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