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 */
25static 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(ALIGN(digest_size, __alignof__(*desc)) + desc_size,
53			 GFP_KERNEL);
54	if (!digest)
55		goto error_no_desc;
56
57	desc = PTR_ALIGN(digest + digest_size, __alignof__(*desc));
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, digest);
66	if (ret < 0)
67		goto error;
68	pr_devel("MsgDigest = [%*ph]\n", 8, digest);
69
70	/* However, if there are authenticated attributes, there must be a
71	 * message digest attribute amongst them which corresponds to the
72	 * digest we just calculated.
73	 */
74	if (sinfo->authattrs) {
75		u8 tag;
76
77		if (!sinfo->msgdigest) {
78			pr_warn("Sig %u: No messageDigest\n", sinfo->index);
79			ret = -EKEYREJECTED;
80			goto error;
81		}
82
83		if (sinfo->msgdigest_len != sinfo->sig.digest_size) {
84			pr_debug("Sig %u: Invalid digest size (%u)\n",
85				 sinfo->index, sinfo->msgdigest_len);
86			ret = -EBADMSG;
87			goto error;
88		}
89
90		if (memcmp(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) {
91			pr_debug("Sig %u: Message digest doesn't match\n",
92				 sinfo->index);
93			ret = -EKEYREJECTED;
94			goto error;
95		}
96
97		/* We then calculate anew, using the authenticated attributes
98		 * as the contents of the digest instead.  Note that we need to
99		 * convert the attributes from a CONT.0 into a SET before we
100		 * hash it.
101		 */
102		memset(digest, 0, sinfo->sig.digest_size);
103
104		ret = crypto_shash_init(desc);
105		if (ret < 0)
106			goto error;
107		tag = ASN1_CONS_BIT | ASN1_SET;
108		ret = crypto_shash_update(desc, &tag, 1);
109		if (ret < 0)
110			goto error;
111		ret = crypto_shash_finup(desc, sinfo->authattrs,
112					 sinfo->authattrs_len, digest);
113		if (ret < 0)
114			goto error;
115		pr_devel("AADigest = [%*ph]\n", 8, digest);
116	}
117
118	sinfo->sig.digest = digest;
119	digest = NULL;
120
121error:
122	kfree(digest);
123error_no_desc:
124	crypto_free_shash(tfm);
125	kleave(" = %d", ret);
126	return ret;
127}
128
129/*
130 * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
131 * uses the issuer's name and the issuing certificate serial number for
132 * matching purposes.  These must match the certificate issuer's name (not
133 * subject's name) and the certificate serial number [RFC 2315 6.7].
134 */
135static int pkcs7_find_key(struct pkcs7_message *pkcs7,
136			  struct pkcs7_signed_info *sinfo)
137{
138	struct x509_certificate *x509;
139	unsigned certix = 1;
140
141	kenter("%u", sinfo->index);
142
143	for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
144		/* I'm _assuming_ that the generator of the PKCS#7 message will
145		 * encode the fields from the X.509 cert in the same way in the
146		 * PKCS#7 message - but I can't be 100% sure of that.  It's
147		 * possible this will need element-by-element comparison.
148		 */
149		if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id))
150			continue;
151		pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
152			 sinfo->index, certix);
153
154		if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
155			pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
156				sinfo->index);
157			continue;
158		}
159
160		sinfo->signer = x509;
161		return 0;
162	}
163
164	/* The relevant X.509 cert isn't found here, but it might be found in
165	 * the trust keyring.
166	 */
167	pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
168		 sinfo->index,
169		 sinfo->signing_cert_id->len, sinfo->signing_cert_id->data);
170	return 0;
171}
172
173/*
174 * Verify the internal certificate chain as best we can.
175 */
176static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
177				  struct pkcs7_signed_info *sinfo)
178{
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		ret = x509_get_sig_params(x509);
194		if (ret < 0)
195			goto maybe_missing_crypto_in_x509;
196
197		pr_debug("- issuer %s\n", x509->issuer);
198		if (x509->akid_id)
199			pr_debug("- authkeyid.id %*phN\n",
200				 x509->akid_id->len, x509->akid_id->data);
201		if (x509->akid_skid)
202			pr_debug("- authkeyid.skid %*phN\n",
203				 x509->akid_skid->len, x509->akid_skid->data);
204
205		if ((!x509->akid_id && !x509->akid_skid) ||
206		    strcmp(x509->subject, x509->issuer) == 0) {
207			/* If there's no authority certificate specified, then
208			 * the certificate must be self-signed and is the root
209			 * of the chain.  Likewise if the cert is its own
210			 * authority.
211			 */
212			pr_debug("- no auth?\n");
213			if (x509->raw_subject_size != x509->raw_issuer_size ||
214			    memcmp(x509->raw_subject, x509->raw_issuer,
215				   x509->raw_issuer_size) != 0)
216				return 0;
217
218			ret = x509_check_signature(x509->pub, x509);
219			if (ret < 0)
220				goto maybe_missing_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 = x509->akid_id;
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 {
239			auth = x509->akid_skid;
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 (x509->akid_skid &&
260		    !asymmetric_key_id_same(p->skid, x509->akid_skid)) {
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 = x509_check_signature(p->pub, x509);
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
284maybe_missing_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->missing_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	if (ret == -ENOPKG)
292		return 0;
293	return ret;
294}
295
296/*
297 * Verify one signed information block from a PKCS#7 message.
298 */
299static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
300			    struct pkcs7_signed_info *sinfo)
301{
302	int ret;
303
304	kenter(",%u", sinfo->index);
305
306	/* First of all, digest the data in the PKCS#7 message and the
307	 * signed information block
308	 */
309	ret = pkcs7_digest(pkcs7, sinfo);
310	if (ret < 0)
311		return ret;
312
313	/* Find the key for the signature if there is one */
314	ret = pkcs7_find_key(pkcs7, sinfo);
315	if (ret < 0)
316		return ret;
317
318	if (!sinfo->signer)
319		return 0;
320
321	pr_devel("Using X.509[%u] for sig %u\n",
322		 sinfo->signer->index, sinfo->index);
323
324	/* Check that the PKCS#7 signing time is valid according to the X.509
325	 * certificate.  We can't, however, check against the system clock
326	 * since that may not have been set yet and may be wrong.
327	 */
328	if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
329		if (sinfo->signing_time < sinfo->signer->valid_from ||
330		    sinfo->signing_time > sinfo->signer->valid_to) {
331			pr_warn("Message signed outside of X.509 validity window\n");
332			return -EKEYREJECTED;
333		}
334	}
335
336	/* Verify the PKCS#7 binary against the key */
337	ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
338	if (ret < 0)
339		return ret;
340
341	pr_devel("Verified signature %u\n", sinfo->index);
342
343	/* Verify the internal certificate chain */
344	return pkcs7_verify_sig_chain(pkcs7, sinfo);
345}
346
347/**
348 * pkcs7_verify - Verify a PKCS#7 message
349 * @pkcs7: The PKCS#7 message to be verified
350 * @usage: The use to which the key is being put
351 *
352 * Verify a PKCS#7 message is internally consistent - that is, the data digest
353 * matches the digest in the AuthAttrs and any signature in the message or one
354 * of the X.509 certificates it carries that matches another X.509 cert in the
355 * message can be verified.
356 *
357 * This does not look to match the contents of the PKCS#7 message against any
358 * external public keys.
359 *
360 * Returns, in order of descending priority:
361 *
362 *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
363 *      odds with the specified usage, or:
364 *
365 *  (*) -EKEYREJECTED if a signature failed to match for which we found an
366 *	appropriate X.509 certificate, or:
367 *
368 *  (*) -EBADMSG if some part of the message was invalid, or:
369 *
370 *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
371 *	crypto modules couldn't be found, or:
372 *
373 *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
374 *	(note that a signature chain may be of zero length), or:
375 */
376int pkcs7_verify(struct pkcs7_message *pkcs7,
377		 enum key_being_used_for usage)
378{
379	struct pkcs7_signed_info *sinfo;
380	struct x509_certificate *x509;
381	int enopkg = -ENOPKG;
382	int ret, n;
383
384	kenter("");
385
386	switch (usage) {
387	case VERIFYING_MODULE_SIGNATURE:
388		if (pkcs7->data_type != OID_data) {
389			pr_warn("Invalid module sig (not pkcs7-data)\n");
390			return -EKEYREJECTED;
391		}
392		if (pkcs7->have_authattrs) {
393			pr_warn("Invalid module sig (has authattrs)\n");
394			return -EKEYREJECTED;
395		}
396		break;
397	case VERIFYING_FIRMWARE_SIGNATURE:
398		if (pkcs7->data_type != OID_data) {
399			pr_warn("Invalid firmware sig (not pkcs7-data)\n");
400			return -EKEYREJECTED;
401		}
402		if (!pkcs7->have_authattrs) {
403			pr_warn("Invalid firmware sig (missing authattrs)\n");
404			return -EKEYREJECTED;
405		}
406		break;
407	case VERIFYING_KEXEC_PE_SIGNATURE:
408		if (pkcs7->data_type != OID_msIndirectData) {
409			pr_warn("Invalid kexec sig (not Authenticode)\n");
410			return -EKEYREJECTED;
411		}
412		/* Authattr presence checked in parser */
413		break;
414	case VERIFYING_UNSPECIFIED_SIGNATURE:
415		if (pkcs7->data_type != OID_data) {
416			pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
417			return -EKEYREJECTED;
418		}
419		break;
420	default:
421		return -EINVAL;
422	}
423
424	for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
425		ret = x509_get_sig_params(x509);
426		if (ret < 0)
427			return ret;
428	}
429
430	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
431		ret = pkcs7_verify_one(pkcs7, sinfo);
432		if (ret < 0) {
433			if (ret == -ENOPKG) {
434				sinfo->unsupported_crypto = true;
435				continue;
436			}
437			kleave(" = %d", ret);
438			return ret;
439		}
440		enopkg = 0;
441	}
442
443	kleave(" = %d", enopkg);
444	return enopkg;
445}
446EXPORT_SYMBOL_GPL(pkcs7_verify);
447
448/**
449 * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
450 * @pkcs7: The PKCS#7 message
451 * @data: The data to be verified
452 * @datalen: The amount of data
453 *
454 * Supply the detached data needed to verify a PKCS#7 message.  Note that no
455 * attempt to retain/pin the data is made.  That is left to the caller.  The
456 * data will not be modified by pkcs7_verify() and will not be freed when the
457 * PKCS#7 message is freed.
458 *
459 * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
460 */
461int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
462			       const void *data, size_t datalen)
463{
464	if (pkcs7->data) {
465		pr_debug("Data already supplied\n");
466		return -EINVAL;
467	}
468	pkcs7->data = data;
469	pkcs7->data_len = datalen;
470	return 0;
471}
472