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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/aes.h>
12#include <crypto/sha.h>
13#include <crypto/skcipher.h>
14#include <linux/key.h>
15
16#include "fscrypt_private.h"
17
18static struct crypto_shash *essiv_hash_tfm;
19
20static struct fscrypt_mode available_modes[] = {
21 [FSCRYPT_MODE_AES_256_XTS] = {
22 .friendly_name = "AES-256-XTS",
23 .cipher_str = "xts(aes)",
24 .keysize = 64,
25 .ivsize = 16,
26 },
27 [FSCRYPT_MODE_AES_256_CTS] = {
28 .friendly_name = "AES-256-CTS-CBC",
29 .cipher_str = "cts(cbc(aes))",
30 .keysize = 32,
31 .ivsize = 16,
32 },
33 [FSCRYPT_MODE_AES_128_CBC] = {
34 .friendly_name = "AES-128-CBC",
35 .cipher_str = "cbc(aes)",
36 .keysize = 16,
37 .ivsize = 16,
38 .needs_essiv = true,
39 },
40 [FSCRYPT_MODE_AES_128_CTS] = {
41 .friendly_name = "AES-128-CTS-CBC",
42 .cipher_str = "cts(cbc(aes))",
43 .keysize = 16,
44 .ivsize = 16,
45 },
46 [FSCRYPT_MODE_ADIANTUM] = {
47 .friendly_name = "Adiantum",
48 .cipher_str = "adiantum(xchacha12,aes)",
49 .keysize = 32,
50 .ivsize = 32,
51 },
52};
53
54static struct fscrypt_mode *
55select_encryption_mode(const union fscrypt_policy *policy,
56 const struct inode *inode)
57{
58 if (S_ISREG(inode->i_mode))
59 return &available_modes[fscrypt_policy_contents_mode(policy)];
60
61 if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))
62 return &available_modes[fscrypt_policy_fnames_mode(policy)];
63
64 WARN_ONCE(1, "fscrypt: filesystem tried to load encryption info for inode %lu, which is not encryptable (file type %d)\n",
65 inode->i_ino, (inode->i_mode & S_IFMT));
66 return ERR_PTR(-EINVAL);
67}
68
69/* Create a symmetric cipher object for the given encryption mode and key */
70struct crypto_skcipher *fscrypt_allocate_skcipher(struct fscrypt_mode *mode,
71 const u8 *raw_key,
72 const struct inode *inode)
73{
74 struct crypto_skcipher *tfm;
75 int err;
76
77 tfm = crypto_alloc_skcipher(mode->cipher_str, 0, 0);
78 if (IS_ERR(tfm)) {
79 if (PTR_ERR(tfm) == -ENOENT) {
80 fscrypt_warn(inode,
81 "Missing crypto API support for %s (API name: \"%s\")",
82 mode->friendly_name, mode->cipher_str);
83 return ERR_PTR(-ENOPKG);
84 }
85 fscrypt_err(inode, "Error allocating '%s' transform: %ld",
86 mode->cipher_str, PTR_ERR(tfm));
87 return tfm;
88 }
89 if (unlikely(!mode->logged_impl_name)) {
90 /*
91 * fscrypt performance can vary greatly depending on which
92 * crypto algorithm implementation is used. Help people debug
93 * performance problems by logging the ->cra_driver_name the
94 * first time a mode is used. Note that multiple threads can
95 * race here, but it doesn't really matter.
96 */
97 mode->logged_impl_name = true;
98 pr_info("fscrypt: %s using implementation \"%s\"\n",
99 mode->friendly_name,
100 crypto_skcipher_alg(tfm)->base.cra_driver_name);
101 }
102 crypto_skcipher_set_flags(tfm, CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
103 err = crypto_skcipher_setkey(tfm, raw_key, mode->keysize);
104 if (err)
105 goto err_free_tfm;
106
107 return tfm;
108
109err_free_tfm:
110 crypto_free_skcipher(tfm);
111 return ERR_PTR(err);
112}
113
114static int derive_essiv_salt(const u8 *key, int keysize, u8 *salt)
115{
116 struct crypto_shash *tfm = READ_ONCE(essiv_hash_tfm);
117
118 /* init hash transform on demand */
119 if (unlikely(!tfm)) {
120 struct crypto_shash *prev_tfm;
121
122 tfm = crypto_alloc_shash("sha256", 0, 0);
123 if (IS_ERR(tfm)) {
124 if (PTR_ERR(tfm) == -ENOENT) {
125 fscrypt_warn(NULL,
126 "Missing crypto API support for SHA-256");
127 return -ENOPKG;
128 }
129 fscrypt_err(NULL,
130 "Error allocating SHA-256 transform: %ld",
131 PTR_ERR(tfm));
132 return PTR_ERR(tfm);
133 }
134 prev_tfm = cmpxchg(&essiv_hash_tfm, NULL, tfm);
135 if (prev_tfm) {
136 crypto_free_shash(tfm);
137 tfm = prev_tfm;
138 }
139 }
140
141 {
142 SHASH_DESC_ON_STACK(desc, tfm);
143 desc->tfm = tfm;
144
145 return crypto_shash_digest(desc, key, keysize, salt);
146 }
147}
148
149static int init_essiv_generator(struct fscrypt_info *ci, const u8 *raw_key,
150 int keysize)
151{
152 int err;
153 struct crypto_cipher *essiv_tfm;
154 u8 salt[SHA256_DIGEST_SIZE];
155
156 if (WARN_ON(ci->ci_mode->ivsize != AES_BLOCK_SIZE))
157 return -EINVAL;
158
159 essiv_tfm = crypto_alloc_cipher("aes", 0, 0);
160 if (IS_ERR(essiv_tfm))
161 return PTR_ERR(essiv_tfm);
162
163 ci->ci_essiv_tfm = essiv_tfm;
164
165 err = derive_essiv_salt(raw_key, keysize, salt);
166 if (err)
167 goto out;
168
169 /*
170 * Using SHA256 to derive the salt/key will result in AES-256 being
171 * used for IV generation. File contents encryption will still use the
172 * configured keysize (AES-128) nevertheless.
173 */
174 err = crypto_cipher_setkey(essiv_tfm, salt, sizeof(salt));
175 if (err)
176 goto out;
177
178out:
179 memzero_explicit(salt, sizeof(salt));
180 return err;
181}
182
183/* Given the per-file key, set up the file's crypto transform object(s) */
184int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key)
185{
186 struct fscrypt_mode *mode = ci->ci_mode;
187 struct crypto_skcipher *ctfm;
188 int err;
189
190 ctfm = fscrypt_allocate_skcipher(mode, derived_key, ci->ci_inode);
191 if (IS_ERR(ctfm))
192 return PTR_ERR(ctfm);
193
194 ci->ci_ctfm = ctfm;
195
196 if (mode->needs_essiv) {
197 err = init_essiv_generator(ci, derived_key, mode->keysize);
198 if (err) {
199 fscrypt_warn(ci->ci_inode,
200 "Error initializing ESSIV generator: %d",
201 err);
202 return err;
203 }
204 }
205 return 0;
206}
207
208static int setup_per_mode_key(struct fscrypt_info *ci,
209 struct fscrypt_master_key *mk)
210{
211 struct fscrypt_mode *mode = ci->ci_mode;
212 u8 mode_num = mode - available_modes;
213 struct crypto_skcipher *tfm, *prev_tfm;
214 u8 mode_key[FSCRYPT_MAX_KEY_SIZE];
215 int err;
216
217 if (WARN_ON(mode_num >= ARRAY_SIZE(mk->mk_mode_keys)))
218 return -EINVAL;
219
220 /* pairs with cmpxchg() below */
221 tfm = READ_ONCE(mk->mk_mode_keys[mode_num]);
222 if (likely(tfm != NULL))
223 goto done;
224
225 BUILD_BUG_ON(sizeof(mode_num) != 1);
226 err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
227 HKDF_CONTEXT_PER_MODE_KEY,
228 &mode_num, sizeof(mode_num),
229 mode_key, mode->keysize);
230 if (err)
231 return err;
232 tfm = fscrypt_allocate_skcipher(mode, mode_key, ci->ci_inode);
233 memzero_explicit(mode_key, mode->keysize);
234 if (IS_ERR(tfm))
235 return PTR_ERR(tfm);
236
237 /* pairs with READ_ONCE() above */
238 prev_tfm = cmpxchg(&mk->mk_mode_keys[mode_num], NULL, tfm);
239 if (prev_tfm != NULL) {
240 crypto_free_skcipher(tfm);
241 tfm = prev_tfm;
242 }
243done:
244 ci->ci_ctfm = tfm;
245 return 0;
246}
247
248static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
249 struct fscrypt_master_key *mk)
250{
251 u8 derived_key[FSCRYPT_MAX_KEY_SIZE];
252 int err;
253
254 if (ci->ci_policy.v2.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) {
255 /*
256 * DIRECT_KEY: instead of deriving per-file keys, the per-file
257 * nonce will be included in all the IVs. But unlike v1
258 * policies, for v2 policies in this case we don't encrypt with
259 * the master key directly but rather derive a per-mode key.
260 * This ensures that the master key is consistently used only
261 * for HKDF, avoiding key reuse issues.
262 */
263 if (!fscrypt_mode_supports_direct_key(ci->ci_mode)) {
264 fscrypt_warn(ci->ci_inode,
265 "Direct key flag not allowed with %s",
266 ci->ci_mode->friendly_name);
267 return -EINVAL;
268 }
269 return setup_per_mode_key(ci, mk);
270 }
271
272 err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
273 HKDF_CONTEXT_PER_FILE_KEY,
274 ci->ci_nonce, FS_KEY_DERIVATION_NONCE_SIZE,
275 derived_key, ci->ci_mode->keysize);
276 if (err)
277 return err;
278
279 err = fscrypt_set_derived_key(ci, derived_key);
280 memzero_explicit(derived_key, ci->ci_mode->keysize);
281 return err;
282}
283
284/*
285 * Find the master key, then set up the inode's actual encryption key.
286 *
287 * If the master key is found in the filesystem-level keyring, then the
288 * corresponding 'struct key' is returned in *master_key_ret with
289 * ->mk_secret_sem read-locked. This is needed to ensure that only one task
290 * links the fscrypt_info into ->mk_decrypted_inodes (as multiple tasks may race
291 * to create an fscrypt_info for the same inode), and to synchronize the master
292 * key being removed with a new inode starting to use it.
293 */
294static int setup_file_encryption_key(struct fscrypt_info *ci,
295 struct key **master_key_ret)
296{
297 struct key *key;
298 struct fscrypt_master_key *mk = NULL;
299 struct fscrypt_key_specifier mk_spec;
300 int err;
301
302 switch (ci->ci_policy.version) {
303 case FSCRYPT_POLICY_V1:
304 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
305 memcpy(mk_spec.u.descriptor,
306 ci->ci_policy.v1.master_key_descriptor,
307 FSCRYPT_KEY_DESCRIPTOR_SIZE);
308 break;
309 case FSCRYPT_POLICY_V2:
310 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
311 memcpy(mk_spec.u.identifier,
312 ci->ci_policy.v2.master_key_identifier,
313 FSCRYPT_KEY_IDENTIFIER_SIZE);
314 break;
315 default:
316 WARN_ON(1);
317 return -EINVAL;
318 }
319
320 key = fscrypt_find_master_key(ci->ci_inode->i_sb, &mk_spec);
321 if (IS_ERR(key)) {
322 if (key != ERR_PTR(-ENOKEY) ||
323 ci->ci_policy.version != FSCRYPT_POLICY_V1)
324 return PTR_ERR(key);
325
326 /*
327 * As a legacy fallback for v1 policies, search for the key in
328 * the current task's subscribed keyrings too. Don't move this
329 * to before the search of ->s_master_keys, since users
330 * shouldn't be able to override filesystem-level keys.
331 */
332 return fscrypt_setup_v1_file_key_via_subscribed_keyrings(ci);
333 }
334
335 mk = key->payload.data[0];
336 down_read(&mk->mk_secret_sem);
337
338 /* Has the secret been removed (via FS_IOC_REMOVE_ENCRYPTION_KEY)? */
339 if (!is_master_key_secret_present(&mk->mk_secret)) {
340 err = -ENOKEY;
341 goto out_release_key;
342 }
343
344 /*
345 * Require that the master key be at least as long as the derived key.
346 * Otherwise, the derived key cannot possibly contain as much entropy as
347 * that required by the encryption mode it will be used for. For v1
348 * policies it's also required for the KDF to work at all.
349 */
350 if (mk->mk_secret.size < ci->ci_mode->keysize) {
351 fscrypt_warn(NULL,
352 "key with %s %*phN is too short (got %u bytes, need %u+ bytes)",
353 master_key_spec_type(&mk_spec),
354 master_key_spec_len(&mk_spec), (u8 *)&mk_spec.u,
355 mk->mk_secret.size, ci->ci_mode->keysize);
356 err = -ENOKEY;
357 goto out_release_key;
358 }
359
360 switch (ci->ci_policy.version) {
361 case FSCRYPT_POLICY_V1:
362 err = fscrypt_setup_v1_file_key(ci, mk->mk_secret.raw);
363 break;
364 case FSCRYPT_POLICY_V2:
365 err = fscrypt_setup_v2_file_key(ci, mk);
366 break;
367 default:
368 WARN_ON(1);
369 err = -EINVAL;
370 break;
371 }
372 if (err)
373 goto out_release_key;
374
375 *master_key_ret = key;
376 return 0;
377
378out_release_key:
379 up_read(&mk->mk_secret_sem);
380 key_put(key);
381 return err;
382}
383
384static void put_crypt_info(struct fscrypt_info *ci)
385{
386 struct key *key;
387
388 if (!ci)
389 return;
390
391 if (ci->ci_direct_key) {
392 fscrypt_put_direct_key(ci->ci_direct_key);
393 } else if ((ci->ci_ctfm != NULL || ci->ci_essiv_tfm != NULL) &&
394 !fscrypt_is_direct_key_policy(&ci->ci_policy)) {
395 crypto_free_skcipher(ci->ci_ctfm);
396 crypto_free_cipher(ci->ci_essiv_tfm);
397 }
398
399 key = ci->ci_master_key;
400 if (key) {
401 struct fscrypt_master_key *mk = key->payload.data[0];
402
403 /*
404 * Remove this inode from the list of inodes that were unlocked
405 * with the master key.
406 *
407 * In addition, if we're removing the last inode from a key that
408 * already had its secret removed, invalidate the key so that it
409 * gets removed from ->s_master_keys.
410 */
411 spin_lock(&mk->mk_decrypted_inodes_lock);
412 list_del(&ci->ci_master_key_link);
413 spin_unlock(&mk->mk_decrypted_inodes_lock);
414 if (refcount_dec_and_test(&mk->mk_refcount))
415 key_invalidate(key);
416 key_put(key);
417 }
418 kmem_cache_free(fscrypt_info_cachep, ci);
419}
420
421int fscrypt_get_encryption_info(struct inode *inode)
422{
423 struct fscrypt_info *crypt_info;
424 union fscrypt_context ctx;
425 struct fscrypt_mode *mode;
426 struct key *master_key = NULL;
427 int res;
428
429 if (fscrypt_has_encryption_key(inode))
430 return 0;
431
432 res = fscrypt_initialize(inode->i_sb->s_cop->flags);
433 if (res)
434 return res;
435
436 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
437 if (res < 0) {
438 if (!fscrypt_dummy_context_enabled(inode) ||
439 IS_ENCRYPTED(inode)) {
440 fscrypt_warn(inode,
441 "Error %d getting encryption context",
442 res);
443 return res;
444 }
445 /* Fake up a context for an unencrypted directory */
446 memset(&ctx, 0, sizeof(ctx));
447 ctx.version = FSCRYPT_CONTEXT_V1;
448 ctx.v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
449 ctx.v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
450 memset(ctx.v1.master_key_descriptor, 0x42,
451 FSCRYPT_KEY_DESCRIPTOR_SIZE);
452 res = sizeof(ctx.v1);
453 }
454
455 crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
456 if (!crypt_info)
457 return -ENOMEM;
458
459 crypt_info->ci_inode = inode;
460
461 res = fscrypt_policy_from_context(&crypt_info->ci_policy, &ctx, res);
462 if (res) {
463 fscrypt_warn(inode,
464 "Unrecognized or corrupt encryption context");
465 goto out;
466 }
467
468 switch (ctx.version) {
469 case FSCRYPT_CONTEXT_V1:
470 memcpy(crypt_info->ci_nonce, ctx.v1.nonce,
471 FS_KEY_DERIVATION_NONCE_SIZE);
472 break;
473 case FSCRYPT_CONTEXT_V2:
474 memcpy(crypt_info->ci_nonce, ctx.v2.nonce,
475 FS_KEY_DERIVATION_NONCE_SIZE);
476 break;
477 default:
478 WARN_ON(1);
479 res = -EINVAL;
480 goto out;
481 }
482
483 if (!fscrypt_supported_policy(&crypt_info->ci_policy, inode)) {
484 res = -EINVAL;
485 goto out;
486 }
487
488 mode = select_encryption_mode(&crypt_info->ci_policy, inode);
489 if (IS_ERR(mode)) {
490 res = PTR_ERR(mode);
491 goto out;
492 }
493 WARN_ON(mode->ivsize > FSCRYPT_MAX_IV_SIZE);
494 crypt_info->ci_mode = mode;
495
496 res = setup_file_encryption_key(crypt_info, &master_key);
497 if (res)
498 goto out;
499
500 if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) {
501 if (master_key) {
502 struct fscrypt_master_key *mk =
503 master_key->payload.data[0];
504
505 refcount_inc(&mk->mk_refcount);
506 crypt_info->ci_master_key = key_get(master_key);
507 spin_lock(&mk->mk_decrypted_inodes_lock);
508 list_add(&crypt_info->ci_master_key_link,
509 &mk->mk_decrypted_inodes);
510 spin_unlock(&mk->mk_decrypted_inodes_lock);
511 }
512 crypt_info = NULL;
513 }
514 res = 0;
515out:
516 if (master_key) {
517 struct fscrypt_master_key *mk = master_key->payload.data[0];
518
519 up_read(&mk->mk_secret_sem);
520 key_put(master_key);
521 }
522 if (res == -ENOKEY)
523 res = 0;
524 put_crypt_info(crypt_info);
525 return res;
526}
527EXPORT_SYMBOL(fscrypt_get_encryption_info);
528
529/**
530 * fscrypt_put_encryption_info - free most of an inode's fscrypt data
531 *
532 * Free the inode's fscrypt_info. Filesystems must call this when the inode is
533 * being evicted. An RCU grace period need not have elapsed yet.
534 */
535void fscrypt_put_encryption_info(struct inode *inode)
536{
537 put_crypt_info(inode->i_crypt_info);
538 inode->i_crypt_info = NULL;
539}
540EXPORT_SYMBOL(fscrypt_put_encryption_info);
541
542/**
543 * fscrypt_free_inode - free an inode's fscrypt data requiring RCU delay
544 *
545 * Free the inode's cached decrypted symlink target, if any. Filesystems must
546 * call this after an RCU grace period, just before they free the inode.
547 */
548void fscrypt_free_inode(struct inode *inode)
549{
550 if (IS_ENCRYPTED(inode) && S_ISLNK(inode->i_mode)) {
551 kfree(inode->i_link);
552 inode->i_link = NULL;
553 }
554}
555EXPORT_SYMBOL(fscrypt_free_inode);
556
557/**
558 * fscrypt_drop_inode - check whether the inode's master key has been removed
559 *
560 * Filesystems supporting fscrypt must call this from their ->drop_inode()
561 * method so that encrypted inodes are evicted as soon as they're no longer in
562 * use and their master key has been removed.
563 *
564 * Return: 1 if fscrypt wants the inode to be evicted now, otherwise 0
565 */
566int fscrypt_drop_inode(struct inode *inode)
567{
568 const struct fscrypt_info *ci = READ_ONCE(inode->i_crypt_info);
569 const struct fscrypt_master_key *mk;
570
571 /*
572 * If ci is NULL, then the inode doesn't have an encryption key set up
573 * so it's irrelevant. If ci_master_key is NULL, then the master key
574 * was provided via the legacy mechanism of the process-subscribed
575 * keyrings, so we don't know whether it's been removed or not.
576 */
577 if (!ci || !ci->ci_master_key)
578 return 0;
579 mk = ci->ci_master_key->payload.data[0];
580
581 /*
582 * Note: since we aren't holding ->mk_secret_sem, the result here can
583 * immediately become outdated. But there's no correctness problem with
584 * unnecessarily evicting. Nor is there a correctness problem with not
585 * evicting while iput() is racing with the key being removed, since
586 * then the thread removing the key will either evict the inode itself
587 * or will correctly detect that it wasn't evicted due to the race.
588 */
589 return !is_master_key_secret_present(&mk->mk_secret);
590}
591EXPORT_SYMBOL_GPL(fscrypt_drop_inode);