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
32static const char tbs_prefix[] = "tbs";
33static const char bin_prefix[] = "bin";
34
35static struct key *blacklist_keyring;
36
37#ifdef CONFIG_SYSTEM_REVOCATION_LIST
38extern __initconst const u8 revocation_certificate_list[];
39extern __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 */
46static 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
70found_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
86static 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
123out:
124	return generic_key_instantiate(key, prep);
125}
126
127static int blacklist_key_update(struct key *key,
128		struct key_preparsed_payload *prep)
129{
130	return -EPERM;
131}
132
133static void blacklist_describe(const struct key *key, struct seq_file *m)
134{
135	seq_puts(m, key->description);
136}
137
138static 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
146static 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 */
182static 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
204int 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 */
224int 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}
244EXPORT_SYMBOL_GPL(is_hash_blacklisted);
245
246int 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}
254EXPORT_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 */
262int 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 */
288int 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
301static 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 */
322static 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 */
359device_initcall(blacklist_init);
360
361#ifdef CONFIG_SYSTEM_REVOCATION_LIST
362/*
363 * Load the compiled-in list of revocation X.509 certificates.
364 */
365static __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}
374late_initcall(load_revocation_certificate_list);
375#endif
376