Merge branch 'master' into next
[linux-3.10.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 <linux/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_check(keyring->payload.subscriptions,
155                                       rcu_read_lock_held() ||
156                                       atomic_read(&keyring->usage) == 0);
157         if (klist) {
158                 for (loop = klist->nkeys - 1; loop >= 0; loop--)
159                         key_put(klist->keys[loop]);
160                 kfree(klist);
161         }
162
163 } /* end keyring_destroy() */
164
165 /*****************************************************************************/
166 /*
167  * describe the keyring
168  */
169 static void keyring_describe(const struct key *keyring, struct seq_file *m)
170 {
171         struct keyring_list *klist;
172
173         if (keyring->description)
174                 seq_puts(m, keyring->description);
175         else
176                 seq_puts(m, "[anon]");
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 = 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                           const struct cred *cred, 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, cred,
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                              const struct cred *cred,
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, cred, 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                                         cred, 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                                         cred, 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->cred,
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 (keyring->user->user_ns != current_user_ns())
543                                 continue;
544
545                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
546                                 continue;
547
548                         if (strcmp(keyring->description, name) != 0)
549                                 continue;
550
551                         if (!skip_perm_check &&
552                             key_permission(make_key_ref(keyring, 0),
553                                            KEY_SEARCH) < 0)
554                                 continue;
555
556                         /* we've got a match */
557                         atomic_inc(&keyring->usage);
558                         read_unlock(&keyring_name_lock);
559                         goto error;
560                 }
561         }
562
563         read_unlock(&keyring_name_lock);
564         keyring = ERR_PTR(-ENOKEY);
565
566 error:
567         return keyring;
568
569 } /* end find_keyring_by_name() */
570
571 /*****************************************************************************/
572 /*
573  * see if a cycle will will be created by inserting acyclic tree B in acyclic
574  * tree A at the topmost level (ie: as a direct child of A)
575  * - since we are adding B to A at the top level, checking for cycles should
576  *   just be a matter of seeing if node A is somewhere in tree B
577  */
578 static int keyring_detect_cycle(struct key *A, struct key *B)
579 {
580         struct {
581                 struct keyring_list *keylist;
582                 int kix;
583         } stack[KEYRING_SEARCH_MAX_DEPTH];
584
585         struct keyring_list *keylist;
586         struct key *subtree, *key;
587         int sp, kix, ret;
588
589         rcu_read_lock();
590
591         ret = -EDEADLK;
592         if (A == B)
593                 goto cycle_detected;
594
595         subtree = B;
596         sp = 0;
597
598         /* start processing a new keyring */
599 descend:
600         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
601                 goto not_this_keyring;
602
603         keylist = rcu_dereference(subtree->payload.subscriptions);
604         if (!keylist)
605                 goto not_this_keyring;
606         kix = 0;
607
608 ascend:
609         /* iterate through the remaining keys in this keyring */
610         for (; kix < keylist->nkeys; kix++) {
611                 key = keylist->keys[kix];
612
613                 if (key == A)
614                         goto cycle_detected;
615
616                 /* recursively check nested keyrings */
617                 if (key->type == &key_type_keyring) {
618                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
619                                 goto too_deep;
620
621                         /* stack the current position */
622                         stack[sp].keylist = keylist;
623                         stack[sp].kix = kix;
624                         sp++;
625
626                         /* begin again with the new keyring */
627                         subtree = key;
628                         goto descend;
629                 }
630         }
631
632         /* the keyring we're looking at was disqualified or didn't contain a
633          * matching key */
634 not_this_keyring:
635         if (sp > 0) {
636                 /* resume the checking of a keyring higher up in the tree */
637                 sp--;
638                 keylist = stack[sp].keylist;
639                 kix = stack[sp].kix + 1;
640                 goto ascend;
641         }
642
643         ret = 0; /* no cycles detected */
644
645 error:
646         rcu_read_unlock();
647         return ret;
648
649 too_deep:
650         ret = -ELOOP;
651         goto error;
652
653 cycle_detected:
654         ret = -EDEADLK;
655         goto error;
656
657 } /* end keyring_detect_cycle() */
658
659 /*****************************************************************************/
660 /*
661  * dispose of a keyring list after the RCU grace period
662  */
663 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
664 {
665         struct keyring_list *klist =
666                 container_of(rcu, struct keyring_list, rcu);
667
668         kfree(klist);
669
670 } /* end keyring_link_rcu_disposal() */
671
672 /*****************************************************************************/
673 /*
674  * dispose of a keyring list after the RCU grace period, freeing the unlinked
675  * key
676  */
677 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
678 {
679         struct keyring_list *klist =
680                 container_of(rcu, struct keyring_list, rcu);
681
682         key_put(klist->keys[klist->delkey]);
683         kfree(klist);
684
685 } /* end keyring_unlink_rcu_disposal() */
686
687 /*****************************************************************************/
688 /*
689  * link a key into to a keyring
690  * - must be called with the keyring's semaphore write-locked
691  * - discard already extant link to matching key if there is one
692  */
693 int __key_link(struct key *keyring, struct key *key)
694 {
695         struct keyring_list *klist, *nklist;
696         unsigned max;
697         size_t size;
698         int loop, ret;
699
700         ret = -EKEYREVOKED;
701         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
702                 goto error;
703
704         ret = -ENOTDIR;
705         if (keyring->type != &key_type_keyring)
706                 goto error;
707
708         /* serialise link/link calls to prevent parallel calls causing a
709          * cycle when applied to two keyring in opposite orders */
710         down_write(&keyring_serialise_link_sem);
711
712         /* check that we aren't going to create a cycle adding one keyring to
713          * another */
714         if (key->type == &key_type_keyring) {
715                 ret = keyring_detect_cycle(keyring, key);
716                 if (ret < 0)
717                         goto error2;
718         }
719
720         /* see if there's a matching key we can displace */
721         klist = keyring->payload.subscriptions;
722
723         if (klist && klist->nkeys > 0) {
724                 struct key_type *type = key->type;
725
726                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
727                         if (klist->keys[loop]->type == type &&
728                             strcmp(klist->keys[loop]->description,
729                                    key->description) == 0
730                             ) {
731                                 /* found a match - replace with new key */
732                                 size = sizeof(struct key *) * klist->maxkeys;
733                                 size += sizeof(*klist);
734                                 BUG_ON(size > PAGE_SIZE);
735
736                                 ret = -ENOMEM;
737                                 nklist = kmemdup(klist, size, GFP_KERNEL);
738                                 if (!nklist)
739                                         goto error2;
740
741                                 /* replace matched key */
742                                 atomic_inc(&key->usage);
743                                 nklist->keys[loop] = key;
744
745                                 rcu_assign_pointer(
746                                         keyring->payload.subscriptions,
747                                         nklist);
748
749                                 /* dispose of the old keyring list and the
750                                  * displaced key */
751                                 klist->delkey = loop;
752                                 call_rcu(&klist->rcu,
753                                          keyring_unlink_rcu_disposal);
754
755                                 goto done;
756                         }
757                 }
758         }
759
760         /* check that we aren't going to overrun the user's quota */
761         ret = key_payload_reserve(keyring,
762                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
763         if (ret < 0)
764                 goto error2;
765
766         klist = keyring->payload.subscriptions;
767
768         if (klist && klist->nkeys < klist->maxkeys) {
769                 /* there's sufficient slack space to add directly */
770                 atomic_inc(&key->usage);
771
772                 klist->keys[klist->nkeys] = key;
773                 smp_wmb();
774                 klist->nkeys++;
775                 smp_wmb();
776         } else {
777                 /* grow the key list */
778                 max = 4;
779                 if (klist)
780                         max += klist->maxkeys;
781
782                 ret = -ENFILE;
783                 if (max > 65535)
784                         goto error3;
785                 size = sizeof(*klist) + sizeof(struct key *) * max;
786                 if (size > PAGE_SIZE)
787                         goto error3;
788
789                 ret = -ENOMEM;
790                 nklist = kmalloc(size, GFP_KERNEL);
791                 if (!nklist)
792                         goto error3;
793                 nklist->maxkeys = max;
794                 nklist->nkeys = 0;
795
796                 if (klist) {
797                         nklist->nkeys = klist->nkeys;
798                         memcpy(nklist->keys,
799                                klist->keys,
800                                sizeof(struct key *) * klist->nkeys);
801                 }
802
803                 /* add the key into the new space */
804                 atomic_inc(&key->usage);
805                 nklist->keys[nklist->nkeys++] = key;
806
807                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
808
809                 /* dispose of the old keyring list */
810                 if (klist)
811                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
812         }
813
814 done:
815         ret = 0;
816 error2:
817         up_write(&keyring_serialise_link_sem);
818 error:
819         return ret;
820
821 error3:
822         /* undo the quota changes */
823         key_payload_reserve(keyring,
824                             keyring->datalen - KEYQUOTA_LINK_BYTES);
825         goto error2;
826
827 } /* end __key_link() */
828
829 /*****************************************************************************/
830 /*
831  * link a key to a keyring
832  */
833 int key_link(struct key *keyring, struct key *key)
834 {
835         int ret;
836
837         key_check(keyring);
838         key_check(key);
839
840         down_write(&keyring->sem);
841         ret = __key_link(keyring, key);
842         up_write(&keyring->sem);
843
844         return ret;
845
846 } /* end key_link() */
847
848 EXPORT_SYMBOL(key_link);
849
850 /*****************************************************************************/
851 /*
852  * unlink the first link to a key from a keyring
853  */
854 int key_unlink(struct key *keyring, struct key *key)
855 {
856         struct keyring_list *klist, *nklist;
857         int loop, ret;
858
859         key_check(keyring);
860         key_check(key);
861
862         ret = -ENOTDIR;
863         if (keyring->type != &key_type_keyring)
864                 goto error;
865
866         down_write(&keyring->sem);
867
868         klist = keyring->payload.subscriptions;
869         if (klist) {
870                 /* search the keyring for the key */
871                 for (loop = 0; loop < klist->nkeys; loop++)
872                         if (klist->keys[loop] == key)
873                                 goto key_is_present;
874         }
875
876         up_write(&keyring->sem);
877         ret = -ENOENT;
878         goto error;
879
880 key_is_present:
881         /* we need to copy the key list for RCU purposes */
882         nklist = kmalloc(sizeof(*klist) +
883                          sizeof(struct key *) * klist->maxkeys,
884                          GFP_KERNEL);
885         if (!nklist)
886                 goto nomem;
887         nklist->maxkeys = klist->maxkeys;
888         nklist->nkeys = klist->nkeys - 1;
889
890         if (loop > 0)
891                 memcpy(&nklist->keys[0],
892                        &klist->keys[0],
893                        loop * sizeof(struct key *));
894
895         if (loop < nklist->nkeys)
896                 memcpy(&nklist->keys[loop],
897                        &klist->keys[loop + 1],
898                        (nklist->nkeys - loop) * sizeof(struct key *));
899
900         /* adjust the user's quota */
901         key_payload_reserve(keyring,
902                             keyring->datalen - KEYQUOTA_LINK_BYTES);
903
904         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
905
906         up_write(&keyring->sem);
907
908         /* schedule for later cleanup */
909         klist->delkey = loop;
910         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
911
912         ret = 0;
913
914 error:
915         return ret;
916 nomem:
917         ret = -ENOMEM;
918         up_write(&keyring->sem);
919         goto error;
920
921 } /* end key_unlink() */
922
923 EXPORT_SYMBOL(key_unlink);
924
925 /*****************************************************************************/
926 /*
927  * dispose of a keyring list after the RCU grace period, releasing the keys it
928  * links to
929  */
930 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
931 {
932         struct keyring_list *klist;
933         int loop;
934
935         klist = container_of(rcu, struct keyring_list, rcu);
936
937         for (loop = klist->nkeys - 1; loop >= 0; loop--)
938                 key_put(klist->keys[loop]);
939
940         kfree(klist);
941
942 } /* end keyring_clear_rcu_disposal() */
943
944 /*****************************************************************************/
945 /*
946  * clear the specified process keyring
947  * - implements keyctl(KEYCTL_CLEAR)
948  */
949 int keyring_clear(struct key *keyring)
950 {
951         struct keyring_list *klist;
952         int ret;
953
954         ret = -ENOTDIR;
955         if (keyring->type == &key_type_keyring) {
956                 /* detach the pointer block with the locks held */
957                 down_write(&keyring->sem);
958
959                 klist = keyring->payload.subscriptions;
960                 if (klist) {
961                         /* adjust the quota */
962                         key_payload_reserve(keyring,
963                                             sizeof(struct keyring_list));
964
965                         rcu_assign_pointer(keyring->payload.subscriptions,
966                                            NULL);
967                 }
968
969                 up_write(&keyring->sem);
970
971                 /* free the keys after the locks have been dropped */
972                 if (klist)
973                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
974
975                 ret = 0;
976         }
977
978         return ret;
979
980 } /* end keyring_clear() */
981
982 EXPORT_SYMBOL(keyring_clear);
983
984 /*****************************************************************************/
985 /*
986  * dispose of the links from a revoked keyring
987  * - called with the key sem write-locked
988  */
989 static void keyring_revoke(struct key *keyring)
990 {
991         struct keyring_list *klist = keyring->payload.subscriptions;
992
993         /* adjust the quota */
994         key_payload_reserve(keyring, 0);
995
996         if (klist) {
997                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
998                 call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
999         }
1000
1001 } /* end keyring_revoke() */
1002
1003 /*
1004  * Determine whether a key is dead
1005  */
1006 static bool key_is_dead(struct key *key, time_t limit)
1007 {
1008         return test_bit(KEY_FLAG_DEAD, &key->flags) ||
1009                 (key->expiry > 0 && key->expiry <= limit);
1010 }
1011
1012 /*
1013  * Collect garbage from the contents of a keyring
1014  */
1015 void keyring_gc(struct key *keyring, time_t limit)
1016 {
1017         struct keyring_list *klist, *new;
1018         struct key *key;
1019         int loop, keep, max;
1020
1021         kenter("{%x,%s}", key_serial(keyring), keyring->description);
1022
1023         down_write(&keyring->sem);
1024
1025         klist = keyring->payload.subscriptions;
1026         if (!klist)
1027                 goto no_klist;
1028
1029         /* work out how many subscriptions we're keeping */
1030         keep = 0;
1031         for (loop = klist->nkeys - 1; loop >= 0; loop--)
1032                 if (!key_is_dead(klist->keys[loop], limit))
1033                         keep++;
1034
1035         if (keep == klist->nkeys)
1036                 goto just_return;
1037
1038         /* allocate a new keyring payload */
1039         max = roundup(keep, 4);
1040         new = kmalloc(sizeof(struct keyring_list) + max * sizeof(struct key *),
1041                       GFP_KERNEL);
1042         if (!new)
1043                 goto nomem;
1044         new->maxkeys = max;
1045         new->nkeys = 0;
1046         new->delkey = 0;
1047
1048         /* install the live keys
1049          * - must take care as expired keys may be updated back to life
1050          */
1051         keep = 0;
1052         for (loop = klist->nkeys - 1; loop >= 0; loop--) {
1053                 key = klist->keys[loop];
1054                 if (!key_is_dead(key, limit)) {
1055                         if (keep >= max)
1056                                 goto discard_new;
1057                         new->keys[keep++] = key_get(key);
1058                 }
1059         }
1060         new->nkeys = keep;
1061
1062         /* adjust the quota */
1063         key_payload_reserve(keyring,
1064                             sizeof(struct keyring_list) +
1065                             KEYQUOTA_LINK_BYTES * keep);
1066
1067         if (keep == 0) {
1068                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1069                 kfree(new);
1070         } else {
1071                 rcu_assign_pointer(keyring->payload.subscriptions, new);
1072         }
1073
1074         up_write(&keyring->sem);
1075
1076         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1077         kleave(" [yes]");
1078         return;
1079
1080 discard_new:
1081         new->nkeys = keep;
1082         keyring_clear_rcu_disposal(&new->rcu);
1083         up_write(&keyring->sem);
1084         kleave(" [discard]");
1085         return;
1086
1087 just_return:
1088         up_write(&keyring->sem);
1089         kleave(" [no dead]");
1090         return;
1091
1092 no_klist:
1093         up_write(&keyring->sem);
1094         kleave(" [no_klist]");
1095         return;
1096
1097 nomem:
1098         up_write(&keyring->sem);
1099         kleave(" [oom]");
1100 }