0b27271c670c93df03f1de6c2e8da8983f9d0821
[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 <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_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         }
176         else {
177                 seq_puts(m, "[anon]");
178         }
179
180         rcu_read_lock();
181         klist = rcu_dereference(keyring->payload.subscriptions);
182         if (klist)
183                 seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
184         else
185                 seq_puts(m, ": empty");
186         rcu_read_unlock();
187
188 } /* end keyring_describe() */
189
190 /*****************************************************************************/
191 /*
192  * read a list of key IDs from the keyring's contents
193  * - the keyring's semaphore is read-locked
194  */
195 static long keyring_read(const struct key *keyring,
196                          char __user *buffer, size_t buflen)
197 {
198         struct keyring_list *klist;
199         struct key *key;
200         size_t qty, tmp;
201         int loop, ret;
202
203         ret = 0;
204         klist = keyring->payload.subscriptions;
205
206         if (klist) {
207                 /* calculate how much data we could return */
208                 qty = klist->nkeys * sizeof(key_serial_t);
209
210                 if (buffer && buflen > 0) {
211                         if (buflen > qty)
212                                 buflen = qty;
213
214                         /* copy the IDs of the subscribed keys into the
215                          * buffer */
216                         ret = -EFAULT;
217
218                         for (loop = 0; loop < klist->nkeys; loop++) {
219                                 key = klist->keys[loop];
220
221                                 tmp = sizeof(key_serial_t);
222                                 if (tmp > buflen)
223                                         tmp = buflen;
224
225                                 if (copy_to_user(buffer,
226                                                  &key->serial,
227                                                  tmp) != 0)
228                                         goto error;
229
230                                 buflen -= tmp;
231                                 if (buflen == 0)
232                                         break;
233                                 buffer += tmp;
234                         }
235                 }
236
237                 ret = qty;
238         }
239
240  error:
241         return ret;
242
243 } /* end keyring_read() */
244
245 /*****************************************************************************/
246 /*
247  * allocate a keyring and link into the destination keyring
248  */
249 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
250                           const struct cred *cred, unsigned long flags,
251                           struct key *dest)
252 {
253         struct key *keyring;
254         int ret;
255
256         keyring = key_alloc(&key_type_keyring, description,
257                             uid, gid, cred,
258                             (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
259                             flags);
260
261         if (!IS_ERR(keyring)) {
262                 ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
263                 if (ret < 0) {
264                         key_put(keyring);
265                         keyring = ERR_PTR(ret);
266                 }
267         }
268
269         return keyring;
270
271 } /* end keyring_alloc() */
272
273 /*****************************************************************************/
274 /*
275  * search the supplied keyring tree for a key that matches the criterion
276  * - perform a breadth-then-depth search up to the prescribed limit
277  * - we only find keys on which we have search permission
278  * - we use the supplied match function to see if the description (or other
279  *   feature of interest) matches
280  * - we rely on RCU to prevent the keyring lists from disappearing on us
281  * - we return -EAGAIN if we didn't find any matching key
282  * - we return -ENOKEY if we only found negative matching keys
283  * - we propagate the possession attribute from the keyring ref to the key ref
284  */
285 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
286                              const struct cred *cred,
287                              struct key_type *type,
288                              const void *description,
289                              key_match_func_t match)
290 {
291         struct {
292                 struct keyring_list *keylist;
293                 int kix;
294         } stack[KEYRING_SEARCH_MAX_DEPTH];
295
296         struct keyring_list *keylist;
297         struct timespec now;
298         unsigned long possessed, kflags;
299         struct key *keyring, *key;
300         key_ref_t key_ref;
301         long err;
302         int sp, kix;
303
304         keyring = key_ref_to_ptr(keyring_ref);
305         possessed = is_key_possessed(keyring_ref);
306         key_check(keyring);
307
308         /* top keyring must have search permission to begin the search */
309         err = key_task_permission(keyring_ref, cred, KEY_SEARCH);
310         if (err < 0) {
311                 key_ref = ERR_PTR(err);
312                 goto error;
313         }
314
315         key_ref = ERR_PTR(-ENOTDIR);
316         if (keyring->type != &key_type_keyring)
317                 goto error;
318
319         rcu_read_lock();
320
321         now = current_kernel_time();
322         err = -EAGAIN;
323         sp = 0;
324
325         /* firstly we should check to see if this top-level keyring is what we
326          * are looking for */
327         key_ref = ERR_PTR(-EAGAIN);
328         kflags = keyring->flags;
329         if (keyring->type == type && match(keyring, description)) {
330                 key = keyring;
331
332                 /* check it isn't negative and hasn't expired or been
333                  * revoked */
334                 if (kflags & (1 << KEY_FLAG_REVOKED))
335                         goto error_2;
336                 if (key->expiry && now.tv_sec >= key->expiry)
337                         goto error_2;
338                 key_ref = ERR_PTR(-ENOKEY);
339                 if (kflags & (1 << KEY_FLAG_NEGATIVE))
340                         goto error_2;
341                 goto found;
342         }
343
344         /* otherwise, the top keyring must not be revoked, expired, or
345          * negatively instantiated if we are to search it */
346         key_ref = ERR_PTR(-EAGAIN);
347         if (kflags & ((1 << KEY_FLAG_REVOKED) | (1 << KEY_FLAG_NEGATIVE)) ||
348             (keyring->expiry && now.tv_sec >= keyring->expiry))
349                 goto error_2;
350
351         /* start processing a new keyring */
352 descend:
353         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
354                 goto not_this_keyring;
355
356         keylist = rcu_dereference(keyring->payload.subscriptions);
357         if (!keylist)
358                 goto not_this_keyring;
359
360         /* iterate through the keys in this keyring first */
361         for (kix = 0; kix < keylist->nkeys; kix++) {
362                 key = keylist->keys[kix];
363                 kflags = key->flags;
364
365                 /* ignore keys not of this type */
366                 if (key->type != type)
367                         continue;
368
369                 /* skip revoked keys and expired keys */
370                 if (kflags & (1 << KEY_FLAG_REVOKED))
371                         continue;
372
373                 if (key->expiry && now.tv_sec >= key->expiry)
374                         continue;
375
376                 /* keys that don't match */
377                 if (!match(key, description))
378                         continue;
379
380                 /* key must have search permissions */
381                 if (key_task_permission(make_key_ref(key, possessed),
382                                         cred, KEY_SEARCH) < 0)
383                         continue;
384
385                 /* we set a different error code if we pass a negative key */
386                 if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
387                         err = -ENOKEY;
388                         continue;
389                 }
390
391                 goto found;
392         }
393
394         /* search through the keyrings nested in this one */
395         kix = 0;
396 ascend:
397         for (; kix < keylist->nkeys; kix++) {
398                 key = keylist->keys[kix];
399                 if (key->type != &key_type_keyring)
400                         continue;
401
402                 /* recursively search nested keyrings
403                  * - only search keyrings for which we have search permission
404                  */
405                 if (sp >= KEYRING_SEARCH_MAX_DEPTH)
406                         continue;
407
408                 if (key_task_permission(make_key_ref(key, possessed),
409                                         cred, KEY_SEARCH) < 0)
410                         continue;
411
412                 /* stack the current position */
413                 stack[sp].keylist = keylist;
414                 stack[sp].kix = kix;
415                 sp++;
416
417                 /* begin again with the new keyring */
418                 keyring = key;
419                 goto descend;
420         }
421
422         /* the keyring we're looking at was disqualified or didn't contain a
423          * matching key */
424 not_this_keyring:
425         if (sp > 0) {
426                 /* resume the processing of a keyring higher up in the tree */
427                 sp--;
428                 keylist = stack[sp].keylist;
429                 kix = stack[sp].kix + 1;
430                 goto ascend;
431         }
432
433         key_ref = ERR_PTR(err);
434         goto error_2;
435
436         /* we found a viable match */
437 found:
438         atomic_inc(&key->usage);
439         key_check(key);
440         key_ref = make_key_ref(key, possessed);
441 error_2:
442         rcu_read_unlock();
443 error:
444         return key_ref;
445
446 } /* end keyring_search_aux() */
447
448 /*****************************************************************************/
449 /*
450  * search the supplied keyring tree for a key that matches the criterion
451  * - perform a breadth-then-depth search up to the prescribed limit
452  * - we only find keys on which we have search permission
453  * - we readlock the keyrings as we search down the tree
454  * - we return -EAGAIN if we didn't find any matching key
455  * - we return -ENOKEY if we only found negative matching keys
456  */
457 key_ref_t keyring_search(key_ref_t keyring,
458                          struct key_type *type,
459                          const char *description)
460 {
461         if (!type->match)
462                 return ERR_PTR(-ENOKEY);
463
464         return keyring_search_aux(keyring, current->cred,
465                                   type, description, type->match);
466
467 } /* end keyring_search() */
468
469 EXPORT_SYMBOL(keyring_search);
470
471 /*****************************************************************************/
472 /*
473  * search the given keyring only (no recursion)
474  * - keyring must be locked by caller
475  * - caller must guarantee that the keyring is a keyring
476  */
477 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
478                                const struct key_type *ktype,
479                                const char *description,
480                                key_perm_t perm)
481 {
482         struct keyring_list *klist;
483         unsigned long possessed;
484         struct key *keyring, *key;
485         int loop;
486
487         keyring = key_ref_to_ptr(keyring_ref);
488         possessed = is_key_possessed(keyring_ref);
489
490         rcu_read_lock();
491
492         klist = rcu_dereference(keyring->payload.subscriptions);
493         if (klist) {
494                 for (loop = 0; loop < klist->nkeys; loop++) {
495                         key = klist->keys[loop];
496
497                         if (key->type == ktype &&
498                             (!key->type->match ||
499                              key->type->match(key, description)) &&
500                             key_permission(make_key_ref(key, possessed),
501                                            perm) == 0 &&
502                             !test_bit(KEY_FLAG_REVOKED, &key->flags)
503                             )
504                                 goto found;
505                 }
506         }
507
508         rcu_read_unlock();
509         return ERR_PTR(-ENOKEY);
510
511  found:
512         atomic_inc(&key->usage);
513         rcu_read_unlock();
514         return make_key_ref(key, possessed);
515
516 } /* end __keyring_search_one() */
517
518 /*****************************************************************************/
519 /*
520  * find a keyring with the specified name
521  * - all named keyrings are searched
522  * - normally only finds keyrings with search permission for the current process
523  */
524 struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
525 {
526         struct key *keyring;
527         int bucket;
528
529         if (!name)
530                 return ERR_PTR(-EINVAL);
531
532         bucket = keyring_hash(name);
533
534         read_lock(&keyring_name_lock);
535
536         if (keyring_name_hash[bucket].next) {
537                 /* search this hash bucket for a keyring with a matching name
538                  * that's readable and that hasn't been revoked */
539                 list_for_each_entry(keyring,
540                                     &keyring_name_hash[bucket],
541                                     type_data.link
542                                     ) {
543                         if (keyring->user->user_ns != current_user_ns())
544                                 continue;
545
546                         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
547                                 continue;
548
549                         if (strcmp(keyring->description, name) != 0)
550                                 continue;
551
552                         if (!skip_perm_check &&
553                             key_permission(make_key_ref(keyring, 0),
554                                            KEY_SEARCH) < 0)
555                                 continue;
556
557                         /* we've got a match but we might end up racing with
558                          * key_cleanup() if the keyring is currently 'dead'
559                          * (ie. it has a zero usage count) */
560                         if (!atomic_inc_not_zero(&keyring->usage))
561                                 continue;
562                         goto out;
563                 }
564         }
565
566         keyring = ERR_PTR(-ENOKEY);
567 out:
568         read_unlock(&keyring_name_lock);
569         return keyring;
570
571 } /* end find_keyring_by_name() */
572
573 /*****************************************************************************/
574 /*
575  * see if a cycle will will be created by inserting acyclic tree B in acyclic
576  * tree A at the topmost level (ie: as a direct child of A)
577  * - since we are adding B to A at the top level, checking for cycles should
578  *   just be a matter of seeing if node A is somewhere in tree B
579  */
580 static int keyring_detect_cycle(struct key *A, struct key *B)
581 {
582         struct {
583                 struct keyring_list *keylist;
584                 int kix;
585         } stack[KEYRING_SEARCH_MAX_DEPTH];
586
587         struct keyring_list *keylist;
588         struct key *subtree, *key;
589         int sp, kix, ret;
590
591         rcu_read_lock();
592
593         ret = -EDEADLK;
594         if (A == B)
595                 goto cycle_detected;
596
597         subtree = B;
598         sp = 0;
599
600         /* start processing a new keyring */
601  descend:
602         if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
603                 goto not_this_keyring;
604
605         keylist = rcu_dereference(subtree->payload.subscriptions);
606         if (!keylist)
607                 goto not_this_keyring;
608         kix = 0;
609
610  ascend:
611         /* iterate through the remaining keys in this keyring */
612         for (; kix < keylist->nkeys; kix++) {
613                 key = keylist->keys[kix];
614
615                 if (key == A)
616                         goto cycle_detected;
617
618                 /* recursively check nested keyrings */
619                 if (key->type == &key_type_keyring) {
620                         if (sp >= KEYRING_SEARCH_MAX_DEPTH)
621                                 goto too_deep;
622
623                         /* stack the current position */
624                         stack[sp].keylist = keylist;
625                         stack[sp].kix = kix;
626                         sp++;
627
628                         /* begin again with the new keyring */
629                         subtree = key;
630                         goto descend;
631                 }
632         }
633
634         /* the keyring we're looking at was disqualified or didn't contain a
635          * matching key */
636  not_this_keyring:
637         if (sp > 0) {
638                 /* resume the checking of a keyring higher up in the tree */
639                 sp--;
640                 keylist = stack[sp].keylist;
641                 kix = stack[sp].kix + 1;
642                 goto ascend;
643         }
644
645         ret = 0; /* no cycles detected */
646
647  error:
648         rcu_read_unlock();
649         return ret;
650
651  too_deep:
652         ret = -ELOOP;
653         goto error;
654
655  cycle_detected:
656         ret = -EDEADLK;
657         goto error;
658
659 } /* end keyring_detect_cycle() */
660
661 /*****************************************************************************/
662 /*
663  * dispose of a keyring list after the RCU grace period
664  */
665 static void keyring_link_rcu_disposal(struct rcu_head *rcu)
666 {
667         struct keyring_list *klist =
668                 container_of(rcu, struct keyring_list, rcu);
669
670         kfree(klist);
671
672 } /* end keyring_link_rcu_disposal() */
673
674 /*****************************************************************************/
675 /*
676  * dispose of a keyring list after the RCU grace period, freeing the unlinked
677  * key
678  */
679 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
680 {
681         struct keyring_list *klist =
682                 container_of(rcu, struct keyring_list, rcu);
683
684         key_put(klist->keys[klist->delkey]);
685         kfree(klist);
686
687 } /* end keyring_unlink_rcu_disposal() */
688
689 /*****************************************************************************/
690 /*
691  * link a key into to a keyring
692  * - must be called with the keyring's semaphore write-locked
693  * - discard already extant link to matching key if there is one
694  */
695 int __key_link(struct key *keyring, struct key *key)
696 {
697         struct keyring_list *klist, *nklist;
698         unsigned max;
699         size_t size;
700         int loop, ret;
701
702         ret = -EKEYREVOKED;
703         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
704                 goto error;
705
706         ret = -ENOTDIR;
707         if (keyring->type != &key_type_keyring)
708                 goto error;
709
710         /* serialise link/link calls to prevent parallel calls causing a
711          * cycle when applied to two keyring in opposite orders */
712         down_write(&keyring_serialise_link_sem);
713
714         /* check that we aren't going to create a cycle adding one keyring to
715          * another */
716         if (key->type == &key_type_keyring) {
717                 ret = keyring_detect_cycle(keyring, key);
718                 if (ret < 0)
719                         goto error2;
720         }
721
722         /* see if there's a matching key we can displace */
723         klist = keyring->payload.subscriptions;
724
725         if (klist && klist->nkeys > 0) {
726                 struct key_type *type = key->type;
727
728                 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
729                         if (klist->keys[loop]->type == type &&
730                             strcmp(klist->keys[loop]->description,
731                                    key->description) == 0
732                             ) {
733                                 /* found a match - replace with new key */
734                                 size = sizeof(struct key *) * klist->maxkeys;
735                                 size += sizeof(*klist);
736                                 BUG_ON(size > PAGE_SIZE);
737
738                                 ret = -ENOMEM;
739                                 nklist = kmemdup(klist, size, GFP_KERNEL);
740                                 if (!nklist)
741                                         goto error2;
742
743                                 /* replace matched key */
744                                 atomic_inc(&key->usage);
745                                 nklist->keys[loop] = key;
746
747                                 rcu_assign_pointer(
748                                         keyring->payload.subscriptions,
749                                         nklist);
750
751                                 /* dispose of the old keyring list and the
752                                  * displaced key */
753                                 klist->delkey = loop;
754                                 call_rcu(&klist->rcu,
755                                          keyring_unlink_rcu_disposal);
756
757                                 goto done;
758                         }
759                 }
760         }
761
762         /* check that we aren't going to overrun the user's quota */
763         ret = key_payload_reserve(keyring,
764                                   keyring->datalen + KEYQUOTA_LINK_BYTES);
765         if (ret < 0)
766                 goto error2;
767
768         klist = keyring->payload.subscriptions;
769
770         if (klist && klist->nkeys < klist->maxkeys) {
771                 /* there's sufficient slack space to add directly */
772                 atomic_inc(&key->usage);
773
774                 klist->keys[klist->nkeys] = key;
775                 smp_wmb();
776                 klist->nkeys++;
777                 smp_wmb();
778         }
779         else {
780                 /* grow the key list */
781                 max = 4;
782                 if (klist)
783                         max += klist->maxkeys;
784
785                 ret = -ENFILE;
786                 if (max > 65535)
787                         goto error3;
788                 size = sizeof(*klist) + sizeof(struct key *) * max;
789                 if (size > PAGE_SIZE)
790                         goto error3;
791
792                 ret = -ENOMEM;
793                 nklist = kmalloc(size, GFP_KERNEL);
794                 if (!nklist)
795                         goto error3;
796                 nklist->maxkeys = max;
797                 nklist->nkeys = 0;
798
799                 if (klist) {
800                         nklist->nkeys = klist->nkeys;
801                         memcpy(nklist->keys,
802                                klist->keys,
803                                sizeof(struct key *) * klist->nkeys);
804                 }
805
806                 /* add the key into the new space */
807                 atomic_inc(&key->usage);
808                 nklist->keys[nklist->nkeys++] = key;
809
810                 rcu_assign_pointer(keyring->payload.subscriptions, nklist);
811
812                 /* dispose of the old keyring list */
813                 if (klist)
814                         call_rcu(&klist->rcu, keyring_link_rcu_disposal);
815         }
816
817 done:
818         ret = 0;
819 error2:
820         up_write(&keyring_serialise_link_sem);
821 error:
822         return ret;
823
824 error3:
825         /* undo the quota changes */
826         key_payload_reserve(keyring,
827                             keyring->datalen - KEYQUOTA_LINK_BYTES);
828         goto error2;
829
830 } /* end __key_link() */
831
832 /*****************************************************************************/
833 /*
834  * link a key to a keyring
835  */
836 int key_link(struct key *keyring, struct key *key)
837 {
838         int ret;
839
840         key_check(keyring);
841         key_check(key);
842
843         down_write(&keyring->sem);
844         ret = __key_link(keyring, key);
845         up_write(&keyring->sem);
846
847         return ret;
848
849 } /* end key_link() */
850
851 EXPORT_SYMBOL(key_link);
852
853 /*****************************************************************************/
854 /*
855  * unlink the first link to a key from a keyring
856  */
857 int key_unlink(struct key *keyring, struct key *key)
858 {
859         struct keyring_list *klist, *nklist;
860         int loop, ret;
861
862         key_check(keyring);
863         key_check(key);
864
865         ret = -ENOTDIR;
866         if (keyring->type != &key_type_keyring)
867                 goto error;
868
869         down_write(&keyring->sem);
870
871         klist = keyring->payload.subscriptions;
872         if (klist) {
873                 /* search the keyring for the key */
874                 for (loop = 0; loop < klist->nkeys; loop++)
875                         if (klist->keys[loop] == key)
876                                 goto key_is_present;
877         }
878
879         up_write(&keyring->sem);
880         ret = -ENOENT;
881         goto error;
882
883 key_is_present:
884         /* we need to copy the key list for RCU purposes */
885         nklist = kmalloc(sizeof(*klist) +
886                          sizeof(struct key *) * klist->maxkeys,
887                          GFP_KERNEL);
888         if (!nklist)
889                 goto nomem;
890         nklist->maxkeys = klist->maxkeys;
891         nklist->nkeys = klist->nkeys - 1;
892
893         if (loop > 0)
894                 memcpy(&nklist->keys[0],
895                        &klist->keys[0],
896                        loop * sizeof(struct key *));
897
898         if (loop < nklist->nkeys)
899                 memcpy(&nklist->keys[loop],
900                        &klist->keys[loop + 1],
901                        (nklist->nkeys - loop) * sizeof(struct key *));
902
903         /* adjust the user's quota */
904         key_payload_reserve(keyring,
905                             keyring->datalen - KEYQUOTA_LINK_BYTES);
906
907         rcu_assign_pointer(keyring->payload.subscriptions, nklist);
908
909         up_write(&keyring->sem);
910
911         /* schedule for later cleanup */
912         klist->delkey = loop;
913         call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
914
915         ret = 0;
916
917 error:
918         return ret;
919 nomem:
920         ret = -ENOMEM;
921         up_write(&keyring->sem);
922         goto error;
923
924 } /* end key_unlink() */
925
926 EXPORT_SYMBOL(key_unlink);
927
928 /*****************************************************************************/
929 /*
930  * dispose of a keyring list after the RCU grace period, releasing the keys it
931  * links to
932  */
933 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
934 {
935         struct keyring_list *klist;
936         int loop;
937
938         klist = container_of(rcu, struct keyring_list, rcu);
939
940         for (loop = klist->nkeys - 1; loop >= 0; loop--)
941                 key_put(klist->keys[loop]);
942
943         kfree(klist);
944
945 } /* end keyring_clear_rcu_disposal() */
946
947 /*****************************************************************************/
948 /*
949  * clear the specified process keyring
950  * - implements keyctl(KEYCTL_CLEAR)
951  */
952 int keyring_clear(struct key *keyring)
953 {
954         struct keyring_list *klist;
955         int ret;
956
957         ret = -ENOTDIR;
958         if (keyring->type == &key_type_keyring) {
959                 /* detach the pointer block with the locks held */
960                 down_write(&keyring->sem);
961
962                 klist = keyring->payload.subscriptions;
963                 if (klist) {
964                         /* adjust the quota */
965                         key_payload_reserve(keyring,
966                                             sizeof(struct keyring_list));
967
968                         rcu_assign_pointer(keyring->payload.subscriptions,
969                                            NULL);
970                 }
971
972                 up_write(&keyring->sem);
973
974                 /* free the keys after the locks have been dropped */
975                 if (klist)
976                         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
977
978                 ret = 0;
979         }
980
981         return ret;
982
983 } /* end keyring_clear() */
984
985 EXPORT_SYMBOL(keyring_clear);
986
987 /*****************************************************************************/
988 /*
989  * dispose of the links from a revoked keyring
990  * - called with the key sem write-locked
991  */
992 static void keyring_revoke(struct key *keyring)
993 {
994         struct keyring_list *klist = keyring->payload.subscriptions;
995
996         /* adjust the quota */
997         key_payload_reserve(keyring, 0);
998
999         if (klist) {
1000                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1001                 call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1002         }
1003
1004 } /* end keyring_revoke() */
1005
1006 /*
1007  * Determine whether a key is dead
1008  */
1009 static bool key_is_dead(struct key *key, time_t limit)
1010 {
1011         return test_bit(KEY_FLAG_DEAD, &key->flags) ||
1012                 (key->expiry > 0 && key->expiry <= limit);
1013 }
1014
1015 /*
1016  * Collect garbage from the contents of a keyring
1017  */
1018 void keyring_gc(struct key *keyring, time_t limit)
1019 {
1020         struct keyring_list *klist, *new;
1021         struct key *key;
1022         int loop, keep, max;
1023
1024         kenter("{%x,%s}", key_serial(keyring), keyring->description);
1025
1026         down_write(&keyring->sem);
1027
1028         klist = keyring->payload.subscriptions;
1029         if (!klist)
1030                 goto no_klist;
1031
1032         /* work out how many subscriptions we're keeping */
1033         keep = 0;
1034         for (loop = klist->nkeys - 1; loop >= 0; loop--)
1035                 if (!key_is_dead(klist->keys[loop], limit))
1036                         keep++;
1037
1038         if (keep == klist->nkeys)
1039                 goto just_return;
1040
1041         /* allocate a new keyring payload */
1042         max = roundup(keep, 4);
1043         new = kmalloc(sizeof(struct keyring_list) + max * sizeof(struct key *),
1044                       GFP_KERNEL);
1045         if (!new)
1046                 goto nomem;
1047         new->maxkeys = max;
1048         new->nkeys = 0;
1049         new->delkey = 0;
1050
1051         /* install the live keys
1052          * - must take care as expired keys may be updated back to life
1053          */
1054         keep = 0;
1055         for (loop = klist->nkeys - 1; loop >= 0; loop--) {
1056                 key = klist->keys[loop];
1057                 if (!key_is_dead(key, limit)) {
1058                         if (keep >= max)
1059                                 goto discard_new;
1060                         new->keys[keep++] = key_get(key);
1061                 }
1062         }
1063         new->nkeys = keep;
1064
1065         /* adjust the quota */
1066         key_payload_reserve(keyring,
1067                             sizeof(struct keyring_list) +
1068                             KEYQUOTA_LINK_BYTES * keep);
1069
1070         if (keep == 0) {
1071                 rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1072                 kfree(new);
1073         } else {
1074                 rcu_assign_pointer(keyring->payload.subscriptions, new);
1075         }
1076
1077         up_write(&keyring->sem);
1078
1079         call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1080         kleave(" [yes]");
1081         return;
1082
1083 discard_new:
1084         new->nkeys = keep;
1085         keyring_clear_rcu_disposal(&new->rcu);
1086         up_write(&keyring->sem);
1087         kleave(" [discard]");
1088         return;
1089
1090 just_return:
1091         up_write(&keyring->sem);
1092         kleave(" [no dead]");
1093         return;
1094
1095 no_klist:
1096         up_write(&keyring->sem);
1097         kleave(" [no_klist]");
1098         return;
1099
1100 nomem:
1101         up_write(&keyring->sem);
1102         kleave(" [oom]");
1103 }