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 fscrypt_hkdf_expand(&mk->mk_secret.hkdf, hkdf_context, hkdf_info,
257 hkdf_infolen, mode_key, mode->keysize);
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 void 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 fscrypt_hkdf_expand(&mk->mk_secret.hkdf, context, info, infolen,
283 (u8 *)key, sizeof(*key));
284 BUILD_BUG_ON(sizeof(*key) != 16);
285 BUILD_BUG_ON(ARRAY_SIZE(key->key) != 2);
286 le64_to_cpus(&key->key[0]);
287 le64_to_cpus(&key->key[1]);
288 }
289
fscrypt_derive_dirhash_key(struct fscrypt_inode_info * ci,const struct fscrypt_master_key * mk)290 void fscrypt_derive_dirhash_key(struct fscrypt_inode_info *ci,
291 const struct fscrypt_master_key *mk)
292 {
293 fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_DIRHASH_KEY,
294 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
295 &ci->ci_dirhash_key);
296 ci->ci_dirhash_key_initialized = true;
297 }
298
fscrypt_hash_inode_number(struct fscrypt_inode_info * ci,const struct fscrypt_master_key * mk)299 void fscrypt_hash_inode_number(struct fscrypt_inode_info *ci,
300 const struct fscrypt_master_key *mk)
301 {
302 WARN_ON_ONCE(ci->ci_inode->i_ino == 0);
303 WARN_ON_ONCE(!mk->mk_ino_hash_key_initialized);
304
305 ci->ci_hashed_ino = (u32)siphash_1u64(ci->ci_inode->i_ino,
306 &mk->mk_ino_hash_key);
307 }
308
fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info * ci,struct fscrypt_master_key * mk)309 static int fscrypt_setup_iv_ino_lblk_32_key(struct fscrypt_inode_info *ci,
310 struct fscrypt_master_key *mk)
311 {
312 int err;
313
314 err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_32_keys,
315 HKDF_CONTEXT_IV_INO_LBLK_32_KEY, true);
316 if (err)
317 return err;
318
319 /* pairs with smp_store_release() below */
320 if (!smp_load_acquire(&mk->mk_ino_hash_key_initialized)) {
321
322 mutex_lock(&fscrypt_mode_key_setup_mutex);
323
324 if (mk->mk_ino_hash_key_initialized)
325 goto unlock;
326
327 fscrypt_derive_siphash_key(mk, HKDF_CONTEXT_INODE_HASH_KEY,
328 NULL, 0, &mk->mk_ino_hash_key);
329 /* pairs with smp_load_acquire() above */
330 smp_store_release(&mk->mk_ino_hash_key_initialized, true);
331 unlock:
332 mutex_unlock(&fscrypt_mode_key_setup_mutex);
333 }
334
335 /*
336 * New inodes may not have an inode number assigned yet.
337 * Hashing their inode number is delayed until later.
338 */
339 if (ci->ci_inode->i_ino)
340 fscrypt_hash_inode_number(ci, mk);
341 return 0;
342 }
343
fscrypt_setup_v2_file_key(struct fscrypt_inode_info * ci,struct fscrypt_master_key * mk,bool need_dirhash_key)344 static int fscrypt_setup_v2_file_key(struct fscrypt_inode_info *ci,
345 struct fscrypt_master_key *mk,
346 bool need_dirhash_key)
347 {
348 int err;
349
350 if (mk->mk_secret.is_hw_wrapped &&
351 !(ci->ci_policy.v2.flags & (FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64 |
352 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))) {
353 fscrypt_warn(ci->ci_inode,
354 "Hardware-wrapped keys are only supported with IV_INO_LBLK policies");
355 return -EINVAL;
356 }
357
358 if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
359 /*
360 * DIRECT_KEY: instead of deriving per-file encryption keys, the
361 * per-file nonce will be included in all the IVs. But unlike
362 * v1 policies, for v2 policies in this case we don't encrypt
363 * with the master key directly but rather derive a per-mode
364 * encryption key. This ensures that the master key is
365 * consistently used only for HKDF, avoiding key reuse issues.
366 */
367 err = setup_per_mode_enc_key(ci, mk, mk->mk_direct_keys,
368 HKDF_CONTEXT_DIRECT_KEY, false);
369 } else if (ci->ci_policy.v2.flags &
370 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
371 /*
372 * IV_INO_LBLK_64: encryption keys are derived from (master_key,
373 * mode_num, filesystem_uuid), and inode number is included in
374 * the IVs. This format is optimized for use with inline
375 * encryption hardware compliant with the UFS standard.
376 */
377 err = setup_per_mode_enc_key(ci, mk, mk->mk_iv_ino_lblk_64_keys,
378 HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
379 true);
380 } else if (ci->ci_policy.v2.flags &
381 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
382 err = fscrypt_setup_iv_ino_lblk_32_key(ci, mk);
383 } else {
384 u8 derived_key[FSCRYPT_MAX_RAW_KEY_SIZE];
385
386 fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
387 HKDF_CONTEXT_PER_FILE_ENC_KEY,
388 ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE,
389 derived_key, ci->ci_mode->keysize);
390 err = fscrypt_set_per_file_enc_key(ci, derived_key);
391 memzero_explicit(derived_key, ci->ci_mode->keysize);
392 }
393 if (err)
394 return err;
395
396 /* Derive a secret dirhash key for directories that need it. */
397 if (need_dirhash_key)
398 fscrypt_derive_dirhash_key(ci, mk);
399
400 return 0;
401 }
402
403 /*
404 * Check whether the size of the given master key (@mk) is appropriate for the
405 * encryption settings which a particular file will use (@ci).
406 *
407 * If the file uses a v1 encryption policy, then the master key must be at least
408 * as long as the derived key, as this is a requirement of the v1 KDF.
409 *
410 * Otherwise, the KDF can accept any size key, so we enforce a slightly looser
411 * requirement: we require that the size of the master key be at least the
412 * maximum security strength of any algorithm whose key will be derived from it
413 * (but in practice we only need to consider @ci->ci_mode, since any other
414 * possible subkeys such as DIRHASH and INODE_HASH will never increase the
415 * required key size over @ci->ci_mode). This allows AES-256-XTS keys to be
416 * derived from a 256-bit master key, which is cryptographically sufficient,
417 * rather than requiring a 512-bit master key which is unnecessarily long. (We
418 * still allow 512-bit master keys if the user chooses to use them, though.)
419 */
fscrypt_valid_master_key_size(const struct fscrypt_master_key * mk,const struct fscrypt_inode_info * ci)420 static bool fscrypt_valid_master_key_size(const struct fscrypt_master_key *mk,
421 const struct fscrypt_inode_info *ci)
422 {
423 unsigned int min_keysize;
424
425 if (ci->ci_policy.version == FSCRYPT_POLICY_V1)
426 min_keysize = ci->ci_mode->keysize;
427 else
428 min_keysize = ci->ci_mode->security_strength;
429
430 if (mk->mk_secret.size < min_keysize) {
431 fscrypt_warn(NULL,
432 "key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
433 master_key_spec_type(&mk->mk_spec),
434 master_key_spec_len(&mk->mk_spec),
435 (u8 *)&mk->mk_spec.u,
436 mk->mk_secret.size, min_keysize);
437 return false;
438 }
439 return true;
440 }
441
442 /*
443 * Find the master key, then set up the inode's actual encryption key.
444 *
445 * If the master key is found in the filesystem-level keyring, then it is
446 * returned in *mk_ret with its semaphore read-locked. This is needed to ensure
447 * that only one task links the fscrypt_inode_info into ->mk_decrypted_inodes
448 * (as multiple tasks may race to create an fscrypt_inode_info for the same
449 * inode), and to synchronize the master key being removed with a new inode
450 * starting to use it.
451 */
setup_file_encryption_key(struct fscrypt_inode_info * ci,bool need_dirhash_key,struct fscrypt_master_key ** mk_ret)452 static int setup_file_encryption_key(struct fscrypt_inode_info *ci,
453 bool need_dirhash_key,
454 struct fscrypt_master_key **mk_ret)
455 {
456 struct super_block *sb = ci->ci_inode->i_sb;
457 struct fscrypt_key_specifier mk_spec;
458 struct fscrypt_master_key *mk;
459 int err;
460
461 err = fscrypt_policy_to_key_spec(&ci->ci_policy, &mk_spec);
462 if (err)
463 return err;
464
465 mk = fscrypt_find_master_key(sb, &mk_spec);
466 if (unlikely(!mk)) {
467 const union fscrypt_policy *dummy_policy =
468 fscrypt_get_dummy_policy(sb);
469
470 /*
471 * Add the test_dummy_encryption key on-demand. In principle,
472 * it should be added at mount time. Do it here instead so that
473 * the individual filesystems don't need to worry about adding
474 * this key at mount time and cleaning up on mount failure.
475 */
476 if (dummy_policy &&
477 fscrypt_policies_equal(dummy_policy, &ci->ci_policy)) {
478 err = fscrypt_add_test_dummy_key(sb, &mk_spec);
479 if (err)
480 return err;
481 mk = fscrypt_find_master_key(sb, &mk_spec);
482 }
483 }
484 if (unlikely(!mk)) {
485 if (ci->ci_policy.version != FSCRYPT_POLICY_V1)
486 return -ENOKEY;
487
488 err = fscrypt_select_encryption_impl(ci, false);
489 if (err)
490 return err;
491
492 /*
493 * As a legacy fallback for v1 policies, search for the key in
494 * the current task's subscribed keyrings too. Don't move this
495 * to before the search of ->s_master_keys, since users
496 * shouldn't be able to override filesystem-level keys.
497 */
498 return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
499 }
500 down_read(&mk->mk_sem);
501
502 if (!mk->mk_present) {
503 /* FS_IOC_REMOVE_ENCRYPTION_KEY has been executed on this key */
504 err = -ENOKEY;
505 goto out_release_key;
506 }
507
508 if (!fscrypt_valid_master_key_size(mk, ci)) {
509 err = -ENOKEY;
510 goto out_release_key;
511 }
512
513 err = fscrypt_select_encryption_impl(ci, mk->mk_secret.is_hw_wrapped);
514 if (err)
515 goto out_release_key;
516
517 switch (ci->ci_policy.version) {
518 case FSCRYPT_POLICY_V1:
519 if (WARN_ON_ONCE(mk->mk_secret.is_hw_wrapped)) {
520 /*
521 * This should never happen, as adding a v1 policy key
522 * that is hardware-wrapped isn't allowed.
523 */
524 err = -EINVAL;
525 goto out_release_key;
526 }
527 err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.bytes);
528 break;
529 case FSCRYPT_POLICY_V2:
530 err = fscrypt_setup_v2_file_key(ci, mk, need_dirhash_key);
531 break;
532 default:
533 WARN_ON_ONCE(1);
534 err = -EINVAL;
535 break;
536 }
537 if (err)
538 goto out_release_key;
539
540 *mk_ret = mk;
541 return 0;
542
543 out_release_key:
544 up_read(&mk->mk_sem);
545 fscrypt_put_master_key(mk);
546 return err;
547 }
548
put_crypt_info(struct fscrypt_inode_info * ci)549 static void put_crypt_info(struct fscrypt_inode_info *ci)
550 {
551 struct fscrypt_master_key *mk;
552
553 if (!ci)
554 return;
555
556 if (ci->ci_direct_key)
557 fscrypt_put_direct_key(ci->ci_direct_key);
558 else if (ci->ci_owns_key)
559 fscrypt_destroy_prepared_key(ci->ci_inode->i_sb,
560 &ci->ci_enc_key);
561
562 mk = ci->ci_master_key;
563 if (mk) {
564 /*
565 * Remove this inode from the list of inodes that were unlocked
566 * with the master key. In addition, if we're removing the last
567 * inode from an incompletely removed key, then complete the
568 * full removal of the key.
569 */
570 spin_lock(&mk->mk_decrypted_inodes_lock);
571 list_del(&ci->ci_master_key_link);
572 spin_unlock(&mk->mk_decrypted_inodes_lock);
573 fscrypt_put_master_key_activeref(ci->ci_inode->i_sb, mk);
574 }
575 memzero_explicit(ci, sizeof(*ci));
576 kmem_cache_free(fscrypt_inode_info_cachep, ci);
577 }
578
579 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)580 fscrypt_setup_encryption_info(struct inode *inode,
581 const union fscrypt_policy *policy,
582 const u8 nonce[FSCRYPT_FILE_NONCE_SIZE],
583 bool need_dirhash_key)
584 {
585 struct fscrypt_inode_info *crypt_info;
586 struct fscrypt_mode *mode;
587 struct fscrypt_master_key *mk = NULL;
588 int res;
589
590 res = fscrypt_initialize(inode->i_sb);
591 if (res)
592 return res;
593
594 crypt_info = kmem_cache_zalloc(fscrypt_inode_info_cachep, GFP_KERNEL);
595 if (!crypt_info)
596 return -ENOMEM;
597
598 crypt_info->ci_inode = inode;
599 crypt_info->ci_policy = *policy;
600 memcpy(crypt_info->ci_nonce, nonce, FSCRYPT_FILE_NONCE_SIZE);
601
602 mode = select_encryption_mode(&crypt_info->ci_policy, inode);
603 if (IS_ERR(mode)) {
604 res = PTR_ERR(mode);
605 goto out;
606 }
607 WARN_ON_ONCE(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
608 crypt_info->ci_mode = mode;
609
610 crypt_info->ci_data_unit_bits =
611 fscrypt_policy_du_bits(&crypt_info->ci_policy, inode);
612 crypt_info->ci_data_units_per_block_bits =
613 inode->i_blkbits - crypt_info->ci_data_unit_bits;
614
615 res = setup_file_encryption_key(crypt_info, need_dirhash_key, &mk);
616 if (res)
617 goto out;
618
619 /*
620 * For existing inodes, multiple tasks may race to set the inode's
621 * fscrypt info pointer. So use cmpxchg_release(). This pairs with the
622 * smp_load_acquire() in fscrypt_get_inode_info(). I.e., publish the
623 * pointer with a RELEASE barrier so that other tasks can ACQUIRE it.
624 */
625 if (cmpxchg_release(fscrypt_inode_info_addr(inode), NULL, crypt_info) ==
626 NULL) {
627 /*
628 * We won the race and set the inode's fscrypt info to our
629 * crypt_info. Now link it into the master key's inode list.
630 */
631 if (mk) {
632 crypt_info->ci_master_key = mk;
633 refcount_inc(&mk->mk_active_refs);
634 spin_lock(&mk->mk_decrypted_inodes_lock);
635 list_add(&crypt_info->ci_master_key_link,
636 &mk->mk_decrypted_inodes);
637 spin_unlock(&mk->mk_decrypted_inodes_lock);
638 }
639 crypt_info = NULL;
640 }
641 res = 0;
642 out:
643 if (mk) {
644 up_read(&mk->mk_sem);
645 fscrypt_put_master_key(mk);
646 }
647 put_crypt_info(crypt_info);
648 return res;
649 }
650
651 /**
652 * fscrypt_get_encryption_info() - set up an inode's encryption key
653 * @inode: the inode to set up the key for. Must be encrypted.
654 * @allow_unsupported: if %true, treat an unsupported encryption policy (or
655 * unrecognized encryption context) the same way as the key
656 * being unavailable, instead of returning an error. Use
657 * %false unless the operation being performed is needed in
658 * order for files (or directories) to be deleted.
659 *
660 * Set up the inode's encryption key, if it hasn't already been done.
661 *
662 * Note: unless the key setup was already done, this isn't %GFP_NOFS-safe. So
663 * generally this shouldn't be called from within a filesystem transaction.
664 *
665 * Return: 0 if the key is now set up, *or* if it couldn't be set up because the
666 * needed master key is absent. (Use fscrypt_has_encryption_key() to
667 * distinguish these cases.) Also can return another -errno code.
668 */
fscrypt_get_encryption_info(struct inode * inode,bool allow_unsupported)669 int fscrypt_get_encryption_info(struct inode *inode, bool allow_unsupported)
670 {
671 int res;
672 union fscrypt_context ctx;
673 union fscrypt_policy policy;
674
675 if (fscrypt_has_encryption_key(inode))
676 return 0;
677
678 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
679 if (res < 0) {
680 if (res == -ERANGE && allow_unsupported)
681 return 0;
682 fscrypt_warn(inode, "Error %d getting encryption context", res);
683 return res;
684 }
685
686 res = fscrypt_policy_from_context(&policy, &ctx, res);
687 if (res) {
688 if (allow_unsupported)
689 return 0;
690 fscrypt_warn(inode,
691 "Unrecognized or corrupt encryption context");
692 return res;
693 }
694
695 if (!fscrypt_supported_policy(&policy, inode)) {
696 if (allow_unsupported)
697 return 0;
698 return -EINVAL;
699 }
700
701 res = fscrypt_setup_encryption_info(inode, &policy,
702 fscrypt_context_nonce(&ctx),
703 IS_CASEFOLDED(inode) &&
704 S_ISDIR(inode->i_mode));
705
706 if (res == -ENOPKG && allow_unsupported) /* Algorithm unavailable? */
707 res = 0;
708 if (res == -ENOKEY)
709 res = 0;
710 return res;
711 }
712
713 /**
714 * fscrypt_prepare_new_inode() - prepare to create a new inode in a directory
715 * @dir: a possibly-encrypted directory
716 * @inode: the new inode. ->i_mode and ->i_blkbits must be set already.
717 * ->i_ino doesn't need to be set yet.
718 * @encrypt_ret: (output) set to %true if the new inode will be encrypted
719 *
720 * If the directory is encrypted, set up its encryption key in preparation for
721 * encrypting the name of the new file. Also, if the new inode will be
722 * encrypted, set up its encryption key too and set *encrypt_ret=true.
723 *
724 * This isn't %GFP_NOFS-safe, and therefore it should be called before starting
725 * any filesystem transaction to create the inode. For this reason, ->i_ino
726 * isn't required to be set yet, as the filesystem may not have set it yet.
727 *
728 * This doesn't persist the new inode's encryption context. That still needs to
729 * be done later by calling fscrypt_set_context().
730 *
731 * Return: 0 on success, -ENOKEY if a key needs to be set up for @dir or @inode
732 * but the needed master key is absent, or another -errno code
733 */
fscrypt_prepare_new_inode(struct inode * dir,struct inode * inode,bool * encrypt_ret)734 int fscrypt_prepare_new_inode(struct inode *dir, struct inode *inode,
735 bool *encrypt_ret)
736 {
737 const union fscrypt_policy *policy;
738 u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
739
740 policy = fscrypt_policy_to_inherit(dir);
741 if (policy == NULL)
742 return 0;
743 if (IS_ERR(policy))
744 return PTR_ERR(policy);
745
746 if (WARN_ON_ONCE(inode->i_blkbits == 0))
747 return -EINVAL;
748
749 if (WARN_ON_ONCE(inode->i_mode == 0))
750 return -EINVAL;
751
752 /*
753 * Only regular files, directories, and symlinks are encrypted.
754 * Special files like device nodes and named pipes aren't.
755 */
756 if (!S_ISREG(inode->i_mode) &&
757 !S_ISDIR(inode->i_mode) &&
758 !S_ISLNK(inode->i_mode))
759 return 0;
760
761 *encrypt_ret = true;
762
763 get_random_bytes(nonce, FSCRYPT_FILE_NONCE_SIZE);
764 return fscrypt_setup_encryption_info(inode, policy, nonce,
765 IS_CASEFOLDED(dir) &&
766 S_ISDIR(inode->i_mode));
767 }
768 EXPORT_SYMBOL_GPL(fscrypt_prepare_new_inode);
769
770 /**
771 * fscrypt_put_encryption_info() - free most of an inode's fscrypt data
772 * @inode: an inode being evicted
773 *
774 * Free the inode's fscrypt_inode_info. Filesystems must call this when the
775 * inode is being evicted. An RCU grace period need not have elapsed yet.
776 */
fscrypt_put_encryption_info(struct inode * inode)777 void fscrypt_put_encryption_info(struct inode *inode)
778 {
779 /*
780 * Ideally we'd start with a lightweight IS_ENCRYPTED() check here
781 * before proceeding to retrieve and check the pointer. However, during
782 * inode creation, the fscrypt_inode_info is set before S_ENCRYPTED. If
783 * an error occurs, it needs to be cleaned up regardless.
784 */
785 struct fscrypt_inode_info **ci_addr = fscrypt_inode_info_addr(inode);
786
787 put_crypt_info(*ci_addr);
788 *ci_addr = NULL;
789 }
790 EXPORT_SYMBOL(fscrypt_put_encryption_info);
791
792 /**
793 * fscrypt_free_inode() - free an inode's fscrypt data requiring RCU delay
794 * @inode: an inode being freed
795 *
796 * Free the inode's cached decrypted symlink target, if any. Filesystems must
797 * call this after an RCU grace period, just before they free the inode.
798 */
fscrypt_free_inode(struct inode * inode)799 void fscrypt_free_inode(struct inode *inode)
800 {
801 if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
802 kfree(inode->i_link);
803 inode->i_link = NULL;
804 }
805 }
806 EXPORT_SYMBOL(fscrypt_free_inode);
807
808 /**
809 * fscrypt_drop_inode() - check whether the inode's master key has been removed
810 * @inode: an inode being considered for eviction
811 *
812 * Filesystems supporting fscrypt must call this from their ->drop_inode()
813 * method so that encrypted inodes are evicted as soon as they're no longer in
814 * use and their master key has been removed.
815 *
816 * Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
817 */
fscrypt_drop_inode(struct inode * inode)818 int fscrypt_drop_inode(struct inode *inode)
819 {
820 const struct fscrypt_inode_info *ci = fscrypt_get_inode_info(inode);
821
822 /*
823 * If ci is NULL, then the inode doesn't have an encryption key set up
824 * so it's irrelevant. If ci_master_key is NULL, then the master key
825 * was provided via the legacy mechanism of the process-subscribed
826 * keyrings, so we don't know whether it's been removed or not.
827 */
828 if (!ci || !ci->ci_master_key)
829 return 0;
830
831 /*
832 * With proper, non-racy use of FS_IOC_REMOVE_ENCRYPTION_KEY, all inodes
833 * protected by the key were cleaned by sync_filesystem(). But if
834 * userspace is still using the files, inodes can be dirtied between
835 * then and now. We mustn't lose any writes, so skip dirty inodes here.
836 */
837 if (inode->i_state & I_DIRTY_ALL)
838 return 0;
839
840 /*
841 * We can't take ->mk_sem here, since this runs in atomic context.
842 * Therefore, ->mk_present can change concurrently, and our result may
843 * immediately become outdated. But there's no correctness problem with
844 * unnecessarily evicting. Nor is there a correctness problem with not
845 * evicting while iput() is racing with the key being removed, since
846 * then the thread removing the key will either evict the inode itself
847 * or will correctly detect that it wasn't evicted due to the race.
848 */
849 return !READ_ONCE(ci->ci_master_key->mk_present);
850 }
851 EXPORT_SYMBOL_GPL(fscrypt_drop_inode);
852