Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6
[sfrench/cifs-2.6.git] / crypto / asymmetric_keys / pkcs7_trust.c
1 /* Validate the trust chain of 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 <linux/key.h>
19 #include <keys/asymmetric-type.h>
20 #include <crypto/public_key.h>
21 #include "pkcs7_parser.h"
22
23 /**
24  * Check the trust on one PKCS#7 SignedInfo block.
25  */
26 static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
27                                     struct pkcs7_signed_info *sinfo,
28                                     struct key *trust_keyring)
29 {
30         struct public_key_signature *sig = &sinfo->sig;
31         struct x509_certificate *x509, *last = NULL, *p;
32         struct key *key;
33         bool trusted;
34         int ret;
35
36         kenter(",%u,", sinfo->index);
37
38         if (sinfo->unsupported_crypto) {
39                 kleave(" = -ENOPKG [cached]");
40                 return -ENOPKG;
41         }
42
43         for (x509 = sinfo->signer; x509; x509 = x509->signer) {
44                 if (x509->seen) {
45                         if (x509->verified) {
46                                 trusted = x509->trusted;
47                                 goto verified;
48                         }
49                         kleave(" = -ENOKEY [cached]");
50                         return -ENOKEY;
51                 }
52                 x509->seen = true;
53
54                 /* Look to see if this certificate is present in the trusted
55                  * keys.
56                  */
57                 key = x509_request_asymmetric_key(trust_keyring,
58                                                   x509->id, x509->skid,
59                                                   false);
60                 if (!IS_ERR(key)) {
61                         /* One of the X.509 certificates in the PKCS#7 message
62                          * is apparently the same as one we already trust.
63                          * Verify that the trusted variant can also validate
64                          * the signature on the descendant.
65                          */
66                         pr_devel("sinfo %u: Cert %u as key %x\n",
67                                  sinfo->index, x509->index, key_serial(key));
68                         goto matched;
69                 }
70                 if (key == ERR_PTR(-ENOMEM))
71                         return -ENOMEM;
72
73                  /* Self-signed certificates form roots of their own, and if we
74                   * don't know them, then we can't accept them.
75                   */
76                 if (x509->next == x509) {
77                         kleave(" = -ENOKEY [unknown self-signed]");
78                         return -ENOKEY;
79                 }
80
81                 might_sleep();
82                 last = x509;
83                 sig = &last->sig;
84         }
85
86         /* No match - see if the root certificate has a signer amongst the
87          * trusted keys.
88          */
89         if (last && (last->akid_id || last->akid_skid)) {
90                 key = x509_request_asymmetric_key(trust_keyring,
91                                                   last->akid_id,
92                                                   last->akid_skid,
93                                                   false);
94                 if (!IS_ERR(key)) {
95                         x509 = last;
96                         pr_devel("sinfo %u: Root cert %u signer is key %x\n",
97                                  sinfo->index, x509->index, key_serial(key));
98                         goto matched;
99                 }
100                 if (PTR_ERR(key) != -ENOKEY)
101                         return PTR_ERR(key);
102         }
103
104         /* As a last resort, see if we have a trusted public key that matches
105          * the signed info directly.
106          */
107         key = x509_request_asymmetric_key(trust_keyring,
108                                           sinfo->signing_cert_id,
109                                           NULL,
110                                           false);
111         if (!IS_ERR(key)) {
112                 pr_devel("sinfo %u: Direct signer is key %x\n",
113                          sinfo->index, key_serial(key));
114                 x509 = NULL;
115                 goto matched;
116         }
117         if (PTR_ERR(key) != -ENOKEY)
118                 return PTR_ERR(key);
119
120         kleave(" = -ENOKEY [no backref]");
121         return -ENOKEY;
122
123 matched:
124         ret = verify_signature(key, sig);
125         trusted = test_bit(KEY_FLAG_TRUSTED, &key->flags);
126         key_put(key);
127         if (ret < 0) {
128                 if (ret == -ENOMEM)
129                         return ret;
130                 kleave(" = -EKEYREJECTED [verify %d]", ret);
131                 return -EKEYREJECTED;
132         }
133
134 verified:
135         if (x509) {
136                 x509->verified = true;
137                 for (p = sinfo->signer; p != x509; p = p->signer) {
138                         p->verified = true;
139                         p->trusted = trusted;
140                 }
141         }
142         sinfo->trusted = trusted;
143         kleave(" = 0");
144         return 0;
145 }
146
147 /**
148  * pkcs7_validate_trust - Validate PKCS#7 trust chain
149  * @pkcs7: The PKCS#7 certificate to validate
150  * @trust_keyring: Signing certificates to use as starting points
151  * @_trusted: Set to true if trustworth, false otherwise
152  *
153  * Validate that the certificate chain inside the PKCS#7 message intersects
154  * keys we already know and trust.
155  *
156  * Returns, in order of descending priority:
157  *
158  *  (*) -EKEYREJECTED if a signature failed to match for which we have a valid
159  *      key, or:
160  *
161  *  (*) 0 if at least one signature chain intersects with the keys in the trust
162  *      keyring, or:
163  *
164  *  (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
165  *      chain.
166  *
167  *  (*) -ENOKEY if we couldn't find a match for any of the signature chains in
168  *      the message.
169  *
170  * May also return -ENOMEM.
171  */
172 int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
173                          struct key *trust_keyring,
174                          bool *_trusted)
175 {
176         struct pkcs7_signed_info *sinfo;
177         struct x509_certificate *p;
178         int cached_ret = -ENOKEY;
179         int ret;
180
181         *_trusted = false;
182
183         for (p = pkcs7->certs; p; p = p->next)
184                 p->seen = false;
185
186         for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
187                 ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
188                 switch (ret) {
189                 case -ENOKEY:
190                         continue;
191                 case -ENOPKG:
192                         if (cached_ret == -ENOKEY)
193                                 cached_ret = -ENOPKG;
194                         continue;
195                 case 0:
196                         *_trusted |= sinfo->trusted;
197                         cached_ret = 0;
198                         continue;
199                 default:
200                         return ret;
201                 }
202         }
203
204         return cached_ret;
205 }
206 EXPORT_SYMBOL_GPL(pkcs7_validate_trust);