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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Filesystem-level keyring for fscrypt
4 *
5 * Copyright 2019 Google LLC
6 */
7
8/*
9 * This file implements management of fscrypt master keys in the
10 * filesystem-level keyring, including the ioctls:
11 *
12 * - FS_IOC_ADD_ENCRYPTION_KEY
13 * - FS_IOC_REMOVE_ENCRYPTION_KEY
14 * - FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS
15 * - FS_IOC_GET_ENCRYPTION_KEY_STATUS
16 *
17 * See the "User API" section of Documentation/filesystems/fscrypt.rst for more
18 * information about these ioctls.
19 */
20
21#include <asm/unaligned.h>
22#include <crypto/skcipher.h>
23#include <linux/key-type.h>
24#include <linux/random.h>
25#include <linux/seq_file.h>
26
27#include "fscrypt_private.h"
28
29/* The master encryption keys for a filesystem (->s_master_keys) */
30struct fscrypt_keyring {
31 /*
32 * Lock that protects ->key_hashtable. It does *not* protect the
33 * fscrypt_master_key structs themselves.
34 */
35 spinlock_t lock;
36
37 /* Hash table that maps fscrypt_key_specifier to fscrypt_master_key */
38 struct hlist_head key_hashtable[128];
39};
40
41static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
42{
43 fscrypt_destroy_hkdf(&secret->hkdf);
44 memzero_explicit(secret, sizeof(*secret));
45}
46
47static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
48 struct fscrypt_master_key_secret *src)
49{
50 memcpy(dst, src, sizeof(*dst));
51 memzero_explicit(src, sizeof(*src));
52}
53
54static void fscrypt_free_master_key(struct rcu_head *head)
55{
56 struct fscrypt_master_key *mk =
57 container_of(head, struct fscrypt_master_key, mk_rcu_head);
58 /*
59 * The master key secret and any embedded subkeys should have already
60 * been wiped when the last active reference to the fscrypt_master_key
61 * struct was dropped; doing it here would be unnecessarily late.
62 * Nevertheless, use kfree_sensitive() in case anything was missed.
63 */
64 kfree_sensitive(mk);
65}
66
67void fscrypt_put_master_key(struct fscrypt_master_key *mk)
68{
69 if (!refcount_dec_and_test(&mk->mk_struct_refs))
70 return;
71 /*
72 * No structural references left, so free ->mk_users, and also free the
73 * fscrypt_master_key struct itself after an RCU grace period ensures
74 * that concurrent keyring lookups can no longer find it.
75 */
76 WARN_ON(refcount_read(&mk->mk_active_refs) != 0);
77 key_put(mk->mk_users);
78 mk->mk_users = NULL;
79 call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key);
80}
81
82void fscrypt_put_master_key_activeref(struct super_block *sb,
83 struct fscrypt_master_key *mk)
84{
85 size_t i;
86
87 if (!refcount_dec_and_test(&mk->mk_active_refs))
88 return;
89 /*
90 * No active references left, so complete the full removal of this
91 * fscrypt_master_key struct by removing it from the keyring and
92 * destroying any subkeys embedded in it.
93 */
94
95 spin_lock(&sb->s_master_keys->lock);
96 hlist_del_rcu(&mk->mk_node);
97 spin_unlock(&sb->s_master_keys->lock);
98
99 /*
100 * ->mk_active_refs == 0 implies that ->mk_secret is not present and
101 * that ->mk_decrypted_inodes is empty.
102 */
103 WARN_ON(is_master_key_secret_present(&mk->mk_secret));
104 WARN_ON(!list_empty(&mk->mk_decrypted_inodes));
105
106 for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {
107 fscrypt_destroy_prepared_key(
108 sb, &mk->mk_direct_keys[i]);
109 fscrypt_destroy_prepared_key(
110 sb, &mk->mk_iv_ino_lblk_64_keys[i]);
111 fscrypt_destroy_prepared_key(
112 sb, &mk->mk_iv_ino_lblk_32_keys[i]);
113 }
114 memzero_explicit(&mk->mk_ino_hash_key,
115 sizeof(mk->mk_ino_hash_key));
116 mk->mk_ino_hash_key_initialized = false;
117
118 /* Drop the structural ref associated with the active refs. */
119 fscrypt_put_master_key(mk);
120}
121
122static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
123{
124 if (spec->__reserved)
125 return false;
126 return master_key_spec_len(spec) != 0;
127}
128
129static int fscrypt_user_key_instantiate(struct key *key,
130 struct key_preparsed_payload *prep)
131{
132 /*
133 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
134 * each key, regardless of the exact key size. The amount of memory
135 * actually used is greater than the size of the raw key anyway.
136 */
137 return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
138}
139
140static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
141{
142 seq_puts(m, key->description);
143}
144
145/*
146 * Type of key in ->mk_users. Each key of this type represents a particular
147 * user who has added a particular master key.
148 *
149 * Note that the name of this key type really should be something like
150 * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen
151 * mainly for simplicity of presentation in /proc/keys when read by a non-root
152 * user. And it is expected to be rare that a key is actually added by multiple
153 * users, since users should keep their encryption keys confidential.
154 */
155static struct key_type key_type_fscrypt_user = {
156 .name = ".fscrypt",
157 .instantiate = fscrypt_user_key_instantiate,
158 .describe = fscrypt_user_key_describe,
159};
160
161#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \
162 (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
163 CONST_STRLEN("-users") + 1)
164
165#define FSCRYPT_MK_USER_DESCRIPTION_SIZE \
166 (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
167
168static void format_mk_users_keyring_description(
169 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
170 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
171{
172 sprintf(description, "fscrypt-%*phN-users",
173 FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
174}
175
176static void format_mk_user_description(
177 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
178 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
179{
180
181 sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
182 mk_identifier, __kuid_val(current_fsuid()));
183}
184
185/* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */
186static int allocate_filesystem_keyring(struct super_block *sb)
187{
188 struct fscrypt_keyring *keyring;
189
190 if (sb->s_master_keys)
191 return 0;
192
193 keyring = kzalloc(sizeof(*keyring), GFP_KERNEL);
194 if (!keyring)
195 return -ENOMEM;
196 spin_lock_init(&keyring->lock);
197 /*
198 * Pairs with the smp_load_acquire() in fscrypt_find_master_key().
199 * I.e., here we publish ->s_master_keys with a RELEASE barrier so that
200 * concurrent tasks can ACQUIRE it.
201 */
202 smp_store_release(&sb->s_master_keys, keyring);
203 return 0;
204}
205
206/*
207 * Release all encryption keys that have been added to the filesystem, along
208 * with the keyring that contains them.
209 *
210 * This is called at unmount time. The filesystem's underlying block device(s)
211 * are still available at this time; this is important because after user file
212 * accesses have been allowed, this function may need to evict keys from the
213 * keyslots of an inline crypto engine, which requires the block device(s).
214 *
215 * This is also called when the super_block is being freed. This is needed to
216 * avoid a memory leak if mounting fails after the "test_dummy_encryption"
217 * option was processed, as in that case the unmount-time call isn't made.
218 */
219void fscrypt_destroy_keyring(struct super_block *sb)
220{
221 struct fscrypt_keyring *keyring = sb->s_master_keys;
222 size_t i;
223
224 if (!keyring)
225 return;
226
227 for (i = 0; i < ARRAY_SIZE(keyring->key_hashtable); i++) {
228 struct hlist_head *bucket = &keyring->key_hashtable[i];
229 struct fscrypt_master_key *mk;
230 struct hlist_node *tmp;
231
232 hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) {
233 /*
234 * Since all inodes were already evicted, every key
235 * remaining in the keyring should have an empty inode
236 * list, and should only still be in the keyring due to
237 * the single active ref associated with ->mk_secret.
238 * There should be no structural refs beyond the one
239 * associated with the active ref.
240 */
241 WARN_ON(refcount_read(&mk->mk_active_refs) != 1);
242 WARN_ON(refcount_read(&mk->mk_struct_refs) != 1);
243 WARN_ON(!is_master_key_secret_present(&mk->mk_secret));
244 wipe_master_key_secret(&mk->mk_secret);
245 fscrypt_put_master_key_activeref(sb, mk);
246 }
247 }
248 kfree_sensitive(keyring);
249 sb->s_master_keys = NULL;
250}
251
252static struct hlist_head *
253fscrypt_mk_hash_bucket(struct fscrypt_keyring *keyring,
254 const struct fscrypt_key_specifier *mk_spec)
255{
256 /*
257 * Since key specifiers should be "random" values, it is sufficient to
258 * use a trivial hash function that just takes the first several bits of
259 * the key specifier.
260 */
261 unsigned long i = get_unaligned((unsigned long *)&mk_spec->u);
262
263 return &keyring->key_hashtable[i % ARRAY_SIZE(keyring->key_hashtable)];
264}
265
266/*
267 * Find the specified master key struct in ->s_master_keys and take a structural
268 * ref to it. The structural ref guarantees that the key struct continues to
269 * exist, but it does *not* guarantee that ->s_master_keys continues to contain
270 * the key struct. The structural ref needs to be dropped by
271 * fscrypt_put_master_key(). Returns NULL if the key struct is not found.
272 */
273struct fscrypt_master_key *
274fscrypt_find_master_key(struct super_block *sb,
275 const struct fscrypt_key_specifier *mk_spec)
276{
277 struct fscrypt_keyring *keyring;
278 struct hlist_head *bucket;
279 struct fscrypt_master_key *mk;
280
281 /*
282 * Pairs with the smp_store_release() in allocate_filesystem_keyring().
283 * I.e., another task can publish ->s_master_keys concurrently,
284 * executing a RELEASE barrier. We need to use smp_load_acquire() here
285 * to safely ACQUIRE the memory the other task published.
286 */
287 keyring = smp_load_acquire(&sb->s_master_keys);
288 if (keyring == NULL)
289 return NULL; /* No keyring yet, so no keys yet. */
290
291 bucket = fscrypt_mk_hash_bucket(keyring, mk_spec);
292 rcu_read_lock();
293 switch (mk_spec->type) {
294 case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
295 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
296 if (mk->mk_spec.type ==
297 FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
298 memcmp(mk->mk_spec.u.descriptor,
299 mk_spec->u.descriptor,
300 FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
301 refcount_inc_not_zero(&mk->mk_struct_refs))
302 goto out;
303 }
304 break;
305 case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
306 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
307 if (mk->mk_spec.type ==
308 FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
309 memcmp(mk->mk_spec.u.identifier,
310 mk_spec->u.identifier,
311 FSCRYPT_KEY_IDENTIFIER_SIZE) == 0 &&
312 refcount_inc_not_zero(&mk->mk_struct_refs))
313 goto out;
314 }
315 break;
316 }
317 mk = NULL;
318out:
319 rcu_read_unlock();
320 return mk;
321}
322
323static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
324{
325 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
326 struct key *keyring;
327
328 format_mk_users_keyring_description(description,
329 mk->mk_spec.u.identifier);
330 keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
331 current_cred(), KEY_POS_SEARCH |
332 KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
333 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
334 if (IS_ERR(keyring))
335 return PTR_ERR(keyring);
336
337 mk->mk_users = keyring;
338 return 0;
339}
340
341/*
342 * Find the current user's "key" in the master key's ->mk_users.
343 * Returns ERR_PTR(-ENOKEY) if not found.
344 */
345static struct key *find_master_key_user(struct fscrypt_master_key *mk)
346{
347 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
348 key_ref_t keyref;
349
350 format_mk_user_description(description, mk->mk_spec.u.identifier);
351
352 /*
353 * We need to mark the keyring reference as "possessed" so that we
354 * acquire permission to search it, via the KEY_POS_SEARCH permission.
355 */
356 keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/),
357 &key_type_fscrypt_user, description, false);
358 if (IS_ERR(keyref)) {
359 if (PTR_ERR(keyref) == -EAGAIN || /* not found */
360 PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
361 keyref = ERR_PTR(-ENOKEY);
362 return ERR_CAST(keyref);
363 }
364 return key_ref_to_ptr(keyref);
365}
366
367/*
368 * Give the current user a "key" in ->mk_users. This charges the user's quota
369 * and marks the master key as added by the current user, so that it cannot be
370 * removed by another user with the key. Either ->mk_sem must be held for
371 * write, or the master key must be still undergoing initialization.
372 */
373static int add_master_key_user(struct fscrypt_master_key *mk)
374{
375 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
376 struct key *mk_user;
377 int err;
378
379 format_mk_user_description(description, mk->mk_spec.u.identifier);
380 mk_user = key_alloc(&key_type_fscrypt_user, description,
381 current_fsuid(), current_gid(), current_cred(),
382 KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
383 if (IS_ERR(mk_user))
384 return PTR_ERR(mk_user);
385
386 err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
387 key_put(mk_user);
388 return err;
389}
390
391/*
392 * Remove the current user's "key" from ->mk_users.
393 * ->mk_sem must be held for write.
394 *
395 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
396 */
397static int remove_master_key_user(struct fscrypt_master_key *mk)
398{
399 struct key *mk_user;
400 int err;
401
402 mk_user = find_master_key_user(mk);
403 if (IS_ERR(mk_user))
404 return PTR_ERR(mk_user);
405 err = key_unlink(mk->mk_users, mk_user);
406 key_put(mk_user);
407 return err;
408}
409
410/*
411 * Allocate a new fscrypt_master_key, transfer the given secret over to it, and
412 * insert it into sb->s_master_keys.
413 */
414static int add_new_master_key(struct super_block *sb,
415 struct fscrypt_master_key_secret *secret,
416 const struct fscrypt_key_specifier *mk_spec)
417{
418 struct fscrypt_keyring *keyring = sb->s_master_keys;
419 struct fscrypt_master_key *mk;
420 int err;
421
422 mk = kzalloc(sizeof(*mk), GFP_KERNEL);
423 if (!mk)
424 return -ENOMEM;
425
426 init_rwsem(&mk->mk_sem);
427 refcount_set(&mk->mk_struct_refs, 1);
428 mk->mk_spec = *mk_spec;
429
430 INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
431 spin_lock_init(&mk->mk_decrypted_inodes_lock);
432
433 if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
434 err = allocate_master_key_users_keyring(mk);
435 if (err)
436 goto out_put;
437 err = add_master_key_user(mk);
438 if (err)
439 goto out_put;
440 }
441
442 move_master_key_secret(&mk->mk_secret, secret);
443 refcount_set(&mk->mk_active_refs, 1); /* ->mk_secret is present */
444
445 spin_lock(&keyring->lock);
446 hlist_add_head_rcu(&mk->mk_node,
447 fscrypt_mk_hash_bucket(keyring, mk_spec));
448 spin_unlock(&keyring->lock);
449 return 0;
450
451out_put:
452 fscrypt_put_master_key(mk);
453 return err;
454}
455
456#define KEY_DEAD 1
457
458static int add_existing_master_key(struct fscrypt_master_key *mk,
459 struct fscrypt_master_key_secret *secret)
460{
461 int err;
462
463 /*
464 * If the current user is already in ->mk_users, then there's nothing to
465 * do. Otherwise, we need to add the user to ->mk_users. (Neither is
466 * applicable for v1 policy keys, which have NULL ->mk_users.)
467 */
468 if (mk->mk_users) {
469 struct key *mk_user = find_master_key_user(mk);
470
471 if (mk_user != ERR_PTR(-ENOKEY)) {
472 if (IS_ERR(mk_user))
473 return PTR_ERR(mk_user);
474 key_put(mk_user);
475 return 0;
476 }
477 err = add_master_key_user(mk);
478 if (err)
479 return err;
480 }
481
482 /* Re-add the secret if needed. */
483 if (!is_master_key_secret_present(&mk->mk_secret)) {
484 if (!refcount_inc_not_zero(&mk->mk_active_refs))
485 return KEY_DEAD;
486 move_master_key_secret(&mk->mk_secret, secret);
487 }
488
489 return 0;
490}
491
492static int do_add_master_key(struct super_block *sb,
493 struct fscrypt_master_key_secret *secret,
494 const struct fscrypt_key_specifier *mk_spec)
495{
496 static DEFINE_MUTEX(fscrypt_add_key_mutex);
497 struct fscrypt_master_key *mk;
498 int err;
499
500 mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
501
502 mk = fscrypt_find_master_key(sb, mk_spec);
503 if (!mk) {
504 /* Didn't find the key in ->s_master_keys. Add it. */
505 err = allocate_filesystem_keyring(sb);
506 if (!err)
507 err = add_new_master_key(sb, secret, mk_spec);
508 } else {
509 /*
510 * Found the key in ->s_master_keys. Re-add the secret if
511 * needed, and add the user to ->mk_users if needed.
512 */
513 down_write(&mk->mk_sem);
514 err = add_existing_master_key(mk, secret);
515 up_write(&mk->mk_sem);
516 if (err == KEY_DEAD) {
517 /*
518 * We found a key struct, but it's already been fully
519 * removed. Ignore the old struct and add a new one.
520 * fscrypt_add_key_mutex means we don't need to worry
521 * about concurrent adds.
522 */
523 err = add_new_master_key(sb, secret, mk_spec);
524 }
525 fscrypt_put_master_key(mk);
526 }
527 mutex_unlock(&fscrypt_add_key_mutex);
528 return err;
529}
530
531static int add_master_key(struct super_block *sb,
532 struct fscrypt_master_key_secret *secret,
533 struct fscrypt_key_specifier *key_spec)
534{
535 int err;
536
537 if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
538 err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,
539 secret->size);
540 if (err)
541 return err;
542
543 /*
544 * Now that the HKDF context is initialized, the raw key is no
545 * longer needed.
546 */
547 memzero_explicit(secret->raw, secret->size);
548
549 /* Calculate the key identifier */
550 err = fscrypt_hkdf_expand(&secret->hkdf,
551 HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,
552 key_spec->u.identifier,
553 FSCRYPT_KEY_IDENTIFIER_SIZE);
554 if (err)
555 return err;
556 }
557 return do_add_master_key(sb, secret, key_spec);
558}
559
560static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
561{
562 const struct fscrypt_provisioning_key_payload *payload = prep->data;
563
564 if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
565 prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
566 return -EINVAL;
567
568 if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
569 payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
570 return -EINVAL;
571
572 if (payload->__reserved)
573 return -EINVAL;
574
575 prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
576 if (!prep->payload.data[0])
577 return -ENOMEM;
578
579 prep->quotalen = prep->datalen;
580 return 0;
581}
582
583static void fscrypt_provisioning_key_free_preparse(
584 struct key_preparsed_payload *prep)
585{
586 kfree_sensitive(prep->payload.data[0]);
587}
588
589static void fscrypt_provisioning_key_describe(const struct key *key,
590 struct seq_file *m)
591{
592 seq_puts(m, key->description);
593 if (key_is_positive(key)) {
594 const struct fscrypt_provisioning_key_payload *payload =
595 key->payload.data[0];
596
597 seq_printf(m, ": %u [%u]", key->datalen, payload->type);
598 }
599}
600
601static void fscrypt_provisioning_key_destroy(struct key *key)
602{
603 kfree_sensitive(key->payload.data[0]);
604}
605
606static struct key_type key_type_fscrypt_provisioning = {
607 .name = "fscrypt-provisioning",
608 .preparse = fscrypt_provisioning_key_preparse,
609 .free_preparse = fscrypt_provisioning_key_free_preparse,
610 .instantiate = generic_key_instantiate,
611 .describe = fscrypt_provisioning_key_describe,
612 .destroy = fscrypt_provisioning_key_destroy,
613};
614
615/*
616 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
617 * store it into 'secret'.
618 *
619 * The key must be of type "fscrypt-provisioning" and must have the field
620 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
621 * only usable with fscrypt with the particular KDF version identified by
622 * 'type'. We don't use the "logon" key type because there's no way to
623 * completely restrict the use of such keys; they can be used by any kernel API
624 * that accepts "logon" keys and doesn't require a specific service prefix.
625 *
626 * The ability to specify the key via Linux keyring key is intended for cases
627 * where userspace needs to re-add keys after the filesystem is unmounted and
628 * re-mounted. Most users should just provide the raw key directly instead.
629 */
630static int get_keyring_key(u32 key_id, u32 type,
631 struct fscrypt_master_key_secret *secret)
632{
633 key_ref_t ref;
634 struct key *key;
635 const struct fscrypt_provisioning_key_payload *payload;
636 int err;
637
638 ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
639 if (IS_ERR(ref))
640 return PTR_ERR(ref);
641 key = key_ref_to_ptr(ref);
642
643 if (key->type != &key_type_fscrypt_provisioning)
644 goto bad_key;
645 payload = key->payload.data[0];
646
647 /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
648 if (payload->type != type)
649 goto bad_key;
650
651 secret->size = key->datalen - sizeof(*payload);
652 memcpy(secret->raw, payload->raw, secret->size);
653 err = 0;
654 goto out_put;
655
656bad_key:
657 err = -EKEYREJECTED;
658out_put:
659 key_ref_put(ref);
660 return err;
661}
662
663/*
664 * Add a master encryption key to the filesystem, causing all files which were
665 * encrypted with it to appear "unlocked" (decrypted) when accessed.
666 *
667 * When adding a key for use by v1 encryption policies, this ioctl is
668 * privileged, and userspace must provide the 'key_descriptor'.
669 *
670 * When adding a key for use by v2+ encryption policies, this ioctl is
671 * unprivileged. This is needed, in general, to allow non-root users to use
672 * encryption without encountering the visibility problems of process-subscribed
673 * keyrings and the inability to properly remove keys. This works by having
674 * each key identified by its cryptographically secure hash --- the
675 * 'key_identifier'. The cryptographic hash ensures that a malicious user
676 * cannot add the wrong key for a given identifier. Furthermore, each added key
677 * is charged to the appropriate user's quota for the keyrings service, which
678 * prevents a malicious user from adding too many keys. Finally, we forbid a
679 * user from removing a key while other users have added it too, which prevents
680 * a user who knows another user's key from causing a denial-of-service by
681 * removing it at an inopportune time. (We tolerate that a user who knows a key
682 * can prevent other users from removing it.)
683 *
684 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
685 * Documentation/filesystems/fscrypt.rst.
686 */
687int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
688{
689 struct super_block *sb = file_inode(filp)->i_sb;
690 struct fscrypt_add_key_arg __user *uarg = _uarg;
691 struct fscrypt_add_key_arg arg;
692 struct fscrypt_master_key_secret secret;
693 int err;
694
695 if (copy_from_user(&arg, uarg, sizeof(arg)))
696 return -EFAULT;
697
698 if (!valid_key_spec(&arg.key_spec))
699 return -EINVAL;
700
701 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
702 return -EINVAL;
703
704 /*
705 * Only root can add keys that are identified by an arbitrary descriptor
706 * rather than by a cryptographic hash --- since otherwise a malicious
707 * user could add the wrong key.
708 */
709 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
710 !capable(CAP_SYS_ADMIN))
711 return -EACCES;
712
713 memset(&secret, 0, sizeof(secret));
714 if (arg.key_id) {
715 if (arg.raw_size != 0)
716 return -EINVAL;
717 err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
718 if (err)
719 goto out_wipe_secret;
720 } else {
721 if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
722 arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
723 return -EINVAL;
724 secret.size = arg.raw_size;
725 err = -EFAULT;
726 if (copy_from_user(secret.raw, uarg->raw, secret.size))
727 goto out_wipe_secret;
728 }
729
730 err = add_master_key(sb, &secret, &arg.key_spec);
731 if (err)
732 goto out_wipe_secret;
733
734 /* Return the key identifier to userspace, if applicable */
735 err = -EFAULT;
736 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
737 copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,
738 FSCRYPT_KEY_IDENTIFIER_SIZE))
739 goto out_wipe_secret;
740 err = 0;
741out_wipe_secret:
742 wipe_master_key_secret(&secret);
743 return err;
744}
745EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
746
747static void
748fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret)
749{
750 static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
751
752 get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
753
754 memset(secret, 0, sizeof(*secret));
755 secret->size = FSCRYPT_MAX_KEY_SIZE;
756 memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE);
757}
758
759int fscrypt_get_test_dummy_key_identifier(
760 u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
761{
762 struct fscrypt_master_key_secret secret;
763 int err;
764
765 fscrypt_get_test_dummy_secret(&secret);
766
767 err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
768 if (err)
769 goto out;
770 err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER,
771 NULL, 0, key_identifier,
772 FSCRYPT_KEY_IDENTIFIER_SIZE);
773out:
774 wipe_master_key_secret(&secret);
775 return err;
776}
777
778/**
779 * fscrypt_add_test_dummy_key() - add the test dummy encryption key
780 * @sb: the filesystem instance to add the key to
781 * @dummy_policy: the encryption policy for test_dummy_encryption
782 *
783 * If needed, add the key for the test_dummy_encryption mount option to the
784 * filesystem. To prevent misuse of this mount option, a per-boot random key is
785 * used instead of a hardcoded one. This makes it so that any encrypted files
786 * created using this option won't be accessible after a reboot.
787 *
788 * Return: 0 on success, -errno on failure
789 */
790int fscrypt_add_test_dummy_key(struct super_block *sb,
791 const struct fscrypt_dummy_policy *dummy_policy)
792{
793 const union fscrypt_policy *policy = dummy_policy->policy;
794 struct fscrypt_key_specifier key_spec;
795 struct fscrypt_master_key_secret secret;
796 int err;
797
798 if (!policy)
799 return 0;
800 err = fscrypt_policy_to_key_spec(policy, &key_spec);
801 if (err)
802 return err;
803 fscrypt_get_test_dummy_secret(&secret);
804 err = add_master_key(sb, &secret, &key_spec);
805 wipe_master_key_secret(&secret);
806 return err;
807}
808EXPORT_SYMBOL_GPL(fscrypt_add_test_dummy_key);
809
810/*
811 * Verify that the current user has added a master key with the given identifier
812 * (returns -ENOKEY if not). This is needed to prevent a user from encrypting
813 * their files using some other user's key which they don't actually know.
814 * Cryptographically this isn't much of a problem, but the semantics of this
815 * would be a bit weird, so it's best to just forbid it.
816 *
817 * The system administrator (CAP_FOWNER) can override this, which should be
818 * enough for any use cases where encryption policies are being set using keys
819 * that were chosen ahead of time but aren't available at the moment.
820 *
821 * Note that the key may have already removed by the time this returns, but
822 * that's okay; we just care whether the key was there at some point.
823 *
824 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
825 */
826int fscrypt_verify_key_added(struct super_block *sb,
827 const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
828{
829 struct fscrypt_key_specifier mk_spec;
830 struct fscrypt_master_key *mk;
831 struct key *mk_user;
832 int err;
833
834 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
835 memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
836
837 mk = fscrypt_find_master_key(sb, &mk_spec);
838 if (!mk) {
839 err = -ENOKEY;
840 goto out;
841 }
842 down_read(&mk->mk_sem);
843 mk_user = find_master_key_user(mk);
844 if (IS_ERR(mk_user)) {
845 err = PTR_ERR(mk_user);
846 } else {
847 key_put(mk_user);
848 err = 0;
849 }
850 up_read(&mk->mk_sem);
851 fscrypt_put_master_key(mk);
852out:
853 if (err == -ENOKEY && capable(CAP_FOWNER))
854 err = 0;
855 return err;
856}
857
858/*
859 * Try to evict the inode's dentries from the dentry cache. If the inode is a
860 * directory, then it can have at most one dentry; however, that dentry may be
861 * pinned by child dentries, so first try to evict the children too.
862 */
863static void shrink_dcache_inode(struct inode *inode)
864{
865 struct dentry *dentry;
866
867 if (S_ISDIR(inode->i_mode)) {
868 dentry = d_find_any_alias(inode);
869 if (dentry) {
870 shrink_dcache_parent(dentry);
871 dput(dentry);
872 }
873 }
874 d_prune_aliases(inode);
875}
876
877static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
878{
879 struct fscrypt_info *ci;
880 struct inode *inode;
881 struct inode *toput_inode = NULL;
882
883 spin_lock(&mk->mk_decrypted_inodes_lock);
884
885 list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
886 inode = ci->ci_inode;
887 spin_lock(&inode->i_lock);
888 if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
889 spin_unlock(&inode->i_lock);
890 continue;
891 }
892 __iget(inode);
893 spin_unlock(&inode->i_lock);
894 spin_unlock(&mk->mk_decrypted_inodes_lock);
895
896 shrink_dcache_inode(inode);
897 iput(toput_inode);
898 toput_inode = inode;
899
900 spin_lock(&mk->mk_decrypted_inodes_lock);
901 }
902
903 spin_unlock(&mk->mk_decrypted_inodes_lock);
904 iput(toput_inode);
905}
906
907static int check_for_busy_inodes(struct super_block *sb,
908 struct fscrypt_master_key *mk)
909{
910 struct list_head *pos;
911 size_t busy_count = 0;
912 unsigned long ino;
913 char ino_str[50] = "";
914
915 spin_lock(&mk->mk_decrypted_inodes_lock);
916
917 list_for_each(pos, &mk->mk_decrypted_inodes)
918 busy_count++;
919
920 if (busy_count == 0) {
921 spin_unlock(&mk->mk_decrypted_inodes_lock);
922 return 0;
923 }
924
925 {
926 /* select an example file to show for debugging purposes */
927 struct inode *inode =
928 list_first_entry(&mk->mk_decrypted_inodes,
929 struct fscrypt_info,
930 ci_master_key_link)->ci_inode;
931 ino = inode->i_ino;
932 }
933 spin_unlock(&mk->mk_decrypted_inodes_lock);
934
935 /* If the inode is currently being created, ino may still be 0. */
936 if (ino)
937 snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino);
938
939 fscrypt_warn(NULL,
940 "%s: %zu inode(s) still busy after removing key with %s %*phN%s",
941 sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
942 master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
943 ino_str);
944 return -EBUSY;
945}
946
947static int try_to_lock_encrypted_files(struct super_block *sb,
948 struct fscrypt_master_key *mk)
949{
950 int err1;
951 int err2;
952
953 /*
954 * An inode can't be evicted while it is dirty or has dirty pages.
955 * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
956 *
957 * Just do it the easy way: call sync_filesystem(). It's overkill, but
958 * it works, and it's more important to minimize the amount of caches we
959 * drop than the amount of data we sync. Also, unprivileged users can
960 * already call sync_filesystem() via sys_syncfs() or sys_sync().
961 */
962 down_read(&sb->s_umount);
963 err1 = sync_filesystem(sb);
964 up_read(&sb->s_umount);
965 /* If a sync error occurs, still try to evict as much as possible. */
966
967 /*
968 * Inodes are pinned by their dentries, so we have to evict their
969 * dentries. shrink_dcache_sb() would suffice, but would be overkill
970 * and inappropriate for use by unprivileged users. So instead go
971 * through the inodes' alias lists and try to evict each dentry.
972 */
973 evict_dentries_for_decrypted_inodes(mk);
974
975 /*
976 * evict_dentries_for_decrypted_inodes() already iput() each inode in
977 * the list; any inodes for which that dropped the last reference will
978 * have been evicted due to fscrypt_drop_inode() detecting the key
979 * removal and telling the VFS to evict the inode. So to finish, we
980 * just need to check whether any inodes couldn't be evicted.
981 */
982 err2 = check_for_busy_inodes(sb, mk);
983
984 return err1 ?: err2;
985}
986
987/*
988 * Try to remove an fscrypt master encryption key.
989 *
990 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
991 * claim to the key, then removes the key itself if no other users have claims.
992 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
993 * key itself.
994 *
995 * To "remove the key itself", first we wipe the actual master key secret, so
996 * that no more inodes can be unlocked with it. Then we try to evict all cached
997 * inodes that had been unlocked with the key.
998 *
999 * If all inodes were evicted, then we unlink the fscrypt_master_key from the
1000 * keyring. Otherwise it remains in the keyring in the "incompletely removed"
1001 * state (without the actual secret key) where it tracks the list of remaining
1002 * inodes. Userspace can execute the ioctl again later to retry eviction, or
1003 * alternatively can re-add the secret key again.
1004 *
1005 * For more details, see the "Removing keys" section of
1006 * Documentation/filesystems/fscrypt.rst.
1007 */
1008static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
1009{
1010 struct super_block *sb = file_inode(filp)->i_sb;
1011 struct fscrypt_remove_key_arg __user *uarg = _uarg;
1012 struct fscrypt_remove_key_arg arg;
1013 struct fscrypt_master_key *mk;
1014 u32 status_flags = 0;
1015 int err;
1016 bool inodes_remain;
1017
1018 if (copy_from_user(&arg, uarg, sizeof(arg)))
1019 return -EFAULT;
1020
1021 if (!valid_key_spec(&arg.key_spec))
1022 return -EINVAL;
1023
1024 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1025 return -EINVAL;
1026
1027 /*
1028 * Only root can add and remove keys that are identified by an arbitrary
1029 * descriptor rather than by a cryptographic hash.
1030 */
1031 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
1032 !capable(CAP_SYS_ADMIN))
1033 return -EACCES;
1034
1035 /* Find the key being removed. */
1036 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1037 if (!mk)
1038 return -ENOKEY;
1039 down_write(&mk->mk_sem);
1040
1041 /* If relevant, remove current user's (or all users) claim to the key */
1042 if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
1043 if (all_users)
1044 err = keyring_clear(mk->mk_users);
1045 else
1046 err = remove_master_key_user(mk);
1047 if (err) {
1048 up_write(&mk->mk_sem);
1049 goto out_put_key;
1050 }
1051 if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
1052 /*
1053 * Other users have still added the key too. We removed
1054 * the current user's claim to the key, but we still
1055 * can't remove the key itself.
1056 */
1057 status_flags |=
1058 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
1059 err = 0;
1060 up_write(&mk->mk_sem);
1061 goto out_put_key;
1062 }
1063 }
1064
1065 /* No user claims remaining. Go ahead and wipe the secret. */
1066 err = -ENOKEY;
1067 if (is_master_key_secret_present(&mk->mk_secret)) {
1068 wipe_master_key_secret(&mk->mk_secret);
1069 fscrypt_put_master_key_activeref(sb, mk);
1070 err = 0;
1071 }
1072 inodes_remain = refcount_read(&mk->mk_active_refs) > 0;
1073 up_write(&mk->mk_sem);
1074
1075 if (inodes_remain) {
1076 /* Some inodes still reference this key; try to evict them. */
1077 err = try_to_lock_encrypted_files(sb, mk);
1078 if (err == -EBUSY) {
1079 status_flags |=
1080 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
1081 err = 0;
1082 }
1083 }
1084 /*
1085 * We return 0 if we successfully did something: removed a claim to the
1086 * key, wiped the secret, or tried locking the files again. Users need
1087 * to check the informational status flags if they care whether the key
1088 * has been fully removed including all files locked.
1089 */
1090out_put_key:
1091 fscrypt_put_master_key(mk);
1092 if (err == 0)
1093 err = put_user(status_flags, &uarg->removal_status_flags);
1094 return err;
1095}
1096
1097int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
1098{
1099 return do_remove_key(filp, uarg, false);
1100}
1101EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
1102
1103int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
1104{
1105 if (!capable(CAP_SYS_ADMIN))
1106 return -EACCES;
1107 return do_remove_key(filp, uarg, true);
1108}
1109EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);
1110
1111/*
1112 * Retrieve the status of an fscrypt master encryption key.
1113 *
1114 * We set ->status to indicate whether the key is absent, present, or
1115 * incompletely removed. "Incompletely removed" means that the master key
1116 * secret has been removed, but some files which had been unlocked with it are
1117 * still in use. This field allows applications to easily determine the state
1118 * of an encrypted directory without using a hack such as trying to open a
1119 * regular file in it (which can confuse the "incompletely removed" state with
1120 * absent or present).
1121 *
1122 * In addition, for v2 policy keys we allow applications to determine, via
1123 * ->status_flags and ->user_count, whether the key has been added by the
1124 * current user, by other users, or by both. Most applications should not need
1125 * this, since ordinarily only one user should know a given key. However, if a
1126 * secret key is shared by multiple users, applications may wish to add an
1127 * already-present key to prevent other users from removing it. This ioctl can
1128 * be used to check whether that really is the case before the work is done to
1129 * add the key --- which might e.g. require prompting the user for a passphrase.
1130 *
1131 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
1132 * Documentation/filesystems/fscrypt.rst.
1133 */
1134int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
1135{
1136 struct super_block *sb = file_inode(filp)->i_sb;
1137 struct fscrypt_get_key_status_arg arg;
1138 struct fscrypt_master_key *mk;
1139 int err;
1140
1141 if (copy_from_user(&arg, uarg, sizeof(arg)))
1142 return -EFAULT;
1143
1144 if (!valid_key_spec(&arg.key_spec))
1145 return -EINVAL;
1146
1147 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1148 return -EINVAL;
1149
1150 arg.status_flags = 0;
1151 arg.user_count = 0;
1152 memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
1153
1154 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1155 if (!mk) {
1156 arg.status = FSCRYPT_KEY_STATUS_ABSENT;
1157 err = 0;
1158 goto out;
1159 }
1160 down_read(&mk->mk_sem);
1161
1162 if (!is_master_key_secret_present(&mk->mk_secret)) {
1163 arg.status = refcount_read(&mk->mk_active_refs) > 0 ?
1164 FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED :
1165 FSCRYPT_KEY_STATUS_ABSENT /* raced with full removal */;
1166 err = 0;
1167 goto out_release_key;
1168 }
1169
1170 arg.status = FSCRYPT_KEY_STATUS_PRESENT;
1171 if (mk->mk_users) {
1172 struct key *mk_user;
1173
1174 arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
1175 mk_user = find_master_key_user(mk);
1176 if (!IS_ERR(mk_user)) {
1177 arg.status_flags |=
1178 FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
1179 key_put(mk_user);
1180 } else if (mk_user != ERR_PTR(-ENOKEY)) {
1181 err = PTR_ERR(mk_user);
1182 goto out_release_key;
1183 }
1184 }
1185 err = 0;
1186out_release_key:
1187 up_read(&mk->mk_sem);
1188 fscrypt_put_master_key(mk);
1189out:
1190 if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
1191 err = -EFAULT;
1192 return err;
1193}
1194EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
1195
1196int __init fscrypt_init_keyring(void)
1197{
1198 int err;
1199
1200 err = register_key_type(&key_type_fscrypt_user);
1201 if (err)
1202 return err;
1203
1204 err = register_key_type(&key_type_fscrypt_provisioning);
1205 if (err)
1206 goto err_unregister_fscrypt_user;
1207
1208 return 0;
1209
1210err_unregister_fscrypt_user:
1211 unregister_key_type(&key_type_fscrypt_user);
1212 return err;
1213}