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  * @id: The issuer & serialNumber to look for or NULL.
69  * @skid: The subjectKeyIdentifier to look for or NULL.
70  * @partial: Use partial match if true, exact if false.
71  *
72  * Find a key in the given keyring by identifier.  The preferred identifier is
73  * the issuer + serialNumber and the fallback identifier is the
74  * subjectKeyIdentifier.  If both are given, the lookup is by the former, but
75  * the latter must also match.
76  */
77 struct key *x509_request_asymmetric_key(struct key *keyring,
78 					const struct asymmetric_key_id *id,
79 					const struct asymmetric_key_id *skid,
80 					bool partial)
81 {
82 	struct key *key;
83 	key_ref_t ref;
84 	const char *lookup;
85 	char *req, *p;
86 	int len;
87 
88 	if (id) {
89 		lookup = id->data;
90 		len = id->len;
91 	} else {
92 		lookup = skid->data;
93 		len = skid->len;
94 	}
95 
96 	/* Construct an identifier "id:<keyid>". */
97 	p = req = kmalloc(2 + 1 + len * 2 + 1, GFP_KERNEL);
98 	if (!req)
99 		return ERR_PTR(-ENOMEM);
100 
101 	if (partial) {
102 		*p++ = 'i';
103 		*p++ = 'd';
104 	} else {
105 		*p++ = 'e';
106 		*p++ = 'x';
107 	}
108 	*p++ = ':';
109 	p = bin2hex(p, lookup, len);
110 	*p = 0;
111 
112 	pr_debug("Look up: \"%s\"\n", req);
113 
114 	ref = keyring_search(make_key_ref(keyring, 1),
115 			     &key_type_asymmetric, req);
116 	if (IS_ERR(ref))
117 		pr_debug("Request for key '%s' err %ld\n", req, PTR_ERR(ref));
118 	kfree(req);
119 
120 	if (IS_ERR(ref)) {
121 		switch (PTR_ERR(ref)) {
122 			/* Hide some search errors */
123 		case -EACCES:
124 		case -ENOTDIR:
125 		case -EAGAIN:
126 			return ERR_PTR(-ENOKEY);
127 		default:
128 			return ERR_CAST(ref);
129 		}
130 	}
131 
132 	key = key_ref_to_ptr(ref);
133 	if (id && skid) {
134 		const struct asymmetric_key_ids *kids = asymmetric_key_ids(key);
135 		if (!kids->id[1]) {
136 			pr_debug("issuer+serial match, but expected SKID missing\n");
137 			goto reject;
138 		}
139 		if (!asymmetric_key_id_same(skid, kids->id[1])) {
140 			pr_debug("issuer+serial match, but SKID does not\n");
141 			goto reject;
142 		}
143 	}
144 
145 	pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key));
146 	return key;
147 
148 reject:
149 	key_put(key);
150 	return ERR_PTR(-EKEYREJECTED);
151 }
152 EXPORT_SYMBOL_GPL(x509_request_asymmetric_key);
153 
154 /*
155  * Set up the signature parameters in an X.509 certificate.  This involves
156  * digesting the signed data and extracting the signature.
157  */
158 int x509_get_sig_params(struct x509_certificate *cert)
159 {
160 	struct crypto_shash *tfm;
161 	struct shash_desc *desc;
162 	size_t digest_size, desc_size;
163 	void *digest;
164 	int ret;
165 
166 	pr_devel("==>%s()\n", __func__);
167 
168 	if (cert->unsupported_crypto)
169 		return -ENOPKG;
170 	if (cert->sig.rsa.s)
171 		return 0;
172 
173 	cert->sig.rsa.s = mpi_read_raw_data(cert->raw_sig, cert->raw_sig_size);
174 	if (!cert->sig.rsa.s)
175 		return -ENOMEM;
176 	cert->sig.nr_mpi = 1;
177 
178 	/* Allocate the hashing algorithm we're going to need and find out how
179 	 * big the hash operational data will be.
180 	 */
181 	tfm = crypto_alloc_shash(hash_algo_name[cert->sig.pkey_hash_algo], 0, 0);
182 	if (IS_ERR(tfm)) {
183 		if (PTR_ERR(tfm) == -ENOENT) {
184 			cert->unsupported_crypto = true;
185 			return -ENOPKG;
186 		}
187 		return PTR_ERR(tfm);
188 	}
189 
190 	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
191 	digest_size = crypto_shash_digestsize(tfm);
192 
193 	/* We allocate the hash operational data storage on the end of the
194 	 * digest storage space.
195 	 */
196 	ret = -ENOMEM;
197 	digest = kzalloc(ALIGN(digest_size, __alignof__(*desc)) + desc_size,
198 			 GFP_KERNEL);
199 	if (!digest)
200 		goto error;
201 
202 	cert->sig.digest = digest;
203 	cert->sig.digest_size = digest_size;
204 
205 	desc = PTR_ALIGN(digest + digest_size, __alignof__(*desc));
206 	desc->tfm = tfm;
207 	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
208 
209 	ret = crypto_shash_init(desc);
210 	if (ret < 0)
211 		goto error;
212 	might_sleep();
213 	ret = crypto_shash_finup(desc, cert->tbs, cert->tbs_size, digest);
214 error:
215 	crypto_free_shash(tfm);
216 	pr_devel("<==%s() = %d\n", __func__, ret);
217 	return ret;
218 }
219 EXPORT_SYMBOL_GPL(x509_get_sig_params);
220 
221 /*
222  * Check the signature on a certificate using the provided public key
223  */
224 int x509_check_signature(const struct public_key *pub,
225 			 struct x509_certificate *cert)
226 {
227 	int ret;
228 
229 	pr_devel("==>%s()\n", __func__);
230 
231 	ret = x509_get_sig_params(cert);
232 	if (ret < 0)
233 		return ret;
234 
235 	ret = public_key_verify_signature(pub, &cert->sig);
236 	if (ret == -ENOPKG)
237 		cert->unsupported_crypto = true;
238 	pr_debug("Cert Verification: %d\n", ret);
239 	return ret;
240 }
241 EXPORT_SYMBOL_GPL(x509_check_signature);
242 
243 /*
244  * Check the new certificate against the ones in the trust keyring.  If one of
245  * those is the signing key and validates the new certificate, then mark the
246  * new certificate as being trusted.
247  *
248  * Return 0 if the new certificate was successfully validated, 1 if we couldn't
249  * find a matching parent certificate in the trusted list and an error if there
250  * is a matching certificate but the signature check fails.
251  */
252 static int x509_validate_trust(struct x509_certificate *cert,
253 			       struct key *trust_keyring)
254 {
255 	struct key *key;
256 	int ret = 1;
257 
258 	if (!trust_keyring)
259 		return -EOPNOTSUPP;
260 
261 	if (ca_keyid && !asymmetric_key_id_partial(cert->akid_skid, ca_keyid))
262 		return -EPERM;
263 
264 	key = x509_request_asymmetric_key(trust_keyring,
265 					  cert->akid_id, cert->akid_skid,
266 					  false);
267 	if (!IS_ERR(key))  {
268 		if (!use_builtin_keys
269 		    || test_bit(KEY_FLAG_BUILTIN, &key->flags))
270 			ret = x509_check_signature(key->payload.data[asym_crypto],
271 						   cert);
272 		key_put(key);
273 	}
274 	return ret;
275 }
276 
277 /*
278  * Attempt to parse a data blob for a key as an X509 certificate.
279  */
280 static int x509_key_preparse(struct key_preparsed_payload *prep)
281 {
282 	struct asymmetric_key_ids *kids;
283 	struct x509_certificate *cert;
284 	const char *q;
285 	size_t srlen, sulen;
286 	char *desc = NULL, *p;
287 	int ret;
288 
289 	cert = x509_cert_parse(prep->data, prep->datalen);
290 	if (IS_ERR(cert))
291 		return PTR_ERR(cert);
292 
293 	pr_devel("Cert Issuer: %s\n", cert->issuer);
294 	pr_devel("Cert Subject: %s\n", cert->subject);
295 
296 	if (cert->pub->pkey_algo >= PKEY_ALGO__LAST ||
297 	    cert->sig.pkey_algo >= PKEY_ALGO__LAST ||
298 	    cert->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
299 	    !pkey_algo[cert->pub->pkey_algo] ||
300 	    !pkey_algo[cert->sig.pkey_algo] ||
301 	    !hash_algo_name[cert->sig.pkey_hash_algo]) {
302 		ret = -ENOPKG;
303 		goto error_free_cert;
304 	}
305 
306 	pr_devel("Cert Key Algo: %s\n", pkey_algo_name[cert->pub->pkey_algo]);
307 	pr_devel("Cert Valid period: %lld-%lld\n", cert->valid_from, cert->valid_to);
308 	pr_devel("Cert Signature: %s + %s\n",
309 		 pkey_algo_name[cert->sig.pkey_algo],
310 		 hash_algo_name[cert->sig.pkey_hash_algo]);
311 
312 	cert->pub->algo = pkey_algo[cert->pub->pkey_algo];
313 	cert->pub->id_type = PKEY_ID_X509;
314 
315 	/* Check the signature on the key if it appears to be self-signed */
316 	if ((!cert->akid_skid && !cert->akid_id) ||
317 	    asymmetric_key_id_same(cert->skid, cert->akid_skid) ||
318 	    asymmetric_key_id_same(cert->id, cert->akid_id)) {
319 		ret = x509_check_signature(cert->pub, cert); /* self-signed */
320 		if (ret < 0)
321 			goto error_free_cert;
322 	} else if (!prep->trusted) {
323 		ret = x509_validate_trust(cert, get_system_trusted_keyring());
324 		if (!ret)
325 			prep->trusted = 1;
326 	}
327 
328 	/* Propose a description */
329 	sulen = strlen(cert->subject);
330 	if (cert->raw_skid) {
331 		srlen = cert->raw_skid_size;
332 		q = cert->raw_skid;
333 	} else {
334 		srlen = cert->raw_serial_size;
335 		q = cert->raw_serial;
336 	}
337 
338 	ret = -ENOMEM;
339 	desc = kmalloc(sulen + 2 + srlen * 2 + 1, GFP_KERNEL);
340 	if (!desc)
341 		goto error_free_cert;
342 	p = memcpy(desc, cert->subject, sulen);
343 	p += sulen;
344 	*p++ = ':';
345 	*p++ = ' ';
346 	p = bin2hex(p, q, srlen);
347 	*p = 0;
348 
349 	kids = kmalloc(sizeof(struct asymmetric_key_ids), GFP_KERNEL);
350 	if (!kids)
351 		goto error_free_desc;
352 	kids->id[0] = cert->id;
353 	kids->id[1] = cert->skid;
354 
355 	/* We're pinning the module by being linked against it */
356 	__module_get(public_key_subtype.owner);
357 	prep->payload.data[asym_subtype] = &public_key_subtype;
358 	prep->payload.data[asym_key_ids] = kids;
359 	prep->payload.data[asym_crypto] = cert->pub;
360 	prep->description = desc;
361 	prep->quotalen = 100;
362 
363 	/* We've finished with the certificate */
364 	cert->pub = NULL;
365 	cert->id = NULL;
366 	cert->skid = NULL;
367 	desc = NULL;
368 	ret = 0;
369 
370 error_free_desc:
371 	kfree(desc);
372 error_free_cert:
373 	x509_free_certificate(cert);
374 	return ret;
375 }
376 
377 static struct asymmetric_key_parser x509_key_parser = {
378 	.owner	= THIS_MODULE,
379 	.name	= "x509",
380 	.parse	= x509_key_preparse,
381 };
382 
383 /*
384  * Module stuff
385  */
386 static int __init x509_key_init(void)
387 {
388 	return register_asymmetric_key_parser(&x509_key_parser);
389 }
390 
391 static void __exit x509_key_exit(void)
392 {
393 	unregister_asymmetric_key_parser(&x509_key_parser);
394 }
395 
396 module_init(x509_key_init);
397 module_exit(x509_key_exit);
398 
399 MODULE_DESCRIPTION("X.509 certificate parser");
400 MODULE_LICENSE("GPL");
401