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_init(desc);
63 	if (ret < 0)
64 		goto error;
65 	ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len,
66 				 sig->digest);
67 	if (ret < 0)
68 		goto error;
69 	pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);
70 
71 	/* However, if there are authenticated attributes, there must be a
72 	 * message digest attribute amongst them which corresponds to the
73 	 * digest we just calculated.
74 	 */
75 	if (sinfo->authattrs) {
76 		u8 tag;
77 
78 		if (!sinfo->msgdigest) {
79 			pr_warn("Sig %u: No messageDigest\n", sinfo->index);
80 			ret = -EKEYREJECTED;
81 			goto error;
82 		}
83 
84 		if (sinfo->msgdigest_len != sig->digest_size) {
85 			pr_debug("Sig %u: Invalid digest size (%u)\n",
86 				 sinfo->index, sinfo->msgdigest_len);
87 			ret = -EBADMSG;
88 			goto error;
89 		}
90 
91 		if (memcmp(sig->digest, sinfo->msgdigest,
92 			   sinfo->msgdigest_len) != 0) {
93 			pr_debug("Sig %u: Message digest doesn't match\n",
94 				 sinfo->index);
95 			ret = -EKEYREJECTED;
96 			goto error;
97 		}
98 
99 		/* We then calculate anew, using the authenticated attributes
100 		 * as the contents of the digest instead.  Note that we need to
101 		 * convert the attributes from a CONT.0 into a SET before we
102 		 * hash it.
103 		 */
104 		memset(sig->digest, 0, sig->digest_size);
105 
106 		ret = crypto_shash_init(desc);
107 		if (ret < 0)
108 			goto error;
109 		tag = ASN1_CONS_BIT | ASN1_SET;
110 		ret = crypto_shash_update(desc, &tag, 1);
111 		if (ret < 0)
112 			goto error;
113 		ret = crypto_shash_finup(desc, sinfo->authattrs,
114 					 sinfo->authattrs_len, sig->digest);
115 		if (ret < 0)
116 			goto error;
117 		pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
118 	}
119 
120 error:
121 	kfree(desc);
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->sig->auth_ids[0]))
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->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->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 public_key_signature *sig;
179 	struct x509_certificate *x509 = sinfo->signer, *p;
180 	struct asymmetric_key_id *auth;
181 	int ret;
182 
183 	kenter("");
184 
185 	for (p = pkcs7->certs; p; p = p->next)
186 		p->seen = false;
187 
188 	for (;;) {
189 		pr_debug("verify %s: %*phN\n",
190 			 x509->subject,
191 			 x509->raw_serial_size, x509->raw_serial);
192 		x509->seen = true;
193 		if (x509->unsupported_key)
194 			goto unsupported_crypto_in_x509;
195 
196 		pr_debug("- issuer %s\n", x509->issuer);
197 		sig = x509->sig;
198 		if (sig->auth_ids[0])
199 			pr_debug("- authkeyid.id %*phN\n",
200 				 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
201 		if (sig->auth_ids[1])
202 			pr_debug("- authkeyid.skid %*phN\n",
203 				 sig->auth_ids[1]->len, sig->auth_ids[1]->data);
204 
205 		if (x509->self_signed) {
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 			if (x509->unsupported_sig)
212 				goto unsupported_crypto_in_x509;
213 			x509->signer = x509;
214 			pr_debug("- self-signed\n");
215 			return 0;
216 		}
217 
218 		/* Look through the X.509 certificates in the PKCS#7 message's
219 		 * list to see if the next one is there.
220 		 */
221 		auth = sig->auth_ids[0];
222 		if (auth) {
223 			pr_debug("- want %*phN\n", auth->len, auth->data);
224 			for (p = pkcs7->certs; p; p = p->next) {
225 				pr_debug("- cmp [%u] %*phN\n",
226 					 p->index, p->id->len, p->id->data);
227 				if (asymmetric_key_id_same(p->id, auth))
228 					goto found_issuer_check_skid;
229 			}
230 		} else if (sig->auth_ids[1]) {
231 			auth = sig->auth_ids[1];
232 			pr_debug("- want %*phN\n", auth->len, auth->data);
233 			for (p = pkcs7->certs; p; p = p->next) {
234 				if (!p->skid)
235 					continue;
236 				pr_debug("- cmp [%u] %*phN\n",
237 					 p->index, p->skid->len, p->skid->data);
238 				if (asymmetric_key_id_same(p->skid, auth))
239 					goto found_issuer;
240 			}
241 		}
242 
243 		/* We didn't find the root of this chain */
244 		pr_debug("- top\n");
245 		return 0;
246 
247 	found_issuer_check_skid:
248 		/* We matched issuer + serialNumber, but if there's an
249 		 * authKeyId.keyId, that must match the CA subjKeyId also.
250 		 */
251 		if (sig->auth_ids[1] &&
252 		    !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
253 			pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
254 				sinfo->index, x509->index, p->index);
255 			return -EKEYREJECTED;
256 		}
257 	found_issuer:
258 		pr_debug("- subject %s\n", p->subject);
259 		if (p->seen) {
260 			pr_warn("Sig %u: X.509 chain contains loop\n",
261 				sinfo->index);
262 			return 0;
263 		}
264 		ret = public_key_verify_signature(p->pub, p->sig);
265 		if (ret < 0)
266 			return ret;
267 		x509->signer = p;
268 		if (x509 == p) {
269 			pr_debug("- self-signed\n");
270 			return 0;
271 		}
272 		x509 = p;
273 		might_sleep();
274 	}
275 
276 unsupported_crypto_in_x509:
277 	/* Just prune the certificate chain at this point if we lack some
278 	 * crypto module to go further.  Note, however, we don't want to set
279 	 * sinfo->unsupported_crypto as the signed info block may still be
280 	 * validatable against an X.509 cert lower in the chain that we have a
281 	 * trusted copy of.
282 	 */
283 	return 0;
284 }
285 
286 /*
287  * Verify one signed information block from a PKCS#7 message.
288  */
289 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
290 			    struct pkcs7_signed_info *sinfo)
291 {
292 	int ret;
293 
294 	kenter(",%u", sinfo->index);
295 
296 	/* First of all, digest the data in the PKCS#7 message and the
297 	 * signed information block
298 	 */
299 	ret = pkcs7_digest(pkcs7, sinfo);
300 	if (ret < 0)
301 		return ret;
302 
303 	/* Find the key for the signature if there is one */
304 	ret = pkcs7_find_key(pkcs7, sinfo);
305 	if (ret < 0)
306 		return ret;
307 
308 	if (!sinfo->signer)
309 		return 0;
310 
311 	pr_devel("Using X.509[%u] for sig %u\n",
312 		 sinfo->signer->index, sinfo->index);
313 
314 	/* Check that the PKCS#7 signing time is valid according to the X.509
315 	 * certificate.  We can't, however, check against the system clock
316 	 * since that may not have been set yet and may be wrong.
317 	 */
318 	if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
319 		if (sinfo->signing_time < sinfo->signer->valid_from ||
320 		    sinfo->signing_time > sinfo->signer->valid_to) {
321 			pr_warn("Message signed outside of X.509 validity window\n");
322 			return -EKEYREJECTED;
323 		}
324 	}
325 
326 	/* Verify the PKCS#7 binary against the key */
327 	ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
328 	if (ret < 0)
329 		return ret;
330 
331 	pr_devel("Verified signature %u\n", sinfo->index);
332 
333 	/* Verify the internal certificate chain */
334 	return pkcs7_verify_sig_chain(pkcs7, sinfo);
335 }
336 
337 /**
338  * pkcs7_verify - Verify a PKCS#7 message
339  * @pkcs7: The PKCS#7 message to be verified
340  * @usage: The use to which the key is being put
341  *
342  * Verify a PKCS#7 message is internally consistent - that is, the data digest
343  * matches the digest in the AuthAttrs and any signature in the message or one
344  * of the X.509 certificates it carries that matches another X.509 cert in the
345  * message can be verified.
346  *
347  * This does not look to match the contents of the PKCS#7 message against any
348  * external public keys.
349  *
350  * Returns, in order of descending priority:
351  *
352  *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
353  *      odds with the specified usage, or:
354  *
355  *  (*) -EKEYREJECTED if a signature failed to match for which we found an
356  *	appropriate X.509 certificate, or:
357  *
358  *  (*) -EBADMSG if some part of the message was invalid, or:
359  *
360  *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
361  *	crypto modules couldn't be found, or:
362  *
363  *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
364  *	(note that a signature chain may be of zero length), or:
365  */
366 int pkcs7_verify(struct pkcs7_message *pkcs7,
367 		 enum key_being_used_for usage)
368 {
369 	struct pkcs7_signed_info *sinfo;
370 	int enopkg = -ENOPKG;
371 	int ret;
372 
373 	kenter("");
374 
375 	switch (usage) {
376 	case VERIFYING_MODULE_SIGNATURE:
377 		if (pkcs7->data_type != OID_data) {
378 			pr_warn("Invalid module sig (not pkcs7-data)\n");
379 			return -EKEYREJECTED;
380 		}
381 		if (pkcs7->have_authattrs) {
382 			pr_warn("Invalid module sig (has authattrs)\n");
383 			return -EKEYREJECTED;
384 		}
385 		break;
386 	case VERIFYING_FIRMWARE_SIGNATURE:
387 		if (pkcs7->data_type != OID_data) {
388 			pr_warn("Invalid firmware sig (not pkcs7-data)\n");
389 			return -EKEYREJECTED;
390 		}
391 		if (!pkcs7->have_authattrs) {
392 			pr_warn("Invalid firmware sig (missing authattrs)\n");
393 			return -EKEYREJECTED;
394 		}
395 		break;
396 	case VERIFYING_KEXEC_PE_SIGNATURE:
397 		if (pkcs7->data_type != OID_msIndirectData) {
398 			pr_warn("Invalid kexec sig (not Authenticode)\n");
399 			return -EKEYREJECTED;
400 		}
401 		/* Authattr presence checked in parser */
402 		break;
403 	case VERIFYING_UNSPECIFIED_SIGNATURE:
404 		if (pkcs7->data_type != OID_data) {
405 			pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
406 			return -EKEYREJECTED;
407 		}
408 		break;
409 	default:
410 		return -EINVAL;
411 	}
412 
413 	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
414 		ret = pkcs7_verify_one(pkcs7, sinfo);
415 		if (ret < 0) {
416 			if (ret == -ENOPKG) {
417 				sinfo->unsupported_crypto = true;
418 				continue;
419 			}
420 			kleave(" = %d", ret);
421 			return ret;
422 		}
423 		enopkg = 0;
424 	}
425 
426 	kleave(" = %d", enopkg);
427 	return enopkg;
428 }
429 EXPORT_SYMBOL_GPL(pkcs7_verify);
430 
431 /**
432  * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
433  * @pkcs7: The PKCS#7 message
434  * @data: The data to be verified
435  * @datalen: The amount of data
436  *
437  * Supply the detached data needed to verify a PKCS#7 message.  Note that no
438  * attempt to retain/pin the data is made.  That is left to the caller.  The
439  * data will not be modified by pkcs7_verify() and will not be freed when the
440  * PKCS#7 message is freed.
441  *
442  * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
443  */
444 int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
445 			       const void *data, size_t datalen)
446 {
447 	if (pkcs7->data) {
448 		pr_debug("Data already supplied\n");
449 		return -EINVAL;
450 	}
451 	pkcs7->data = data;
452 	pkcs7->data_len = datalen;
453 	return 0;
454 }
455