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_or_update(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 		pr_err("Problem blacklisting hash (%ld)\n", PTR_ERR(key));
196 		return PTR_ERR(key);
197 	}
198 	return 0;
199 }
200 
mark_hash_blacklisted(const u8 * hash,size_t hash_len,enum blacklist_hash_type hash_type)201 int mark_hash_blacklisted(const u8 *hash, size_t hash_len,
202 		enum blacklist_hash_type hash_type)
203 {
204 	const char *buffer;
205 	int err;
206 
207 	buffer = get_raw_hash(hash, hash_len, hash_type);
208 	if (IS_ERR(buffer))
209 		return PTR_ERR(buffer);
210 	err = mark_raw_hash_blacklisted(buffer);
211 	kfree(buffer);
212 	return err;
213 }
214 
215 /**
216  * is_hash_blacklisted - Determine if a hash is blacklisted
217  * @hash: The hash to be checked as a binary blob
218  * @hash_len: The length of the binary hash
219  * @hash_type: Type of hash
220  */
is_hash_blacklisted(const u8 * hash,size_t hash_len,enum blacklist_hash_type hash_type)221 int is_hash_blacklisted(const u8 *hash, size_t hash_len,
222 		enum blacklist_hash_type hash_type)
223 {
224 	key_ref_t kref;
225 	const char *buffer;
226 	int ret = 0;
227 
228 	buffer = get_raw_hash(hash, hash_len, hash_type);
229 	if (IS_ERR(buffer))
230 		return PTR_ERR(buffer);
231 	kref = keyring_search(make_key_ref(blacklist_keyring, true),
232 			      &key_type_blacklist, buffer, false);
233 	if (!IS_ERR(kref)) {
234 		key_ref_put(kref);
235 		ret = -EKEYREJECTED;
236 	}
237 
238 	kfree(buffer);
239 	return ret;
240 }
241 EXPORT_SYMBOL_GPL(is_hash_blacklisted);
242 
is_binary_blacklisted(const u8 * hash,size_t hash_len)243 int is_binary_blacklisted(const u8 *hash, size_t hash_len)
244 {
245 	if (is_hash_blacklisted(hash, hash_len, BLACKLIST_HASH_BINARY) ==
246 			-EKEYREJECTED)
247 		return -EPERM;
248 
249 	return 0;
250 }
251 EXPORT_SYMBOL_GPL(is_binary_blacklisted);
252 
253 #ifdef CONFIG_SYSTEM_REVOCATION_LIST
254 /**
255  * add_key_to_revocation_list - Add a revocation certificate to the blacklist
256  * @data: The data blob containing the certificate
257  * @size: The size of data blob
258  */
add_key_to_revocation_list(const char * data,size_t size)259 int add_key_to_revocation_list(const char *data, size_t size)
260 {
261 	key_ref_t key;
262 
263 	key = key_create_or_update(make_key_ref(blacklist_keyring, true),
264 				   "asymmetric",
265 				   NULL,
266 				   data,
267 				   size,
268 				   KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH
269 				   | KEY_USR_VIEW,
270 				   KEY_ALLOC_NOT_IN_QUOTA | KEY_ALLOC_BUILT_IN
271 				   | KEY_ALLOC_BYPASS_RESTRICTION);
272 
273 	if (IS_ERR(key)) {
274 		pr_err("Problem with revocation key (%ld)\n", PTR_ERR(key));
275 		return PTR_ERR(key);
276 	}
277 
278 	return 0;
279 }
280 
281 /**
282  * is_key_on_revocation_list - Determine if the key for a PKCS#7 message is revoked
283  * @pkcs7: The PKCS#7 message to check
284  */
is_key_on_revocation_list(struct pkcs7_message * pkcs7)285 int is_key_on_revocation_list(struct pkcs7_message *pkcs7)
286 {
287 	int ret;
288 
289 	ret = pkcs7_validate_trust(pkcs7, blacklist_keyring);
290 
291 	if (ret == 0)
292 		return -EKEYREJECTED;
293 
294 	return -ENOKEY;
295 }
296 #endif
297 
restrict_link_for_blacklist(struct key * dest_keyring,const struct key_type * type,const union key_payload * payload,struct key * restrict_key)298 static int restrict_link_for_blacklist(struct key *dest_keyring,
299 		const struct key_type *type, const union key_payload *payload,
300 		struct key *restrict_key)
301 {
302 	if (type == &key_type_blacklist)
303 		return 0;
304 	return -EOPNOTSUPP;
305 }
306 
307 /*
308  * Initialise the blacklist
309  *
310  * The blacklist_init() function is registered as an initcall via
311  * device_initcall().  As a result if the blacklist_init() function fails for
312  * any reason the kernel continues to execute.  While cleanly returning -ENODEV
313  * could be acceptable for some non-critical kernel parts, if the blacklist
314  * keyring fails to load it defeats the certificate/key based deny list for
315  * signed modules.  If a critical piece of security functionality that users
316  * expect to be present fails to initialize, panic()ing is likely the right
317  * thing to do.
318  */
blacklist_init(void)319 static int __init blacklist_init(void)
320 {
321 	const char *const *bl;
322 	struct key_restriction *restriction;
323 
324 	if (register_key_type(&key_type_blacklist) < 0)
325 		panic("Can't allocate system blacklist key type\n");
326 
327 	restriction = kzalloc(sizeof(*restriction), GFP_KERNEL);
328 	if (!restriction)
329 		panic("Can't allocate blacklist keyring restriction\n");
330 	restriction->check = restrict_link_for_blacklist;
331 
332 	blacklist_keyring =
333 		keyring_alloc(".blacklist",
334 			      GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
335 			      KEY_POS_VIEW | KEY_POS_READ | KEY_POS_SEARCH |
336 			      KEY_POS_WRITE |
337 			      KEY_USR_VIEW | KEY_USR_READ | KEY_USR_SEARCH
338 #ifdef CONFIG_SYSTEM_BLACKLIST_AUTH_UPDATE
339 			      | KEY_USR_WRITE
340 #endif
341 			      , KEY_ALLOC_NOT_IN_QUOTA |
342 			      KEY_ALLOC_SET_KEEP,
343 			      restriction, NULL);
344 	if (IS_ERR(blacklist_keyring))
345 		panic("Can't allocate system blacklist keyring\n");
346 
347 	for (bl = blacklist_hashes; *bl; bl++)
348 		if (mark_raw_hash_blacklisted(*bl) < 0)
349 			pr_err("- blacklisting failed\n");
350 	return 0;
351 }
352 
353 /*
354  * Must be initialised before we try and load the keys into the keyring.
355  */
356 device_initcall(blacklist_init);
357 
358 #ifdef CONFIG_SYSTEM_REVOCATION_LIST
359 /*
360  * Load the compiled-in list of revocation X.509 certificates.
361  */
load_revocation_certificate_list(void)362 static __init int load_revocation_certificate_list(void)
363 {
364 	if (revocation_certificate_list_size)
365 		pr_notice("Loading compiled-in revocation X.509 certificates\n");
366 
367 	return x509_load_certificate_list(revocation_certificate_list,
368 					  revocation_certificate_list_size,
369 					  blacklist_keyring);
370 }
371 late_initcall(load_revocation_certificate_list);
372 #endif
373