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