1 /* Instantiate a public key crypto key from an X.509 Certificate
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) "X.509: "fmt
13 #include <linux/module.h>
14 #include <linux/kernel.h>
15 #include <linux/slab.h>
16 #include <keys/asymmetric-subtype.h>
17 #include <keys/asymmetric-parser.h>
18 #include <keys/system_keyring.h>
19 #include <crypto/hash.h>
20 #include "asymmetric_keys.h"
21 #include "x509_parser.h"
22 
23 /*
24  * Set up the signature parameters in an X.509 certificate.  This involves
25  * digesting the signed data and extracting the signature.
26  */
x509_get_sig_params(struct x509_certificate * cert)27 int x509_get_sig_params(struct x509_certificate *cert)
28 {
29 	struct public_key_signature *sig = cert->sig;
30 	struct crypto_shash *tfm;
31 	struct shash_desc *desc;
32 	size_t desc_size;
33 	int ret;
34 
35 	pr_devel("==>%s()\n", __func__);
36 
37 	if (!cert->pub->pkey_algo)
38 		cert->unsupported_key = true;
39 
40 	if (!sig->pkey_algo)
41 		cert->unsupported_sig = true;
42 
43 	/* We check the hash if we can - even if we can't then verify it */
44 	if (!sig->hash_algo) {
45 		cert->unsupported_sig = true;
46 		return 0;
47 	}
48 
49 	sig->s = kmemdup(cert->raw_sig, cert->raw_sig_size, GFP_KERNEL);
50 	if (!sig->s)
51 		return -ENOMEM;
52 
53 	sig->s_size = cert->raw_sig_size;
54 
55 	/* Allocate the hashing algorithm we're going to need and find out how
56 	 * big the hash operational data will be.
57 	 */
58 	tfm = crypto_alloc_shash(sig->hash_algo, 0, 0);
59 	if (IS_ERR(tfm)) {
60 		if (PTR_ERR(tfm) == -ENOENT) {
61 			cert->unsupported_sig = true;
62 			return 0;
63 		}
64 		return PTR_ERR(tfm);
65 	}
66 
67 	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
68 	sig->digest_size = crypto_shash_digestsize(tfm);
69 
70 	ret = -ENOMEM;
71 	sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
72 	if (!sig->digest)
73 		goto error;
74 
75 	desc = kzalloc(desc_size, GFP_KERNEL);
76 	if (!desc)
77 		goto error;
78 
79 	desc->tfm = tfm;
80 	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
81 
82 	ret = crypto_shash_digest(desc, cert->tbs, cert->tbs_size, sig->digest);
83 	if (ret < 0)
84 		goto error_2;
85 
86 	ret = is_hash_blacklisted(sig->digest, sig->digest_size, "tbs");
87 	if (ret == -EKEYREJECTED) {
88 		pr_err("Cert %*phN is blacklisted\n",
89 		       sig->digest_size, sig->digest);
90 		cert->blacklisted = true;
91 		ret = 0;
92 	}
93 
94 error_2:
95 	kfree(desc);
96 error:
97 	crypto_free_shash(tfm);
98 	pr_devel("<==%s() = %d\n", __func__, ret);
99 	return ret;
100 }
101 
102 /*
103  * Check for self-signedness in an X.509 cert and if found, check the signature
104  * immediately if we can.
105  */
x509_check_for_self_signed(struct x509_certificate * cert)106 int x509_check_for_self_signed(struct x509_certificate *cert)
107 {
108 	int ret = 0;
109 
110 	pr_devel("==>%s()\n", __func__);
111 
112 	if (cert->raw_subject_size != cert->raw_issuer_size ||
113 	    memcmp(cert->raw_subject, cert->raw_issuer,
114 		   cert->raw_issuer_size) != 0)
115 		goto not_self_signed;
116 
117 	if (cert->sig->auth_ids[0] || cert->sig->auth_ids[1]) {
118 		/* If the AKID is present it may have one or two parts.  If
119 		 * both are supplied, both must match.
120 		 */
121 		bool a = asymmetric_key_id_same(cert->skid, cert->sig->auth_ids[1]);
122 		bool b = asymmetric_key_id_same(cert->id, cert->sig->auth_ids[0]);
123 
124 		if (!a && !b)
125 			goto not_self_signed;
126 
127 		ret = -EKEYREJECTED;
128 		if (((a && !b) || (b && !a)) &&
129 		    cert->sig->auth_ids[0] && cert->sig->auth_ids[1])
130 			goto out;
131 	}
132 
133 	ret = -EKEYREJECTED;
134 	if (strcmp(cert->pub->pkey_algo, cert->sig->pkey_algo) != 0)
135 		goto out;
136 
137 	if (cert->unsupported_sig) {
138 		ret = 0;
139 		goto out;
140 	}
141 
142 	ret = public_key_verify_signature(cert->pub, cert->sig);
143 	if (ret < 0) {
144 		if (ret == -ENOPKG) {
145 			cert->unsupported_sig = true;
146 			ret = 0;
147 		}
148 		goto out;
149 	}
150 
151 	pr_devel("Cert Self-signature verified");
152 	cert->self_signed = true;
153 
154 out:
155 	pr_devel("<==%s() = %d\n", __func__, ret);
156 	return ret;
157 
158 not_self_signed:
159 	pr_devel("<==%s() = 0 [not]\n", __func__);
160 	return 0;
161 }
162 
163 /*
164  * Attempt to parse a data blob for a key as an X509 certificate.
165  */
x509_key_preparse(struct key_preparsed_payload * prep)166 static int x509_key_preparse(struct key_preparsed_payload *prep)
167 {
168 	struct asymmetric_key_ids *kids;
169 	struct x509_certificate *cert;
170 	const char *q;
171 	size_t srlen, sulen;
172 	char *desc = NULL, *p;
173 	int ret;
174 
175 	cert = x509_cert_parse(prep->data, prep->datalen);
176 	if (IS_ERR(cert))
177 		return PTR_ERR(cert);
178 
179 	pr_devel("Cert Issuer: %s\n", cert->issuer);
180 	pr_devel("Cert Subject: %s\n", cert->subject);
181 
182 	if (cert->unsupported_key) {
183 		ret = -ENOPKG;
184 		goto error_free_cert;
185 	}
186 
187 	pr_devel("Cert Key Algo: %s\n", cert->pub->pkey_algo);
188 	pr_devel("Cert Valid period: %lld-%lld\n", cert->valid_from, cert->valid_to);
189 
190 	cert->pub->id_type = "X509";
191 
192 	if (cert->unsupported_sig) {
193 		public_key_signature_free(cert->sig);
194 		cert->sig = NULL;
195 	} else {
196 		pr_devel("Cert Signature: %s + %s\n",
197 			 cert->sig->pkey_algo, cert->sig->hash_algo);
198 	}
199 
200 	/* Don't permit addition of blacklisted keys */
201 	ret = -EKEYREJECTED;
202 	if (cert->blacklisted)
203 		goto error_free_cert;
204 
205 	/* Propose a description */
206 	sulen = strlen(cert->subject);
207 	if (cert->raw_skid) {
208 		srlen = cert->raw_skid_size;
209 		q = cert->raw_skid;
210 	} else {
211 		srlen = cert->raw_serial_size;
212 		q = cert->raw_serial;
213 	}
214 
215 	ret = -ENOMEM;
216 	desc = kmalloc(sulen + 2 + srlen * 2 + 1, GFP_KERNEL);
217 	if (!desc)
218 		goto error_free_cert;
219 	p = memcpy(desc, cert->subject, sulen);
220 	p += sulen;
221 	*p++ = ':';
222 	*p++ = ' ';
223 	p = bin2hex(p, q, srlen);
224 	*p = 0;
225 
226 	kids = kmalloc(sizeof(struct asymmetric_key_ids), GFP_KERNEL);
227 	if (!kids)
228 		goto error_free_desc;
229 	kids->id[0] = cert->id;
230 	kids->id[1] = cert->skid;
231 
232 	/* We're pinning the module by being linked against it */
233 	__module_get(public_key_subtype.owner);
234 	prep->payload.data[asym_subtype] = &public_key_subtype;
235 	prep->payload.data[asym_key_ids] = kids;
236 	prep->payload.data[asym_crypto] = cert->pub;
237 	prep->payload.data[asym_auth] = cert->sig;
238 	prep->description = desc;
239 	prep->quotalen = 100;
240 
241 	/* We've finished with the certificate */
242 	cert->pub = NULL;
243 	cert->id = NULL;
244 	cert->skid = NULL;
245 	cert->sig = NULL;
246 	desc = NULL;
247 	ret = 0;
248 
249 error_free_desc:
250 	kfree(desc);
251 error_free_cert:
252 	x509_free_certificate(cert);
253 	return ret;
254 }
255 
256 static struct asymmetric_key_parser x509_key_parser = {
257 	.owner	= THIS_MODULE,
258 	.name	= "x509",
259 	.parse	= x509_key_preparse,
260 };
261 
262 /*
263  * Module stuff
264  */
x509_key_init(void)265 static int __init x509_key_init(void)
266 {
267 	return register_asymmetric_key_parser(&x509_key_parser);
268 }
269 
x509_key_exit(void)270 static void __exit x509_key_exit(void)
271 {
272 	unregister_asymmetric_key_parser(&x509_key_parser);
273 }
274 
275 module_init(x509_key_init);
276 module_exit(x509_key_exit);
277 
278 MODULE_DESCRIPTION("X.509 certificate parser");
279 MODULE_AUTHOR("Red Hat, Inc.");
280 MODULE_LICENSE("GPL");
281