aboutsummaryrefslogtreecommitdiffstats
path: root/security/keys/key.c
blob: 14948cf83ef6acc6ea19811465201ff5ae8660f0 (plain) (blame)
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
/* Basic authentication token and access key management
 *
 * Copyright (C) 2004-2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/poison.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/workqueue.h>
#include <linux/random.h>
#include <linux/err.h>
#include "internal.h"

static struct kmem_cache	*key_jar;
struct rb_root		key_serial_tree; /* tree of keys indexed by serial */
DEFINE_SPINLOCK(key_serial_lock);

struct rb_root	key_user_tree; /* tree of quota records indexed by UID */
DEFINE_SPINLOCK(key_user_lock);

unsigned int key_quota_root_maxkeys = 200;	/* root's key count quota */
unsigned int key_quota_root_maxbytes = 20000;	/* root's key space quota */
unsigned int key_quota_maxkeys = 200;		/* general key count quota */
unsigned int key_quota_maxbytes = 20000;	/* general key space quota */

static LIST_HEAD(key_types_list);
static DECLARE_RWSEM(key_types_sem);

static void key_cleanup(struct work_struct *work);
static DECLARE_WORK(key_cleanup_task, key_cleanup);

/* we serialise key instantiation and link */
DEFINE_MUTEX(key_construction_mutex);

/* any key who's type gets unegistered will be re-typed to this */
static struct key_type key_type_dead = {
	.name		= "dead",
};

#ifdef KEY_DEBUGGING
void __key_check(const struct key *key)
{
	printk("__key_check: key %p {%08x} should be {%08x}\n",
	       key, key->magic, KEY_DEBUG_MAGIC);
	BUG();
}
#endif

/*****************************************************************************/
/*
 * get the key quota record for a user, allocating a new record if one doesn't
 * already exist
 */
struct key_user *key_user_lookup(uid_t uid)
{
	struct key_user *candidate = NULL, *user;
	struct rb_node *parent = NULL;
	struct rb_node **p;

 try_again:
	p = &key_user_tree.rb_node;
	spin_lock(&key_user_lock);

	/* search the tree for a user record with a matching UID */
	while (*p) {
		parent = *p;
		user = rb_entry(parent, struct key_user, node);

		if (uid < user->uid)
			p = &(*p)->rb_left;
		else if (uid > user->uid)
			p = &(*p)->rb_right;
		else
			goto found;
	}

	/* if we get here, we failed to find a match in the tree */
	if (!candidate) {
		/* allocate a candidate user record if we don't already have
		 * one */
		spin_unlock(&key_user_lock);

		user = NULL;
		candidate = kmalloc(sizeof(struct key_user), GFP_KERNEL);
		if (unlikely(!candidate))
			goto out;

		/* the allocation may have scheduled, so we need to repeat the
		 * search lest someone else added the record whilst we were
		 * asleep */
		goto try_again;
	}

	/* if we get here, then the user record still hadn't appeared on the
	 * second pass - so we use the candidate record */
	atomic_set(&candidate->usage, 1);
	atomic_set(&candidate->nkeys, 0);
	atomic_set(&candidate->nikeys, 0);
	candidate->uid = uid;
	candidate->qnkeys = 0;
	candidate->qnbytes = 0;
	spin_lock_init(&candidate->lock);
	mutex_init(&candidate->cons_lock);

	rb_link_node(&candidate->node, parent, p);
	rb_insert_color(&candidate->node, &key_user_tree);
	spin_unlock(&key_user_lock);
	user = candidate;
	goto out;

	/* okay - we found a user record for this UID */
 found:
	atomic_inc(&user->usage);
	spin_unlock(&key_user_lock);
	kfree(candidate);
 out:
	return user;

} /* end key_user_lookup() */

/*****************************************************************************/
/*
 * dispose of a user structure
 */
void key_user_put(struct key_user *user)
{
	if (atomic_dec_and_lock(&user->usage, &key_user_lock)) {
		rb_erase(&user->node, &key_user_tree);
		spin_unlock(&key_user_lock);

		kfree(user);
	}

} /* end key_user_put() */

/*****************************************************************************/
/*
 * assign a key the next unique serial number
 * - these are assigned randomly to avoid security issues through covert
 *   channel problems
 */
static inline void key_alloc_serial(struct key *key)
{
	struct rb_node *parent, **p;
	struct key *xkey;

	/* propose a random serial number and look for a hole for it in the
	 * serial number tree */
	do {
		get_random_bytes(&key->serial, sizeof(key->serial));

		key->serial >>= 1; /* negative numbers are not permitted */
	} while (key->serial < 3);

	spin_lock(&key_serial_lock);

attempt_insertion:
	parent = NULL;
	p = &key_serial_tree.rb_node;

	while (*p) {
		parent = *p;
		xkey = rb_entry(parent, struct key, serial_node);

		if (key->serial < xkey->serial)
			p = &(*p)->rb_left;
		else if (key->serial > xkey->serial)
			p = &(*p)->rb_right;
		else
			goto serial_exists;
	}

	/* we've found a suitable hole - arrange for this key to occupy it */
	rb_link_node(&key->serial_node, parent, p);
	rb_insert_color(&key->serial_node, &key_serial_tree);

	spin_unlock(&key_serial_lock);
	return;

	/* we found a key with the proposed serial number - walk the tree from
	 * that point looking for the next unused serial number */
serial_exists:
	for (;;) {
		key->serial++;
		if (key->serial < 3) {
			key->serial = 3;
			goto attempt_insertion;
		}

		parent = rb_next(parent);
		if (!parent)
			goto attempt_insertion;

		xkey = rb_entry(parent, struct key, serial_node);
		if (key->serial < xkey->serial)
			goto attempt_insertion;
	}

} /* end key_alloc_serial() */

/*****************************************************************************/
/*
 * allocate a key of the specified type
 * - update the user's quota to reflect the existence of the key
 * - called from a key-type operation with key_types_sem read-locked by
 *   key_create_or_update()
 *   - this prevents unregistration of the key type
 * - upon return the key is as yet uninstantiated; the caller needs to either
 *   instantiate the key or discard it before returning
 */
struct key *key_alloc(struct key_type *type, const char *desc,
		      uid_t uid, gid_t gid, struct task_struct *ctx,
		      key_perm_t perm, unsigned long flags)
{
	struct key_user *user = NULL;
	struct key *key;
	size_t desclen, quotalen;
	int ret;

	key = ERR_PTR(-EINVAL);
	if (!desc || !*desc)
		goto error;

	desclen = strlen(desc) + 1;
	quotalen = desclen + type->def_datalen;

	/* get hold of the key tracking for this user */
	user = key_user_lookup(uid);
	if (!user)
		goto no_memory_1;

	/* check that the user's quota permits allocation of another key and
	 * its description */
	if (!(flags & KEY_ALLOC_NOT_IN_QUOTA)) {
		unsigned maxkeys = (uid == 0) ?
			key_quota_root_maxkeys : key_quota_maxkeys;
		unsigned maxbytes = (uid == 0) ?
			key_quota_root_maxbytes : key_quota_maxbytes;

		spin_lock(&user->lock);
		if (!(flags & KEY_ALLOC_QUOTA_OVERRUN)) {
			if (user->qnkeys + 1 >= maxkeys ||
			    user->qnbytes + quotalen >= maxbytes ||
			    user->qnbytes + quotalen < user->qnbytes)
				goto no_quota;
		}

		user->qnkeys++;
		user->qnbytes += quotalen;
		spin_unlock(&user->lock);
	}

	/* allocate and initialise the key and its description */
	key = kmem_cache_alloc(key_jar, GFP_KERNEL);
	if (!key)
		goto no_memory_2;

	if (desc) {
		key->description = kmemdup(desc, desclen, GFP_KERNEL);
		if (!key->description)
			goto no_memory_3;
	}

	atomic_set(&key->usage, 1);
	init_rwsem(&key->sem);
	key->type = type;
	key->user = user;
	key->quotalen = quotalen;
	key->datalen = type->def_datalen;
	key->uid = uid;
	key->gid = gid;
	key->perm = perm;
	key->flags = 0;
	key->expiry = 0;
	key->payload.data = NULL;
	key->security = NULL;

	if (!(flags & KEY_ALLOC_NOT_IN_QUOTA))
		key->flags |= 1 << KEY_FLAG_IN_QUOTA;

	memset(&key->type_data, 0, sizeof(key->type_data));

#ifdef KEY_DEBUGGING
	key->magic = KEY_DEBUG_MAGIC;
#endif

	/* let the security module know about the key */
	ret = security_key_alloc(key, ctx, flags);
	if (ret < 0)
		goto security_error;

	/* publish the key by giving it a serial number */
	atomic_inc(&user->nkeys);
	key_alloc_serial(key);

error:
	return key;

security_error:
	kfree(key->description);
	kmem_cache_free(key_jar, key);
	if (!(flags & KEY_ALLOC_NOT_IN_QUOTA)) {
		spin_lock(&user->lock);
		user->qnkeys--;
		user->qnbytes -= quotalen;
		spin_unlock(&user->lock);
	}
	key_user_put(user);
	key = ERR_PTR(ret);
	goto error;

no_memory_3:
	kmem_cache_free(key_jar, key);
no_memory_2:
	if (!(flags & KEY_ALLOC_NOT_IN_QUOTA)) {
		spin_lock(&user->lock);
		user->qnkeys--;
		user->qnbytes -= quotalen;
		spin_unlock(&user->lock);
	}
	key_user_put(user);
no_memory_1:
	key = ERR_PTR(-ENOMEM);
	goto error;

no_quota:
	spin_unlock(&user->lock);
	key_user_put(user);
	key = ERR_PTR(-EDQUOT);
	goto error;

} /* end key_alloc() */

EXPORT_SYMBOL(key_alloc);

/*****************************************************************************/
/*
 * reserve an amount of quota for the key's payload
 */
int key_payload_reserve(struct key *key, size_t datalen)
{
	int delta = (int) datalen - key->datalen;
	int ret = 0;

	key_check(key);

	/* contemplate the quota adjustment */
	if (delta != 0 && test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
		unsigned maxbytes = (key->user->uid == 0) ?
			key_quota_root_maxbytes : key_quota_maxbytes;

		spin_lock(&key->user->lock);

		if (delta > 0 &&
		    (key->user->qnbytes + delta >= maxbytes ||
		     key->user->qnbytes + delta < key->user->qnbytes)) {
			ret = -EDQUOT;
		}
		else {
			key->user->qnbytes += delta;
			key->quotalen += delta;
		}
		spin_unlock(&key->user->lock);
	}

	/* change the recorded data length if that didn't generate an error */
	if (ret == 0)
		key->datalen = datalen;

	return ret;

} /* end key_payload_reserve() */

EXPORT_SYMBOL(key_payload_reserve);

/*****************************************************************************/
/*
 * instantiate a key and link it into the target keyring atomically
 * - called with the target keyring's semaphore writelocked
 */
static int __key_instantiate_and_link(struct key *key,
				      const void *data,
				      size_t datalen,
				      struct key *keyring,
				      struct key *instkey)
{
	int ret, awaken;

	key_check(key);
	key_check(keyring);

	awaken = 0;
	ret = -EBUSY;

	mutex_lock(&key_construction_mutex);

	/* can't instantiate twice */
	if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
		/* instantiate the key */
		ret = key->type->instantiate(key, data, datalen);

		if (ret == 0) {
			/* mark the key as being instantiated */
			atomic_inc(&key->user->nikeys);
			set_bit(KEY_FLAG_INSTANTIATED, &key->flags);

			if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
				awaken = 1;

			/* and link it into the destination keyring */
			if (keyring)
				ret = __key_link(keyring, key);

			/* disable the authorisation key */
			if (instkey)
				key_revoke(instkey);
		}
	}

	mutex_unlock(&key_construction_mutex);

	/* wake up anyone waiting for a key to be constructed */
	if (awaken)
		wake_up_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT);

	return ret;

} /* end __key_instantiate_and_link() */

/*****************************************************************************/
/*
 * instantiate a key and link it into the target keyring atomically
 */
int key_instantiate_and_link(struct key *key,
			     const void *data,
			     size_t datalen,
			     struct key *keyring,
			     struct key *instkey)
{
	int ret;

	if (keyring)
		down_write(&keyring->sem);

	ret = __key_instantiate_and_link(key, data, datalen, keyring, instkey);

	if (keyring)
		up_write(&keyring->sem);

	return ret;

} /* end key_instantiate_and_link() */

EXPORT_SYMBOL(key_instantiate_and_link);

/*****************************************************************************/
/*
 * negatively instantiate a key and link it into the target keyring atomically
 */
int key_negate_and_link(struct key *key,
			unsigned timeout,
			struct key *keyring,
			struct key *instkey)
{
	struct timespec now;
	int ret, awaken;

	key_check(key);
	key_check(keyring);

	awaken = 0;
	ret = -EBUSY;

	if (keyring)
		down_write(&keyring->sem);

	mutex_lock(&key_construction_mutex);

	/* can't instantiate twice */
	if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
		/* mark the key as being negatively instantiated */
		atomic_inc(&key->user->nikeys);
		set_bit(KEY_FLAG_NEGATIVE, &key->flags);
		set_bit(KEY_FLAG_INSTANTIATED, &key->flags);
		now = current_kernel_time();
		key->expiry = now.tv_sec + timeout;

		if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
			awaken = 1;

		ret = 0;

		/* and link it into the destination keyring */
		if (keyring)
			ret = __key_link(keyring, key);

		/* disable the authorisation key */
		if (instkey)
			key_revoke(instkey);
	}

	mutex_unlock(&key_construction_mutex);

	if (keyring)
		up_write(&keyring->sem);

	/* wake up anyone waiting for a key to be constructed */
	if (awaken)
		wake_up_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT);

	return ret;

} /* end key_negate_and_link() */

EXPORT_SYMBOL(key_negate_and_link);

/*****************************************************************************/
/*
 * do cleaning up in process context so that we don't have to disable
 * interrupts all over the place
 */
static void key_cleanup(struct work_struct *work)
{
	struct rb_node *_n;
	struct key *key;

 go_again:
	/* look for a dead key in the tree */
	spin_lock(&key_serial_lock);

	for (_n = rb_first(&key_serial_tree); _n; _n = rb_next(_n)) {
		key = rb_entry(_n, struct key, serial_node);

		if (atomic_read(&key->usage) == 0)
			goto found_dead_key;
	}

	spin_unlock(&key_serial_lock);
	return;

 found_dead_key:
	/* we found a dead key - once we've removed it from the tree, we can
	 * drop the lock */
	rb_erase(&key->serial_node, &key_serial_tree);
	spin_unlock(&key_serial_lock);

	key_check(key);

	security_key_free(key);

	/* deal with the user's key tracking and quota */
	if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
		spin_lock(&key->user->lock);
		key->user->qnkeys--;
		key->user->qnbytes -= key->quotalen;
		spin_unlock(&key->user->lock);
	}

	atomic_dec(&key->user->nkeys);
	if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
		atomic_dec(&key->user->nikeys);

	key_user_put(key->user);

	/* now throw away the key memory */
	if (key->type->destroy)
		key->type->destroy(key);

	kfree(key->description);

#ifdef KEY_DEBUGGING
	key->magic = KEY_DEBUG_MAGIC_X;
#endif
	kmem_cache_free(key_jar, key);

	/* there may, of course, be more than one key to destroy */
	goto go_again;

} /* end key_cleanup() */

/*****************************************************************************/
/*
 * dispose of a reference to a key
 * - when all the references are gone, we schedule the cleanup task to come and
 *   pull it out of the tree in definite process context
 */
void key_put(struct key *key)
{
	if (key) {
		key_check(key);

		if (atomic_dec_and_test(&key->usage))
			schedule_work(&key_cleanup_task);
	}

} /* end key_put() */

EXPORT_SYMBOL(key_put);

/*****************************************************************************/
/*
 * find a key by its serial number
 */
struct key *key_lookup(key_serial_t id)
{
	struct rb_node *n;
	struct key *key;

	spin_lock(&key_serial_lock);

	/* search the tree for the specified key */
	n = key_serial_tree.rb_node;
	while (n) {
		key = rb_entry(n, struct key, serial_node);

		if (id < key->serial)
			n = n->rb_left;
		else if (id > key->serial)
			n = n->rb_right;
		else
			goto found;
	}

 not_found:
	key = ERR_PTR(-ENOKEY);
	goto error;

 found:
	/* pretend it doesn't exist if it's dead */
	if (atomic_read(&key->usage) == 0 ||
	    test_bit(KEY_FLAG_DEAD, &key->flags) ||
	    key->type == &key_type_dead)
		goto not_found;

	/* this races with key_put(), but that doesn't matter since key_put()
	 * doesn't actually change the key
	 */
	atomic_inc(&key->usage);

 error:
	spin_unlock(&key_serial_lock);
	return key;

} /* end key_lookup() */

/*****************************************************************************/
/*
 * find and lock the specified key type against removal
 * - we return with the sem readlocked
 */
struct key_type *key_type_lookup(const char *type)
{
	struct key_type *ktype;

	down_read(&key_types_sem);

	/* look up the key type to see if it's one of the registered kernel
	 * types */
	list_for_each_entry(ktype, &key_types_list, link) {
		if (strcmp(ktype->name, type) == 0)
			goto found_kernel_type;
	}

	up_read(&key_types_sem);
	ktype = ERR_PTR(-ENOKEY);

 found_kernel_type:
	return ktype;

} /* end key_type_lookup() */

/*****************************************************************************/
/*
 * unlock a key type
 */
void key_type_put(struct key_type *ktype)
{
	up_read(&key_types_sem);

} /* end key_type_put() */

/*****************************************************************************/
/*
 * attempt to update an existing key
 * - the key has an incremented refcount
 * - we need to put the key if we get an error
 */
static inline key_ref_t __key_update(key_ref_t key_ref,
				     const void *payload, size_t plen)
{
	struct key *key = key_ref_to_ptr(key_ref);
	int ret;

	/* need write permission on the key to update it */
	ret = key_permission(key_ref, KEY_WRITE);
	if (ret < 0)
		goto error;

	ret = -EEXIST;
	if (!key->type->update)
		goto error;

	down_write(&key->sem);

	ret = key->type->update(key, payload, plen);
	if (ret == 0)
		/* updating a negative key instantiates it */
		clear_bit(KEY_FLAG_NEGATIVE, &key->flags);

	up_write(&key->sem);

	if (ret < 0)
		goto error;
out:
	return key_ref;

error:
	key_put(key);
	key_ref = ERR_PTR(ret);
	goto out;

} /* end __key_update() */

/*****************************************************************************/
/*
 * search the specified keyring for a key of the same description; if one is
 * found, update it, otherwise add a new one
 */
key_ref_t key_create_or_update(key_ref_t keyring_ref,
			       const char *type,
			       const char *description,
			       const void *payload,
			       size_t plen,
			       key_perm_t perm,
			       unsigned long flags)
{
	struct key_type *ktype;
	struct key *keyring, *key = NULL;
	key_ref_t key_ref;
	int ret;

	/* look up the key type to see if it's one of the registered kernel
	 * types */
	ktype = key_type_lookup(type);
	if (IS_ERR(ktype)) {
		key_ref = ERR_PTR(-ENODEV);
		goto error;
	}

	key_ref = ERR_PTR(-EINVAL);
	if (!ktype->match || !ktype->instantiate)
		goto error_2;

	keyring = key_ref_to_ptr(keyring_ref);

	key_check(keyring);

	key_ref = ERR_PTR(-ENOTDIR);
	if (keyring->type != &key_type_keyring)
		goto error_2;

	down_write(&keyring->sem);

	/* if we're going to allocate a new key, we're going to have
	 * to modify the keyring */
	ret = key_permission(keyring_ref, KEY_WRITE);
	if (ret < 0) {
		key_ref = ERR_PTR(ret);
		goto error_3;
	}

	/* if it's possible to update this type of key, search for an existing
	 * key of the same type and description in the destination keyring and
	 * update that instead if possible
	 */
	if (ktype->update) {
		key_ref = __keyring_search_one(keyring_ref, ktype, description,
					       0);
		if (!IS_ERR(key_ref))
			goto found_matching_key;
	}

	/* if the client doesn't provide, decide on the permissions we want */
	if (perm == KEY_PERM_UNDEF) {
		perm = KEY_POS_VIEW | KEY_POS_SEARCH | KEY_POS_LINK | KEY_POS_SETATTR;
		perm |= KEY_USR_VIEW | KEY_USR_SEARCH | KEY_USR_LINK | KEY_USR_SETATTR;

		if (ktype->read)
			perm |= KEY_POS_READ | KEY_USR_READ;

		if (ktype == &key_type_keyring || ktype->update)
			perm |= KEY_USR_WRITE;
	}

	/* allocate a new key */
	key = key_alloc(ktype, description, current->fsuid, current->fsgid,
			current, perm, flags);
	if (IS_ERR(key)) {
		key_ref = ERR_CAST(key);
		goto error_3;
	}

	/* instantiate it and link it into the target keyring */
	ret = __key_instantiate_and_link(key, payload, plen, keyring, NULL);
	if (ret < 0) {
		key_put(key);
		key_ref = ERR_PTR(ret);
		goto error_3;
	}

	key_ref = make_key_ref(key, is_key_possessed(keyring_ref));

 error_3:
	up_write(&keyring->sem);
 error_2:
	key_type_put(ktype);
 error:
	return key_ref;

 found_matching_key:
	/* we found a matching key, so we're going to try to update it
	 * - we can drop the locks first as we have the key pinned
	 */
	up_write(&keyring->sem);
	key_type_put(ktype);

	key_ref = __key_update(key_ref, payload, plen);
	goto error;

} /* end key_create_or_update() */

EXPORT_SYMBOL(key_create_or_update);

/*****************************************************************************/
/*
 * update a key
 */
int key_update(key_ref_t key_ref, const void *payload, size_t plen)
{
	struct key *key = key_ref_to_ptr(key_ref);
	int ret;

	key_check(key);

	/* the key must be writable */
	ret = key_permission(key_ref, KEY_WRITE);
	if (ret < 0)
		goto error;

	/* attempt to update it if supported */
	ret = -EOPNOTSUPP;
	if (key->type->update) {
		down_write(&key->sem);

		ret = key->type->update(key, payload, plen);
		if (ret == 0)
			/* updating a negative key instantiates it */
			clear_bit(KEY_FLAG_NEGATIVE, &key->flags);

		up_write(&key->sem);
	}

 error:
	return ret;

} /* end key_update() */

EXPORT_SYMBOL(key_update);

/*****************************************************************************/
/*
 * revoke a key
 */
void key_revoke(struct key *key)
{
	key_check(key);

	/* make sure no one's trying to change or use the key when we mark it
	 * - we tell lockdep that we might nest because we might be revoking an
	 *   authorisation key whilst holding the sem on a key we've just
	 *   instantiated
	 */
	down_write_nested(&key->sem, 1);
	if (!test_and_set_bit(KEY_FLAG_REVOKED, &key->flags) &&
	    key->type->revoke)
		key->type->revoke(key);

	up_write(&key->sem);

} /* end key_revoke() */

EXPORT_SYMBOL(key_revoke);

/*****************************************************************************/
/*
 * register a type of key
 */
int register_key_type(struct key_type *ktype)
{
	struct key_type *p;
	int ret;

	ret = -EEXIST;
	down_write(&key_types_sem);

	/* disallow key types with the same name */
	list_for_each_entry(p, &key_types_list, link) {
		if (strcmp(p->name, ktype->name) == 0)
			goto out;
	}

	/* store the type */
	list_add(&ktype->link, &key_types_list);
	ret = 0;

 out:
	up_write(&key_types_sem);
	return ret;

} /* end register_key_type() */

EXPORT_SYMBOL(register_key_type);

/*****************************************************************************/
/*
 * unregister a type of key
 */
void unregister_key_type(struct key_type *ktype)
{
	struct rb_node *_n;
	struct key *key;

	down_write(&key_types_sem);

	/* withdraw the key type */
	list_del_init(&ktype->link);

	/* mark all the keys of this type dead */
	spin_lock(&key_serial_lock);

	for (_n = rb_first(&key_serial_tree); _n; _n = rb_next(_n)) {
		key = rb_entry(_n, struct key, serial_node);

		if (key->type == ktype)
			key->type = &key_type_dead;
	}

	spin_unlock(&key_serial_lock);

	/* make sure everyone revalidates their keys */
	synchronize_rcu();

	/* we should now be able to destroy the payloads of all the keys of
	 * this type with impunity */
	spin_lock(&key_serial_lock);

	for (_n = rb_first(&key_serial_tree); _n; _n = rb_next(_n)) {
		key = rb_entry(_n, struct key, serial_node);

		if (key->type == ktype) {
			if (ktype->destroy)
				ktype->destroy(key);
			memset(&key->payload, KEY_DESTROY, sizeof(key->payload));
		}
	}

	spin_unlock(&key_serial_lock);
	up_write(&key_types_sem);

} /* end unregister_key_type() */

EXPORT_SYMBOL(unregister_key_type);

/*****************************************************************************/
/*
 * initialise the key management stuff
 */
void __init key_init(void)
{
	/* allocate a slab in which we can store keys */
	key_jar = kmem_cache_create("key_jar", sizeof(struct key),
			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);

	/* add the special key types */
	list_add_tail(&key_type_keyring.link, &key_types_list);
	list_add_tail(&key_type_dead.link, &key_types_list);
	list_add_tail(&key_type_user.link, &key_types_list);

	/* record the root user tracking */
	rb_link_node(&root_key_user.node,
		     NULL,
		     &key_user_tree.rb_node);

	rb_insert_color(&root_key_user.node,
			&key_user_tree);

} /* end key_init() */