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 | */ |
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 | |
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(data: key->description, |
109 | strlen(key->description), raw_pkcs7: prep->data, pkcs7_len: prep->datalen, |
110 | NULL, usage: 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 | |
127 | static int blacklist_key_update(struct key *key, |
128 | struct key_preparsed_payload *prep) |
129 | { |
130 | return -EPERM; |
131 | } |
132 | |
133 | static void blacklist_describe(const struct key *key, struct seq_file *m) |
134 | { |
135 | seq_puts(m, s: 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 | |
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(error: -EINVAL); |
165 | } |
166 | buffer = kmalloc(size: type_len + 1 + hash_len * 2 + 1, GFP_KERNEL); |
167 | if (!buffer) |
168 | return ERR_PTR(error: -ENOMEM); |
169 | p = memcpy(buffer, type_prefix, type_len); |
170 | p += type_len; |
171 | *p++ = ':'; |
172 | bin2hex(dst: p, src: hash, count: 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 | */ |
182 | static int mark_raw_hash_blacklisted(const char *hash) |
183 | { |
184 | key_ref_t key; |
185 | |
186 | key = key_create(keyring: make_key_ref(key: blacklist_keyring, possession: true), |
187 | type: "blacklist" , |
188 | description: hash, |
189 | NULL, |
190 | plen: 0, |
191 | BLACKLIST_KEY_PERM, |
192 | KEY_ALLOC_NOT_IN_QUOTA | |
193 | KEY_ALLOC_BUILT_IN); |
194 | if (IS_ERR(ptr: key)) { |
195 | if (PTR_ERR(ptr: 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(ptr: key); |
200 | } |
201 | return 0; |
202 | } |
203 | |
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(ptr: buffer)) |
212 | return PTR_ERR(ptr: buffer); |
213 | err = mark_raw_hash_blacklisted(hash: buffer); |
214 | kfree(objp: 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 | */ |
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(ptr: buffer)) |
233 | return PTR_ERR(ptr: buffer); |
234 | kref = keyring_search(keyring: make_key_ref(key: blacklist_keyring, possession: true), |
235 | type: &key_type_blacklist, description: buffer, recurse: false); |
236 | if (!IS_ERR(ptr: kref)) { |
237 | key_ref_put(key_ref: kref); |
238 | ret = -EKEYREJECTED; |
239 | } |
240 | |
241 | kfree(objp: buffer); |
242 | return ret; |
243 | } |
244 | EXPORT_SYMBOL_GPL(is_hash_blacklisted); |
245 | |
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 | */ |
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(keyring: make_key_ref(key: blacklist_keyring, possession: true), |
267 | type: "asymmetric" , |
268 | NULL, |
269 | payload: data, |
270 | plen: 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(ptr: key)) { |
277 | pr_err("Problem with revocation key (%ld)\n" , PTR_ERR(key)); |
278 | return PTR_ERR(ptr: 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 | */ |
288 | int is_key_on_revocation_list(struct pkcs7_message *pkcs7) |
289 | { |
290 | int ret; |
291 | |
292 | ret = pkcs7_validate_trust(pkcs7, trust_keyring: blacklist_keyring); |
293 | |
294 | if (ret == 0) |
295 | return -EKEYREJECTED; |
296 | |
297 | return -ENOKEY; |
298 | } |
299 | #endif |
300 | |
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 | */ |
322 | static int __init blacklist_init(void) |
323 | { |
324 | const char *const *bl; |
325 | struct key_restriction *restriction; |
326 | |
327 | if (register_key_type(ktype: &key_type_blacklist) < 0) |
328 | panic(fmt: "Can't allocate system blacklist key type\n" ); |
329 | |
330 | restriction = kzalloc(size: sizeof(*restriction), GFP_KERNEL); |
331 | if (!restriction) |
332 | panic(fmt: "Can't allocate blacklist keyring restriction\n" ); |
333 | restriction->check = restrict_link_for_blacklist; |
334 | |
335 | blacklist_keyring = |
336 | keyring_alloc(description: ".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 | restrict_link: 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 | */ |
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(cert_list: revocation_certificate_list, |
371 | list_size: revocation_certificate_list_size, |
372 | keyring: blacklist_keyring); |
373 | } |
374 | late_initcall(load_revocation_certificate_list); |
375 | #endif |
376 | |