keys: don't generate user and user session keyrings unless they're accessed
[linux-2.6.git] / security / keys / keyring.c
1 /* Keyring handling
2  *
3  * Copyright (C) 2004-2005, 2008 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 static 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, kflags;
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         /* firstly we should check to see if this top-level keyring is what we
323          * are looking for */
324         key_ref = ERR_PTR(-EAGAIN);
325         kflags = keyring->flags;
326         if (keyring->type == type && match(keyring, description)) {
327                 key = keyring;
328
329                 /* check it isn't negative and hasn't expired or been
330                  * revoked */
331                 if (kflags & (1 << KEY_FLAG_REVOKED))
332                         goto error_2;
333                 if (key->expiry && now.tv_sec >= key->expiry)
334                         goto error_2;
335                 key_ref = ERR_PTR(-ENOKEY);
336                 if (kflags & (1 << KEY_FLAG_NEGATIVE))
337                         goto error_2;
338                 goto found;
339         }
340
341         /* otherwise, the top keyring must not be revoked, expired, or
342          * negatively instantiated if we are to search it */
343         key_ref = ERR_PTR(-EAGAIN);
344         if (kflags & ((1 << KEY_FLAG_REVOKED) | (1 << KEY_FLAG_NEGATIVE)) ||
345             (keyring->expiry && now.tv_sec >= keyring->expiry))
346                 goto error_2;
347
348         /* start processing a new keyring */
349 descend:
350         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
351                 goto not_this_keyring;
352
353         keylist = rcu_dereference(keyring->payload.subscriptions);
354         if (!keylist)
355                 goto not_this_keyring;
356
357         /* iterate through the keys in this keyring first */
358         for (kix = 0; kix < keylist->nkeys; kix++) {
359                 key = keylist->keys[kix];
360                 kflags = key->flags;
361
362                 /* ignore keys not of this type */
363                 if (key->type != type)
364                         continue;
365
366                 /* skip revoked keys and expired keys */
367                 if (kflags & (1 << KEY_FLAG_REVOKED))
368                         continue;
369
370                 if (key->expiry && now.tv_sec >= key->expiry)
371                         continue;
372
373                 /* keys that don't match */
374                 if (!match(key, description))
375                         continue;
376
377                 /* key must have search permissions */
378                 if (key_task_permission(make_key_ref(key, possessed),
379                                         context, KEY_SEARCH) < 0)
380                         continue;
381
382                 /* we set a different error code if we pass a negative key */
383                 if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
384                         err = -ENOKEY;
385                         continue;
386                 }
387
388                 goto found;
389         }
390
391         /* search through the keyrings nested in this one */
392         kix = 0;
393 ascend:
394         for (; kix < keylist->nkeys; kix++) {
395                 key = keylist->keys[kix];
396                 if (key->type != &key_type_keyring)
397                         continue;
398
399                 /* recursively search nested keyrings
400                  * - only search keyrings for which we have search permission
401                  */
402                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
403                         continue;
404
405                 if (key_task_permission(make_key_ref(key, possessed),
406                                         context, KEY_SEARCH) < 0)
407                         continue;
408
409                 /* stack the current position */
410                 stack[sp].keylist = keylist;
411                 stack[sp].kix = kix;
412                 sp++;
413
414                 /* begin again with the new keyring */
415                 keyring = key;
416                 goto descend;
417         }
418
419         /* the keyring we're looking at was disqualified or didn't contain a
420          * matching key */
421 not_this_keyring:
422         if (sp > 0) {
423                 /* resume the processing of a keyring higher up in the tree */
424                 sp--;
425                 keylist = stack[sp].keylist;
426                 kix = stack[sp].kix + 1;
427                 goto ascend;
428         }
429
430         key_ref = ERR_PTR(err);
431         goto error_2;
432
433         /* we found a viable match */
434 found:
435         atomic_inc(&key->usage);
436         key_check(key);
437         key_ref = make_key_ref(key, possessed);
438 error_2:
439         rcu_read_unlock();
440 error:
441         return key_ref;
442
443 } /* end keyring_search_aux() */
444
445 /*****************************************************************************/
446 /*
447  * search the supplied keyring tree for a key that matches the criterion
448  * - perform a breadth-then-depth search up to the prescribed limit
449  * - we only find keys on which we have search permission
450  * - we readlock the keyrings as we search down the tree
451  * - we return -EAGAIN if we didn't find any matching key
452  * - we return -ENOKEY if we only found negative matching keys
453  */
454 key_ref_t keyring_search(key_ref_t keyring,
455                          struct key_type *type,
456                          const char *description)
457 {
458         if (!type->match)
459                 return ERR_PTR(-ENOKEY);
460
461         return keyring_search_aux(keyring, current,
462                                   type, description, type->match);
463
464 } /* end keyring_search() */
465
466 EXPORT_SYMBOL(keyring_search);
467
468 /*****************************************************************************/
469 /*
470  * search the given keyring only (no recursion)
471  * - keyring must be locked by caller
472  * - caller must guarantee that the keyring is a keyring
473  */
474 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
475                                const struct key_type *ktype,
476                                const char *description,
477                                key_perm_t perm)
478 {
479         struct keyring_list *klist;
480         unsigned long possessed;
481         struct key *keyring, *key;
482         int loop;
483
484         keyring = key_ref_to_ptr(keyring_ref);
485         possessed = is_key_possessed(keyring_ref);
486
487         rcu_read_lock();
488
489         klist = rcu_dereference(keyring->payload.subscriptions);
490         if (klist) {
491                 for (loop = 0; loop < klist->nkeys; loop++) {
492                         key = klist->keys[loop];
493
494                         if (key->type == ktype &&
495                             (!key->type->match ||
496                              key->type->match(key, description)) &&
497                             key_permission(make_key_ref(key, possessed),
498                                            perm) == 0 &&
499                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
500                             )
501                                 goto found;
502                 }
503         }
504
505         rcu_read_unlock();
506         return ERR_PTR(-ENOKEY);
507
508  found:
509         atomic_inc(&key->usage);
510         rcu_read_unlock();
511         return make_key_ref(key, possessed);
512
513 } /* end __keyring_search_one() */
514
515 /*****************************************************************************/
516 /*
517  * find a keyring with the specified name
518  * - all named keyrings are searched
519  * - normally only finds keyrings with search permission for the current process
520  */
521 struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
522 {
523         struct key *keyring;
524         int bucket;
525
526         keyring = ERR_PTR(-EINVAL);
527         if (!name)
528                 goto error;
529
530         bucket = keyring_hash(name);
531
532         read_lock(&keyring_name_lock);
533
534         if (keyring_name_hash[bucket].next) {
535                 /* search this hash bucket for a keyring with a matching name
536                  * that's readable and that hasn't been revoked */
537                 list_for_each_entry(keyring,
538                                     &keyring_name_hash[bucket],
539                                     type_data.link
540                                     ) {
541                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
542                                 continue;
543
544                         if (strcmp(keyring->description, name) != 0)
545                                 continue;
546
547                         if (!skip_perm_check &&
548                             key_permission(make_key_ref(keyring, 0),
549                                            KEY_SEARCH) < 0)
550                                 continue;
551
552                         /* we've got a match */
553                         atomic_inc(&keyring->usage);
554                         read_unlock(&keyring_name_lock);
555                         goto error;
556                 }
557         }
558
559         read_unlock(&keyring_name_lock);
560         keyring = ERR_PTR(-ENOKEY);
561
562  error:
563         return keyring;
564
565 } /* end find_keyring_by_name() */
566
567 /*****************************************************************************/
568 /*
569  * see if a cycle will will be created by inserting acyclic tree B in acyclic
570  * tree A at the topmost level (ie: as a direct child of A)
571  * - since we are adding B to A at the top level, checking for cycles should
572  *   just be a matter of seeing if node A is somewhere in tree B
573  */
574 static int keyring_detect_cycle(struct key *A, struct key *B)
575 {
576         struct {
577                 struct keyring_list *keylist;
578                 int kix;
579         } stack[KEYRING_SEARCH_MAX_DEPTH];
580
581         struct keyring_list *keylist;
582         struct key *subtree, *key;
583         int sp, kix, ret;
584
585         rcu_read_lock();
586
587         ret = -EDEADLK;
588         if (A == B)
589                 goto cycle_detected;
590
591         subtree = B;
592         sp = 0;
593
594         /* start processing a new keyring */
595  descend:
596         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
597                 goto not_this_keyring;
598
599         keylist = rcu_dereference(subtree->payload.subscriptions);
600         if (!keylist)
601                 goto not_this_keyring;
602         kix = 0;
603
604  ascend:
605         /* iterate through the remaining keys in this keyring */
606         for (; kix < keylist->nkeys; kix++) {
607                 key = keylist->keys[kix];
608
609                 if (key == A)
610                         goto cycle_detected;
611
612                 /* recursively check nested keyrings */
613                 if (key->type == &key_type_keyring) {
614                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
615                                 goto too_deep;
616
617                         /* stack the current position */
618                         stack[sp].keylist = keylist;
619                         stack[sp].kix = kix;
620                         sp++;
621
622                         /* begin again with the new keyring */
623                         subtree = key;
624                         goto descend;
625                 }
626         }
627
628         /* the keyring we're looking at was disqualified or didn't contain a
629          * matching key */
630  not_this_keyring:
631         if (sp > 0) {
632                 /* resume the checking of a keyring higher up in the tree */
633                 sp--;
634                 keylist = stack[sp].keylist;
635                 kix = stack[sp].kix + 1;
636                 goto ascend;
637         }
638
639         ret = 0; /* no cycles detected */
640
641  error:
642         rcu_read_unlock();
643         return ret;
644
645  too_deep:
646         ret = -ELOOP;
647         goto error;
648
649  cycle_detected:
650         ret = -EDEADLK;
651         goto error;
652
653 } /* end keyring_detect_cycle() */
654
655 /*****************************************************************************/
656 /*
657  * dispose of a keyring list after the RCU grace period
658  */
659 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
660 {
661         struct keyring_list *klist =
662                 container_of(rcu, struct keyring_list, rcu);
663
664         kfree(klist);
665
666 } /* end keyring_link_rcu_disposal() */
667
668 /*****************************************************************************/
669 /*
670  * dispose of a keyring list after the RCU grace period, freeing the unlinked
671  * key
672  */
673 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
674 {
675         struct keyring_list *klist =
676                 container_of(rcu, struct keyring_list, rcu);
677
678         key_put(klist->keys[klist->delkey]);
679         kfree(klist);
680
681 } /* end keyring_unlink_rcu_disposal() */
682
683 /*****************************************************************************/
684 /*
685  * link a key into to a keyring
686  * - must be called with the keyring's semaphore write-locked
687  * - discard already extant link to matching key if there is one
688  */
689 int __key_link(struct key *keyring, struct key *key)
690 {
691         struct keyring_list *klist, *nklist;
692         unsigned max;
693         size_t size;
694         int loop, ret;
695
696         ret = -EKEYREVOKED;
697         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
698                 goto error;
699
700         ret = -ENOTDIR;
701         if (keyring->type != &key_type_keyring)
702                 goto error;
703
704         /* serialise link/link calls to prevent parallel calls causing a
705          * cycle when applied to two keyring in opposite orders */
706         down_write(&keyring_serialise_link_sem);
707
708         /* check that we aren't going to create a cycle adding one keyring to
709          * another */
710         if (key->type == &key_type_keyring) {
711                 ret = keyring_detect_cycle(keyring, key);
712                 if (ret < 0)
713                         goto error2;
714         }
715
716         /* see if there's a matching key we can displace */
717         klist = keyring->payload.subscriptions;
718
719         if (klist && klist->nkeys > 0) {
720                 struct key_type *type = key->type;
721
722                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
723                         if (klist->keys[loop]->type == type &&
724                             strcmp(klist->keys[loop]->description,
725                                    key->description) == 0
726                             ) {
727                                 /* found a match - replace with new key */
728                                 size = sizeof(struct key *) * klist->maxkeys;
729                                 size += sizeof(*klist);
730                                 BUG_ON(size > PAGE_SIZE);
731
732                                 ret = -ENOMEM;
733                                 nklist = kmemdup(klist, size, GFP_KERNEL);
734                                 if (!nklist)
735                                         goto error2;
736
737                                 /* replace matched key */
738                                 atomic_inc(&key->usage);
739                                 nklist->keys[loop] = key;
740
741                                 rcu_assign_pointer(
742                                         keyring->payload.subscriptions,
743                                         nklist);
744
745                                 /* dispose of the old keyring list and the
746                                  * displaced key */
747                                 klist->delkey = loop;
748                                 call_rcu(&klist->rcu,
749                                          keyring_unlink_rcu_disposal);
750
751                                 goto done;
752                         }
753                 }
754         }
755
756         /* check that we aren't going to overrun the user's quota */
757         ret = key_payload_reserve(keyring,
758                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
759         if (ret < 0)
760                 goto error2;
761
762         klist = keyring->payload.subscriptions;
763
764         if (klist && klist->nkeys < klist->maxkeys) {
765                 /* there's sufficient slack space to add directly */
766                 atomic_inc(&key->usage);
767
768                 klist->keys[klist->nkeys] = key;
769                 smp_wmb();
770                 klist->nkeys++;
771                 smp_wmb();
772         }
773         else {
774                 /* grow the key list */
775                 max = 4;
776                 if (klist)
777                         max += klist->maxkeys;
778
779                 ret = -ENFILE;
780                 if (max > 65535)
781                         goto error3;
782                 size = sizeof(*klist) + sizeof(struct key *) * max;
783                 if (size > PAGE_SIZE)
784                         goto error3;
785
786                 ret = -ENOMEM;
787                 nklist = kmalloc(size, GFP_KERNEL);
788                 if (!nklist)
789                         goto error3;
790                 nklist->maxkeys = max;
791                 nklist->nkeys = 0;
792
793                 if (klist) {
794                         nklist->nkeys = klist->nkeys;
795                         memcpy(nklist->keys,
796                                klist->keys,
797                                sizeof(struct key *) * klist->nkeys);
798                 }
799
800                 /* add the key into the new space */
801                 atomic_inc(&key->usage);
802                 nklist->keys[nklist->nkeys++] = key;
803
804                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
805
806                 /* dispose of the old keyring list */
807                 if (klist)
808                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
809         }
810
811 done:
812         ret = 0;
813 error2:
814         up_write(&keyring_serialise_link_sem);
815 error:
816         return ret;
817
818 error3:
819         /* undo the quota changes */
820         key_payload_reserve(keyring,
821                             keyring->datalen - KEYQUOTA_LINK_BYTES);
822         goto error2;
823
824 } /* end __key_link() */
825
826 /*****************************************************************************/
827 /*
828  * link a key to a keyring
829  */
830 int key_link(struct key *keyring, struct key *key)
831 {
832         int ret;
833
834         key_check(keyring);
835         key_check(key);
836
837         down_write(&keyring->sem);
838         ret = __key_link(keyring, key);
839         up_write(&keyring->sem);
840
841         return ret;
842
843 } /* end key_link() */
844
845 EXPORT_SYMBOL(key_link);
846
847 /*****************************************************************************/
848 /*
849  * unlink the first link to a key from a keyring
850  */
851 int key_unlink(struct key *keyring, struct key *key)
852 {
853         struct keyring_list *klist, *nklist;
854         int loop, ret;
855
856         key_check(keyring);
857         key_check(key);
858
859         ret = -ENOTDIR;
860         if (keyring->type != &key_type_keyring)
861                 goto error;
862
863         down_write(&keyring->sem);
864
865         klist = keyring->payload.subscriptions;
866         if (klist) {
867                 /* search the keyring for the key */
868                 for (loop = 0; loop < klist->nkeys; loop++)
869                         if (klist->keys[loop] == key)
870                                 goto key_is_present;
871         }
872
873         up_write(&keyring->sem);
874         ret = -ENOENT;
875         goto error;
876
877 key_is_present:
878         /* we need to copy the key list for RCU purposes */
879         nklist = kmalloc(sizeof(*klist) +
880                          sizeof(struct key *) * klist->maxkeys,
881                          GFP_KERNEL);
882         if (!nklist)
883                 goto nomem;
884         nklist->maxkeys = klist->maxkeys;
885         nklist->nkeys = klist->nkeys - 1;
886
887         if (loop > 0)
888                 memcpy(&nklist->keys[0],
889                        &klist->keys[0],
890                        loop * sizeof(struct key *));
891
892         if (loop < nklist->nkeys)
893                 memcpy(&nklist->keys[loop],
894                        &klist->keys[loop + 1],
895                        (nklist->nkeys - loop) * sizeof(struct key *));
896
897         /* adjust the user's quota */
898         key_payload_reserve(keyring,
899                             keyring->datalen - KEYQUOTA_LINK_BYTES);
900
901         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
902
903         up_write(&keyring->sem);
904
905         /* schedule for later cleanup */
906         klist->delkey = loop;
907         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
908
909         ret = 0;
910
911 error:
912         return ret;
913 nomem:
914         ret = -ENOMEM;
915         up_write(&keyring->sem);
916         goto error;
917
918 } /* end key_unlink() */
919
920 EXPORT_SYMBOL(key_unlink);
921
922 /*****************************************************************************/
923 /*
924  * dispose of a keyring list after the RCU grace period, releasing the keys it
925  * links to
926  */
927 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
928 {
929         struct keyring_list *klist;
930         int loop;
931
932         klist = container_of(rcu, struct keyring_list, rcu);
933
934         for (loop = klist->nkeys - 1; loop >= 0; loop--)
935                 key_put(klist->keys[loop]);
936
937         kfree(klist);
938
939 } /* end keyring_clear_rcu_disposal() */
940
941 /*****************************************************************************/
942 /*
943  * clear the specified process keyring
944  * - implements keyctl(KEYCTL_CLEAR)
945  */
946 int keyring_clear(struct key *keyring)
947 {
948         struct keyring_list *klist;
949         int ret;
950
951         ret = -ENOTDIR;
952         if (keyring->type == &key_type_keyring) {
953                 /* detach the pointer block with the locks held */
954                 down_write(&keyring->sem);
955
956                 klist = keyring->payload.subscriptions;
957                 if (klist) {
958                         /* adjust the quota */
959                         key_payload_reserve(keyring,
960                                             sizeof(struct keyring_list));
961
962                         rcu_assign_pointer(keyring->payload.subscriptions,
963                                            NULL);
964                 }
965
966                 up_write(&keyring->sem);
967
968                 /* free the keys after the locks have been dropped */
969                 if (klist)
970                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
971
972                 ret = 0;
973         }
974
975         return ret;
976
977 } /* end keyring_clear() */
978
979 EXPORT_SYMBOL(keyring_clear);
980
981 /*****************************************************************************/
982 /*
983  * dispose of the links from a revoked keyring
984  * - called with the key sem write-locked
985  */
986 static void keyring_revoke(struct key *keyring)
987 {
988         struct keyring_list *klist = keyring->payload.subscriptions;
989
990         /* adjust the quota */
991         key_payload_reserve(keyring, 0);
992
993         if (klist) {
994                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
995                 call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
996         }
997
998 } /* end keyring_revoke() */