < 0)
194 			goto maybe_missing_crypto_in_x509;
195 
196 		pr_debug("- issuer %s\n", x509->issuer);
197 		if (x509->akid_id)
198 			pr_debug("- authkeyid.id %*phN\n",
199 				 x509->akid_id->len, x509->akid_id->data);
200 		if (x509->akid_skid)
201 			pr_debug("- authkeyid.skid %*phN\n",
202 				 x509->akid_skid->len, x509->akid_skid->data);
203 
204 		if ((!x509->akid_id && !x509->akid_skid) ||
205 		    strcmp(x509->subject, x509->issuer) == 0) {
206 			/* If there's no authority certificate specified, then
207 			 * the certificate must be self-signed and is the root
208 			 * of the chain.  Likewise if the cert is its own
209 			 * authority.
210 			 */
211 			pr_debug("- no auth?\n");
212 			if (x509->raw_subject_size != x509->raw_issuer_size ||
213 			    memcmp(x509->raw_subject, x509->raw_issuer,
214 				   x509->raw_issuer_size) != 0)
215 				return 0;
216 
217 			ret = x509_check_signature(x509->pub, x509);
218 			if (ret < 0)
219 				goto maybe_missing_crypto_in_x509;
220 			x509->signer = x509;
221 			pr_debug("- self-signed\n");
222 			return 0;
223 		}
224 
225 		/* Look through the X.509 certificates in the PKCS#7 message's
226 		 * list to see if the next one is there.
227 		 */
228 		auth = x509->akid_id;
229 		if (auth) {
230 			pr_debug("- want %*phN\n", auth->len, auth->data);
231 			for (p = pkcs7->certs; p; p = p->next) {
232 				pr_debug("- cmp [%u] %*phN\n",
233 					 p->index, p->id->len, p->id->data);
234 				if (asymmetric_key_id_same(p->id, auth))
235 					goto found_issuer_check_skid;
236 			}
237 		} else {
238 			auth = x509->akid_skid;
239 			pr_debug("- want %*phN\n", auth->len, auth->data);
240 			for (p = pkcs7->certs; p; p = p->next) {
241 				if (!p->skid)
242 					continue;
243 				pr_debug("- cmp [%u] %*phN\n",
244 					 p->index, p->skid->len, p->skid->data);
245 				if (asymmetric_key_id_same(p->skid, auth))
246 					goto found_issuer;
247 			}
248 		}
249 
250 		/* We didn't find the root of this chain */
251 		pr_debug("- top\n");
252 		return 0;
253 
254 	found_issuer_check_skid:
255 		/* We matched issuer + serialNumber, but if there's an
256 		 * authKeyId.keyId, that must match the CA subjKeyId also.
257 		 */
258 		if (x509->akid_skid &&
259 		    !asymmetric_key_id_same(p->skid, x509->akid_skid)) {
260 			pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
261 				sinfo->index, x509->index, p->index);
262 			return -EKEYREJECTED;
263 		}
264 	found_issuer:
265 		pr_debug("- subject %s\n", p->subject);
266 		if (p->seen) {
267 			pr_warn("Sig %u: X.509 chain contains loop\n",
268 				sinfo->index);
269 			return 0;
270 		}
271 		ret = x509_check_signature(p->pub, x509);
272 		if (ret < 0)
273 			return ret;
274 		x509->signer = p;
275 		if (x509 == p) {
276 			pr_debug("- self-signed\n");
277 			return 0;
278 		}
279 		x509 = p;
280 		might_sleep();
281 	}
282 
283 maybe_missing_crypto_in_x509:
284 	/* Just prune the certificate chain at this point if we lack some
285 	 * crypto module to go further.  Note, however, we don't want to set
286 	 * sinfo->missing_crypto as the signed info block may still be
287 	 * validatable against an X.509 cert lower in the chain that we have a
288 	 * trusted copy of.
289 	 */
290 	if (ret == -ENOPKG)
291 		return 0;
292 	return ret;
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  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
370  *	crypto modules couldn't be found, or:
371  *
372  *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
373  *	(note that a signature chain may be of zero length), or:
374  */
375 int pkcs7_verify(struct pkcs7_message *pkcs7,
376 		 enum key_being_used_for usage)
377 {
378 	struct pkcs7_signed_info *sinfo;
379 	struct x509_certificate *x509;
380 	int enopkg = -ENOPKG;
381 	int ret, n;
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 (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
424 		ret = x509_get_sig_params(x509);
425 		if (ret < 0)
426 			return ret;
427 	}
428 
429 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
430 		ret = pkcs7_verify_one(pkcs7, sinfo);
431 		if (ret < 0) {
432 			if (ret == -ENOPKG) {
433 				sinfo->unsupported_crypto = true;
434 				continue;
435 			}
436 			kleave(" = %d", ret);
437 			return ret;
438 		}
439 		enopkg = 0;
440 	}
441 
442 	kleave(" = %d", enopkg);
443 	return enopkg;
444 }
445 EXPORT_SYMBOL_GPL(pkcs7_verify);
446 
447 /**
448  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
449  * @pkcs7: The PKCS#7 message
450  * @data: The data to be verified
451  * @datalen: The amount of data
452  *
453  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
454  * attempt to retain/pin the data is made.  That is left to the caller.  The
455  * data will not be modified by pkcs7_verify() and will not be freed when the
456  * PKCS#7 message is freed.
457  *
458  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
459  */
460 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
461 			       const void *data, size_t datalen)
462 {
463 	if (pkcs7->data) {
464 		pr_debug("Data already supplied\n");
465 		return -EINVAL;
466 	}
467 	pkcs7->data = data;
468 	pkcs7->data_len = datalen;
469 	return 0;
470 }
471