xref: /openbmc/linux/certs/blacklist.c (revision c95e8f6f)
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* System hash blacklist.
3  *
4  * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
5  * Written by David Howells (dhowells@redhat.com)
6  */
7 
8 #define pr_fmt(fmt) "blacklist: "fmt
9 #include <linux/module.h>
10 #include <linux/slab.h>
11 #include <linux/key.h>
12 #include <linux/key-type.h>
13 #include <linux/sched.h>
14 #include <linux/ctype.h>
15 #include <linux/err.h>
16 #include <linux/seq_file.h>
17 #include <linux/uidgid.h>
18 #include <keys/asymmetric-type.h>
19 #include <keys/system_keyring.h>
20 #include "blacklist.h"
21 
22 /*
23  * According to crypto/asymmetric_keys/x509_cert_parser.c:x509_note_pkey_algo(),
24  * the size of the currently longest supported hash algorithm is 512 bits,
25  * which translates into 128 hex characters.
26  */
27 #define MAX_HASH_LEN	128
28 
29 #define BLACKLIST_KEY_PERM (KEY_POS_SEARCH | KEY_POS_VIEW | \
30 			    KEY_USR_SEARCH | KEY_USR_VIEW)
31 
32 static const char tbs_prefix[] = "tbs";
33 static const char bin_prefix[] = "bin";
34 
35 static struct key *blacklist_keyring;
36 
37 #ifdef CONFIG_SYSTEM_REVOCATION_LIST
38 extern __initconst const u8 revocation_certificate_list[];
39 extern __initconst const unsigned long revocation_certificate_list_size;
40 #endif
41 
42 /*
43  * The description must be a type prefix, a colon and then an even number of
44  * hex digits.  The hash is kept in the description.
45  */
blacklist_vet_description(const char * desc)46 static int blacklist_vet_description(const char *desc)
47 {
48 	int i, prefix_len, tbs_step = 0, bin_step = 0;
49 
50 	/* The following algorithm only works if prefix lengths match. */
51 	BUILD_BUG_ON(sizeof(tbs_prefix) != sizeof(bin_prefix));
52 	prefix_len = sizeof(tbs_prefix) - 1;
53 	for (i = 0; *desc; desc++, i++) {
54 		if (*desc == ':') {
55 			if (tbs_step == prefix_len)
56 				goto found_colon;
57 			if (bin_step == prefix_len)
58 				goto found_colon;
59 			return -EINVAL;
60 		}
61 		if (i >= prefix_len)
62 			return -EINVAL;
63 		if (*desc == tbs_prefix[i])
64 			tbs_step++;
65 		if (*desc == bin_prefix[i])
66 			bin_step++;
67 	}
68 	return -EINVAL;
69 
70 found_colon:
71 	desc++;
72 	for (i = 0; *desc && i < MAX_HASH_LEN; desc++, i++) {
73 		if (!isxdigit(*desc) || isupper(*desc))
74 			return -EINVAL;
75 	}
76 	if (*desc)
77 		/* The hash is greater than MAX_HASH_LEN. */
78 		return -ENOPKG;
79 
80 	/* Checks for an even number of hexadecimal characters. */
81 	if (i == 0 || i & 1)
82 		return -EINVAL;
83 	return 0;
84 }
85 
blacklist_key_instantiate(struct key * key,struct key_preparsed_payload * prep)86 static int blacklist_key_instantiate(struct key *key,
87 		struct key_preparsed_payload *prep)
88 {
89 #ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
90 	int err;
91 #endif
92 
93 	/* Sets safe default permissions for keys loaded by user space. */
94 	key->perm = BLACKLIST_KEY_PERM;
95 
96 	/*
97 	 * Skips the authentication step for builtin hashes, they are not
98 	 * signed but still trusted.
99 	 */
100 	if (key->flags & (1 << KEY_FLAG_BUILTIN))
101 		goto out;
102 
103 #ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
104 	/*
105 	 * Verifies the description's PKCS#7 signature against the builtin
106 	 * trusted keyring.
107 	 */
108 	err = verify_pkcs7_signature(key->description,
109 			strlen(key->description), prep->data, prep->datalen,
110 			NULL, VERIFYING_UNSPECIFIED_SIGNATURE, NULL, NULL);
111 	if (err)
112 		return err;
113 #else
114 	/*
115 	 * It should not be possible to come here because the keyring doesn't
116 	 * have KEY_USR_WRITE and the only other way to call this function is
117 	 * for builtin hashes.
118 	 */
119 	WARN_ON_ONCE(1);
120 	return -EPERM;
121 #endif
122 
123 out:
124 	return generic_key_instantiate(key, prep);
125 }
126 
blacklist_key_update(struct key * key,struct key_preparsed_payload * prep)127 static int blacklist_key_update(struct key *key,
128 		struct key_preparsed_payload *prep)
129 {
130 	return -EPERM;
131 }
132 
blacklist_describe(const struct key * key,struct seq_file * m)133 static void blacklist_describe(const struct key *key, struct seq_file *m)
134 {
135 	seq_puts(m, key->description);
136 }
137 
138 static struct key_type key_type_blacklist = {
139 	.name			= "blacklist",
140 	.vet_description	= blacklist_vet_description,
141 	.instantiate		= blacklist_key_instantiate,
142 	.update			= blacklist_key_update,
143 	.describe		= blacklist_describe,
144 };
145 
get_raw_hash(const u8 * hash,size_t hash_len,enum blacklist_hash_type hash_type)146 static char *get_raw_hash(const u8 *hash, size_t hash_len,
147 		enum blacklist_hash_type hash_type)
148 {
149 	size_t type_len;
150 	const char *type_prefix;
151 	char *buffer, *p;
152 
153 	switch (hash_type) {
154 	case BLACKLIST_HASH_X509_TBS:
155 		type_len = sizeof(tbs_prefix) - 1;
156 		type_prefix = tbs_prefix;
157 		break;
158 	case BLACKLIST_HASH_BINARY:
159 		type_len = sizeof(bin_prefix) - 1;
160 		type_prefix = bin_prefix;
161 		break;
162 	default:
163 		WARN_ON_ONCE(1);
164 		return ERR_PTR(-EINVAL);
165 	}
166 	buffer = kmalloc(type_len + 1 + hash_len * 2 + 1, GFP_KERNEL);
167 	if (!buffer)
168 		return ERR_PTR(-ENOMEM);
169 	p = memcpy(buffer, type_prefix, type_len);
170 	p += type_len;
171 	*p++ = ':';
172 	bin2hex(p, hash, hash_len);
173 	p += hash_len * 2;
174 	*p = '\0';
175 	return buffer;
176 }
177 
178 /**
179  * mark_raw_hash_blacklisted - Add a hash to the system blacklist
180  * @hash: The hash as a hex string with a type prefix (eg. "tbs:23aa429783")
181  */
mark_raw_hash_blacklisted(const char * hash)182 static int mark_raw_hash_blacklisted(const char *hash)
183 {
184 	key_ref_t key;
185 
186 	key = key_create(make_key_ref(blacklist_keyring, true),
187 			 "blacklist",
188 			 hash,
189 			 NULL,
190 			 0,
191 			 BLACKLIST_KEY_PERM,
192 			 KEY_ALLOC_NOT_IN_QUOTA |
193 			 KEY_ALLOC_BUILT_IN);
194 	if (IS_ERR(key)) {
195 		if (PTR_ERR(key) == -EEXIST)
196 			pr_warn("Duplicate blacklisted hash %s\n", hash);
197 		else
198 			pr_err("Problem blacklisting hash %s: %pe\n", hash, key);
199 		return PTR_ERR(key);
200 	}
201 	return 0;
202 }
203 
mark_hash_blacklisted(const u8 * hash,size_t hash_len,enum blacklist_hash_type hash_type)204 int mark_hash_blacklisted(const u8 *hash, size_t hash_len,
205 		enum blacklist_hash_type hash_type)
206 {
207 	const char *buffer;
208 	int err;
209 
210 	buffer = get_raw_hash(hash, hash_len, hash_type);
211 	if (IS_ERR(buffer))
212 		return PTR_ERR(buffer);
213 	err = mark_raw_hash_blacklisted(buffer);
214 	kfree(buffer);
215 	return err;
216 }
217 
218 /**
219  * is_hash_blacklisted - Determine if a hash is blacklisted
220  * @hash: The hash to be checked as a binary blob
221  * @hash_len: The length of the binary hash
222  * @hash_type: Type of hash
223  */
is_hash_blacklisted(const u8 * hash,size_t hash_len,enum blacklist_hash_type hash_type)224 int is_hash_blacklisted(const u8 *hash, size_t hash_len,
225 		enum blacklist_hash_type hash_type)
226 {
227 	key_ref_t kref;
228 	const char *buffer;
229 	int ret = 0;
230 
231 	buffer = get_raw_hash(hash, hash_len, hash_type);
232 	if (IS_ERR(buffer))
233 		return PTR_ERR(buffer);
234 	kref = keyring_search(make_key_ref(blacklist_keyring, true),
235 			      &key_type_blacklist, buffer, false);
236 	if (!IS_ERR(kref)) {
237 		key_ref_put(kref);
238 		ret = -EKEYREJECTED;
239 	}
240 
241 	kfree(buffer);
242 	return ret;
243 }
244 EXPORT_SYMBOL_GPL(is_hash_blacklisted);
245 
is_binary_blacklisted(const u8 * hash,size_t hash_len)246 int is_binary_blacklisted(const u8 *hash, size_t hash_len)
247 {
248 	if (is_hash_blacklisted(hash, hash_len, BLACKLIST_HASH_BINARY) ==
249 			-EKEYREJECTED)
250 		return -EPERM;
251 
252 	return 0;
253 }
254 EXPORT_SYMBOL_GPL(is_binary_blacklisted);
255 
256 #ifdef CONFIG_SYSTEM_REVOCATION_LIST
257 /**
258  * add_key_to_revocation_list - Add a revocation certificate to the blacklist
259  * @data: The data blob containing the certificate
260  * @size: The size of data blob
261  */
add_key_to_revocation_list(const char * data,size_t size)262 int add_key_to_revocation_list(const char *data, size_t size)
263 {
264 	key_ref_t key;
265 
266 	key = key_create_or_update(make_key_ref(blacklist_keyring, true),
267 				   "asymmetric",
268 				   NULL,
269 				   data,
270 				   size,
271 				   KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH
272 				   | KEY_USR_VIEW,
273 				   KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN
274 				   | KEY_ALLOC_BYPASS_RESTRICTION);
275 
276 	if (IS_ERR(key)) {
277 		pr_err("Problem with revocation key (%ld)\n", PTR_ERR(key));
278 		return PTR_ERR(key);
279 	}
280 
281 	return 0;
282 }
283 
284 /**
285  * is_key_on_revocation_list - Determine if the key for a PKCS#7 message is revoked
286  * @pkcs7: The PKCS#7 message to check
287  */
is_key_on_revocation_list(struct pkcs7_message * pkcs7)288 int is_key_on_revocation_list(struct pkcs7_message *pkcs7)
289 {
290 	int ret;
291 
292 	ret = pkcs7_validate_trust(pkcs7, blacklist_keyring);
293 
294 	if (ret == 0)
295 		return -EKEYREJECTED;
296 
297 	return -ENOKEY;
298 }
299 #endif
300 
restrict_link_for_blacklist(struct key * dest_keyring,const struct key_type * type,const union key_payload * payload,struct key * restrict_key)301 static int restrict_link_for_blacklist(struct key *dest_keyring,
302 		const struct key_type *type, const union key_payload *payload,
303 		struct key *restrict_key)
304 {
305 	if (type == &key_type_blacklist)
306 		return 0;
307 	return -EOPNOTSUPP;
308 }
309 
310 /*
311  * Initialise the blacklist
312  *
313  * The blacklist_init() function is registered as an initcall via
314  * device_initcall().  As a result if the blacklist_init() function fails for
315  * any reason the kernel continues to execute.  While cleanly returning -ENODEV
316  * could be acceptable for some non-critical kernel parts, if the blacklist
317  * keyring fails to load it defeats the certificate/key based deny list for
318  * signed modules.  If a critical piece of security functionality that users
319  * expect to be present fails to initialize, panic()ing is likely the right
320  * thing to do.
321  */
blacklist_init(void)322 static int __init blacklist_init(void)
323 {
324 	const char *const *bl;
325 	struct key_restriction *restriction;
326 
327 	if (register_key_type(&key_type_blacklist) < 0)
328 		panic("Can't allocate system blacklist key type\n");
329 
330 	restriction = kzalloc(sizeof(*restriction), GFP_KERNEL);
331 	if (!restriction)
332 		panic("Can't allocate blacklist keyring restriction\n");
333 	restriction->check = restrict_link_for_blacklist;
334 
335 	blacklist_keyring =
336 		keyring_alloc(".blacklist",
337 			      GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
338 			      KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH |
339 			      KEY_POS_WRITE |
340 			      KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH
341 #ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
342 			      | KEY_USR_WRITE
343 #endif
344 			      , KEY_ALLOC_NOT_IN_QUOTA |
345 			      KEY_ALLOC_SET_KEEP,
346 			      restriction, NULL);
347 	if (IS_ERR(blacklist_keyring))
348 		panic("Can't allocate system blacklist keyring\n");
349 
350 	for (bl = blacklist_hashes; *bl; bl++)
351 		if (mark_raw_hash_blacklisted(*bl) < 0)
352 			pr_err("- blacklisting failed\n");
353 	return 0;
354 }
355 
356 /*
357  * Must be initialised before we try and load the keys into the keyring.
358  */
359 device_initcall(blacklist_init);
360 
361 #ifdef CONFIG_SYSTEM_REVOCATION_LIST
362 /*
363  * Load the compiled-in list of revocation X.509 certificates.
364  */
load_revocation_certificate_list(void)365 static __init int load_revocation_certificate_list(void)
366 {
367 	if (revocation_certificate_list_size)
368 		pr_notice("Loading compiled-in revocation X.509 certificates\n");
369 
370 	return x509_load_certificate_list(revocation_certificate_list,
371 					  revocation_certificate_list_size,
372 					  blacklist_keyring);
373 }
374 late_initcall(load_revocation_certificate_list);
375 #endif
376