1 /* Verify the signature on a PKCS#7 message.
3 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
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.
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"
23 * Digest the relevant parts of the PKCS#7 data
25 static int pkcs7_digest(struct pkcs7_message *pkcs7,
26 struct pkcs7_signed_info *sinfo)
28 struct crypto_shash *tfm;
29 struct shash_desc *desc;
30 size_t digest_size, desc_size;
34 kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo);
36 if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
37 !hash_algo_name[sinfo->sig.pkey_hash_algo])
40 /* Allocate the hashing algorithm we're going to need and find out how
41 * big the hash operational data will be.
43 tfm = crypto_alloc_shash(hash_algo_name[sinfo->sig.pkey_hash_algo],
46 return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
48 desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
49 sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm);
52 digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
56 desc = digest + digest_size;
58 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
60 /* Digest the message [RFC2315 9.3] */
61 ret = crypto_shash_init(desc);
64 ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest);
67 pr_devel("MsgDigest = [%*ph]\n", 8, digest);
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.
73 if (sinfo->msgdigest) {
76 if (sinfo->msgdigest_len != sinfo->sig.digest_size) {
77 pr_debug("Sig %u: Invalid digest size (%u)\n",
78 sinfo->index, sinfo->msgdigest_len);
83 if (memcmp(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) {
84 pr_debug("Sig %u: Message digest doesn't match\n",
90 /* We then calculate anew, using the authenticated attributes
91 * as the contents of the digest instead. Note that we need to
92 * convert the attributes from a CONT.0 into a SET before we
95 memset(digest, 0, sinfo->sig.digest_size);
97 ret = crypto_shash_init(desc);
100 tag = ASN1_CONS_BIT | ASN1_SET;
101 ret = crypto_shash_update(desc, &tag, 1);
104 ret = crypto_shash_finup(desc, sinfo->authattrs,
105 sinfo->authattrs_len, digest);
108 pr_devel("AADigest = [%*ph]\n", 8, digest);
111 sinfo->sig.digest = digest;
117 crypto_free_shash(tfm);
118 kleave(" = %d", ret);
123 * Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7
124 * uses the issuer's name and the issuing certificate serial number for
125 * matching purposes. These must match the certificate issuer's name (not
126 * subject's name) and the certificate serial number [RFC 2315 6.7].
128 static int pkcs7_find_key(struct pkcs7_message *pkcs7,
129 struct pkcs7_signed_info *sinfo)
131 struct x509_certificate *x509;
134 kenter("%u", sinfo->index);
136 for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
137 /* I'm _assuming_ that the generator of the PKCS#7 message will
138 * encode the fields from the X.509 cert in the same way in the
139 * PKCS#7 message - but I can't be 100% sure of that. It's
140 * possible this will need element-by-element comparison.
142 if (!asymmetric_key_id_same(x509->id, sinfo->signing_cert_id))
144 pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
145 sinfo->index, certix);
147 if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
148 pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
153 sinfo->signer = x509;
157 /* The relevant X.509 cert isn't found here, but it might be found in
160 pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
162 sinfo->signing_cert_id->len, sinfo->signing_cert_id->data);
167 * Verify the internal certificate chain as best we can.
169 static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
170 struct pkcs7_signed_info *sinfo)
172 struct x509_certificate *x509 = sinfo->signer, *p;
177 for (p = pkcs7->certs; p; p = p->next)
181 pr_debug("verify %s: %*phN\n",
183 x509->raw_serial_size, x509->raw_serial);
185 ret = x509_get_sig_params(x509);
187 goto maybe_missing_crypto_in_x509;
189 pr_debug("- issuer %s\n", x509->issuer);
191 pr_debug("- authkeyid %*phN\n",
192 x509->authority->len, x509->authority->data);
194 if (!x509->authority ||
195 strcmp(x509->subject, x509->issuer) == 0) {
196 /* If there's no authority certificate specified, then
197 * the certificate must be self-signed and is the root
198 * of the chain. Likewise if the cert is its own
201 pr_debug("- no auth?\n");
202 if (x509->raw_subject_size != x509->raw_issuer_size ||
203 memcmp(x509->raw_subject, x509->raw_issuer,
204 x509->raw_issuer_size) != 0)
207 ret = x509_check_signature(x509->pub, x509);
209 goto maybe_missing_crypto_in_x509;
211 pr_debug("- self-signed\n");
215 /* Look through the X.509 certificates in the PKCS#7 message's
216 * list to see if the next one is there.
218 pr_debug("- want %*phN\n",
219 x509->authority->len, x509->authority->data);
220 for (p = pkcs7->certs; p; p = p->next) {
223 pr_debug("- cmp [%u] %*phN\n",
224 p->index, p->skid->len, p->skid->data);
225 if (asymmetric_key_id_same(p->skid, x509->authority))
229 /* We didn't find the root of this chain */
234 pr_debug("- subject %s\n", p->subject);
236 pr_warn("Sig %u: X.509 chain contains loop\n",
240 ret = x509_check_signature(p->pub, x509);
245 pr_debug("- self-signed\n");
252 maybe_missing_crypto_in_x509:
253 /* Just prune the certificate chain at this point if we lack some
254 * crypto module to go further. Note, however, we don't want to set
255 * sinfo->missing_crypto as the signed info block may still be
256 * validatable against an X.509 cert lower in the chain that we have a
265 * Verify one signed information block from a PKCS#7 message.
267 static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
268 struct pkcs7_signed_info *sinfo)
272 kenter(",%u", sinfo->index);
274 /* First of all, digest the data in the PKCS#7 message and the
275 * signed information block
277 ret = pkcs7_digest(pkcs7, sinfo);
281 /* Find the key for the signature if there is one */
282 ret = pkcs7_find_key(pkcs7, sinfo);
289 pr_devel("Using X.509[%u] for sig %u\n",
290 sinfo->signer->index, sinfo->index);
292 /* Verify the PKCS#7 binary against the key */
293 ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
297 pr_devel("Verified signature %u\n", sinfo->index);
299 /* Verify the internal certificate chain */
300 return pkcs7_verify_sig_chain(pkcs7, sinfo);
304 * pkcs7_verify - Verify a PKCS#7 message
305 * @pkcs7: The PKCS#7 message to be verified
307 * Verify a PKCS#7 message is internally consistent - that is, the data digest
308 * matches the digest in the AuthAttrs and any signature in the message or one
309 * of the X.509 certificates it carries that matches another X.509 cert in the
310 * message can be verified.
312 * This does not look to match the contents of the PKCS#7 message against any
313 * external public keys.
315 * Returns, in order of descending priority:
317 * (*) -EKEYREJECTED if a signature failed to match for which we found an
318 * appropriate X.509 certificate, or:
320 * (*) -EBADMSG if some part of the message was invalid, or:
322 * (*) -ENOPKG if none of the signature chains are verifiable because suitable
323 * crypto modules couldn't be found, or:
325 * (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
326 * (note that a signature chain may be of zero length), or:
328 int pkcs7_verify(struct pkcs7_message *pkcs7)
330 struct pkcs7_signed_info *sinfo;
331 struct x509_certificate *x509;
332 int enopkg = -ENOPKG;
337 for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
338 ret = x509_get_sig_params(x509);
341 pr_debug("X.509[%u] %*phN\n",
342 n, x509->authority->len, x509->authority->data);
345 for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
346 ret = pkcs7_verify_one(pkcs7, sinfo);
348 if (ret == -ENOPKG) {
349 sinfo->unsupported_crypto = true;
352 kleave(" = %d", ret);
358 kleave(" = %d", enopkg);
361 EXPORT_SYMBOL_GPL(pkcs7_verify);