1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Verify the signature on a PKCS#7 message.
3 *
4 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8#define pr_fmt(fmt) "PKCS7: "fmt
9#include <linux/kernel.h>
10#include <linux/export.h>
11#include <linux/slab.h>
12#include <linux/err.h>
13#include <linux/asn1.h>
14#include <crypto/hash.h>
15#include <crypto/hash_info.h>
16#include <crypto/public_key.h>
17#include "pkcs7_parser.h"
18
19/*
20 * Digest the relevant parts of the PKCS#7 data
21 */
22static int pkcs7_digest(struct pkcs7_message *pkcs7,
23			struct pkcs7_signed_info *sinfo)
24{
25	struct public_key_signature *sig = sinfo->sig;
26	struct crypto_shash *tfm;
27	struct shash_desc *desc;
28	size_t desc_size;
29	int ret;
30
31	kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);
32
33	/* The digest was calculated already. */
34	if (sig->digest)
35		return 0;
36
37	if (!sinfo->sig->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(sinfo->sig->hash_algo, 0, 0);
44	if (IS_ERR(tfm))
45		return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
46
47	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
48	sig->digest_size = crypto_shash_digestsize(tfm);
49
50	ret = -ENOMEM;
51	sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
52	if (!sig->digest)
53		goto error_no_desc;
54
55	desc = kzalloc(desc_size, GFP_KERNEL);
56	if (!desc)
57		goto error_no_desc;
58
59	desc->tfm   = tfm;
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_warn("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_warn("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
117error:
118	kfree(desc);
119error_no_desc:
120	crypto_free_shash(tfm);
121	kleave(" = %d", ret);
122	return ret;
123}
124
125int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf, u32 *len,
126		     enum hash_algo *hash_algo)
127{
128	struct pkcs7_signed_info *sinfo = pkcs7->signed_infos;
129	int i, ret;
130
131	/*
132	 * This function doesn't support messages with more than one signature.
133	 */
134	if (sinfo == NULL || sinfo->next != NULL)
135		return -EBADMSG;
136
137	ret = pkcs7_digest(pkcs7, sinfo);
138	if (ret)
139		return ret;
140
141	*buf = sinfo->sig->digest;
142	*len = sinfo->sig->digest_size;
143
144	i = match_string(hash_algo_name, HASH_ALGO__LAST,
145			 sinfo->sig->hash_algo);
146	if (i >= 0)
147		*hash_algo = i;
148
149	return 0;
150}
151
152/*
153 * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
154 * uses the issuer's name and the issuing certificate serial number for
155 * matching purposes.  These must match the certificate issuer's name (not
156 * subject's name) and the certificate serial number [RFC 2315 6.7].
157 */
158static int pkcs7_find_key(struct pkcs7_message *pkcs7,
159			  struct pkcs7_signed_info *sinfo)
160{
161	struct x509_certificate *x509;
162	unsigned certix = 1;
163
164	kenter("%u", sinfo->index);
165
166	for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
167		/* I'm _assuming_ that the generator of the PKCS#7 message will
168		 * encode the fields from the X.509 cert in the same way in the
169		 * PKCS#7 message - but I can't be 100% sure of that.  It's
170		 * possible this will need element-by-element comparison.
171		 */
172		if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
173			continue;
174		pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
175			 sinfo->index, certix);
176
177		sinfo->signer = x509;
178		return 0;
179	}
180
181	/* The relevant X.509 cert isn't found here, but it might be found in
182	 * the trust keyring.
183	 */
184	pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
185		 sinfo->index,
186		 sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
187	return 0;
188}
189
190/*
191 * Verify the internal certificate chain as best we can.
192 */
193static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
194				  struct pkcs7_signed_info *sinfo)
195{
196	struct public_key_signature *sig;
197	struct x509_certificate *x509 = sinfo->signer, *p;
198	struct asymmetric_key_id *auth;
199	int ret;
200
201	kenter("");
202
203	for (p = pkcs7->certs; p; p = p->next)
204		p->seen = false;
205
206	for (;;) {
207		pr_debug("verify %s: %*phN\n",
208			 x509->subject,
209			 x509->raw_serial_size, x509->raw_serial);
210		x509->seen = true;
211
212		if (x509->blacklisted) {
213			/* If this cert is blacklisted, then mark everything
214			 * that depends on this as blacklisted too.
215			 */
216			sinfo->blacklisted = true;
217			for (p = sinfo->signer; p != x509; p = p->signer)
218				p->blacklisted = true;
219			pr_debug("- blacklisted\n");
220			return 0;
221		}
222
223		pr_debug("- issuer %s\n", x509->issuer);
224		sig = x509->sig;
225		if (sig->auth_ids[0])
226			pr_debug("- authkeyid.id %*phN\n",
227				 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
228		if (sig->auth_ids[1])
229			pr_debug("- authkeyid.skid %*phN\n",
230				 sig->auth_ids[1]->len, sig->auth_ids[1]->data);
231
232		if (x509->self_signed) {
233			/* If there's no authority certificate specified, then
234			 * the certificate must be self-signed and is the root
235			 * of the chain.  Likewise if the cert is its own
236			 * authority.
237			 */
238			if (x509->unsupported_sig)
239				goto unsupported_sig_in_x509;
240			x509->signer = x509;
241			pr_debug("- self-signed\n");
242			return 0;
243		}
244
245		/* Look through the X.509 certificates in the PKCS#7 message's
246		 * list to see if the next one is there.
247		 */
248		auth = sig->auth_ids[0];
249		if (auth) {
250			pr_debug("- want %*phN\n", auth->len, auth->data);
251			for (p = pkcs7->certs; p; p = p->next) {
252				pr_debug("- cmp [%u] %*phN\n",
253					 p->index, p->id->len, p->id->data);
254				if (asymmetric_key_id_same(p->id, auth))
255					goto found_issuer_check_skid;
256			}
257		} else if (sig->auth_ids[1]) {
258			auth = sig->auth_ids[1];
259			pr_debug("- want %*phN\n", auth->len, auth->data);
260			for (p = pkcs7->certs; p; p = p->next) {
261				if (!p->skid)
262					continue;
263				pr_debug("- cmp [%u] %*phN\n",
264					 p->index, p->skid->len, p->skid->data);
265				if (asymmetric_key_id_same(p->skid, auth))
266					goto found_issuer;
267			}
268		}
269
270		/* We didn't find the root of this chain */
271		pr_debug("- top\n");
272		return 0;
273
274	found_issuer_check_skid:
275		/* We matched issuer + serialNumber, but if there's an
276		 * authKeyId.keyId, that must match the CA subjKeyId also.
277		 */
278		if (sig->auth_ids[1] &&
279		    !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
280			pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
281				sinfo->index, x509->index, p->index);
282			return -EKEYREJECTED;
283		}
284	found_issuer:
285		pr_debug("- subject %s\n", p->subject);
286		if (p->seen) {
287			pr_warn("Sig %u: X.509 chain contains loop\n",
288				sinfo->index);
289			return 0;
290		}
291		ret = public_key_verify_signature(p->pub, x509->sig);
292		if (ret < 0)
293			return ret;
294		x509->signer = p;
295		if (x509 == p) {
296			pr_debug("- self-signed\n");
297			return 0;
298		}
299		x509 = p;
300		might_sleep();
301	}
302
303unsupported_sig_in_x509:
304	/* Just prune the certificate chain at this point if we lack some
305	 * crypto module to go further.  Note, however, we don't want to set
306	 * sinfo->unsupported_crypto as the signed info block may still be
307	 * validatable against an X.509 cert lower in the chain that we have a
308	 * trusted copy of.
309	 */
310	return 0;
311}
312
313/*
314 * Verify one signed information block from a PKCS#7 message.
315 */
316static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
317			    struct pkcs7_signed_info *sinfo)
318{
319	int ret;
320
321	kenter(",%u", sinfo->index);
322
323	/* First of all, digest the data in the PKCS#7 message and the
324	 * signed information block
325	 */
326	ret = pkcs7_digest(pkcs7, sinfo);
327	if (ret < 0)
328		return ret;
329
330	/* Find the key for the signature if there is one */
331	ret = pkcs7_find_key(pkcs7, sinfo);
332	if (ret < 0)
333		return ret;
334
335	if (!sinfo->signer)
336		return 0;
337
338	pr_devel("Using X.509[%u] for sig %u\n",
339		 sinfo->signer->index, sinfo->index);
340
341	/* Check that the PKCS#7 signing time is valid according to the X.509
342	 * certificate.  We can't, however, check against the system clock
343	 * since that may not have been set yet and may be wrong.
344	 */
345	if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
346		if (sinfo->signing_time < sinfo->signer->valid_from ||
347		    sinfo->signing_time > sinfo->signer->valid_to) {
348			pr_warn("Message signed outside of X.509 validity window\n");
349			return -EKEYREJECTED;
350		}
351	}
352
353	/* Verify the PKCS#7 binary against the key */
354	ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
355	if (ret < 0)
356		return ret;
357
358	pr_devel("Verified signature %u\n", sinfo->index);
359
360	/* Verify the internal certificate chain */
361	return pkcs7_verify_sig_chain(pkcs7, sinfo);
362}
363
364/**
365 * pkcs7_verify - Verify a PKCS#7 message
366 * @pkcs7: The PKCS#7 message to be verified
367 * @usage: The use to which the key is being put
368 *
369 * Verify a PKCS#7 message is internally consistent - that is, the data digest
370 * matches the digest in the AuthAttrs and any signature in the message or one
371 * of the X.509 certificates it carries that matches another X.509 cert in the
372 * message can be verified.
373 *
374 * This does not look to match the contents of the PKCS#7 message against any
375 * external public keys.
376 *
377 * Returns, in order of descending priority:
378 *
379 *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
380 *      odds with the specified usage, or:
381 *
382 *  (*) -EKEYREJECTED if a signature failed to match for which we found an
383 *	appropriate X.509 certificate, or:
384 *
385 *  (*) -EBADMSG if some part of the message was invalid, or:
386 *
387 *  (*) 0 if a signature chain passed verification, or:
388 *
389 *  (*) -EKEYREJECTED if a blacklisted key was encountered, or:
390 *
391 *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
392 *	crypto modules couldn't be found.
393 */
394int pkcs7_verify(struct pkcs7_message *pkcs7,
395		 enum key_being_used_for usage)
396{
397	struct pkcs7_signed_info *sinfo;
398	int actual_ret = -ENOPKG;
399	int ret;
400
401	kenter("");
402
403	switch (usage) {
404	case VERIFYING_MODULE_SIGNATURE:
405		if (pkcs7->data_type != OID_data) {
406			pr_warn("Invalid module sig (not pkcs7-data)\n");
407			return -EKEYREJECTED;
408		}
409		if (pkcs7->have_authattrs) {
410			pr_warn("Invalid module sig (has authattrs)\n");
411			return -EKEYREJECTED;
412		}
413		break;
414	case VERIFYING_FIRMWARE_SIGNATURE:
415		if (pkcs7->data_type != OID_data) {
416			pr_warn("Invalid firmware sig (not pkcs7-data)\n");
417			return -EKEYREJECTED;
418		}
419		if (!pkcs7->have_authattrs) {
420			pr_warn("Invalid firmware sig (missing authattrs)\n");
421			return -EKEYREJECTED;
422		}
423		break;
424	case VERIFYING_KEXEC_PE_SIGNATURE:
425		if (pkcs7->data_type != OID_msIndirectData) {
426			pr_warn("Invalid kexec sig (not Authenticode)\n");
427			return -EKEYREJECTED;
428		}
429		/* Authattr presence checked in parser */
430		break;
431	case VERIFYING_UNSPECIFIED_SIGNATURE:
432		if (pkcs7->data_type != OID_data) {
433			pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
434			return -EKEYREJECTED;
435		}
436		break;
437	default:
438		return -EINVAL;
439	}
440
441	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
442		ret = pkcs7_verify_one(pkcs7, sinfo);
443		if (sinfo->blacklisted) {
444			if (actual_ret == -ENOPKG)
445				actual_ret = -EKEYREJECTED;
446			continue;
447		}
448		if (ret < 0) {
449			if (ret == -ENOPKG) {
450				sinfo->unsupported_crypto = true;
451				continue;
452			}
453			kleave(" = %d", ret);
454			return ret;
455		}
456		actual_ret = 0;
457	}
458
459	kleave(" = %d", actual_ret);
460	return actual_ret;
461}
462EXPORT_SYMBOL_GPL(pkcs7_verify);
463
464/**
465 * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
466 * @pkcs7: The PKCS#7 message
467 * @data: The data to be verified
468 * @datalen: The amount of data
469 *
470 * Supply the detached data needed to verify a PKCS#7 message.  Note that no
471 * attempt to retain/pin the data is made.  That is left to the caller.  The
472 * data will not be modified by pkcs7_verify() and will not be freed when the
473 * PKCS#7 message is freed.
474 *
475 * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
476 */
477int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
478			       const void *data, size_t datalen)
479{
480	if (pkcs7->data) {
481		pr_warn("Data already supplied\n");
482		return -EINVAL;
483	}
484	pkcs7->data = data;
485	pkcs7->data_len = datalen;
486	return 0;
487}
488EXPORT_SYMBOL_GPL(pkcs7_supply_detached_data);
489