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 <linux/err.h>
17 #include <linux/mpi.h>
18 #include <linux/asn1_decoder.h>
19 #include <keys/asymmetric-subtype.h>
20 #include <keys/asymmetric-parser.h>
21 #include <keys/system_keyring.h>
22 #include <crypto/hash.h>
23 #include "asymmetric_keys.h"
24 #include "public_key.h"
25 #include "x509_parser.h"
26 
27 static bool use_builtin_keys;
28 static struct asymmetric_key_id *ca_keyid;
29 
30 #ifndef MODULE
31 static struct {
32 	struct asymmetric_key_id id;
33 	unsigned char data[10];
34 } cakey;
35 
36 static int __init ca_keys_setup(char *str)
37 {
38 	if (!str)		/* default system keyring */
39 		return 1;
40 
41 	if (strncmp(str, "id:", 3) == 0) {
42 		struct asymmetric_key_id *p = &cakey.id;
43 		size_t hexlen = (strlen(str) - 3) / 2;
44 		int ret;
45 
46 		if (hexlen == 0 || hexlen > sizeof(cakey.data)) {
47 			pr_err("Missing or invalid ca_keys id\n");
48 			return 1;
49 		}
50 
51 		ret = __asymmetric_key_hex_to_key_id(str + 3, p, hexlen);
52 		if (ret < 0)
53 			pr_err("Unparsable ca_keys id hex string\n");
54 		else
55 			ca_keyid = p;	/* owner key 'id:xxxxxx' */
56 	} else if (strcmp(str, "builtin") == 0) {
57 		use_builtin_keys = true;
58 	}
59 
60 	return 1;
61 }
62 __setup("ca_keys=", ca_keys_setup);
63 #endif
64 
65 /**
66  * x509_request_asymmetric_key - Request a key by X.509 certificate params.
67  * @keyring: The keys to search.
68  * @kid: The key ID.
69  * @partial: Use partial match if true, exact if false.
70  *
71  * Find a key in the given keyring by subject name and key ID.  These might,
72  * for instance, be the issuer name and the authority key ID of an X.509
73  * certificate that needs to be verified.
74  */
75 struct key *x509_request_asymmetric_key(struct key *keyring,
76 					const struct asymmetric_key_id *kid,
77 					bool partial)
78 {
79 	key_ref_t key;
80 	char *id, *p;
81 
82 	/* Construct an identifier "id:<keyid>". */
83 	p = id = kmalloc(2 + 1 + kid->len * 2 + 1, GFP_KERNEL);
84 	if (!id)
85 		return ERR_PTR(-ENOMEM);
86 
87 	if (partial) {
88 		*p++ = 'i';
89 		*p++ = 'd';
90 	} else {
91 		*p++ = 'e';
92 		*p++ = 'x';
93 	}
94 	*p++ = ':';
95 	p = bin2hex(p, kid->data, kid->len);
96 	*p = 0;
97 
98 	pr_debug("Look up: \"%s\"\n", id);
99 
100 	key = keyring_search(make_key_ref(keyring, 1),
101 			     &key_type_asymmetric, id);
102 	if (IS_ERR(key))
103 		pr_debug("Request for key '%s' err %ld\n", id, PTR_ERR(key));
104 	kfree(id);
105 
106 	if (IS_ERR(key)) {
107 		switch (PTR_ERR(key)) {
108 			/* Hide some search errors */
109 		case -EACCES:
110 		case -ENOTDIR:
111 		case -EAGAIN:
112 			return ERR_PTR(-ENOKEY);
113 		default:
114 			return ERR_CAST(key);
115 		}
116 	}
117 
118 	pr_devel("<==%s() = 0 [%x]\n", __func__,
119 		 key_serial(key_ref_to_ptr(key)));
120 	return key_ref_to_ptr(key);
121 }
122 EXPORT_SYMBOL_GPL(x509_request_asymmetric_key);
123 
124 /*
125  * Set up the signature parameters in an X.509 certificate.  This involves
126  * digesting the signed data and extracting the signature.
127  */
128 int x509_get_sig_params(struct x509_certificate *cert)
129 {
130 	struct crypto_shash *tfm;
131 	struct shash_desc *desc;
132 	size_t digest_size, desc_size;
133 	void *digest;
134 	int ret;
135 
136 	pr_devel("==>%s()\n", __func__);
137 
138 	if (cert->unsupported_crypto)
139 		return -ENOPKG;
140 	if (cert->sig.rsa.s)
141 		return 0;
142 
143 	cert->sig.rsa.s = mpi_read_raw_data(cert->raw_sig, cert->raw_sig_size);
144 	if (!cert->sig.rsa.s)
145 		return -ENOMEM;
146 	cert->sig.nr_mpi = 1;
147 
148 	/* Allocate the hashing algorithm we're going to need and find out how
149 	 * big the hash operational data will be.
150 	 */
151 	tfm = crypto_alloc_shash(hash_algo_name[cert->sig.pkey_hash_algo], 0, 0);
152 	if (IS_ERR(tfm)) {
153 		if (PTR_ERR(tfm) == -ENOENT) {
154 			cert->unsupported_crypto = true;
155 			return -ENOPKG;
156 		}
157 		return PTR_ERR(tfm);
158 	}
159 
160 	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
161 	digest_size = crypto_shash_digestsize(tfm);
162 
163 	/* We allocate the hash operational data storage on the end of the
164 	 * digest storage space.
165 	 */
166 	ret = -ENOMEM;
167 	digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
168 	if (!digest)
169 		goto error;
170 
171 	cert->sig.digest = digest;
172 	cert->sig.digest_size = digest_size;
173 
174 	desc = digest + digest_size;
175 	desc->tfm = tfm;
176 	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
177 
178 	ret = crypto_shash_init(desc);
179 	if (ret < 0)
180 		goto error;
181 	might_sleep();
182 	ret = crypto_shash_finup(desc, cert->tbs, cert->tbs_size, digest);
183 error:
184 	crypto_free_shash(tfm);
185 	pr_devel("<==%s() = %d\n", __func__, ret);
186 	return ret;
187 }
188 EXPORT_SYMBOL_GPL(x509_get_sig_params);
189 
190 /*
191  * Check the signature on a certificate using the provided public key
192  */
193 int x509_check_signature(const struct public_key *pub,
194 			 struct x509_certificate *cert)
195 {
196 	int ret;
197 
198 	pr_devel("==>%s()\n", __func__);
199 
200 	ret = x509_get_sig_params(cert);
201 	if (ret < 0)
202 		return ret;
203 
204 	ret = public_key_verify_signature(pub, &cert->sig);
205 	if (ret == -ENOPKG)
206 		cert->unsupported_crypto = true;
207 	pr_debug("Cert Verification: %d\n", ret);
208 	return ret;
209 }
210 EXPORT_SYMBOL_GPL(x509_check_signature);
211 
212 /*
213  * Check the new certificate against the ones in the trust keyring.  If one of
214  * those is the signing key and validates the new certificate, then mark the
215  * new certificate as being trusted.
216  *
217  * Return 0 if the new certificate was successfully validated, 1 if we couldn't
218  * find a matching parent certificate in the trusted list and an error if there
219  * is a matching certificate but the signature check fails.
220  */
221 static int x509_validate_trust(struct x509_certificate *cert,
222 			       struct key *trust_keyring)
223 {
224 	struct key *key;
225 	int ret = 1;
226 
227 	if (!trust_keyring)
228 		return -EOPNOTSUPP;
229 
230 	if (ca_keyid && !asymmetric_key_id_partial(cert->authority, ca_keyid))
231 		return -EPERM;
232 
233 	key = x509_request_asymmetric_key(trust_keyring, cert->authority,
234 					  false);
235 	if (!IS_ERR(key))  {
236 		if (!use_builtin_keys
237 		    || test_bit(KEY_FLAG_BUILTIN, &key->flags))
238 			ret = x509_check_signature(key->payload.data, cert);
239 		key_put(key);
240 	}
241 	return ret;
242 }
243 
244 /*
245  * Attempt to parse a data blob for a key as an X509 certificate.
246  */
247 static int x509_key_preparse(struct key_preparsed_payload *prep)
248 {
249 	struct asymmetric_key_ids *kids;
250 	struct x509_certificate *cert;
251 	const char *q;
252 	size_t srlen, sulen;
253 	char *desc = NULL, *p;
254 	int ret;
255 
256 	cert = x509_cert_parse(prep->data, prep->datalen);
257 	if (IS_ERR(cert))
258 		return PTR_ERR(cert);
259 
260 	pr_devel("Cert Issuer: %s\n", cert->issuer);
261 	pr_devel("Cert Subject: %s\n", cert->subject);
262 
263 	if (cert->pub->pkey_algo >= PKEY_ALGO__LAST ||
264 	    cert->sig.pkey_algo >= PKEY_ALGO__LAST ||
265 	    cert->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
266 	    !pkey_algo[cert->pub->pkey_algo] ||
267 	    !pkey_algo[cert->sig.pkey_algo] ||
268 	    !hash_algo_name[cert->sig.pkey_hash_algo]) {
269 		ret = -ENOPKG;
270 		goto error_free_cert;
271 	}
272 
273 	pr_devel("Cert Key Algo: %s\n", pkey_algo_name[cert->pub->pkey_algo]);
274 	pr_devel("Cert Valid From: %04ld-%02d-%02d %02d:%02d:%02d\n",
275 		 cert->valid_from.tm_year + 1900, cert->valid_from.tm_mon + 1,
276 		 cert->valid_from.tm_mday, cert->valid_from.tm_hour,
277 		 cert->valid_from.tm_min,  cert->valid_from.tm_sec);
278 	pr_devel("Cert Valid To: %04ld-%02d-%02d %02d:%02d:%02d\n",
279 		 cert->valid_to.tm_year + 1900, cert->valid_to.tm_mon + 1,
280 		 cert->valid_to.tm_mday, cert->valid_to.tm_hour,
281 		 cert->valid_to.tm_min,  cert->valid_to.tm_sec);
282 	pr_devel("Cert Signature: %s + %s\n",
283 		 pkey_algo_name[cert->sig.pkey_algo],
284 		 hash_algo_name[cert->sig.pkey_hash_algo]);
285 
286 	cert->pub->algo = pkey_algo[cert->pub->pkey_algo];
287 	cert->pub->id_type = PKEY_ID_X509;
288 
289 	/* Check the signature on the key if it appears to be self-signed */
290 	if (!cert->authority ||
291 	    asymmetric_key_id_same(cert->skid, cert->authority)) {
292 		ret = x509_check_signature(cert->pub, cert); /* self-signed */
293 		if (ret < 0)
294 			goto error_free_cert;
295 	} else if (!prep->trusted) {
296 		ret = x509_validate_trust(cert, get_system_trusted_keyring());
297 		if (!ret)
298 			prep->trusted = 1;
299 	}
300 
301 	/* Propose a description */
302 	sulen = strlen(cert->subject);
303 	if (cert->raw_skid) {
304 		srlen = cert->raw_skid_size;
305 		q = cert->raw_skid;
306 	} else {
307 		srlen = cert->raw_serial_size;
308 		q = cert->raw_serial;
309 	}
310 	if (srlen > 1 && *q == 0) {
311 		srlen--;
312 		q++;
313 	}
314 
315 	ret = -ENOMEM;
316 	desc = kmalloc(sulen + 2 + srlen * 2 + 1, GFP_KERNEL);
317 	if (!desc)
318 		goto error_free_cert;
319 	p = memcpy(desc, cert->subject, sulen);
320 	p += sulen;
321 	*p++ = ':';
322 	*p++ = ' ';
323 	p = bin2hex(p, q, srlen);
324 	*p = 0;
325 
326 	kids = kmalloc(sizeof(struct asymmetric_key_ids), GFP_KERNEL);
327 	if (!kids)
328 		goto error_free_desc;
329 	kids->id[0] = cert->id;
330 	kids->id[1] = cert->skid;
331 
332 	/* We're pinning the module by being linked against it */
333 	__module_get(public_key_subtype.owner);
334 	prep->type_data[0] = &public_key_subtype;
335 	prep->type_data[1] = kids;
336 	prep->payload[0] = cert->pub;
337 	prep->description = desc;
338 	prep->quotalen = 100;
339 
340 	/* We've finished with the certificate */
341 	cert->pub = NULL;
342 	cert->id = NULL;
343 	cert->skid = NULL;
344 	desc = NULL;
345 	ret = 0;
346 
347 error_free_desc:
348 	kfree(desc);
349 error_free_cert:
350 	x509_free_certificate(cert);
351 	return ret;
352 }
353 
354 static struct asymmetric_key_parser x509_key_parser = {
355 	.owner	= THIS_MODULE,
356 	.name	= "x509",
357 	.parse	= x509_key_preparse,
358 };
359 
360 /*
361  * Module stuff
362  */
363 static int __init x509_key_init(void)
364 {
365 	return register_asymmetric_key_parser(&x509_key_parser);
366 }
367 
368 static void __exit x509_key_exit(void)
369 {
370 	unregister_asymmetric_key_parser(&x509_key_parser);
371 }
372 
373 module_init(x509_key_init);
374 module_exit(x509_key_exit);
375 
376 MODULE_DESCRIPTION("X.509 certificate parser");
377 MODULE_LICENSE("GPL");
378