KEYS: Disperse linux/key_ui.h
[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 <keys/keyring-type.h>
20 #include <asm/uaccess.h>
21 #include "internal.h"
22
23 /*
24  * when plumbing the depths of the key tree, this sets a hard limit set on how
25  * deep we're willing to go
26  */
27 #define KEYRING_SEARCH_MAX_DEPTH 6
28
29 /*
30  * we keep all named keyrings in a hash to speed looking them up
31  */
32 #define KEYRING_NAME_HASH_SIZE  (1 << 5)
33
34 static struct list_head keyring_name_hash[KEYRING_NAME_HASH_SIZE];
35 static DEFINE_RWLOCK(keyring_name_lock);
36
37 static inline unsigned keyring_hash(const char *desc)
38 {
39         unsigned bucket = 0;
40
41         for (; *desc; desc++)
42                 bucket += (unsigned char) *desc;
43
44         return bucket & (KEYRING_NAME_HASH_SIZE - 1);
45 }
46
47 /*
48  * the keyring type definition
49  */
50 static int keyring_instantiate(struct key *keyring,
51                                const void *data, size_t datalen);
52 static int keyring_match(const struct key *keyring, const void *criterion);
53 static void keyring_revoke(struct key *keyring);
54 static void keyring_destroy(struct key *keyring);
55 static void keyring_describe(const struct key *keyring, struct seq_file *m);
56 static long keyring_read(const struct key *keyring,
57                          char __user *buffer, size_t buflen);
58
59 struct key_type key_type_keyring = {
60         .name           = "keyring",
61         .def_datalen    = sizeof(struct keyring_list),
62         .instantiate    = keyring_instantiate,
63         .match          = keyring_match,
64         .revoke         = keyring_revoke,
65         .destroy        = keyring_destroy,
66         .describe       = keyring_describe,
67         .read           = keyring_read,
68 };
69
70 EXPORT_SYMBOL(key_type_keyring);
71
72 /*
73  * semaphore to serialise link/link calls to prevent two link calls in parallel
74  * introducing a cycle
75  */
76 static DECLARE_RWSEM(keyring_serialise_link_sem);
77
78 /*****************************************************************************/
79 /*
80  * publish the name of a keyring so that it can be found by name (if it has
81  * one)
82  */
83 static void keyring_publish_name(struct key *keyring)
84 {
85         int bucket;
86
87         if (keyring->description) {
88                 bucket = keyring_hash(keyring->description);
89
90                 write_lock(&keyring_name_lock);
91
92                 if (!keyring_name_hash[bucket].next)
93                         INIT_LIST_HEAD(&keyring_name_hash[bucket]);
94
95                 list_add_tail(&keyring->type_data.link,
96                               &keyring_name_hash[bucket]);
97
98                 write_unlock(&keyring_name_lock);
99         }
100
101 } /* end keyring_publish_name() */
102
103 /*****************************************************************************/
104 /*
105  * initialise a keyring
106  * - we object if we were given any data
107  */
108 static int keyring_instantiate(struct key *keyring,
109                                const void *data, size_t datalen)
110 {
111         int ret;
112
113         ret = -EINVAL;
114         if (datalen == 0) {
115                 /* make the keyring available by name if it has one */
116                 keyring_publish_name(keyring);
117                 ret = 0;
118         }
119
120         return ret;
121
122 } /* end keyring_instantiate() */
123
124 /*****************************************************************************/
125 /*
126  * match keyrings on their name
127  */
128 static int keyring_match(const struct key *keyring, const void *description)
129 {
130         return keyring->description &&
131                 strcmp(keyring->description, description) == 0;
132
133 } /* end keyring_match() */
134
135 /*****************************************************************************/
136 /*
137  * dispose of the data dangling from the corpse of a keyring
138  */
139 static void keyring_destroy(struct key *keyring)
140 {
141         struct keyring_list *klist;
142         int loop;
143
144         if (keyring->description) {
145                 write_lock(&keyring_name_lock);
146
147                 if (keyring->type_data.link.next != NULL &&
148                     !list_empty(&keyring->type_data.link))
149                         list_del(&keyring->type_data.link);
150
151                 write_unlock(&keyring_name_lock);
152         }
153
154         klist = rcu_dereference(keyring->payload.subscriptions);
155         if (klist) {
156                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
157                         key_put(klist->keys[loop]);
158                 kfree(klist);
159         }
160
161 } /* end keyring_destroy() */
162
163 /*****************************************************************************/
164 /*
165  * describe the keyring
166  */
167 static void keyring_describe(const struct key *keyring, struct seq_file *m)
168 {
169         struct keyring_list *klist;
170
171         if (keyring->description) {
172                 seq_puts(m, keyring->description);
173         }
174         else {
175                 seq_puts(m, "[anon]");
176         }
177
178         rcu_read_lock();
179         klist = rcu_dereference(keyring->payload.subscriptions);
180         if (klist)
181                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
182         else
183                 seq_puts(m, ": empty");
184         rcu_read_unlock();
185
186 } /* end keyring_describe() */
187
188 /*****************************************************************************/
189 /*
190  * read a list of key IDs from the keyring's contents
191  * - the keyring's semaphore is read-locked
192  */
193 static long keyring_read(const struct key *keyring,
194                          char __user *buffer, size_t buflen)
195 {
196         struct keyring_list *klist;
197         struct key *key;
198         size_t qty, tmp;
199         int loop, ret;
200
201         ret = 0;
202         klist = rcu_dereference(keyring->payload.subscriptions);
203
204         if (klist) {
205                 /* calculate how much data we could return */
206                 qty = klist->nkeys * sizeof(key_serial_t);
207
208                 if (buffer && buflen > 0) {
209                         if (buflen > qty)
210                                 buflen = qty;
211
212                         /* copy the IDs of the subscribed keys into the
213                          * buffer */
214                         ret = -EFAULT;
215
216                         for (loop = 0; loop < klist->nkeys; loop++) {
217                                 key = klist->keys[loop];
218
219                                 tmp = sizeof(key_serial_t);
220                                 if (tmp > buflen)
221                                         tmp = buflen;
222
223                                 if (copy_to_user(buffer,
224                                                  &key->serial,
225                                                  tmp) != 0)
226                                         goto error;
227
228                                 buflen -= tmp;
229                                 if (buflen == 0)
230                                         break;
231                                 buffer += tmp;
232                         }
233                 }
234
235                 ret = qty;
236         }
237
238  error:
239         return ret;
240
241 } /* end keyring_read() */
242
243 /*****************************************************************************/
244 /*
245  * allocate a keyring and link into the destination keyring
246  */
247 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
248                           struct task_struct *ctx, unsigned long flags,
249                           struct key *dest)
250 {
251         struct key *keyring;
252         int ret;
253
254         keyring = key_alloc(&key_type_keyring, description,
255                             uid, gid, ctx,
256                             (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
257                             flags);
258
259         if (!IS_ERR(keyring)) {
260                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
261                 if (ret < 0) {
262                         key_put(keyring);
263                         keyring = ERR_PTR(ret);
264                 }
265         }
266
267         return keyring;
268
269 } /* end keyring_alloc() */
270
271 /*****************************************************************************/
272 /*
273  * search the supplied keyring tree for a key that matches the criterion
274  * - perform a breadth-then-depth search up to the prescribed limit
275  * - we only find keys on which we have search permission
276  * - we use the supplied match function to see if the description (or other
277  *   feature of interest) matches
278  * - we rely on RCU to prevent the keyring lists from disappearing on us
279  * - we return -EAGAIN if we didn't find any matching key
280  * - we return -ENOKEY if we only found negative matching keys
281  * - we propagate the possession attribute from the keyring ref to the key ref
282  */
283 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
284                              struct task_struct *context,
285                              struct key_type *type,
286                              const void *description,
287                              key_match_func_t match)
288 {
289         struct {
290                 struct keyring_list *keylist;
291                 int kix;
292         } stack[KEYRING_SEARCH_MAX_DEPTH];
293
294         struct keyring_list *keylist;
295         struct timespec now;
296         unsigned long possessed, kflags;
297         struct key *keyring, *key;
298         key_ref_t key_ref;
299         long err;
300         int sp, kix;
301
302         keyring = key_ref_to_ptr(keyring_ref);
303         possessed = is_key_possessed(keyring_ref);
304         key_check(keyring);
305
306         /* top keyring must have search permission to begin the search */
307         err = key_task_permission(keyring_ref, context, KEY_SEARCH);
308         if (err < 0) {
309                 key_ref = ERR_PTR(err);
310                 goto error;
311         }
312
313         key_ref = ERR_PTR(-ENOTDIR);
314         if (keyring->type != &key_type_keyring)
315                 goto error;
316
317         rcu_read_lock();
318
319         now = current_kernel_time();
320         err = -EAGAIN;
321         sp = 0;
322
323         /* firstly we should check to see if this top-level keyring is what we
324          * are looking for */
325         key_ref = ERR_PTR(-EAGAIN);
326         kflags = keyring->flags;
327         if (keyring->type == type && match(keyring, description)) {
328                 key = keyring;
329
330                 /* check it isn't negative and hasn't expired or been
331                  * revoked */
332                 if (kflags & (1 << KEY_FLAG_REVOKED))
333                         goto error_2;
334                 if (key->expiry && now.tv_sec >= key->expiry)
335                         goto error_2;
336                 key_ref = ERR_PTR(-ENOKEY);
337                 if (kflags & (1 << KEY_FLAG_NEGATIVE))
338                         goto error_2;
339                 goto found;
340         }
341
342         /* otherwise, the top keyring must not be revoked, expired, or
343          * negatively instantiated if we are to search it */
344         key_ref = ERR_PTR(-EAGAIN);
345         if (kflags & ((1 << KEY_FLAG_REVOKED) | (1 << KEY_FLAG_NEGATIVE)) ||
346             (keyring->expiry && now.tv_sec >= keyring->expiry))
347                 goto error_2;
348
349         /* start processing a new keyring */
350 descend:
351         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
352                 goto not_this_keyring;
353
354         keylist = rcu_dereference(keyring->payload.subscriptions);
355         if (!keylist)
356                 goto not_this_keyring;
357
358         /* iterate through the keys in this keyring first */
359         for (kix = 0; kix < keylist->nkeys; kix++) {
360                 key = keylist->keys[kix];
361                 kflags = key->flags;
362
363                 /* ignore keys not of this type */
364                 if (key->type != type)
365                         continue;
366
367                 /* skip revoked keys and expired keys */
368                 if (kflags & (1 << KEY_FLAG_REVOKED))
369                         continue;
370
371                 if (key->expiry && now.tv_sec >= key->expiry)
372                         continue;
373
374                 /* keys that don't match */
375                 if (!match(key, description))
376                         continue;
377
378                 /* key must have search permissions */
379                 if (key_task_permission(make_key_ref(key, possessed),
380                                         context, KEY_SEARCH) < 0)
381                         continue;
382
383                 /* we set a different error code if we pass a negative key */
384                 if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
385                         err = -ENOKEY;
386                         continue;
387                 }
388
389                 goto found;
390         }
391
392         /* search through the keyrings nested in this one */
393         kix = 0;
394 ascend:
395         for (; kix < keylist->nkeys; kix++) {
396                 key = keylist->keys[kix];
397                 if (key->type != &key_type_keyring)
398                         continue;
399
400                 /* recursively search nested keyrings
401                  * - only search keyrings for which we have search permission
402                  */
403                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
404                         continue;
405
406                 if (key_task_permission(make_key_ref(key, possessed),
407                                         context, KEY_SEARCH) < 0)
408                         continue;
409
410                 /* stack the current position */
411                 stack[sp].keylist = keylist;
412                 stack[sp].kix = kix;
413                 sp++;
414
415                 /* begin again with the new keyring */
416                 keyring = key;
417                 goto descend;
418         }
419
420         /* the keyring we're looking at was disqualified or didn't contain a
421          * matching key */
422 not_this_keyring:
423         if (sp > 0) {
424                 /* resume the processing of a keyring higher up in the tree */
425                 sp--;
426                 keylist = stack[sp].keylist;
427                 kix = stack[sp].kix + 1;
428                 goto ascend;
429         }
430
431         key_ref = ERR_PTR(err);
432         goto error_2;
433
434         /* we found a viable match */
435 found:
436         atomic_inc(&key->usage);
437         key_check(key);
438         key_ref = make_key_ref(key, possessed);
439 error_2:
440         rcu_read_unlock();
441 error:
442         return key_ref;
443
444 } /* end keyring_search_aux() */
445
446 /*****************************************************************************/
447 /*
448  * search the supplied keyring tree for a key that matches the criterion
449  * - perform a breadth-then-depth search up to the prescribed limit
450  * - we only find keys on which we have search permission
451  * - we readlock the keyrings as we search down the tree
452  * - we return -EAGAIN if we didn't find any matching key
453  * - we return -ENOKEY if we only found negative matching keys
454  */
455 key_ref_t keyring_search(key_ref_t keyring,
456                          struct key_type *type,
457                          const char *description)
458 {
459         if (!type->match)
460                 return ERR_PTR(-ENOKEY);
461
462         return keyring_search_aux(keyring, current,
463                                   type, description, type->match);
464
465 } /* end keyring_search() */
466
467 EXPORT_SYMBOL(keyring_search);
468
469 /*****************************************************************************/
470 /*
471  * search the given keyring only (no recursion)
472  * - keyring must be locked by caller
473  * - caller must guarantee that the keyring is a keyring
474  */
475 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
476                                const struct key_type *ktype,
477                                const char *description,
478                                key_perm_t perm)
479 {
480         struct keyring_list *klist;
481         unsigned long possessed;
482         struct key *keyring, *key;
483         int loop;
484
485         keyring = key_ref_to_ptr(keyring_ref);
486         possessed = is_key_possessed(keyring_ref);
487
488         rcu_read_lock();
489
490         klist = rcu_dereference(keyring->payload.subscriptions);
491         if (klist) {
492                 for (loop = 0; loop < klist->nkeys; loop++) {
493                         key = klist->keys[loop];
494
495                         if (key->type == ktype &&
496                             (!key->type->match ||
497                              key->type->match(key, description)) &&
498                             key_permission(make_key_ref(key, possessed),
499                                            perm) == 0 &&
500                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
501                             )
502                                 goto found;
503                 }
504         }
505
506         rcu_read_unlock();
507         return ERR_PTR(-ENOKEY);
508
509  found:
510         atomic_inc(&key->usage);
511         rcu_read_unlock();
512         return make_key_ref(key, possessed);
513
514 } /* end __keyring_search_one() */
515
516 /*****************************************************************************/
517 /*
518  * find a keyring with the specified name
519  * - all named keyrings are searched
520  * - normally only finds keyrings with search permission for the current process
521  */
522 struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
523 {
524         struct key *keyring;
525         int bucket;
526
527         keyring = ERR_PTR(-EINVAL);
528         if (!name)
529                 goto error;
530
531         bucket = keyring_hash(name);
532
533         read_lock(&keyring_name_lock);
534
535         if (keyring_name_hash[bucket].next) {
536                 /* search this hash bucket for a keyring with a matching name
537                  * that's readable and that hasn't been revoked */
538                 list_for_each_entry(keyring,
539                                     &keyring_name_hash[bucket],
540                                     type_data.link
541                                     ) {
542                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
543                                 continue;
544
545                         if (strcmp(keyring->description, name) != 0)
546                                 continue;
547
548                         if (!skip_perm_check &&
549                             key_permission(make_key_ref(keyring, 0),
550                                            KEY_SEARCH) < 0)
551                                 continue;
552
553                         /* we've got a match */
554                         atomic_inc(&keyring->usage);
555                         read_unlock(&keyring_name_lock);
556                         goto error;
557                 }
558         }
559
560         read_unlock(&keyring_name_lock);
561         keyring = ERR_PTR(-ENOKEY);
562
563  error:
564         return keyring;
565
566 } /* end find_keyring_by_name() */
567
568 /*****************************************************************************/
569 /*
570  * see if a cycle will will be created by inserting acyclic tree B in acyclic
571  * tree A at the topmost level (ie: as a direct child of A)
572  * - since we are adding B to A at the top level, checking for cycles should
573  *   just be a matter of seeing if node A is somewhere in tree B
574  */
575 static int keyring_detect_cycle(struct key *A, struct key *B)
576 {
577         struct {
578                 struct keyring_list *keylist;
579                 int kix;
580         } stack[KEYRING_SEARCH_MAX_DEPTH];
581
582         struct keyring_list *keylist;
583         struct key *subtree, *key;
584         int sp, kix, ret;
585
586         rcu_read_lock();
587
588         ret = -EDEADLK;
589         if (A == B)
590                 goto cycle_detected;
591
592         subtree = B;
593         sp = 0;
594
595         /* start processing a new keyring */
596  descend:
597         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
598                 goto not_this_keyring;
599
600         keylist = rcu_dereference(subtree->payload.subscriptions);
601         if (!keylist)
602                 goto not_this_keyring;
603         kix = 0;
604
605  ascend:
606         /* iterate through the remaining keys in this keyring */
607         for (; kix < keylist->nkeys; kix++) {
608                 key = keylist->keys[kix];
609
610                 if (key == A)
611                         goto cycle_detected;
612
613                 /* recursively check nested keyrings */
614                 if (key->type == &key_type_keyring) {
615                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
616                                 goto too_deep;
617
618                         /* stack the current position */
619                         stack[sp].keylist = keylist;
620                         stack[sp].kix = kix;
621                         sp++;
622
623                         /* begin again with the new keyring */
624                         subtree = key;
625                         goto descend;
626                 }
627         }
628
629         /* the keyring we're looking at was disqualified or didn't contain a
630          * matching key */
631  not_this_keyring:
632         if (sp > 0) {
633                 /* resume the checking of a keyring higher up in the tree */
634                 sp--;
635                 keylist = stack[sp].keylist;
636                 kix = stack[sp].kix + 1;
637                 goto ascend;
638         }
639
640         ret = 0; /* no cycles detected */
641
642  error:
643         rcu_read_unlock();
644         return ret;
645
646  too_deep:
647         ret = -ELOOP;
648         goto error;
649
650  cycle_detected:
651         ret = -EDEADLK;
652         goto error;
653
654 } /* end keyring_detect_cycle() */
655
656 /*****************************************************************************/
657 /*
658  * dispose of a keyring list after the RCU grace period
659  */
660 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
661 {
662         struct keyring_list *klist =
663                 container_of(rcu, struct keyring_list, rcu);
664
665         kfree(klist);
666
667 } /* end keyring_link_rcu_disposal() */
668
669 /*****************************************************************************/
670 /*
671  * dispose of a keyring list after the RCU grace period, freeing the unlinked
672  * key
673  */
674 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
675 {
676         struct keyring_list *klist =
677                 container_of(rcu, struct keyring_list, rcu);
678
679         key_put(klist->keys[klist->delkey]);
680         kfree(klist);
681
682 } /* end keyring_unlink_rcu_disposal() */
683
684 /*****************************************************************************/
685 /*
686  * link a key into to a keyring
687  * - must be called with the keyring's semaphore write-locked
688  * - discard already extant link to matching key if there is one
689  */
690 int __key_link(struct key *keyring, struct key *key)
691 {
692         struct keyring_list *klist, *nklist;
693         unsigned max;
694         size_t size;
695         int loop, ret;
696
697         ret = -EKEYREVOKED;
698         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
699                 goto error;
700
701         ret = -ENOTDIR;
702         if (keyring->type != &key_type_keyring)
703                 goto error;
704
705         /* serialise link/link calls to prevent parallel calls causing a
706          * cycle when applied to two keyring in opposite orders */
707         down_write(&keyring_serialise_link_sem);
708
709         /* check that we aren't going to create a cycle adding one keyring to
710          * another */
711         if (key->type == &key_type_keyring) {
712                 ret = keyring_detect_cycle(keyring, key);
713                 if (ret < 0)
714                         goto error2;
715         }
716
717         /* see if there's a matching key we can displace */
718         klist = keyring->payload.subscriptions;
719
720         if (klist && klist->nkeys > 0) {
721                 struct key_type *type = key->type;
722
723                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
724                         if (klist->keys[loop]->type == type &&
725                             strcmp(klist->keys[loop]->description,
726                                    key->description) == 0
727                             ) {
728                                 /* found a match - replace with new key */
729                                 size = sizeof(struct key *) * klist->maxkeys;
730                                 size += sizeof(*klist);
731                                 BUG_ON(size > PAGE_SIZE);
732
733                                 ret = -ENOMEM;
734                                 nklist = kmemdup(klist, size, GFP_KERNEL);
735                                 if (!nklist)
736                                         goto error2;
737
738                                 /* replace matched key */
739                                 atomic_inc(&key->usage);
740                                 nklist->keys[loop] = key;
741
742                                 rcu_assign_pointer(
743                                         keyring->payload.subscriptions,
744                                         nklist);
745
746                                 /* dispose of the old keyring list and the
747                                  * displaced key */
748                                 klist->delkey = loop;
749                                 call_rcu(&klist->rcu,
750                                          keyring_unlink_rcu_disposal);
751
752                                 goto done;
753                         }
754                 }
755         }
756
757         /* check that we aren't going to overrun the user's quota */
758         ret = key_payload_reserve(keyring,
759                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
760         if (ret < 0)
761                 goto error2;
762
763         klist = keyring->payload.subscriptions;
764
765         if (klist && klist->nkeys < klist->maxkeys) {
766                 /* there's sufficient slack space to add directly */
767                 atomic_inc(&key->usage);
768
769                 klist->keys[klist->nkeys] = key;
770                 smp_wmb();
771                 klist->nkeys++;
772                 smp_wmb();
773         }
774         else {
775                 /* grow the key list */
776                 max = 4;
777                 if (klist)
778                         max += klist->maxkeys;
779
780                 ret = -ENFILE;
781                 if (max > 65535)
782                         goto error3;
783                 size = sizeof(*klist) + sizeof(struct key *) * max;
784                 if (size > PAGE_SIZE)
785                         goto error3;
786
787                 ret = -ENOMEM;
788                 nklist = kmalloc(size, GFP_KERNEL);
789                 if (!nklist)
790                         goto error3;
791                 nklist->maxkeys = max;
792                 nklist->nkeys = 0;
793
794                 if (klist) {
795                         nklist->nkeys = klist->nkeys;
796                         memcpy(nklist->keys,
797                                klist->keys,
798                                sizeof(struct key *) * klist->nkeys);
799                 }
800
801                 /* add the key into the new space */
802                 atomic_inc(&key->usage);
803                 nklist->keys[nklist->nkeys++] = key;
804
805                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
806
807                 /* dispose of the old keyring list */
808                 if (klist)
809                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
810         }
811
812 done:
813         ret = 0;
814 error2:
815         up_write(&keyring_serialise_link_sem);
816 error:
817         return ret;
818
819 error3:
820         /* undo the quota changes */
821         key_payload_reserve(keyring,
822                             keyring->datalen - KEYQUOTA_LINK_BYTES);
823         goto error2;
824
825 } /* end __key_link() */
826
827 /*****************************************************************************/
828 /*
829  * link a key to a keyring
830  */
831 int key_link(struct key *keyring, struct key *key)
832 {
833         int ret;
834
835         key_check(keyring);
836         key_check(key);
837
838         down_write(&keyring->sem);
839         ret = __key_link(keyring, key);
840         up_write(&keyring->sem);
841
842         return ret;
843
844 } /* end key_link() */
845
846 EXPORT_SYMBOL(key_link);
847
848 /*****************************************************************************/
849 /*
850  * unlink the first link to a key from a keyring
851  */
852 int key_unlink(struct key *keyring, struct key *key)
853 {
854         struct keyring_list *klist, *nklist;
855         int loop, ret;
856
857         key_check(keyring);
858         key_check(key);
859
860         ret = -ENOTDIR;
861         if (keyring->type != &key_type_keyring)
862                 goto error;
863
864         down_write(&keyring->sem);
865
866         klist = keyring->payload.subscriptions;
867         if (klist) {
868                 /* search the keyring for the key */
869                 for (loop = 0; loop < klist->nkeys; loop++)
870                         if (klist->keys[loop] == key)
871                                 goto key_is_present;
872         }
873
874         up_write(&keyring->sem);
875         ret = -ENOENT;
876         goto error;
877
878 key_is_present:
879         /* we need to copy the key list for RCU purposes */
880         nklist = kmalloc(sizeof(*klist) +
881                          sizeof(struct key *) * klist->maxkeys,
882                          GFP_KERNEL);
883         if (!nklist)
884                 goto nomem;
885         nklist->maxkeys = klist->maxkeys;
886         nklist->nkeys = klist->nkeys - 1;
887
888         if (loop > 0)
889                 memcpy(&nklist->keys[0],
890                        &klist->keys[0],
891                        loop * sizeof(struct key *));
892
893         if (loop < nklist->nkeys)
894                 memcpy(&nklist->keys[loop],
895                        &klist->keys[loop + 1],
896                        (nklist->nkeys - loop) * sizeof(struct key *));
897
898         /* adjust the user's quota */
899         key_payload_reserve(keyring,
900                             keyring->datalen - KEYQUOTA_LINK_BYTES);
901
902         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
903
904         up_write(&keyring->sem);
905
906         /* schedule for later cleanup */
907         klist->delkey = loop;
908         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
909
910         ret = 0;
911
912 error:
913         return ret;
914 nomem:
915         ret = -ENOMEM;
916         up_write(&keyring->sem);
917         goto error;
918
919 } /* end key_unlink() */
920
921 EXPORT_SYMBOL(key_unlink);
922
923 /*****************************************************************************/
924 /*
925  * dispose of a keyring list after the RCU grace period, releasing the keys it
926  * links to
927  */
928 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
929 {
930         struct keyring_list *klist;
931         int loop;
932
933         klist = container_of(rcu, struct keyring_list, rcu);
934
935         for (loop = klist->nkeys - 1; loop >= 0; loop--)
936                 key_put(klist->keys[loop]);
937
938         kfree(klist);
939
940 } /* end keyring_clear_rcu_disposal() */
941
942 /*****************************************************************************/
943 /*
944  * clear the specified process keyring
945  * - implements keyctl(KEYCTL_CLEAR)
946  */
947 int keyring_clear(struct key *keyring)
948 {
949         struct keyring_list *klist;
950         int ret;
951
952         ret = -ENOTDIR;
953         if (keyring->type == &key_type_keyring) {
954                 /* detach the pointer block with the locks held */
955                 down_write(&keyring->sem);
956
957                 klist = keyring->payload.subscriptions;
958                 if (klist) {
959                         /* adjust the quota */
960                         key_payload_reserve(keyring,
961                                             sizeof(struct keyring_list));
962
963                         rcu_assign_pointer(keyring->payload.subscriptions,
964                                            NULL);
965                 }
966
967                 up_write(&keyring->sem);
968
969                 /* free the keys after the locks have been dropped */
970                 if (klist)
971                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
972
973                 ret = 0;
974         }
975
976         return ret;
977
978 } /* end keyring_clear() */
979
980 EXPORT_SYMBOL(keyring_clear);
981
982 /*****************************************************************************/
983 /*
984  * dispose of the links from a revoked keyring
985  * - called with the key sem write-locked
986  */
987 static void keyring_revoke(struct key *keyring)
988 {
989         struct keyring_list *klist = keyring->payload.subscriptions;
990
991         /* adjust the quota */
992         key_payload_reserve(keyring, 0);
993
994         if (klist) {
995                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
996                 call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
997         }
998
999 } /* end keyring_revoke() */