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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 <linux/unaligned.h>
22#include <crypto/skcipher.h>
23#include <linux/key-type.h>
24#include <linux/random.h>
25#include <linux/once.h>
26#include <linux/seq_file.h>
27
28#include "fscrypt_private.h"
29
30/* The master encryption keys for a filesystem (->s_master_keys) */
31struct fscrypt_keyring {
32 /*
33 * Lock that protects ->key_hashtable. It does *not* protect the
34 * fscrypt_master_key structs themselves.
35 */
36 spinlock_t lock;
37
38 /* Hash table that maps fscrypt_key_specifier to fscrypt_master_key */
39 struct hlist_head key_hashtable[128];
40};
41
42static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
43{
44 fscrypt_destroy_hkdf(&secret->hkdf);
45 memzero_explicit(secret, sizeof(*secret));
46}
47
48static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
49 struct fscrypt_master_key_secret *src)
50{
51 memcpy(dst, src, sizeof(*dst));
52 memzero_explicit(src, sizeof(*src));
53}
54
55static void fscrypt_free_master_key(struct rcu_head *head)
56{
57 struct fscrypt_master_key *mk =
58 container_of(head, struct fscrypt_master_key, mk_rcu_head);
59 /*
60 * The master key secret and any embedded subkeys should have already
61 * been wiped when the last active reference to the fscrypt_master_key
62 * struct was dropped; doing it here would be unnecessarily late.
63 * Nevertheless, use kfree_sensitive() in case anything was missed.
64 */
65 kfree_sensitive(mk);
66}
67
68void fscrypt_put_master_key(struct fscrypt_master_key *mk)
69{
70 if (!refcount_dec_and_test(&mk->mk_struct_refs))
71 return;
72 /*
73 * No structural references left, so free ->mk_users, and also free the
74 * fscrypt_master_key struct itself after an RCU grace period ensures
75 * that concurrent keyring lookups can no longer find it.
76 */
77 WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 0);
78 if (mk->mk_users) {
79 /* Clear the keyring so the quota gets released right away. */
80 keyring_clear(mk->mk_users);
81 key_put(mk->mk_users);
82 mk->mk_users = NULL;
83 }
84 call_rcu(&mk->mk_rcu_head, fscrypt_free_master_key);
85}
86
87void fscrypt_put_master_key_activeref(struct super_block *sb,
88 struct fscrypt_master_key *mk)
89{
90 size_t i;
91
92 if (!refcount_dec_and_test(&mk->mk_active_refs))
93 return;
94 /*
95 * No active references left, so complete the full removal of this
96 * fscrypt_master_key struct by removing it from the keyring and
97 * destroying any subkeys embedded in it.
98 */
99
100 if (WARN_ON_ONCE(!sb->s_master_keys))
101 return;
102 spin_lock(&sb->s_master_keys->lock);
103 hlist_del_rcu(&mk->mk_node);
104 spin_unlock(&sb->s_master_keys->lock);
105
106 /*
107 * ->mk_active_refs == 0 implies that ->mk_present is false and
108 * ->mk_decrypted_inodes is empty.
109 */
110 WARN_ON_ONCE(mk->mk_present);
111 WARN_ON_ONCE(!list_empty(&mk->mk_decrypted_inodes));
112
113 for (i = 0; i <= FSCRYPT_MODE_MAX; i++) {
114 fscrypt_destroy_prepared_key(
115 sb, &mk->mk_direct_keys[i]);
116 fscrypt_destroy_prepared_key(
117 sb, &mk->mk_iv_ino_lblk_64_keys[i]);
118 fscrypt_destroy_prepared_key(
119 sb, &mk->mk_iv_ino_lblk_32_keys[i]);
120 }
121 memzero_explicit(&mk->mk_ino_hash_key,
122 sizeof(mk->mk_ino_hash_key));
123 mk->mk_ino_hash_key_initialized = false;
124
125 /* Drop the structural ref associated with the active refs. */
126 fscrypt_put_master_key(mk);
127}
128
129/*
130 * This transitions the key state from present to incompletely removed, and then
131 * potentially to absent (depending on whether inodes remain).
132 */
133static void fscrypt_initiate_key_removal(struct super_block *sb,
134 struct fscrypt_master_key *mk)
135{
136 WRITE_ONCE(mk->mk_present, false);
137 wipe_master_key_secret(&mk->mk_secret);
138 fscrypt_put_master_key_activeref(sb, mk);
139}
140
141static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
142{
143 if (spec->__reserved)
144 return false;
145 return master_key_spec_len(spec) != 0;
146}
147
148static int fscrypt_user_key_instantiate(struct key *key,
149 struct key_preparsed_payload *prep)
150{
151 /*
152 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
153 * each key, regardless of the exact key size. The amount of memory
154 * actually used is greater than the size of the raw key anyway.
155 */
156 return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
157}
158
159static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
160{
161 seq_puts(m, key->description);
162}
163
164/*
165 * Type of key in ->mk_users. Each key of this type represents a particular
166 * user who has added a particular master key.
167 *
168 * Note that the name of this key type really should be something like
169 * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen
170 * mainly for simplicity of presentation in /proc/keys when read by a non-root
171 * user. And it is expected to be rare that a key is actually added by multiple
172 * users, since users should keep their encryption keys confidential.
173 */
174static struct key_type key_type_fscrypt_user = {
175 .name = ".fscrypt",
176 .instantiate = fscrypt_user_key_instantiate,
177 .describe = fscrypt_user_key_describe,
178};
179
180#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \
181 (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
182 CONST_STRLEN("-users") + 1)
183
184#define FSCRYPT_MK_USER_DESCRIPTION_SIZE \
185 (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
186
187static void format_mk_users_keyring_description(
188 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
189 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
190{
191 sprintf(description, "fscrypt-%*phN-users",
192 FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
193}
194
195static void format_mk_user_description(
196 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
197 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
198{
199
200 sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
201 mk_identifier, __kuid_val(current_fsuid()));
202}
203
204/* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */
205static int allocate_filesystem_keyring(struct super_block *sb)
206{
207 struct fscrypt_keyring *keyring;
208
209 if (sb->s_master_keys)
210 return 0;
211
212 keyring = kzalloc(sizeof(*keyring), GFP_KERNEL);
213 if (!keyring)
214 return -ENOMEM;
215 spin_lock_init(&keyring->lock);
216 /*
217 * Pairs with the smp_load_acquire() in fscrypt_find_master_key().
218 * I.e., here we publish ->s_master_keys with a RELEASE barrier so that
219 * concurrent tasks can ACQUIRE it.
220 */
221 smp_store_release(&sb->s_master_keys, keyring);
222 return 0;
223}
224
225/*
226 * Release all encryption keys that have been added to the filesystem, along
227 * with the keyring that contains them.
228 *
229 * This is called at unmount time, after all potentially-encrypted inodes have
230 * been evicted. The filesystem's underlying block device(s) are still
231 * available at this time; this is important because after user file accesses
232 * have been allowed, this function may need to evict keys from the keyslots of
233 * an inline crypto engine, which requires the block device(s).
234 */
235void fscrypt_destroy_keyring(struct super_block *sb)
236{
237 struct fscrypt_keyring *keyring = sb->s_master_keys;
238 size_t i;
239
240 if (!keyring)
241 return;
242
243 for (i = 0; i < ARRAY_SIZE(keyring->key_hashtable); i++) {
244 struct hlist_head *bucket = &keyring->key_hashtable[i];
245 struct fscrypt_master_key *mk;
246 struct hlist_node *tmp;
247
248 hlist_for_each_entry_safe(mk, tmp, bucket, mk_node) {
249 /*
250 * Since all potentially-encrypted inodes were already
251 * evicted, every key remaining in the keyring should
252 * have an empty inode list, and should only still be in
253 * the keyring due to the single active ref associated
254 * with ->mk_present. There should be no structural
255 * refs beyond the one associated with the active ref.
256 */
257 WARN_ON_ONCE(refcount_read(&mk->mk_active_refs) != 1);
258 WARN_ON_ONCE(refcount_read(&mk->mk_struct_refs) != 1);
259 WARN_ON_ONCE(!mk->mk_present);
260 fscrypt_initiate_key_removal(sb, mk);
261 }
262 }
263 kfree_sensitive(keyring);
264 sb->s_master_keys = NULL;
265}
266
267static struct hlist_head *
268fscrypt_mk_hash_bucket(struct fscrypt_keyring *keyring,
269 const struct fscrypt_key_specifier *mk_spec)
270{
271 /*
272 * Since key specifiers should be "random" values, it is sufficient to
273 * use a trivial hash function that just takes the first several bits of
274 * the key specifier.
275 */
276 unsigned long i = get_unaligned((unsigned long *)&mk_spec->u);
277
278 return &keyring->key_hashtable[i % ARRAY_SIZE(keyring->key_hashtable)];
279}
280
281/*
282 * Find the specified master key struct in ->s_master_keys and take a structural
283 * ref to it. The structural ref guarantees that the key struct continues to
284 * exist, but it does *not* guarantee that ->s_master_keys continues to contain
285 * the key struct. The structural ref needs to be dropped by
286 * fscrypt_put_master_key(). Returns NULL if the key struct is not found.
287 */
288struct fscrypt_master_key *
289fscrypt_find_master_key(struct super_block *sb,
290 const struct fscrypt_key_specifier *mk_spec)
291{
292 struct fscrypt_keyring *keyring;
293 struct hlist_head *bucket;
294 struct fscrypt_master_key *mk;
295
296 /*
297 * Pairs with the smp_store_release() in allocate_filesystem_keyring().
298 * I.e., another task can publish ->s_master_keys concurrently,
299 * executing a RELEASE barrier. We need to use smp_load_acquire() here
300 * to safely ACQUIRE the memory the other task published.
301 */
302 keyring = smp_load_acquire(&sb->s_master_keys);
303 if (keyring == NULL)
304 return NULL; /* No keyring yet, so no keys yet. */
305
306 bucket = fscrypt_mk_hash_bucket(keyring, mk_spec);
307 rcu_read_lock();
308 switch (mk_spec->type) {
309 case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
310 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
311 if (mk->mk_spec.type ==
312 FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
313 memcmp(mk->mk_spec.u.descriptor,
314 mk_spec->u.descriptor,
315 FSCRYPT_KEY_DESCRIPTOR_SIZE) == 0 &&
316 refcount_inc_not_zero(&mk->mk_struct_refs))
317 goto out;
318 }
319 break;
320 case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
321 hlist_for_each_entry_rcu(mk, bucket, mk_node) {
322 if (mk->mk_spec.type ==
323 FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
324 memcmp(mk->mk_spec.u.identifier,
325 mk_spec->u.identifier,
326 FSCRYPT_KEY_IDENTIFIER_SIZE) == 0 &&
327 refcount_inc_not_zero(&mk->mk_struct_refs))
328 goto out;
329 }
330 break;
331 }
332 mk = NULL;
333out:
334 rcu_read_unlock();
335 return mk;
336}
337
338static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
339{
340 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
341 struct key *keyring;
342
343 format_mk_users_keyring_description(description,
344 mk->mk_spec.u.identifier);
345 keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
346 current_cred(), KEY_POS_SEARCH |
347 KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
348 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
349 if (IS_ERR(keyring))
350 return PTR_ERR(keyring);
351
352 mk->mk_users = keyring;
353 return 0;
354}
355
356/*
357 * Find the current user's "key" in the master key's ->mk_users.
358 * Returns ERR_PTR(-ENOKEY) if not found.
359 */
360static struct key *find_master_key_user(struct fscrypt_master_key *mk)
361{
362 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
363 key_ref_t keyref;
364
365 format_mk_user_description(description, mk->mk_spec.u.identifier);
366
367 /*
368 * We need to mark the keyring reference as "possessed" so that we
369 * acquire permission to search it, via the KEY_POS_SEARCH permission.
370 */
371 keyref = keyring_search(make_key_ref(mk->mk_users, true /*possessed*/),
372 &key_type_fscrypt_user, description, false);
373 if (IS_ERR(keyref)) {
374 if (PTR_ERR(keyref) == -EAGAIN || /* not found */
375 PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
376 keyref = ERR_PTR(-ENOKEY);
377 return ERR_CAST(keyref);
378 }
379 return key_ref_to_ptr(keyref);
380}
381
382/*
383 * Give the current user a "key" in ->mk_users. This charges the user's quota
384 * and marks the master key as added by the current user, so that it cannot be
385 * removed by another user with the key. Either ->mk_sem must be held for
386 * write, or the master key must be still undergoing initialization.
387 */
388static int add_master_key_user(struct fscrypt_master_key *mk)
389{
390 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
391 struct key *mk_user;
392 int err;
393
394 format_mk_user_description(description, mk->mk_spec.u.identifier);
395 mk_user = key_alloc(&key_type_fscrypt_user, description,
396 current_fsuid(), current_gid(), current_cred(),
397 KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
398 if (IS_ERR(mk_user))
399 return PTR_ERR(mk_user);
400
401 err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
402 key_put(mk_user);
403 return err;
404}
405
406/*
407 * Remove the current user's "key" from ->mk_users.
408 * ->mk_sem must be held for write.
409 *
410 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
411 */
412static int remove_master_key_user(struct fscrypt_master_key *mk)
413{
414 struct key *mk_user;
415 int err;
416
417 mk_user = find_master_key_user(mk);
418 if (IS_ERR(mk_user))
419 return PTR_ERR(mk_user);
420 err = key_unlink(mk->mk_users, mk_user);
421 key_put(mk_user);
422 return err;
423}
424
425/*
426 * Allocate a new fscrypt_master_key, transfer the given secret over to it, and
427 * insert it into sb->s_master_keys.
428 */
429static int add_new_master_key(struct super_block *sb,
430 struct fscrypt_master_key_secret *secret,
431 const struct fscrypt_key_specifier *mk_spec)
432{
433 struct fscrypt_keyring *keyring = sb->s_master_keys;
434 struct fscrypt_master_key *mk;
435 int err;
436
437 mk = kzalloc(sizeof(*mk), GFP_KERNEL);
438 if (!mk)
439 return -ENOMEM;
440
441 init_rwsem(&mk->mk_sem);
442 refcount_set(&mk->mk_struct_refs, 1);
443 mk->mk_spec = *mk_spec;
444
445 INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
446 spin_lock_init(&mk->mk_decrypted_inodes_lock);
447
448 if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
449 err = allocate_master_key_users_keyring(mk);
450 if (err)
451 goto out_put;
452 err = add_master_key_user(mk);
453 if (err)
454 goto out_put;
455 }
456
457 move_master_key_secret(&mk->mk_secret, secret);
458 mk->mk_present = true;
459 refcount_set(&mk->mk_active_refs, 1); /* ->mk_present is true */
460
461 spin_lock(&keyring->lock);
462 hlist_add_head_rcu(&mk->mk_node,
463 fscrypt_mk_hash_bucket(keyring, mk_spec));
464 spin_unlock(&keyring->lock);
465 return 0;
466
467out_put:
468 fscrypt_put_master_key(mk);
469 return err;
470}
471
472#define KEY_DEAD 1
473
474static int add_existing_master_key(struct fscrypt_master_key *mk,
475 struct fscrypt_master_key_secret *secret)
476{
477 int err;
478
479 /*
480 * If the current user is already in ->mk_users, then there's nothing to
481 * do. Otherwise, we need to add the user to ->mk_users. (Neither is
482 * applicable for v1 policy keys, which have NULL ->mk_users.)
483 */
484 if (mk->mk_users) {
485 struct key *mk_user = find_master_key_user(mk);
486
487 if (mk_user != ERR_PTR(-ENOKEY)) {
488 if (IS_ERR(mk_user))
489 return PTR_ERR(mk_user);
490 key_put(mk_user);
491 return 0;
492 }
493 err = add_master_key_user(mk);
494 if (err)
495 return err;
496 }
497
498 /* If the key is incompletely removed, make it present again. */
499 if (!mk->mk_present) {
500 if (!refcount_inc_not_zero(&mk->mk_active_refs)) {
501 /*
502 * Raced with the last active ref being dropped, so the
503 * key has become, or is about to become, "absent".
504 * Therefore, we need to allocate a new key struct.
505 */
506 return KEY_DEAD;
507 }
508 move_master_key_secret(&mk->mk_secret, secret);
509 WRITE_ONCE(mk->mk_present, true);
510 }
511
512 return 0;
513}
514
515static int do_add_master_key(struct super_block *sb,
516 struct fscrypt_master_key_secret *secret,
517 const struct fscrypt_key_specifier *mk_spec)
518{
519 static DEFINE_MUTEX(fscrypt_add_key_mutex);
520 struct fscrypt_master_key *mk;
521 int err;
522
523 mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
524
525 mk = fscrypt_find_master_key(sb, mk_spec);
526 if (!mk) {
527 /* Didn't find the key in ->s_master_keys. Add it. */
528 err = allocate_filesystem_keyring(sb);
529 if (!err)
530 err = add_new_master_key(sb, secret, mk_spec);
531 } else {
532 /*
533 * Found the key in ->s_master_keys. Add the user to ->mk_users
534 * if needed, and make the key "present" again if possible.
535 */
536 down_write(&mk->mk_sem);
537 err = add_existing_master_key(mk, secret);
538 up_write(&mk->mk_sem);
539 if (err == KEY_DEAD) {
540 /*
541 * We found a key struct, but it's already been fully
542 * removed. Ignore the old struct and add a new one.
543 * fscrypt_add_key_mutex means we don't need to worry
544 * about concurrent adds.
545 */
546 err = add_new_master_key(sb, secret, mk_spec);
547 }
548 fscrypt_put_master_key(mk);
549 }
550 mutex_unlock(&fscrypt_add_key_mutex);
551 return err;
552}
553
554static int add_master_key(struct super_block *sb,
555 struct fscrypt_master_key_secret *secret,
556 struct fscrypt_key_specifier *key_spec)
557{
558 int err;
559
560 if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
561 err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,
562 secret->size);
563 if (err)
564 return err;
565
566 /*
567 * Now that the HKDF context is initialized, the raw key is no
568 * longer needed.
569 */
570 memzero_explicit(secret->raw, secret->size);
571
572 /* Calculate the key identifier */
573 err = fscrypt_hkdf_expand(&secret->hkdf,
574 HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,
575 key_spec->u.identifier,
576 FSCRYPT_KEY_IDENTIFIER_SIZE);
577 if (err)
578 return err;
579 }
580 return do_add_master_key(sb, secret, key_spec);
581}
582
583static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
584{
585 const struct fscrypt_provisioning_key_payload *payload = prep->data;
586
587 if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
588 prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
589 return -EINVAL;
590
591 if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
592 payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
593 return -EINVAL;
594
595 if (payload->__reserved)
596 return -EINVAL;
597
598 prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
599 if (!prep->payload.data[0])
600 return -ENOMEM;
601
602 prep->quotalen = prep->datalen;
603 return 0;
604}
605
606static void fscrypt_provisioning_key_free_preparse(
607 struct key_preparsed_payload *prep)
608{
609 kfree_sensitive(prep->payload.data[0]);
610}
611
612static void fscrypt_provisioning_key_describe(const struct key *key,
613 struct seq_file *m)
614{
615 seq_puts(m, key->description);
616 if (key_is_positive(key)) {
617 const struct fscrypt_provisioning_key_payload *payload =
618 key->payload.data[0];
619
620 seq_printf(m, ": %u [%u]", key->datalen, payload->type);
621 }
622}
623
624static void fscrypt_provisioning_key_destroy(struct key *key)
625{
626 kfree_sensitive(key->payload.data[0]);
627}
628
629static struct key_type key_type_fscrypt_provisioning = {
630 .name = "fscrypt-provisioning",
631 .preparse = fscrypt_provisioning_key_preparse,
632 .free_preparse = fscrypt_provisioning_key_free_preparse,
633 .instantiate = generic_key_instantiate,
634 .describe = fscrypt_provisioning_key_describe,
635 .destroy = fscrypt_provisioning_key_destroy,
636};
637
638/*
639 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
640 * store it into 'secret'.
641 *
642 * The key must be of type "fscrypt-provisioning" and must have the field
643 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
644 * only usable with fscrypt with the particular KDF version identified by
645 * 'type'. We don't use the "logon" key type because there's no way to
646 * completely restrict the use of such keys; they can be used by any kernel API
647 * that accepts "logon" keys and doesn't require a specific service prefix.
648 *
649 * The ability to specify the key via Linux keyring key is intended for cases
650 * where userspace needs to re-add keys after the filesystem is unmounted and
651 * re-mounted. Most users should just provide the raw key directly instead.
652 */
653static int get_keyring_key(u32 key_id, u32 type,
654 struct fscrypt_master_key_secret *secret)
655{
656 key_ref_t ref;
657 struct key *key;
658 const struct fscrypt_provisioning_key_payload *payload;
659 int err;
660
661 ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
662 if (IS_ERR(ref))
663 return PTR_ERR(ref);
664 key = key_ref_to_ptr(ref);
665
666 if (key->type != &key_type_fscrypt_provisioning)
667 goto bad_key;
668 payload = key->payload.data[0];
669
670 /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
671 if (payload->type != type)
672 goto bad_key;
673
674 secret->size = key->datalen - sizeof(*payload);
675 memcpy(secret->raw, payload->raw, secret->size);
676 err = 0;
677 goto out_put;
678
679bad_key:
680 err = -EKEYREJECTED;
681out_put:
682 key_ref_put(ref);
683 return err;
684}
685
686/*
687 * Add a master encryption key to the filesystem, causing all files which were
688 * encrypted with it to appear "unlocked" (decrypted) when accessed.
689 *
690 * When adding a key for use by v1 encryption policies, this ioctl is
691 * privileged, and userspace must provide the 'key_descriptor'.
692 *
693 * When adding a key for use by v2+ encryption policies, this ioctl is
694 * unprivileged. This is needed, in general, to allow non-root users to use
695 * encryption without encountering the visibility problems of process-subscribed
696 * keyrings and the inability to properly remove keys. This works by having
697 * each key identified by its cryptographically secure hash --- the
698 * 'key_identifier'. The cryptographic hash ensures that a malicious user
699 * cannot add the wrong key for a given identifier. Furthermore, each added key
700 * is charged to the appropriate user's quota for the keyrings service, which
701 * prevents a malicious user from adding too many keys. Finally, we forbid a
702 * user from removing a key while other users have added it too, which prevents
703 * a user who knows another user's key from causing a denial-of-service by
704 * removing it at an inopportune time. (We tolerate that a user who knows a key
705 * can prevent other users from removing it.)
706 *
707 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
708 * Documentation/filesystems/fscrypt.rst.
709 */
710int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
711{
712 struct super_block *sb = file_inode(filp)->i_sb;
713 struct fscrypt_add_key_arg __user *uarg = _uarg;
714 struct fscrypt_add_key_arg arg;
715 struct fscrypt_master_key_secret secret;
716 int err;
717
718 if (copy_from_user(&arg, uarg, sizeof(arg)))
719 return -EFAULT;
720
721 if (!valid_key_spec(&arg.key_spec))
722 return -EINVAL;
723
724 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
725 return -EINVAL;
726
727 /*
728 * Only root can add keys that are identified by an arbitrary descriptor
729 * rather than by a cryptographic hash --- since otherwise a malicious
730 * user could add the wrong key.
731 */
732 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
733 !capable(CAP_SYS_ADMIN))
734 return -EACCES;
735
736 memset(&secret, 0, sizeof(secret));
737 if (arg.key_id) {
738 if (arg.raw_size != 0)
739 return -EINVAL;
740 err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
741 if (err)
742 goto out_wipe_secret;
743 } else {
744 if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
745 arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
746 return -EINVAL;
747 secret.size = arg.raw_size;
748 err = -EFAULT;
749 if (copy_from_user(secret.raw, uarg->raw, secret.size))
750 goto out_wipe_secret;
751 }
752
753 err = add_master_key(sb, &secret, &arg.key_spec);
754 if (err)
755 goto out_wipe_secret;
756
757 /* Return the key identifier to userspace, if applicable */
758 err = -EFAULT;
759 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
760 copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,
761 FSCRYPT_KEY_IDENTIFIER_SIZE))
762 goto out_wipe_secret;
763 err = 0;
764out_wipe_secret:
765 wipe_master_key_secret(&secret);
766 return err;
767}
768EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
769
770static void
771fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret)
772{
773 static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
774
775 get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
776
777 memset(secret, 0, sizeof(*secret));
778 secret->size = FSCRYPT_MAX_KEY_SIZE;
779 memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE);
780}
781
782int fscrypt_get_test_dummy_key_identifier(
783 u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
784{
785 struct fscrypt_master_key_secret secret;
786 int err;
787
788 fscrypt_get_test_dummy_secret(&secret);
789
790 err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
791 if (err)
792 goto out;
793 err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER,
794 NULL, 0, key_identifier,
795 FSCRYPT_KEY_IDENTIFIER_SIZE);
796out:
797 wipe_master_key_secret(&secret);
798 return err;
799}
800
801/**
802 * fscrypt_add_test_dummy_key() - add the test dummy encryption key
803 * @sb: the filesystem instance to add the key to
804 * @key_spec: the key specifier of the test dummy encryption key
805 *
806 * Add the key for the test_dummy_encryption mount option to the filesystem. To
807 * prevent misuse of this mount option, a per-boot random key is used instead of
808 * a hardcoded one. This makes it so that any encrypted files created using
809 * this option won't be accessible after a reboot.
810 *
811 * Return: 0 on success, -errno on failure
812 */
813int fscrypt_add_test_dummy_key(struct super_block *sb,
814 struct fscrypt_key_specifier *key_spec)
815{
816 struct fscrypt_master_key_secret secret;
817 int err;
818
819 fscrypt_get_test_dummy_secret(&secret);
820 err = add_master_key(sb, &secret, key_spec);
821 wipe_master_key_secret(&secret);
822 return err;
823}
824
825/*
826 * Verify that the current user has added a master key with the given identifier
827 * (returns -ENOKEY if not). This is needed to prevent a user from encrypting
828 * their files using some other user's key which they don't actually know.
829 * Cryptographically this isn't much of a problem, but the semantics of this
830 * would be a bit weird, so it's best to just forbid it.
831 *
832 * The system administrator (CAP_FOWNER) can override this, which should be
833 * enough for any use cases where encryption policies are being set using keys
834 * that were chosen ahead of time but aren't available at the moment.
835 *
836 * Note that the key may have already removed by the time this returns, but
837 * that's okay; we just care whether the key was there at some point.
838 *
839 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
840 */
841int fscrypt_verify_key_added(struct super_block *sb,
842 const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
843{
844 struct fscrypt_key_specifier mk_spec;
845 struct fscrypt_master_key *mk;
846 struct key *mk_user;
847 int err;
848
849 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
850 memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
851
852 mk = fscrypt_find_master_key(sb, &mk_spec);
853 if (!mk) {
854 err = -ENOKEY;
855 goto out;
856 }
857 down_read(&mk->mk_sem);
858 mk_user = find_master_key_user(mk);
859 if (IS_ERR(mk_user)) {
860 err = PTR_ERR(mk_user);
861 } else {
862 key_put(mk_user);
863 err = 0;
864 }
865 up_read(&mk->mk_sem);
866 fscrypt_put_master_key(mk);
867out:
868 if (err == -ENOKEY && capable(CAP_FOWNER))
869 err = 0;
870 return err;
871}
872
873/*
874 * Try to evict the inode's dentries from the dentry cache. If the inode is a
875 * directory, then it can have at most one dentry; however, that dentry may be
876 * pinned by child dentries, so first try to evict the children too.
877 */
878static void shrink_dcache_inode(struct inode *inode)
879{
880 struct dentry *dentry;
881
882 if (S_ISDIR(inode->i_mode)) {
883 dentry = d_find_any_alias(inode);
884 if (dentry) {
885 shrink_dcache_parent(dentry);
886 dput(dentry);
887 }
888 }
889 d_prune_aliases(inode);
890}
891
892static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
893{
894 struct fscrypt_inode_info *ci;
895 struct inode *inode;
896 struct inode *toput_inode = NULL;
897
898 spin_lock(&mk->mk_decrypted_inodes_lock);
899
900 list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
901 inode = ci->ci_inode;
902 spin_lock(&inode->i_lock);
903 if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
904 spin_unlock(&inode->i_lock);
905 continue;
906 }
907 __iget(inode);
908 spin_unlock(&inode->i_lock);
909 spin_unlock(&mk->mk_decrypted_inodes_lock);
910
911 shrink_dcache_inode(inode);
912 iput(toput_inode);
913 toput_inode = inode;
914
915 spin_lock(&mk->mk_decrypted_inodes_lock);
916 }
917
918 spin_unlock(&mk->mk_decrypted_inodes_lock);
919 iput(toput_inode);
920}
921
922static int check_for_busy_inodes(struct super_block *sb,
923 struct fscrypt_master_key *mk)
924{
925 struct list_head *pos;
926 size_t busy_count = 0;
927 unsigned long ino;
928 char ino_str[50] = "";
929
930 spin_lock(&mk->mk_decrypted_inodes_lock);
931
932 list_for_each(pos, &mk->mk_decrypted_inodes)
933 busy_count++;
934
935 if (busy_count == 0) {
936 spin_unlock(&mk->mk_decrypted_inodes_lock);
937 return 0;
938 }
939
940 {
941 /* select an example file to show for debugging purposes */
942 struct inode *inode =
943 list_first_entry(&mk->mk_decrypted_inodes,
944 struct fscrypt_inode_info,
945 ci_master_key_link)->ci_inode;
946 ino = inode->i_ino;
947 }
948 spin_unlock(&mk->mk_decrypted_inodes_lock);
949
950 /* If the inode is currently being created, ino may still be 0. */
951 if (ino)
952 snprintf(ino_str, sizeof(ino_str), ", including ino %lu", ino);
953
954 fscrypt_warn(NULL,
955 "%s: %zu inode(s) still busy after removing key with %s %*phN%s",
956 sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
957 master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
958 ino_str);
959 return -EBUSY;
960}
961
962static int try_to_lock_encrypted_files(struct super_block *sb,
963 struct fscrypt_master_key *mk)
964{
965 int err1;
966 int err2;
967
968 /*
969 * An inode can't be evicted while it is dirty or has dirty pages.
970 * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
971 *
972 * Just do it the easy way: call sync_filesystem(). It's overkill, but
973 * it works, and it's more important to minimize the amount of caches we
974 * drop than the amount of data we sync. Also, unprivileged users can
975 * already call sync_filesystem() via sys_syncfs() or sys_sync().
976 */
977 down_read(&sb->s_umount);
978 err1 = sync_filesystem(sb);
979 up_read(&sb->s_umount);
980 /* If a sync error occurs, still try to evict as much as possible. */
981
982 /*
983 * Inodes are pinned by their dentries, so we have to evict their
984 * dentries. shrink_dcache_sb() would suffice, but would be overkill
985 * and inappropriate for use by unprivileged users. So instead go
986 * through the inodes' alias lists and try to evict each dentry.
987 */
988 evict_dentries_for_decrypted_inodes(mk);
989
990 /*
991 * evict_dentries_for_decrypted_inodes() already iput() each inode in
992 * the list; any inodes for which that dropped the last reference will
993 * have been evicted due to fscrypt_drop_inode() detecting the key
994 * removal and telling the VFS to evict the inode. So to finish, we
995 * just need to check whether any inodes couldn't be evicted.
996 */
997 err2 = check_for_busy_inodes(sb, mk);
998
999 return err1 ?: err2;
1000}
1001
1002/*
1003 * Try to remove an fscrypt master encryption key.
1004 *
1005 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
1006 * claim to the key, then removes the key itself if no other users have claims.
1007 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
1008 * key itself.
1009 *
1010 * To "remove the key itself", first we transition the key to the "incompletely
1011 * removed" state, so that no more inodes can be unlocked with it. Then we try
1012 * to evict all cached inodes that had been unlocked with the key.
1013 *
1014 * If all inodes were evicted, then we unlink the fscrypt_master_key from the
1015 * keyring. Otherwise it remains in the keyring in the "incompletely removed"
1016 * state where it tracks the list of remaining inodes. Userspace can execute
1017 * the ioctl again later to retry eviction, or alternatively can re-add the key.
1018 *
1019 * For more details, see the "Removing keys" section of
1020 * Documentation/filesystems/fscrypt.rst.
1021 */
1022static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
1023{
1024 struct super_block *sb = file_inode(filp)->i_sb;
1025 struct fscrypt_remove_key_arg __user *uarg = _uarg;
1026 struct fscrypt_remove_key_arg arg;
1027 struct fscrypt_master_key *mk;
1028 u32 status_flags = 0;
1029 int err;
1030 bool inodes_remain;
1031
1032 if (copy_from_user(&arg, uarg, sizeof(arg)))
1033 return -EFAULT;
1034
1035 if (!valid_key_spec(&arg.key_spec))
1036 return -EINVAL;
1037
1038 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1039 return -EINVAL;
1040
1041 /*
1042 * Only root can add and remove keys that are identified by an arbitrary
1043 * descriptor rather than by a cryptographic hash.
1044 */
1045 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
1046 !capable(CAP_SYS_ADMIN))
1047 return -EACCES;
1048
1049 /* Find the key being removed. */
1050 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1051 if (!mk)
1052 return -ENOKEY;
1053 down_write(&mk->mk_sem);
1054
1055 /* If relevant, remove current user's (or all users) claim to the key */
1056 if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
1057 if (all_users)
1058 err = keyring_clear(mk->mk_users);
1059 else
1060 err = remove_master_key_user(mk);
1061 if (err) {
1062 up_write(&mk->mk_sem);
1063 goto out_put_key;
1064 }
1065 if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
1066 /*
1067 * Other users have still added the key too. We removed
1068 * the current user's claim to the key, but we still
1069 * can't remove the key itself.
1070 */
1071 status_flags |=
1072 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
1073 err = 0;
1074 up_write(&mk->mk_sem);
1075 goto out_put_key;
1076 }
1077 }
1078
1079 /* No user claims remaining. Initiate removal of the key. */
1080 err = -ENOKEY;
1081 if (mk->mk_present) {
1082 fscrypt_initiate_key_removal(sb, mk);
1083 err = 0;
1084 }
1085 inodes_remain = refcount_read(&mk->mk_active_refs) > 0;
1086 up_write(&mk->mk_sem);
1087
1088 if (inodes_remain) {
1089 /* Some inodes still reference this key; try to evict them. */
1090 err = try_to_lock_encrypted_files(sb, mk);
1091 if (err == -EBUSY) {
1092 status_flags |=
1093 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
1094 err = 0;
1095 }
1096 }
1097 /*
1098 * We return 0 if we successfully did something: removed a claim to the
1099 * key, initiated removal of the key, or tried locking the files again.
1100 * Users need to check the informational status flags if they care
1101 * whether the key has been fully removed including all files locked.
1102 */
1103out_put_key:
1104 fscrypt_put_master_key(mk);
1105 if (err == 0)
1106 err = put_user(status_flags, &uarg->removal_status_flags);
1107 return err;
1108}
1109
1110int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
1111{
1112 return do_remove_key(filp, uarg, false);
1113}
1114EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
1115
1116int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
1117{
1118 if (!capable(CAP_SYS_ADMIN))
1119 return -EACCES;
1120 return do_remove_key(filp, uarg, true);
1121}
1122EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);
1123
1124/*
1125 * Retrieve the status of an fscrypt master encryption key.
1126 *
1127 * We set ->status to indicate whether the key is absent, present, or
1128 * incompletely removed. (For an explanation of what these statuses mean and
1129 * how they are represented internally, see struct fscrypt_master_key.) This
1130 * field allows applications to easily determine the status of an encrypted
1131 * directory without using a hack such as trying to open a regular file in it
1132 * (which can confuse the "incompletely removed" status with absent or present).
1133 *
1134 * In addition, for v2 policy keys we allow applications to determine, via
1135 * ->status_flags and ->user_count, whether the key has been added by the
1136 * current user, by other users, or by both. Most applications should not need
1137 * this, since ordinarily only one user should know a given key. However, if a
1138 * secret key is shared by multiple users, applications may wish to add an
1139 * already-present key to prevent other users from removing it. This ioctl can
1140 * be used to check whether that really is the case before the work is done to
1141 * add the key --- which might e.g. require prompting the user for a passphrase.
1142 *
1143 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
1144 * Documentation/filesystems/fscrypt.rst.
1145 */
1146int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
1147{
1148 struct super_block *sb = file_inode(filp)->i_sb;
1149 struct fscrypt_get_key_status_arg arg;
1150 struct fscrypt_master_key *mk;
1151 int err;
1152
1153 if (copy_from_user(&arg, uarg, sizeof(arg)))
1154 return -EFAULT;
1155
1156 if (!valid_key_spec(&arg.key_spec))
1157 return -EINVAL;
1158
1159 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1160 return -EINVAL;
1161
1162 arg.status_flags = 0;
1163 arg.user_count = 0;
1164 memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
1165
1166 mk = fscrypt_find_master_key(sb, &arg.key_spec);
1167 if (!mk) {
1168 arg.status = FSCRYPT_KEY_STATUS_ABSENT;
1169 err = 0;
1170 goto out;
1171 }
1172 down_read(&mk->mk_sem);
1173
1174 if (!mk->mk_present) {
1175 arg.status = refcount_read(&mk->mk_active_refs) > 0 ?
1176 FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED :
1177 FSCRYPT_KEY_STATUS_ABSENT /* raced with full removal */;
1178 err = 0;
1179 goto out_release_key;
1180 }
1181
1182 arg.status = FSCRYPT_KEY_STATUS_PRESENT;
1183 if (mk->mk_users) {
1184 struct key *mk_user;
1185
1186 arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
1187 mk_user = find_master_key_user(mk);
1188 if (!IS_ERR(mk_user)) {
1189 arg.status_flags |=
1190 FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
1191 key_put(mk_user);
1192 } else if (mk_user != ERR_PTR(-ENOKEY)) {
1193 err = PTR_ERR(mk_user);
1194 goto out_release_key;
1195 }
1196 }
1197 err = 0;
1198out_release_key:
1199 up_read(&mk->mk_sem);
1200 fscrypt_put_master_key(mk);
1201out:
1202 if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
1203 err = -EFAULT;
1204 return err;
1205}
1206EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
1207
1208int __init fscrypt_init_keyring(void)
1209{
1210 int err;
1211
1212 err = register_key_type(&key_type_fscrypt_user);
1213 if (err)
1214 return err;
1215
1216 err = register_key_type(&key_type_fscrypt_provisioning);
1217 if (err)
1218 goto err_unregister_fscrypt_user;
1219
1220 return 0;
1221
1222err_unregister_fscrypt_user:
1223 unregister_key_type(&key_type_fscrypt_user);
1224 return err;
1225}