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(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 } 126 127 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, 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(-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 */ 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 } 203 204 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 */ 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); 245 246 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(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 */ 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 300 301 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(&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 */ 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