xref: /linux/crypto/asymmetric_keys/restrict.c (revision 905e46acd3272d04566fec49afbd7ad9e2ed9ae3)
1 /* Instantiate a public key crypto key from an X.509 Certificate
2  *
3  * Copyright (C) 2012, 2016 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) "ASYM: "fmt
13 #include <linux/module.h>
14 #include <linux/kernel.h>
15 #include <linux/err.h>
16 #include <crypto/public_key.h>
17 #include "asymmetric_keys.h"
18 
19 static bool use_builtin_keys;
20 static struct asymmetric_key_id *ca_keyid;
21 
22 #ifndef MODULE
23 static struct {
24 	struct asymmetric_key_id id;
25 	unsigned char data[10];
26 } cakey;
27 
28 static int __init ca_keys_setup(char *str)
29 {
30 	if (!str)		/* default system keyring */
31 		return 1;
32 
33 	if (strncmp(str, "id:", 3) == 0) {
34 		struct asymmetric_key_id *p = &cakey.id;
35 		size_t hexlen = (strlen(str) - 3) / 2;
36 		int ret;
37 
38 		if (hexlen == 0 || hexlen > sizeof(cakey.data)) {
39 			pr_err("Missing or invalid ca_keys id\n");
40 			return 1;
41 		}
42 
43 		ret = __asymmetric_key_hex_to_key_id(str + 3, p, hexlen);
44 		if (ret < 0)
45 			pr_err("Unparsable ca_keys id hex string\n");
46 		else
47 			ca_keyid = p;	/* owner key 'id:xxxxxx' */
48 	} else if (strcmp(str, "builtin") == 0) {
49 		use_builtin_keys = true;
50 	}
51 
52 	return 1;
53 }
54 __setup("ca_keys=", ca_keys_setup);
55 #endif
56 
57 /**
58  * restrict_link_by_signature - Restrict additions to a ring of public keys
59  * @dest_keyring: Keyring being linked to.
60  * @type: The type of key being added.
61  * @payload: The payload of the new key.
62  * @trust_keyring: A ring of keys that can be used to vouch for the new cert.
63  *
64  * Check the new certificate against the ones in the trust keyring.  If one of
65  * those is the signing key and validates the new certificate, then mark the
66  * new certificate as being trusted.
67  *
68  * Returns 0 if the new certificate was accepted, -ENOKEY if we couldn't find a
69  * matching parent certificate in the trusted list, -EKEYREJECTED if the
70  * signature check fails or the key is blacklisted and some other error if
71  * there is a matching certificate but the signature check cannot be performed.
72  */
73 int restrict_link_by_signature(struct key *dest_keyring,
74 			       const struct key_type *type,
75 			       const union key_payload *payload,
76 			       struct key *trust_keyring)
77 {
78 	const struct public_key_signature *sig;
79 	struct key *key;
80 	int ret;
81 
82 	pr_devel("==>%s()\n", __func__);
83 
84 	if (!trust_keyring)
85 		return -ENOKEY;
86 
87 	if (type != &key_type_asymmetric)
88 		return -EOPNOTSUPP;
89 
90 	sig = payload->data[asym_auth];
91 	if (!sig->auth_ids[0] && !sig->auth_ids[1])
92 		return -ENOKEY;
93 
94 	if (ca_keyid && !asymmetric_key_id_partial(sig->auth_ids[1], ca_keyid))
95 		return -EPERM;
96 
97 	/* See if we have a key that signed this one. */
98 	key = find_asymmetric_key(trust_keyring,
99 				  sig->auth_ids[0], sig->auth_ids[1],
100 				  false);
101 	if (IS_ERR(key))
102 		return -ENOKEY;
103 
104 	if (use_builtin_keys && !test_bit(KEY_FLAG_BUILTIN, &key->flags))
105 		ret = -ENOKEY;
106 	else
107 		ret = verify_signature(key, sig);
108 	key_put(key);
109 	return ret;
110 }
111 
112 static bool match_either_id(const struct asymmetric_key_ids *pair,
113 			    const struct asymmetric_key_id *single)
114 {
115 	return (asymmetric_key_id_same(pair->id[0], single) ||
116 		asymmetric_key_id_same(pair->id[1], single));
117 }
118 
119 static int key_or_keyring_common(struct key *dest_keyring,
120 				 const struct key_type *type,
121 				 const union key_payload *payload,
122 				 struct key *trusted, bool check_dest)
123 {
124 	const struct public_key_signature *sig;
125 	struct key *key = NULL;
126 	int ret;
127 
128 	pr_devel("==>%s()\n", __func__);
129 
130 	if (!dest_keyring)
131 		return -ENOKEY;
132 	else if (dest_keyring->type != &key_type_keyring)
133 		return -EOPNOTSUPP;
134 
135 	if (!trusted && !check_dest)
136 		return -ENOKEY;
137 
138 	if (type != &key_type_asymmetric)
139 		return -EOPNOTSUPP;
140 
141 	sig = payload->data[asym_auth];
142 	if (!sig->auth_ids[0] && !sig->auth_ids[1])
143 		return -ENOKEY;
144 
145 	if (trusted) {
146 		if (trusted->type == &key_type_keyring) {
147 			/* See if we have a key that signed this one. */
148 			key = find_asymmetric_key(trusted, sig->auth_ids[0],
149 						  sig->auth_ids[1], false);
150 			if (IS_ERR(key))
151 				key = NULL;
152 		} else if (trusted->type == &key_type_asymmetric) {
153 			const struct asymmetric_key_ids *signer_ids;
154 
155 			signer_ids = asymmetric_key_ids(trusted);
156 
157 			/*
158 			 * The auth_ids come from the candidate key (the
159 			 * one that is being considered for addition to
160 			 * dest_keyring) and identify the key that was
161 			 * used to sign.
162 			 *
163 			 * The signer_ids are identifiers for the
164 			 * signing key specified for dest_keyring.
165 			 *
166 			 * The first auth_id is the preferred id, and
167 			 * the second is the fallback. If only one
168 			 * auth_id is present, it may match against
169 			 * either signer_id. If two auth_ids are
170 			 * present, the first auth_id must match one
171 			 * signer_id and the second auth_id must match
172 			 * the second signer_id.
173 			 */
174 			if (!sig->auth_ids[0] || !sig->auth_ids[1]) {
175 				const struct asymmetric_key_id *auth_id;
176 
177 				auth_id = sig->auth_ids[0] ?: sig->auth_ids[1];
178 				if (match_either_id(signer_ids, auth_id))
179 					key = __key_get(trusted);
180 
181 			} else if (asymmetric_key_id_same(signer_ids->id[1],
182 							  sig->auth_ids[1]) &&
183 				   match_either_id(signer_ids,
184 						   sig->auth_ids[0])) {
185 				key = __key_get(trusted);
186 			}
187 		} else {
188 			return -EOPNOTSUPP;
189 		}
190 	}
191 
192 	if (check_dest && !key) {
193 		/* See if the destination has a key that signed this one. */
194 		key = find_asymmetric_key(dest_keyring, sig->auth_ids[0],
195 					  sig->auth_ids[1], false);
196 		if (IS_ERR(key))
197 			key = NULL;
198 	}
199 
200 	if (!key)
201 		return -ENOKEY;
202 
203 	ret = key_validate(key);
204 	if (ret == 0)
205 		ret = verify_signature(key, sig);
206 
207 	key_put(key);
208 	return ret;
209 }
210 
211 /**
212  * restrict_link_by_key_or_keyring - Restrict additions to a ring of public
213  * keys using the restrict_key information stored in the ring.
214  * @dest_keyring: Keyring being linked to.
215  * @type: The type of key being added.
216  * @payload: The payload of the new key.
217  * @trusted: A key or ring of keys that can be used to vouch for the new cert.
218  *
219  * Check the new certificate only against the key or keys passed in the data
220  * parameter. If one of those is the signing key and validates the new
221  * certificate, then mark the new certificate as being ok to link.
222  *
223  * Returns 0 if the new certificate was accepted, -ENOKEY if we
224  * couldn't find a matching parent certificate in the trusted list,
225  * -EKEYREJECTED if the signature check fails, and some other error if
226  * there is a matching certificate but the signature check cannot be
227  * performed.
228  */
229 int restrict_link_by_key_or_keyring(struct key *dest_keyring,
230 				    const struct key_type *type,
231 				    const union key_payload *payload,
232 				    struct key *trusted)
233 {
234 	return key_or_keyring_common(dest_keyring, type, payload, trusted,
235 				     false);
236 }
237 
238 /**
239  * restrict_link_by_key_or_keyring_chain - Restrict additions to a ring of
240  * public keys using the restrict_key information stored in the ring.
241  * @dest_keyring: Keyring being linked to.
242  * @type: The type of key being added.
243  * @payload: The payload of the new key.
244  * @trusted: A key or ring of keys that can be used to vouch for the new cert.
245  *
246  * Check the new certificate only against the key or keys passed in the data
247  * parameter. If one of those is the signing key and validates the new
248  * certificate, then mark the new certificate as being ok to link.
249  *
250  * Returns 0 if the new certificate was accepted, -ENOKEY if we
251  * couldn't find a matching parent certificate in the trusted list,
252  * -EKEYREJECTED if the signature check fails, and some other error if
253  * there is a matching certificate but the signature check cannot be
254  * performed.
255  */
256 int restrict_link_by_key_or_keyring_chain(struct key *dest_keyring,
257 					  const struct key_type *type,
258 					  const union key_payload *payload,
259 					  struct key *trusted)
260 {
261 	return key_or_keyring_common(dest_keyring, type, payload, trusted,
262 				     true);
263 }
264