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
27static bool use_builtin_keys;
28static struct asymmetric_key_id *ca_keyid;
29
30#ifndef MODULE
31static struct {
32	struct asymmetric_key_id id;
33	unsigned char data[10];
34} cakey;
35
36static 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 */
75struct 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}
122EXPORT_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 */
128int 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);
183error:
184	crypto_free_shash(tfm);
185	pr_devel("<==%s() = %d\n", __func__, ret);
186	return ret;
187}
188EXPORT_SYMBOL_GPL(x509_get_sig_params);
189
190/*
191 * Check the signature on a certificate using the provided public key
192 */
193int 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}
210EXPORT_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 */
221static 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->akid_skid, ca_keyid))
231		return -EPERM;
232
233	key = x509_request_asymmetric_key(trust_keyring, cert->akid_skid,
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 */
247static 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 period: %lld-%lld\n", cert->valid_from, cert->valid_to);
275	pr_devel("Cert Signature: %s + %s\n",
276		 pkey_algo_name[cert->sig.pkey_algo],
277		 hash_algo_name[cert->sig.pkey_hash_algo]);
278
279	cert->pub->algo = pkey_algo[cert->pub->pkey_algo];
280	cert->pub->id_type = PKEY_ID_X509;
281
282	/* Check the signature on the key if it appears to be self-signed */
283	if (!cert->akid_skid ||
284	    asymmetric_key_id_same(cert->skid, cert->akid_skid)) {
285		ret = x509_check_signature(cert->pub, cert); /* self-signed */
286		if (ret < 0)
287			goto error_free_cert;
288	} else if (!prep->trusted) {
289		ret = x509_validate_trust(cert, get_system_trusted_keyring());
290		if (!ret)
291			prep->trusted = 1;
292	}
293
294	/* Propose a description */
295	sulen = strlen(cert->subject);
296	if (cert->raw_skid) {
297		srlen = cert->raw_skid_size;
298		q = cert->raw_skid;
299	} else {
300		srlen = cert->raw_serial_size;
301		q = cert->raw_serial;
302	}
303
304	ret = -ENOMEM;
305	desc = kmalloc(sulen + 2 + srlen * 2 + 1, GFP_KERNEL);
306	if (!desc)
307		goto error_free_cert;
308	p = memcpy(desc, cert->subject, sulen);
309	p += sulen;
310	*p++ = ':';
311	*p++ = ' ';
312	p = bin2hex(p, q, srlen);
313	*p = 0;
314
315	kids = kmalloc(sizeof(struct asymmetric_key_ids), GFP_KERNEL);
316	if (!kids)
317		goto error_free_desc;
318	kids->id[0] = cert->id;
319	kids->id[1] = cert->skid;
320
321	/* We're pinning the module by being linked against it */
322	__module_get(public_key_subtype.owner);
323	prep->type_data[0] = &public_key_subtype;
324	prep->type_data[1] = kids;
325	prep->payload[0] = cert->pub;
326	prep->description = desc;
327	prep->quotalen = 100;
328
329	/* We've finished with the certificate */
330	cert->pub = NULL;
331	cert->id = NULL;
332	cert->skid = NULL;
333	desc = NULL;
334	ret = 0;
335
336error_free_desc:
337	kfree(desc);
338error_free_cert:
339	x509_free_certificate(cert);
340	return ret;
341}
342
343static struct asymmetric_key_parser x509_key_parser = {
344	.owner	= THIS_MODULE,
345	.name	= "x509",
346	.parse	= x509_key_preparse,
347};
348
349/*
350 * Module stuff
351 */
352static int __init x509_key_init(void)
353{
354	return register_asymmetric_key_parser(&x509_key_parser);
355}
356
357static void __exit x509_key_exit(void)
358{
359	unregister_asymmetric_key_parser(&x509_key_parser);
360}
361
362module_init(x509_key_init);
363module_exit(x509_key_exit);
364
365MODULE_DESCRIPTION("X.509 certificate parser");
366MODULE_LICENSE("GPL");
367