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