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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 if (mk->mk_users) {
78 /* Clear the keyring so the quota gets released right away. */
79 keyring_clear(mk->mk_users);
80 key_put(mk->mk_users);
81 mk->mk_users = NULL;
82 }
83 call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key);
84}
85
86void fscrypt_put_master_key_activeref(struct super_block *sb,
87 struct fscrypt_master_key *mk)
88{
89 size_t i;
90
91 if (!refcount_dec_and_test(&mk->mk_active_refs))
92 return;
93 /*
94 * No active references left, so complete the full removal of this
95 * fscrypt_master_key struct by removing it from the keyring and
96 * destroying any subkeys embedded in it.
97 */
98
99 if (WARN_ON_ONCE(!sb->s_master_keys))
100 return;
101 spin_lock(&sb->s_master_keys->lock);
102 hlist_del_rcu(&mk->mk_node);
103 spin_unlock(&sb->s_master_keys->lock);
104
105 /*
106 * ->mk_active_refs == 0 implies that ->mk_present is false and
107 * ->mk_decrypted_inodes is empty.
108 */
109 WARN_ON_ONCE(mk->mk_present);
110 WARN_ON_ONCE(!list_empty(&mk->mk_decrypted_inodes));
111
112 for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {
113 fscrypt_destroy_prepared_key(
114 sb, &mk->mk_direct_keys[i]);
115 fscrypt_destroy_prepared_key(
116 sb, &mk->mk_iv_ino_lblk_64_keys[i]);
117 fscrypt_destroy_prepared_key(
118 sb, &mk->mk_iv_ino_lblk_32_keys[i]);
119 }
120 memzero_explicit(&mk->mk_ino_hash_key,
121 sizeof(mk->mk_ino_hash_key));
122 mk->mk_ino_hash_key_initialized = false;
123
124 /* Drop the structural ref associated with the active refs. */
125 fscrypt_put_master_key(mk);
126}
127
128/*
129 * This transitions the key state from present to incompletely removed, and then
130 * potentially to absent (depending on whether inodes remain).
131 */
132static void fscrypt_initiate_key_removal(struct super_block *sb,
133 struct fscrypt_master_key *mk)
134{
135 WRITE_ONCE(mk->mk_present, false);
136 wipe_master_key_secret(&mk->mk_secret);
137 fscrypt_put_master_key_activeref(sb, mk);
138}
139
140static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
141{
142 if (spec->__reserved)
143 return false;
144 return master_key_spec_len(spec) != 0;
145}
146
147static int fscrypt_user_key_instantiate(struct key *key,
148 struct key_preparsed_payload *prep)
149{
150 /*
151 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
152 * each key, regardless of the exact key size. The amount of memory
153 * actually used is greater than the size of the raw key anyway.
154 */
155 return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
156}
157
158static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
159{
160 seq_puts(m, key->description);
161}
162
163/*
164 * Type of key in ->mk_users. Each key of this type represents a particular
165 * user who has added a particular master key.
166 *
167 * Note that the name of this key type really should be something like
168 * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen
169 * mainly for simplicity of presentation in /proc/keys when read by a non-root
170 * user. And it is expected to be rare that a key is actually added by multiple
171 * users, since users should keep their encryption keys confidential.
172 */
173static struct key_type key_type_fscrypt_user = {
174 .name = ".fscrypt",
175 .instantiate = fscrypt_user_key_instantiate,
176 .describe = fscrypt_user_key_describe,
177};
178
179#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \
180 (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
181 CONST_STRLEN("-users") + 1)
182
183#define FSCRYPT_MK_USER_DESCRIPTION_SIZE \
184 (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
185
186static void format_mk_users_keyring_description(
187 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
188 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
189{
190 sprintf(description, "fscrypt-%*phN-users",
191 FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
192}
193
194static void format_mk_user_description(
195 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
196 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
197{
198
199 sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
200 mk_identifier, __kuid_val(current_fsuid()));
201}
202
203/* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */
204static int allocate_filesystem_keyring(struct super_block *sb)
205{
206 struct fscrypt_keyring *keyring;
207
208 if (sb->s_master_keys)
209 return 0;
210
211 keyring = kzalloc(sizeof(*keyring), GFP_KERNEL);
212 if (!keyring)
213 return -ENOMEM;
214 spin_lock_init(&keyring->lock);
215 /*
216 * Pairs with the smp_load_acquire() in fscrypt_find_master_key().
217 * I.e., here we publish ->s_master_keys with a RELEASE barrier so that
218 * concurrent tasks can ACQUIRE it.
219 */
220 smp_store_release(&sb->s_master_keys, keyring);
221 return 0;
222}
223
224/*
225 * Release all encryption keys that have been added to the filesystem, along
226 * with the keyring that contains them.
227 *
228 * This is called at unmount time, after all potentially-encrypted inodes have
229 * been evicted. The filesystem's underlying block device(s) are still
230 * available at this time; this is important because after user file accesses
231 * have been allowed, this function may need to evict keys from the keyslots of
232 * an inline crypto engine, which requires the block device(s).
233 */
234void fscrypt_destroy_keyring(struct super_block *sb)
235{
236 struct fscrypt_keyring *keyring = sb->s_master_keys;
237 size_t i;
238
239 if (!keyring)
240 return;
241
242 for (i = 0; i < ARRAY_SIZE(keyring->key_hashtable); i++) {
243 struct hlist_head *bucket = &keyring->key_hashtable[i];
244 struct fscrypt_master_key *mk;
245 struct hlist_node *tmp;
246
247 hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) {
248 /*
249 * Since all potentially-encrypted inodes were already
250 * evicted, every key remaining in the keyring should
251 * have an empty inode list, and should only still be in
252 * the keyring due to the single active ref associated
253 * with ->mk_present. There should be no structural
254 * refs beyond the one associated with the active ref.
255 */
256 WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 1);
257 WARN_ON_ONCE(refcount_read(&mk->mk_struct_refs) != 1);
258 WARN_ON_ONCE(!mk->mk_present);
259 fscrypt_initiate_key_removal(sb, mk);
260 }
261 }
262 kfree_sensitive(keyring);
263 sb->s_master_keys = NULL;
264}
265
266static struct hlist_head *
267fscrypt_mk_hash_bucket(struct fscrypt_keyring *keyring,
268 const struct fscrypt_key_specifier *mk_spec)
269{
270 /*
271 * Since key specifiers should be "random" values, it is sufficient to
272 * use a trivial hash function that just takes the first several bits of
273 * the key specifier.
274 */
275 unsigned long i = get_unaligned((unsigned long *)&mk_spec->u);
276
277 return &keyring->key_hashtable[i % ARRAY_SIZE(keyring->key_hashtable)];
278}
279
280/*
281 * Find the specified master key struct in ->s_master_keys and take a structural
282 * ref to it. The structural ref guarantees that the key struct continues to
283 * exist, but it does *not* guarantee that ->s_master_keys continues to contain
284 * the key struct. The structural ref needs to be dropped by
285 * fscrypt_put_master_key(). Returns NULL if the key struct is not found.
286 */
287struct fscrypt_master_key *
288fscrypt_find_master_key(struct super_block *sb,
289 const struct fscrypt_key_specifier *mk_spec)
290{
291 struct fscrypt_keyring *keyring;
292 struct hlist_head *bucket;
293 struct fscrypt_master_key *mk;
294
295 /*
296 * Pairs with the smp_store_release() in allocate_filesystem_keyring().
297 * I.e., another task can publish ->s_master_keys concurrently,
298 * executing a RELEASE barrier. We need to use smp_load_acquire() here
299 * to safely ACQUIRE the memory the other task published.
300 */
301 keyring = smp_load_acquire(&sb->s_master_keys);
302 if (keyring == NULL)
303 return NULL; /* No keyring yet, so no keys yet. */
304
305 bucket = fscrypt_mk_hash_bucket(keyring, mk_spec);
306 rcu_read_lock();
307 switch (mk_spec->type) {
308 case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
309 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
310 if (mk->mk_spec.type ==
311 FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
312 memcmp(mk->mk_spec.u.descriptor,
313 mk_spec->u.descriptor,
314 FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
315 refcount_inc_not_zero(&mk->mk_struct_refs))
316 goto out;
317 }
318 break;
319 case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
320 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
321 if (mk->mk_spec.type ==
322 FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
323 memcmp(mk->mk_spec.u.identifier,
324 mk_spec->u.identifier,
325 FSCRYPT_KEY_IDENTIFIER_SIZE) == 0 &&
326 refcount_inc_not_zero(&mk->mk_struct_refs))
327 goto out;
328 }
329 break;
330 }
331 mk = NULL;
332out:
333 rcu_read_unlock();
334 return mk;
335}
336
337static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
338{
339 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
340 struct key *keyring;
341
342 format_mk_users_keyring_description(description,
343 mk->mk_spec.u.identifier);
344 keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
345 current_cred(), KEY_POS_SEARCH |
346 KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
347 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
348 if (IS_ERR(keyring))
349 return PTR_ERR(keyring);
350
351 mk->mk_users = keyring;
352 return 0;
353}
354
355/*
356 * Find the current user's "key" in the master key's ->mk_users.
357 * Returns ERR_PTR(-ENOKEY) if not found.
358 */
359static struct key *find_master_key_user(struct fscrypt_master_key *mk)
360{
361 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
362 key_ref_t keyref;
363
364 format_mk_user_description(description, mk->mk_spec.u.identifier);
365
366 /*
367 * We need to mark the keyring reference as "possessed" so that we
368 * acquire permission to search it, via the KEY_POS_SEARCH permission.
369 */
370 keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/),
371 &key_type_fscrypt_user, description, false);
372 if (IS_ERR(keyref)) {
373 if (PTR_ERR(keyref) == -EAGAIN || /* not found */
374 PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
375 keyref = ERR_PTR(-ENOKEY);
376 return ERR_CAST(keyref);
377 }
378 return key_ref_to_ptr(keyref);
379}
380
381/*
382 * Give the current user a "key" in ->mk_users. This charges the user's quota
383 * and marks the master key as added by the current user, so that it cannot be
384 * removed by another user with the key. Either ->mk_sem must be held for
385 * write, or the master key must be still undergoing initialization.
386 */
387static int add_master_key_user(struct fscrypt_master_key *mk)
388{
389 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
390 struct key *mk_user;
391 int err;
392
393 format_mk_user_description(description, mk->mk_spec.u.identifier);
394 mk_user = key_alloc(&key_type_fscrypt_user, description,
395 current_fsuid(), current_gid(), current_cred(),
396 KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
397 if (IS_ERR(mk_user))
398 return PTR_ERR(mk_user);
399
400 err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
401 key_put(mk_user);
402 return err;
403}
404
405/*
406 * Remove the current user's "key" from ->mk_users.
407 * ->mk_sem must be held for write.
408 *
409 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
410 */
411static int remove_master_key_user(struct fscrypt_master_key *mk)
412{
413 struct key *mk_user;
414 int err;
415
416 mk_user = find_master_key_user(mk);
417 if (IS_ERR(mk_user))
418 return PTR_ERR(mk_user);
419 err = key_unlink(mk->mk_users, mk_user);
420 key_put(mk_user);
421 return err;
422}
423
424/*
425 * Allocate a new fscrypt_master_key, transfer the given secret over to it, and
426 * insert it into sb->s_master_keys.
427 */
428static int add_new_master_key(struct super_block *sb,
429 struct fscrypt_master_key_secret *secret,
430 const struct fscrypt_key_specifier *mk_spec)
431{
432 struct fscrypt_keyring *keyring = sb->s_master_keys;
433 struct fscrypt_master_key *mk;
434 int err;
435
436 mk = kzalloc(sizeof(*mk), GFP_KERNEL);
437 if (!mk)
438 return -ENOMEM;
439
440 init_rwsem(&mk->mk_sem);
441 refcount_set(&mk->mk_struct_refs, 1);
442 mk->mk_spec = *mk_spec;
443
444 INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
445 spin_lock_init(&mk->mk_decrypted_inodes_lock);
446
447 if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
448 err = allocate_master_key_users_keyring(mk);
449 if (err)
450 goto out_put;
451 err = add_master_key_user(mk);
452 if (err)
453 goto out_put;
454 }
455
456 move_master_key_secret(&mk->mk_secret, secret);
457 mk->mk_present = true;
458 refcount_set(&mk->mk_active_refs, 1); /* ->mk_present is true */
459
460 spin_lock(&keyring->lock);
461 hlist_add_head_rcu(&mk->mk_node,
462 fscrypt_mk_hash_bucket(keyring, mk_spec));
463 spin_unlock(&keyring->lock);
464 return 0;
465
466out_put:
467 fscrypt_put_master_key(mk);
468 return err;
469}
470
471#define KEY_DEAD 1
472
473static int add_existing_master_key(struct fscrypt_master_key *mk,
474 struct fscrypt_master_key_secret *secret)
475{
476 int err;
477
478 /*
479 * If the current user is already in ->mk_users, then there's nothing to
480 * do. Otherwise, we need to add the user to ->mk_users. (Neither is
481 * applicable for v1 policy keys, which have NULL ->mk_users.)
482 */
483 if (mk->mk_users) {
484 struct key *mk_user = find_master_key_user(mk);
485
486 if (mk_user != ERR_PTR(-ENOKEY)) {
487 if (IS_ERR(mk_user))
488 return PTR_ERR(mk_user);
489 key_put(mk_user);
490 return 0;
491 }
492 err = add_master_key_user(mk);
493 if (err)
494 return err;
495 }
496
497 /* If the key is incompletely removed, make it present again. */
498 if (!mk->mk_present) {
499 if (!refcount_inc_not_zero(&mk->mk_active_refs)) {
500 /*
501 * Raced with the last active ref being dropped, so the
502 * key has become, or is about to become, "absent".
503 * Therefore, we need to allocate a new key struct.
504 */
505 return KEY_DEAD;
506 }
507 move_master_key_secret(&mk->mk_secret, secret);
508 WRITE_ONCE(mk->mk_present, true);
509 }
510
511 return 0;
512}
513
514static int do_add_master_key(struct super_block *sb,
515 struct fscrypt_master_key_secret *secret,
516 const struct fscrypt_key_specifier *mk_spec)
517{
518 static DEFINE_MUTEX(fscrypt_add_key_mutex);
519 struct fscrypt_master_key *mk;
520 int err;
521
522 mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
523
524 mk = fscrypt_find_master_key(sb, mk_spec);
525 if (!mk) {
526 /* Didn't find the key in ->s_master_keys. Add it. */
527 err = allocate_filesystem_keyring(sb);
528 if (!err)
529 err = add_new_master_key(sb, secret, mk_spec);
530 } else {
531 /*
532 * Found the key in ->s_master_keys. Add the user to ->mk_users
533 * if needed, and make the key "present" again if possible.
534 */
535 down_write(&mk->mk_sem);
536 err = add_existing_master_key(mk, secret);
537 up_write(&mk->mk_sem);
538 if (err == KEY_DEAD) {
539 /*
540 * We found a key struct, but it's already been fully
541 * removed. Ignore the old struct and add a new one.
542 * fscrypt_add_key_mutex means we don't need to worry
543 * about concurrent adds.
544 */
545 err = add_new_master_key(sb, secret, mk_spec);
546 }
547 fscrypt_put_master_key(mk);
548 }
549 mutex_unlock(&fscrypt_add_key_mutex);
550 return err;
551}
552
553static int add_master_key(struct super_block *sb,
554 struct fscrypt_master_key_secret *secret,
555 struct fscrypt_key_specifier *key_spec)
556{
557 int err;
558
559 if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
560 err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,
561 secret->size);
562 if (err)
563 return err;
564
565 /*
566 * Now that the HKDF context is initialized, the raw key is no
567 * longer needed.
568 */
569 memzero_explicit(secret->raw, secret->size);
570
571 /* Calculate the key identifier */
572 err = fscrypt_hkdf_expand(&secret->hkdf,
573 HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,
574 key_spec->u.identifier,
575 FSCRYPT_KEY_IDENTIFIER_SIZE);
576 if (err)
577 return err;
578 }
579 return do_add_master_key(sb, secret, key_spec);
580}
581
582static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
583{
584 const struct fscrypt_provisioning_key_payload *payload = prep->data;
585
586 if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
587 prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
588 return -EINVAL;
589
590 if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
591 payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
592 return -EINVAL;
593
594 if (payload->__reserved)
595 return -EINVAL;
596
597 prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
598 if (!prep->payload.data[0])
599 return -ENOMEM;
600
601 prep->quotalen = prep->datalen;
602 return 0;
603}
604
605static void fscrypt_provisioning_key_free_preparse(
606 struct key_preparsed_payload *prep)
607{
608 kfree_sensitive(prep->payload.data[0]);
609}
610
611static void fscrypt_provisioning_key_describe(const struct key *key,
612 struct seq_file *m)
613{
614 seq_puts(m, key->description);
615 if (key_is_positive(key)) {
616 const struct fscrypt_provisioning_key_payload *payload =
617 key->payload.data[0];
618
619 seq_printf(m, ": %u [%u]", key->datalen, payload->type);
620 }
621}
622
623static void fscrypt_provisioning_key_destroy(struct key *key)
624{
625 kfree_sensitive(key->payload.data[0]);
626}
627
628static struct key_type key_type_fscrypt_provisioning = {
629 .name = "fscrypt-provisioning",
630 .preparse = fscrypt_provisioning_key_preparse,
631 .free_preparse = fscrypt_provisioning_key_free_preparse,
632 .instantiate = generic_key_instantiate,
633 .describe = fscrypt_provisioning_key_describe,
634 .destroy = fscrypt_provisioning_key_destroy,
635};
636
637/*
638 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
639 * store it into 'secret'.
640 *
641 * The key must be of type "fscrypt-provisioning" and must have the field
642 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
643 * only usable with fscrypt with the particular KDF version identified by
644 * 'type'. We don't use the "logon" key type because there's no way to
645 * completely restrict the use of such keys; they can be used by any kernel API
646 * that accepts "logon" keys and doesn't require a specific service prefix.
647 *
648 * The ability to specify the key via Linux keyring key is intended for cases
649 * where userspace needs to re-add keys after the filesystem is unmounted and
650 * re-mounted. Most users should just provide the raw key directly instead.
651 */
652static int get_keyring_key(u32 key_id, u32 type,
653 struct fscrypt_master_key_secret *secret)
654{
655 key_ref_t ref;
656 struct key *key;
657 const struct fscrypt_provisioning_key_payload *payload;
658 int err;
659
660 ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
661 if (IS_ERR(ref))
662 return PTR_ERR(ref);
663 key = key_ref_to_ptr(ref);
664
665 if (key->type != &key_type_fscrypt_provisioning)
666 goto bad_key;
667 payload = key->payload.data[0];
668
669 /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
670 if (payload->type != type)
671 goto bad_key;
672
673 secret->size = key->datalen - sizeof(*payload);
674 memcpy(secret->raw, payload->raw, secret->size);
675 err = 0;
676 goto out_put;
677
678bad_key:
679 err = -EKEYREJECTED;
680out_put:
681 key_ref_put(ref);
682 return err;
683}
684
685/*
686 * Add a master encryption key to the filesystem, causing all files which were
687 * encrypted with it to appear "unlocked" (decrypted) when accessed.
688 *
689 * When adding a key for use by v1 encryption policies, this ioctl is
690 * privileged, and userspace must provide the 'key_descriptor'.
691 *
692 * When adding a key for use by v2+ encryption policies, this ioctl is
693 * unprivileged. This is needed, in general, to allow non-root users to use
694 * encryption without encountering the visibility problems of process-subscribed
695 * keyrings and the inability to properly remove keys. This works by having
696 * each key identified by its cryptographically secure hash --- the
697 * 'key_identifier'. The cryptographic hash ensures that a malicious user
698 * cannot add the wrong key for a given identifier. Furthermore, each added key
699 * is charged to the appropriate user's quota for the keyrings service, which
700 * prevents a malicious user from adding too many keys. Finally, we forbid a
701 * user from removing a key while other users have added it too, which prevents
702 * a user who knows another user's key from causing a denial-of-service by
703 * removing it at an inopportune time. (We tolerate that a user who knows a key
704 * can prevent other users from removing it.)
705 *
706 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
707 * Documentation/filesystems/fscrypt.rst.
708 */
709int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
710{
711 struct super_block *sb = file_inode(filp)->i_sb;
712 struct fscrypt_add_key_arg __user *uarg = _uarg;
713 struct fscrypt_add_key_arg arg;
714 struct fscrypt_master_key_secret secret;
715 int err;
716
717 if (copy_from_user(&arg, uarg, sizeof(arg)))
718 return -EFAULT;
719
720 if (!valid_key_spec(&arg.key_spec))
721 return -EINVAL;
722
723 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
724 return -EINVAL;
725
726 /*
727 * Only root can add keys that are identified by an arbitrary descriptor
728 * rather than by a cryptographic hash --- since otherwise a malicious
729 * user could add the wrong key.
730 */
731 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
732 !capable(CAP_SYS_ADMIN))
733 return -EACCES;
734
735 memset(&secret, 0, sizeof(secret));
736 if (arg.key_id) {
737 if (arg.raw_size != 0)
738 return -EINVAL;
739 err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
740 if (err)
741 goto out_wipe_secret;
742 } else {
743 if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
744 arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
745 return -EINVAL;
746 secret.size = arg.raw_size;
747 err = -EFAULT;
748 if (copy_from_user(secret.raw, uarg->raw, secret.size))
749 goto out_wipe_secret;
750 }
751
752 err = add_master_key(sb, &secret, &arg.key_spec);
753 if (err)
754 goto out_wipe_secret;
755
756 /* Return the key identifier to userspace, if applicable */
757 err = -EFAULT;
758 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
759 copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,
760 FSCRYPT_KEY_IDENTIFIER_SIZE))
761 goto out_wipe_secret;
762 err = 0;
763out_wipe_secret:
764 wipe_master_key_secret(&secret);
765 return err;
766}
767EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
768
769static void
770fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret)
771{
772 static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
773
774 get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
775
776 memset(secret, 0, sizeof(*secret));
777 secret->size = FSCRYPT_MAX_KEY_SIZE;
778 memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE);
779}
780
781int fscrypt_get_test_dummy_key_identifier(
782 u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
783{
784 struct fscrypt_master_key_secret secret;
785 int err;
786
787 fscrypt_get_test_dummy_secret(&secret);
788
789 err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
790 if (err)
791 goto out;
792 err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER,
793 NULL, 0, key_identifier,
794 FSCRYPT_KEY_IDENTIFIER_SIZE);
795out:
796 wipe_master_key_secret(&secret);
797 return err;
798}
799
800/**
801 * fscrypt_add_test_dummy_key() - add the test dummy encryption key
802 * @sb: the filesystem instance to add the key to
803 * @key_spec: the key specifier of the test dummy encryption key
804 *
805 * Add the key for the test_dummy_encryption mount option to the filesystem. To
806 * prevent misuse of this mount option, a per-boot random key is used instead of
807 * a hardcoded one. This makes it so that any encrypted files created using
808 * this option won't be accessible after a reboot.
809 *
810 * Return: 0 on success, -errno on failure
811 */
812int fscrypt_add_test_dummy_key(struct super_block *sb,
813 struct fscrypt_key_specifier *key_spec)
814{
815 struct fscrypt_master_key_secret secret;
816 int err;
817
818 fscrypt_get_test_dummy_secret(&secret);
819 err = add_master_key(sb, &secret, key_spec);
820 wipe_master_key_secret(&secret);
821 return err;
822}
823
824/*
825 * Verify that the current user has added a master key with the given identifier
826 * (returns -ENOKEY if not). This is needed to prevent a user from encrypting
827 * their files using some other user's key which they don't actually know.
828 * Cryptographically this isn't much of a problem, but the semantics of this
829 * would be a bit weird, so it's best to just forbid it.
830 *
831 * The system administrator (CAP_FOWNER) can override this, which should be
832 * enough for any use cases where encryption policies are being set using keys
833 * that were chosen ahead of time but aren't available at the moment.
834 *
835 * Note that the key may have already removed by the time this returns, but
836 * that's okay; we just care whether the key was there at some point.
837 *
838 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
839 */
840int fscrypt_verify_key_added(struct super_block *sb,
841 const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
842{
843 struct fscrypt_key_specifier mk_spec;
844 struct fscrypt_master_key *mk;
845 struct key *mk_user;
846 int err;
847
848 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
849 memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
850
851 mk = fscrypt_find_master_key(sb, &mk_spec);
852 if (!mk) {
853 err = -ENOKEY;
854 goto out;
855 }
856 down_read(&mk->mk_sem);
857 mk_user = find_master_key_user(mk);
858 if (IS_ERR(mk_user)) {
859 err = PTR_ERR(mk_user);
860 } else {
861 key_put(mk_user);
862 err = 0;
863 }
864 up_read(&mk->mk_sem);
865 fscrypt_put_master_key(mk);
866out:
867 if (err == -ENOKEY && capable(CAP_FOWNER))
868 err = 0;
869 return err;
870}
871
872/*
873 * Try to evict the inode's dentries from the dentry cache. If the inode is a
874 * directory, then it can have at most one dentry; however, that dentry may be
875 * pinned by child dentries, so first try to evict the children too.
876 */
877static void shrink_dcache_inode(struct inode *inode)
878{
879 struct dentry *dentry;
880
881 if (S_ISDIR(inode->i_mode)) {
882 dentry = d_find_any_alias(inode);
883 if (dentry) {
884 shrink_dcache_parent(dentry);
885 dput(dentry);
886 }
887 }
888 d_prune_aliases(inode);
889}
890
891static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
892{
893 struct fscrypt_inode_info *ci;
894 struct inode *inode;
895 struct inode *toput_inode = NULL;
896
897 spin_lock(&mk->mk_decrypted_inodes_lock);
898
899 list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
900 inode = ci->ci_inode;
901 spin_lock(&inode->i_lock);
902 if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
903 spin_unlock(&inode->i_lock);
904 continue;
905 }
906 __iget(inode);
907 spin_unlock(&inode->i_lock);
908 spin_unlock(&mk->mk_decrypted_inodes_lock);
909
910 shrink_dcache_inode(inode);
911 iput(toput_inode);
912 toput_inode = inode;
913
914 spin_lock(&mk->mk_decrypted_inodes_lock);
915 }
916
917 spin_unlock(&mk->mk_decrypted_inodes_lock);
918 iput(toput_inode);
919}
920
921static int check_for_busy_inodes(struct super_block *sb,
922 struct fscrypt_master_key *mk)
923{
924 struct list_head *pos;
925 size_t busy_count = 0;
926 unsigned long ino;
927 char ino_str[50] = "";
928
929 spin_lock(&mk->mk_decrypted_inodes_lock);
930
931 list_for_each(pos, &mk->mk_decrypted_inodes)
932 busy_count++;
933
934 if (busy_count == 0) {
935 spin_unlock(&mk->mk_decrypted_inodes_lock);
936 return 0;
937 }
938
939 {
940 /* select an example file to show for debugging purposes */
941 struct inode *inode =
942 list_first_entry(&mk->mk_decrypted_inodes,
943 struct fscrypt_inode_info,
944 ci_master_key_link)->ci_inode;
945 ino = inode->i_ino;
946 }
947 spin_unlock(&mk->mk_decrypted_inodes_lock);
948
949 /* If the inode is currently being created, ino may still be 0. */
950 if (ino)
951 snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino);
952
953 fscrypt_warn(NULL,
954 "%s: %zu inode(s) still busy after removing key with %s %*phN%s",
955 sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
956 master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
957 ino_str);
958 return -EBUSY;
959}
960
961static int try_to_lock_encrypted_files(struct super_block *sb,
962 struct fscrypt_master_key *mk)
963{
964 int err1;
965 int err2;
966
967 /*
968 * An inode can't be evicted while it is dirty or has dirty pages.
969 * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
970 *
971 * Just do it the easy way: call sync_filesystem(). It's overkill, but
972 * it works, and it's more important to minimize the amount of caches we
973 * drop than the amount of data we sync. Also, unprivileged users can
974 * already call sync_filesystem() via sys_syncfs() or sys_sync().
975 */
976 down_read(&sb->s_umount);
977 err1 = sync_filesystem(sb);
978 up_read(&sb->s_umount);
979 /* If a sync error occurs, still try to evict as much as possible. */
980
981 /*
982 * Inodes are pinned by their dentries, so we have to evict their
983 * dentries. shrink_dcache_sb() would suffice, but would be overkill
984 * and inappropriate for use by unprivileged users. So instead go
985 * through the inodes' alias lists and try to evict each dentry.
986 */
987 evict_dentries_for_decrypted_inodes(mk);
988
989 /*
990 * evict_dentries_for_decrypted_inodes() already iput() each inode in
991 * the list; any inodes for which that dropped the last reference will
992 * have been evicted due to fscrypt_drop_inode() detecting the key
993 * removal and telling the VFS to evict the inode. So to finish, we
994 * just need to check whether any inodes couldn't be evicted.
995 */
996 err2 = check_for_busy_inodes(sb, mk);
997
998 return err1 ?: err2;
999}
1000
1001/*
1002 * Try to remove an fscrypt master encryption key.
1003 *
1004 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
1005 * claim to the key, then removes the key itself if no other users have claims.
1006 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
1007 * key itself.
1008 *
1009 * To "remove the key itself", first we transition the key to the "incompletely
1010 * removed" state, so that no more inodes can be unlocked with it. Then we try
1011 * to evict all cached inodes that had been unlocked with the key.
1012 *
1013 * If all inodes were evicted, then we unlink the fscrypt_master_key from the
1014 * keyring. Otherwise it remains in the keyring in the "incompletely removed"
1015 * state where it tracks the list of remaining inodes. Userspace can execute
1016 * the ioctl again later to retry eviction, or alternatively can re-add the key.
1017 *
1018 * For more details, see the "Removing keys" section of
1019 * Documentation/filesystems/fscrypt.rst.
1020 */
1021static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
1022{
1023 struct super_block *sb = file_inode(filp)->i_sb;
1024 struct fscrypt_remove_key_arg __user *uarg = _uarg;
1025 struct fscrypt_remove_key_arg arg;
1026 struct fscrypt_master_key *mk;
1027 u32 status_flags = 0;
1028 int err;
1029 bool inodes_remain;
1030
1031 if (copy_from_user(&arg, uarg, sizeof(arg)))
1032 return -EFAULT;
1033
1034 if (!valid_key_spec(&arg.key_spec))
1035 return -EINVAL;
1036
1037 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1038 return -EINVAL;
1039
1040 /*
1041 * Only root can add and remove keys that are identified by an arbitrary
1042 * descriptor rather than by a cryptographic hash.
1043 */
1044 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
1045 !capable(CAP_SYS_ADMIN))
1046 return -EACCES;
1047
1048 /* Find the key being removed. */
1049 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1050 if (!mk)
1051 return -ENOKEY;
1052 down_write(&mk->mk_sem);
1053
1054 /* If relevant, remove current user's (or all users) claim to the key */
1055 if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
1056 if (all_users)
1057 err = keyring_clear(mk->mk_users);
1058 else
1059 err = remove_master_key_user(mk);
1060 if (err) {
1061 up_write(&mk->mk_sem);
1062 goto out_put_key;
1063 }
1064 if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
1065 /*
1066 * Other users have still added the key too. We removed
1067 * the current user's claim to the key, but we still
1068 * can't remove the key itself.
1069 */
1070 status_flags |=
1071 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
1072 err = 0;
1073 up_write(&mk->mk_sem);
1074 goto out_put_key;
1075 }
1076 }
1077
1078 /* No user claims remaining. Initiate removal of the key. */
1079 err = -ENOKEY;
1080 if (mk->mk_present) {
1081 fscrypt_initiate_key_removal(sb, mk);
1082 err = 0;
1083 }
1084 inodes_remain = refcount_read(&mk->mk_active_refs) > 0;
1085 up_write(&mk->mk_sem);
1086
1087 if (inodes_remain) {
1088 /* Some inodes still reference this key; try to evict them. */
1089 err = try_to_lock_encrypted_files(sb, mk);
1090 if (err == -EBUSY) {
1091 status_flags |=
1092 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
1093 err = 0;
1094 }
1095 }
1096 /*
1097 * We return 0 if we successfully did something: removed a claim to the
1098 * key, initiated removal of the key, or tried locking the files again.
1099 * Users need to check the informational status flags if they care
1100 * whether the key has been fully removed including all files locked.
1101 */
1102out_put_key:
1103 fscrypt_put_master_key(mk);
1104 if (err == 0)
1105 err = put_user(status_flags, &uarg->removal_status_flags);
1106 return err;
1107}
1108
1109int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
1110{
1111 return do_remove_key(filp, uarg, false);
1112}
1113EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
1114
1115int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
1116{
1117 if (!capable(CAP_SYS_ADMIN))
1118 return -EACCES;
1119 return do_remove_key(filp, uarg, true);
1120}
1121EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);
1122
1123/*
1124 * Retrieve the status of an fscrypt master encryption key.
1125 *
1126 * We set ->status to indicate whether the key is absent, present, or
1127 * incompletely removed. (For an explanation of what these statuses mean and
1128 * how they are represented internally, see struct fscrypt_master_key.) This
1129 * field allows applications to easily determine the status of an encrypted
1130 * directory without using a hack such as trying to open a regular file in it
1131 * (which can confuse the "incompletely removed" status with absent or present).
1132 *
1133 * In addition, for v2 policy keys we allow applications to determine, via
1134 * ->status_flags and ->user_count, whether the key has been added by the
1135 * current user, by other users, or by both. Most applications should not need
1136 * this, since ordinarily only one user should know a given key. However, if a
1137 * secret key is shared by multiple users, applications may wish to add an
1138 * already-present key to prevent other users from removing it. This ioctl can
1139 * be used to check whether that really is the case before the work is done to
1140 * add the key --- which might e.g. require prompting the user for a passphrase.
1141 *
1142 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
1143 * Documentation/filesystems/fscrypt.rst.
1144 */
1145int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
1146{
1147 struct super_block *sb = file_inode(filp)->i_sb;
1148 struct fscrypt_get_key_status_arg arg;
1149 struct fscrypt_master_key *mk;
1150 int err;
1151
1152 if (copy_from_user(&arg, uarg, sizeof(arg)))
1153 return -EFAULT;
1154
1155 if (!valid_key_spec(&arg.key_spec))
1156 return -EINVAL;
1157
1158 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1159 return -EINVAL;
1160
1161 arg.status_flags = 0;
1162 arg.user_count = 0;
1163 memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
1164
1165 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1166 if (!mk) {
1167 arg.status = FSCRYPT_KEY_STATUS_ABSENT;
1168 err = 0;
1169 goto out;
1170 }
1171 down_read(&mk->mk_sem);
1172
1173 if (!mk->mk_present) {
1174 arg.status = refcount_read(&mk->mk_active_refs) > 0 ?
1175 FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED :
1176 FSCRYPT_KEY_STATUS_ABSENT /* raced with full removal */;
1177 err = 0;
1178 goto out_release_key;
1179 }
1180
1181 arg.status = FSCRYPT_KEY_STATUS_PRESENT;
1182 if (mk->mk_users) {
1183 struct key *mk_user;
1184
1185 arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
1186 mk_user = find_master_key_user(mk);
1187 if (!IS_ERR(mk_user)) {
1188 arg.status_flags |=
1189 FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
1190 key_put(mk_user);
1191 } else if (mk_user != ERR_PTR(-ENOKEY)) {
1192 err = PTR_ERR(mk_user);
1193 goto out_release_key;
1194 }
1195 }
1196 err = 0;
1197out_release_key:
1198 up_read(&mk->mk_sem);
1199 fscrypt_put_master_key(mk);
1200out:
1201 if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
1202 err = -EFAULT;
1203 return err;
1204}
1205EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
1206
1207int __init fscrypt_init_keyring(void)
1208{
1209 int err;
1210
1211 err = register_key_type(&key_type_fscrypt_user);
1212 if (err)
1213 return err;
1214
1215 err = register_key_type(&key_type_fscrypt_provisioning);
1216 if (err)
1217 goto err_unregister_fscrypt_user;
1218
1219 return 0;
1220
1221err_unregister_fscrypt_user:
1222 unregister_key_type(&key_type_fscrypt_user);
1223 return err;
1224}