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