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 
ca_keys_setup(char * str)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, -ENOPKG if the signature
71  * uses unsupported crypto, or some other error if there is a matching
72  * certificate but the signature check cannot be performed.
73  */
restrict_link_by_signature(struct key * dest_keyring,const struct key_type * type,const union key_payload * payload,struct key * trust_keyring)74 int restrict_link_by_signature(struct key *dest_keyring,
75 			       const struct key_type *type,
76 			       const union key_payload *payload,
77 			       struct key *trust_keyring)
78 {
79 	const struct public_key_signature *sig;
80 	struct key *key;
81 	int ret;
82 
83 	pr_devel("==>%s()\n", __func__);
84 
85 	if (!trust_keyring)
86 		return -ENOKEY;
87 
88 	if (type != &key_type_asymmetric)
89 		return -EOPNOTSUPP;
90 
91 	sig = payload->data[asym_auth];
92 	if (!sig)
93 		return -ENOPKG;
94 	if (!sig->auth_ids[0] && !sig->auth_ids[1])
95 		return -ENOKEY;
96 
97 	if (ca_keyid && !asymmetric_key_id_partial(sig->auth_ids[1], ca_keyid))
98 		return -EPERM;
99 
100 	/* See if we have a key that signed this one. */
101 	key = find_asymmetric_key(trust_keyring,
102 				  sig->auth_ids[0], sig->auth_ids[1],
103 				  false);
104 	if (IS_ERR(key))
105 		return -ENOKEY;
106 
107 	if (use_builtin_keys && !test_bit(KEY_FLAG_BUILTIN, &key->flags))
108 		ret = -ENOKEY;
109 	else
110 		ret = verify_signature(key, sig);
111 	key_put(key);
112 	return ret;
113 }
114 
match_either_id(const struct asymmetric_key_ids * pair,const struct asymmetric_key_id * single)115 static bool match_either_id(const struct asymmetric_key_ids *pair,
116 			    const struct asymmetric_key_id *single)
117 {
118 	return (asymmetric_key_id_same(pair->id[0], single) ||
119 		asymmetric_key_id_same(pair->id[1], single));
120 }
121 
key_or_keyring_common(struct key * dest_keyring,const struct key_type * type,const union key_payload * payload,struct key * trusted,bool check_dest)122 static int key_or_keyring_common(struct key *dest_keyring,
123 				 const struct key_type *type,
124 				 const union key_payload *payload,
125 				 struct key *trusted, bool check_dest)
126 {
127 	const struct public_key_signature *sig;
128 	struct key *key = NULL;
129 	int ret;
130 
131 	pr_devel("==>%s()\n", __func__);
132 
133 	if (!dest_keyring)
134 		return -ENOKEY;
135 	else if (dest_keyring->type != &key_type_keyring)
136 		return -EOPNOTSUPP;
137 
138 	if (!trusted && !check_dest)
139 		return -ENOKEY;
140 
141 	if (type != &key_type_asymmetric)
142 		return -EOPNOTSUPP;
143 
144 	sig = payload->data[asym_auth];
145 	if (!sig)
146 		return -ENOPKG;
147 	if (!sig->auth_ids[0] && !sig->auth_ids[1])
148 		return -ENOKEY;
149 
150 	if (trusted) {
151 		if (trusted->type == &key_type_keyring) {
152 			/* See if we have a key that signed this one. */
153 			key = find_asymmetric_key(trusted, sig->auth_ids[0],
154 						  sig->auth_ids[1], false);
155 			if (IS_ERR(key))
156 				key = NULL;
157 		} else if (trusted->type == &key_type_asymmetric) {
158 			const struct asymmetric_key_ids *signer_ids;
159 
160 			signer_ids = asymmetric_key_ids(trusted);
161 
162 			/*
163 			 * The auth_ids come from the candidate key (the
164 			 * one that is being considered for addition to
165 			 * dest_keyring) and identify the key that was
166 			 * used to sign.
167 			 *
168 			 * The signer_ids are identifiers for the
169 			 * signing key specified for dest_keyring.
170 			 *
171 			 * The first auth_id is the preferred id, and
172 			 * the second is the fallback. If only one
173 			 * auth_id is present, it may match against
174 			 * either signer_id. If two auth_ids are
175 			 * present, the first auth_id must match one
176 			 * signer_id and the second auth_id must match
177 			 * the second signer_id.
178 			 */
179 			if (!sig->auth_ids[0] || !sig->auth_ids[1]) {
180 				const struct asymmetric_key_id *auth_id;
181 
182 				auth_id = sig->auth_ids[0] ?: sig->auth_ids[1];
183 				if (match_either_id(signer_ids, auth_id))
184 					key = __key_get(trusted);
185 
186 			} else if (asymmetric_key_id_same(signer_ids->id[1],
187 							  sig->auth_ids[1]) &&
188 				   match_either_id(signer_ids,
189 						   sig->auth_ids[0])) {
190 				key = __key_get(trusted);
191 			}
192 		} else {
193 			return -EOPNOTSUPP;
194 		}
195 	}
196 
197 	if (check_dest && !key) {
198 		/* See if the destination has a key that signed this one. */
199 		key = find_asymmetric_key(dest_keyring, sig->auth_ids[0],
200 					  sig->auth_ids[1], false);
201 		if (IS_ERR(key))
202 			key = NULL;
203 	}
204 
205 	if (!key)
206 		return -ENOKEY;
207 
208 	ret = key_validate(key);
209 	if (ret == 0)
210 		ret = verify_signature(key, sig);
211 
212 	key_put(key);
213 	return ret;
214 }
215 
216 /**
217  * restrict_link_by_key_or_keyring - Restrict additions to a ring of public
218  * keys using the restrict_key information stored in the ring.
219  * @dest_keyring: Keyring being linked to.
220  * @type: The type of key being added.
221  * @payload: The payload of the new key.
222  * @trusted: A key or ring of keys that can be used to vouch for the new cert.
223  *
224  * Check the new certificate only against the key or keys passed in the data
225  * parameter. If one of those is the signing key and validates the new
226  * certificate, then mark the new certificate as being ok to link.
227  *
228  * Returns 0 if the new certificate was accepted, -ENOKEY if we
229  * couldn't find a matching parent certificate in the trusted list,
230  * -EKEYREJECTED if the signature check fails, -ENOPKG if the signature uses
231  * unsupported crypto, or some other error if there is a matching certificate
232  * but the signature check cannot be performed.
233  */
restrict_link_by_key_or_keyring(struct key * dest_keyring,const struct key_type * type,const union key_payload * payload,struct key * trusted)234 int restrict_link_by_key_or_keyring(struct key *dest_keyring,
235 				    const struct key_type *type,
236 				    const union key_payload *payload,
237 				    struct key *trusted)
238 {
239 	return key_or_keyring_common(dest_keyring, type, payload, trusted,
240 				     false);
241 }
242 
243 /**
244  * restrict_link_by_key_or_keyring_chain - Restrict additions to a ring of
245  * public keys using the restrict_key information stored in the ring.
246  * @dest_keyring: Keyring being linked to.
247  * @type: The type of key being added.
248  * @payload: The payload of the new key.
249  * @trusted: A key or ring of keys that can be used to vouch for the new cert.
250  *
251  * Check the new certificate only against the key or keys passed in the data
252  * parameter. If one of those is the signing key and validates the new
253  * certificate, then mark the new certificate as being ok to link.
254  *
255  * Returns 0 if the new certificate was accepted, -ENOKEY if we
256  * couldn't find a matching parent certificate in the trusted list,
257  * -EKEYREJECTED if the signature check fails, -ENOPKG if the signature uses
258  * unsupported crypto, or some other error if there is a matching certificate
259  * but the signature check cannot be performed.
260  */
restrict_link_by_key_or_keyring_chain(struct key * dest_keyring,const struct key_type * type,const union key_payload * payload,struct key * trusted)261 int restrict_link_by_key_or_keyring_chain(struct key *dest_keyring,
262 					  const struct key_type *type,
263 					  const union key_payload *payload,
264 					  struct key *trusted)
265 {
266 	return key_or_keyring_common(dest_keyring, type, payload, trusted,
267 				     true);
268 }
269