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 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,%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 	sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm);
48 
49 	ret = -ENOMEM;
50 	digest = kzalloc(ALIGN(digest_size, __alignof__(*desc)) + desc_size,
51 			 GFP_KERNEL);
52 	if (!digest)
53 		goto error_no_desc;
54 
55 	desc = PTR_ALIGN(digest + digest_size, __alignof__(*desc));
56 	desc->tfm   = tfm;
57 	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
58 
59 	/* Digest the message [RFC2315 9.3] */
60 	ret = crypto_shash_init(desc);
61 	if (ret < 0)
62 		goto error;
63 	ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest);
64 	if (ret < 0)
65 		goto error;
66 	pr_devel("MsgDigest = [%*ph]\n", 8, 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 != sinfo->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(digest, sinfo->msgdigest, 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(digest, 0, sinfo->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, digest);
111 		if (ret < 0)
112 			goto error;
113 		pr_devel("AADigest = [%*ph]\n", 8, digest);
114 	}
115 
116 	sinfo->sig.digest = digest;
117 	digest = NULL;
118 
119 error:
120 	kfree(digest);
121 error_no_desc:
122 	crypto_free_shash(tfm);
123 	kleave(" = %d", ret);
124 	return ret;
125 }
126 
127 /*
128  * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
129  * uses the issuer's name and the issuing certificate serial number for
130  * matching purposes.  These must match the certificate issuer's name (not
131  * subject's name) and the certificate serial number [RFC 2315 6.7].
132  */
133 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
134 			  struct pkcs7_signed_info *sinfo)
135 {
136 	struct x509_certificate *x509;
137 	unsigned certix = 1;
138 
139 	kenter("%u", sinfo->index);
140 
141 	for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
142 		/* I'm _assuming_ that the generator of the PKCS#7 message will
143 		 * encode the fields from the X.509 cert in the same way in the
144 		 * PKCS#7 message - but I can't be 100% sure of that.  It's
145 		 * possible this will need element-by-element comparison.
146 		 */
147 		if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id))
148 			continue;
149 		pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
150 			 sinfo->index, certix);
151 
152 		if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
153 			pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
154 				sinfo->index);
155 			continue;
156 		}
157 
158 		sinfo->signer = x509;
159 		return 0;
160 	}
161 
162 	/* The relevant X.509 cert isn't found here, but it might be found in
163 	 * the trust keyring.
164 	 */
165 	pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
166 		 sinfo->index,
167 		 sinfo->signing_cert_id->len, sinfo->signing_cert_id->data);
168 	return 0;
169 }
170 
171 /*
172  * Verify the internal certificate chain as best we can.
173  */
174 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
175 				  struct pkcs7_signed_info *sinfo)
176 {
177 	struct x509_certificate *x509 = sinfo->signer, *p;
178 	struct asymmetric_key_id *auth;
179 	int ret;
180 
181 	kenter("");
182 
183 	for (p = pkcs7->certs; p; p = p->next)
184 		p->seen = false;
185 
186 	for (;;) {
187 		pr_debug("verify %s: %*phN\n",
188 			 x509->subject,
189 			 x509->raw_serial_size, x509->raw_serial);
190 		x509->seen = true;
191 		ret = x509_get_sig_params(x509);
192 		if (ret < 0)
193 			goto maybe_missing_crypto_in_x509;
194 
195 		pr_debug("- issuer %s\n", x509->issuer);
196 		if (x509->akid_id)
197 			pr_debug("- authkeyid.id %*phN\n",
198 				 x509->akid_id->len, x509->akid_id->data);
199 		if (x509->akid_skid)
200 			pr_debug("- authkeyid.skid %*phN\n",
201 				 x509->akid_skid->len, x509->akid_skid->data);
202 
203 		if ((!x509->akid_id && !x509->akid_skid) ||
204 		    strcmp(x509->subject, x509->issuer) == 0) {
205 			/* If there's no authority certificate specified, then
206 			 * the certificate must be self-signed and is the root
207 			 * of the chain.  Likewise if the cert is its own
208 			 * authority.
209 			 */
210 			pr_debug("- no auth?\n");
211 			if (x509->raw_subject_size != x509->raw_issuer_size ||
212 			    memcmp(x509->raw_subject, x509->raw_issuer,
213 				   x509->raw_issuer_size) != 0)
214 				return 0;
215 
216 			ret = x509_check_signature(x509->pub, x509);
217 			if (ret < 0)
218 				goto maybe_missing_crypto_in_x509;
219 			x509->signer = x509;
220 			pr_debug("- self-signed\n");
221 			return 0;
222 		}
223 
224 		/* Look through the X.509 certificates in the PKCS#7 message's
225 		 * list to see if the next one is there.
226 		 */
227 		auth = x509->akid_id;
228 		if (auth) {
229 			pr_debug("- want %*phN\n", auth->len, auth->data);
230 			for (p = pkcs7->certs; p; p = p->next) {
231 				pr_debug("- cmp [%u] %*phN\n",
232 					 p->index, p->id->len, p->id->data);
233 				if (asymmetric_key_id_same(p->id, auth))
234 					goto found_issuer_check_skid;
235 			}
236 		} else {
237 			auth = x509->akid_skid;
238 			pr_debug("- want %*phN\n", auth->len, auth->data);
239 			for (p = pkcs7->certs; p; p = p->next) {
240 				if (!p->skid)
241 					continue;
242 				pr_debug("- cmp [%u] %*phN\n",
243 					 p->index, p->skid->len, p->skid->data);
244 				if (asymmetric_key_id_same(p->skid, auth))
245 					goto found_issuer;
246 			}
247 		}
248 
249 		/* We didn't find the root of this chain */
250 		pr_debug("- top\n");
251 		return 0;
252 
253 	found_issuer_check_skid:
254 		/* We matched issuer + serialNumber, but if there's an
255 		 * authKeyId.keyId, that must match the CA subjKeyId also.
256 		 */
257 		if (x509->akid_skid &&
258 		    !asymmetric_key_id_same(p->skid, x509->akid_skid)) {
259 			pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
260 				sinfo->index, x509->index, p->index);
261 			return -EKEYREJECTED;
262 		}
263 	found_issuer:
264 		pr_debug("- subject %s\n", p->subject);
265 		if (p->seen) {
266 			pr_warn("Sig %u: X.509 chain contains loop\n",
267 				sinfo->index);
268 			return 0;
269 		}
270 		ret = x509_check_signature(p->pub, x509);
271 		if (ret < 0)
272 			return ret;
273 		x509->signer = p;
274 		if (x509 == p) {
275 			pr_debug("- self-signed\n");
276 			return 0;
277 		}
278 		x509 = p;
279 		might_sleep();
280 	}
281 
282 maybe_missing_crypto_in_x509:
283 	/* Just prune the certificate chain at this point if we lack some
284 	 * crypto module to go further.  Note, however, we don't want to set
285 	 * sinfo->missing_crypto as the signed info block may still be
286 	 * validatable against an X.509 cert lower in the chain that we have a
287 	 * trusted copy of.
288 	 */
289 	if (ret == -ENOPKG)
290 		return 0;
291 	return ret;
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  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
369  *	crypto modules couldn't be found, or:
370  *
371  *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
372  *	(note that a signature chain may be of zero length), or:
373  */
374 int pkcs7_verify(struct pkcs7_message *pkcs7,
375 		 enum key_being_used_for usage)
376 {
377 	struct pkcs7_signed_info *sinfo;
378 	struct x509_certificate *x509;
379 	int enopkg = -ENOPKG;
380 	int ret, n;
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 (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
423 		ret = x509_get_sig_params(x509);
424 		if (ret < 0)
425 			return ret;
426 	}
427 
428 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
429 		ret = pkcs7_verify_one(pkcs7, sinfo);
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 		enopkg = 0;
439 	}
440 
441 	kleave(" = %d", enopkg);
442 	return enopkg;
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