[PATCH] Keys: Base keyring size on key pointer not key struct
[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/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, NULL);
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 rely on RCU to prevent the keyring lists from disappearing on us
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 task_struct *context,
335                                struct key_type *type,
336                                const void *description,
337                                key_match_func_t match)
338 {
339         struct {
340                 struct keyring_list *keylist;
341                 int kix;
342         } stack[KEYRING_SEARCH_MAX_DEPTH];
343
344         struct keyring_list *keylist;
345         struct timespec now;
346         struct key *key;
347         long err;
348         int sp, kix;
349
350         key_check(keyring);
351
352         rcu_read_lock();
353
354         /* top keyring must have search permission to begin the search */
355         key = ERR_PTR(-EACCES);
356         if (!key_task_permission(keyring, context, KEY_SEARCH))
357                 goto error;
358
359         key = ERR_PTR(-ENOTDIR);
360         if (keyring->type != &key_type_keyring)
361                 goto error;
362
363         now = current_kernel_time();
364         err = -EAGAIN;
365         sp = 0;
366
367         /* start processing a new keyring */
368  descend:
369         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
370                 goto not_this_keyring;
371
372         keylist = rcu_dereference(keyring->payload.subscriptions);
373         if (!keylist)
374                 goto not_this_keyring;
375
376         /* iterate through the keys in this keyring first */
377         for (kix = 0; kix < keylist->nkeys; kix++) {
378                 key = keylist->keys[kix];
379
380                 /* ignore keys not of this type */
381                 if (key->type != type)
382                         continue;
383
384                 /* skip revoked keys and expired keys */
385                 if (test_bit(KEY_FLAG_REVOKED, &key->flags))
386                         continue;
387
388                 if (key->expiry && now.tv_sec >= key->expiry)
389                         continue;
390
391                 /* keys that don't match */
392                 if (!match(key, description))
393                         continue;
394
395                 /* key must have search permissions */
396                 if (!key_task_permission(key, context, KEY_SEARCH))
397                         continue;
398
399                 /* we set a different error code if we find a negative key */
400                 if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
401                         err = -ENOKEY;
402                         continue;
403                 }
404
405                 goto found;
406         }
407
408         /* search through the keyrings nested in this one */
409         kix = 0;
410  ascend:
411         for (; kix < keylist->nkeys; kix++) {
412                 key = keylist->keys[kix];
413                 if (key->type != &key_type_keyring)
414                         continue;
415
416                 /* recursively search nested keyrings
417                  * - only search keyrings for which we have search permission
418                  */
419                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
420                         continue;
421
422                 if (!key_task_permission(key, context, KEY_SEARCH))
423                         continue;
424
425                 /* stack the current position */
426                 stack[sp].keylist = keylist;
427                 stack[sp].kix = kix;
428                 sp++;
429
430                 /* begin again with the new keyring */
431                 keyring = key;
432                 goto descend;
433         }
434
435         /* the keyring we're looking at was disqualified or didn't contain a
436          * matching key */
437  not_this_keyring:
438         if (sp > 0) {
439                 /* resume the processing of a keyring higher up in the tree */
440                 sp--;
441                 keylist = stack[sp].keylist;
442                 kix = stack[sp].kix + 1;
443                 goto ascend;
444         }
445
446         key = ERR_PTR(err);
447         goto error;
448
449         /* we found a viable match */
450  found:
451         atomic_inc(&key->usage);
452         key_check(key);
453  error:
454         rcu_read_unlock();
455         return key;
456
457 } /* end keyring_search_aux() */
458
459 /*****************************************************************************/
460 /*
461  * search the supplied keyring tree for a key that matches the criterion
462  * - perform a breadth-then-depth search up to the prescribed limit
463  * - we only find keys on which we have search permission
464  * - we readlock the keyrings as we search down the tree
465  * - we return -EAGAIN if we didn't find any matching key
466  * - we return -ENOKEY if we only found negative matching keys
467  */
468 struct key *keyring_search(struct key *keyring,
469                            struct key_type *type,
470                            const char *description)
471 {
472         if (!type->match)
473                 return ERR_PTR(-ENOKEY);
474
475         return keyring_search_aux(keyring, current,
476                                   type, description, type->match);
477
478 } /* end keyring_search() */
479
480 EXPORT_SYMBOL(keyring_search);
481
482 /*****************************************************************************/
483 /*
484  * search the given keyring only (no recursion)
485  * - keyring must be locked by caller
486  */
487 struct key *__keyring_search_one(struct key *keyring,
488                                  const struct key_type *ktype,
489                                  const char *description,
490                                  key_perm_t perm)
491 {
492         struct keyring_list *klist;
493         struct key *key;
494         int loop;
495
496         rcu_read_lock();
497
498         klist = rcu_dereference(keyring->payload.subscriptions);
499         if (klist) {
500                 for (loop = 0; loop < klist->nkeys; loop++) {
501                         key = klist->keys[loop];
502
503                         if (key->type == ktype &&
504                             (!key->type->match ||
505                              key->type->match(key, description)) &&
506                             key_permission(key, perm) &&
507                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
508                             )
509                                 goto found;
510                 }
511         }
512
513         key = ERR_PTR(-ENOKEY);
514         goto error;
515
516  found:
517         atomic_inc(&key->usage);
518  error:
519         rcu_read_unlock();
520         return key;
521
522 } /* end __keyring_search_one() */
523
524 /*****************************************************************************/
525 /*
526  * search for an instantiation authorisation key matching a target key
527  * - the RCU read lock must be held by the caller
528  * - a target_id of zero specifies any valid token
529  */
530 struct key *keyring_search_instkey(struct key *keyring,
531                                    key_serial_t target_id)
532 {
533         struct request_key_auth *rka;
534         struct keyring_list *klist;
535         struct key *instkey;
536         int loop;
537
538         klist = rcu_dereference(keyring->payload.subscriptions);
539         if (klist) {
540                 for (loop = 0; loop < klist->nkeys; loop++) {
541                         instkey = klist->keys[loop];
542
543                         if (instkey->type != &key_type_request_key_auth)
544                                 continue;
545
546                         rka = instkey->payload.data;
547                         if (target_id && rka->target_key->serial != target_id)
548                                 continue;
549
550                         /* the auth key is revoked during instantiation */
551                         if (!test_bit(KEY_FLAG_REVOKED, &instkey->flags))
552                                 goto found;
553
554                         instkey = ERR_PTR(-EKEYREVOKED);
555                         goto error;
556                 }
557         }
558
559         instkey = ERR_PTR(-EACCES);
560         goto error;
561
562 found:
563         atomic_inc(&instkey->usage);
564 error:
565         return instkey;
566
567 } /* end keyring_search_instkey() */
568
569 /*****************************************************************************/
570 /*
571  * find a keyring with the specified name
572  * - all named keyrings are searched
573  * - only find keyrings with search permission for the process
574  * - only find keyrings with a serial number greater than the one specified
575  */
576 struct key *find_keyring_by_name(const char *name, key_serial_t bound)
577 {
578         struct key *keyring;
579         int bucket;
580
581         keyring = ERR_PTR(-EINVAL);
582         if (!name)
583                 goto error;
584
585         bucket = keyring_hash(name);
586
587         read_lock(&keyring_name_lock);
588
589         if (keyring_name_hash[bucket].next) {
590                 /* search this hash bucket for a keyring with a matching name
591                  * that's readable and that hasn't been revoked */
592                 list_for_each_entry(keyring,
593                                     &keyring_name_hash[bucket],
594                                     type_data.link
595                                     ) {
596                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
597                                 continue;
598
599                         if (strcmp(keyring->description, name) != 0)
600                                 continue;
601
602                         if (!key_permission(keyring, KEY_SEARCH))
603                                 continue;
604
605                         /* found a potential candidate, but we still need to
606                          * check the serial number */
607                         if (keyring->serial <= bound)
608                                 continue;
609
610                         /* we've got a match */
611                         atomic_inc(&keyring->usage);
612                         read_unlock(&keyring_name_lock);
613                         goto error;
614                 }
615         }
616
617         read_unlock(&keyring_name_lock);
618         keyring = ERR_PTR(-ENOKEY);
619
620  error:
621         return keyring;
622
623 } /* end find_keyring_by_name() */
624
625 /*****************************************************************************/
626 /*
627  * see if a cycle will will be created by inserting acyclic tree B in acyclic
628  * tree A at the topmost level (ie: as a direct child of A)
629  * - since we are adding B to A at the top level, checking for cycles should
630  *   just be a matter of seeing if node A is somewhere in tree B
631  */
632 static int keyring_detect_cycle(struct key *A, struct key *B)
633 {
634         struct {
635                 struct keyring_list *keylist;
636                 int kix;
637         } stack[KEYRING_SEARCH_MAX_DEPTH];
638
639         struct keyring_list *keylist;
640         struct key *subtree, *key;
641         int sp, kix, ret;
642
643         rcu_read_lock();
644
645         ret = -EDEADLK;
646         if (A == B)
647                 goto cycle_detected;
648
649         subtree = B;
650         sp = 0;
651
652         /* start processing a new keyring */
653  descend:
654         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
655                 goto not_this_keyring;
656
657         keylist = rcu_dereference(subtree->payload.subscriptions);
658         if (!keylist)
659                 goto not_this_keyring;
660         kix = 0;
661
662  ascend:
663         /* iterate through the remaining keys in this keyring */
664         for (; kix < keylist->nkeys; kix++) {
665                 key = keylist->keys[kix];
666
667                 if (key == A)
668                         goto cycle_detected;
669
670                 /* recursively check nested keyrings */
671                 if (key->type == &key_type_keyring) {
672                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
673                                 goto too_deep;
674
675                         /* stack the current position */
676                         stack[sp].keylist = keylist;
677                         stack[sp].kix = kix;
678                         sp++;
679
680                         /* begin again with the new keyring */
681                         subtree = key;
682                         goto descend;
683                 }
684         }
685
686         /* the keyring we're looking at was disqualified or didn't contain a
687          * matching key */
688  not_this_keyring:
689         if (sp > 0) {
690                 /* resume the checking of a keyring higher up in the tree */
691                 sp--;
692                 keylist = stack[sp].keylist;
693                 kix = stack[sp].kix + 1;
694                 goto ascend;
695         }
696
697         ret = 0; /* no cycles detected */
698
699  error:
700         rcu_read_unlock();
701         return ret;
702
703  too_deep:
704         ret = -ELOOP;
705         goto error;
706
707  cycle_detected:
708         ret = -EDEADLK;
709         goto error;
710
711 } /* end keyring_detect_cycle() */
712
713 /*****************************************************************************/
714 /*
715  * dispose of a keyring list after the RCU grace period
716  */
717 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
718 {
719         struct keyring_list *klist =
720                 container_of(rcu, struct keyring_list, rcu);
721
722         kfree(klist);
723
724 } /* end keyring_link_rcu_disposal() */
725
726 /*****************************************************************************/
727 /*
728  * link a key into to a keyring
729  * - must be called with the keyring's semaphore write-locked
730  */
731 int __key_link(struct key *keyring, struct key *key)
732 {
733         struct keyring_list *klist, *nklist;
734         unsigned max;
735         size_t size;
736         int ret;
737
738         ret = -EKEYREVOKED;
739         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
740                 goto error;
741
742         ret = -ENOTDIR;
743         if (keyring->type != &key_type_keyring)
744                 goto error;
745
746         /* serialise link/link calls to prevent parallel calls causing a
747          * cycle when applied to two keyring in opposite orders */
748         down_write(&keyring_serialise_link_sem);
749
750         /* check that we aren't going to create a cycle adding one keyring to
751          * another */
752         if (key->type == &key_type_keyring) {
753                 ret = keyring_detect_cycle(keyring, key);
754                 if (ret < 0)
755                         goto error2;
756         }
757
758         /* check that we aren't going to overrun the user's quota */
759         ret = key_payload_reserve(keyring,
760                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
761         if (ret < 0)
762                 goto error2;
763
764         klist = keyring->payload.subscriptions;
765
766         if (klist && klist->nkeys < klist->maxkeys) {
767                 /* there's sufficient slack space to add directly */
768                 atomic_inc(&key->usage);
769
770                 klist->keys[klist->nkeys] = key;
771                 smp_wmb();
772                 klist->nkeys++;
773                 smp_wmb();
774
775                 ret = 0;
776         }
777         else {
778                 /* grow the key list */
779                 max = 4;
780                 if (klist)
781                         max += klist->maxkeys;
782
783                 ret = -ENFILE;
784                 if (max > 65535)
785                         goto error3;
786                 size = sizeof(*klist) + sizeof(struct key *) * max;
787                 if (size > PAGE_SIZE)
788                         goto error3;
789
790                 ret = -ENOMEM;
791                 nklist = kmalloc(size, GFP_KERNEL);
792                 if (!nklist)
793                         goto error3;
794                 nklist->maxkeys = max;
795                 nklist->nkeys = 0;
796
797                 if (klist) {
798                         nklist->nkeys = klist->nkeys;
799                         memcpy(nklist->keys,
800                                klist->keys,
801                                sizeof(struct key *) * klist->nkeys);
802                 }
803
804                 /* add the key into the new space */
805                 atomic_inc(&key->usage);
806                 nklist->keys[nklist->nkeys++] = key;
807
808                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
809
810                 /* dispose of the old keyring list */
811                 if (klist)
812                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
813
814                 ret = 0;
815         }
816
817  error2:
818         up_write(&keyring_serialise_link_sem);
819  error:
820         return ret;
821
822  error3:
823         /* undo the quota changes */
824         key_payload_reserve(keyring,
825                             keyring->datalen - KEYQUOTA_LINK_BYTES);
826         goto error2;
827
828 } /* end __key_link() */
829
830 /*****************************************************************************/
831 /*
832  * link a key to a keyring
833  */
834 int key_link(struct key *keyring, struct key *key)
835 {
836         int ret;
837
838         key_check(keyring);
839         key_check(key);
840
841         down_write(&keyring->sem);
842         ret = __key_link(keyring, key);
843         up_write(&keyring->sem);
844
845         return ret;
846
847 } /* end key_link() */
848
849 EXPORT_SYMBOL(key_link);
850
851 /*****************************************************************************/
852 /*
853  * dispose of a keyring list after the RCU grace period, freeing the unlinked
854  * key
855  */
856 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
857 {
858         struct keyring_list *klist =
859                 container_of(rcu, struct keyring_list, rcu);
860
861         key_put(klist->keys[klist->delkey]);
862         kfree(klist);
863
864 } /* end keyring_unlink_rcu_disposal() */
865
866 /*****************************************************************************/
867 /*
868  * unlink the first link to a key from a keyring
869  */
870 int key_unlink(struct key *keyring, struct key *key)
871 {
872         struct keyring_list *klist, *nklist;
873         int loop, ret;
874
875         key_check(keyring);
876         key_check(key);
877
878         ret = -ENOTDIR;
879         if (keyring->type != &key_type_keyring)
880                 goto error;
881
882         down_write(&keyring->sem);
883
884         klist = keyring->payload.subscriptions;
885         if (klist) {
886                 /* search the keyring for the key */
887                 for (loop = 0; loop < klist->nkeys; loop++)
888                         if (klist->keys[loop] == key)
889                                 goto key_is_present;
890         }
891
892         up_write(&keyring->sem);
893         ret = -ENOENT;
894         goto error;
895
896 key_is_present:
897         /* we need to copy the key list for RCU purposes */
898         nklist = kmalloc(sizeof(*klist) +
899                          sizeof(struct key *) * klist->maxkeys,
900                          GFP_KERNEL);
901         if (!nklist)
902                 goto nomem;
903         nklist->maxkeys = klist->maxkeys;
904         nklist->nkeys = klist->nkeys - 1;
905
906         if (loop > 0)
907                 memcpy(&nklist->keys[0],
908                        &klist->keys[0],
909                        loop * sizeof(struct key *));
910
911         if (loop < nklist->nkeys)
912                 memcpy(&nklist->keys[loop],
913                        &klist->keys[loop + 1],
914                        (nklist->nkeys - loop) * sizeof(struct key *));
915
916         /* adjust the user's quota */
917         key_payload_reserve(keyring,
918                             keyring->datalen - KEYQUOTA_LINK_BYTES);
919
920         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
921
922         up_write(&keyring->sem);
923
924         /* schedule for later cleanup */
925         klist->delkey = loop;
926         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
927
928         ret = 0;
929
930 error:
931         return ret;
932 nomem:
933         ret = -ENOMEM;
934         up_write(&keyring->sem);
935         goto error;
936
937 } /* end key_unlink() */
938
939 EXPORT_SYMBOL(key_unlink);
940
941 /*****************************************************************************/
942 /*
943  * dispose of a keyring list after the RCU grace period, releasing the keys it
944  * links to
945  */
946 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
947 {
948         struct keyring_list *klist;
949         int loop;
950
951         klist = container_of(rcu, struct keyring_list, rcu);
952
953         for (loop = klist->nkeys - 1; loop >= 0; loop--)
954                 key_put(klist->keys[loop]);
955
956         kfree(klist);
957
958 } /* end keyring_clear_rcu_disposal() */
959
960 /*****************************************************************************/
961 /*
962  * clear the specified process keyring
963  * - implements keyctl(KEYCTL_CLEAR)
964  */
965 int keyring_clear(struct key *keyring)
966 {
967         struct keyring_list *klist;
968         int ret;
969
970         ret = -ENOTDIR;
971         if (keyring->type == &key_type_keyring) {
972                 /* detach the pointer block with the locks held */
973                 down_write(&keyring->sem);
974
975                 klist = keyring->payload.subscriptions;
976                 if (klist) {
977                         /* adjust the quota */
978                         key_payload_reserve(keyring,
979                                             sizeof(struct keyring_list));
980
981                         rcu_assign_pointer(keyring->payload.subscriptions,
982                                            NULL);
983                 }
984
985                 up_write(&keyring->sem);
986
987                 /* free the keys after the locks have been dropped */
988                 if (klist)
989                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
990
991                 ret = 0;
992         }
993
994         return ret;
995
996 } /* end keyring_clear() */
997
998 EXPORT_SYMBOL(keyring_clear);