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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_ONCE(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 if (WARN_ON_ONCE(!sb->s_master_keys))
96 return;
97 spin_lock(&sb->s_master_keys->lock);
98 hlist_del_rcu(&mk->mk_node);
99 spin_unlock(&sb->s_master_keys->lock);
100
101 /*
102 * ->mk_active_refs == 0 implies that ->mk_present is false and
103 * ->mk_decrypted_inodes is empty.
104 */
105 WARN_ON_ONCE(mk->mk_present);
106 WARN_ON_ONCE(!list_empty(&mk->mk_decrypted_inodes));
107
108 for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {
109 fscrypt_destroy_prepared_key(
110 sb, &mk->mk_direct_keys[i]);
111 fscrypt_destroy_prepared_key(
112 sb, &mk->mk_iv_ino_lblk_64_keys[i]);
113 fscrypt_destroy_prepared_key(
114 sb, &mk->mk_iv_ino_lblk_32_keys[i]);
115 }
116 memzero_explicit(&mk->mk_ino_hash_key,
117 sizeof(mk->mk_ino_hash_key));
118 mk->mk_ino_hash_key_initialized = false;
119
120 /* Drop the structural ref associated with the active refs. */
121 fscrypt_put_master_key(mk);
122}
123
124/*
125 * This transitions the key state from present to incompletely removed, and then
126 * potentially to absent (depending on whether inodes remain).
127 */
128static void fscrypt_initiate_key_removal(struct super_block *sb,
129 struct fscrypt_master_key *mk)
130{
131 WRITE_ONCE(mk->mk_present, false);
132 wipe_master_key_secret(&mk->mk_secret);
133 fscrypt_put_master_key_activeref(sb, mk);
134}
135
136static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
137{
138 if (spec->__reserved)
139 return false;
140 return master_key_spec_len(spec) != 0;
141}
142
143static int fscrypt_user_key_instantiate(struct key *key,
144 struct key_preparsed_payload *prep)
145{
146 /*
147 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
148 * each key, regardless of the exact key size. The amount of memory
149 * actually used is greater than the size of the raw key anyway.
150 */
151 return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
152}
153
154static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
155{
156 seq_puts(m, key->description);
157}
158
159/*
160 * Type of key in ->mk_users. Each key of this type represents a particular
161 * user who has added a particular master key.
162 *
163 * Note that the name of this key type really should be something like
164 * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen
165 * mainly for simplicity of presentation in /proc/keys when read by a non-root
166 * user. And it is expected to be rare that a key is actually added by multiple
167 * users, since users should keep their encryption keys confidential.
168 */
169static struct key_type key_type_fscrypt_user = {
170 .name = ".fscrypt",
171 .instantiate = fscrypt_user_key_instantiate,
172 .describe = fscrypt_user_key_describe,
173};
174
175#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \
176 (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
177 CONST_STRLEN("-users") + 1)
178
179#define FSCRYPT_MK_USER_DESCRIPTION_SIZE \
180 (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
181
182static void format_mk_users_keyring_description(
183 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
184 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
185{
186 sprintf(description, "fscrypt-%*phN-users",
187 FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
188}
189
190static void format_mk_user_description(
191 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
192 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
193{
194
195 sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
196 mk_identifier, __kuid_val(current_fsuid()));
197}
198
199/* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */
200static int allocate_filesystem_keyring(struct super_block *sb)
201{
202 struct fscrypt_keyring *keyring;
203
204 if (sb->s_master_keys)
205 return 0;
206
207 keyring = kzalloc(sizeof(*keyring), GFP_KERNEL);
208 if (!keyring)
209 return -ENOMEM;
210 spin_lock_init(&keyring->lock);
211 /*
212 * Pairs with the smp_load_acquire() in fscrypt_find_master_key().
213 * I.e., here we publish ->s_master_keys with a RELEASE barrier so that
214 * concurrent tasks can ACQUIRE it.
215 */
216 smp_store_release(&sb->s_master_keys, keyring);
217 return 0;
218}
219
220/*
221 * Release all encryption keys that have been added to the filesystem, along
222 * with the keyring that contains them.
223 *
224 * This is called at unmount time, after all potentially-encrypted inodes have
225 * been evicted. The filesystem's underlying block device(s) are still
226 * available at this time; this is important because after user file accesses
227 * have been allowed, this function may need to evict keys from the keyslots of
228 * an inline crypto engine, which requires the block device(s).
229 */
230void fscrypt_destroy_keyring(struct super_block *sb)
231{
232 struct fscrypt_keyring *keyring = sb->s_master_keys;
233 size_t i;
234
235 if (!keyring)
236 return;
237
238 for (i = 0; i < ARRAY_SIZE(keyring->key_hashtable); i++) {
239 struct hlist_head *bucket = &keyring->key_hashtable[i];
240 struct fscrypt_master_key *mk;
241 struct hlist_node *tmp;
242
243 hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) {
244 /*
245 * Since all potentially-encrypted inodes were already
246 * evicted, every key remaining in the keyring should
247 * have an empty inode list, and should only still be in
248 * the keyring due to the single active ref associated
249 * with ->mk_present. There should be no structural
250 * refs beyond the one associated with the active ref.
251 */
252 WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 1);
253 WARN_ON_ONCE(refcount_read(&mk->mk_struct_refs) != 1);
254 WARN_ON_ONCE(!mk->mk_present);
255 fscrypt_initiate_key_removal(sb, mk);
256 }
257 }
258 kfree_sensitive(keyring);
259 sb->s_master_keys = NULL;
260}
261
262static struct hlist_head *
263fscrypt_mk_hash_bucket(struct fscrypt_keyring *keyring,
264 const struct fscrypt_key_specifier *mk_spec)
265{
266 /*
267 * Since key specifiers should be "random" values, it is sufficient to
268 * use a trivial hash function that just takes the first several bits of
269 * the key specifier.
270 */
271 unsigned long i = get_unaligned((unsigned long *)&mk_spec->u);
272
273 return &keyring->key_hashtable[i % ARRAY_SIZE(keyring->key_hashtable)];
274}
275
276/*
277 * Find the specified master key struct in ->s_master_keys and take a structural
278 * ref to it. The structural ref guarantees that the key struct continues to
279 * exist, but it does *not* guarantee that ->s_master_keys continues to contain
280 * the key struct. The structural ref needs to be dropped by
281 * fscrypt_put_master_key(). Returns NULL if the key struct is not found.
282 */
283struct fscrypt_master_key *
284fscrypt_find_master_key(struct super_block *sb,
285 const struct fscrypt_key_specifier *mk_spec)
286{
287 struct fscrypt_keyring *keyring;
288 struct hlist_head *bucket;
289 struct fscrypt_master_key *mk;
290
291 /*
292 * Pairs with the smp_store_release() in allocate_filesystem_keyring().
293 * I.e., another task can publish ->s_master_keys concurrently,
294 * executing a RELEASE barrier. We need to use smp_load_acquire() here
295 * to safely ACQUIRE the memory the other task published.
296 */
297 keyring = smp_load_acquire(&sb->s_master_keys);
298 if (keyring == NULL)
299 return NULL; /* No keyring yet, so no keys yet. */
300
301 bucket = fscrypt_mk_hash_bucket(keyring, mk_spec);
302 rcu_read_lock();
303 switch (mk_spec->type) {
304 case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
305 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
306 if (mk->mk_spec.type ==
307 FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
308 memcmp(mk->mk_spec.u.descriptor,
309 mk_spec->u.descriptor,
310 FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
311 refcount_inc_not_zero(&mk->mk_struct_refs))
312 goto out;
313 }
314 break;
315 case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
316 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
317 if (mk->mk_spec.type ==
318 FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
319 memcmp(mk->mk_spec.u.identifier,
320 mk_spec->u.identifier,
321 FSCRYPT_KEY_IDENTIFIER_SIZE) == 0 &&
322 refcount_inc_not_zero(&mk->mk_struct_refs))
323 goto out;
324 }
325 break;
326 }
327 mk = NULL;
328out:
329 rcu_read_unlock();
330 return mk;
331}
332
333static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
334{
335 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
336 struct key *keyring;
337
338 format_mk_users_keyring_description(description,
339 mk->mk_spec.u.identifier);
340 keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
341 current_cred(), KEY_POS_SEARCH |
342 KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
343 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
344 if (IS_ERR(keyring))
345 return PTR_ERR(keyring);
346
347 mk->mk_users = keyring;
348 return 0;
349}
350
351/*
352 * Find the current user's "key" in the master key's ->mk_users.
353 * Returns ERR_PTR(-ENOKEY) if not found.
354 */
355static struct key *find_master_key_user(struct fscrypt_master_key *mk)
356{
357 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
358 key_ref_t keyref;
359
360 format_mk_user_description(description, mk->mk_spec.u.identifier);
361
362 /*
363 * We need to mark the keyring reference as "possessed" so that we
364 * acquire permission to search it, via the KEY_POS_SEARCH permission.
365 */
366 keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/),
367 &key_type_fscrypt_user, description, false);
368 if (IS_ERR(keyref)) {
369 if (PTR_ERR(keyref) == -EAGAIN || /* not found */
370 PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
371 keyref = ERR_PTR(-ENOKEY);
372 return ERR_CAST(keyref);
373 }
374 return key_ref_to_ptr(keyref);
375}
376
377/*
378 * Give the current user a "key" in ->mk_users. This charges the user's quota
379 * and marks the master key as added by the current user, so that it cannot be
380 * removed by another user with the key. Either ->mk_sem must be held for
381 * write, or the master key must be still undergoing initialization.
382 */
383static int add_master_key_user(struct fscrypt_master_key *mk)
384{
385 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
386 struct key *mk_user;
387 int err;
388
389 format_mk_user_description(description, mk->mk_spec.u.identifier);
390 mk_user = key_alloc(&key_type_fscrypt_user, description,
391 current_fsuid(), current_gid(), current_cred(),
392 KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
393 if (IS_ERR(mk_user))
394 return PTR_ERR(mk_user);
395
396 err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
397 key_put(mk_user);
398 return err;
399}
400
401/*
402 * Remove the current user's "key" from ->mk_users.
403 * ->mk_sem must be held for write.
404 *
405 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
406 */
407static int remove_master_key_user(struct fscrypt_master_key *mk)
408{
409 struct key *mk_user;
410 int err;
411
412 mk_user = find_master_key_user(mk);
413 if (IS_ERR(mk_user))
414 return PTR_ERR(mk_user);
415 err = key_unlink(mk->mk_users, mk_user);
416 key_put(mk_user);
417 return err;
418}
419
420/*
421 * Allocate a new fscrypt_master_key, transfer the given secret over to it, and
422 * insert it into sb->s_master_keys.
423 */
424static int add_new_master_key(struct super_block *sb,
425 struct fscrypt_master_key_secret *secret,
426 const struct fscrypt_key_specifier *mk_spec)
427{
428 struct fscrypt_keyring *keyring = sb->s_master_keys;
429 struct fscrypt_master_key *mk;
430 int err;
431
432 mk = kzalloc(sizeof(*mk), GFP_KERNEL);
433 if (!mk)
434 return -ENOMEM;
435
436 init_rwsem(&mk->mk_sem);
437 refcount_set(&mk->mk_struct_refs, 1);
438 mk->mk_spec = *mk_spec;
439
440 INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
441 spin_lock_init(&mk->mk_decrypted_inodes_lock);
442
443 if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
444 err = allocate_master_key_users_keyring(mk);
445 if (err)
446 goto out_put;
447 err = add_master_key_user(mk);
448 if (err)
449 goto out_put;
450 }
451
452 move_master_key_secret(&mk->mk_secret, secret);
453 mk->mk_present = true;
454 refcount_set(&mk->mk_active_refs, 1); /* ->mk_present is true */
455
456 spin_lock(&keyring->lock);
457 hlist_add_head_rcu(&mk->mk_node,
458 fscrypt_mk_hash_bucket(keyring, mk_spec));
459 spin_unlock(&keyring->lock);
460 return 0;
461
462out_put:
463 fscrypt_put_master_key(mk);
464 return err;
465}
466
467#define KEY_DEAD 1
468
469static int add_existing_master_key(struct fscrypt_master_key *mk,
470 struct fscrypt_master_key_secret *secret)
471{
472 int err;
473
474 /*
475 * If the current user is already in ->mk_users, then there's nothing to
476 * do. Otherwise, we need to add the user to ->mk_users. (Neither is
477 * applicable for v1 policy keys, which have NULL ->mk_users.)
478 */
479 if (mk->mk_users) {
480 struct key *mk_user = find_master_key_user(mk);
481
482 if (mk_user != ERR_PTR(-ENOKEY)) {
483 if (IS_ERR(mk_user))
484 return PTR_ERR(mk_user);
485 key_put(mk_user);
486 return 0;
487 }
488 err = add_master_key_user(mk);
489 if (err)
490 return err;
491 }
492
493 /* If the key is incompletely removed, make it present again. */
494 if (!mk->mk_present) {
495 if (!refcount_inc_not_zero(&mk->mk_active_refs)) {
496 /*
497 * Raced with the last active ref being dropped, so the
498 * key has become, or is about to become, "absent".
499 * Therefore, we need to allocate a new key struct.
500 */
501 return KEY_DEAD;
502 }
503 move_master_key_secret(&mk->mk_secret, secret);
504 WRITE_ONCE(mk->mk_present, true);
505 }
506
507 return 0;
508}
509
510static int do_add_master_key(struct super_block *sb,
511 struct fscrypt_master_key_secret *secret,
512 const struct fscrypt_key_specifier *mk_spec)
513{
514 static DEFINE_MUTEX(fscrypt_add_key_mutex);
515 struct fscrypt_master_key *mk;
516 int err;
517
518 mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
519
520 mk = fscrypt_find_master_key(sb, mk_spec);
521 if (!mk) {
522 /* Didn't find the key in ->s_master_keys. Add it. */
523 err = allocate_filesystem_keyring(sb);
524 if (!err)
525 err = add_new_master_key(sb, secret, mk_spec);
526 } else {
527 /*
528 * Found the key in ->s_master_keys. Add the user to ->mk_users
529 * if needed, and make the key "present" again if possible.
530 */
531 down_write(&mk->mk_sem);
532 err = add_existing_master_key(mk, secret);
533 up_write(&mk->mk_sem);
534 if (err == KEY_DEAD) {
535 /*
536 * We found a key struct, but it's already been fully
537 * removed. Ignore the old struct and add a new one.
538 * fscrypt_add_key_mutex means we don't need to worry
539 * about concurrent adds.
540 */
541 err = add_new_master_key(sb, secret, mk_spec);
542 }
543 fscrypt_put_master_key(mk);
544 }
545 mutex_unlock(&fscrypt_add_key_mutex);
546 return err;
547}
548
549static int add_master_key(struct super_block *sb,
550 struct fscrypt_master_key_secret *secret,
551 struct fscrypt_key_specifier *key_spec)
552{
553 int err;
554
555 if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
556 err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,
557 secret->size);
558 if (err)
559 return err;
560
561 /*
562 * Now that the HKDF context is initialized, the raw key is no
563 * longer needed.
564 */
565 memzero_explicit(secret->raw, secret->size);
566
567 /* Calculate the key identifier */
568 err = fscrypt_hkdf_expand(&secret->hkdf,
569 HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,
570 key_spec->u.identifier,
571 FSCRYPT_KEY_IDENTIFIER_SIZE);
572 if (err)
573 return err;
574 }
575 return do_add_master_key(sb, secret, key_spec);
576}
577
578static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
579{
580 const struct fscrypt_provisioning_key_payload *payload = prep->data;
581
582 if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
583 prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
584 return -EINVAL;
585
586 if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
587 payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
588 return -EINVAL;
589
590 if (payload->__reserved)
591 return -EINVAL;
592
593 prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
594 if (!prep->payload.data[0])
595 return -ENOMEM;
596
597 prep->quotalen = prep->datalen;
598 return 0;
599}
600
601static void fscrypt_provisioning_key_free_preparse(
602 struct key_preparsed_payload *prep)
603{
604 kfree_sensitive(prep->payload.data[0]);
605}
606
607static void fscrypt_provisioning_key_describe(const struct key *key,
608 struct seq_file *m)
609{
610 seq_puts(m, key->description);
611 if (key_is_positive(key)) {
612 const struct fscrypt_provisioning_key_payload *payload =
613 key->payload.data[0];
614
615 seq_printf(m, ": %u [%u]", key->datalen, payload->type);
616 }
617}
618
619static void fscrypt_provisioning_key_destroy(struct key *key)
620{
621 kfree_sensitive(key->payload.data[0]);
622}
623
624static struct key_type key_type_fscrypt_provisioning = {
625 .name = "fscrypt-provisioning",
626 .preparse = fscrypt_provisioning_key_preparse,
627 .free_preparse = fscrypt_provisioning_key_free_preparse,
628 .instantiate = generic_key_instantiate,
629 .describe = fscrypt_provisioning_key_describe,
630 .destroy = fscrypt_provisioning_key_destroy,
631};
632
633/*
634 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
635 * store it into 'secret'.
636 *
637 * The key must be of type "fscrypt-provisioning" and must have the field
638 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
639 * only usable with fscrypt with the particular KDF version identified by
640 * 'type'. We don't use the "logon" key type because there's no way to
641 * completely restrict the use of such keys; they can be used by any kernel API
642 * that accepts "logon" keys and doesn't require a specific service prefix.
643 *
644 * The ability to specify the key via Linux keyring key is intended for cases
645 * where userspace needs to re-add keys after the filesystem is unmounted and
646 * re-mounted. Most users should just provide the raw key directly instead.
647 */
648static int get_keyring_key(u32 key_id, u32 type,
649 struct fscrypt_master_key_secret *secret)
650{
651 key_ref_t ref;
652 struct key *key;
653 const struct fscrypt_provisioning_key_payload *payload;
654 int err;
655
656 ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
657 if (IS_ERR(ref))
658 return PTR_ERR(ref);
659 key = key_ref_to_ptr(ref);
660
661 if (key->type != &key_type_fscrypt_provisioning)
662 goto bad_key;
663 payload = key->payload.data[0];
664
665 /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
666 if (payload->type != type)
667 goto bad_key;
668
669 secret->size = key->datalen - sizeof(*payload);
670 memcpy(secret->raw, payload->raw, secret->size);
671 err = 0;
672 goto out_put;
673
674bad_key:
675 err = -EKEYREJECTED;
676out_put:
677 key_ref_put(ref);
678 return err;
679}
680
681/*
682 * Add a master encryption key to the filesystem, causing all files which were
683 * encrypted with it to appear "unlocked" (decrypted) when accessed.
684 *
685 * When adding a key for use by v1 encryption policies, this ioctl is
686 * privileged, and userspace must provide the 'key_descriptor'.
687 *
688 * When adding a key for use by v2+ encryption policies, this ioctl is
689 * unprivileged. This is needed, in general, to allow non-root users to use
690 * encryption without encountering the visibility problems of process-subscribed
691 * keyrings and the inability to properly remove keys. This works by having
692 * each key identified by its cryptographically secure hash --- the
693 * 'key_identifier'. The cryptographic hash ensures that a malicious user
694 * cannot add the wrong key for a given identifier. Furthermore, each added key
695 * is charged to the appropriate user's quota for the keyrings service, which
696 * prevents a malicious user from adding too many keys. Finally, we forbid a
697 * user from removing a key while other users have added it too, which prevents
698 * a user who knows another user's key from causing a denial-of-service by
699 * removing it at an inopportune time. (We tolerate that a user who knows a key
700 * can prevent other users from removing it.)
701 *
702 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
703 * Documentation/filesystems/fscrypt.rst.
704 */
705int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
706{
707 struct super_block *sb = file_inode(filp)->i_sb;
708 struct fscrypt_add_key_arg __user *uarg = _uarg;
709 struct fscrypt_add_key_arg arg;
710 struct fscrypt_master_key_secret secret;
711 int err;
712
713 if (copy_from_user(&arg, uarg, sizeof(arg)))
714 return -EFAULT;
715
716 if (!valid_key_spec(&arg.key_spec))
717 return -EINVAL;
718
719 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
720 return -EINVAL;
721
722 /*
723 * Only root can add keys that are identified by an arbitrary descriptor
724 * rather than by a cryptographic hash --- since otherwise a malicious
725 * user could add the wrong key.
726 */
727 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
728 !capable(CAP_SYS_ADMIN))
729 return -EACCES;
730
731 memset(&secret, 0, sizeof(secret));
732 if (arg.key_id) {
733 if (arg.raw_size != 0)
734 return -EINVAL;
735 err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
736 if (err)
737 goto out_wipe_secret;
738 } else {
739 if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
740 arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
741 return -EINVAL;
742 secret.size = arg.raw_size;
743 err = -EFAULT;
744 if (copy_from_user(secret.raw, uarg->raw, secret.size))
745 goto out_wipe_secret;
746 }
747
748 err = add_master_key(sb, &secret, &arg.key_spec);
749 if (err)
750 goto out_wipe_secret;
751
752 /* Return the key identifier to userspace, if applicable */
753 err = -EFAULT;
754 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
755 copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,
756 FSCRYPT_KEY_IDENTIFIER_SIZE))
757 goto out_wipe_secret;
758 err = 0;
759out_wipe_secret:
760 wipe_master_key_secret(&secret);
761 return err;
762}
763EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
764
765static void
766fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret)
767{
768 static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
769
770 get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
771
772 memset(secret, 0, sizeof(*secret));
773 secret->size = FSCRYPT_MAX_KEY_SIZE;
774 memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE);
775}
776
777int fscrypt_get_test_dummy_key_identifier(
778 u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
779{
780 struct fscrypt_master_key_secret secret;
781 int err;
782
783 fscrypt_get_test_dummy_secret(&secret);
784
785 err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
786 if (err)
787 goto out;
788 err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER,
789 NULL, 0, key_identifier,
790 FSCRYPT_KEY_IDENTIFIER_SIZE);
791out:
792 wipe_master_key_secret(&secret);
793 return err;
794}
795
796/**
797 * fscrypt_add_test_dummy_key() - add the test dummy encryption key
798 * @sb: the filesystem instance to add the key to
799 * @key_spec: the key specifier of the test dummy encryption key
800 *
801 * Add the key for the test_dummy_encryption mount option to the filesystem. To
802 * prevent misuse of this mount option, a per-boot random key is used instead of
803 * a hardcoded one. This makes it so that any encrypted files created using
804 * this option won't be accessible after a reboot.
805 *
806 * Return: 0 on success, -errno on failure
807 */
808int fscrypt_add_test_dummy_key(struct super_block *sb,
809 struct fscrypt_key_specifier *key_spec)
810{
811 struct fscrypt_master_key_secret secret;
812 int err;
813
814 fscrypt_get_test_dummy_secret(&secret);
815 err = add_master_key(sb, &secret, key_spec);
816 wipe_master_key_secret(&secret);
817 return err;
818}
819
820/*
821 * Verify that the current user has added a master key with the given identifier
822 * (returns -ENOKEY if not). This is needed to prevent a user from encrypting
823 * their files using some other user's key which they don't actually know.
824 * Cryptographically this isn't much of a problem, but the semantics of this
825 * would be a bit weird, so it's best to just forbid it.
826 *
827 * The system administrator (CAP_FOWNER) can override this, which should be
828 * enough for any use cases where encryption policies are being set using keys
829 * that were chosen ahead of time but aren't available at the moment.
830 *
831 * Note that the key may have already removed by the time this returns, but
832 * that's okay; we just care whether the key was there at some point.
833 *
834 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
835 */
836int fscrypt_verify_key_added(struct super_block *sb,
837 const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
838{
839 struct fscrypt_key_specifier mk_spec;
840 struct fscrypt_master_key *mk;
841 struct key *mk_user;
842 int err;
843
844 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
845 memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
846
847 mk = fscrypt_find_master_key(sb, &mk_spec);
848 if (!mk) {
849 err = -ENOKEY;
850 goto out;
851 }
852 down_read(&mk->mk_sem);
853 mk_user = find_master_key_user(mk);
854 if (IS_ERR(mk_user)) {
855 err = PTR_ERR(mk_user);
856 } else {
857 key_put(mk_user);
858 err = 0;
859 }
860 up_read(&mk->mk_sem);
861 fscrypt_put_master_key(mk);
862out:
863 if (err == -ENOKEY && capable(CAP_FOWNER))
864 err = 0;
865 return err;
866}
867
868/*
869 * Try to evict the inode's dentries from the dentry cache. If the inode is a
870 * directory, then it can have at most one dentry; however, that dentry may be
871 * pinned by child dentries, so first try to evict the children too.
872 */
873static void shrink_dcache_inode(struct inode *inode)
874{
875 struct dentry *dentry;
876
877 if (S_ISDIR(inode->i_mode)) {
878 dentry = d_find_any_alias(inode);
879 if (dentry) {
880 shrink_dcache_parent(dentry);
881 dput(dentry);
882 }
883 }
884 d_prune_aliases(inode);
885}
886
887static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
888{
889 struct fscrypt_inode_info *ci;
890 struct inode *inode;
891 struct inode *toput_inode = NULL;
892
893 spin_lock(&mk->mk_decrypted_inodes_lock);
894
895 list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
896 inode = ci->ci_inode;
897 spin_lock(&inode->i_lock);
898 if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
899 spin_unlock(&inode->i_lock);
900 continue;
901 }
902 __iget(inode);
903 spin_unlock(&inode->i_lock);
904 spin_unlock(&mk->mk_decrypted_inodes_lock);
905
906 shrink_dcache_inode(inode);
907 iput(toput_inode);
908 toput_inode = inode;
909
910 spin_lock(&mk->mk_decrypted_inodes_lock);
911 }
912
913 spin_unlock(&mk->mk_decrypted_inodes_lock);
914 iput(toput_inode);
915}
916
917static int check_for_busy_inodes(struct super_block *sb,
918 struct fscrypt_master_key *mk)
919{
920 struct list_head *pos;
921 size_t busy_count = 0;
922 unsigned long ino;
923 char ino_str[50] = "";
924
925 spin_lock(&mk->mk_decrypted_inodes_lock);
926
927 list_for_each(pos, &mk->mk_decrypted_inodes)
928 busy_count++;
929
930 if (busy_count == 0) {
931 spin_unlock(&mk->mk_decrypted_inodes_lock);
932 return 0;
933 }
934
935 {
936 /* select an example file to show for debugging purposes */
937 struct inode *inode =
938 list_first_entry(&mk->mk_decrypted_inodes,
939 struct fscrypt_inode_info,
940 ci_master_key_link)->ci_inode;
941 ino = inode->i_ino;
942 }
943 spin_unlock(&mk->mk_decrypted_inodes_lock);
944
945 /* If the inode is currently being created, ino may still be 0. */
946 if (ino)
947 snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino);
948
949 fscrypt_warn(NULL,
950 "%s: %zu inode(s) still busy after removing key with %s %*phN%s",
951 sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
952 master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
953 ino_str);
954 return -EBUSY;
955}
956
957static int try_to_lock_encrypted_files(struct super_block *sb,
958 struct fscrypt_master_key *mk)
959{
960 int err1;
961 int err2;
962
963 /*
964 * An inode can't be evicted while it is dirty or has dirty pages.
965 * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
966 *
967 * Just do it the easy way: call sync_filesystem(). It's overkill, but
968 * it works, and it's more important to minimize the amount of caches we
969 * drop than the amount of data we sync. Also, unprivileged users can
970 * already call sync_filesystem() via sys_syncfs() or sys_sync().
971 */
972 down_read(&sb->s_umount);
973 err1 = sync_filesystem(sb);
974 up_read(&sb->s_umount);
975 /* If a sync error occurs, still try to evict as much as possible. */
976
977 /*
978 * Inodes are pinned by their dentries, so we have to evict their
979 * dentries. shrink_dcache_sb() would suffice, but would be overkill
980 * and inappropriate for use by unprivileged users. So instead go
981 * through the inodes' alias lists and try to evict each dentry.
982 */
983 evict_dentries_for_decrypted_inodes(mk);
984
985 /*
986 * evict_dentries_for_decrypted_inodes() already iput() each inode in
987 * the list; any inodes for which that dropped the last reference will
988 * have been evicted due to fscrypt_drop_inode() detecting the key
989 * removal and telling the VFS to evict the inode. So to finish, we
990 * just need to check whether any inodes couldn't be evicted.
991 */
992 err2 = check_for_busy_inodes(sb, mk);
993
994 return err1 ?: err2;
995}
996
997/*
998 * Try to remove an fscrypt master encryption key.
999 *
1000 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
1001 * claim to the key, then removes the key itself if no other users have claims.
1002 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
1003 * key itself.
1004 *
1005 * To "remove the key itself", first we transition the key to the "incompletely
1006 * removed" state, so that no more inodes can be unlocked with it. Then we try
1007 * to evict all cached inodes that had been unlocked with the key.
1008 *
1009 * If all inodes were evicted, then we unlink the fscrypt_master_key from the
1010 * keyring. Otherwise it remains in the keyring in the "incompletely removed"
1011 * state where it tracks the list of remaining inodes. Userspace can execute
1012 * the ioctl again later to retry eviction, or alternatively can re-add the key.
1013 *
1014 * For more details, see the "Removing keys" section of
1015 * Documentation/filesystems/fscrypt.rst.
1016 */
1017static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
1018{
1019 struct super_block *sb = file_inode(filp)->i_sb;
1020 struct fscrypt_remove_key_arg __user *uarg = _uarg;
1021 struct fscrypt_remove_key_arg arg;
1022 struct fscrypt_master_key *mk;
1023 u32 status_flags = 0;
1024 int err;
1025 bool inodes_remain;
1026
1027 if (copy_from_user(&arg, uarg, sizeof(arg)))
1028 return -EFAULT;
1029
1030 if (!valid_key_spec(&arg.key_spec))
1031 return -EINVAL;
1032
1033 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1034 return -EINVAL;
1035
1036 /*
1037 * Only root can add and remove keys that are identified by an arbitrary
1038 * descriptor rather than by a cryptographic hash.
1039 */
1040 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
1041 !capable(CAP_SYS_ADMIN))
1042 return -EACCES;
1043
1044 /* Find the key being removed. */
1045 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1046 if (!mk)
1047 return -ENOKEY;
1048 down_write(&mk->mk_sem);
1049
1050 /* If relevant, remove current user's (or all users) claim to the key */
1051 if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
1052 if (all_users)
1053 err = keyring_clear(mk->mk_users);
1054 else
1055 err = remove_master_key_user(mk);
1056 if (err) {
1057 up_write(&mk->mk_sem);
1058 goto out_put_key;
1059 }
1060 if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
1061 /*
1062 * Other users have still added the key too. We removed
1063 * the current user's claim to the key, but we still
1064 * can't remove the key itself.
1065 */
1066 status_flags |=
1067 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
1068 err = 0;
1069 up_write(&mk->mk_sem);
1070 goto out_put_key;
1071 }
1072 }
1073
1074 /* No user claims remaining. Initiate removal of the key. */
1075 err = -ENOKEY;
1076 if (mk->mk_present) {
1077 fscrypt_initiate_key_removal(sb, mk);
1078 err = 0;
1079 }
1080 inodes_remain = refcount_read(&mk->mk_active_refs) > 0;
1081 up_write(&mk->mk_sem);
1082
1083 if (inodes_remain) {
1084 /* Some inodes still reference this key; try to evict them. */
1085 err = try_to_lock_encrypted_files(sb, mk);
1086 if (err == -EBUSY) {
1087 status_flags |=
1088 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
1089 err = 0;
1090 }
1091 }
1092 /*
1093 * We return 0 if we successfully did something: removed a claim to the
1094 * key, initiated removal of the key, or tried locking the files again.
1095 * Users need to check the informational status flags if they care
1096 * whether the key has been fully removed including all files locked.
1097 */
1098out_put_key:
1099 fscrypt_put_master_key(mk);
1100 if (err == 0)
1101 err = put_user(status_flags, &uarg->removal_status_flags);
1102 return err;
1103}
1104
1105int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
1106{
1107 return do_remove_key(filp, uarg, false);
1108}
1109EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
1110
1111int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
1112{
1113 if (!capable(CAP_SYS_ADMIN))
1114 return -EACCES;
1115 return do_remove_key(filp, uarg, true);
1116}
1117EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);
1118
1119/*
1120 * Retrieve the status of an fscrypt master encryption key.
1121 *
1122 * We set ->status to indicate whether the key is absent, present, or
1123 * incompletely removed. (For an explanation of what these statuses mean and
1124 * how they are represented internally, see struct fscrypt_master_key.) This
1125 * field allows applications to easily determine the status of an encrypted
1126 * directory without using a hack such as trying to open a regular file in it
1127 * (which can confuse the "incompletely removed" status with absent or present).
1128 *
1129 * In addition, for v2 policy keys we allow applications to determine, via
1130 * ->status_flags and ->user_count, whether the key has been added by the
1131 * current user, by other users, or by both. Most applications should not need
1132 * this, since ordinarily only one user should know a given key. However, if a
1133 * secret key is shared by multiple users, applications may wish to add an
1134 * already-present key to prevent other users from removing it. This ioctl can
1135 * be used to check whether that really is the case before the work is done to
1136 * add the key --- which might e.g. require prompting the user for a passphrase.
1137 *
1138 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
1139 * Documentation/filesystems/fscrypt.rst.
1140 */
1141int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
1142{
1143 struct super_block *sb = file_inode(filp)->i_sb;
1144 struct fscrypt_get_key_status_arg arg;
1145 struct fscrypt_master_key *mk;
1146 int err;
1147
1148 if (copy_from_user(&arg, uarg, sizeof(arg)))
1149 return -EFAULT;
1150
1151 if (!valid_key_spec(&arg.key_spec))
1152 return -EINVAL;
1153
1154 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1155 return -EINVAL;
1156
1157 arg.status_flags = 0;
1158 arg.user_count = 0;
1159 memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
1160
1161 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1162 if (!mk) {
1163 arg.status = FSCRYPT_KEY_STATUS_ABSENT;
1164 err = 0;
1165 goto out;
1166 }
1167 down_read(&mk->mk_sem);
1168
1169 if (!mk->mk_present) {
1170 arg.status = refcount_read(&mk->mk_active_refs) > 0 ?
1171 FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED :
1172 FSCRYPT_KEY_STATUS_ABSENT /* raced with full removal */;
1173 err = 0;
1174 goto out_release_key;
1175 }
1176
1177 arg.status = FSCRYPT_KEY_STATUS_PRESENT;
1178 if (mk->mk_users) {
1179 struct key *mk_user;
1180
1181 arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
1182 mk_user = find_master_key_user(mk);
1183 if (!IS_ERR(mk_user)) {
1184 arg.status_flags |=
1185 FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
1186 key_put(mk_user);
1187 } else if (mk_user != ERR_PTR(-ENOKEY)) {
1188 err = PTR_ERR(mk_user);
1189 goto out_release_key;
1190 }
1191 }
1192 err = 0;
1193out_release_key:
1194 up_read(&mk->mk_sem);
1195 fscrypt_put_master_key(mk);
1196out:
1197 if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
1198 err = -EFAULT;
1199 return err;
1200}
1201EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
1202
1203int __init fscrypt_init_keyring(void)
1204{
1205 int err;
1206
1207 err = register_key_type(&key_type_fscrypt_user);
1208 if (err)
1209 return err;
1210
1211 err = register_key_type(&key_type_fscrypt_provisioning);
1212 if (err)
1213 goto err_unregister_fscrypt_user;
1214
1215 return 0;
1216
1217err_unregister_fscrypt_user:
1218 unregister_key_type(&key_type_fscrypt_user);
1219 return err;
1220}