1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Key setup facility for FS encryption support.
4 *
5 * Copyright (C) 2015, Google, Inc.
6 *
7 * Originally written by Michael Halcrow, Ildar Muslukhov, and Uday Savagaonkar.
8 * Heavily modified since then.
9 */
10
11 #include <crypto/skcipher.h>
12 #include <linux/export.h>
13 #include <linux/random.h>
14
15 #include "fscrypt_private.h"
16
17 struct fscrypt_mode fscrypt_modes[] = {
18 [FSCRYPT_MODE_AES_256_XTS] = {
19 .friendly_name = "AES-256-XTS",
20 .cipher_str = "xts(aes)",
21 .keysize = 64,
22 .security_strength = 32,
23 .ivsize = 16,
24 .blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_256_XTS,
25 },
26 [FSCRYPT_MODE_AES_256_CTS] = {
27 .friendly_name = "AES-256-CBC-CTS",
28 .cipher_str = "cts(cbc(aes))",
29 .keysize = 32,
30 .security_strength = 32,
31 .ivsize = 16,
32 },
33 [FSCRYPT_MODE_AES_128_CBC] = {
34 .friendly_name = "AES-128-CBC-ESSIV",
35 .cipher_str = "essiv(cbc(aes),sha256)",
36 .keysize = 16,
37 .security_strength = 16,
38 .ivsize = 16,
39 .blk_crypto_mode = BLK_ENCRYPTION_MODE_AES_128_CBC_ESSIV,
40 },
41 [FSCRYPT_MODE_AES_128_CTS] = {
42 .friendly_name = "AES-128-CBC-CTS",
43 .cipher_str = "cts(cbc(aes))",
44 .keysize = 16,
45 .security_strength = 16,
46 .ivsize = 16,
47 },
48 [FSCRYPT_MODE_SM4_XTS] = {
49 .friendly_name = "SM4-XTS",
50 .cipher_str = "xts(sm4)",
51 .keysize = 32,
52 .security_strength = 16,
53 .ivsize = 16,
54 .blk_crypto_mode = BLK_ENCRYPTION_MODE_SM4_XTS,
55 },
56 [FSCRYPT_MODE_SM4_CTS] = {
57 .friendly_name = "SM4-CBC-CTS",
58 .cipher_str = "cts(cbc(sm4))",
59 .keysize = 16,
60 .security_strength = 16,
61 .ivsize = 16,
62 },
63 [FSCRYPT_MODE_ADIANTUM] = {
64 .friendly_name = "Adiantum",
65 .cipher_str = "adiantum(xchacha12,aes)",
66 .keysize = 32,
67 .security_strength = 32,
68 .ivsize = 32,
69 .blk_crypto_mode = BLK_ENCRYPTION_MODE_ADIANTUM,
70 },
71 [FSCRYPT_MODE_AES_256_HCTR2] = {
72 .friendly_name = "AES-256-HCTR2",
73 .cipher_str = "hctr2(aes)",
74 .keysize = 32,
75 .security_strength = 32,
76 .ivsize = 32,
77 },
78 };
79
80 static DEFINE_MUTEX(fscrypt_mode_key_setup_mutex);
81
82 static struct fscrypt_mode *
select_encryption_mode(const union fscrypt_policy * policy,const struct inode * inode)83 select_encryption_mode(const union fscrypt_policy *policy,
84 const struct inode *inode)
85 {
86 BUILD_BUG_ON(ARRAY_SIZE(fscrypt_modes) != FSCRYPT_MODE_MAX + 1);
87
88 if (S_ISREG(inode->i_mode))
89 return &fscrypt_modes[fscrypt_policy_contents_mode(policy)];
90
91 if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
92 return &fscrypt_modes[fscrypt_policy_fnames_mode(policy)];
93
94 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
95 inode->i_ino, (inode->i_mode & S_IFMT));
96 return ERR_PTR(-EINVAL);
97 }
98
99 /* Create a symmetric cipher object for the given encryption mode and key */
100 static struct crypto_sync_skcipher *
fscrypt_allocate_skcipher(struct fscrypt_mode * mode,const u8 * raw_key,const struct inode * inode)101 fscrypt_allocate_skcipher(struct fscrypt_mode *mode, const u8 *raw_key,
102 const struct inode *inode)
103 {
104 struct crypto_sync_skcipher *tfm;
105 int err;
106
107 tfm = crypto_alloc_sync_skcipher(mode->cipher_str, 0,
108 FSCRYPT_CRYPTOAPI_MASK);
109 if (IS_ERR(tfm)) {
110 if (PTR_ERR(tfm) == -ENOENT) {
111 fscrypt_warn(inode,
112 "Missing crypto API support for %s (API name: \"%s\")",
113 mode->friendly_name, mode->cipher_str);
114 return ERR_PTR(-ENOPKG);
115 }
116 fscrypt_err(inode, "Error allocating '%s' transform: %ld",
117 mode->cipher_str, PTR_ERR(tfm));
118 return tfm;
119 }
120 if (!xchg(&mode->logged_cryptoapi_impl, 1)) {
121 /*
122 * fscrypt performance can vary greatly depending on which
123 * crypto algorithm implementation is used. Help people debug
124 * performance problems by logging the ->cra_driver_name the
125 * first time a mode is used.
126 */
127 pr_info("fscrypt: %s using implementation \"%s\"\n",
128 mode->friendly_name,
129 crypto_skcipher_driver_name(&tfm->base));
130 }
131 if (WARN_ON_ONCE(crypto_sync_skcipher_ivsize(tfm) != mode->ivsize)) {
132 err = -EINVAL;
133 goto err_free_tfm;
134 }
135 crypto_sync_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
136 err = crypto_sync_skcipher_setkey(tfm, raw_key, mode->keysize);
137 if (err)
138 goto err_free_tfm;
139
140 return tfm;
141
142 err_free_tfm:
143 crypto_free_sync_skcipher(tfm);
144 return ERR_PTR(err);
145 }
146
147 /*
148 * Prepare the crypto transform object or blk-crypto key in @prep_key, given the
149 * raw key, encryption mode (@ci->ci_mode), flag indicating which encryption
150 * implementation (fs-layer or blk-crypto) will be used (@ci->ci_inlinecrypt),
151 * and IV generation method (@ci->ci_policy.flags).
152 */
fscrypt_prepare_key(struct fscrypt_prepared_key * prep_key,const u8 * raw_key,const struct fscrypt_inode_info * ci)153 int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key,
154 const u8 *raw_key, const struct fscrypt_inode_info *ci)
155 {
156 struct crypto_sync_skcipher *tfm;
157
158 if (fscrypt_using_inline_encryption(ci))
159 return fscrypt_prepare_inline_crypt_key(prep_key, raw_key,
160 ci->ci_mode->keysize,
161 false, ci);
162
163 tfm = fscrypt_allocate_skcipher(ci->ci_mode, raw_key, ci->ci_inode);
164 if (IS_ERR(tfm))
165 return PTR_ERR(tfm);
166 /*
167 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
168 * I.e., here we publish ->tfm with a RELEASE barrier so that
169 * concurrent tasks can ACQUIRE it. Note that this concurrency is only
170 * possible for per-mode keys, not for per-file keys.
171 */
172 smp_store_release(&prep_key->tfm, tfm);
173 return 0;
174 }
175
176 /* Destroy a crypto transform object and/or blk-crypto key. */
fscrypt_destroy_prepared_key(struct super_block * sb,struct fscrypt_prepared_key * prep_key)177 void fscrypt_destroy_prepared_key(struct super_block *sb,
178 struct fscrypt_prepared_key *prep_key)
179 {
180 crypto_free_sync_skcipher(prep_key->tfm);
181 fscrypt_destroy_inline_crypt_key(sb, prep_key);
182 memzero_explicit(prep_key, sizeof(*prep_key));
183 }
184
185 /* Given a per-file encryption key, set up the file's crypto transform object */
fscrypt_set_per_file_enc_key(struct fscrypt_inode_info * ci,const u8 * raw_key)186 int fscrypt_set_per_file_enc_key(struct fscrypt_inode_info *ci,
187 const u8 *raw_key)
188 {
189 ci->ci_owns_key = true;
190 return fscrypt_prepare_key(&ci->ci_enc_key, raw_key, ci);
191 }
192
setup_per_mode_enc_key(struct fscrypt_inode_info * ci,struct fscrypt_master_key * mk,struct fscrypt_prepared_key * keys,u8 hkdf_context,bool include_fs_uuid)193 static int setup_per_mode_enc_key(struct fscrypt_inode_info *ci,
194 struct fscrypt_master_key *mk,
195 struct fscrypt_prepared_key *keys,
196 u8 hkdf_context, bool include_fs_uuid)
197 {
198 const struct inode *inode = ci->ci_inode;
199 const struct super_block *sb = inode->i_sb;
200 struct fscrypt_mode *mode = ci->ci_mode;
201 const u8 mode_num = mode - fscrypt_modes;
202 struct fscrypt_prepared_key *prep_key;
203 u8 mode_key[FSCRYPT_MAX_RAW_KEY_SIZE];
204 u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
205 unsigned int hkdf_infolen = 0;
206 bool use_hw_wrapped_key = false;
207 int err;
208
209 if (WARN_ON_ONCE(mode_num > FSCRYPT_MODE_MAX))
210 return -EINVAL;
211
212 if (mk->mk_secret.is_hw_wrapped && S_ISREG(inode->i_mode)) {
213 /* Using a hardware-wrapped key for file contents encryption */
214 if (!fscrypt_using_inline_encryption(ci)) {
215 if (sb->s_flags & SB_INLINECRYPT)
216 fscrypt_warn(ci->ci_inode,
217 "Hardware-wrapped key required, but no suitable inline encryption capabilities are available");
218 else
219 fscrypt_warn(ci->ci_inode,
220 "Hardware-wrapped keys require inline encryption (-o inlinecrypt)");
221 return -EINVAL;
222 }
223 use_hw_wrapped_key = true;
224 }
225
226 prep_key = &keys[mode_num];
227 if (fscrypt_is_key_prepared(prep_key, ci)) {
228 ci->ci_enc_key = *prep_key;
229 return 0;
230 }
231
232 mutex_lock(&fscrypt_mode_key_setup_mutex);
233
234 if (fscrypt_is_key_prepared(prep_key, ci))
235 goto done_unlock;
236
237 if (use_hw_wrapped_key) {
238 err = fscrypt_prepare_inline_crypt_key(prep_key,
239 mk->mk_secret.bytes,
240 mk->mk_secret.size, true,
241 ci);
242 if (err)
243 goto out_unlock;
244 goto done_unlock;
245 }
246
247 BUILD_BUG_ON(sizeof(mode_num) != 1);
248 BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
249 BUILD_BUG_ON(sizeof(hkdf_info) != 17);
250 hkdf_info[hkdf_infolen++] = mode_num;
251 if (include_fs_uuid) {
252 memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
253 sizeof(sb->s_uuid));
254 hkdf_infolen += sizeof(sb->s_uuid);
255 }
256 err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
257 hkdf_context, hkdf_info, hkdf_infolen,
258 mode_key, mode->keysize);
259 if (err)
260 goto out_unlock;
261 err = fscrypt_prepare_key(prep_key, mode_key, ci);
262 memzero_explicit(mode_key, mode->keysize);
263 if (err)
264 goto out_unlock;
265 done_unlock:
266 ci->ci_enc_key = *prep_key;
267 err = 0;
268 out_unlock:
269 mutex_unlock(&fscrypt_mode_key_setup_mutex);
270 return err;
271 }
272
273 /*
274 * Derive a SipHash key from the given fscrypt master key and the given
275 * application-specific information string.
276 *
277 * Note that the KDF produces a byte array, but the SipHash APIs expect the key
278 * as a pair of 64-bit words. Therefore, on big endian CPUs we have to do an
279 * endianness swap in order to get the same results as on little endian CPUs.
280 */
fscrypt_derive_siphash_key(const struct fscrypt_master_key * mk,u8 context,const u8 * info,unsigned int infolen,siphash_key_t * key)281 static int fscrypt_derive_siphash_key(const struct fscrypt_master_key *mk,
282 u8 context, const u8 *info,
283 unsigned int infolen, siphash_key_t *key)
284 {
285 int err;
286
287 err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen,
288 (u8 *)key, sizeof(*key));
289 if (err)
290 return err;
291
292 BUILD_BUG_ON(sizeof(*key) != 16);
293 BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2);
294 le64_to_cpus(&key->key[0]);
295 le64_to_cpus(&key->key[1]);
296 return 0;
297 }
298
fscrypt_derive_dirhash_key(struct fscrypt_inode_info * ci,const struct fscrypt_master_key * mk)299 int fscrypt_derive_dirhash_key(struct fscrypt_inode_info *ci,
300 const struct fscrypt_master_key *mk)
301 {
302 int err;
303
304 err = fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,
305 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
306 &ci->ci_dirhash_key);
307 if (err)
308 return err;
309 ci->ci_dirhash_key_initialized = true;
310 return 0;
311 }
312
fscrypt_hash_inode_number(struct fscrypt_inode_info * ci,const struct fscrypt_master_key * mk)313 void fscrypt_hash_inode_number(struct fscrypt_inode_info *ci,
314 const struct fscrypt_master_key *mk)
315 {
316 WARN_ON_ONCE(ci->ci_inode->i_ino == 0);
317 WARN_ON_ONCE(!mk->mk_ino_hash_key_initialized);
318
319 ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino,
320 &mk->mk_ino_hash_key);
321 }
322
fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info * ci,struct fscrypt_master_key * mk)323 static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info *ci,
324 struct fscrypt_master_key *mk)
325 {
326 int err;
327
328 err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_32_keys,
329 HKDF_CONTEXT_IV_INO_LBLK_32_KEY, true);
330 if (err)
331 return err;
332
333 /* pairs with smp_store_release() below */
334 if (!smp_load_acquire(&mk->mk_ino_hash_key_initialized)) {
335
336 mutex_lock(&fscrypt_mode_key_setup_mutex);
337
338 if (mk->mk_ino_hash_key_initialized)
339 goto unlock;
340
341 err = fscrypt_derive_siphash_key(mk,
342 HKDF_CONTEXT_INODE_HASH_KEY,
343 NULL, 0, &mk->mk_ino_hash_key);
344 if (err)
345 goto unlock;
346 /* pairs with smp_load_acquire() above */
347 smp_store_release(&mk->mk_ino_hash_key_initialized, true);
348 unlock:
349 mutex_unlock(&fscrypt_mode_key_setup_mutex);
350 if (err)
351 return err;
352 }
353
354 /*
355 * New inodes may not have an inode number assigned yet.
356 * Hashing their inode number is delayed until later.
357 */
358 if (ci->ci_inode->i_ino)
359 fscrypt_hash_inode_number(ci, mk);
360 return 0;
361 }
362
fscrypt_setup_v2_file_key(struct fscrypt_inode_info * ci,struct fscrypt_master_key * mk,bool need_dirhash_key)363 static int fscrypt_setup_v2_file_key(struct fscrypt_inode_info *ci,
364 struct fscrypt_master_key *mk,
365 bool need_dirhash_key)
366 {
367 int err;
368
369 if (mk->mk_secret.is_hw_wrapped &&
370 !(ci->ci_policy.v2.flags & (FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 |
371 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))) {
372 fscrypt_warn(ci->ci_inode,
373 "Hardware-wrapped keys are only supported with IV_INO_LBLK policies");
374 return -EINVAL;
375 }
376
377 if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
378 /*
379 * DIRECT_KEY: instead of deriving per-file encryption keys, the
380 * per-file nonce will be included in all the IVs. But unlike
381 * v1 policies, for v2 policies in this case we don't encrypt
382 * with the master key directly but rather derive a per-mode
383 * encryption key. This ensures that the master key is
384 * consistently used only for HKDF, avoiding key reuse issues.
385 */
386 err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_keys,
387 HKDF_CONTEXT_DIRECT_KEY, false);
388 } else if (ci->ci_policy.v2.flags &
389 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
390 /*
391 * IV_INO_LBLK_64: encryption keys are derived from (master_key,
392 * mode_num, filesystem_uuid), and inode number is included in
393 * the IVs. This format is optimized for use with inline
394 * encryption hardware compliant with the UFS standard.
395 */
396 err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_keys,
397 HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
398 true);
399 } else if (ci->ci_policy.v2.flags &
400 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
401 err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk);
402 } else {
403 u8 derived_key[FSCRYPT_MAX_RAW_KEY_SIZE];
404
405 err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
406 HKDF_CONTEXT_PER_FILE_ENC_KEY,
407 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
408 derived_key, ci->ci_mode->keysize);
409 if (err)
410 return err;
411
412 err = fscrypt_set_per_file_enc_key(ci, derived_key);
413 memzero_explicit(derived_key, ci->ci_mode->keysize);
414 }
415 if (err)
416 return err;
417
418 /* Derive a secret dirhash key for directories that need it. */
419 if (need_dirhash_key) {
420 err = fscrypt_derive_dirhash_key(ci, mk);
421 if (err)
422 return err;
423 }
424
425 return 0;
426 }
427
428 /*
429 * Check whether the size of the given master key (@mk) is appropriate for the
430 * encryption settings which a particular file will use (@ci).
431 *
432 * If the file uses a v1 encryption policy, then the master key must be at least
433 * as long as the derived key, as this is a requirement of the v1 KDF.
434 *
435 * Otherwise, the KDF can accept any size key, so we enforce a slightly looser
436 * requirement: we require that the size of the master key be at least the
437 * maximum security strength of any algorithm whose key will be derived from it
438 * (but in practice we only need to consider @ci->ci_mode, since any other
439 * possible subkeys such as DIRHASH and INODE_HASH will never increase the
440 * required key size over @ci->ci_mode). This allows AES-256-XTS keys to be
441 * derived from a 256-bit master key, which is cryptographically sufficient,
442 * rather than requiring a 512-bit master key which is unnecessarily long. (We
443 * still allow 512-bit master keys if the user chooses to use them, though.)
444 */
fscrypt_valid_master_key_size(const struct fscrypt_master_key * mk,const struct fscrypt_inode_info * ci)445 static bool fscrypt_valid_master_key_size(const struct fscrypt_master_key *mk,
446 const struct fscrypt_inode_info *ci)
447 {
448 unsigned int min_keysize;
449
450 if (ci->ci_policy.version == FSCRYPT_POLICY_V1)
451 min_keysize = ci->ci_mode->keysize;
452 else
453 min_keysize = ci->ci_mode->security_strength;
454
455 if (mk->mk_secret.size < min_keysize) {
456 fscrypt_warn(NULL,
457 "key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
458 master_key_spec_type(&mk->mk_spec),
459 master_key_spec_len(&mk->mk_spec),
460 (u8 *)&mk->mk_spec.u,
461 mk->mk_secret.size, min_keysize);
462 return false;
463 }
464 return true;
465 }
466
467 /*
468 * Find the master key, then set up the inode's actual encryption key.
469 *
470 * If the master key is found in the filesystem-level keyring, then it is
471 * returned in *mk_ret with its semaphore read-locked. This is needed to ensure
472 * that only one task links the fscrypt_inode_info into ->mk_decrypted_inodes
473 * (as multiple tasks may race to create an fscrypt_inode_info for the same
474 * inode), and to synchronize the master key being removed with a new inode
475 * starting to use it.
476 */
setup_file_encryption_key(struct fscrypt_inode_info * ci,bool need_dirhash_key,struct fscrypt_master_key ** mk_ret)477 static int setup_file_encryption_key(struct fscrypt_inode_info *ci,
478 bool need_dirhash_key,
479 struct fscrypt_master_key **mk_ret)
480 {
481 struct super_block *sb = ci->ci_inode->i_sb;
482 struct fscrypt_key_specifier mk_spec;
483 struct fscrypt_master_key *mk;
484 int err;
485
486 err = fscrypt_policy_to_key_spec(&ci->ci_policy, &mk_spec);
487 if (err)
488 return err;
489
490 mk = fscrypt_find_master_key(sb, &mk_spec);
491 if (unlikely(!mk)) {
492 const union fscrypt_policy *dummy_policy =
493 fscrypt_get_dummy_policy(sb);
494
495 /*
496 * Add the test_dummy_encryption key on-demand. In principle,
497 * it should be added at mount time. Do it here instead so that
498 * the individual filesystems don't need to worry about adding
499 * this key at mount time and cleaning up on mount failure.
500 */
501 if (dummy_policy &&
502 fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {
503 err = fscrypt_add_test_dummy_key(sb, &mk_spec);
504 if (err)
505 return err;
506 mk = fscrypt_find_master_key(sb, &mk_spec);
507 }
508 }
509 if (unlikely(!mk)) {
510 if (ci->ci_policy.version != FSCRYPT_POLICY_V1)
511 return -ENOKEY;
512
513 err = fscrypt_select_encryption_impl(ci, false);
514 if (err)
515 return err;
516
517 /*
518 * As a legacy fallback for v1 policies, search for the key in
519 * the current task's subscribed keyrings too. Don't move this
520 * to before the search of ->s_master_keys, since users
521 * shouldn't be able to override filesystem-level keys.
522 */
523 return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
524 }
525 down_read(&mk->mk_sem);
526
527 if (!mk->mk_present) {
528 /* FS_IOC_REMOVE_ENCRYPTION_KEY has been executed on this key */
529 err = -ENOKEY;
530 goto out_release_key;
531 }
532
533 if (!fscrypt_valid_master_key_size(mk, ci)) {
534 err = -ENOKEY;
535 goto out_release_key;
536 }
537
538 err = fscrypt_select_encryption_impl(ci, mk->mk_secret.is_hw_wrapped);
539 if (err)
540 goto out_release_key;
541
542 switch (ci->ci_policy.version) {
543 case FSCRYPT_POLICY_V1:
544 if (WARN_ON_ONCE(mk->mk_secret.is_hw_wrapped)) {
545 /*
546 * This should never happen, as adding a v1 policy key
547 * that is hardware-wrapped isn't allowed.
548 */
549 err = -EINVAL;
550 goto out_release_key;
551 }
552 err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.bytes);
553 break;
554 case FSCRYPT_POLICY_V2:
555 err = fscrypt_setup_v2_file_key(ci, mk, need_dirhash_key);
556 break;
557 default:
558 WARN_ON_ONCE(1);
559 err = -EINVAL;
560 break;
561 }
562 if (err)
563 goto out_release_key;
564
565 *mk_ret = mk;
566 return 0;
567
568 out_release_key:
569 up_read(&mk->mk_sem);
570 fscrypt_put_master_key(mk);
571 return err;
572 }
573
put_crypt_info(struct fscrypt_inode_info * ci)574 static void put_crypt_info(struct fscrypt_inode_info *ci)
575 {
576 struct fscrypt_master_key *mk;
577
578 if (!ci)
579 return;
580
581 if (ci->ci_direct_key)
582 fscrypt_put_direct_key(ci->ci_direct_key);
583 else if (ci->ci_owns_key)
584 fscrypt_destroy_prepared_key(ci->ci_inode->i_sb,
585 &ci->ci_enc_key);
586
587 mk = ci->ci_master_key;
588 if (mk) {
589 /*
590 * Remove this inode from the list of inodes that were unlocked
591 * with the master key. In addition, if we're removing the last
592 * inode from an incompletely removed key, then complete the
593 * full removal of the key.
594 */
595 spin_lock(&mk->mk_decrypted_inodes_lock);
596 list_del(&ci->ci_master_key_link);
597 spin_unlock(&mk->mk_decrypted_inodes_lock);
598 fscrypt_put_master_key_activeref(ci->ci_inode->i_sb, mk);
599 }
600 memzero_explicit(ci, sizeof(*ci));
601 kmem_cache_free(fscrypt_inode_info_cachep, ci);
602 }
603
604 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)605 fscrypt_setup_encryption_info(struct inode *inode,
606 const union fscrypt_policy *policy,
607 const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],
608 bool need_dirhash_key)
609 {
610 struct fscrypt_inode_info *crypt_info;
611 struct fscrypt_mode *mode;
612 struct fscrypt_master_key *mk = NULL;
613 int res;
614
615 res = fscrypt_initialize(inode->i_sb);
616 if (res)
617 return res;
618
619 crypt_info = kmem_cache_zalloc(fscrypt_inode_info_cachep, GFP_KERNEL);
620 if (!crypt_info)
621 return -ENOMEM;
622
623 crypt_info->ci_inode = inode;
624 crypt_info->ci_policy = *policy;
625 memcpy(crypt_info->ci_nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
626
627 mode = select_encryption_mode(&crypt_info->ci_policy, inode);
628 if (IS_ERR(mode)) {
629 res = PTR_ERR(mode);
630 goto out;
631 }
632 WARN_ON_ONCE(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
633 crypt_info->ci_mode = mode;
634
635 crypt_info->ci_data_unit_bits =
636 fscrypt_policy_du_bits(&crypt_info->ci_policy, inode);
637 crypt_info->ci_data_units_per_block_bits =
638 inode->i_blkbits - crypt_info->ci_data_unit_bits;
639
640 res = setup_file_encryption_key(crypt_info, need_dirhash_key, &mk);
641 if (res)
642 goto out;
643
644 /*
645 * For existing inodes, multiple tasks may race to set ->i_crypt_info.
646 * So use cmpxchg_release(). This pairs with the smp_load_acquire() in
647 * fscrypt_get_inode_info(). I.e., here we publish ->i_crypt_info with
648 * a RELEASE barrier so that other tasks can ACQUIRE it.
649 */
650 if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) {
651 /*
652 * We won the race and set ->i_crypt_info to our crypt_info.
653 * Now link it into the master key's inode list.
654 */
655 if (mk) {
656 crypt_info->ci_master_key = mk;
657 refcount_inc(&mk->mk_active_refs);
658 spin_lock(&mk->mk_decrypted_inodes_lock);
659 list_add(&crypt_info->ci_master_key_link,
660 &mk->mk_decrypted_inodes);
661 spin_unlock(&mk->mk_decrypted_inodes_lock);
662 }
663 crypt_info = NULL;
664 }
665 res = 0;
666 out:
667 if (mk) {
668 up_read(&mk->mk_sem);
669 fscrypt_put_master_key(mk);
670 }
671 put_crypt_info(crypt_info);
672 return res;
673 }
674
675 /**
676 * fscrypt_get_encryption_info() - set up an inode's encryption key
677 * @inode: the inode to set up the key for. Must be encrypted.
678 * @allow_unsupported: if %true, treat an unsupported encryption policy (or
679 * unrecognized encryption context) the same way as the key
680 * being unavailable, instead of returning an error. Use
681 * %false unless the operation being performed is needed in
682 * order for files (or directories) to be deleted.
683 *
684 * Set up ->i_crypt_info, if it hasn't already been done.
685 *
686 * Note: unless ->i_crypt_info is already set, this isn't %GFP_NOFS-safe. So
687 * generally this shouldn't be called from within a filesystem transaction.
688 *
689 * Return: 0 if ->i_crypt_info was set or was already set, *or* if the
690 * encryption key is unavailable. (Use fscrypt_has_encryption_key() to
691 * distinguish these cases.) Also can return another -errno code.
692 */
fscrypt_get_encryption_info(struct inode * inode,bool allow_unsupported)693 int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)
694 {
695 int res;
696 union fscrypt_context ctx;
697 union fscrypt_policy policy;
698
699 if (fscrypt_has_encryption_key(inode))
700 return 0;
701
702 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
703 if (res < 0) {
704 if (res == -ERANGE && allow_unsupported)
705 return 0;
706 fscrypt_warn(inode, "Error %d getting encryption context", res);
707 return res;
708 }
709
710 res = fscrypt_policy_from_context(&policy, &ctx, res);
711 if (res) {
712 if (allow_unsupported)
713 return 0;
714 fscrypt_warn(inode,
715 "Unrecognized or corrupt encryption context");
716 return res;
717 }
718
719 if (!fscrypt_supported_policy(&policy, inode)) {
720 if (allow_unsupported)
721 return 0;
722 return -EINVAL;
723 }
724
725 res = fscrypt_setup_encryption_info(inode, &policy,
726 fscrypt_context_nonce(&ctx),
727 IS_CASEFOLDED(inode) &&
728 S_ISDIR(inode->i_mode));
729
730 if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */
731 res = 0;
732 if (res == -ENOKEY)
733 res = 0;
734 return res;
735 }
736
737 /**
738 * fscrypt_prepare_new_inode() - prepare to create a new inode in a directory
739 * @dir: a possibly-encrypted directory
740 * @inode: the new inode. ->i_mode and ->i_blkbits must be set already.
741 * ->i_ino doesn't need to be set yet.
742 * @encrypt_ret: (output) set to %true if the new inode will be encrypted
743 *
744 * If the directory is encrypted, set up its ->i_crypt_info in preparation for
745 * encrypting the name of the new file. Also, if the new inode will be
746 * encrypted, set up its ->i_crypt_info and set *encrypt_ret=true.
747 *
748 * This isn't %GFP_NOFS-safe, and therefore it should be called before starting
749 * any filesystem transaction to create the inode. For this reason, ->i_ino
750 * isn't required to be set yet, as the filesystem may not have set it yet.
751 *
752 * This doesn't persist the new inode's encryption context. That still needs to
753 * be done later by calling fscrypt_set_context().
754 *
755 * Return: 0 on success, -ENOKEY if the encryption key is missing, or another
756 * -errno code
757 */
fscrypt_prepare_new_inode(struct inode * dir,struct inode * inode,bool * encrypt_ret)758 int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
759 bool *encrypt_ret)
760 {
761 const union fscrypt_policy *policy;
762 u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
763
764 policy = fscrypt_policy_to_inherit(dir);
765 if (policy == NULL)
766 return 0;
767 if (IS_ERR(policy))
768 return PTR_ERR(policy);
769
770 if (WARN_ON_ONCE(inode->i_blkbits == 0))
771 return -EINVAL;
772
773 if (WARN_ON_ONCE(inode->i_mode == 0))
774 return -EINVAL;
775
776 /*
777 * Only regular files, directories, and symlinks are encrypted.
778 * Special files like device nodes and named pipes aren't.
779 */
780 if (!S_ISREG(inode->i_mode) &&
781 !S_ISDIR(inode->i_mode) &&
782 !S_ISLNK(inode->i_mode))
783 return 0;
784
785 *encrypt_ret = true;
786
787 get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);
788 return fscrypt_setup_encryption_info(inode, policy, nonce,
789 IS_CASEFOLDED(dir) &&
790 S_ISDIR(inode->i_mode));
791 }
792 EXPORT_SYMBOL_GPL(fscrypt_prepare_new_inode);
793
794 /**
795 * fscrypt_put_encryption_info() - free most of an inode's fscrypt data
796 * @inode: an inode being evicted
797 *
798 * Free the inode's fscrypt_inode_info. Filesystems must call this when the
799 * inode is being evicted. An RCU grace period need not have elapsed yet.
800 */
fscrypt_put_encryption_info(struct inode * inode)801 void fscrypt_put_encryption_info(struct inode *inode)
802 {
803 put_crypt_info(inode->i_crypt_info);
804 inode->i_crypt_info = NULL;
805 }
806 EXPORT_SYMBOL(fscrypt_put_encryption_info);
807
808 /**
809 * fscrypt_free_inode() - free an inode's fscrypt data requiring RCU delay
810 * @inode: an inode being freed
811 *
812 * Free the inode's cached decrypted symlink target, if any. Filesystems must
813 * call this after an RCU grace period, just before they free the inode.
814 */
fscrypt_free_inode(struct inode * inode)815 void fscrypt_free_inode(struct inode *inode)
816 {
817 if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
818 kfree(inode->i_link);
819 inode->i_link = NULL;
820 }
821 }
822 EXPORT_SYMBOL(fscrypt_free_inode);
823
824 /**
825 * fscrypt_drop_inode() - check whether the inode's master key has been removed
826 * @inode: an inode being considered for eviction
827 *
828 * Filesystems supporting fscrypt must call this from their ->drop_inode()
829 * method so that encrypted inodes are evicted as soon as they're no longer in
830 * use and their master key has been removed.
831 *
832 * Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
833 */
fscrypt_drop_inode(struct inode * inode)834 int fscrypt_drop_inode(struct inode *inode)
835 {
836 const struct fscrypt_inode_info *ci = fscrypt_get_inode_info(inode);
837
838 /*
839 * If ci is NULL, then the inode doesn't have an encryption key set up
840 * so it's irrelevant. If ci_master_key is NULL, then the master key
841 * was provided via the legacy mechanism of the process-subscribed
842 * keyrings, so we don't know whether it's been removed or not.
843 */
844 if (!ci || !ci->ci_master_key)
845 return 0;
846
847 /*
848 * With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
849 * protected by the key were cleaned by sync_filesystem(). But if
850 * userspace is still using the files, inodes can be dirtied between
851 * then and now. We mustn't lose any writes, so skip dirty inodes here.
852 */
853 if (inode->i_state & I_DIRTY_ALL)
854 return 0;
855
856 /*
857 * We can't take ->mk_sem here, since this runs in atomic context.
858 * Therefore, ->mk_present can change concurrently, and our result may
859 * immediately become outdated. But there's no correctness problem with
860 * unnecessarily evicting. Nor is there a correctness problem with not
861 * evicting while iput() is racing with the key being removed, since
862 * then the thread removing the key will either evict the inode itself
863 * or will correctly detect that it wasn't evicted due to the race.
864 */
865 return !READ_ONCE(ci->ci_master_key->mk_present);
866 }
867 EXPORT_SYMBOL_GPL(fscrypt_drop_inode);
868