aboutsummaryrefslogtreecommitdiff
path: root/fs/crypto/keyring.c
blob: ab41b25d4fa1ba3cc0390d33a5fa7d52a2c18dc2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
// SPDX-License-Identifier: GPL-2.0
/*
 * Filesystem-level keyring for fscrypt
 *
 * Copyright 2019 Google LLC
 */

/*
 * This file implements management of fscrypt master keys in the
 * filesystem-level keyring, including the ioctls:
 *
 * - FS_IOC_ADD_ENCRYPTION_KEY
 * - FS_IOC_REMOVE_ENCRYPTION_KEY
 * - FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS
 * - FS_IOC_GET_ENCRYPTION_KEY_STATUS
 *
 * See the "User API" section of Documentation/filesystems/fscrypt.rst for more
 * information about these ioctls.
 */

#include <crypto/skcipher.h>
#include <linux/key-type.h>
#include <linux/seq_file.h>

#include "fscrypt_private.h"

static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
{
	fscrypt_destroy_hkdf(&secret->hkdf);
	memzero_explicit(secret, sizeof(*secret));
}

static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
				   struct fscrypt_master_key_secret *src)
{
	memcpy(dst, src, sizeof(*dst));
	memzero_explicit(src, sizeof(*src));
}

static void free_master_key(struct fscrypt_master_key *mk)
{
	size_t i;

	wipe_master_key_secret(&mk->mk_secret);

	for (i = 0; i <= __FSCRYPT_MODE_MAX; i++) {
		crypto_free_skcipher(mk->mk_direct_tfms[i]);
		crypto_free_skcipher(mk->mk_iv_ino_lblk_64_tfms[i]);
	}

	key_put(mk->mk_users);
	kzfree(mk);
}

static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
{
	if (spec->__reserved)
		return false;
	return master_key_spec_len(spec) != 0;
}

static int fscrypt_key_instantiate(struct key *key,
				   struct key_preparsed_payload *prep)
{
	key->payload.data[0] = (struct fscrypt_master_key *)prep->data;
	return 0;
}

static void fscrypt_key_destroy(struct key *key)
{
	free_master_key(key->payload.data[0]);
}

static void fscrypt_key_describe(const struct key *key, struct seq_file *m)
{
	seq_puts(m, key->description);

	if (key_is_positive(key)) {
		const struct fscrypt_master_key *mk = key->payload.data[0];

		if (!is_master_key_secret_present(&mk->mk_secret))
			seq_puts(m, ": secret removed");
	}
}

/*
 * Type of key in ->s_master_keys.  Each key of this type represents a master
 * key which has been added to the filesystem.  Its payload is a
 * 'struct fscrypt_master_key'.  The "." prefix in the key type name prevents
 * users from adding keys of this type via the keyrings syscalls rather than via
 * the intended method of FS_IOC_ADD_ENCRYPTION_KEY.
 */
static struct key_type key_type_fscrypt = {
	.name			= "._fscrypt",
	.instantiate		= fscrypt_key_instantiate,
	.destroy		= fscrypt_key_destroy,
	.describe		= fscrypt_key_describe,
};

static int fscrypt_user_key_instantiate(struct key *key,
					struct key_preparsed_payload *prep)
{
	/*
	 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
	 * each key, regardless of the exact key size.  The amount of memory
	 * actually used is greater than the size of the raw key anyway.
	 */
	return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
}

static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
{
	seq_puts(m, key->description);
}

/*
 * Type of key in ->mk_users.  Each key of this type represents a particular
 * user who has added a particular master key.
 *
 * Note that the name of this key type really should be something like
 * ".fscrypt-user" instead of simply ".fscrypt".  But the shorter name is chosen
 * mainly for simplicity of presentation in /proc/keys when read by a non-root
 * user.  And it is expected to be rare that a key is actually added by multiple
 * users, since users should keep their encryption keys confidential.
 */
static struct key_type key_type_fscrypt_user = {
	.name			= ".fscrypt",
	.instantiate		= fscrypt_user_key_instantiate,
	.describe		= fscrypt_user_key_describe,
};

/* Search ->s_master_keys or ->mk_users */
static struct key *search_fscrypt_keyring(struct key *keyring,
					  struct key_type *type,
					  const char *description)
{
	/*
	 * We need to mark the keyring reference as "possessed" so that we
	 * acquire permission to search it, via the KEY_POS_SEARCH permission.
	 */
	key_ref_t keyref = make_key_ref(keyring, true /* possessed */);

	keyref = keyring_search(keyref, type, description, false);
	if (IS_ERR(keyref)) {
		if (PTR_ERR(keyref) == -EAGAIN || /* not found */
		    PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
			keyref = ERR_PTR(-ENOKEY);
		return ERR_CAST(keyref);
	}
	return key_ref_to_ptr(keyref);
}

#define FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE	\
	(CONST_STRLEN("fscrypt-") + sizeof_field(struct super_block, s_id))

#define FSCRYPT_MK_DESCRIPTION_SIZE	(2 * FSCRYPT_KEY_IDENTIFIER_SIZE + 1)

#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE	\
	(CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
	 CONST_STRLEN("-users") + 1)

#define FSCRYPT_MK_USER_DESCRIPTION_SIZE	\
	(2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)

static void format_fs_keyring_description(
			char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE],
			const struct super_block *sb)
{
	sprintf(description, "fscrypt-%s", sb->s_id);
}

static void format_mk_description(
			char description[FSCRYPT_MK_DESCRIPTION_SIZE],
			const struct fscrypt_key_specifier *mk_spec)
{
	sprintf(description, "%*phN",
		master_key_spec_len(mk_spec), (u8 *)&mk_spec->u);
}

static void format_mk_users_keyring_description(
			char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
			const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
{
	sprintf(description, "fscrypt-%*phN-users",
		FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
}

static void format_mk_user_description(
			char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
			const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
{

	sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
		mk_identifier, __kuid_val(current_fsuid()));
}

/* Create ->s_master_keys if needed.  Synchronized by fscrypt_add_key_mutex. */
static int allocate_filesystem_keyring(struct super_block *sb)
{
	char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE];
	struct key *keyring;

	if (sb->s_master_keys)
		return 0;

	format_fs_keyring_description(description, sb);
	keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
				current_cred(), KEY_POS_SEARCH |
				  KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
				KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
	if (IS_ERR(keyring))
		return PTR_ERR(keyring);

	/* Pairs with READ_ONCE() in fscrypt_find_master_key() */
	smp_store_release(&sb->s_master_keys, keyring);
	return 0;
}

void fscrypt_sb_free(struct super_block *sb)
{
	key_put(sb->s_master_keys);
	sb->s_master_keys = NULL;
}

/*
 * Find the specified master key in ->s_master_keys.
 * Returns ERR_PTR(-ENOKEY) if not found.
 */
struct key *fscrypt_find_master_key(struct super_block *sb,
				    const struct fscrypt_key_specifier *mk_spec)
{
	struct key *keyring;
	char description[FSCRYPT_MK_DESCRIPTION_SIZE];

	/* pairs with smp_store_release() in allocate_filesystem_keyring() */
	keyring = READ_ONCE(sb->s_master_keys);
	if (keyring == NULL)
		return ERR_PTR(-ENOKEY); /* No keyring yet, so no keys yet. */

	format_mk_description(description, mk_spec);
	return search_fscrypt_keyring(keyring, &key_type_fscrypt, description);
}

static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
{
	char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
	struct key *keyring;

	format_mk_users_keyring_description(description,
					    mk->mk_spec.u.identifier);
	keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
				current_cred(), KEY_POS_SEARCH |
				  KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
				KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
	if (IS_ERR(keyring))
		return PTR_ERR(keyring);

	mk->mk_users = keyring;
	return 0;
}

/*
 * Find the current user's "key" in the master key's ->mk_users.
 * Returns ERR_PTR(-ENOKEY) if not found.
 */
static struct key *find_master_key_user(struct fscrypt_master_key *mk)
{
	char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];

	format_mk_user_description(description, mk->mk_spec.u.identifier);
	return search_fscrypt_keyring(mk->mk_users, &key_type_fscrypt_user,
				      description);
}

/*
 * Give the current user a "key" in ->mk_users.  This charges the user's quota
 * and marks the master key as added by the current user, so that it cannot be
 * removed by another user with the key.  Either the master key's key->sem must
 * be held for write, or the master key must be still undergoing initialization.
 */
static int add_master_key_user(struct fscrypt_master_key *mk)
{
	char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
	struct key *mk_user;
	int err;

	format_mk_user_description(description, mk->mk_spec.u.identifier);
	mk_user = key_alloc(&key_type_fscrypt_user, description,
			    current_fsuid(), current_gid(), current_cred(),
			    KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
	if (IS_ERR(mk_user))
		return PTR_ERR(mk_user);

	err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
	key_put(mk_user);
	return err;
}

/*
 * Remove the current user's "key" from ->mk_users.
 * The master key's key->sem must be held for write.
 *
 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
 */
static int remove_master_key_user(struct fscrypt_master_key *mk)
{
	struct key *mk_user;
	int err;

	mk_user = find_master_key_user(mk);
	if (IS_ERR(mk_user))
		return PTR_ERR(mk_user);
	err = key_unlink(mk->mk_users, mk_user);
	key_put(mk_user);
	return err;
}

/*
 * Allocate a new fscrypt_master_key which contains the given secret, set it as
 * the payload of a new 'struct key' of type fscrypt, and link the 'struct key'
 * into the given keyring.  Synchronized by fscrypt_add_key_mutex.
 */
static int add_new_master_key(struct fscrypt_master_key_secret *secret,
			      const struct fscrypt_key_specifier *mk_spec,
			      struct key *keyring)
{
	struct fscrypt_master_key *mk;
	char description[FSCRYPT_MK_DESCRIPTION_SIZE];
	struct key *key;
	int err;

	mk = kzalloc(sizeof(*mk), GFP_KERNEL);
	if (!mk)
		return -ENOMEM;

	mk->mk_spec = *mk_spec;

	move_master_key_secret(&mk->mk_secret, secret);
	init_rwsem(&mk->mk_secret_sem);

	refcount_set(&mk->mk_refcount, 1); /* secret is present */
	INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
	spin_lock_init(&mk->mk_decrypted_inodes_lock);

	if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
		err = allocate_master_key_users_keyring(mk);
		if (err)
			goto out_free_mk;
		err = add_master_key_user(mk);
		if (err)
			goto out_free_mk;
	}

	/*
	 * Note that we don't charge this key to anyone's quota, since when
	 * ->mk_users is in use those keys are charged instead, and otherwise
	 * (when ->mk_users isn't in use) only root can add these keys.
	 */
	format_mk_description(description, mk_spec);
	key = key_alloc(&key_type_fscrypt, description,
			GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
			KEY_POS_SEARCH | KEY_USR_SEARCH | KEY_USR_VIEW,
			KEY_ALLOC_NOT_IN_QUOTA, NULL);
	if (IS_ERR(key)) {
		err = PTR_ERR(key);
		goto out_free_mk;
	}
	err = key_instantiate_and_link(key, mk, sizeof(*mk), keyring, NULL);
	key_put(key);
	if (err)
		goto out_free_mk;

	return 0;

out_free_mk:
	free_master_key(mk);
	return err;
}

#define KEY_DEAD	1

static int add_existing_master_key(struct fscrypt_master_key *mk,
				   struct fscrypt_master_key_secret *secret)
{
	struct key *mk_user;
	bool rekey;
	int err;

	/*
	 * If the current user is already in ->mk_users, then there's nothing to
	 * do.  (Not applicable for v1 policy keys, which have NULL ->mk_users.)
	 */
	if (mk->mk_users) {
		mk_user = find_master_key_user(mk);
		if (mk_user != ERR_PTR(-ENOKEY)) {
			if (IS_ERR(mk_user))
				return PTR_ERR(mk_user);
			key_put(mk_user);
			return 0;
		}
	}

	/* If we'll be re-adding ->mk_secret, try to take the reference. */
	rekey = !is_master_key_secret_present(&mk->mk_secret);
	if (rekey && !refcount_inc_not_zero(&mk->mk_refcount))
		return KEY_DEAD;

	/* Add the current user to ->mk_users, if applicable. */
	if (mk->mk_users) {
		err = add_master_key_user(mk);
		if (err) {
			if (rekey && refcount_dec_and_test(&mk->mk_refcount))
				return KEY_DEAD;
			return err;
		}
	}

	/* Re-add the secret if needed. */
	if (rekey) {
		down_write(&mk->mk_secret_sem);
		move_master_key_secret(&mk->mk_secret, secret);
		up_write(&mk->mk_secret_sem);
	}
	return 0;
}

static int add_master_key(struct super_block *sb,
			  struct fscrypt_master_key_secret *secret,
			  const struct fscrypt_key_specifier *mk_spec)
{
	static DEFINE_MUTEX(fscrypt_add_key_mutex);
	struct key *key;
	int err;

	mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
retry:
	key = fscrypt_find_master_key(sb, mk_spec);
	if (IS_ERR(key)) {
		err = PTR_ERR(key);
		if (err != -ENOKEY)
			goto out_unlock;
		/* Didn't find the key in ->s_master_keys.  Add it. */
		err = allocate_filesystem_keyring(sb);
		if (err)
			goto out_unlock;
		err = add_new_master_key(secret, mk_spec, sb->s_master_keys);
	} else {
		/*
		 * Found the key in ->s_master_keys.  Re-add the secret if
		 * needed, and add the user to ->mk_users if needed.
		 */
		down_write(&key->sem);
		err = add_existing_master_key(key->payload.data[0], secret);
		up_write(&key->sem);
		if (err == KEY_DEAD) {
			/* Key being removed or needs to be removed */
			key_invalidate(key);
			key_put(key);
			goto retry;
		}
		key_put(key);
	}
out_unlock:
	mutex_unlock(&fscrypt_add_key_mutex);
	return err;
}

static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
{
	const struct fscrypt_provisioning_key_payload *payload = prep->data;

	if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
	    prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
		return -EINVAL;

	if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
	    payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
		return -EINVAL;

	if (payload->__reserved)
		return -EINVAL;

	prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
	if (!prep->payload.data[0])
		return -ENOMEM;

	prep->quotalen = prep->datalen;
	return 0;
}

static void fscrypt_provisioning_key_free_preparse(
					struct key_preparsed_payload *prep)
{
	kzfree(prep->payload.data[0]);
}

static void fscrypt_provisioning_key_describe(const struct key *key,
					      struct seq_file *m)
{
	seq_puts(m, key->description);
	if (key_is_positive(key)) {
		const struct fscrypt_provisioning_key_payload *payload =
			key->payload.data[0];

		seq_printf(m, ": %u [%u]", key->datalen, payload->type);
	}
}

static void fscrypt_provisioning_key_destroy(struct key *key)
{
	kzfree(key->payload.data[0]);
}

static struct key_type key_type_fscrypt_provisioning = {
	.name			= "fscrypt-provisioning",
	.preparse		= fscrypt_provisioning_key_preparse,
	.free_preparse		= fscrypt_provisioning_key_free_preparse,
	.instantiate		= generic_key_instantiate,
	.describe		= fscrypt_provisioning_key_describe,
	.destroy		= fscrypt_provisioning_key_destroy,
};

/*
 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
 * store it into 'secret'.
 *
 * The key must be of type "fscrypt-provisioning" and must have the field
 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
 * only usable with fscrypt with the particular KDF version identified by
 * 'type'.  We don't use the "logon" key type because there's no way to
 * completely restrict the use of such keys; they can be used by any kernel API
 * that accepts "logon" keys and doesn't require a specific service prefix.
 *
 * The ability to specify the key via Linux keyring key is intended for cases
 * where userspace needs to re-add keys after the filesystem is unmounted and
 * re-mounted.  Most users should just provide the raw key directly instead.
 */
static int get_keyring_key(u32 key_id, u32 type,
			   struct fscrypt_master_key_secret *secret)
{
	key_ref_t ref;
	struct key *key;
	const struct fscrypt_provisioning_key_payload *payload;
	int err;

	ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
	if (IS_ERR(ref))
		return PTR_ERR(ref);
	key = key_ref_to_ptr(ref);

	if (key->type != &key_type_fscrypt_provisioning)
		goto bad_key;
	payload = key->payload.data[0];

	/* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
	if (payload->type != type)
		goto bad_key;

	secret->size = key->datalen - sizeof(*payload);
	memcpy(secret->raw, payload->raw, secret->size);
	err = 0;
	goto out_put;

bad_key:
	err = -EKEYREJECTED;
out_put:
	key_ref_put(ref);
	return err;
}

/*
 * Add a master encryption key to the filesystem, causing all files which were
 * encrypted with it to appear "unlocked" (decrypted) when accessed.
 *
 * When adding a key for use by v1 encryption policies, this ioctl is
 * privileged, and userspace must provide the 'key_descriptor'.
 *
 * When adding a key for use by v2+ encryption policies, this ioctl is
 * unprivileged.  This is needed, in general, to allow non-root users to use
 * encryption without encountering the visibility problems of process-subscribed
 * keyrings and the inability to properly remove keys.  This works by having
 * each key identified by its cryptographically secure hash --- the
 * 'key_identifier'.  The cryptographic hash ensures that a malicious user
 * cannot add the wrong key for a given identifier.  Furthermore, each added key
 * is charged to the appropriate user's quota for the keyrings service, which
 * prevents a malicious user from adding too many keys.  Finally, we forbid a
 * user from removing a key while other users have added it too, which prevents
 * a user who knows another user's key from causing a denial-of-service by
 * removing it at an inopportune time.  (We tolerate that a user who knows a key
 * can prevent other users from removing it.)
 *
 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
 * Documentation/filesystems/fscrypt.rst.
 */
int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
{
	struct super_block *sb = file_inode(filp)->i_sb;
	struct fscrypt_add_key_arg __user *uarg = _uarg;
	struct fscrypt_add_key_arg arg;
	struct fscrypt_master_key_secret secret;
	int err;

	if (copy_from_user(&arg, uarg, sizeof(arg)))
		return -EFAULT;

	if (!valid_key_spec(&arg.key_spec))
		return -EINVAL;

	if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
		return -EINVAL;

	memset(&secret, 0, sizeof(secret));
	if (arg.key_id) {
		if (arg.raw_size != 0)
			return -EINVAL;
		err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
		if (err)
			goto out_wipe_secret;
	} else {
		if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
		    arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
			return -EINVAL;
		secret.size = arg.raw_size;
		err = -EFAULT;
		if (copy_from_user(secret.raw, uarg->raw, secret.size))
			goto out_wipe_secret;
	}

	switch (arg.key_spec.type) {
	case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR:
		/*
		 * Only root can add keys that are identified by an arbitrary
		 * descriptor rather than by a cryptographic hash --- since
		 * otherwise a malicious user could add the wrong key.
		 */
		err = -EACCES;
		if (!capable(CAP_SYS_ADMIN))
			goto out_wipe_secret;
		break;
	case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER:
		err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
		if (err)
			goto out_wipe_secret;

		/*
		 * Now that the HKDF context is initialized, the raw key is no
		 * longer needed.
		 */
		memzero_explicit(secret.raw, secret.size);

		/* Calculate the key identifier and return it to userspace. */
		err = fscrypt_hkdf_expand(&secret.hkdf,
					  HKDF_CONTEXT_KEY_IDENTIFIER,
					  NULL, 0, arg.key_spec.u.identifier,
					  FSCRYPT_KEY_IDENTIFIER_SIZE);
		if (err)
			goto out_wipe_secret;
		err = -EFAULT;
		if (copy_to_user(uarg->key_spec.u.identifier,
				 arg.key_spec.u.identifier,
				 FSCRYPT_KEY_IDENTIFIER_SIZE))
			goto out_wipe_secret;
		break;
	default:
		WARN_ON(1);
		err = -EINVAL;
		goto out_wipe_secret;
	}

	err = add_master_key(sb, &secret, &arg.key_spec);
out_wipe_secret:
	wipe_master_key_secret(&secret);
	return err;
}
EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);

/*
 * Verify that the current user has added a master key with the given identifier
 * (returns -ENOKEY if not).  This is needed to prevent a user from encrypting
 * their files using some other user's key which they don't actually know.
 * Cryptographically this isn't much of a problem, but the semantics of this
 * would be a bit weird, so it's best to just forbid it.
 *
 * The system administrator (CAP_FOWNER) can override this, which should be
 * enough for any use cases where encryption policies are being set using keys
 * that were chosen ahead of time but aren't available at the moment.
 *
 * Note that the key may have already removed by the time this returns, but
 * that's okay; we just care whether the key was there at some point.
 *
 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
 */
int fscrypt_verify_key_added(struct super_block *sb,
			     const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
{
	struct fscrypt_key_specifier mk_spec;
	struct key *key, *mk_user;
	struct fscrypt_master_key *mk;
	int err;

	mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
	memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);

	key = fscrypt_find_master_key(sb, &mk_spec);
	if (IS_ERR(key)) {
		err = PTR_ERR(key);
		goto out;
	}
	mk = key->payload.data[0];
	mk_user = find_master_key_user(mk);
	if (IS_ERR(mk_user)) {
		err = PTR_ERR(mk_user);
	} else {
		key_put(mk_user);
		err = 0;
	}
	key_put(key);
out:
	if (err == -ENOKEY && capable(CAP_FOWNER))
		err = 0;
	return err;
}

/*
 * Try to evict the inode's dentries from the dentry cache.  If the inode is a
 * directory, then it can have at most one dentry; however, that dentry may be
 * pinned by child dentries, so first try to evict the children too.
 */
static void shrink_dcache_inode(struct inode *inode)
{
	struct dentry *dentry;

	if (S_ISDIR(inode->i_mode)) {
		dentry = d_find_any_alias(inode);
		if (dentry) {
			shrink_dcache_parent(dentry);
			dput(dentry);
		}
	}
	d_prune_aliases(inode);
}

static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
{
	struct fscrypt_info *ci;
	struct inode *inode;
	struct inode *toput_inode = NULL;

	spin_lock(&mk->mk_decrypted_inodes_lock);

	list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
		inode = ci->ci_inode;
		spin_lock(&inode->i_lock);
		if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
			spin_unlock(&inode->i_lock);
			continue;
		}
		__iget(inode);
		spin_unlock(&inode->i_lock);
		spin_unlock(&mk->mk_decrypted_inodes_lock);

		shrink_dcache_inode(inode);
		iput(toput_inode);
		toput_inode = inode;

		spin_lock(&mk->mk_decrypted_inodes_lock);
	}

	spin_unlock(&mk->mk_decrypted_inodes_lock);
	iput(toput_inode);
}

static int check_for_busy_inodes(struct super_block *sb,
				 struct fscrypt_master_key *mk)
{
	struct list_head *pos;
	size_t busy_count = 0;
	unsigned long ino;

	spin_lock(&mk->mk_decrypted_inodes_lock);

	list_for_each(pos, &mk->mk_decrypted_inodes)
		busy_count++;

	if (busy_count == 0) {
		spin_unlock(&mk->mk_decrypted_inodes_lock);
		return 0;
	}

	{
		/* select an example file to show for debugging purposes */
		struct inode *inode =
			list_first_entry(&mk->mk_decrypted_inodes,
					 struct fscrypt_info,
					 ci_master_key_link)->ci_inode;
		ino = inode->i_ino;
	}
	spin_unlock(&mk->mk_decrypted_inodes_lock);

	fscrypt_warn(NULL,
		     "%s: %zu inode(s) still busy after removing key with %s %*phN, including ino %lu",
		     sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
		     master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
		     ino);
	return -EBUSY;
}

static int try_to_lock_encrypted_files(struct super_block *sb,
				       struct fscrypt_master_key *mk)
{
	int err1;
	int err2;

	/*
	 * An inode can't be evicted while it is dirty or has dirty pages.
	 * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
	 *
	 * Just do it the easy way: call sync_filesystem().  It's overkill, but
	 * it works, and it's more important to minimize the amount of caches we
	 * drop than the amount of data we sync.  Also, unprivileged users can
	 * already call sync_filesystem() via sys_syncfs() or sys_sync().
	 */
	down_read(&sb->s_umount);
	err1 = sync_filesystem(sb);
	up_read(&sb->s_umount);
	/* If a sync error occurs, still try to evict as much as possible. */

	/*
	 * Inodes are pinned by their dentries, so we have to evict their
	 * dentries.  shrink_dcache_sb() would suffice, but would be overkill
	 * and inappropriate for use by unprivileged users.  So instead go
	 * through the inodes' alias lists and try to evict each dentry.
	 */
	evict_dentries_for_decrypted_inodes(mk);

	/*
	 * evict_dentries_for_decrypted_inodes() already iput() each inode in
	 * the list; any inodes for which that dropped the last reference will
	 * have been evicted due to fscrypt_drop_inode() detecting the key
	 * removal and telling the VFS to evict the inode.  So to finish, we
	 * just need to check whether any inodes couldn't be evicted.
	 */
	err2 = check_for_busy_inodes(sb, mk);

	return err1 ?: err2;
}

/*
 * Try to remove an fscrypt master encryption key.
 *
 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
 * claim to the key, then removes the key itself if no other users have claims.
 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
 * key itself.
 *
 * To "remove the key itself", first we wipe the actual master key secret, so
 * that no more inodes can be unlocked with it.  Then we try to evict all cached
 * inodes that had been unlocked with the key.
 *
 * If all inodes were evicted, then we unlink the fscrypt_master_key from the
 * keyring.  Otherwise it remains in the keyring in the "incompletely removed"
 * state (without the actual secret key) where it tracks the list of remaining
 * inodes.  Userspace can execute the ioctl again later to retry eviction, or
 * alternatively can re-add the secret key again.
 *
 * For more details, see the "Removing keys" section of
 * Documentation/filesystems/fscrypt.rst.
 */
static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
{
	struct super_block *sb = file_inode(filp)->i_sb;
	struct fscrypt_remove_key_arg __user *uarg = _uarg;
	struct fscrypt_remove_key_arg arg;
	struct key *key;
	struct fscrypt_master_key *mk;
	u32 status_flags = 0;
	int err;
	bool dead;

	if (copy_from_user(&arg, uarg, sizeof(arg)))
		return -EFAULT;

	if (!valid_key_spec(&arg.key_spec))
		return -EINVAL;

	if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
		return -EINVAL;

	/*
	 * Only root can add and remove keys that are identified by an arbitrary
	 * descriptor rather than by a cryptographic hash.
	 */
	if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
	    !capable(CAP_SYS_ADMIN))
		return -EACCES;

	/* Find the key being removed. */
	key = fscrypt_find_master_key(sb, &arg.key_spec);
	if (IS_ERR(key))
		return PTR_ERR(key);
	mk = key->payload.data[0];

	down_write(&key->sem);

	/* If relevant, remove current user's (or all users) claim to the key */
	if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
		if (all_users)
			err = keyring_clear(mk->mk_users);
		else
			err = remove_master_key_user(mk);
		if (err) {
			up_write(&key->sem);
			goto out_put_key;
		}
		if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
			/*
			 * Other users have still added the key too.  We removed
			 * the current user's claim to the key, but we still
			 * can't remove the key itself.
			 */
			status_flags |=
				FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
			err = 0;
			up_write(&key->sem);
			goto out_put_key;
		}
	}

	/* No user claims remaining.  Go ahead and wipe the secret. */
	dead = false;
	if (is_master_key_secret_present(&mk->mk_secret)) {
		down_write(&mk->mk_secret_sem);
		wipe_master_key_secret(&mk->mk_secret);
		dead = refcount_dec_and_test(&mk->mk_refcount);
		up_write(&mk->mk_secret_sem);
	}
	up_write(&key->sem);
	if (dead) {
		/*
		 * No inodes reference the key, and we wiped the secret, so the
		 * key object is free to be removed from the keyring.
		 */
		key_invalidate(key);
		err = 0;
	} else {
		/* Some inodes still reference this key; try to evict them. */
		err = try_to_lock_encrypted_files(sb, mk);
		if (err == -EBUSY) {
			status_flags |=
				FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
			err = 0;
		}
	}
	/*
	 * We return 0 if we successfully did something: removed a claim to the
	 * key, wiped the secret, or tried locking the files again.  Users need
	 * to check the informational status flags if they care whether the key
	 * has been fully removed including all files locked.
	 */
out_put_key:
	key_put(key);
	if (err == 0)
		err = put_user(status_flags, &uarg->removal_status_flags);
	return err;
}

int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
{
	return do_remove_key(filp, uarg, false);
}
EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);

int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
{
	if (!capable(CAP_SYS_ADMIN))
		return -EACCES;
	return do_remove_key(filp, uarg, true);
}
EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);

/*
 * Retrieve the status of an fscrypt master encryption key.
 *
 * We set ->status to indicate whether the key is absent, present, or
 * incompletely removed.  "Incompletely removed" means that the master key
 * secret has been removed, but some files which had been unlocked with it are
 * still in use.  This field allows applications to easily determine the state
 * of an encrypted directory without using a hack such as trying to open a
 * regular file in it (which can confuse the "incompletely removed" state with
 * absent or present).
 *
 * In addition, for v2 policy keys we allow applications to determine, via
 * ->status_flags and ->user_count, whether the key has been added by the
 * current user, by other users, or by both.  Most applications should not need
 * this, since ordinarily only one user should know a given key.  However, if a
 * secret key is shared by multiple users, applications may wish to add an
 * already-present key to prevent other users from removing it.  This ioctl can
 * be used to check whether that really is the case before the work is done to
 * add the key --- which might e.g. require prompting the user for a passphrase.
 *
 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
 * Documentation/filesystems/fscrypt.rst.
 */
int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
{
	struct super_block *sb = file_inode(filp)->i_sb;
	struct fscrypt_get_key_status_arg arg;
	struct key *key;
	struct fscrypt_master_key *mk;
	int err;

	if (copy_from_user(&arg, uarg, sizeof(arg)))
		return -EFAULT;

	if (!valid_key_spec(&arg.key_spec))
		return -EINVAL;

	if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
		return -EINVAL;

	arg.status_flags = 0;
	arg.user_count = 0;
	memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));

	key = fscrypt_find_master_key(sb, &arg.key_spec);
	if (IS_ERR(key)) {
		if (key != ERR_PTR(-ENOKEY))
			return PTR_ERR(key);
		arg.status = FSCRYPT_KEY_STATUS_ABSENT;
		err = 0;
		goto out;
	}
	mk = key->payload.data[0];
	down_read(&key->sem);

	if (!is_master_key_secret_present(&mk->mk_secret)) {
		arg.status = FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED;
		err = 0;
		goto out_release_key;
	}

	arg.status = FSCRYPT_KEY_STATUS_PRESENT;
	if (mk->mk_users) {
		struct key *mk_user;

		arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
		mk_user = find_master_key_user(mk);
		if (!IS_ERR(mk_user)) {
			arg.status_flags |=
				FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
			key_put(mk_user);
		} else if (mk_user != ERR_PTR(-ENOKEY)) {
			err = PTR_ERR(mk_user);
			goto out_release_key;
		}
	}
	err = 0;
out_release_key:
	up_read(&key->sem);
	key_put(key);
out:
	if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
		err = -EFAULT;
	return err;
}
EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);

int __init fscrypt_init_keyring(void)
{
	int err;

	err = register_key_type(&key_type_fscrypt);
	if (err)
		return err;

	err = register_key_type(&key_type_fscrypt_user);
	if (err)
		goto err_unregister_fscrypt;

	err = register_key_type(&key_type_fscrypt_provisioning);
	if (err)
		goto err_unregister_fscrypt_user;

	return 0;

err_unregister_fscrypt_user:
	unregister_key_type(&key_type_fscrypt_user);
err_unregister_fscrypt:
	unregister_key_type(&key_type_fscrypt);
	return err;
}