SELinux: requesting no permissions in avc_has_perm_noaudit is a BUG()
[linux-2.6.git] / security / keys / keyring.c
1 /* keyring.c: keyring handling
2  *
3  * Copyright (C) 2004-5 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/security.h>
17 #include <linux/seq_file.h>
18 #include <linux/err.h>
19 #include <asm/uaccess.h>
20 #include "internal.h"
21
22 /*
23  * when plumbing the depths of the key tree, this sets a hard limit set on how
24  * deep we're willing to go
25  */
26 #define KEYRING_SEARCH_MAX_DEPTH 6
27
28 /*
29  * we keep all named keyrings in a hash to speed looking them up
30  */
31 #define KEYRING_NAME_HASH_SIZE  (1 << 5)
32
33 static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
34 static DEFINE_RWLOCK(keyring_name_lock);
35
36 static inline unsigned keyring_hash(const char *desc)
37 {
38         unsigned bucket = 0;
39
40         for (; *desc; desc++)
41                 bucket += (unsigned char) *desc;
42
43         return bucket & (KEYRING_NAME_HASH_SIZE - 1);
44 }
45
46 /*
47  * the keyring type definition
48  */
49 static int keyring_instantiate(struct key *keyring,
50                                const void *data, size_t datalen);
51 static int keyring_match(const struct key *keyring, const void *criterion);
52 static void keyring_revoke(struct key *keyring);
53 static void keyring_destroy(struct key *keyring);
54 static void keyring_describe(const struct key *keyring, struct seq_file *m);
55 static long keyring_read(const struct key *keyring,
56                          char __user *buffer, size_t buflen);
57
58 struct key_type key_type_keyring = {
59         .name           = "keyring",
60         .def_datalen    = sizeof(struct keyring_list),
61         .instantiate    = keyring_instantiate,
62         .match          = keyring_match,
63         .revoke         = keyring_revoke,
64         .destroy        = keyring_destroy,
65         .describe       = keyring_describe,
66         .read           = keyring_read,
67 };
68
69 EXPORT_SYMBOL(key_type_keyring);
70
71 /*
72  * semaphore to serialise link/link calls to prevent two link calls in parallel
73  * introducing a cycle
74  */
75 static DECLARE_RWSEM(keyring_serialise_link_sem);
76
77 /*****************************************************************************/
78 /*
79  * publish the name of a keyring so that it can be found by name (if it has
80  * one)
81  */
82 void keyring_publish_name(struct key *keyring)
83 {
84         int bucket;
85
86         if (keyring->description) {
87                 bucket = keyring_hash(keyring->description);
88
89                 write_lock(&keyring_name_lock);
90
91                 if (!keyring_name_hash[bucket].next)
92                         INIT_LIST_HEAD(&keyring_name_hash[bucket]);
93
94                 list_add_tail(&keyring->type_data.link,
95                               &keyring_name_hash[bucket]);
96
97                 write_unlock(&keyring_name_lock);
98         }
99
100 } /* end keyring_publish_name() */
101
102 /*****************************************************************************/
103 /*
104  * initialise a keyring
105  * - we object if we were given any data
106  */
107 static int keyring_instantiate(struct key *keyring,
108                                const void *data, size_t datalen)
109 {
110         int ret;
111
112         ret = -EINVAL;
113         if (datalen == 0) {
114                 /* make the keyring available by name if it has one */
115                 keyring_publish_name(keyring);
116                 ret = 0;
117         }
118
119         return ret;
120
121 } /* end keyring_instantiate() */
122
123 /*****************************************************************************/
124 /*
125  * match keyrings on their name
126  */
127 static int keyring_match(const struct key *keyring, const void *description)
128 {
129         return keyring->description &&
130                 strcmp(keyring->description, description) == 0;
131
132 } /* end keyring_match() */
133
134 /*****************************************************************************/
135 /*
136  * dispose of the data dangling from the corpse of a keyring
137  */
138 static void keyring_destroy(struct key *keyring)
139 {
140         struct keyring_list *klist;
141         int loop;
142
143         if (keyring->description) {
144                 write_lock(&keyring_name_lock);
145
146                 if (keyring->type_data.link.next != NULL &&
147                     !list_empty(&keyring->type_data.link))
148                         list_del(&keyring->type_data.link);
149
150                 write_unlock(&keyring_name_lock);
151         }
152
153         klist = rcu_dereference(keyring->payload.subscriptions);
154         if (klist) {
155                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
156                         key_put(klist->keys[loop]);
157                 kfree(klist);
158         }
159
160 } /* end keyring_destroy() */
161
162 /*****************************************************************************/
163 /*
164  * describe the keyring
165  */
166 static void keyring_describe(const struct key *keyring, struct seq_file *m)
167 {
168         struct keyring_list *klist;
169
170         if (keyring->description) {
171                 seq_puts(m, keyring->description);
172         }
173         else {
174                 seq_puts(m, "[anon]");
175         }
176
177         rcu_read_lock();
178         klist = rcu_dereference(keyring->payload.subscriptions);
179         if (klist)
180                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
181         else
182                 seq_puts(m, ": empty");
183         rcu_read_unlock();
184
185 } /* end keyring_describe() */
186
187 /*****************************************************************************/
188 /*
189  * read a list of key IDs from the keyring's contents
190  * - the keyring's semaphore is read-locked
191  */
192 static long keyring_read(const struct key *keyring,
193                          char __user *buffer, size_t buflen)
194 {
195         struct keyring_list *klist;
196         struct key *key;
197         size_t qty, tmp;
198         int loop, ret;
199
200         ret = 0;
201         klist = rcu_dereference(keyring->payload.subscriptions);
202
203         if (klist) {
204                 /* calculate how much data we could return */
205                 qty = klist->nkeys * sizeof(key_serial_t);
206
207                 if (buffer && buflen > 0) {
208                         if (buflen > qty)
209                                 buflen = qty;
210
211                         /* copy the IDs of the subscribed keys into the
212                          * buffer */
213                         ret = -EFAULT;
214
215                         for (loop = 0; loop < klist->nkeys; loop++) {
216                                 key = klist->keys[loop];
217
218                                 tmp = sizeof(key_serial_t);
219                                 if (tmp > buflen)
220                                         tmp = buflen;
221
222                                 if (copy_to_user(buffer,
223                                                  &key->serial,
224                                                  tmp) != 0)
225                                         goto error;
226
227                                 buflen -= tmp;
228                                 if (buflen == 0)
229                                         break;
230                                 buffer += tmp;
231                         }
232                 }
233
234                 ret = qty;
235         }
236
237  error:
238         return ret;
239
240 } /* end keyring_read() */
241
242 /*****************************************************************************/
243 /*
244  * allocate a keyring and link into the destination keyring
245  */
246 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
247                           struct task_struct *ctx, unsigned long flags,
248                           struct key *dest)
249 {
250         struct key *keyring;
251         int ret;
252
253         keyring = key_alloc(&key_type_keyring, description,
254                             uid, gid, ctx,
255                             (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
256                             flags);
257
258         if (!IS_ERR(keyring)) {
259                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
260                 if (ret < 0) {
261                         key_put(keyring);
262                         keyring = ERR_PTR(ret);
263                 }
264         }
265
266         return keyring;
267
268 } /* end keyring_alloc() */
269
270 /*****************************************************************************/
271 /*
272  * search the supplied keyring tree for a key that matches the criterion
273  * - perform a breadth-then-depth search up to the prescribed limit
274  * - we only find keys on which we have search permission
275  * - we use the supplied match function to see if the description (or other
276  *   feature of interest) matches
277  * - we rely on RCU to prevent the keyring lists from disappearing on us
278  * - we return -EAGAIN if we didn't find any matching key
279  * - we return -ENOKEY if we only found negative matching keys
280  * - we propagate the possession attribute from the keyring ref to the key ref
281  */
282 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
283                              struct task_struct *context,
284                              struct key_type *type,
285                              const void *description,
286                              key_match_func_t match)
287 {
288         struct {
289                 struct keyring_list *keylist;
290                 int kix;
291         } stack[KEYRING_SEARCH_MAX_DEPTH];
292
293         struct keyring_list *keylist;
294         struct timespec now;
295         unsigned long possessed;
296         struct key *keyring, *key;
297         key_ref_t key_ref;
298         long err;
299         int sp, kix;
300
301         keyring = key_ref_to_ptr(keyring_ref);
302         possessed = is_key_possessed(keyring_ref);
303         key_check(keyring);
304
305         /* top keyring must have search permission to begin the search */
306         err = key_task_permission(keyring_ref, context, KEY_SEARCH);
307         if (err < 0) {
308                 key_ref = ERR_PTR(err);
309                 goto error;
310         }
311
312         key_ref = ERR_PTR(-ENOTDIR);
313         if (keyring->type != &key_type_keyring)
314                 goto error;
315
316         rcu_read_lock();
317
318         now = current_kernel_time();
319         err = -EAGAIN;
320         sp = 0;
321
322         /* start processing a new keyring */
323 descend:
324         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
325                 goto not_this_keyring;
326
327         keylist = rcu_dereference(keyring->payload.subscriptions);
328         if (!keylist)
329                 goto not_this_keyring;
330
331         /* iterate through the keys in this keyring first */
332         for (kix = 0; kix < keylist->nkeys; kix++) {
333                 key = keylist->keys[kix];
334
335                 /* ignore keys not of this type */
336                 if (key->type != type)
337                         continue;
338
339                 /* skip revoked keys and expired keys */
340                 if (test_bit(KEY_FLAG_REVOKED, &key->flags))
341                         continue;
342
343                 if (key->expiry && now.tv_sec >= key->expiry)
344                         continue;
345
346                 /* keys that don't match */
347                 if (!match(key, description))
348                         continue;
349
350                 /* key must have search permissions */
351                 if (key_task_permission(make_key_ref(key, possessed),
352                                         context, KEY_SEARCH) < 0)
353                         continue;
354
355                 /* we set a different error code if we find a negative key */
356                 if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
357                         err = -ENOKEY;
358                         continue;
359                 }
360
361                 goto found;
362         }
363
364         /* search through the keyrings nested in this one */
365         kix = 0;
366 ascend:
367         for (; kix < keylist->nkeys; kix++) {
368                 key = keylist->keys[kix];
369                 if (key->type != &key_type_keyring)
370                         continue;
371
372                 /* recursively search nested keyrings
373                  * - only search keyrings for which we have search permission
374                  */
375                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
376                         continue;
377
378                 if (key_task_permission(make_key_ref(key, possessed),
379                                         context, KEY_SEARCH) < 0)
380                         continue;
381
382                 /* stack the current position */
383                 stack[sp].keylist = keylist;
384                 stack[sp].kix = kix;
385                 sp++;
386
387                 /* begin again with the new keyring */
388                 keyring = key;
389                 goto descend;
390         }
391
392         /* the keyring we're looking at was disqualified or didn't contain a
393          * matching key */
394 not_this_keyring:
395         if (sp > 0) {
396                 /* resume the processing of a keyring higher up in the tree */
397                 sp--;
398                 keylist = stack[sp].keylist;
399                 kix = stack[sp].kix + 1;
400                 goto ascend;
401         }
402
403         key_ref = ERR_PTR(err);
404         goto error_2;
405
406         /* we found a viable match */
407 found:
408         atomic_inc(&key->usage);
409         key_check(key);
410         key_ref = make_key_ref(key, possessed);
411 error_2:
412         rcu_read_unlock();
413 error:
414         return key_ref;
415
416 } /* end keyring_search_aux() */
417
418 /*****************************************************************************/
419 /*
420  * search the supplied keyring tree for a key that matches the criterion
421  * - perform a breadth-then-depth search up to the prescribed limit
422  * - we only find keys on which we have search permission
423  * - we readlock the keyrings as we search down the tree
424  * - we return -EAGAIN if we didn't find any matching key
425  * - we return -ENOKEY if we only found negative matching keys
426  */
427 key_ref_t keyring_search(key_ref_t keyring,
428                          struct key_type *type,
429                          const char *description)
430 {
431         if (!type->match)
432                 return ERR_PTR(-ENOKEY);
433
434         return keyring_search_aux(keyring, current,
435                                   type, description, type->match);
436
437 } /* end keyring_search() */
438
439 EXPORT_SYMBOL(keyring_search);
440
441 /*****************************************************************************/
442 /*
443  * search the given keyring only (no recursion)
444  * - keyring must be locked by caller
445  * - caller must guarantee that the keyring is a keyring
446  */
447 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
448                                const struct key_type *ktype,
449                                const char *description,
450                                key_perm_t perm)
451 {
452         struct keyring_list *klist;
453         unsigned long possessed;
454         struct key *keyring, *key;
455         int loop;
456
457         keyring = key_ref_to_ptr(keyring_ref);
458         possessed = is_key_possessed(keyring_ref);
459
460         rcu_read_lock();
461
462         klist = rcu_dereference(keyring->payload.subscriptions);
463         if (klist) {
464                 for (loop = 0; loop < klist->nkeys; loop++) {
465                         key = klist->keys[loop];
466
467                         if (key->type == ktype &&
468                             (!key->type->match ||
469                              key->type->match(key, description)) &&
470                             key_permission(make_key_ref(key, possessed),
471                                            perm) == 0 &&
472                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
473                             )
474                                 goto found;
475                 }
476         }
477
478         rcu_read_unlock();
479         return ERR_PTR(-ENOKEY);
480
481  found:
482         atomic_inc(&key->usage);
483         rcu_read_unlock();
484         return make_key_ref(key, possessed);
485
486 } /* end __keyring_search_one() */
487
488 /*****************************************************************************/
489 /*
490  * find a keyring with the specified name
491  * - all named keyrings are searched
492  * - only find keyrings with search permission for the process
493  * - only find keyrings with a serial number greater than the one specified
494  */
495 struct key *find_keyring_by_name(const char *name, key_serial_t bound)
496 {
497         struct key *keyring;
498         int bucket;
499
500         keyring = ERR_PTR(-EINVAL);
501         if (!name)
502                 goto error;
503
504         bucket = keyring_hash(name);
505
506         read_lock(&keyring_name_lock);
507
508         if (keyring_name_hash[bucket].next) {
509                 /* search this hash bucket for a keyring with a matching name
510                  * that's readable and that hasn't been revoked */
511                 list_for_each_entry(keyring,
512                                     &keyring_name_hash[bucket],
513                                     type_data.link
514                                     ) {
515                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
516                                 continue;
517
518                         if (strcmp(keyring->description, name) != 0)
519                                 continue;
520
521                         if (key_permission(make_key_ref(keyring, 0),
522                                            KEY_SEARCH) < 0)
523                                 continue;
524
525                         /* found a potential candidate, but we still need to
526                          * check the serial number */
527                         if (keyring->serial <= bound)
528                                 continue;
529
530                         /* we've got a match */
531                         atomic_inc(&keyring->usage);
532                         read_unlock(&keyring_name_lock);
533                         goto error;
534                 }
535         }
536
537         read_unlock(&keyring_name_lock);
538         keyring = ERR_PTR(-ENOKEY);
539
540  error:
541         return keyring;
542
543 } /* end find_keyring_by_name() */
544
545 /*****************************************************************************/
546 /*
547  * see if a cycle will will be created by inserting acyclic tree B in acyclic
548  * tree A at the topmost level (ie: as a direct child of A)
549  * - since we are adding B to A at the top level, checking for cycles should
550  *   just be a matter of seeing if node A is somewhere in tree B
551  */
552 static int keyring_detect_cycle(struct key *A, struct key *B)
553 {
554         struct {
555                 struct keyring_list *keylist;
556                 int kix;
557         } stack[KEYRING_SEARCH_MAX_DEPTH];
558
559         struct keyring_list *keylist;
560         struct key *subtree, *key;
561         int sp, kix, ret;
562
563         rcu_read_lock();
564
565         ret = -EDEADLK;
566         if (A == B)
567                 goto cycle_detected;
568
569         subtree = B;
570         sp = 0;
571
572         /* start processing a new keyring */
573  descend:
574         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
575                 goto not_this_keyring;
576
577         keylist = rcu_dereference(subtree->payload.subscriptions);
578         if (!keylist)
579                 goto not_this_keyring;
580         kix = 0;
581
582  ascend:
583         /* iterate through the remaining keys in this keyring */
584         for (; kix < keylist->nkeys; kix++) {
585                 key = keylist->keys[kix];
586
587                 if (key == A)
588                         goto cycle_detected;
589
590                 /* recursively check nested keyrings */
591                 if (key->type == &key_type_keyring) {
592                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
593                                 goto too_deep;
594
595                         /* stack the current position */
596                         stack[sp].keylist = keylist;
597                         stack[sp].kix = kix;
598                         sp++;
599
600                         /* begin again with the new keyring */
601                         subtree = key;
602                         goto descend;
603                 }
604         }
605
606         /* the keyring we're looking at was disqualified or didn't contain a
607          * matching key */
608  not_this_keyring:
609         if (sp > 0) {
610                 /* resume the checking of a keyring higher up in the tree */
611                 sp--;
612                 keylist = stack[sp].keylist;
613                 kix = stack[sp].kix + 1;
614                 goto ascend;
615         }
616
617         ret = 0; /* no cycles detected */
618
619  error:
620         rcu_read_unlock();
621         return ret;
622
623  too_deep:
624         ret = -ELOOP;
625         goto error;
626
627  cycle_detected:
628         ret = -EDEADLK;
629         goto error;
630
631 } /* end keyring_detect_cycle() */
632
633 /*****************************************************************************/
634 /*
635  * dispose of a keyring list after the RCU grace period
636  */
637 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
638 {
639         struct keyring_list *klist =
640                 container_of(rcu, struct keyring_list, rcu);
641
642         kfree(klist);
643
644 } /* end keyring_link_rcu_disposal() */
645
646 /*****************************************************************************/
647 /*
648  * dispose of a keyring list after the RCU grace period, freeing the unlinked
649  * key
650  */
651 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
652 {
653         struct keyring_list *klist =
654                 container_of(rcu, struct keyring_list, rcu);
655
656         key_put(klist->keys[klist->delkey]);
657         kfree(klist);
658
659 } /* end keyring_unlink_rcu_disposal() */
660
661 /*****************************************************************************/
662 /*
663  * link a key into to a keyring
664  * - must be called with the keyring's semaphore write-locked
665  * - discard already extant link to matching key if there is one
666  */
667 int __key_link(struct key *keyring, struct key *key)
668 {
669         struct keyring_list *klist, *nklist;
670         unsigned max;
671         size_t size;
672         int loop, ret;
673
674         ret = -EKEYREVOKED;
675         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
676                 goto error;
677
678         ret = -ENOTDIR;
679         if (keyring->type != &key_type_keyring)
680                 goto error;
681
682         /* serialise link/link calls to prevent parallel calls causing a
683          * cycle when applied to two keyring in opposite orders */
684         down_write(&keyring_serialise_link_sem);
685
686         /* check that we aren't going to create a cycle adding one keyring to
687          * another */
688         if (key->type == &key_type_keyring) {
689                 ret = keyring_detect_cycle(keyring, key);
690                 if (ret < 0)
691                         goto error2;
692         }
693
694         /* see if there's a matching key we can displace */
695         klist = keyring->payload.subscriptions;
696
697         if (klist && klist->nkeys > 0) {
698                 struct key_type *type = key->type;
699
700                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
701                         if (klist->keys[loop]->type == type &&
702                             strcmp(klist->keys[loop]->description,
703                                    key->description) == 0
704                             ) {
705                                 /* found a match - replace with new key */
706                                 size = sizeof(struct key *) * klist->maxkeys;
707                                 size += sizeof(*klist);
708                                 BUG_ON(size > PAGE_SIZE);
709
710                                 ret = -ENOMEM;
711                                 nklist = kmemdup(klist, size, GFP_KERNEL);
712                                 if (!nklist)
713                                         goto error2;
714
715                                 /* replace matched key */
716                                 atomic_inc(&key->usage);
717                                 nklist->keys[loop] = key;
718
719                                 rcu_assign_pointer(
720                                         keyring->payload.subscriptions,
721                                         nklist);
722
723                                 /* dispose of the old keyring list and the
724                                  * displaced key */
725                                 klist->delkey = loop;
726                                 call_rcu(&klist->rcu,
727                                          keyring_unlink_rcu_disposal);
728
729                                 goto done;
730                         }
731                 }
732         }
733
734         /* check that we aren't going to overrun the user's quota */
735         ret = key_payload_reserve(keyring,
736                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
737         if (ret < 0)
738                 goto error2;
739
740         klist = keyring->payload.subscriptions;
741
742         if (klist && klist->nkeys < klist->maxkeys) {
743                 /* there's sufficient slack space to add directly */
744                 atomic_inc(&key->usage);
745
746                 klist->keys[klist->nkeys] = key;
747                 smp_wmb();
748                 klist->nkeys++;
749                 smp_wmb();
750         }
751         else {
752                 /* grow the key list */
753                 max = 4;
754                 if (klist)
755                         max += klist->maxkeys;
756
757                 ret = -ENFILE;
758                 if (max > 65535)
759                         goto error3;
760                 size = sizeof(*klist) + sizeof(struct key *) * max;
761                 if (size > PAGE_SIZE)
762                         goto error3;
763
764                 ret = -ENOMEM;
765                 nklist = kmalloc(size, GFP_KERNEL);
766                 if (!nklist)
767                         goto error3;
768                 nklist->maxkeys = max;
769                 nklist->nkeys = 0;
770
771                 if (klist) {
772                         nklist->nkeys = klist->nkeys;
773                         memcpy(nklist->keys,
774                                klist->keys,
775                                sizeof(struct key *) * klist->nkeys);
776                 }
777
778                 /* add the key into the new space */
779                 atomic_inc(&key->usage);
780                 nklist->keys[nklist->nkeys++] = key;
781
782                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
783
784                 /* dispose of the old keyring list */
785                 if (klist)
786                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
787         }
788
789 done:
790         ret = 0;
791 error2:
792         up_write(&keyring_serialise_link_sem);
793 error:
794         return ret;
795
796 error3:
797         /* undo the quota changes */
798         key_payload_reserve(keyring,
799                             keyring->datalen - KEYQUOTA_LINK_BYTES);
800         goto error2;
801
802 } /* end __key_link() */
803
804 /*****************************************************************************/
805 /*
806  * link a key to a keyring
807  */
808 int key_link(struct key *keyring, struct key *key)
809 {
810         int ret;
811
812         key_check(keyring);
813         key_check(key);
814
815         down_write(&keyring->sem);
816         ret = __key_link(keyring, key);
817         up_write(&keyring->sem);
818
819         return ret;
820
821 } /* end key_link() */
822
823 EXPORT_SYMBOL(key_link);
824
825 /*****************************************************************************/
826 /*
827  * unlink the first link to a key from a keyring
828  */
829 int key_unlink(struct key *keyring, struct key *key)
830 {
831         struct keyring_list *klist, *nklist;
832         int loop, ret;
833
834         key_check(keyring);
835         key_check(key);
836
837         ret = -ENOTDIR;
838         if (keyring->type != &key_type_keyring)
839                 goto error;
840
841         down_write(&keyring->sem);
842
843         klist = keyring->payload.subscriptions;
844         if (klist) {
845                 /* search the keyring for the key */
846                 for (loop = 0; loop < klist->nkeys; loop++)
847                         if (klist->keys[loop] == key)
848                                 goto key_is_present;
849         }
850
851         up_write(&keyring->sem);
852         ret = -ENOENT;
853         goto error;
854
855 key_is_present:
856         /* we need to copy the key list for RCU purposes */
857         nklist = kmalloc(sizeof(*klist) +
858                          sizeof(struct key *) * klist->maxkeys,
859                          GFP_KERNEL);
860         if (!nklist)
861                 goto nomem;
862         nklist->maxkeys = klist->maxkeys;
863         nklist->nkeys = klist->nkeys - 1;
864
865         if (loop > 0)
866                 memcpy(&nklist->keys[0],
867                        &klist->keys[0],
868                        loop * sizeof(struct key *));
869
870         if (loop < nklist->nkeys)
871                 memcpy(&nklist->keys[loop],
872                        &klist->keys[loop + 1],
873                        (nklist->nkeys - loop) * sizeof(struct key *));
874
875         /* adjust the user's quota */
876         key_payload_reserve(keyring,
877                             keyring->datalen - KEYQUOTA_LINK_BYTES);
878
879         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
880
881         up_write(&keyring->sem);
882
883         /* schedule for later cleanup */
884         klist->delkey = loop;
885         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
886
887         ret = 0;
888
889 error:
890         return ret;
891 nomem:
892         ret = -ENOMEM;
893         up_write(&keyring->sem);
894         goto error;
895
896 } /* end key_unlink() */
897
898 EXPORT_SYMBOL(key_unlink);
899
900 /*****************************************************************************/
901 /*
902  * dispose of a keyring list after the RCU grace period, releasing the keys it
903  * links to
904  */
905 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
906 {
907         struct keyring_list *klist;
908         int loop;
909
910         klist = container_of(rcu, struct keyring_list, rcu);
911
912         for (loop = klist->nkeys - 1; loop >= 0; loop--)
913                 key_put(klist->keys[loop]);
914
915         kfree(klist);
916
917 } /* end keyring_clear_rcu_disposal() */
918
919 /*****************************************************************************/
920 /*
921  * clear the specified process keyring
922  * - implements keyctl(KEYCTL_CLEAR)
923  */
924 int keyring_clear(struct key *keyring)
925 {
926         struct keyring_list *klist;
927         int ret;
928
929         ret = -ENOTDIR;
930         if (keyring->type == &key_type_keyring) {
931                 /* detach the pointer block with the locks held */
932                 down_write(&keyring->sem);
933
934                 klist = keyring->payload.subscriptions;
935                 if (klist) {
936                         /* adjust the quota */
937                         key_payload_reserve(keyring,
938                                             sizeof(struct keyring_list));
939
940                         rcu_assign_pointer(keyring->payload.subscriptions,
941                                            NULL);
942                 }
943
944                 up_write(&keyring->sem);
945
946                 /* free the keys after the locks have been dropped */
947                 if (klist)
948                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
949
950                 ret = 0;
951         }
952
953         return ret;
954
955 } /* end keyring_clear() */
956
957 EXPORT_SYMBOL(keyring_clear);
958
959 /*****************************************************************************/
960 /*
961  * dispose of the links from a revoked keyring
962  * - called with the key sem write-locked
963  */
964 static void keyring_revoke(struct key *keyring)
965 {
966         struct keyring_list *klist = keyring->payload.subscriptions;
967
968         /* adjust the quota */
969         key_payload_reserve(keyring, 0);
970
971         if (klist) {
972                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
973                 call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
974         }
975
976 } /* end keyring_revoke() */