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
