Merge branch 'audit.b21' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/audit...
[linux-3.10.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_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         .match          = keyring_match,
62         .destroy        = keyring_destroy,
63         .describe       = keyring_describe,
64         .read           = keyring_read,
65 };
66
67 /*
68  * semaphore to serialise link/link calls to prevent two link calls in parallel
69  * introducing a cycle
70  */
71 static DECLARE_RWSEM(keyring_serialise_link_sem);
72
73 /*****************************************************************************/
74 /*
75  * publish the name of a keyring so that it can be found by name (if it has
76  * one)
77  */
78 void keyring_publish_name(struct key *keyring)
79 {
80         int bucket;
81
82         if (keyring->description) {
83                 bucket = keyring_hash(keyring->description);
84
85                 write_lock(&keyring_name_lock);
86
87                 if (!keyring_name_hash[bucket].next)
88                         INIT_LIST_HEAD(&keyring_name_hash[bucket]);
89
90                 list_add_tail(&keyring->type_data.link,
91                               &keyring_name_hash[bucket]);
92
93                 write_unlock(&keyring_name_lock);
94         }
95
96 } /* end keyring_publish_name() */
97
98 /*****************************************************************************/
99 /*
100  * initialise a keyring
101  * - we object if we were given any data
102  */
103 static int keyring_instantiate(struct key *keyring,
104                                const void *data, size_t datalen)
105 {
106         int ret;
107
108         ret = -EINVAL;
109         if (datalen == 0) {
110                 /* make the keyring available by name if it has one */
111                 keyring_publish_name(keyring);
112                 ret = 0;
113         }
114
115         return ret;
116
117 } /* end keyring_instantiate() */
118
119 /*****************************************************************************/
120 /*
121  * match keyrings on their name
122  */
123 static int keyring_match(const struct key *keyring, const void *description)
124 {
125         return keyring->description &&
126                 strcmp(keyring->description, description) == 0;
127
128 } /* end keyring_match() */
129
130 /*****************************************************************************/
131 /*
132  * dispose of the data dangling from the corpse of a keyring
133  */
134 static void keyring_destroy(struct key *keyring)
135 {
136         struct keyring_list *klist;
137         int loop;
138
139         if (keyring->description) {
140                 write_lock(&keyring_name_lock);
141
142                 if (keyring->type_data.link.next != NULL &&
143                     !list_empty(&keyring->type_data.link))
144                         list_del(&keyring->type_data.link);
145
146                 write_unlock(&keyring_name_lock);
147         }
148
149         klist = rcu_dereference(keyring->payload.subscriptions);
150         if (klist) {
151                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
152                         key_put(klist->keys[loop]);
153                 kfree(klist);
154         }
155
156 } /* end keyring_destroy() */
157
158 /*****************************************************************************/
159 /*
160  * describe the keyring
161  */
162 static void keyring_describe(const struct key *keyring, struct seq_file *m)
163 {
164         struct keyring_list *klist;
165
166         if (keyring->description) {
167                 seq_puts(m, keyring->description);
168         }
169         else {
170                 seq_puts(m, "[anon]");
171         }
172
173         rcu_read_lock();
174         klist = rcu_dereference(keyring->payload.subscriptions);
175         if (klist)
176                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
177         else
178                 seq_puts(m, ": empty");
179         rcu_read_unlock();
180
181 } /* end keyring_describe() */
182
183 /*****************************************************************************/
184 /*
185  * read a list of key IDs from the keyring's contents
186  * - the keyring's semaphore is read-locked
187  */
188 static long keyring_read(const struct key *keyring,
189                          char __user *buffer, size_t buflen)
190 {
191         struct keyring_list *klist;
192         struct key *key;
193         size_t qty, tmp;
194         int loop, ret;
195
196         ret = 0;
197         klist = rcu_dereference(keyring->payload.subscriptions);
198
199         if (klist) {
200                 /* calculate how much data we could return */
201                 qty = klist->nkeys * sizeof(key_serial_t);
202
203                 if (buffer && buflen > 0) {
204                         if (buflen > qty)
205                                 buflen = qty;
206
207                         /* copy the IDs of the subscribed keys into the
208                          * buffer */
209                         ret = -EFAULT;
210
211                         for (loop = 0; loop < klist->nkeys; loop++) {
212                                 key = klist->keys[loop];
213
214                                 tmp = sizeof(key_serial_t);
215                                 if (tmp > buflen)
216                                         tmp = buflen;
217
218                                 if (copy_to_user(buffer,
219                                                  &key->serial,
220                                                  tmp) != 0)
221                                         goto error;
222
223                                 buflen -= tmp;
224                                 if (buflen == 0)
225                                         break;
226                                 buffer += tmp;
227                         }
228                 }
229
230                 ret = qty;
231         }
232
233  error:
234         return ret;
235
236 } /* end keyring_read() */
237
238 /*****************************************************************************/
239 /*
240  * allocate a keyring and link into the destination keyring
241  */
242 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
243                           int not_in_quota, struct key *dest)
244 {
245         struct key *keyring;
246         int ret;
247
248         keyring = key_alloc(&key_type_keyring, description,
249                             uid, gid,
250                             (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
251                             not_in_quota);
252
253         if (!IS_ERR(keyring)) {
254                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
255                 if (ret < 0) {
256                         key_put(keyring);
257                         keyring = ERR_PTR(ret);
258                 }
259         }
260
261         return keyring;
262
263 } /* end keyring_alloc() */
264
265 /*****************************************************************************/
266 /*
267  * search the supplied keyring tree for a key that matches the criterion
268  * - perform a breadth-then-depth search up to the prescribed limit
269  * - we only find keys on which we have search permission
270  * - we use the supplied match function to see if the description (or other
271  *   feature of interest) matches
272  * - we rely on RCU to prevent the keyring lists from disappearing on us
273  * - we return -EAGAIN if we didn't find any matching key
274  * - we return -ENOKEY if we only found negative matching keys
275  * - we propagate the possession attribute from the keyring ref to the key ref
276  */
277 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
278                              struct task_struct *context,
279                              struct key_type *type,
280                              const void *description,
281                              key_match_func_t match)
282 {
283         struct {
284                 struct keyring_list *keylist;
285                 int kix;
286         } stack[KEYRING_SEARCH_MAX_DEPTH];
287
288         struct keyring_list *keylist;
289         struct timespec now;
290         unsigned long possessed;
291         struct key *keyring, *key;
292         key_ref_t key_ref;
293         long err;
294         int sp, kix;
295
296         keyring = key_ref_to_ptr(keyring_ref);
297         possessed = is_key_possessed(keyring_ref);
298         key_check(keyring);
299
300         /* top keyring must have search permission to begin the search */
301         err = key_task_permission(keyring_ref, context, KEY_SEARCH);
302         if (err < 0) {
303                 key_ref = ERR_PTR(err);
304                 goto error;
305         }
306
307         key_ref = ERR_PTR(-ENOTDIR);
308         if (keyring->type != &key_type_keyring)
309                 goto error;
310
311         rcu_read_lock();
312
313         now = current_kernel_time();
314         err = -EAGAIN;
315         sp = 0;
316
317         /* start processing a new keyring */
318 descend:
319         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
320                 goto not_this_keyring;
321
322         keylist = rcu_dereference(keyring->payload.subscriptions);
323         if (!keylist)
324                 goto not_this_keyring;
325
326         /* iterate through the keys in this keyring first */
327         for (kix = 0; kix < keylist->nkeys; kix++) {
328                 key = keylist->keys[kix];
329
330                 /* ignore keys not of this type */
331                 if (key->type != type)
332                         continue;
333
334                 /* skip revoked keys and expired keys */
335                 if (test_bit(KEY_FLAG_REVOKED, &key->flags))
336                         continue;
337
338                 if (key->expiry && now.tv_sec >= key->expiry)
339                         continue;
340
341                 /* keys that don't match */
342                 if (!match(key, description))
343                         continue;
344
345                 /* key must have search permissions */
346                 if (key_task_permission(make_key_ref(key, possessed),
347                                         context, KEY_SEARCH) < 0)
348                         continue;
349
350                 /* we set a different error code if we find a negative key */
351                 if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
352                         err = -ENOKEY;
353                         continue;
354                 }
355
356                 goto found;
357         }
358
359         /* search through the keyrings nested in this one */
360         kix = 0;
361 ascend:
362         for (; kix < keylist->nkeys; kix++) {
363                 key = keylist->keys[kix];
364                 if (key->type != &key_type_keyring)
365                         continue;
366
367                 /* recursively search nested keyrings
368                  * - only search keyrings for which we have search permission
369                  */
370                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
371                         continue;
372
373                 if (key_task_permission(make_key_ref(key, possessed),
374                                         context, KEY_SEARCH) < 0)
375                         continue;
376
377                 /* stack the current position */
378                 stack[sp].keylist = keylist;
379                 stack[sp].kix = kix;
380                 sp++;
381
382                 /* begin again with the new keyring */
383                 keyring = key;
384                 goto descend;
385         }
386
387         /* the keyring we're looking at was disqualified or didn't contain a
388          * matching key */
389 not_this_keyring:
390         if (sp > 0) {
391                 /* resume the processing of a keyring higher up in the tree */
392                 sp--;
393                 keylist = stack[sp].keylist;
394                 kix = stack[sp].kix + 1;
395                 goto ascend;
396         }
397
398         key_ref = ERR_PTR(err);
399         goto error_2;
400
401         /* we found a viable match */
402 found:
403         atomic_inc(&key->usage);
404         key_check(key);
405         key_ref = make_key_ref(key, possessed);
406 error_2:
407         rcu_read_unlock();
408 error:
409         return key_ref;
410
411 } /* end keyring_search_aux() */
412
413 /*****************************************************************************/
414 /*
415  * search the supplied keyring tree for a key that matches the criterion
416  * - perform a breadth-then-depth search up to the prescribed limit
417  * - we only find keys on which we have search permission
418  * - we readlock the keyrings as we search down the tree
419  * - we return -EAGAIN if we didn't find any matching key
420  * - we return -ENOKEY if we only found negative matching keys
421  */
422 key_ref_t keyring_search(key_ref_t keyring,
423                          struct key_type *type,
424                          const char *description)
425 {
426         if (!type->match)
427                 return ERR_PTR(-ENOKEY);
428
429         return keyring_search_aux(keyring, current,
430                                   type, description, type->match);
431
432 } /* end keyring_search() */
433
434 EXPORT_SYMBOL(keyring_search);
435
436 /*****************************************************************************/
437 /*
438  * search the given keyring only (no recursion)
439  * - keyring must be locked by caller
440  * - caller must guarantee that the keyring is a keyring
441  */
442 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
443                                const struct key_type *ktype,
444                                const char *description,
445                                key_perm_t perm)
446 {
447         struct keyring_list *klist;
448         unsigned long possessed;
449         struct key *keyring, *key;
450         int loop;
451
452         keyring = key_ref_to_ptr(keyring_ref);
453         possessed = is_key_possessed(keyring_ref);
454
455         rcu_read_lock();
456
457         klist = rcu_dereference(keyring->payload.subscriptions);
458         if (klist) {
459                 for (loop = 0; loop < klist->nkeys; loop++) {
460                         key = klist->keys[loop];
461
462                         if (key->type == ktype &&
463                             (!key->type->match ||
464                              key->type->match(key, description)) &&
465                             key_permission(make_key_ref(key, possessed),
466                                            perm) == 0 &&
467                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
468                             )
469                                 goto found;
470                 }
471         }
472
473         rcu_read_unlock();
474         return ERR_PTR(-ENOKEY);
475
476  found:
477         atomic_inc(&key->usage);
478         rcu_read_unlock();
479         return make_key_ref(key, possessed);
480
481 } /* end __keyring_search_one() */
482
483 /*****************************************************************************/
484 /*
485  * find a keyring with the specified name
486  * - all named keyrings are searched
487  * - only find keyrings with search permission for the process
488  * - only find keyrings with a serial number greater than the one specified
489  */
490 struct key *find_keyring_by_name(const char *name, key_serial_t bound)
491 {
492         struct key *keyring;
493         int bucket;
494
495         keyring = ERR_PTR(-EINVAL);
496         if (!name)
497                 goto error;
498
499         bucket = keyring_hash(name);
500
501         read_lock(&keyring_name_lock);
502
503         if (keyring_name_hash[bucket].next) {
504                 /* search this hash bucket for a keyring with a matching name
505                  * that's readable and that hasn't been revoked */
506                 list_for_each_entry(keyring,
507                                     &keyring_name_hash[bucket],
508                                     type_data.link
509                                     ) {
510                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
511                                 continue;
512
513                         if (strcmp(keyring->description, name) != 0)
514                                 continue;
515
516                         if (key_permission(make_key_ref(keyring, 0),
517                                            KEY_SEARCH) < 0)
518                                 continue;
519
520                         /* found a potential candidate, but we still need to
521                          * check the serial number */
522                         if (keyring->serial <= bound)
523                                 continue;
524
525                         /* we've got a match */
526                         atomic_inc(&keyring->usage);
527                         read_unlock(&keyring_name_lock);
528                         goto error;
529                 }
530         }
531
532         read_unlock(&keyring_name_lock);
533         keyring = ERR_PTR(-ENOKEY);
534
535  error:
536         return keyring;
537
538 } /* end find_keyring_by_name() */
539
540 /*****************************************************************************/
541 /*
542  * see if a cycle will will be created by inserting acyclic tree B in acyclic
543  * tree A at the topmost level (ie: as a direct child of A)
544  * - since we are adding B to A at the top level, checking for cycles should
545  *   just be a matter of seeing if node A is somewhere in tree B
546  */
547 static int keyring_detect_cycle(struct key *A, struct key *B)
548 {
549         struct {
550                 struct keyring_list *keylist;
551                 int kix;
552         } stack[KEYRING_SEARCH_MAX_DEPTH];
553
554         struct keyring_list *keylist;
555         struct key *subtree, *key;
556         int sp, kix, ret;
557
558         rcu_read_lock();
559
560         ret = -EDEADLK;
561         if (A == B)
562                 goto cycle_detected;
563
564         subtree = B;
565         sp = 0;
566
567         /* start processing a new keyring */
568  descend:
569         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
570                 goto not_this_keyring;
571
572         keylist = rcu_dereference(subtree->payload.subscriptions);
573         if (!keylist)
574                 goto not_this_keyring;
575         kix = 0;
576
577  ascend:
578         /* iterate through the remaining keys in this keyring */
579         for (; kix < keylist->nkeys; kix++) {
580                 key = keylist->keys[kix];
581
582                 if (key == A)
583                         goto cycle_detected;
584
585                 /* recursively check nested keyrings */
586                 if (key->type == &key_type_keyring) {
587                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
588                                 goto too_deep;
589
590                         /* stack the current position */
591                         stack[sp].keylist = keylist;
592                         stack[sp].kix = kix;
593                         sp++;
594
595                         /* begin again with the new keyring */
596                         subtree = key;
597                         goto descend;
598                 }
599         }
600
601         /* the keyring we're looking at was disqualified or didn't contain a
602          * matching key */
603  not_this_keyring:
604         if (sp > 0) {
605                 /* resume the checking of a keyring higher up in the tree */
606                 sp--;
607                 keylist = stack[sp].keylist;
608                 kix = stack[sp].kix + 1;
609                 goto ascend;
610         }
611
612         ret = 0; /* no cycles detected */
613
614  error:
615         rcu_read_unlock();
616         return ret;
617
618  too_deep:
619         ret = -ELOOP;
620         goto error;
621
622  cycle_detected:
623         ret = -EDEADLK;
624         goto error;
625
626 } /* end keyring_detect_cycle() */
627
628 /*****************************************************************************/
629 /*
630  * dispose of a keyring list after the RCU grace period
631  */
632 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
633 {
634         struct keyring_list *klist =
635                 container_of(rcu, struct keyring_list, rcu);
636
637         kfree(klist);
638
639 } /* end keyring_link_rcu_disposal() */
640
641 /*****************************************************************************/
642 /*
643  * dispose of a keyring list after the RCU grace period, freeing the unlinked
644  * key
645  */
646 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
647 {
648         struct keyring_list *klist =
649                 container_of(rcu, struct keyring_list, rcu);
650
651         key_put(klist->keys[klist->delkey]);
652         kfree(klist);
653
654 } /* end keyring_unlink_rcu_disposal() */
655
656 /*****************************************************************************/
657 /*
658  * link a key into to a keyring
659  * - must be called with the keyring's semaphore write-locked
660  * - discard already extant link to matching key if there is one
661  */
662 int __key_link(struct key *keyring, struct key *key)
663 {
664         struct keyring_list *klist, *nklist;
665         unsigned max;
666         size_t size;
667         int loop, ret;
668
669         ret = -EKEYREVOKED;
670         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
671                 goto error;
672
673         ret = -ENOTDIR;
674         if (keyring->type != &key_type_keyring)
675                 goto error;
676
677         /* serialise link/link calls to prevent parallel calls causing a
678          * cycle when applied to two keyring in opposite orders */
679         down_write(&keyring_serialise_link_sem);
680
681         /* check that we aren't going to create a cycle adding one keyring to
682          * another */
683         if (key->type == &key_type_keyring) {
684                 ret = keyring_detect_cycle(keyring, key);
685                 if (ret < 0)
686                         goto error2;
687         }
688
689         /* see if there's a matching key we can displace */
690         klist = keyring->payload.subscriptions;
691
692         if (klist && klist->nkeys > 0) {
693                 struct key_type *type = key->type;
694
695                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
696                         if (klist->keys[loop]->type == type &&
697                             strcmp(klist->keys[loop]->description,
698                                    key->description) == 0
699                             ) {
700                                 /* found a match - replace with new key */
701                                 size = sizeof(struct key *) * klist->maxkeys;
702                                 size += sizeof(*klist);
703                                 BUG_ON(size > PAGE_SIZE);
704
705                                 ret = -ENOMEM;
706                                 nklist = kmalloc(size, GFP_KERNEL);
707                                 if (!nklist)
708                                         goto error2;
709
710                                 memcpy(nklist, klist, size);
711
712                                 /* replace matched key */
713                                 atomic_inc(&key->usage);
714                                 nklist->keys[loop] = key;
715
716                                 rcu_assign_pointer(
717                                         keyring->payload.subscriptions,
718                                         nklist);
719
720                                 /* dispose of the old keyring list and the
721                                  * displaced key */
722                                 klist->delkey = loop;
723                                 call_rcu(&klist->rcu,
724                                          keyring_unlink_rcu_disposal);
725
726                                 goto done;
727                         }
728                 }
729         }
730
731         /* check that we aren't going to overrun the user's quota */
732         ret = key_payload_reserve(keyring,
733                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
734         if (ret < 0)
735                 goto error2;
736
737         klist = keyring->payload.subscriptions;
738
739         if (klist && klist->nkeys < klist->maxkeys) {
740                 /* there's sufficient slack space to add directly */
741                 atomic_inc(&key->usage);
742
743                 klist->keys[klist->nkeys] = key;
744                 smp_wmb();
745                 klist->nkeys++;
746                 smp_wmb();
747         }
748         else {
749                 /* grow the key list */
750                 max = 4;
751                 if (klist)
752                         max += klist->maxkeys;
753
754                 ret = -ENFILE;
755                 if (max > 65535)
756                         goto error3;
757                 size = sizeof(*klist) + sizeof(struct key *) * max;
758                 if (size > PAGE_SIZE)
759                         goto error3;
760
761                 ret = -ENOMEM;
762                 nklist = kmalloc(size, GFP_KERNEL);
763                 if (!nklist)
764                         goto error3;
765                 nklist->maxkeys = max;
766                 nklist->nkeys = 0;
767
768                 if (klist) {
769                         nklist->nkeys = klist->nkeys;
770                         memcpy(nklist->keys,
771                                klist->keys,
772                                sizeof(struct key *) * klist->nkeys);
773                 }
774
775                 /* add the key into the new space */
776                 atomic_inc(&key->usage);
777                 nklist->keys[nklist->nkeys++] = key;
778
779                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
780
781                 /* dispose of the old keyring list */
782                 if (klist)
783                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
784         }
785
786 done:
787         ret = 0;
788 error2:
789         up_write(&keyring_serialise_link_sem);
790 error:
791         return ret;
792
793 error3:
794         /* undo the quota changes */
795         key_payload_reserve(keyring,
796                             keyring->datalen - KEYQUOTA_LINK_BYTES);
797         goto error2;
798
799 } /* end __key_link() */
800
801 /*****************************************************************************/
802 /*
803  * link a key to a keyring
804  */
805 int key_link(struct key *keyring, struct key *key)
806 {
807         int ret;
808
809         key_check(keyring);
810         key_check(key);
811
812         down_write(&keyring->sem);
813         ret = __key_link(keyring, key);
814         up_write(&keyring->sem);
815
816         return ret;
817
818 } /* end key_link() */
819
820 EXPORT_SYMBOL(key_link);
821
822 /*****************************************************************************/
823 /*
824  * unlink the first link to a key from a keyring
825  */
826 int key_unlink(struct key *keyring, struct key *key)
827 {
828         struct keyring_list *klist, *nklist;
829         int loop, ret;
830
831         key_check(keyring);
832         key_check(key);
833
834         ret = -ENOTDIR;
835         if (keyring->type != &key_type_keyring)
836                 goto error;
837
838         down_write(&keyring->sem);
839
840         klist = keyring->payload.subscriptions;
841         if (klist) {
842                 /* search the keyring for the key */
843                 for (loop = 0; loop < klist->nkeys; loop++)
844                         if (klist->keys[loop] == key)
845                                 goto key_is_present;
846         }
847
848         up_write(&keyring->sem);
849         ret = -ENOENT;
850         goto error;
851
852 key_is_present:
853         /* we need to copy the key list for RCU purposes */
854         nklist = kmalloc(sizeof(*klist) +
855                          sizeof(struct key *) * klist->maxkeys,
856                          GFP_KERNEL);
857         if (!nklist)
858                 goto nomem;
859         nklist->maxkeys = klist->maxkeys;
860         nklist->nkeys = klist->nkeys - 1;
861
862         if (loop > 0)
863                 memcpy(&nklist->keys[0],
864                        &klist->keys[0],
865                        loop * sizeof(struct key *));
866
867         if (loop < nklist->nkeys)
868                 memcpy(&nklist->keys[loop],
869                        &klist->keys[loop + 1],
870                        (nklist->nkeys - loop) * sizeof(struct key *));
871
872         /* adjust the user's quota */
873         key_payload_reserve(keyring,
874                             keyring->datalen - KEYQUOTA_LINK_BYTES);
875
876         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
877
878         up_write(&keyring->sem);
879
880         /* schedule for later cleanup */
881         klist->delkey = loop;
882         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
883
884         ret = 0;
885
886 error:
887         return ret;
888 nomem:
889         ret = -ENOMEM;
890         up_write(&keyring->sem);
891         goto error;
892
893 } /* end key_unlink() */
894
895 EXPORT_SYMBOL(key_unlink);
896
897 /*****************************************************************************/
898 /*
899  * dispose of a keyring list after the RCU grace period, releasing the keys it
900  * links to
901  */
902 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
903 {
904         struct keyring_list *klist;
905         int loop;
906
907         klist = container_of(rcu, struct keyring_list, rcu);
908
909         for (loop = klist->nkeys - 1; loop >= 0; loop--)
910                 key_put(klist->keys[loop]);
911
912         kfree(klist);
913
914 } /* end keyring_clear_rcu_disposal() */
915
916 /*****************************************************************************/
917 /*
918  * clear the specified process keyring
919  * - implements keyctl(KEYCTL_CLEAR)
920  */
921 int keyring_clear(struct key *keyring)
922 {
923         struct keyring_list *klist;
924         int ret;
925
926         ret = -ENOTDIR;
927         if (keyring->type == &key_type_keyring) {
928                 /* detach the pointer block with the locks held */
929                 down_write(&keyring->sem);
930
931                 klist = keyring->payload.subscriptions;
932                 if (klist) {
933                         /* adjust the quota */
934                         key_payload_reserve(keyring,
935                                             sizeof(struct keyring_list));
936
937                         rcu_assign_pointer(keyring->payload.subscriptions,
938                                            NULL);
939                 }
940
941                 up_write(&keyring->sem);
942
943                 /* free the keys after the locks have been dropped */
944                 if (klist)
945                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
946
947                 ret = 0;
948         }
949
950         return ret;
951
952 } /* end keyring_clear() */
953
954 EXPORT_SYMBOL(keyring_clear);