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08815b62 DH |
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> | |
db6c43bd | 20 | #include <crypto/public_key.h> |
08815b62 DH |
21 | #include "pkcs7_parser.h" |
22 | ||
08815b62 DH |
23 | /** |
24 | * Check the trust on one PKCS#7 SignedInfo block. | |
25 | */ | |
15155b9a DH |
26 | static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7, |
27 | struct pkcs7_signed_info *sinfo, | |
28 | struct key *trust_keyring) | |
08815b62 DH |
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 | ||
41559420 DH |
38 | if (sinfo->unsupported_crypto) { |
39 | kleave(" = -ENOPKG [cached]"); | |
40 | return -ENOPKG; | |
41 | } | |
42 | ||
08815b62 DH |
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 | */ | |
4573b64a DH |
57 | key = x509_request_asymmetric_key(trust_keyring, |
58 | x509->id, x509->skid, | |
f1b731db | 59 | false); |
757932e6 | 60 | if (!IS_ERR(key)) { |
08815b62 DH |
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 | */ | |
757932e6 DH |
66 | pr_devel("sinfo %u: Cert %u as key %x\n", |
67 | sinfo->index, x509->index, key_serial(key)); | |
08815b62 | 68 | goto matched; |
757932e6 | 69 | } |
08815b62 DH |
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 | */ | |
4573b64a DH |
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, | |
f1b731db | 93 | false); |
757932e6 DH |
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); | |
08815b62 DH |
102 | } |
103 | ||
757932e6 DH |
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, | |
f1b731db | 108 | sinfo->signing_cert_id, |
4573b64a | 109 | NULL, |
f1b731db | 110 | false); |
757932e6 DH |
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; | |
08815b62 DH |
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: | |
757932e6 DH |
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 | } | |
08815b62 DH |
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; | |
41559420 DH |
178 | int cached_ret = -ENOKEY; |
179 | int ret; | |
08815b62 DH |
180 | |
181 | for (p = pkcs7->certs; p; p = p->next) | |
182 | p->seen = false; | |
183 | ||
184 | for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) { | |
185 | ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring); | |
41559420 DH |
186 | switch (ret) { |
187 | case -ENOKEY: | |
188 | continue; | |
189 | case -ENOPKG: | |
190 | if (cached_ret == -ENOKEY) | |
08815b62 | 191 | cached_ret = -ENOPKG; |
41559420 DH |
192 | continue; |
193 | case 0: | |
194 | *_trusted |= sinfo->trusted; | |
195 | cached_ret = 0; | |
196 | continue; | |
197 | default: | |
198 | return ret; | |
08815b62 | 199 | } |
08815b62 DH |
200 | } |
201 | ||
202 | return cached_ret; | |
203 | } | |
204 | EXPORT_SYMBOL_GPL(pkcs7_validate_trust); |