[PATCH] keys: Discard key spinlock and use RCU for key payload
[linux-3.10.git] / security / keys / keyring.c
1 /* keyring.c: keyring handling
2  *
3  * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
4  * Written by David Howells (dhowells@redhat.com)
5  *
6  * This program is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public License
8  * as published by the Free Software Foundation; either version
9  * 2 of the License, or (at your option) any later version.
10  */
11
12 #include <linux/module.h>
13 #include <linux/init.h>
14 #include <linux/sched.h>
15 #include <linux/slab.h>
16 #include <linux/seq_file.h>
17 #include <linux/err.h>
18 #include <asm/uaccess.h>
19 #include "internal.h"
20
21 /*
22  * when plumbing the depths of the key tree, this sets a hard limit set on how
23  * deep we're willing to go
24  */
25 #define KEYRING_SEARCH_MAX_DEPTH 6
26
27 /*
28  * we keep all named keyrings in a hash to speed looking them up
29  */
30 #define KEYRING_NAME_HASH_SIZE  (1 << 5)
31
32 static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
33 static DEFINE_RWLOCK(keyring_name_lock);
34
35 static inline unsigned keyring_hash(const char *desc)
36 {
37         unsigned bucket = 0;
38
39         for (; *desc; desc++)
40                 bucket += (unsigned char) *desc;
41
42         return bucket & (KEYRING_NAME_HASH_SIZE - 1);
43 }
44
45 /*
46  * the keyring type definition
47  */
48 static int keyring_instantiate(struct key *keyring,
49                                const void *data, size_t datalen);
50 static int keyring_duplicate(struct key *keyring, const struct key *source);
51 static int keyring_match(const struct key *keyring, const void *criterion);
52 static void keyring_destroy(struct key *keyring);
53 static void keyring_describe(const struct key *keyring, struct seq_file *m);
54 static long keyring_read(const struct key *keyring,
55                          char __user *buffer, size_t buflen);
56
57 struct key_type key_type_keyring = {
58         .name           = "keyring",
59         .def_datalen    = sizeof(struct keyring_list),
60         .instantiate    = keyring_instantiate,
61         .duplicate      = keyring_duplicate,
62         .match          = keyring_match,
63         .destroy        = keyring_destroy,
64         .describe       = keyring_describe,
65         .read           = keyring_read,
66 };
67
68 /*
69  * semaphore to serialise link/link calls to prevent two link calls in parallel
70  * introducing a cycle
71  */
72 DECLARE_RWSEM(keyring_serialise_link_sem);
73
74 /*****************************************************************************/
75 /*
76  * publish the name of a keyring so that it can be found by name (if it has
77  * one)
78  */
79 void keyring_publish_name(struct key *keyring)
80 {
81         int bucket;
82
83         if (keyring->description) {
84                 bucket = keyring_hash(keyring->description);
85
86                 write_lock(&keyring_name_lock);
87
88                 if (!keyring_name_hash[bucket].next)
89                         INIT_LIST_HEAD(&keyring_name_hash[bucket]);
90
91                 list_add_tail(&keyring->type_data.link,
92                               &keyring_name_hash[bucket]);
93
94                 write_unlock(&keyring_name_lock);
95         }
96
97 } /* end keyring_publish_name() */
98
99 /*****************************************************************************/
100 /*
101  * initialise a keyring
102  * - we object if we were given any data
103  */
104 static int keyring_instantiate(struct key *keyring,
105                                const void *data, size_t datalen)
106 {
107         int ret;
108
109         ret = -EINVAL;
110         if (datalen == 0) {
111                 /* make the keyring available by name if it has one */
112                 keyring_publish_name(keyring);
113                 ret = 0;
114         }
115
116         return ret;
117
118 } /* end keyring_instantiate() */
119
120 /*****************************************************************************/
121 /*
122  * duplicate the list of subscribed keys from a source keyring into this one
123  */
124 static int keyring_duplicate(struct key *keyring, const struct key *source)
125 {
126         struct keyring_list *sklist, *klist;
127         unsigned max;
128         size_t size;
129         int loop, ret;
130
131         const unsigned limit =
132                 (PAGE_SIZE - sizeof(*klist)) / sizeof(struct key);
133
134         ret = 0;
135
136         /* find out how many keys are currently linked */
137         rcu_read_lock();
138         sklist = rcu_dereference(source->payload.subscriptions);
139         max = 0;
140         if (sklist)
141                 max = sklist->nkeys;
142         rcu_read_unlock();
143
144         /* allocate a new payload and stuff load with key links */
145         if (max > 0) {
146                 BUG_ON(max > limit);
147
148                 max = (max + 3) & ~3;
149                 if (max > limit)
150                         max = limit;
151
152                 ret = -ENOMEM;
153                 size = sizeof(*klist) + sizeof(struct key) * max;
154                 klist = kmalloc(size, GFP_KERNEL);
155                 if (!klist)
156                         goto error;
157
158                 /* set links */
159                 rcu_read_lock();
160                 sklist = rcu_dereference(source->payload.subscriptions);
161
162                 klist->maxkeys = max;
163                 klist->nkeys = sklist->nkeys;
164                 memcpy(klist->keys,
165                        sklist->keys,
166                        sklist->nkeys * sizeof(struct key));
167
168                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
169                         atomic_inc(&klist->keys[loop]->usage);
170
171                 rcu_read_unlock();
172
173                 rcu_assign_pointer(keyring->payload.subscriptions, klist);
174                 ret = 0;
175         }
176
177  error:
178         return ret;
179
180 } /* end keyring_duplicate() */
181
182 /*****************************************************************************/
183 /*
184  * match keyrings on their name
185  */
186 static int keyring_match(const struct key *keyring, const void *description)
187 {
188         return keyring->description &&
189                 strcmp(keyring->description, description) == 0;
190
191 } /* end keyring_match() */
192
193 /*****************************************************************************/
194 /*
195  * dispose of the data dangling from the corpse of a keyring
196  */
197 static void keyring_destroy(struct key *keyring)
198 {
199         struct keyring_list *klist;
200         int loop;
201
202         if (keyring->description) {
203                 write_lock(&keyring_name_lock);
204                 list_del(&keyring->type_data.link);
205                 write_unlock(&keyring_name_lock);
206         }
207
208         klist = rcu_dereference(keyring->payload.subscriptions);
209         if (klist) {
210                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
211                         key_put(klist->keys[loop]);
212                 kfree(klist);
213         }
214
215 } /* end keyring_destroy() */
216
217 /*****************************************************************************/
218 /*
219  * describe the keyring
220  */
221 static void keyring_describe(const struct key *keyring, struct seq_file *m)
222 {
223         struct keyring_list *klist;
224
225         if (keyring->description) {
226                 seq_puts(m, keyring->description);
227         }
228         else {
229                 seq_puts(m, "[anon]");
230         }
231
232         rcu_read_lock();
233         klist = rcu_dereference(keyring->payload.subscriptions);
234         if (klist)
235                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
236         else
237                 seq_puts(m, ": empty");
238         rcu_read_unlock();
239
240 } /* end keyring_describe() */
241
242 /*****************************************************************************/
243 /*
244  * read a list of key IDs from the keyring's contents
245  * - the keyring's semaphore is read-locked
246  */
247 static long keyring_read(const struct key *keyring,
248                          char __user *buffer, size_t buflen)
249 {
250         struct keyring_list *klist;
251         struct key *key;
252         size_t qty, tmp;
253         int loop, ret;
254
255         ret = 0;
256         klist = rcu_dereference(keyring->payload.subscriptions);
257
258         if (klist) {
259                 /* calculate how much data we could return */
260                 qty = klist->nkeys * sizeof(key_serial_t);
261
262                 if (buffer && buflen > 0) {
263                         if (buflen > qty)
264                                 buflen = qty;
265
266                         /* copy the IDs of the subscribed keys into the
267                          * buffer */
268                         ret = -EFAULT;
269
270                         for (loop = 0; loop < klist->nkeys; loop++) {
271                                 key = klist->keys[loop];
272
273                                 tmp = sizeof(key_serial_t);
274                                 if (tmp > buflen)
275                                         tmp = buflen;
276
277                                 if (copy_to_user(buffer,
278                                                  &key->serial,
279                                                  tmp) != 0)
280                                         goto error;
281
282                                 buflen -= tmp;
283                                 if (buflen == 0)
284                                         break;
285                                 buffer += tmp;
286                         }
287                 }
288
289                 ret = qty;
290         }
291
292  error:
293         return ret;
294
295 } /* end keyring_read() */
296
297 /*****************************************************************************/
298 /*
299  * allocate a keyring and link into the destination keyring
300  */
301 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
302                           int not_in_quota, struct key *dest)
303 {
304         struct key *keyring;
305         int ret;
306
307         keyring = key_alloc(&key_type_keyring, description,
308                             uid, gid, KEY_USR_ALL, not_in_quota);
309
310         if (!IS_ERR(keyring)) {
311                 ret = key_instantiate_and_link(keyring, NULL, 0, dest);
312                 if (ret < 0) {
313                         key_put(keyring);
314                         keyring = ERR_PTR(ret);
315                 }
316         }
317
318         return keyring;
319
320 } /* end keyring_alloc() */
321
322 /*****************************************************************************/
323 /*
324  * search the supplied keyring tree for a key that matches the criterion
325  * - perform a breadth-then-depth search up to the prescribed limit
326  * - we only find keys on which we have search permission
327  * - we use the supplied match function to see if the description (or other
328  *   feature of interest) matches
329  * - we readlock the keyrings as we search down the tree
330  * - we return -EAGAIN if we didn't find any matching key
331  * - we return -ENOKEY if we only found negative matching keys
332  */
333 struct key *keyring_search_aux(struct key *keyring,
334                                struct key_type *type,
335                                const void *description,
336                                key_match_func_t match)
337 {
338         struct {
339                 struct keyring_list *keylist;
340                 int kix;
341         } stack[KEYRING_SEARCH_MAX_DEPTH];
342
343         struct keyring_list *keylist;
344         struct timespec now;
345         struct key *key;
346         long err;
347         int sp, kix;
348
349         key_check(keyring);
350
351         rcu_read_lock();
352
353         /* top keyring must have search permission to begin the search */
354         key = ERR_PTR(-EACCES);
355         if (!key_permission(keyring, KEY_SEARCH))
356                 goto error;
357
358         key = ERR_PTR(-ENOTDIR);
359         if (keyring->type != &key_type_keyring)
360                 goto error;
361
362         now = current_kernel_time();
363         err = -EAGAIN;
364         sp = 0;
365
366         /* start processing a new keyring */
367  descend:
368         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
369                 goto not_this_keyring;
370
371         keylist = rcu_dereference(keyring->payload.subscriptions);
372         if (!keylist)
373                 goto not_this_keyring;
374
375         /* iterate through the keys in this keyring first */
376         for (kix = 0; kix < keylist->nkeys; kix++) {
377                 key = keylist->keys[kix];
378
379                 /* ignore keys not of this type */
380                 if (key->type != type)
381                         continue;
382
383                 /* skip revoked keys and expired keys */
384                 if (test_bit(KEY_FLAG_REVOKED, &key->flags))
385                         continue;
386
387                 if (key->expiry && now.tv_sec >= key->expiry)
388                         continue;
389
390                 /* keys that don't match */
391                 if (!match(key, description))
392                         continue;
393
394                 /* key must have search permissions */
395                 if (!key_permission(key, KEY_SEARCH))
396                         continue;
397
398                 /* we set a different error code if we find a negative key */
399                 if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
400                         err = -ENOKEY;
401                         continue;
402                 }
403
404                 goto found;
405         }
406
407         /* search through the keyrings nested in this one */
408         kix = 0;
409  ascend:
410         for (; kix < keylist->nkeys; kix++) {
411                 key = keylist->keys[kix];
412                 if (key->type != &key_type_keyring)
413                         continue;
414
415                 /* recursively search nested keyrings
416                  * - only search keyrings for which we have search permission
417                  */
418                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
419                         continue;
420
421                 if (!key_permission(key, KEY_SEARCH))
422                         continue;
423
424                 /* stack the current position */
425                 stack[sp].keylist = keylist;
426                 stack[sp].kix = kix;
427                 sp++;
428
429                 /* begin again with the new keyring */
430                 keyring = key;
431                 goto descend;
432         }
433
434         /* the keyring we're looking at was disqualified or didn't contain a
435          * matching key */
436  not_this_keyring:
437         if (sp > 0) {
438                 /* resume the processing of a keyring higher up in the tree */
439                 sp--;
440                 keylist = stack[sp].keylist;
441                 kix = stack[sp].kix + 1;
442                 goto ascend;
443         }
444
445         key = ERR_PTR(err);
446         goto error;
447
448         /* we found a viable match */
449  found:
450         atomic_inc(&key->usage);
451         key_check(key);
452  error:
453         rcu_read_unlock();
454         return key;
455
456 } /* end keyring_search_aux() */
457
458 /*****************************************************************************/
459 /*
460  * search the supplied keyring tree for a key that matches the criterion
461  * - perform a breadth-then-depth search up to the prescribed limit
462  * - we only find keys on which we have search permission
463  * - we readlock the keyrings as we search down the tree
464  * - we return -EAGAIN if we didn't find any matching key
465  * - we return -ENOKEY if we only found negative matching keys
466  */
467 struct key *keyring_search(struct key *keyring,
468                            struct key_type *type,
469                            const char *description)
470 {
471         return keyring_search_aux(keyring, type, description, type->match);
472
473 } /* end keyring_search() */
474
475 EXPORT_SYMBOL(keyring_search);
476
477 /*****************************************************************************/
478 /*
479  * search the given keyring only (no recursion)
480  * - keyring must be locked by caller
481  */
482 struct key *__keyring_search_one(struct key *keyring,
483                                  const struct key_type *ktype,
484                                  const char *description,
485                                  key_perm_t perm)
486 {
487         struct keyring_list *klist;
488         struct key *key;
489         int loop;
490
491         rcu_read_lock();
492
493         klist = rcu_dereference(keyring->payload.subscriptions);
494         if (klist) {
495                 for (loop = 0; loop < klist->nkeys; loop++) {
496                         key = klist->keys[loop];
497
498                         if (key->type == ktype &&
499                             key->type->match(key, description) &&
500                             key_permission(key, perm) &&
501                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
502                             )
503                                 goto found;
504                 }
505         }
506
507         key = ERR_PTR(-ENOKEY);
508         goto error;
509
510  found:
511         atomic_inc(&key->usage);
512  error:
513         rcu_read_unlock();
514         return key;
515
516 } /* end __keyring_search_one() */
517
518 /*****************************************************************************/
519 /*
520  * find a keyring with the specified name
521  * - all named keyrings are searched
522  * - only find keyrings with search permission for the process
523  * - only find keyrings with a serial number greater than the one specified
524  */
525 struct key *find_keyring_by_name(const char *name, key_serial_t bound)
526 {
527         struct key *keyring;
528         int bucket;
529
530         keyring = ERR_PTR(-EINVAL);
531         if (!name)
532                 goto error;
533
534         bucket = keyring_hash(name);
535
536         read_lock(&keyring_name_lock);
537
538         if (keyring_name_hash[bucket].next) {
539                 /* search this hash bucket for a keyring with a matching name
540                  * that's readable and that hasn't been revoked */
541                 list_for_each_entry(keyring,
542                                     &keyring_name_hash[bucket],
543                                     type_data.link
544                                     ) {
545                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
546                                 continue;
547
548                         if (strcmp(keyring->description, name) != 0)
549                                 continue;
550
551                         if (!key_permission(keyring, KEY_SEARCH))
552                                 continue;
553
554                         /* found a potential candidate, but we still need to
555                          * check the serial number */
556                         if (keyring->serial <= bound)
557                                 continue;
558
559                         /* we've got a match */
560                         atomic_inc(&keyring->usage);
561                         read_unlock(&keyring_name_lock);
562                         goto error;
563                 }
564         }
565
566         read_unlock(&keyring_name_lock);
567         keyring = ERR_PTR(-ENOKEY);
568
569  error:
570         return keyring;
571
572 } /* end find_keyring_by_name() */
573
574 /*****************************************************************************/
575 /*
576  * see if a cycle will will be created by inserting acyclic tree B in acyclic
577  * tree A at the topmost level (ie: as a direct child of A)
578  * - since we are adding B to A at the top level, checking for cycles should
579  *   just be a matter of seeing if node A is somewhere in tree B
580  */
581 static int keyring_detect_cycle(struct key *A, struct key *B)
582 {
583         struct {
584                 struct keyring_list *keylist;
585                 int kix;
586         } stack[KEYRING_SEARCH_MAX_DEPTH];
587
588         struct keyring_list *keylist;
589         struct key *subtree, *key;
590         int sp, kix, ret;
591
592         rcu_read_lock();
593
594         ret = -EDEADLK;
595         if (A == B)
596                 goto cycle_detected;
597
598         subtree = B;
599         sp = 0;
600
601         /* start processing a new keyring */
602  descend:
603         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
604                 goto not_this_keyring;
605
606         keylist = rcu_dereference(subtree->payload.subscriptions);
607         if (!keylist)
608                 goto not_this_keyring;
609         kix = 0;
610
611  ascend:
612         /* iterate through the remaining keys in this keyring */
613         for (; kix < keylist->nkeys; kix++) {
614                 key = keylist->keys[kix];
615
616                 if (key == A)
617                         goto cycle_detected;
618
619                 /* recursively check nested keyrings */
620                 if (key->type == &key_type_keyring) {
621                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
622                                 goto too_deep;
623
624                         /* stack the current position */
625                         stack[sp].keylist = keylist;
626                         stack[sp].kix = kix;
627                         sp++;
628
629                         /* begin again with the new keyring */
630                         subtree = key;
631                         goto descend;
632                 }
633         }
634
635         /* the keyring we're looking at was disqualified or didn't contain a
636          * matching key */
637  not_this_keyring:
638         if (sp > 0) {
639                 /* resume the checking of a keyring higher up in the tree */
640                 sp--;
641                 keylist = stack[sp].keylist;
642                 kix = stack[sp].kix + 1;
643                 goto ascend;
644         }
645
646         ret = 0; /* no cycles detected */
647
648  error:
649         rcu_read_unlock();
650         return ret;
651
652  too_deep:
653         ret = -ELOOP;
654         goto error;
655
656  cycle_detected:
657         ret = -EDEADLK;
658         goto error;
659
660 } /* end keyring_detect_cycle() */
661
662 /*****************************************************************************/
663 /*
664  * dispose of a keyring list after the RCU grace period
665  */
666 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
667 {
668         struct keyring_list *klist =
669                 container_of(rcu, struct keyring_list, rcu);
670
671         kfree(klist);
672
673 } /* end keyring_link_rcu_disposal() */
674
675 /*****************************************************************************/
676 /*
677  * link a key into to a keyring
678  * - must be called with the keyring's semaphore write-locked
679  */
680 int __key_link(struct key *keyring, struct key *key)
681 {
682         struct keyring_list *klist, *nklist;
683         unsigned max;
684         size_t size;
685         int ret;
686
687         ret = -EKEYREVOKED;
688         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
689                 goto error;
690
691         ret = -ENOTDIR;
692         if (keyring->type != &key_type_keyring)
693                 goto error;
694
695         /* serialise link/link calls to prevent parallel calls causing a
696          * cycle when applied to two keyring in opposite orders */
697         down_write(&keyring_serialise_link_sem);
698
699         /* check that we aren't going to create a cycle adding one keyring to
700          * another */
701         if (key->type == &key_type_keyring) {
702                 ret = keyring_detect_cycle(keyring, key);
703                 if (ret < 0)
704                         goto error2;
705         }
706
707         /* check that we aren't going to overrun the user's quota */
708         ret = key_payload_reserve(keyring,
709                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
710         if (ret < 0)
711                 goto error2;
712
713         klist = keyring->payload.subscriptions;
714
715         if (klist && klist->nkeys < klist->maxkeys) {
716                 /* there's sufficient slack space to add directly */
717                 atomic_inc(&key->usage);
718
719                 klist->keys[klist->nkeys] = key;
720                 smp_wmb();
721                 klist->nkeys++;
722                 smp_wmb();
723
724                 ret = 0;
725         }
726         else {
727                 /* grow the key list */
728                 max = 4;
729                 if (klist)
730                         max += klist->maxkeys;
731
732                 ret = -ENFILE;
733                 if (max > 65535)
734                         goto error3;
735                 size = sizeof(*klist) + sizeof(*key) * max;
736                 if (size > PAGE_SIZE)
737                         goto error3;
738
739                 ret = -ENOMEM;
740                 nklist = kmalloc(size, GFP_KERNEL);
741                 if (!nklist)
742                         goto error3;
743                 nklist->maxkeys = max;
744                 nklist->nkeys = 0;
745
746                 if (klist) {
747                         nklist->nkeys = klist->nkeys;
748                         memcpy(nklist->keys,
749                                klist->keys,
750                                sizeof(struct key *) * klist->nkeys);
751                 }
752
753                 /* add the key into the new space */
754                 atomic_inc(&key->usage);
755                 nklist->keys[nklist->nkeys++] = key;
756
757                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
758
759                 /* dispose of the old keyring list */
760                 if (klist)
761                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
762
763                 ret = 0;
764         }
765
766  error2:
767         up_write(&keyring_serialise_link_sem);
768  error:
769         return ret;
770
771  error3:
772         /* undo the quota changes */
773         key_payload_reserve(keyring,
774                             keyring->datalen - KEYQUOTA_LINK_BYTES);
775         goto error2;
776
777 } /* end __key_link() */
778
779 /*****************************************************************************/
780 /*
781  * link a key to a keyring
782  */
783 int key_link(struct key *keyring, struct key *key)
784 {
785         int ret;
786
787         key_check(keyring);
788         key_check(key);
789
790         down_write(&keyring->sem);
791         ret = __key_link(keyring, key);
792         up_write(&keyring->sem);
793
794         return ret;
795
796 } /* end key_link() */
797
798 EXPORT_SYMBOL(key_link);
799
800 /*****************************************************************************/
801 /*
802  * dispose of a keyring list after the RCU grace period, freeing the unlinked
803  * key
804  */
805 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
806 {
807         struct keyring_list *klist =
808                 container_of(rcu, struct keyring_list, rcu);
809
810         key_put(klist->keys[klist->delkey]);
811         kfree(klist);
812
813 } /* end keyring_unlink_rcu_disposal() */
814
815 /*****************************************************************************/
816 /*
817  * unlink the first link to a key from a keyring
818  */
819 int key_unlink(struct key *keyring, struct key *key)
820 {
821         struct keyring_list *klist, *nklist;
822         int loop, ret;
823
824         key_check(keyring);
825         key_check(key);
826
827         ret = -ENOTDIR;
828         if (keyring->type != &key_type_keyring)
829                 goto error;
830
831         down_write(&keyring->sem);
832
833         klist = keyring->payload.subscriptions;
834         if (klist) {
835                 /* search the keyring for the key */
836                 for (loop = 0; loop < klist->nkeys; loop++)
837                         if (klist->keys[loop] == key)
838                                 goto key_is_present;
839         }
840
841         up_write(&keyring->sem);
842         ret = -ENOENT;
843         goto error;
844
845 key_is_present:
846         /* we need to copy the key list for RCU purposes */
847         nklist = kmalloc(sizeof(*klist) + sizeof(*key) * klist->maxkeys,
848                          GFP_KERNEL);
849         if (!nklist)
850                 goto nomem;
851         nklist->maxkeys = klist->maxkeys;
852         nklist->nkeys = klist->nkeys - 1;
853
854         if (loop > 0)
855                 memcpy(&nklist->keys[0],
856                        &klist->keys[0],
857                        loop * sizeof(klist->keys[0]));
858
859         if (loop < nklist->nkeys)
860                 memcpy(&nklist->keys[loop],
861                        &klist->keys[loop + 1],
862                        (nklist->nkeys - loop) * sizeof(klist->keys[0]));
863
864         /* adjust the user's quota */
865         key_payload_reserve(keyring,
866                             keyring->datalen - KEYQUOTA_LINK_BYTES);
867
868         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
869
870         up_write(&keyring->sem);
871
872         /* schedule for later cleanup */
873         klist->delkey = loop;
874         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
875
876         ret = 0;
877
878 error:
879         return ret;
880 nomem:
881         ret = -ENOMEM;
882         up_write(&keyring->sem);
883         goto error;
884
885 } /* end key_unlink() */
886
887 EXPORT_SYMBOL(key_unlink);
888
889 /*****************************************************************************/
890 /*
891  * dispose of a keyring list after the RCU grace period, releasing the keys it
892  * links to
893  */
894 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
895 {
896         struct keyring_list *klist;
897         int loop;
898
899         klist = container_of(rcu, struct keyring_list, rcu);
900
901         for (loop = klist->nkeys - 1; loop >= 0; loop--)
902                 key_put(klist->keys[loop]);
903
904         kfree(klist);
905
906 } /* end keyring_clear_rcu_disposal() */
907
908 /*****************************************************************************/
909 /*
910  * clear the specified process keyring
911  * - implements keyctl(KEYCTL_CLEAR)
912  */
913 int keyring_clear(struct key *keyring)
914 {
915         struct keyring_list *klist;
916         int ret;
917
918         ret = -ENOTDIR;
919         if (keyring->type == &key_type_keyring) {
920                 /* detach the pointer block with the locks held */
921                 down_write(&keyring->sem);
922
923                 klist = keyring->payload.subscriptions;
924                 if (klist) {
925                         /* adjust the quota */
926                         key_payload_reserve(keyring,
927                                             sizeof(struct keyring_list));
928
929                         rcu_assign_pointer(keyring->payload.subscriptions,
930                                            NULL);
931                 }
932
933                 up_write(&keyring->sem);
934
935                 /* free the keys after the locks have been dropped */
936                 if (klist)
937                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
938
939                 ret = 0;
940         }
941
942         return ret;
943
944 } /* end keyring_clear() */
945
946 EXPORT_SYMBOL(keyring_clear);