xref: /linux/security/keys/keyring.c (revision 26b0d14106954ae46d2f4f7eec3481828a210f7d)
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 #define rcu_dereference_locked_keyring(keyring)				\
24 	(rcu_dereference_protected(					\
25 		(keyring)->payload.subscriptions,			\
26 		rwsem_is_locked((struct rw_semaphore *)&(keyring)->sem)))
27 
28 #define rcu_deref_link_locked(klist, index, keyring)			\
29 	(rcu_dereference_protected(					\
30 		(klist)->keys[index],					\
31 		rwsem_is_locked((struct rw_semaphore *)&(keyring)->sem)))
32 
33 #define MAX_KEYRING_LINKS						\
34 	min_t(size_t, USHRT_MAX - 1,					\
35 	      ((PAGE_SIZE - sizeof(struct keyring_list)) / sizeof(struct key *)))
36 
37 #define KEY_LINK_FIXQUOTA 1UL
38 
39 /*
40  * When plumbing the depths of the key tree, this sets a hard limit
41  * set on how deep we're willing to go.
42  */
43 #define KEYRING_SEARCH_MAX_DEPTH 6
44 
45 /*
46  * We keep all named keyrings in a hash to speed looking them up.
47  */
48 #define KEYRING_NAME_HASH_SIZE	(1 << 5)
49 
50 static struct list_head	keyring_name_hash[KEYRING_NAME_HASH_SIZE];
51 static DEFINE_RWLOCK(keyring_name_lock);
52 
53 static inline unsigned keyring_hash(const char *desc)
54 {
55 	unsigned bucket = 0;
56 
57 	for (; *desc; desc++)
58 		bucket += (unsigned char)*desc;
59 
60 	return bucket & (KEYRING_NAME_HASH_SIZE - 1);
61 }
62 
63 /*
64  * The keyring key type definition.  Keyrings are simply keys of this type and
65  * can be treated as ordinary keys in addition to having their own special
66  * operations.
67  */
68 static int keyring_instantiate(struct key *keyring,
69 			       const void *data, size_t datalen);
70 static int keyring_match(const struct key *keyring, const void *criterion);
71 static void keyring_revoke(struct key *keyring);
72 static void keyring_destroy(struct key *keyring);
73 static void keyring_describe(const struct key *keyring, struct seq_file *m);
74 static long keyring_read(const struct key *keyring,
75 			 char __user *buffer, size_t buflen);
76 
77 struct key_type key_type_keyring = {
78 	.name		= "keyring",
79 	.def_datalen	= sizeof(struct keyring_list),
80 	.instantiate	= keyring_instantiate,
81 	.match		= keyring_match,
82 	.revoke		= keyring_revoke,
83 	.destroy	= keyring_destroy,
84 	.describe	= keyring_describe,
85 	.read		= keyring_read,
86 };
87 EXPORT_SYMBOL(key_type_keyring);
88 
89 /*
90  * Semaphore to serialise link/link calls to prevent two link calls in parallel
91  * introducing a cycle.
92  */
93 static DECLARE_RWSEM(keyring_serialise_link_sem);
94 
95 /*
96  * Publish the name of a keyring so that it can be found by name (if it has
97  * one).
98  */
99 static void keyring_publish_name(struct key *keyring)
100 {
101 	int bucket;
102 
103 	if (keyring->description) {
104 		bucket = keyring_hash(keyring->description);
105 
106 		write_lock(&keyring_name_lock);
107 
108 		if (!keyring_name_hash[bucket].next)
109 			INIT_LIST_HEAD(&keyring_name_hash[bucket]);
110 
111 		list_add_tail(&keyring->type_data.link,
112 			      &keyring_name_hash[bucket]);
113 
114 		write_unlock(&keyring_name_lock);
115 	}
116 }
117 
118 /*
119  * Initialise a keyring.
120  *
121  * Returns 0 on success, -EINVAL if given any data.
122  */
123 static int keyring_instantiate(struct key *keyring,
124 			       const void *data, size_t datalen)
125 {
126 	int ret;
127 
128 	ret = -EINVAL;
129 	if (datalen == 0) {
130 		/* make the keyring available by name if it has one */
131 		keyring_publish_name(keyring);
132 		ret = 0;
133 	}
134 
135 	return ret;
136 }
137 
138 /*
139  * Match keyrings on their name
140  */
141 static int keyring_match(const struct key *keyring, const void *description)
142 {
143 	return keyring->description &&
144 		strcmp(keyring->description, description) == 0;
145 }
146 
147 /*
148  * Clean up a keyring when it is destroyed.  Unpublish its name if it had one
149  * and dispose of its data.
150  *
151  * The garbage collector detects the final key_put(), removes the keyring from
152  * the serial number tree and then does RCU synchronisation before coming here,
153  * so we shouldn't need to worry about code poking around here with the RCU
154  * readlock held by this time.
155  */
156 static void keyring_destroy(struct key *keyring)
157 {
158 	struct keyring_list *klist;
159 	int loop;
160 
161 	if (keyring->description) {
162 		write_lock(&keyring_name_lock);
163 
164 		if (keyring->type_data.link.next != NULL &&
165 		    !list_empty(&keyring->type_data.link))
166 			list_del(&keyring->type_data.link);
167 
168 		write_unlock(&keyring_name_lock);
169 	}
170 
171 	klist = rcu_access_pointer(keyring->payload.subscriptions);
172 	if (klist) {
173 		for (loop = klist->nkeys - 1; loop >= 0; loop--)
174 			key_put(rcu_access_pointer(klist->keys[loop]));
175 		kfree(klist);
176 	}
177 }
178 
179 /*
180  * Describe a keyring for /proc.
181  */
182 static void keyring_describe(const struct key *keyring, struct seq_file *m)
183 {
184 	struct keyring_list *klist;
185 
186 	if (keyring->description)
187 		seq_puts(m, keyring->description);
188 	else
189 		seq_puts(m, "[anon]");
190 
191 	if (key_is_instantiated(keyring)) {
192 		rcu_read_lock();
193 		klist = rcu_dereference(keyring->payload.subscriptions);
194 		if (klist)
195 			seq_printf(m, ": %u/%u", klist->nkeys, klist->maxkeys);
196 		else
197 			seq_puts(m, ": empty");
198 		rcu_read_unlock();
199 	}
200 }
201 
202 /*
203  * Read a list of key IDs from the keyring's contents in binary form
204  *
205  * The keyring's semaphore is read-locked by the caller.
206  */
207 static long keyring_read(const struct key *keyring,
208 			 char __user *buffer, size_t buflen)
209 {
210 	struct keyring_list *klist;
211 	struct key *key;
212 	size_t qty, tmp;
213 	int loop, ret;
214 
215 	ret = 0;
216 	klist = rcu_dereference_locked_keyring(keyring);
217 	if (klist) {
218 		/* calculate how much data we could return */
219 		qty = klist->nkeys * sizeof(key_serial_t);
220 
221 		if (buffer && buflen > 0) {
222 			if (buflen > qty)
223 				buflen = qty;
224 
225 			/* copy the IDs of the subscribed keys into the
226 			 * buffer */
227 			ret = -EFAULT;
228 
229 			for (loop = 0; loop < klist->nkeys; loop++) {
230 				key = rcu_deref_link_locked(klist, loop,
231 							    keyring);
232 
233 				tmp = sizeof(key_serial_t);
234 				if (tmp > buflen)
235 					tmp = buflen;
236 
237 				if (copy_to_user(buffer,
238 						 &key->serial,
239 						 tmp) != 0)
240 					goto error;
241 
242 				buflen -= tmp;
243 				if (buflen == 0)
244 					break;
245 				buffer += tmp;
246 			}
247 		}
248 
249 		ret = qty;
250 	}
251 
252 error:
253 	return ret;
254 }
255 
256 /*
257  * Allocate a keyring and link into the destination keyring.
258  */
259 struct key *keyring_alloc(const char *description, uid_t uid, gid_t gid,
260 			  const struct cred *cred, unsigned long flags,
261 			  struct key *dest)
262 {
263 	struct key *keyring;
264 	int ret;
265 
266 	keyring = key_alloc(&key_type_keyring, description,
267 			    uid, gid, cred,
268 			    (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL,
269 			    flags);
270 
271 	if (!IS_ERR(keyring)) {
272 		ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
273 		if (ret < 0) {
274 			key_put(keyring);
275 			keyring = ERR_PTR(ret);
276 		}
277 	}
278 
279 	return keyring;
280 }
281 
282 /**
283  * keyring_search_aux - Search a keyring tree for a key matching some criteria
284  * @keyring_ref: A pointer to the keyring with possession indicator.
285  * @cred: The credentials to use for permissions checks.
286  * @type: The type of key to search for.
287  * @description: Parameter for @match.
288  * @match: Function to rule on whether or not a key is the one required.
289  * @no_state_check: Don't check if a matching key is bad
290  *
291  * Search the supplied keyring tree for a key that matches the criteria given.
292  * The root keyring and any linked keyrings must grant Search permission to the
293  * caller to be searchable and keys can only be found if they too grant Search
294  * to the caller. The possession flag on the root keyring pointer controls use
295  * of the possessor bits in permissions checking of the entire tree.  In
296  * addition, the LSM gets to forbid keyring searches and key matches.
297  *
298  * The search is performed as a breadth-then-depth search up to the prescribed
299  * limit (KEYRING_SEARCH_MAX_DEPTH).
300  *
301  * Keys are matched to the type provided and are then filtered by the match
302  * function, which is given the description to use in any way it sees fit.  The
303  * match function may use any attributes of a key that it wishes to to
304  * determine the match.  Normally the match function from the key type would be
305  * used.
306  *
307  * RCU is used to prevent the keyring key lists from disappearing without the
308  * need to take lots of locks.
309  *
310  * Returns a pointer to the found key and increments the key usage count if
311  * successful; -EAGAIN if no matching keys were found, or if expired or revoked
312  * keys were found; -ENOKEY if only negative keys were found; -ENOTDIR if the
313  * specified keyring wasn't a keyring.
314  *
315  * In the case of a successful return, the possession attribute from
316  * @keyring_ref is propagated to the returned key reference.
317  */
318 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
319 			     const struct cred *cred,
320 			     struct key_type *type,
321 			     const void *description,
322 			     key_match_func_t match,
323 			     bool no_state_check)
324 {
325 	struct {
326 		/* Need a separate keylist pointer for RCU purposes */
327 		struct key *keyring;
328 		struct keyring_list *keylist;
329 		int kix;
330 	} stack[KEYRING_SEARCH_MAX_DEPTH];
331 
332 	struct keyring_list *keylist;
333 	struct timespec now;
334 	unsigned long possessed, kflags;
335 	struct key *keyring, *key;
336 	key_ref_t key_ref;
337 	long err;
338 	int sp, nkeys, kix;
339 
340 	keyring = key_ref_to_ptr(keyring_ref);
341 	possessed = is_key_possessed(keyring_ref);
342 	key_check(keyring);
343 
344 	/* top keyring must have search permission to begin the search */
345 	err = key_task_permission(keyring_ref, cred, KEY_SEARCH);
346 	if (err < 0) {
347 		key_ref = ERR_PTR(err);
348 		goto error;
349 	}
350 
351 	key_ref = ERR_PTR(-ENOTDIR);
352 	if (keyring->type != &key_type_keyring)
353 		goto error;
354 
355 	rcu_read_lock();
356 
357 	now = current_kernel_time();
358 	err = -EAGAIN;
359 	sp = 0;
360 
361 	/* firstly we should check to see if this top-level keyring is what we
362 	 * are looking for */
363 	key_ref = ERR_PTR(-EAGAIN);
364 	kflags = keyring->flags;
365 	if (keyring->type == type && match(keyring, description)) {
366 		key = keyring;
367 		if (no_state_check)
368 			goto found;
369 
370 		/* check it isn't negative and hasn't expired or been
371 		 * revoked */
372 		if (kflags & (1 << KEY_FLAG_REVOKED))
373 			goto error_2;
374 		if (key->expiry && now.tv_sec >= key->expiry)
375 			goto error_2;
376 		key_ref = ERR_PTR(key->type_data.reject_error);
377 		if (kflags & (1 << KEY_FLAG_NEGATIVE))
378 			goto error_2;
379 		goto found;
380 	}
381 
382 	/* otherwise, the top keyring must not be revoked, expired, or
383 	 * negatively instantiated if we are to search it */
384 	key_ref = ERR_PTR(-EAGAIN);
385 	if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
386 		      (1 << KEY_FLAG_REVOKED) |
387 		      (1 << KEY_FLAG_NEGATIVE)) ||
388 	    (keyring->expiry && now.tv_sec >= keyring->expiry))
389 		goto error_2;
390 
391 	/* start processing a new keyring */
392 descend:
393 	kflags = keyring->flags;
394 	if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
395 		      (1 << KEY_FLAG_REVOKED)))
396 		goto not_this_keyring;
397 
398 	keylist = rcu_dereference(keyring->payload.subscriptions);
399 	if (!keylist)
400 		goto not_this_keyring;
401 
402 	/* iterate through the keys in this keyring first */
403 	nkeys = keylist->nkeys;
404 	smp_rmb();
405 	for (kix = 0; kix < nkeys; kix++) {
406 		key = rcu_dereference(keylist->keys[kix]);
407 		kflags = key->flags;
408 
409 		/* ignore keys not of this type */
410 		if (key->type != type)
411 			continue;
412 
413 		/* skip invalidated, revoked and expired keys */
414 		if (!no_state_check) {
415 			if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
416 				      (1 << KEY_FLAG_REVOKED)))
417 				continue;
418 
419 			if (key->expiry && now.tv_sec >= key->expiry)
420 				continue;
421 		}
422 
423 		/* keys that don't match */
424 		if (!match(key, description))
425 			continue;
426 
427 		/* key must have search permissions */
428 		if (key_task_permission(make_key_ref(key, possessed),
429 					cred, KEY_SEARCH) < 0)
430 			continue;
431 
432 		if (no_state_check)
433 			goto found;
434 
435 		/* we set a different error code if we pass a negative key */
436 		if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
437 			err = key->type_data.reject_error;
438 			continue;
439 		}
440 
441 		goto found;
442 	}
443 
444 	/* search through the keyrings nested in this one */
445 	kix = 0;
446 ascend:
447 	nkeys = keylist->nkeys;
448 	smp_rmb();
449 	for (; kix < nkeys; kix++) {
450 		key = rcu_dereference(keylist->keys[kix]);
451 		if (key->type != &key_type_keyring)
452 			continue;
453 
454 		/* recursively search nested keyrings
455 		 * - only search keyrings for which we have search permission
456 		 */
457 		if (sp >= KEYRING_SEARCH_MAX_DEPTH)
458 			continue;
459 
460 		if (key_task_permission(make_key_ref(key, possessed),
461 					cred, KEY_SEARCH) < 0)
462 			continue;
463 
464 		/* stack the current position */
465 		stack[sp].keyring = keyring;
466 		stack[sp].keylist = keylist;
467 		stack[sp].kix = kix;
468 		sp++;
469 
470 		/* begin again with the new keyring */
471 		keyring = key;
472 		goto descend;
473 	}
474 
475 	/* the keyring we're looking at was disqualified or didn't contain a
476 	 * matching key */
477 not_this_keyring:
478 	if (sp > 0) {
479 		/* resume the processing of a keyring higher up in the tree */
480 		sp--;
481 		keyring = stack[sp].keyring;
482 		keylist = stack[sp].keylist;
483 		kix = stack[sp].kix + 1;
484 		goto ascend;
485 	}
486 
487 	key_ref = ERR_PTR(err);
488 	goto error_2;
489 
490 	/* we found a viable match */
491 found:
492 	atomic_inc(&key->usage);
493 	key->last_used_at = now.tv_sec;
494 	keyring->last_used_at = now.tv_sec;
495 	while (sp > 0)
496 		stack[--sp].keyring->last_used_at = now.tv_sec;
497 	key_check(key);
498 	key_ref = make_key_ref(key, possessed);
499 error_2:
500 	rcu_read_unlock();
501 error:
502 	return key_ref;
503 }
504 
505 /**
506  * keyring_search - Search the supplied keyring tree for a matching key
507  * @keyring: The root of the keyring tree to be searched.
508  * @type: The type of keyring we want to find.
509  * @description: The name of the keyring we want to find.
510  *
511  * As keyring_search_aux() above, but using the current task's credentials and
512  * type's default matching function.
513  */
514 key_ref_t keyring_search(key_ref_t keyring,
515 			 struct key_type *type,
516 			 const char *description)
517 {
518 	if (!type->match)
519 		return ERR_PTR(-ENOKEY);
520 
521 	return keyring_search_aux(keyring, current->cred,
522 				  type, description, type->match, false);
523 }
524 EXPORT_SYMBOL(keyring_search);
525 
526 /*
527  * Search the given keyring only (no recursion).
528  *
529  * The caller must guarantee that the keyring is a keyring and that the
530  * permission is granted to search the keyring as no check is made here.
531  *
532  * RCU is used to make it unnecessary to lock the keyring key list here.
533  *
534  * Returns a pointer to the found key with usage count incremented if
535  * successful and returns -ENOKEY if not found.  Revoked keys and keys not
536  * providing the requested permission are skipped over.
537  *
538  * If successful, the possession indicator is propagated from the keyring ref
539  * to the returned key reference.
540  */
541 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
542 			       const struct key_type *ktype,
543 			       const char *description,
544 			       key_perm_t perm)
545 {
546 	struct keyring_list *klist;
547 	unsigned long possessed;
548 	struct key *keyring, *key;
549 	int nkeys, loop;
550 
551 	keyring = key_ref_to_ptr(keyring_ref);
552 	possessed = is_key_possessed(keyring_ref);
553 
554 	rcu_read_lock();
555 
556 	klist = rcu_dereference(keyring->payload.subscriptions);
557 	if (klist) {
558 		nkeys = klist->nkeys;
559 		smp_rmb();
560 		for (loop = 0; loop < nkeys ; loop++) {
561 			key = rcu_dereference(klist->keys[loop]);
562 			if (key->type == ktype &&
563 			    (!key->type->match ||
564 			     key->type->match(key, description)) &&
565 			    key_permission(make_key_ref(key, possessed),
566 					   perm) == 0 &&
567 			    !(key->flags & ((1 << KEY_FLAG_INVALIDATED) |
568 					    (1 << KEY_FLAG_REVOKED)))
569 			    )
570 				goto found;
571 		}
572 	}
573 
574 	rcu_read_unlock();
575 	return ERR_PTR(-ENOKEY);
576 
577 found:
578 	atomic_inc(&key->usage);
579 	keyring->last_used_at = key->last_used_at =
580 		current_kernel_time().tv_sec;
581 	rcu_read_unlock();
582 	return make_key_ref(key, possessed);
583 }
584 
585 /*
586  * Find a keyring with the specified name.
587  *
588  * All named keyrings in the current user namespace are searched, provided they
589  * grant Search permission directly to the caller (unless this check is
590  * skipped).  Keyrings whose usage points have reached zero or who have been
591  * revoked are skipped.
592  *
593  * Returns a pointer to the keyring with the keyring's refcount having being
594  * incremented on success.  -ENOKEY is returned if a key could not be found.
595  */
596 struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
597 {
598 	struct key *keyring;
599 	int bucket;
600 
601 	if (!name)
602 		return ERR_PTR(-EINVAL);
603 
604 	bucket = keyring_hash(name);
605 
606 	read_lock(&keyring_name_lock);
607 
608 	if (keyring_name_hash[bucket].next) {
609 		/* search this hash bucket for a keyring with a matching name
610 		 * that's readable and that hasn't been revoked */
611 		list_for_each_entry(keyring,
612 				    &keyring_name_hash[bucket],
613 				    type_data.link
614 				    ) {
615 			if (keyring->user->user_ns != current_user_ns())
616 				continue;
617 
618 			if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
619 				continue;
620 
621 			if (strcmp(keyring->description, name) != 0)
622 				continue;
623 
624 			if (!skip_perm_check &&
625 			    key_permission(make_key_ref(keyring, 0),
626 					   KEY_SEARCH) < 0)
627 				continue;
628 
629 			/* we've got a match but we might end up racing with
630 			 * key_cleanup() if the keyring is currently 'dead'
631 			 * (ie. it has a zero usage count) */
632 			if (!atomic_inc_not_zero(&keyring->usage))
633 				continue;
634 			keyring->last_used_at = current_kernel_time().tv_sec;
635 			goto out;
636 		}
637 	}
638 
639 	keyring = ERR_PTR(-ENOKEY);
640 out:
641 	read_unlock(&keyring_name_lock);
642 	return keyring;
643 }
644 
645 /*
646  * See if a cycle will will be created by inserting acyclic tree B in acyclic
647  * tree A at the topmost level (ie: as a direct child of A).
648  *
649  * Since we are adding B to A at the top level, checking for cycles should just
650  * be a matter of seeing if node A is somewhere in tree B.
651  */
652 static int keyring_detect_cycle(struct key *A, struct key *B)
653 {
654 	struct {
655 		struct keyring_list *keylist;
656 		int kix;
657 	} stack[KEYRING_SEARCH_MAX_DEPTH];
658 
659 	struct keyring_list *keylist;
660 	struct key *subtree, *key;
661 	int sp, nkeys, kix, ret;
662 
663 	rcu_read_lock();
664 
665 	ret = -EDEADLK;
666 	if (A == B)
667 		goto cycle_detected;
668 
669 	subtree = B;
670 	sp = 0;
671 
672 	/* start processing a new keyring */
673 descend:
674 	if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
675 		goto not_this_keyring;
676 
677 	keylist = rcu_dereference(subtree->payload.subscriptions);
678 	if (!keylist)
679 		goto not_this_keyring;
680 	kix = 0;
681 
682 ascend:
683 	/* iterate through the remaining keys in this keyring */
684 	nkeys = keylist->nkeys;
685 	smp_rmb();
686 	for (; kix < nkeys; kix++) {
687 		key = rcu_dereference(keylist->keys[kix]);
688 
689 		if (key == A)
690 			goto cycle_detected;
691 
692 		/* recursively check nested keyrings */
693 		if (key->type == &key_type_keyring) {
694 			if (sp >= KEYRING_SEARCH_MAX_DEPTH)
695 				goto too_deep;
696 
697 			/* stack the current position */
698 			stack[sp].keylist = keylist;
699 			stack[sp].kix = kix;
700 			sp++;
701 
702 			/* begin again with the new keyring */
703 			subtree = key;
704 			goto descend;
705 		}
706 	}
707 
708 	/* the keyring we're looking at was disqualified or didn't contain a
709 	 * matching key */
710 not_this_keyring:
711 	if (sp > 0) {
712 		/* resume the checking of a keyring higher up in the tree */
713 		sp--;
714 		keylist = stack[sp].keylist;
715 		kix = stack[sp].kix + 1;
716 		goto ascend;
717 	}
718 
719 	ret = 0; /* no cycles detected */
720 
721 error:
722 	rcu_read_unlock();
723 	return ret;
724 
725 too_deep:
726 	ret = -ELOOP;
727 	goto error;
728 
729 cycle_detected:
730 	ret = -EDEADLK;
731 	goto error;
732 }
733 
734 /*
735  * Dispose of a keyring list after the RCU grace period, freeing the unlinked
736  * key
737  */
738 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
739 {
740 	struct keyring_list *klist =
741 		container_of(rcu, struct keyring_list, rcu);
742 
743 	if (klist->delkey != USHRT_MAX)
744 		key_put(rcu_access_pointer(klist->keys[klist->delkey]));
745 	kfree(klist);
746 }
747 
748 /*
749  * Preallocate memory so that a key can be linked into to a keyring.
750  */
751 int __key_link_begin(struct key *keyring, const struct key_type *type,
752 		     const char *description, unsigned long *_prealloc)
753 	__acquires(&keyring->sem)
754 {
755 	struct keyring_list *klist, *nklist;
756 	unsigned long prealloc;
757 	unsigned max;
758 	time_t lowest_lru;
759 	size_t size;
760 	int loop, lru, ret;
761 
762 	kenter("%d,%s,%s,", key_serial(keyring), type->name, description);
763 
764 	if (keyring->type != &key_type_keyring)
765 		return -ENOTDIR;
766 
767 	down_write(&keyring->sem);
768 
769 	ret = -EKEYREVOKED;
770 	if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
771 		goto error_krsem;
772 
773 	/* serialise link/link calls to prevent parallel calls causing a cycle
774 	 * when linking two keyring in opposite orders */
775 	if (type == &key_type_keyring)
776 		down_write(&keyring_serialise_link_sem);
777 
778 	klist = rcu_dereference_locked_keyring(keyring);
779 
780 	/* see if there's a matching key we can displace */
781 	lru = -1;
782 	if (klist && klist->nkeys > 0) {
783 		lowest_lru = TIME_T_MAX;
784 		for (loop = klist->nkeys - 1; loop >= 0; loop--) {
785 			struct key *key = rcu_deref_link_locked(klist, loop,
786 								keyring);
787 			if (key->type == type &&
788 			    strcmp(key->description, description) == 0) {
789 				/* Found a match - we'll replace the link with
790 				 * one to the new key.  We record the slot
791 				 * position.
792 				 */
793 				klist->delkey = loop;
794 				prealloc = 0;
795 				goto done;
796 			}
797 			if (key->last_used_at < lowest_lru) {
798 				lowest_lru = key->last_used_at;
799 				lru = loop;
800 			}
801 		}
802 	}
803 
804 	/* If the keyring is full then do an LRU discard */
805 	if (klist &&
806 	    klist->nkeys == klist->maxkeys &&
807 	    klist->maxkeys >= MAX_KEYRING_LINKS) {
808 		kdebug("LRU discard %d\n", lru);
809 		klist->delkey = lru;
810 		prealloc = 0;
811 		goto done;
812 	}
813 
814 	/* check that we aren't going to overrun the user's quota */
815 	ret = key_payload_reserve(keyring,
816 				  keyring->datalen + KEYQUOTA_LINK_BYTES);
817 	if (ret < 0)
818 		goto error_sem;
819 
820 	if (klist && klist->nkeys < klist->maxkeys) {
821 		/* there's sufficient slack space to append directly */
822 		klist->delkey = klist->nkeys;
823 		prealloc = KEY_LINK_FIXQUOTA;
824 	} else {
825 		/* grow the key list */
826 		max = 4;
827 		if (klist) {
828 			max += klist->maxkeys;
829 			if (max > MAX_KEYRING_LINKS)
830 				max = MAX_KEYRING_LINKS;
831 			BUG_ON(max <= klist->maxkeys);
832 		}
833 
834 		size = sizeof(*klist) + sizeof(struct key *) * max;
835 
836 		ret = -ENOMEM;
837 		nklist = kmalloc(size, GFP_KERNEL);
838 		if (!nklist)
839 			goto error_quota;
840 
841 		nklist->maxkeys = max;
842 		if (klist) {
843 			memcpy(nklist->keys, klist->keys,
844 			       sizeof(struct key *) * klist->nkeys);
845 			nklist->delkey = klist->nkeys;
846 			nklist->nkeys = klist->nkeys + 1;
847 			klist->delkey = USHRT_MAX;
848 		} else {
849 			nklist->nkeys = 1;
850 			nklist->delkey = 0;
851 		}
852 
853 		/* add the key into the new space */
854 		RCU_INIT_POINTER(nklist->keys[nklist->delkey], NULL);
855 		prealloc = (unsigned long)nklist | KEY_LINK_FIXQUOTA;
856 	}
857 
858 done:
859 	*_prealloc = prealloc;
860 	kleave(" = 0");
861 	return 0;
862 
863 error_quota:
864 	/* undo the quota changes */
865 	key_payload_reserve(keyring,
866 			    keyring->datalen - KEYQUOTA_LINK_BYTES);
867 error_sem:
868 	if (type == &key_type_keyring)
869 		up_write(&keyring_serialise_link_sem);
870 error_krsem:
871 	up_write(&keyring->sem);
872 	kleave(" = %d", ret);
873 	return ret;
874 }
875 
876 /*
877  * Check already instantiated keys aren't going to be a problem.
878  *
879  * The caller must have called __key_link_begin(). Don't need to call this for
880  * keys that were created since __key_link_begin() was called.
881  */
882 int __key_link_check_live_key(struct key *keyring, struct key *key)
883 {
884 	if (key->type == &key_type_keyring)
885 		/* check that we aren't going to create a cycle by linking one
886 		 * keyring to another */
887 		return keyring_detect_cycle(keyring, key);
888 	return 0;
889 }
890 
891 /*
892  * Link a key into to a keyring.
893  *
894  * Must be called with __key_link_begin() having being called.  Discards any
895  * already extant link to matching key if there is one, so that each keyring
896  * holds at most one link to any given key of a particular type+description
897  * combination.
898  */
899 void __key_link(struct key *keyring, struct key *key,
900 		unsigned long *_prealloc)
901 {
902 	struct keyring_list *klist, *nklist;
903 	struct key *discard;
904 
905 	nklist = (struct keyring_list *)(*_prealloc & ~KEY_LINK_FIXQUOTA);
906 	*_prealloc = 0;
907 
908 	kenter("%d,%d,%p", keyring->serial, key->serial, nklist);
909 
910 	klist = rcu_dereference_locked_keyring(keyring);
911 
912 	atomic_inc(&key->usage);
913 	keyring->last_used_at = key->last_used_at =
914 		current_kernel_time().tv_sec;
915 
916 	/* there's a matching key we can displace or an empty slot in a newly
917 	 * allocated list we can fill */
918 	if (nklist) {
919 		kdebug("reissue %hu/%hu/%hu",
920 		       nklist->delkey, nklist->nkeys, nklist->maxkeys);
921 
922 		RCU_INIT_POINTER(nklist->keys[nklist->delkey], key);
923 
924 		rcu_assign_pointer(keyring->payload.subscriptions, nklist);
925 
926 		/* dispose of the old keyring list and, if there was one, the
927 		 * displaced key */
928 		if (klist) {
929 			kdebug("dispose %hu/%hu/%hu",
930 			       klist->delkey, klist->nkeys, klist->maxkeys);
931 			call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
932 		}
933 	} else if (klist->delkey < klist->nkeys) {
934 		kdebug("replace %hu/%hu/%hu",
935 		       klist->delkey, klist->nkeys, klist->maxkeys);
936 
937 		discard = rcu_dereference_protected(
938 			klist->keys[klist->delkey],
939 			rwsem_is_locked(&keyring->sem));
940 		rcu_assign_pointer(klist->keys[klist->delkey], key);
941 		/* The garbage collector will take care of RCU
942 		 * synchronisation */
943 		key_put(discard);
944 	} else {
945 		/* there's sufficient slack space to append directly */
946 		kdebug("append %hu/%hu/%hu",
947 		       klist->delkey, klist->nkeys, klist->maxkeys);
948 
949 		RCU_INIT_POINTER(klist->keys[klist->delkey], key);
950 		smp_wmb();
951 		klist->nkeys++;
952 	}
953 }
954 
955 /*
956  * Finish linking a key into to a keyring.
957  *
958  * Must be called with __key_link_begin() having being called.
959  */
960 void __key_link_end(struct key *keyring, struct key_type *type,
961 		    unsigned long prealloc)
962 	__releases(&keyring->sem)
963 {
964 	BUG_ON(type == NULL);
965 	BUG_ON(type->name == NULL);
966 	kenter("%d,%s,%lx", keyring->serial, type->name, prealloc);
967 
968 	if (type == &key_type_keyring)
969 		up_write(&keyring_serialise_link_sem);
970 
971 	if (prealloc) {
972 		if (prealloc & KEY_LINK_FIXQUOTA)
973 			key_payload_reserve(keyring,
974 					    keyring->datalen -
975 					    KEYQUOTA_LINK_BYTES);
976 		kfree((struct keyring_list *)(prealloc & ~KEY_LINK_FIXQUOTA));
977 	}
978 	up_write(&keyring->sem);
979 }
980 
981 /**
982  * key_link - Link a key to a keyring
983  * @keyring: The keyring to make the link in.
984  * @key: The key to link to.
985  *
986  * Make a link in a keyring to a key, such that the keyring holds a reference
987  * on that key and the key can potentially be found by searching that keyring.
988  *
989  * This function will write-lock the keyring's semaphore and will consume some
990  * of the user's key data quota to hold the link.
991  *
992  * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring,
993  * -EKEYREVOKED if the keyring has been revoked, -ENFILE if the keyring is
994  * full, -EDQUOT if there is insufficient key data quota remaining to add
995  * another link or -ENOMEM if there's insufficient memory.
996  *
997  * It is assumed that the caller has checked that it is permitted for a link to
998  * be made (the keyring should have Write permission and the key Link
999  * permission).
1000  */
1001 int key_link(struct key *keyring, struct key *key)
1002 {
1003 	unsigned long prealloc;
1004 	int ret;
1005 
1006 	key_check(keyring);
1007 	key_check(key);
1008 
1009 	ret = __key_link_begin(keyring, key->type, key->description, &prealloc);
1010 	if (ret == 0) {
1011 		ret = __key_link_check_live_key(keyring, key);
1012 		if (ret == 0)
1013 			__key_link(keyring, key, &prealloc);
1014 		__key_link_end(keyring, key->type, prealloc);
1015 	}
1016 
1017 	return ret;
1018 }
1019 EXPORT_SYMBOL(key_link);
1020 
1021 /**
1022  * key_unlink - Unlink the first link to a key from a keyring.
1023  * @keyring: The keyring to remove the link from.
1024  * @key: The key the link is to.
1025  *
1026  * Remove a link from a keyring to a key.
1027  *
1028  * This function will write-lock the keyring's semaphore.
1029  *
1030  * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring, -ENOENT if
1031  * the key isn't linked to by the keyring or -ENOMEM if there's insufficient
1032  * memory.
1033  *
1034  * It is assumed that the caller has checked that it is permitted for a link to
1035  * be removed (the keyring should have Write permission; no permissions are
1036  * required on the key).
1037  */
1038 int key_unlink(struct key *keyring, struct key *key)
1039 {
1040 	struct keyring_list *klist, *nklist;
1041 	int loop, ret;
1042 
1043 	key_check(keyring);
1044 	key_check(key);
1045 
1046 	ret = -ENOTDIR;
1047 	if (keyring->type != &key_type_keyring)
1048 		goto error;
1049 
1050 	down_write(&keyring->sem);
1051 
1052 	klist = rcu_dereference_locked_keyring(keyring);
1053 	if (klist) {
1054 		/* search the keyring for the key */
1055 		for (loop = 0; loop < klist->nkeys; loop++)
1056 			if (rcu_access_pointer(klist->keys[loop]) == key)
1057 				goto key_is_present;
1058 	}
1059 
1060 	up_write(&keyring->sem);
1061 	ret = -ENOENT;
1062 	goto error;
1063 
1064 key_is_present:
1065 	/* we need to copy the key list for RCU purposes */
1066 	nklist = kmalloc(sizeof(*klist) +
1067 			 sizeof(struct key *) * klist->maxkeys,
1068 			 GFP_KERNEL);
1069 	if (!nklist)
1070 		goto nomem;
1071 	nklist->maxkeys = klist->maxkeys;
1072 	nklist->nkeys = klist->nkeys - 1;
1073 
1074 	if (loop > 0)
1075 		memcpy(&nklist->keys[0],
1076 		       &klist->keys[0],
1077 		       loop * sizeof(struct key *));
1078 
1079 	if (loop < nklist->nkeys)
1080 		memcpy(&nklist->keys[loop],
1081 		       &klist->keys[loop + 1],
1082 		       (nklist->nkeys - loop) * sizeof(struct key *));
1083 
1084 	/* adjust the user's quota */
1085 	key_payload_reserve(keyring,
1086 			    keyring->datalen - KEYQUOTA_LINK_BYTES);
1087 
1088 	rcu_assign_pointer(keyring->payload.subscriptions, nklist);
1089 
1090 	up_write(&keyring->sem);
1091 
1092 	/* schedule for later cleanup */
1093 	klist->delkey = loop;
1094 	call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
1095 
1096 	ret = 0;
1097 
1098 error:
1099 	return ret;
1100 nomem:
1101 	ret = -ENOMEM;
1102 	up_write(&keyring->sem);
1103 	goto error;
1104 }
1105 EXPORT_SYMBOL(key_unlink);
1106 
1107 /*
1108  * Dispose of a keyring list after the RCU grace period, releasing the keys it
1109  * links to.
1110  */
1111 static void keyring_clear_rcu_disposal(struct rcu_head *rcu)
1112 {
1113 	struct keyring_list *klist;
1114 	int loop;
1115 
1116 	klist = container_of(rcu, struct keyring_list, rcu);
1117 
1118 	for (loop = klist->nkeys - 1; loop >= 0; loop--)
1119 		key_put(rcu_access_pointer(klist->keys[loop]));
1120 
1121 	kfree(klist);
1122 }
1123 
1124 /**
1125  * keyring_clear - Clear a keyring
1126  * @keyring: The keyring to clear.
1127  *
1128  * Clear the contents of the specified keyring.
1129  *
1130  * Returns 0 if successful or -ENOTDIR if the keyring isn't a keyring.
1131  */
1132 int keyring_clear(struct key *keyring)
1133 {
1134 	struct keyring_list *klist;
1135 	int ret;
1136 
1137 	ret = -ENOTDIR;
1138 	if (keyring->type == &key_type_keyring) {
1139 		/* detach the pointer block with the locks held */
1140 		down_write(&keyring->sem);
1141 
1142 		klist = rcu_dereference_locked_keyring(keyring);
1143 		if (klist) {
1144 			/* adjust the quota */
1145 			key_payload_reserve(keyring,
1146 					    sizeof(struct keyring_list));
1147 
1148 			rcu_assign_pointer(keyring->payload.subscriptions,
1149 					   NULL);
1150 		}
1151 
1152 		up_write(&keyring->sem);
1153 
1154 		/* free the keys after the locks have been dropped */
1155 		if (klist)
1156 			call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1157 
1158 		ret = 0;
1159 	}
1160 
1161 	return ret;
1162 }
1163 EXPORT_SYMBOL(keyring_clear);
1164 
1165 /*
1166  * Dispose of the links from a revoked keyring.
1167  *
1168  * This is called with the key sem write-locked.
1169  */
1170 static void keyring_revoke(struct key *keyring)
1171 {
1172 	struct keyring_list *klist;
1173 
1174 	klist = rcu_dereference_locked_keyring(keyring);
1175 
1176 	/* adjust the quota */
1177 	key_payload_reserve(keyring, 0);
1178 
1179 	if (klist) {
1180 		rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1181 		call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1182 	}
1183 }
1184 
1185 /*
1186  * Collect garbage from the contents of a keyring, replacing the old list with
1187  * a new one with the pointers all shuffled down.
1188  *
1189  * Dead keys are classed as oned that are flagged as being dead or are revoked,
1190  * expired or negative keys that were revoked or expired before the specified
1191  * limit.
1192  */
1193 void keyring_gc(struct key *keyring, time_t limit)
1194 {
1195 	struct keyring_list *klist, *new;
1196 	struct key *key;
1197 	int loop, keep, max;
1198 
1199 	kenter("{%x,%s}", key_serial(keyring), keyring->description);
1200 
1201 	down_write(&keyring->sem);
1202 
1203 	klist = rcu_dereference_locked_keyring(keyring);
1204 	if (!klist)
1205 		goto no_klist;
1206 
1207 	/* work out how many subscriptions we're keeping */
1208 	keep = 0;
1209 	for (loop = klist->nkeys - 1; loop >= 0; loop--)
1210 		if (!key_is_dead(rcu_deref_link_locked(klist, loop, keyring),
1211 				 limit))
1212 			keep++;
1213 
1214 	if (keep == klist->nkeys)
1215 		goto just_return;
1216 
1217 	/* allocate a new keyring payload */
1218 	max = roundup(keep, 4);
1219 	new = kmalloc(sizeof(struct keyring_list) + max * sizeof(struct key *),
1220 		      GFP_KERNEL);
1221 	if (!new)
1222 		goto nomem;
1223 	new->maxkeys = max;
1224 	new->nkeys = 0;
1225 	new->delkey = 0;
1226 
1227 	/* install the live keys
1228 	 * - must take care as expired keys may be updated back to life
1229 	 */
1230 	keep = 0;
1231 	for (loop = klist->nkeys - 1; loop >= 0; loop--) {
1232 		key = rcu_deref_link_locked(klist, loop, keyring);
1233 		if (!key_is_dead(key, limit)) {
1234 			if (keep >= max)
1235 				goto discard_new;
1236 			RCU_INIT_POINTER(new->keys[keep++], key_get(key));
1237 		}
1238 	}
1239 	new->nkeys = keep;
1240 
1241 	/* adjust the quota */
1242 	key_payload_reserve(keyring,
1243 			    sizeof(struct keyring_list) +
1244 			    KEYQUOTA_LINK_BYTES * keep);
1245 
1246 	if (keep == 0) {
1247 		rcu_assign_pointer(keyring->payload.subscriptions, NULL);
1248 		kfree(new);
1249 	} else {
1250 		rcu_assign_pointer(keyring->payload.subscriptions, new);
1251 	}
1252 
1253 	up_write(&keyring->sem);
1254 
1255 	call_rcu(&klist->rcu, keyring_clear_rcu_disposal);
1256 	kleave(" [yes]");
1257 	return;
1258 
1259 discard_new:
1260 	new->nkeys = keep;
1261 	keyring_clear_rcu_disposal(&new->rcu);
1262 	up_write(&keyring->sem);
1263 	kleave(" [discard]");
1264 	return;
1265 
1266 just_return:
1267 	up_write(&keyring->sem);
1268 	kleave(" [no dead]");
1269 	return;
1270 
1271 no_klist:
1272 	up_write(&keyring->sem);
1273 	kleave(" [no_klist]");
1274 	return;
1275 
1276 nomem:
1277 	up_write(&keyring->sem);
1278 	kleave(" [oom]");
1279 }
1280