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/random.h>
13
14 #include "fscrypt_private.h"
15
16 struct fscrypt_mode fscrypt_modes[] = {
17 [FSCRYPT_MODE_AES_256_XTS] = {
18 .friendly_name = "AES-256-XTS",
19 .cipher_str = "xts(aes)",
20 .keysize = 64,
21 .security_strength = 32,
22 .ivsize = 16,
23 .blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_256_XTS,
24 },
25 [FSCRYPT_MODE_AES_256_CTS] = {
26 .friendly_name = "AES-256-CTS-CBC",
27 .cipher_str = "cts(cbc(aes))",
28 .keysize = 32,
29 .security_strength = 32,
30 .ivsize = 16,
31 },
32 [FSCRYPT_MODE_AES_128_CBC] = {
33 .friendly_name = "AES-128-CBC-ESSIV",
34 .cipher_str = "essiv(cbc(aes),sha256)",
35 .keysize = 16,
36 .security_strength = 16,
37 .ivsize = 16,
38 .blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_128_CBC_ESSIV,
39 },
40 [FSCRYPT_MODE_AES_128_CTS] = {
41 .friendly_name = "AES-128-CTS-CBC",
42 .cipher_str = "cts(cbc(aes))",
43 .keysize = 16,
44 .security_strength = 16,
45 .ivsize = 16,
46 },
47 [FSCRYPT_MODE_SM4_XTS] = {
48 .friendly_name = "SM4-XTS",
49 .cipher_str = "xts(sm4)",
50 .keysize = 32,
51 .security_strength = 16,
52 .ivsize = 16,
53 .blk_crypto_mode = BLK_ENCRYPTION_MODE_SM4_XTS,
54 },
55 [FSCRYPT_MODE_SM4_CTS] = {
56 .friendly_name = "SM4-CTS-CBC",
57 .cipher_str = "cts(cbc(sm4))",
58 .keysize = 16,
59 .security_strength = 16,
60 .ivsize = 16,
61 },
62 [FSCRYPT_MODE_ADIANTUM] = {
63 .friendly_name = "Adiantum",
64 .cipher_str = "adiantum(xchacha12,aes)",
65 .keysize = 32,
66 .security_strength = 32,
67 .ivsize = 32,
68 .blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM,
69 },
70 [FSCRYPT_MODE_AES_256_HCTR2] = {
71 .friendly_name = "AES-256-HCTR2",
72 .cipher_str = "hctr2(aes)",
73 .keysize = 32,
74 .security_strength = 32,
75 .ivsize = 32,
76 },
77 };
78
79 static DEFINE_MUTEX(fscrypt_mode_key_setup_mutex);
80
81 static struct fscrypt_mode *
select_encryption_mode(const union fscrypt_policy * policy,const struct inode * inode)82 select_encryption_mode(const union fscrypt_policy *policy,
83 const struct inode *inode)
84 {
85 BUILD_BUG_ON(ARRAY_SIZE(fscrypt_modes) != FSCRYPT_MODE_MAX + 1);
86
87 if (S_ISREG(inode->i_mode))
88 return &fscrypt_modes[fscrypt_policy_contents_mode(policy)];
89
90 if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
91 return &fscrypt_modes[fscrypt_policy_fnames_mode(policy)];
92
93 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
94 inode->i_ino, (inode->i_mode & S_IFMT));
95 return ERR_PTR(-EINVAL);
96 }
97
98 /* Create a symmetric cipher object for the given encryption mode and key */
99 static struct crypto_skcipher *
fscrypt_allocate_skcipher(struct fscrypt_mode * mode,const u8 * raw_key,const struct inode * inode)100 fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
101 const struct inode *inode)
102 {
103 struct crypto_skcipher *tfm;
104 int err;
105
106 tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
107 if (IS_ERR(tfm)) {
108 if (PTR_ERR(tfm) == -ENOENT) {
109 fscrypt_warn(inode,
110 "Missing crypto API support for %s (API name: \"%s\")",
111 mode->friendly_name, mode->cipher_str);
112 return ERR_PTR(-ENOPKG);
113 }
114 fscrypt_err(inode, "Error allocating '%s' transform: %ld",
115 mode->cipher_str, PTR_ERR(tfm));
116 return tfm;
117 }
118 if (!xchg(&mode->logged_cryptoapi_impl, 1)) {
119 /*
120 * fscrypt performance can vary greatly depending on which
121 * crypto algorithm implementation is used. Help people debug
122 * performance problems by logging the ->cra_driver_name the
123 * first time a mode is used.
124 */
125 pr_info("fscrypt: %s using implementation \"%s\"\n",
126 mode->friendly_name, crypto_skcipher_driver_name(tfm));
127 }
128 if (WARN_ON_ONCE(crypto_skcipher_ivsize(tfm) != mode->ivsize)) {
129 err = -EINVAL;
130 goto err_free_tfm;
131 }
132 crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
133 err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
134 if (err)
135 goto err_free_tfm;
136
137 return tfm;
138
139 err_free_tfm:
140 crypto_free_skcipher(tfm);
141 return ERR_PTR(err);
142 }
143
144 /*
145 * Prepare the crypto transform object or blk-crypto key in @prep_key, given the
146 * raw key, encryption mode (@ci->ci_mode), flag indicating which encryption
147 * implementation (fs-layer or blk-crypto) will be used (@ci->ci_inlinecrypt),
148 * and IV generation method (@ci->ci_policy.flags).
149 */
fscrypt_prepare_key(struct fscrypt_prepared_key * prep_key,const u8 * raw_key,const struct fscrypt_info * ci)150 int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key,
151 const u8 *raw_key, const struct fscrypt_info *ci)
152 {
153 struct crypto_skcipher *tfm;
154
155 if (fscrypt_using_inline_encryption(ci))
156 return fscrypt_prepare_inline_crypt_key(prep_key, raw_key,
157 ci->ci_mode->keysize,
158 false, ci);
159
160 tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode);
161 if (IS_ERR(tfm))
162 return PTR_ERR(tfm);
163 /*
164 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
165 * I.e., here we publish ->tfm with a RELEASE barrier so that
166 * concurrent tasks can ACQUIRE it. Note that this concurrency is only
167 * possible for per-mode keys, not for per-file keys.
168 */
169 smp_store_release(&prep_key->tfm, tfm);
170 return 0;
171 }
172
173 /* Destroy a crypto transform object and/or blk-crypto key. */
fscrypt_destroy_prepared_key(struct super_block * sb,struct fscrypt_prepared_key * prep_key)174 void fscrypt_destroy_prepared_key(struct super_block *sb,
175 struct fscrypt_prepared_key *prep_key)
176 {
177 crypto_free_skcipher(prep_key->tfm);
178 fscrypt_destroy_inline_crypt_key(sb, prep_key);
179 memzero_explicit(prep_key, sizeof(*prep_key));
180 }
181
182 /* Given a per-file encryption key, set up the file's crypto transform object */
fscrypt_set_per_file_enc_key(struct fscrypt_info * ci,const u8 * raw_key)183 int fscrypt_set_per_file_enc_key(struct fscrypt_info *ci, const u8 *raw_key)
184 {
185 ci->ci_owns_key = true;
186 return fscrypt_prepare_key(&ci->ci_enc_key, raw_key, ci);
187 }
188
setup_per_mode_enc_key(struct fscrypt_info * ci,struct fscrypt_master_key * mk,struct fscrypt_prepared_key * keys,u8 hkdf_context,bool include_fs_uuid)189 static int setup_per_mode_enc_key(struct fscrypt_info *ci,
190 struct fscrypt_master_key *mk,
191 struct fscrypt_prepared_key *keys,
192 u8 hkdf_context, bool include_fs_uuid)
193 {
194 const struct inode *inode = ci->ci_inode;
195 const struct super_block *sb = inode->i_sb;
196 struct fscrypt_mode *mode = ci->ci_mode;
197 const u8 mode_num = mode - fscrypt_modes;
198 struct fscrypt_prepared_key *prep_key;
199 u8 mode_key[FSCRYPT_MAX_STANDARD_KEY_SIZE];
200 u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
201 unsigned int hkdf_infolen = 0;
202 bool use_hw_wrapped_key = false;
203 int err;
204
205 if (WARN_ON_ONCE(mode_num > FSCRYPT_MODE_MAX))
206 return -EINVAL;
207
208 if (mk->mk_secret.is_hw_wrapped && S_ISREG(inode->i_mode)) {
209 /* Using a hardware-wrapped key for file contents encryption */
210 if (!fscrypt_using_inline_encryption(ci)) {
211 if (sb->s_flags & SB_INLINECRYPT)
212 fscrypt_warn(ci->ci_inode,
213 "Hardware-wrapped key required, but no suitable inline encryption capabilities are available");
214 else
215 fscrypt_warn(ci->ci_inode,
216 "Hardware-wrapped keys require inline encryption (-o inlinecrypt)");
217 return -EINVAL;
218 }
219 use_hw_wrapped_key = true;
220 }
221
222 prep_key = &keys[mode_num];
223 if (fscrypt_is_key_prepared(prep_key, ci)) {
224 ci->ci_enc_key = *prep_key;
225 return 0;
226 }
227
228 mutex_lock(&fscrypt_mode_key_setup_mutex);
229
230 if (fscrypt_is_key_prepared(prep_key, ci))
231 goto done_unlock;
232
233 if (use_hw_wrapped_key) {
234 err = fscrypt_prepare_inline_crypt_key(prep_key,
235 mk->mk_secret.raw,
236 mk->mk_secret.size, true,
237 ci);
238 if (err)
239 goto out_unlock;
240 goto done_unlock;
241 }
242
243 BUILD_BUG_ON(sizeof(mode_num) != 1);
244 BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
245 BUILD_BUG_ON(sizeof(hkdf_info) != 17);
246 hkdf_info[hkdf_infolen++] = mode_num;
247 if (include_fs_uuid) {
248 memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
249 sizeof(sb->s_uuid));
250 hkdf_infolen += sizeof(sb->s_uuid);
251 }
252 err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
253 hkdf_context, hkdf_info, hkdf_infolen,
254 mode_key, mode->keysize);
255 if (err)
256 goto out_unlock;
257 err = fscrypt_prepare_key(prep_key, mode_key, ci);
258 memzero_explicit(mode_key, mode->keysize);
259 if (err)
260 goto out_unlock;
261 done_unlock:
262 ci->ci_enc_key = *prep_key;
263 err = 0;
264 out_unlock:
265 mutex_unlock(&fscrypt_mode_key_setup_mutex);
266 return err;
267 }
268
269 /*
270 * Derive a SipHash key from the given fscrypt master key and the given
271 * application-specific information string.
272 *
273 * Note that the KDF produces a byte array, but the SipHash APIs expect the key
274 * as a pair of 64-bit words. Therefore, on big endian CPUs we have to do an
275 * endianness swap in order to get the same results as on little endian CPUs.
276 */
fscrypt_derive_siphash_key(const struct fscrypt_master_key * mk,u8 context,const u8 * info,unsigned int infolen,siphash_key_t * key)277 static int fscrypt_derive_siphash_key(const struct fscrypt_master_key *mk,
278 u8 context, const u8 *info,
279 unsigned int infolen, siphash_key_t *key)
280 {
281 int err;
282
283 err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen,
284 (u8 *)key, sizeof(*key));
285 if (err)
286 return err;
287
288 BUILD_BUG_ON(sizeof(*key) != 16);
289 BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2);
290 le64_to_cpus(&key->key[0]);
291 le64_to_cpus(&key->key[1]);
292 return 0;
293 }
294
fscrypt_derive_dirhash_key(struct fscrypt_info * ci,const struct fscrypt_master_key * mk)295 int fscrypt_derive_dirhash_key(struct fscrypt_info *ci,
296 const struct fscrypt_master_key *mk)
297 {
298 int err;
299
300 err = fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,
301 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
302 &ci->ci_dirhash_key);
303 if (err)
304 return err;
305 ci->ci_dirhash_key_initialized = true;
306 return 0;
307 }
308
fscrypt_hash_inode_number(struct fscrypt_info * ci,const struct fscrypt_master_key * mk)309 void fscrypt_hash_inode_number(struct fscrypt_info *ci,
310 const struct fscrypt_master_key *mk)
311 {
312 WARN_ON_ONCE(ci->ci_inode->i_ino == 0);
313 WARN_ON_ONCE(!mk->mk_ino_hash_key_initialized);
314
315 ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino,
316 &mk->mk_ino_hash_key);
317 }
318
fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_info * ci,struct fscrypt_master_key * mk)319 static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_info *ci,
320 struct fscrypt_master_key *mk)
321 {
322 int err;
323
324 err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_32_keys,
325 HKDF_CONTEXT_IV_INO_LBLK_32_KEY, true);
326 if (err)
327 return err;
328
329 /* pairs with smp_store_release() below */
330 if (!smp_load_acquire(&mk->mk_ino_hash_key_initialized)) {
331
332 mutex_lock(&fscrypt_mode_key_setup_mutex);
333
334 if (mk->mk_ino_hash_key_initialized)
335 goto unlock;
336
337 err = fscrypt_derive_siphash_key(mk,
338 HKDF_CONTEXT_INODE_HASH_KEY,
339 NULL, 0, &mk->mk_ino_hash_key);
340 if (err)
341 goto unlock;
342 /* pairs with smp_load_acquire() above */
343 smp_store_release(&mk->mk_ino_hash_key_initialized, true);
344 unlock:
345 mutex_unlock(&fscrypt_mode_key_setup_mutex);
346 if (err)
347 return err;
348 }
349
350 /*
351 * New inodes may not have an inode number assigned yet.
352 * Hashing their inode number is delayed until later.
353 */
354 if (ci->ci_inode->i_ino)
355 fscrypt_hash_inode_number(ci, mk);
356 return 0;
357 }
358
fscrypt_setup_v2_file_key(struct fscrypt_info * ci,struct fscrypt_master_key * mk,bool need_dirhash_key)359 static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
360 struct fscrypt_master_key *mk,
361 bool need_dirhash_key)
362 {
363 int err;
364
365 if (mk->mk_secret.is_hw_wrapped &&
366 !(ci->ci_policy.v2.flags & (FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 |
367 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))) {
368 fscrypt_warn(ci->ci_inode,
369 "Hardware-wrapped keys are only supported with IV_INO_LBLK policies");
370 return -EINVAL;
371 }
372
373 if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
374 /*
375 * DIRECT_KEY: instead of deriving per-file encryption keys, the
376 * per-file nonce will be included in all the IVs. But unlike
377 * v1 policies, for v2 policies in this case we don't encrypt
378 * with the master key directly but rather derive a per-mode
379 * encryption key. This ensures that the master key is
380 * consistently used only for HKDF, avoiding key reuse issues.
381 */
382 err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_keys,
383 HKDF_CONTEXT_DIRECT_KEY, false);
384 } else if (ci->ci_policy.v2.flags &
385 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
386 /*
387 * IV_INO_LBLK_64: encryption keys are derived from (master_key,
388 * mode_num, filesystem_uuid), and inode number is included in
389 * the IVs. This format is optimized for use with inline
390 * encryption hardware compliant with the UFS standard.
391 */
392 err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_keys,
393 HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
394 true);
395 } else if (ci->ci_policy.v2.flags &
396 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
397 err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk);
398 } else {
399 u8 derived_key[FSCRYPT_MAX_STANDARD_KEY_SIZE];
400
401 err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
402 HKDF_CONTEXT_PER_FILE_ENC_KEY,
403 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
404 derived_key, ci->ci_mode->keysize);
405 if (err)
406 return err;
407
408 err = fscrypt_set_per_file_enc_key(ci, derived_key);
409 memzero_explicit(derived_key, ci->ci_mode->keysize);
410 }
411 if (err)
412 return err;
413
414 /* Derive a secret dirhash key for directories that need it. */
415 if (need_dirhash_key) {
416 err = fscrypt_derive_dirhash_key(ci, mk);
417 if (err)
418 return err;
419 }
420
421 return 0;
422 }
423
424 /*
425 * Check whether the size of the given master key (@mk) is appropriate for the
426 * encryption settings which a particular file will use (@ci).
427 *
428 * If the file uses a v1 encryption policy, then the master key must be at least
429 * as long as the derived key, as this is a requirement of the v1 KDF.
430 *
431 * Otherwise, the KDF can accept any size key, so we enforce a slightly looser
432 * requirement: we require that the size of the master key be at least the
433 * maximum security strength of any algorithm whose key will be derived from it
434 * (but in practice we only need to consider @ci->ci_mode, since any other
435 * possible subkeys such as DIRHASH and INODE_HASH will never increase the
436 * required key size over @ci->ci_mode). This allows AES-256-XTS keys to be
437 * derived from a 256-bit master key, which is cryptographically sufficient,
438 * rather than requiring a 512-bit master key which is unnecessarily long. (We
439 * still allow 512-bit master keys if the user chooses to use them, though.)
440 */
fscrypt_valid_master_key_size(const struct fscrypt_master_key * mk,const struct fscrypt_info * ci)441 static bool fscrypt_valid_master_key_size(const struct fscrypt_master_key *mk,
442 const struct fscrypt_info *ci)
443 {
444 unsigned int min_keysize;
445
446 if (ci->ci_policy.version == FSCRYPT_POLICY_V1)
447 min_keysize = ci->ci_mode->keysize;
448 else
449 min_keysize = ci->ci_mode->security_strength;
450
451 if (mk->mk_secret.size < min_keysize) {
452 fscrypt_warn(NULL,
453 "key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
454 master_key_spec_type(&mk->mk_spec),
455 master_key_spec_len(&mk->mk_spec),
456 (u8 *)&mk->mk_spec.u,
457 mk->mk_secret.size, min_keysize);
458 return false;
459 }
460 return true;
461 }
462
463 /*
464 * Find the master key, then set up the inode's actual encryption key.
465 *
466 * If the master key is found in the filesystem-level keyring, then it is
467 * returned in *mk_ret with its semaphore read-locked. This is needed to ensure
468 * that only one task links the fscrypt_info into ->mk_decrypted_inodes (as
469 * multiple tasks may race to create an fscrypt_info for the same inode), and to
470 * synchronize the master key being removed with a new inode starting to use it.
471 */
setup_file_encryption_key(struct fscrypt_info * ci,bool need_dirhash_key,struct fscrypt_master_key ** mk_ret)472 static int setup_file_encryption_key(struct fscrypt_info *ci,
473 bool need_dirhash_key,
474 struct fscrypt_master_key **mk_ret)
475 {
476 struct super_block *sb = ci->ci_inode->i_sb;
477 struct fscrypt_key_specifier mk_spec;
478 struct fscrypt_master_key *mk;
479 int err;
480
481 err = fscrypt_policy_to_key_spec(&ci->ci_policy, &mk_spec);
482 if (err)
483 return err;
484
485 mk = fscrypt_find_master_key(sb, &mk_spec);
486 if (unlikely(!mk)) {
487 const union fscrypt_policy *dummy_policy =
488 fscrypt_get_dummy_policy(sb);
489
490 /*
491 * Add the test_dummy_encryption key on-demand. In principle,
492 * it should be added at mount time. Do it here instead so that
493 * the individual filesystems don't need to worry about adding
494 * this key at mount time and cleaning up on mount failure.
495 */
496 if (dummy_policy &&
497 fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {
498 err = fscrypt_add_test_dummy_key(sb, &mk_spec);
499 if (err)
500 return err;
501 mk = fscrypt_find_master_key(sb, &mk_spec);
502 }
503 }
504 if (unlikely(!mk)) {
505 if (ci->ci_policy.version != FSCRYPT_POLICY_V1)
506 return -ENOKEY;
507
508 err = fscrypt_select_encryption_impl(ci, false);
509 if (err)
510 return err;
511
512 /*
513 * As a legacy fallback for v1 policies, search for the key in
514 * the current task's subscribed keyrings too. Don't move this
515 * to before the search of ->s_master_keys, since users
516 * shouldn't be able to override filesystem-level keys.
517 */
518 return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
519 }
520 down_read(&mk->mk_sem);
521
522 /* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */
523 if (!is_master_key_secret_present(&mk->mk_secret)) {
524 err = -ENOKEY;
525 goto out_release_key;
526 }
527
528 if (!fscrypt_valid_master_key_size(mk, ci)) {
529 err = -ENOKEY;
530 goto out_release_key;
531 }
532
533 err = fscrypt_select_encryption_impl(ci, mk->mk_secret.is_hw_wrapped);
534 if (err)
535 goto out_release_key;
536
537 switch (ci->ci_policy.version) {
538 case FSCRYPT_POLICY_V1:
539 if (WARN_ON(mk->mk_secret.is_hw_wrapped)) {
540 /*
541 * This should never happen, as adding a v1 policy key
542 * that is hardware-wrapped isn't allowed.
543 */
544 err = -EINVAL;
545 goto out_release_key;
546 }
547 err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
548 break;
549 case FSCRYPT_POLICY_V2:
550 err = fscrypt_setup_v2_file_key(ci, mk, need_dirhash_key);
551 break;
552 default:
553 WARN_ON_ONCE(1);
554 err = -EINVAL;
555 break;
556 }
557 if (err)
558 goto out_release_key;
559
560 *mk_ret = mk;
561 return 0;
562
563 out_release_key:
564 up_read(&mk->mk_sem);
565 fscrypt_put_master_key(mk);
566 return err;
567 }
568
put_crypt_info(struct fscrypt_info * ci)569 static void put_crypt_info(struct fscrypt_info *ci)
570 {
571 struct fscrypt_master_key *mk;
572
573 if (!ci)
574 return;
575
576 if (ci->ci_direct_key)
577 fscrypt_put_direct_key(ci->ci_direct_key);
578 else if (ci->ci_owns_key)
579 fscrypt_destroy_prepared_key(ci->ci_inode->i_sb,
580 &ci->ci_enc_key);
581
582 mk = ci->ci_master_key;
583 if (mk) {
584 /*
585 * Remove this inode from the list of inodes that were unlocked
586 * with the master key. In addition, if we're removing the last
587 * inode from a master key struct that already had its secret
588 * removed, then complete the full removal of the struct.
589 */
590 spin_lock(&mk->mk_decrypted_inodes_lock);
591 list_del(&ci->ci_master_key_link);
592 spin_unlock(&mk->mk_decrypted_inodes_lock);
593 fscrypt_put_master_key_activeref(ci->ci_inode->i_sb, mk);
594 }
595 memzero_explicit(ci, sizeof(*ci));
596 kmem_cache_free(fscrypt_info_cachep, ci);
597 }
598
599 static int
fscrypt_setup_encryption_info(struct inode * inode,const union fscrypt_policy * policy,const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],bool need_dirhash_key)600 fscrypt_setup_encryption_info(struct inode *inode,
601 const union fscrypt_policy *policy,
602 const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],
603 bool need_dirhash_key)
604 {
605 struct fscrypt_info *crypt_info;
606 struct fscrypt_mode *mode;
607 struct fscrypt_master_key *mk = NULL;
608 int res;
609
610 res = fscrypt_initialize(inode->i_sb);
611 if (res)
612 return res;
613
614 crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_KERNEL);
615 if (!crypt_info)
616 return -ENOMEM;
617
618 crypt_info->ci_inode = inode;
619 crypt_info->ci_policy = *policy;
620 memcpy(crypt_info->ci_nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
621
622 mode = select_encryption_mode(&crypt_info->ci_policy, inode);
623 if (IS_ERR(mode)) {
624 res = PTR_ERR(mode);
625 goto out;
626 }
627 WARN_ON_ONCE(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
628 crypt_info->ci_mode = mode;
629
630 crypt_info->ci_data_unit_bits =
631 fscrypt_policy_du_bits(&crypt_info->ci_policy, inode);
632 crypt_info->ci_data_units_per_block_bits =
633 inode->i_blkbits - crypt_info->ci_data_unit_bits;
634
635 res = setup_file_encryption_key(crypt_info, need_dirhash_key, &mk);
636 if (res)
637 goto out;
638
639 /*
640 * For existing inodes, multiple tasks may race to set ->i_crypt_info.
641 * So use cmpxchg_release(). This pairs with the smp_load_acquire() in
642 * fscrypt_get_info(). I.e., here we publish ->i_crypt_info with a
643 * RELEASE barrier so that other tasks can ACQUIRE it.
644 */
645 if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) {
646 /*
647 * We won the race and set ->i_crypt_info to our crypt_info.
648 * Now link it into the master key's inode list.
649 */
650 if (mk) {
651 crypt_info->ci_master_key = mk;
652 refcount_inc(&mk->mk_active_refs);
653 spin_lock(&mk->mk_decrypted_inodes_lock);
654 list_add(&crypt_info->ci_master_key_link,
655 &mk->mk_decrypted_inodes);
656 spin_unlock(&mk->mk_decrypted_inodes_lock);
657 }
658 crypt_info = NULL;
659 }
660 res = 0;
661 out:
662 if (mk) {
663 up_read(&mk->mk_sem);
664 fscrypt_put_master_key(mk);
665 }
666 put_crypt_info(crypt_info);
667 return res;
668 }
669
670 /**
671 * fscrypt_get_encryption_info() - set up an inode's encryption key
672 * @inode: the inode to set up the key for. Must be encrypted.
673 * @allow_unsupported: if %true, treat an unsupported encryption policy (or
674 * unrecognized encryption context) the same way as the key
675 * being unavailable, instead of returning an error. Use
676 * %false unless the operation being performed is needed in
677 * order for files (or directories) to be deleted.
678 *
679 * Set up ->i_crypt_info, if it hasn't already been done.
680 *
681 * Note: unless ->i_crypt_info is already set, this isn't %GFP_NOFS-safe. So
682 * generally this shouldn't be called from within a filesystem transaction.
683 *
684 * Return: 0 if ->i_crypt_info was set or was already set, *or* if the
685 * encryption key is unavailable. (Use fscrypt_has_encryption_key() to
686 * distinguish these cases.) Also can return another -errno code.
687 */
fscrypt_get_encryption_info(struct inode * inode,bool allow_unsupported)688 int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)
689 {
690 int res;
691 union fscrypt_context ctx;
692 union fscrypt_policy policy;
693
694 if (fscrypt_has_encryption_key(inode))
695 return 0;
696
697 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
698 if (res < 0) {
699 if (res == -ERANGE && allow_unsupported)
700 return 0;
701 fscrypt_warn(inode, "Error %d getting encryption context", res);
702 return res;
703 }
704
705 res = fscrypt_policy_from_context(&policy, &ctx, res);
706 if (res) {
707 if (allow_unsupported)
708 return 0;
709 fscrypt_warn(inode,
710 "Unrecognized or corrupt encryption context");
711 return res;
712 }
713
714 if (!fscrypt_supported_policy(&policy, inode)) {
715 if (allow_unsupported)
716 return 0;
717 return -EINVAL;
718 }
719
720 res = fscrypt_setup_encryption_info(inode, &policy,
721 fscrypt_context_nonce(&ctx),
722 IS_CASEFOLDED(inode) &&
723 S_ISDIR(inode->i_mode));
724
725 if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */
726 res = 0;
727 if (res == -ENOKEY)
728 res = 0;
729 return res;
730 }
731
732 /**
733 * fscrypt_prepare_new_inode() - prepare to create a new inode in a directory
734 * @dir: a possibly-encrypted directory
735 * @inode: the new inode. ->i_mode must be set already.
736 * ->i_ino doesn't need to be set yet.
737 * @encrypt_ret: (output) set to %true if the new inode will be encrypted
738 *
739 * If the directory is encrypted, set up its ->i_crypt_info in preparation for
740 * encrypting the name of the new file. Also, if the new inode will be
741 * encrypted, set up its ->i_crypt_info and set *encrypt_ret=true.
742 *
743 * This isn't %GFP_NOFS-safe, and therefore it should be called before starting
744 * any filesystem transaction to create the inode. For this reason, ->i_ino
745 * isn't required to be set yet, as the filesystem may not have set it yet.
746 *
747 * This doesn't persist the new inode's encryption context. That still needs to
748 * be done later by calling fscrypt_set_context().
749 *
750 * Return: 0 on success, -ENOKEY if the encryption key is missing, or another
751 * -errno code
752 */
fscrypt_prepare_new_inode(struct inode * dir,struct inode * inode,bool * encrypt_ret)753 int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
754 bool *encrypt_ret)
755 {
756 const union fscrypt_policy *policy;
757 u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
758
759 policy = fscrypt_policy_to_inherit(dir);
760 if (policy == NULL)
761 return 0;
762 if (IS_ERR(policy))
763 return PTR_ERR(policy);
764
765 if (WARN_ON_ONCE(inode->i_mode == 0))
766 return -EINVAL;
767
768 /*
769 * Only regular files, directories, and symlinks are encrypted.
770 * Special files like device nodes and named pipes aren't.
771 */
772 if (!S_ISREG(inode->i_mode) &&
773 !S_ISDIR(inode->i_mode) &&
774 !S_ISLNK(inode->i_mode))
775 return 0;
776
777 *encrypt_ret = true;
778
779 get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);
780 return fscrypt_setup_encryption_info(inode, policy, nonce,
781 IS_CASEFOLDED(dir) &&
782 S_ISDIR(inode->i_mode));
783 }
784 EXPORT_SYMBOL_GPL(fscrypt_prepare_new_inode);
785
786 /**
787 * fscrypt_put_encryption_info() - free most of an inode's fscrypt data
788 * @inode: an inode being evicted
789 *
790 * Free the inode's fscrypt_info. Filesystems must call this when the inode is
791 * being evicted. An RCU grace period need not have elapsed yet.
792 */
fscrypt_put_encryption_info(struct inode * inode)793 void fscrypt_put_encryption_info(struct inode *inode)
794 {
795 put_crypt_info(inode->i_crypt_info);
796 inode->i_crypt_info = NULL;
797 }
798 EXPORT_SYMBOL(fscrypt_put_encryption_info);
799
800 /**
801 * fscrypt_free_inode() - free an inode's fscrypt data requiring RCU delay
802 * @inode: an inode being freed
803 *
804 * Free the inode's cached decrypted symlink target, if any. Filesystems must
805 * call this after an RCU grace period, just before they free the inode.
806 */
fscrypt_free_inode(struct inode * inode)807 void fscrypt_free_inode(struct inode *inode)
808 {
809 if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
810 kfree(inode->i_link);
811 inode->i_link = NULL;
812 }
813 }
814 EXPORT_SYMBOL(fscrypt_free_inode);
815
816 /**
817 * fscrypt_drop_inode() - check whether the inode's master key has been removed
818 * @inode: an inode being considered for eviction
819 *
820 * Filesystems supporting fscrypt must call this from their ->drop_inode()
821 * method so that encrypted inodes are evicted as soon as they're no longer in
822 * use and their master key has been removed.
823 *
824 * Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
825 */
fscrypt_drop_inode(struct inode * inode)826 int fscrypt_drop_inode(struct inode *inode)
827 {
828 const struct fscrypt_info *ci = fscrypt_get_info(inode);
829
830 /*
831 * If ci is NULL, then the inode doesn't have an encryption key set up
832 * so it's irrelevant. If ci_master_key is NULL, then the master key
833 * was provided via the legacy mechanism of the process-subscribed
834 * keyrings, so we don't know whether it's been removed or not.
835 */
836 if (!ci || !ci->ci_master_key)
837 return 0;
838
839 /*
840 * With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
841 * protected by the key were cleaned by sync_filesystem(). But if
842 * userspace is still using the files, inodes can be dirtied between
843 * then and now. We mustn't lose any writes, so skip dirty inodes here.
844 */
845 if (inode->i_state & I_DIRTY_ALL)
846 return 0;
847
848 /*
849 * Note: since we aren't holding the key semaphore, the result here can
850 * immediately become outdated. But there's no correctness problem with
851 * unnecessarily evicting. Nor is there a correctness problem with not
852 * evicting while iput() is racing with the key being removed, since
853 * then the thread removing the key will either evict the inode itself
854 * or will correctly detect that it wasn't evicted due to the race.
855 */
856 return !is_master_key_secret_present(&ci->ci_master_key->mk_secret);
857 }
858 EXPORT_SYMBOL_GPL(fscrypt_drop_inode);
859