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