1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Key setup facility for FS encryption support. 4 * 5 * Copyright (C) 2015, Google, Inc. 6 * 7 * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar. 8 * Heavily modified since then. 9 */ 10 11 #include <crypto/skcipher.h> 12 #include <linux/export.h> 13 #include <linux/random.h> 14 15 #include "fscrypt_private.h" 16 17 struct fscrypt_mode fscrypt_modes[] = { 18 [FSCRYPT_MODE_AES_256_XTS] = { 19 .friendly_name = "AES-256-XTS", 20 .cipher_str = "xts(aes)", 21 .keysize = 64, 22 .security_strength = 32, 23 .ivsize = 16, 24 .blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_256_XTS, 25 }, 26 [FSCRYPT_MODE_AES_256_CTS] = { 27 .friendly_name = "AES-256-CBC-CTS", 28 .cipher_str = "cts(cbc(aes))", 29 .keysize = 32, 30 .security_strength = 32, 31 .ivsize = 16, 32 }, 33 [FSCRYPT_MODE_AES_128_CBC] = { 34 .friendly_name = "AES-128-CBC-ESSIV", 35 .cipher_str = "essiv(cbc(aes),sha256)", 36 .keysize = 16, 37 .security_strength = 16, 38 .ivsize = 16, 39 .blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_128_CBC_ESSIV, 40 }, 41 [FSCRYPT_MODE_AES_128_CTS] = { 42 .friendly_name = "AES-128-CBC-CTS", 43 .cipher_str = "cts(cbc(aes))", 44 .keysize = 16, 45 .security_strength = 16, 46 .ivsize = 16, 47 }, 48 [FSCRYPT_MODE_SM4_XTS] = { 49 .friendly_name = "SM4-XTS", 50 .cipher_str = "xts(sm4)", 51 .keysize = 32, 52 .security_strength = 16, 53 .ivsize = 16, 54 .blk_crypto_mode = BLK_ENCRYPTION_MODE_SM4_XTS, 55 }, 56 [FSCRYPT_MODE_SM4_CTS] = { 57 .friendly_name = "SM4-CBC-CTS", 58 .cipher_str = "cts(cbc(sm4))", 59 .keysize = 16, 60 .security_strength = 16, 61 .ivsize = 16, 62 }, 63 [FSCRYPT_MODE_ADIANTUM] = { 64 .friendly_name = "Adiantum", 65 .cipher_str = "adiantum(xchacha12,aes)", 66 .keysize = 32, 67 .security_strength = 32, 68 .ivsize = 32, 69 .blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM, 70 }, 71 [FSCRYPT_MODE_AES_256_HCTR2] = { 72 .friendly_name = "AES-256-HCTR2", 73 .cipher_str = "hctr2(aes)", 74 .keysize = 32, 75 .security_strength = 32, 76 .ivsize = 32, 77 }, 78 }; 79 80 static DEFINE_MUTEX(fscrypt_mode_key_setup_mutex); 81 82 static struct fscrypt_mode * 83 select_encryption_mode(const union fscrypt_policy *policy, 84 const struct inode *inode) 85 { 86 BUILD_BUG_ON(ARRAY_SIZE(fscrypt_modes) != FSCRYPT_MODE_MAX + 1); 87 88 if (S_ISREG(inode->i_mode)) 89 return &fscrypt_modes[fscrypt_policy_contents_mode(policy)]; 90 91 if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode)) 92 return &fscrypt_modes[fscrypt_policy_fnames_mode(policy)]; 93 94 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %llu, which is not encryptable (file type %d)\n", 95 inode->i_ino, (inode->i_mode & S_IFMT)); 96 return ERR_PTR(-EINVAL); 97 } 98 99 /* Create a symmetric cipher object for the given encryption mode and key */ 100 static struct crypto_sync_skcipher * 101 fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key, 102 const struct inode *inode) 103 { 104 struct crypto_sync_skcipher *tfm; 105 int err; 106 107 tfm = crypto_alloc_sync_skcipher(mode->cipher_str, 0, 108 FSCRYPT_CRYPTOAPI_MASK); 109 if (IS_ERR(tfm)) { 110 if (PTR_ERR(tfm) == -ENOENT) { 111 fscrypt_warn(inode, 112 "Missing crypto API support for %s (API name: \"%s\")", 113 mode->friendly_name, mode->cipher_str); 114 return ERR_PTR(-ENOPKG); 115 } 116 fscrypt_err(inode, "Error allocating '%s' transform: %ld", 117 mode->cipher_str, PTR_ERR(tfm)); 118 return tfm; 119 } 120 if (!xchg(&mode->logged_cryptoapi_impl, 1)) { 121 /* 122 * fscrypt performance can vary greatly depending on which 123 * crypto algorithm implementation is used. Help people debug 124 * performance problems by logging the ->cra_driver_name the 125 * first time a mode is used. 126 */ 127 pr_info("fscrypt: %s using implementation \"%s\"\n", 128 mode->friendly_name, 129 crypto_skcipher_driver_name(&tfm->base)); 130 } 131 if (WARN_ON_ONCE(crypto_sync_skcipher_ivsize(tfm) != mode->ivsize)) { 132 err = -EINVAL; 133 goto err_free_tfm; 134 } 135 crypto_sync_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS); 136 err = crypto_sync_skcipher_setkey(tfm, raw_key, mode->keysize); 137 if (err) 138 goto err_free_tfm; 139 140 return tfm; 141 142 err_free_tfm: 143 crypto_free_sync_skcipher(tfm); 144 return ERR_PTR(err); 145 } 146 147 /* 148 * Prepare the crypto transform object or blk-crypto key in @prep_key, given the 149 * raw key, encryption mode (@ci->ci_mode), flag indicating which encryption 150 * implementation (fs-layer or blk-crypto) will be used (@ci->ci_inlinecrypt), 151 * and IV generation method (@ci->ci_policy.flags). 152 */ 153 int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key, 154 const u8 *raw_key, const struct fscrypt_inode_info *ci) 155 { 156 struct crypto_sync_skcipher *tfm; 157 158 if (fscrypt_using_inline_encryption(ci)) 159 return fscrypt_prepare_inline_crypt_key(prep_key, raw_key, 160 ci->ci_mode->keysize, 161 false, ci); 162 163 tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode); 164 if (IS_ERR(tfm)) 165 return PTR_ERR(tfm); 166 prep_key->tfm = tfm; 167 return 0; 168 } 169 170 /* Destroy a crypto transform object and/or blk-crypto key. */ 171 void fscrypt_destroy_prepared_key(struct super_block *sb, 172 struct fscrypt_prepared_key *prep_key) 173 { 174 crypto_free_sync_skcipher(prep_key->tfm); 175 fscrypt_destroy_inline_crypt_key(sb, prep_key); 176 memzero_explicit(prep_key, sizeof(*prep_key)); 177 } 178 179 /* Given a per-file encryption key, set up the file's crypto transform object */ 180 int fscrypt_set_per_file_enc_key(struct fscrypt_inode_info *ci, 181 const u8 *raw_key) 182 { 183 ci->ci_owns_key = true; 184 return fscrypt_prepare_key(&ci->ci_enc_key, raw_key, ci); 185 } 186 187 /* 188 * Find the fscrypt_prepared_key (if any) for a particular (mk, hkdf_context, 189 * mode_num, data_unit_bits, inlinecrypt) combination. 190 * 191 * The caller must hold ->mk_sem for reading and ->mk_present must be true, 192 * ensuring that ->mk_mode_keys is still append-only. 193 */ 194 static struct fscrypt_prepared_key * 195 fscrypt_find_mode_key(struct fscrypt_master_key *mk, u8 hkdf_context, 196 u8 mode_num, const struct fscrypt_inode_info *ci) 197 { 198 struct fscrypt_mode_key *node; 199 200 /* 201 * The RCU read lock here is used only to synchronize with concurrent 202 * list_add_tail_rcu(). Concurrent deletions are impossible here, so 203 * returning a pointer to a node without taking any refcount is safe. 204 */ 205 guard(rcu)(); 206 list_for_each_entry_rcu(node, &mk->mk_mode_keys, link) { 207 if (node->hkdf_context == hkdf_context && 208 node->mode_num == mode_num && 209 node->data_unit_bits == ci->ci_data_unit_bits && 210 fscrypt_is_key_prepared(&node->key, ci)) 211 return &node->key; 212 } 213 return NULL; 214 } 215 216 static int setup_per_mode_enc_key(struct fscrypt_inode_info *ci, 217 struct fscrypt_master_key *mk, 218 u8 hkdf_context, bool include_fs_uuid) 219 { 220 const struct inode *inode = ci->ci_inode; 221 const struct super_block *sb = inode->i_sb; 222 struct fscrypt_mode *mode = ci->ci_mode; 223 const u8 mode_num = mode - fscrypt_modes; 224 struct fscrypt_prepared_key *prep_key; 225 struct fscrypt_mode_key *new_node; 226 u8 raw_mode_key[FSCRYPT_MAX_RAW_KEY_SIZE]; 227 u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)]; 228 unsigned int hkdf_infolen = 0; 229 bool use_hw_wrapped_key = false; 230 int err; 231 232 if (WARN_ON_ONCE(mode_num > FSCRYPT_MODE_MAX)) 233 return -EINVAL; 234 235 if (mk->mk_secret.is_hw_wrapped && S_ISREG(inode->i_mode)) { 236 /* Using a hardware-wrapped key for file contents encryption */ 237 if (!fscrypt_using_inline_encryption(ci)) { 238 if (sb->s_flags & SB_INLINECRYPT) 239 fscrypt_warn(ci->ci_inode, 240 "Hardware-wrapped key required, but no suitable inline encryption capabilities are available"); 241 else 242 fscrypt_warn(ci->ci_inode, 243 "Hardware-wrapped keys require inline encryption (-o inlinecrypt)"); 244 return -EINVAL; 245 } 246 use_hw_wrapped_key = true; 247 } 248 249 prep_key = fscrypt_find_mode_key(mk, hkdf_context, mode_num, ci); 250 if (prep_key) { 251 ci->ci_enc_key = *prep_key; 252 return 0; 253 } 254 255 guard(mutex)(&fscrypt_mode_key_setup_mutex); 256 257 prep_key = fscrypt_find_mode_key(mk, hkdf_context, mode_num, ci); 258 if (prep_key) { 259 ci->ci_enc_key = *prep_key; 260 return 0; 261 } 262 263 new_node = kzalloc_obj(*new_node); 264 if (!new_node) 265 return -ENOMEM; 266 new_node->hkdf_context = hkdf_context; 267 new_node->mode_num = mode_num; 268 new_node->data_unit_bits = ci->ci_data_unit_bits; 269 prep_key = &new_node->key; 270 271 if (use_hw_wrapped_key) { 272 err = fscrypt_prepare_inline_crypt_key(prep_key, 273 mk->mk_secret.bytes, 274 mk->mk_secret.size, true, 275 ci); 276 } else { 277 static_assert(sizeof(mode_num) == 1); 278 static_assert(sizeof(sb->s_uuid) == 16); 279 static_assert(sizeof(hkdf_info) == 17); 280 hkdf_info[hkdf_infolen++] = mode_num; 281 if (include_fs_uuid) { 282 memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid, 283 sizeof(sb->s_uuid)); 284 hkdf_infolen += sizeof(sb->s_uuid); 285 } 286 fscrypt_hkdf_expand(&mk->mk_secret.hkdf, hkdf_context, 287 hkdf_info, hkdf_infolen, raw_mode_key, 288 mode->keysize); 289 err = fscrypt_prepare_key(prep_key, raw_mode_key, ci); 290 memzero_explicit(raw_mode_key, mode->keysize); 291 } 292 if (err) { 293 kfree(new_node); 294 return err; 295 } 296 list_add_tail_rcu(&new_node->link, &mk->mk_mode_keys); 297 ci->ci_enc_key = *prep_key; 298 return 0; 299 } 300 301 /* 302 * Derive a SipHash key from the given fscrypt master key and the given 303 * application-specific information string. 304 * 305 * Note that the KDF produces a byte array, but the SipHash APIs expect the key 306 * as a pair of 64-bit words. Therefore, on big endian CPUs we have to do an 307 * endianness swap in order to get the same results as on little endian CPUs. 308 */ 309 static void fscrypt_derive_siphash_key(const struct fscrypt_master_key *mk, 310 u8 context, const u8 *info, 311 unsigned int infolen, siphash_key_t *key) 312 { 313 fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen, 314 (u8 *)key, sizeof(*key)); 315 BUILD_BUG_ON(sizeof(*key) != 16); 316 BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2); 317 le64_to_cpus(&key->key[0]); 318 le64_to_cpus(&key->key[1]); 319 } 320 321 void fscrypt_derive_dirhash_key(struct fscrypt_inode_info *ci, 322 const struct fscrypt_master_key *mk) 323 { 324 fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY, 325 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE, 326 &ci->ci_dirhash_key); 327 ci->ci_dirhash_key_initialized = true; 328 } 329 330 void fscrypt_hash_inode_number(struct fscrypt_inode_info *ci, 331 const struct fscrypt_master_key *mk) 332 { 333 WARN_ON_ONCE(ci->ci_inode->i_ino == 0); 334 WARN_ON_ONCE(!mk->mk_ino_hash_key_initialized); 335 336 ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino, 337 &mk->mk_ino_hash_key); 338 } 339 340 static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info *ci, 341 struct fscrypt_master_key *mk) 342 { 343 int err; 344 345 err = setup_per_mode_enc_key(ci, mk, HKDF_CONTEXT_IV_INO_LBLK_32_KEY, 346 true); 347 if (err) 348 return err; 349 350 /* pairs with smp_store_release() below */ 351 if (!smp_load_acquire(&mk->mk_ino_hash_key_initialized)) { 352 353 mutex_lock(&fscrypt_mode_key_setup_mutex); 354 355 if (mk->mk_ino_hash_key_initialized) 356 goto unlock; 357 358 fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_INODE_HASH_KEY, 359 NULL, 0, &mk->mk_ino_hash_key); 360 /* pairs with smp_load_acquire() above */ 361 smp_store_release(&mk->mk_ino_hash_key_initialized, true); 362 unlock: 363 mutex_unlock(&fscrypt_mode_key_setup_mutex); 364 } 365 366 /* 367 * New inodes may not have an inode number assigned yet. 368 * Hashing their inode number is delayed until later. 369 */ 370 if (ci->ci_inode->i_ino) 371 fscrypt_hash_inode_number(ci, mk); 372 return 0; 373 } 374 375 static int fscrypt_setup_v2_file_key(struct fscrypt_inode_info *ci, 376 struct fscrypt_master_key *mk, 377 bool need_dirhash_key) 378 { 379 int err; 380 381 if (mk->mk_secret.is_hw_wrapped && 382 !(ci->ci_policy.v2.flags & (FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 | 383 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))) { 384 fscrypt_warn(ci->ci_inode, 385 "Hardware-wrapped keys are only supported with IV_INO_LBLK policies"); 386 return -EINVAL; 387 } 388 389 if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) { 390 /* 391 * DIRECT_KEY: instead of deriving per-file encryption keys, the 392 * per-file nonce will be included in all the IVs. But unlike 393 * v1 policies, for v2 policies in this case we don't encrypt 394 * with the master key directly but rather derive a per-mode 395 * encryption key. This ensures that the master key is 396 * consistently used only for HKDF, avoiding key reuse issues. 397 */ 398 err = setup_per_mode_enc_key(ci, mk, HKDF_CONTEXT_DIRECT_KEY, 399 false); 400 } else if (ci->ci_policy.v2.flags & 401 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) { 402 /* 403 * IV_INO_LBLK_64: encryption keys are derived from (master_key, 404 * mode_num, filesystem_uuid), and inode number is included in 405 * the IVs. This format is optimized for use with inline 406 * encryption hardware compliant with the UFS standard. 407 */ 408 err = setup_per_mode_enc_key( 409 ci, mk, HKDF_CONTEXT_IV_INO_LBLK_64_KEY, true); 410 } else if (ci->ci_policy.v2.flags & 411 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) { 412 err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk); 413 } else { 414 u8 derived_key[FSCRYPT_MAX_RAW_KEY_SIZE]; 415 416 fscrypt_hkdf_expand(&mk->mk_secret.hkdf, 417 HKDF_CONTEXT_PER_FILE_ENC_KEY, 418 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE, 419 derived_key, ci->ci_mode->keysize); 420 err = fscrypt_set_per_file_enc_key(ci, derived_key); 421 memzero_explicit(derived_key, ci->ci_mode->keysize); 422 } 423 if (err) 424 return err; 425 426 /* Derive a secret dirhash key for directories that need it. */ 427 if (need_dirhash_key) 428 fscrypt_derive_dirhash_key(ci, mk); 429 430 return 0; 431 } 432 433 /* 434 * Check whether the size of the given master key (@mk) is appropriate for the 435 * encryption settings which a particular file will use (@ci). 436 * 437 * If the file uses a v1 encryption policy, then the master key must be at least 438 * as long as the derived key, as this is a requirement of the v1 KDF. 439 * 440 * Otherwise, the KDF can accept any size key, so we enforce a slightly looser 441 * requirement: we require that the size of the master key be at least the 442 * maximum security strength of any algorithm whose key will be derived from it 443 * (but in practice we only need to consider @ci->ci_mode, since any other 444 * possible subkeys such as DIRHASH and INODE_HASH will never increase the 445 * required key size over @ci->ci_mode). This allows AES-256-XTS keys to be 446 * derived from a 256-bit master key, which is cryptographically sufficient, 447 * rather than requiring a 512-bit master key which is unnecessarily long. (We 448 * still allow 512-bit master keys if the user chooses to use them, though.) 449 */ 450 static bool fscrypt_valid_master_key_size(const struct fscrypt_master_key *mk, 451 const struct fscrypt_inode_info *ci) 452 { 453 unsigned int min_keysize; 454 455 if (ci->ci_policy.version == FSCRYPT_POLICY_V1) 456 min_keysize = ci->ci_mode->keysize; 457 else 458 min_keysize = ci->ci_mode->security_strength; 459 460 if (mk->mk_secret.size < min_keysize) { 461 fscrypt_warn(NULL, 462 "key with %s %*phN is too short (got %u bytes, need %u+ bytes)", 463 master_key_spec_type(&mk->mk_spec), 464 master_key_spec_len(&mk->mk_spec), 465 (u8 *)&mk->mk_spec.u, 466 mk->mk_secret.size, min_keysize); 467 return false; 468 } 469 return true; 470 } 471 472 /* 473 * Find the master key, then set up the inode's actual encryption key. 474 * 475 * If the master key is found in the filesystem-level keyring, then it is 476 * returned in *mk_ret with its semaphore read-locked. This is needed to ensure 477 * that only one task links the fscrypt_inode_info into ->mk_decrypted_inodes 478 * (as multiple tasks may race to create an fscrypt_inode_info for the same 479 * inode), and to synchronize the master key being removed with a new inode 480 * starting to use it. 481 */ 482 static int setup_file_encryption_key(struct fscrypt_inode_info *ci, 483 bool need_dirhash_key, 484 struct fscrypt_master_key **mk_ret) 485 { 486 struct super_block *sb = ci->ci_inode->i_sb; 487 struct fscrypt_key_specifier mk_spec; 488 struct fscrypt_master_key *mk; 489 int err; 490 491 err = fscrypt_policy_to_key_spec(&ci->ci_policy, &mk_spec); 492 if (err) 493 return err; 494 495 mk = fscrypt_find_master_key(sb, &mk_spec); 496 if (unlikely(!mk)) { 497 const union fscrypt_policy *dummy_policy = 498 fscrypt_get_dummy_policy(sb); 499 500 /* 501 * Add the test_dummy_encryption key on-demand. In principle, 502 * it should be added at mount time. Do it here instead so that 503 * the individual filesystems don't need to worry about adding 504 * this key at mount time and cleaning up on mount failure. 505 */ 506 if (dummy_policy && 507 fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) { 508 err = fscrypt_add_test_dummy_key(sb, &mk_spec); 509 if (err) 510 return err; 511 mk = fscrypt_find_master_key(sb, &mk_spec); 512 } 513 } 514 if (unlikely(!mk)) { 515 if (ci->ci_policy.version != FSCRYPT_POLICY_V1) 516 return -ENOKEY; 517 518 err = fscrypt_select_encryption_impl(ci, false); 519 if (err) 520 return err; 521 522 /* 523 * As a legacy fallback for v1 policies, search for the key in 524 * the current task's subscribed keyrings too. Don't move this 525 * to before the search of ->s_master_keys, since users 526 * shouldn't be able to override filesystem-level keys. 527 */ 528 return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci); 529 } 530 down_read(&mk->mk_sem); 531 532 if (!mk->mk_present) { 533 /* FS_IOC_REMOVE_ENCRYPTION_KEY has been executed on this key */ 534 err = -ENOKEY; 535 goto out_release_key; 536 } 537 538 if (!fscrypt_valid_master_key_size(mk, ci)) { 539 err = -ENOKEY; 540 goto out_release_key; 541 } 542 543 err = fscrypt_select_encryption_impl(ci, mk->mk_secret.is_hw_wrapped); 544 if (err) 545 goto out_release_key; 546 547 switch (ci->ci_policy.version) { 548 case FSCRYPT_POLICY_V1: 549 if (WARN_ON_ONCE(mk->mk_secret.is_hw_wrapped)) { 550 /* 551 * This should never happen, as adding a v1 policy key 552 * that is hardware-wrapped isn't allowed. 553 */ 554 err = -EINVAL; 555 goto out_release_key; 556 } 557 err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.bytes); 558 break; 559 case FSCRYPT_POLICY_V2: 560 err = fscrypt_setup_v2_file_key(ci, mk, need_dirhash_key); 561 break; 562 default: 563 WARN_ON_ONCE(1); 564 err = -EINVAL; 565 break; 566 } 567 if (err) 568 goto out_release_key; 569 570 *mk_ret = mk; 571 return 0; 572 573 out_release_key: 574 up_read(&mk->mk_sem); 575 fscrypt_put_master_key(mk); 576 return err; 577 } 578 579 static void put_crypt_info(struct fscrypt_inode_info *ci) 580 { 581 struct fscrypt_master_key *mk; 582 583 if (!ci) 584 return; 585 586 if (ci->ci_direct_key) 587 fscrypt_put_direct_key(ci->ci_direct_key); 588 else if (ci->ci_owns_key) 589 fscrypt_destroy_prepared_key(ci->ci_inode->i_sb, 590 &ci->ci_enc_key); 591 592 mk = ci->ci_master_key; 593 if (mk) { 594 /* 595 * Remove this inode from the list of inodes that were unlocked 596 * with the master key. In addition, if we're removing the last 597 * inode from an incompletely removed key, then complete the 598 * full removal of the key. 599 */ 600 spin_lock(&mk->mk_decrypted_inodes_lock); 601 list_del(&ci->ci_master_key_link); 602 spin_unlock(&mk->mk_decrypted_inodes_lock); 603 fscrypt_put_master_key_activeref(ci->ci_inode->i_sb, mk); 604 } 605 memzero_explicit(ci, sizeof(*ci)); 606 kmem_cache_free(fscrypt_inode_info_cachep, ci); 607 } 608 609 static int 610 fscrypt_setup_encryption_info(struct inode *inode, 611 const union fscrypt_policy *policy, 612 const u8 nonce[FSCRYPT_FILE_NONCE_SIZE], 613 bool need_dirhash_key) 614 { 615 struct fscrypt_inode_info *crypt_info; 616 struct fscrypt_mode *mode; 617 struct fscrypt_master_key *mk = NULL; 618 int res; 619 620 res = fscrypt_initialize(inode->i_sb); 621 if (res) 622 return res; 623 624 crypt_info = kmem_cache_zalloc(fscrypt_inode_info_cachep, GFP_KERNEL); 625 if (!crypt_info) 626 return -ENOMEM; 627 628 crypt_info->ci_inode = inode; 629 crypt_info->ci_policy = *policy; 630 memcpy(crypt_info->ci_nonce, nonce, FSCRYPT_FILE_NONCE_SIZE); 631 632 mode = select_encryption_mode(&crypt_info->ci_policy, inode); 633 if (IS_ERR(mode)) { 634 res = PTR_ERR(mode); 635 goto out; 636 } 637 WARN_ON_ONCE(mode->ivsize > FSCRYPT_MAX_IV_SIZE); 638 crypt_info->ci_mode = mode; 639 640 crypt_info->ci_data_unit_bits = 641 fscrypt_policy_du_bits(&crypt_info->ci_policy, inode); 642 643 res = setup_file_encryption_key(crypt_info, need_dirhash_key, &mk); 644 if (res) 645 goto out; 646 647 /* 648 * For existing inodes, multiple tasks may race to set the inode's 649 * fscrypt info pointer. So use cmpxchg_release(). This pairs with the 650 * smp_load_acquire() in fscrypt_get_inode_info(). I.e., publish the 651 * pointer with a RELEASE barrier so that other tasks can ACQUIRE it. 652 */ 653 if (cmpxchg_release(fscrypt_inode_info_addr(inode), NULL, crypt_info) == 654 NULL) { 655 /* 656 * We won the race and set the inode's fscrypt info to our 657 * crypt_info. Now link it into the master key's inode list. 658 */ 659 if (mk) { 660 crypt_info->ci_master_key = mk; 661 refcount_inc(&mk->mk_active_refs); 662 spin_lock(&mk->mk_decrypted_inodes_lock); 663 list_add(&crypt_info->ci_master_key_link, 664 &mk->mk_decrypted_inodes); 665 spin_unlock(&mk->mk_decrypted_inodes_lock); 666 } 667 crypt_info = NULL; 668 } 669 res = 0; 670 out: 671 if (mk) { 672 up_read(&mk->mk_sem); 673 fscrypt_put_master_key(mk); 674 } 675 put_crypt_info(crypt_info); 676 return res; 677 } 678 679 /** 680 * fscrypt_get_encryption_info() - set up an inode's encryption key 681 * @inode: the inode to set up the key for. Must be encrypted. 682 * @allow_unsupported: if %true, treat an unsupported encryption policy (or 683 * unrecognized encryption context) the same way as the key 684 * being unavailable, instead of returning an error. Use 685 * %false unless the operation being performed is needed in 686 * order for files (or directories) to be deleted. 687 * 688 * Set up the inode's encryption key, if it hasn't already been done. 689 * 690 * Note: unless the key setup was already done, this isn't %GFP_NOFS-safe. So 691 * generally this shouldn't be called from within a filesystem transaction. 692 * 693 * Return: 0 if the key is now set up, *or* if it couldn't be set up because the 694 * needed master key is absent. (Use fscrypt_has_encryption_key() to 695 * distinguish these cases.) Also can return another -errno code. 696 */ 697 int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported) 698 { 699 int res; 700 union fscrypt_context ctx; 701 union fscrypt_policy policy; 702 703 if (fscrypt_has_encryption_key(inode)) 704 return 0; 705 706 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx)); 707 if (res < 0) { 708 if (res == -ERANGE && allow_unsupported) 709 return 0; 710 fscrypt_warn(inode, "Error %d getting encryption context", res); 711 return res; 712 } 713 714 res = fscrypt_policy_from_context(&policy, &ctx, res); 715 if (res) { 716 if (allow_unsupported) 717 return 0; 718 fscrypt_warn(inode, 719 "Unrecognized or corrupt encryption context"); 720 return res; 721 } 722 723 if (!fscrypt_supported_policy(&policy, inode)) { 724 if (allow_unsupported) 725 return 0; 726 return -EINVAL; 727 } 728 729 res = fscrypt_setup_encryption_info(inode, &policy, 730 fscrypt_context_nonce(&ctx), 731 IS_CASEFOLDED(inode) && 732 S_ISDIR(inode->i_mode)); 733 734 if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */ 735 res = 0; 736 if (res == -ENOKEY) 737 res = 0; 738 return res; 739 } 740 741 /** 742 * fscrypt_prepare_new_inode() - prepare to create a new inode in a directory 743 * @dir: a possibly-encrypted directory 744 * @inode: the new inode. ->i_mode and ->i_blkbits must be set already. 745 * ->i_ino doesn't need to be set yet. 746 * @encrypt_ret: (output) set to %true if the new inode will be encrypted 747 * 748 * If the directory is encrypted, set up its encryption key in preparation for 749 * encrypting the name of the new file. Also, if the new inode will be 750 * encrypted, set up its encryption key too and set *encrypt_ret=true. 751 * 752 * This isn't %GFP_NOFS-safe, and therefore it should be called before starting 753 * any filesystem transaction to create the inode. For this reason, ->i_ino 754 * isn't required to be set yet, as the filesystem may not have set it yet. 755 * 756 * This doesn't persist the new inode's encryption context. That still needs to 757 * be done later by calling fscrypt_set_context(). 758 * 759 * Return: 0 on success, -ENOKEY if a key needs to be set up for @dir or @inode 760 * but the needed master key is absent, or another -errno code 761 */ 762 int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode, 763 bool *encrypt_ret) 764 { 765 const union fscrypt_policy *policy; 766 u8 nonce[FSCRYPT_FILE_NONCE_SIZE]; 767 768 policy = fscrypt_policy_to_inherit(dir); 769 if (policy == NULL) 770 return 0; 771 if (IS_ERR(policy)) 772 return PTR_ERR(policy); 773 774 if (WARN_ON_ONCE(inode->i_blkbits == 0)) 775 return -EINVAL; 776 777 if (WARN_ON_ONCE(inode->i_mode == 0)) 778 return -EINVAL; 779 780 /* 781 * Only regular files, directories, and symlinks are encrypted. 782 * Special files like device nodes and named pipes aren't. 783 */ 784 if (!S_ISREG(inode->i_mode) && 785 !S_ISDIR(inode->i_mode) && 786 !S_ISLNK(inode->i_mode)) 787 return 0; 788 789 *encrypt_ret = true; 790 791 get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE); 792 return fscrypt_setup_encryption_info(inode, policy, nonce, 793 IS_CASEFOLDED(dir) && 794 S_ISDIR(inode->i_mode)); 795 } 796 EXPORT_SYMBOL_GPL(fscrypt_prepare_new_inode); 797 798 /** 799 * fscrypt_put_encryption_info() - free most of an inode's fscrypt data 800 * @inode: an inode being evicted 801 * 802 * Free the inode's fscrypt_inode_info. Filesystems must call this when the 803 * inode is being evicted. An RCU grace period need not have elapsed yet. 804 */ 805 void fscrypt_put_encryption_info(struct inode *inode) 806 { 807 /* 808 * Ideally we'd start with a lightweight IS_ENCRYPTED() check here 809 * before proceeding to retrieve and check the pointer. However, during 810 * inode creation, the fscrypt_inode_info is set before S_ENCRYPTED. If 811 * an error occurs, it needs to be cleaned up regardless. 812 */ 813 struct fscrypt_inode_info **ci_addr = fscrypt_inode_info_addr(inode); 814 815 put_crypt_info(*ci_addr); 816 *ci_addr = NULL; 817 } 818 EXPORT_SYMBOL(fscrypt_put_encryption_info); 819 820 /** 821 * fscrypt_free_inode() - free an inode's fscrypt data requiring RCU delay 822 * @inode: an inode being freed 823 * 824 * Free the inode's cached decrypted symlink target, if any. Filesystems must 825 * call this after an RCU grace period, just before they free the inode. 826 */ 827 void fscrypt_free_inode(struct inode *inode) 828 { 829 if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) { 830 kfree(inode->i_link); 831 inode->i_link = NULL; 832 } 833 } 834 EXPORT_SYMBOL(fscrypt_free_inode); 835 836 /** 837 * fscrypt_drop_inode() - check whether the inode's master key has been removed 838 * @inode: an inode being considered for eviction 839 * 840 * Filesystems supporting fscrypt must call this from their ->drop_inode() 841 * method so that encrypted inodes are evicted as soon as they're no longer in 842 * use and their master key has been removed. 843 * 844 * Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0 845 */ 846 int fscrypt_drop_inode(struct inode *inode) 847 { 848 const struct fscrypt_inode_info *ci = fscrypt_get_inode_info(inode); 849 850 /* 851 * If ci is NULL, then the inode doesn't have an encryption key set up 852 * so it's irrelevant. If ci_master_key is NULL, then the master key 853 * was provided via the legacy mechanism of the process-subscribed 854 * keyrings, so we don't know whether it's been removed or not. 855 */ 856 if (!ci || !ci->ci_master_key) 857 return 0; 858 859 /* 860 * With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes 861 * protected by the key were cleaned by sync_filesystem(). But if 862 * userspace is still using the files, inodes can be dirtied between 863 * then and now. We mustn't lose any writes, so skip dirty inodes here. 864 */ 865 if (inode_state_read(inode) & I_DIRTY_ALL) 866 return 0; 867 868 /* 869 * We can't take ->mk_sem here, since this runs in atomic context. 870 * Therefore, ->mk_present can change concurrently, and our result may 871 * immediately become outdated. But there's no correctness problem with 872 * unnecessarily evicting. Nor is there a correctness problem with not 873 * evicting while iput() is racing with the key being removed, since 874 * then the thread removing the key will either evict the inode itself 875 * or will correctly detect that it wasn't evicted due to the race. 876 */ 877 return !READ_ONCE(ci->ci_master_key->mk_present); 878 } 879 EXPORT_SYMBOL_GPL(fscrypt_drop_inode); 880