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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 
keyring_hash(const char * desc)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 			       struct key_preparsed_payload *prep);
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  */
keyring_publish_name(struct key * keyring)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  */
keyring_instantiate(struct key * keyring,struct key_preparsed_payload * prep)123 static int keyring_instantiate(struct key *keyring,
124 			       struct key_preparsed_payload *prep)
125 {
126 	int ret;
127 
128 	ret = -EINVAL;
129 	if (prep->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  */
keyring_match(const struct key * keyring,const void * description)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  */
keyring_destroy(struct key * keyring)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  */
keyring_describe(const struct key * keyring,struct seq_file * m)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  */
keyring_read(const struct key * keyring,char __user * buffer,size_t buflen)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  */
keyring_alloc(const char * description,kuid_t uid,kgid_t gid,const struct cred * cred,key_perm_t perm,unsigned long flags,struct key * dest)259 struct key *keyring_alloc(const char *description, kuid_t uid, kgid_t gid,
260 			  const struct cred *cred, key_perm_t perm,
261 			  unsigned long flags, struct key *dest)
262 {
263 	struct key *keyring;
264 	int ret;
265 
266 	keyring = key_alloc(&key_type_keyring, description,
267 			    uid, gid, cred, perm, flags);
268 	if (!IS_ERR(keyring)) {
269 		ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
270 		if (ret < 0) {
271 			key_put(keyring);
272 			keyring = ERR_PTR(ret);
273 		}
274 	}
275 
276 	return keyring;
277 }
278 EXPORT_SYMBOL(keyring_alloc);
279 
280 /**
281  * keyring_search_aux - Search a keyring tree for a key matching some criteria
282  * @keyring_ref: A pointer to the keyring with possession indicator.
283  * @cred: The credentials to use for permissions checks.
284  * @type: The type of key to search for.
285  * @description: Parameter for @match.
286  * @match: Function to rule on whether or not a key is the one required.
287  * @no_state_check: Don't check if a matching key is bad
288  *
289  * Search the supplied keyring tree for a key that matches the criteria given.
290  * The root keyring and any linked keyrings must grant Search permission to the
291  * caller to be searchable and keys can only be found if they too grant Search
292  * to the caller. The possession flag on the root keyring pointer controls use
293  * of the possessor bits in permissions checking of the entire tree.  In
294  * addition, the LSM gets to forbid keyring searches and key matches.
295  *
296  * The search is performed as a breadth-then-depth search up to the prescribed
297  * limit (KEYRING_SEARCH_MAX_DEPTH).
298  *
299  * Keys are matched to the type provided and are then filtered by the match
300  * function, which is given the description to use in any way it sees fit.  The
301  * match function may use any attributes of a key that it wishes to to
302  * determine the match.  Normally the match function from the key type would be
303  * used.
304  *
305  * RCU is used to prevent the keyring key lists from disappearing without the
306  * need to take lots of locks.
307  *
308  * Returns a pointer to the found key and increments the key usage count if
309  * successful; -EAGAIN if no matching keys were found, or if expired or revoked
310  * keys were found; -ENOKEY if only negative keys were found; -ENOTDIR if the
311  * specified keyring wasn't a keyring.
312  *
313  * In the case of a successful return, the possession attribute from
314  * @keyring_ref is propagated to the returned key reference.
315  */
keyring_search_aux(key_ref_t keyring_ref,const struct cred * cred,struct key_type * type,const void * description,key_match_func_t match,bool no_state_check)316 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
317 			     const struct cred *cred,
318 			     struct key_type *type,
319 			     const void *description,
320 			     key_match_func_t match,
321 			     bool no_state_check)
322 {
323 	struct {
324 		/* Need a separate keylist pointer for RCU purposes */
325 		struct key *keyring;
326 		struct keyring_list *keylist;
327 		int kix;
328 	} stack[KEYRING_SEARCH_MAX_DEPTH];
329 
330 	struct keyring_list *keylist;
331 	struct timespec now;
332 	unsigned long possessed, kflags;
333 	struct key *keyring, *key;
334 	key_ref_t key_ref;
335 	long err;
336 	int sp, nkeys, kix;
337 
338 	keyring = key_ref_to_ptr(keyring_ref);
339 	possessed = is_key_possessed(keyring_ref);
340 	key_check(keyring);
341 
342 	/* top keyring must have search permission to begin the search */
343 	err = key_task_permission(keyring_ref, cred, KEY_SEARCH);
344 	if (err < 0) {
345 		key_ref = ERR_PTR(err);
346 		goto error;
347 	}
348 
349 	key_ref = ERR_PTR(-ENOTDIR);
350 	if (keyring->type != &key_type_keyring)
351 		goto error;
352 
353 	rcu_read_lock();
354 
355 	now = current_kernel_time();
356 	err = -EAGAIN;
357 	sp = 0;
358 
359 	/* firstly we should check to see if this top-level keyring is what we
360 	 * are looking for */
361 	key_ref = ERR_PTR(-EAGAIN);
362 	kflags = keyring->flags;
363 	if (keyring->type == type && match(keyring, description)) {
364 		key = keyring;
365 		if (no_state_check)
366 			goto found;
367 
368 		/* check it isn't negative and hasn't expired or been
369 		 * revoked */
370 		if (kflags & (1 << KEY_FLAG_REVOKED))
371 			goto error_2;
372 		if (key->expiry && now.tv_sec >= key->expiry)
373 			goto error_2;
374 		key_ref = ERR_PTR(key->type_data.reject_error);
375 		if (kflags & (1 << KEY_FLAG_NEGATIVE))
376 			goto error_2;
377 		goto found;
378 	}
379 
380 	/* otherwise, the top keyring must not be revoked, expired, or
381 	 * negatively instantiated if we are to search it */
382 	key_ref = ERR_PTR(-EAGAIN);
383 	if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
384 		      (1 << KEY_FLAG_REVOKED) |
385 		      (1 << KEY_FLAG_NEGATIVE)) ||
386 	    (keyring->expiry && now.tv_sec >= keyring->expiry))
387 		goto error_2;
388 
389 	/* start processing a new keyring */
390 descend:
391 	kflags = keyring->flags;
392 	if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
393 		      (1 << KEY_FLAG_REVOKED)))
394 		goto not_this_keyring;
395 
396 	keylist = rcu_dereference(keyring->payload.subscriptions);
397 	if (!keylist)
398 		goto not_this_keyring;
399 
400 	/* iterate through the keys in this keyring first */
401 	nkeys = keylist->nkeys;
402 	smp_rmb();
403 	for (kix = 0; kix < nkeys; kix++) {
404 		key = rcu_dereference(keylist->keys[kix]);
405 		kflags = key->flags;
406 
407 		/* ignore keys not of this type */
408 		if (key->type != type)
409 			continue;
410 
411 		/* skip invalidated, revoked and expired keys */
412 		if (!no_state_check) {
413 			if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
414 				      (1 << KEY_FLAG_REVOKED)))
415 				continue;
416 
417 			if (key->expiry && now.tv_sec >= key->expiry)
418 				continue;
419 		}
420 
421 		/* keys that don't match */
422 		if (!match(key, description))
423 			continue;
424 
425 		/* key must have search permissions */
426 		if (key_task_permission(make_key_ref(key, possessed),
427 					cred, KEY_SEARCH) < 0)
428 			continue;
429 
430 		if (no_state_check)
431 			goto found;
432 
433 		/* we set a different error code if we pass a negative key */
434 		if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
435 			err = key->type_data.reject_error;
436 			continue;
437 		}
438 
439 		goto found;
440 	}
441 
442 	/* search through the keyrings nested in this one */
443 	kix = 0;
444 ascend:
445 	nkeys = keylist->nkeys;
446 	smp_rmb();
447 	for (; kix < nkeys; kix++) {
448 		key = rcu_dereference(keylist->keys[kix]);
449 		if (key->type != &key_type_keyring)
450 			continue;
451 
452 		/* recursively search nested keyrings
453 		 * - only search keyrings for which we have search permission
454 		 */
455 		if (sp >= KEYRING_SEARCH_MAX_DEPTH)
456 			continue;
457 
458 		if (key_task_permission(make_key_ref(key, possessed),
459 					cred, KEY_SEARCH) < 0)
460 			continue;
461 
462 		/* stack the current position */
463 		stack[sp].keyring = keyring;
464 		stack[sp].keylist = keylist;
465 		stack[sp].kix = kix;
466 		sp++;
467 
468 		/* begin again with the new keyring */
469 		keyring = key;
470 		goto descend;
471 	}
472 
473 	/* the keyring we're looking at was disqualified or didn't contain a
474 	 * matching key */
475 not_this_keyring:
476 	if (sp > 0) {
477 		/* resume the processing of a keyring higher up in the tree */
478 		sp--;
479 		keyring = stack[sp].keyring;
480 		keylist = stack[sp].keylist;
481 		kix = stack[sp].kix + 1;
482 		goto ascend;
483 	}
484 
485 	key_ref = ERR_PTR(err);
486 	goto error_2;
487 
488 	/* we found a viable match */
489 found:
490 	atomic_inc(&key->usage);
491 	key->last_used_at = now.tv_sec;
492 	keyring->last_used_at = now.tv_sec;
493 	while (sp > 0)
494 		stack[--sp].keyring->last_used_at = now.tv_sec;
495 	key_check(key);
496 	key_ref = make_key_ref(key, possessed);
497 error_2:
498 	rcu_read_unlock();
499 error:
500 	return key_ref;
501 }
502 
503 /**
504  * keyring_search - Search the supplied keyring tree for a matching key
505  * @keyring: The root of the keyring tree to be searched.
506  * @type: The type of keyring we want to find.
507  * @description: The name of the keyring we want to find.
508  *
509  * As keyring_search_aux() above, but using the current task's credentials and
510  * type's default matching function.
511  */
keyring_search(key_ref_t keyring,struct key_type * type,const char * description)512 key_ref_t keyring_search(key_ref_t keyring,
513 			 struct key_type *type,
514 			 const char *description)
515 {
516 	if (!type->match)
517 		return ERR_PTR(-ENOKEY);
518 
519 	return keyring_search_aux(keyring, current->cred,
520 				  type, description, type->match, false);
521 }
522 EXPORT_SYMBOL(keyring_search);
523 
524 /*
525  * Search the given keyring only (no recursion).
526  *
527  * The caller must guarantee that the keyring is a keyring and that the
528  * permission is granted to search the keyring as no check is made here.
529  *
530  * RCU is used to make it unnecessary to lock the keyring key list here.
531  *
532  * Returns a pointer to the found key with usage count incremented if
533  * successful and returns -ENOKEY if not found.  Revoked keys and keys not
534  * providing the requested permission are skipped over.
535  *
536  * If successful, the possession indicator is propagated from the keyring ref
537  * to the returned key reference.
538  */
__keyring_search_one(key_ref_t keyring_ref,const struct key_type * ktype,const char * description,key_perm_t perm)539 key_ref_t __keyring_search_one(key_ref_t keyring_ref,
540 			       const struct key_type *ktype,
541 			       const char *description,
542 			       key_perm_t perm)
543 {
544 	struct keyring_list *klist;
545 	unsigned long possessed;
546 	struct key *keyring, *key;
547 	int nkeys, loop;
548 
549 	keyring = key_ref_to_ptr(keyring_ref);
550 	possessed = is_key_possessed(keyring_ref);
551 
552 	rcu_read_lock();
553 
554 	klist = rcu_dereference(keyring->payload.subscriptions);
555 	if (klist) {
556 		nkeys = klist->nkeys;
557 		smp_rmb();
558 		for (loop = 0; loop < nkeys ; loop++) {
559 			key = rcu_dereference(klist->keys[loop]);
560 			if (key->type == ktype &&
561 			    (!key->type->match ||
562 			     key->type->match(key, description)) &&
563 			    key_permission(make_key_ref(key, possessed),
564 					   perm) == 0 &&
565 			    !(key->flags & ((1 << KEY_FLAG_INVALIDATED) |
566 					    (1 << KEY_FLAG_REVOKED)))
567 			    )
568 				goto found;
569 		}
570 	}
571 
572 	rcu_read_unlock();
573 	return ERR_PTR(-ENOKEY);
574 
575 found:
576 	atomic_inc(&key->usage);
577 	keyring->last_used_at = key->last_used_at =
578 		current_kernel_time().tv_sec;
579 	rcu_read_unlock();
580 	return make_key_ref(key, possessed);
581 }
582 
583 /*
584  * Find a keyring with the specified name.
585  *
586  * All named keyrings in the current user namespace are searched, provided they
587  * grant Search permission directly to the caller (unless this check is
588  * skipped).  Keyrings whose usage points have reached zero or who have been
589  * revoked are skipped.
590  *
591  * Returns a pointer to the keyring with the keyring's refcount having being
592  * incremented on success.  -ENOKEY is returned if a key could not be found.
593  */
find_keyring_by_name(const char * name,bool skip_perm_check)594 struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
595 {
596 	struct key *keyring;
597 	int bucket;
598 
599 	if (!name)
600 		return ERR_PTR(-EINVAL);
601 
602 	bucket = keyring_hash(name);
603 
604 	read_lock(&keyring_name_lock);
605 
606 	if (keyring_name_hash[bucket].next) {
607 		/* search this hash bucket for a keyring with a matching name
608 		 * that's readable and that hasn't been revoked */
609 		list_for_each_entry(keyring,
610 				    &keyring_name_hash[bucket],
611 				    type_data.link
612 				    ) {
613 			if (!kuid_has_mapping(current_user_ns(), keyring->user->uid))
614 				continue;
615 
616 			if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
617 				continue;
618 
619 			if (strcmp(keyring->description, name) != 0)
620 				continue;
621 
622 			if (!skip_perm_check &&
623 			    key_permission(make_key_ref(keyring, 0),
624 					   KEY_SEARCH) < 0)
625 				continue;
626 
627 			/* we've got a match but we might end up racing with
628 			 * key_cleanup() if the keyring is currently 'dead'
629 			 * (ie. it has a zero usage count) */
630 			if (!atomic_inc_not_zero(&keyring->usage))
631 				continue;
632 			keyring->last_used_at = current_kernel_time().tv_sec;
633 			goto out;
634 		}
635 	}
636 
637 	keyring = ERR_PTR(-ENOKEY);
638 out:
639 	read_unlock(&keyring_name_lock);
640 	return keyring;
641 }
642 
643 /*
644  * See if a cycle will will be created by inserting acyclic tree B in acyclic
645  * tree A at the topmost level (ie: as a direct child of A).
646  *
647  * Since we are adding B to A at the top level, checking for cycles should just
648  * be a matter of seeing if node A is somewhere in tree B.
649  */
keyring_detect_cycle(struct key * A,struct key * B)650 static int keyring_detect_cycle(struct key *A, struct key *B)
651 {
652 	struct {
653 		struct keyring_list *keylist;
654 		int kix;
655 	} stack[KEYRING_SEARCH_MAX_DEPTH];
656 
657 	struct keyring_list *keylist;
658 	struct key *subtree, *key;
659 	int sp, nkeys, kix, ret;
660 
661 	rcu_read_lock();
662 
663 	ret = -EDEADLK;
664 	if (A == B)
665 		goto cycle_detected;
666 
667 	subtree = B;
668 	sp = 0;
669 
670 	/* start processing a new keyring */
671 descend:
672 	if (test_bit(KEY_FLAG_REVOKED, &subtree->flags))
673 		goto not_this_keyring;
674 
675 	keylist = rcu_dereference(subtree->payload.subscriptions);
676 	if (!keylist)
677 		goto not_this_keyring;
678 	kix = 0;
679 
680 ascend:
681 	/* iterate through the remaining keys in this keyring */
682 	nkeys = keylist->nkeys;
683 	smp_rmb();
684 	for (; kix < nkeys; kix++) {
685 		key = rcu_dereference(keylist->keys[kix]);
686 
687 		if (key == A)
688 			goto cycle_detected;
689 
690 		/* recursively check nested keyrings */
691 		if (key->type == &key_type_keyring) {
692 			if (sp >= KEYRING_SEARCH_MAX_DEPTH)
693 				goto too_deep;
694 
695 			/* stack the current position */
696 			stack[sp].keylist = keylist;
697 			stack[sp].kix = kix;
698 			sp++;
699 
700 			/* begin again with the new keyring */
701 			subtree = key;
702 			goto descend;
703 		}
704 	}
705 
706 	/* the keyring we're looking at was disqualified or didn't contain a
707 	 * matching key */
708 not_this_keyring:
709 	if (sp > 0) {
710 		/* resume the checking of a keyring higher up in the tree */
711 		sp--;
712 		keylist = stack[sp].keylist;
713 		kix = stack[sp].kix + 1;
714 		goto ascend;
715 	}
716 
717 	ret = 0; /* no cycles detected */
718 
719 error:
720 	rcu_read_unlock();
721 	return ret;
722 
723 too_deep:
724 	ret = -ELOOP;
725 	goto error;
726 
727 cycle_detected:
728 	ret = -EDEADLK;
729 	goto error;
730 }
731 
732 /*
733  * Dispose of a keyring list after the RCU grace period, freeing the unlinked
734  * key
735  */
keyring_unlink_rcu_disposal(struct rcu_head * rcu)736 static void keyring_unlink_rcu_disposal(struct rcu_head *rcu)
737 {
738 	struct keyring_list *klist =
739 		container_of(rcu, struct keyring_list, rcu);
740 
741 	if (klist->delkey != USHRT_MAX)
742 		key_put(rcu_access_pointer(klist->keys[klist->delkey]));
743 	kfree(klist);
744 }
745 
746 /*
747  * Preallocate memory so that a key can be linked into to a keyring.
748  */
__key_link_begin(struct key * keyring,const struct key_type * type,const char * description,unsigned long * _prealloc)749 int __key_link_begin(struct key *keyring, const struct key_type *type,
750 		     const char *description, unsigned long *_prealloc)
751 	__acquires(&keyring->sem)
752 	__acquires(&keyring_serialise_link_sem)
753 {
754 	struct keyring_list *klist, *nklist;
755 	unsigned long prealloc;
756 	unsigned max;
757 	time_t lowest_lru;
758 	size_t size;
759 	int loop, lru, ret;
760 
761 	kenter("%d,%s,%s,", key_serial(keyring), type->name, description);
762 
763 	if (keyring->type != &key_type_keyring)
764 		return -ENOTDIR;
765 
766 	down_write(&keyring->sem);
767 
768 	ret = -EKEYREVOKED;
769 	if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
770 		goto error_krsem;
771 
772 	/* serialise link/link calls to prevent parallel calls causing a cycle
773 	 * when linking two keyring in opposite orders */
774 	if (type == &key_type_keyring)
775 		down_write(&keyring_serialise_link_sem);
776 
777 	klist = rcu_dereference_locked_keyring(keyring);
778 
779 	/* see if there's a matching key we can displace */
780 	lru = -1;
781 	if (klist && klist->nkeys > 0) {
782 		lowest_lru = TIME_T_MAX;
783 		for (loop = klist->nkeys - 1; loop >= 0; loop--) {
784 			struct key *key = rcu_deref_link_locked(klist, loop,
785 								keyring);
786 			if (key->type == type &&
787 			    strcmp(key->description, description) == 0) {
788 				/* Found a match - we'll replace the link with
789 				 * one to the new key.  We record the slot
790 				 * position.
791 				 */
792 				klist->delkey = loop;
793 				prealloc = 0;
794 				goto done;
795 			}
796 			if (key->last_used_at < lowest_lru) {
797 				lowest_lru = key->last_used_at;
798 				lru = loop;
799 			}
800 		}
801 	}
802 
803 	/* If the keyring is full then do an LRU discard */
804 	if (klist &&
805 	    klist->nkeys == klist->maxkeys &&
806 	    klist->maxkeys >= MAX_KEYRING_LINKS) {
807 		kdebug("LRU discard %d\n", lru);
808 		klist->delkey = lru;
809 		prealloc = 0;
810 		goto done;
811 	}
812 
813 	/* check that we aren't going to overrun the user's quota */
814 	ret = key_payload_reserve(keyring,
815 				  keyring->datalen + KEYQUOTA_LINK_BYTES);
816 	if (ret < 0)
817 		goto error_sem;
818 
819 	if (klist && klist->nkeys < klist->maxkeys) {
820 		/* there's sufficient slack space to append directly */
821 		klist->delkey = klist->nkeys;
822 		prealloc = KEY_LINK_FIXQUOTA;
823 	} else {
824 		/* grow the key list */
825 		max = 4;
826 		if (klist) {
827 			max += klist->maxkeys;
828 			if (max > MAX_KEYRING_LINKS)
829 				max = MAX_KEYRING_LINKS;
830 			BUG_ON(max <= klist->maxkeys);
831 		}
832 
833 		size = sizeof(*klist) + sizeof(struct key *) * max;
834 
835 		ret = -ENOMEM;
836 		nklist = kmalloc(size, GFP_KERNEL);
837 		if (!nklist)
838 			goto error_quota;
839 
840 		nklist->maxkeys = max;
841 		if (klist) {
842 			memcpy(nklist->keys, klist->keys,
843 			       sizeof(struct key *) * klist->nkeys);
844 			nklist->delkey = klist->nkeys;
845 			nklist->nkeys = klist->nkeys + 1;
846 			klist->delkey = USHRT_MAX;
847 		} else {
848 			nklist->nkeys = 1;
849 			nklist->delkey = 0;
850 		}
851 
852 		/* add the key into the new space */
853 		RCU_INIT_POINTER(nklist->keys[nklist->delkey], NULL);
854 		prealloc = (unsigned long)nklist | KEY_LINK_FIXQUOTA;
855 	}
856 
857 done:
858 	*_prealloc = prealloc;
859 	kleave(" = 0");
860 	return 0;
861 
862 error_quota:
863 	/* undo the quota changes */
864 	key_payload_reserve(keyring,
865 			    keyring->datalen - KEYQUOTA_LINK_BYTES);
866 error_sem:
867 	if (type == &key_type_keyring)
868 		up_write(&keyring_serialise_link_sem);
869 error_krsem:
870 	up_write(&keyring->sem);
871 	kleave(" = %d", ret);
872 	return ret;
873 }
874 
875 /*
876  * Check already instantiated keys aren't going to be a problem.
877  *
878  * The caller must have called __key_link_begin(). Don't need to call this for
879  * keys that were created since __key_link_begin() was called.
880  */
__key_link_check_live_key(struct key * keyring,struct key * key)881 int __key_link_check_live_key(struct key *keyring, struct key *key)
882 {
883 	if (key->type == &key_type_keyring)
884 		/* check that we aren't going to create a cycle by linking one
885 		 * keyring to another */
886 		return keyring_detect_cycle(keyring, key);
887 	return 0;
888 }
889 
890 /*
891  * Link a key into to a keyring.
892  *
893  * Must be called with __key_link_begin() having being called.  Discards any
894  * already extant link to matching key if there is one, so that each keyring
895  * holds at most one link to any given key of a particular type+description
896  * combination.
897  */
__key_link(struct key * keyring,struct key * key,unsigned long * _prealloc)898 void __key_link(struct key *keyring, struct key *key,
899 		unsigned long *_prealloc)
900 {
901 	struct keyring_list *klist, *nklist;
902 	struct key *discard;
903 
904 	nklist = (struct keyring_list *)(*_prealloc & ~KEY_LINK_FIXQUOTA);
905 	*_prealloc = 0;
906 
907 	kenter("%d,%d,%p", keyring->serial, key->serial, nklist);
908 
909 	klist = rcu_dereference_locked_keyring(keyring);
910 
911 	atomic_inc(&key->usage);
912 	keyring->last_used_at = key->last_used_at =
913 		current_kernel_time().tv_sec;
914 
915 	/* there's a matching key we can displace or an empty slot in a newly
916 	 * allocated list we can fill */
917 	if (nklist) {
918 		kdebug("reissue %hu/%hu/%hu",
919 		       nklist->delkey, nklist->nkeys, nklist->maxkeys);
920 
921 		RCU_INIT_POINTER(nklist->keys[nklist->delkey], key);
922 
923 		rcu_assign_pointer(keyring->payload.subscriptions, nklist);
924 
925 		/* dispose of the old keyring list and, if there was one, the
926 		 * displaced key */
927 		if (klist) {
928 			kdebug("dispose %hu/%hu/%hu",
929 			       klist->delkey, klist->nkeys, klist->maxkeys);
930 			call_rcu(&klist->rcu, keyring_unlink_rcu_disposal);
931 		}
932 	} else if (klist->delkey < klist->nkeys) {
933 		kdebug("replace %hu/%hu/%hu",
934 		       klist->delkey, klist->nkeys, klist->maxkeys);
935 
936 		discard = rcu_dereference_protected(
937 			klist->keys[klist->delkey],
938 			rwsem_is_locked(&keyring->sem));
939 		rcu_assign_pointer(klist->keys[klist->delkey], key);
940 		/* The garbage collector will take care of RCU
941 		 * synchronisation */
942 		key_put(discard);
943 	} else {
944 		/* there's sufficient slack space to append directly */
945 		kdebug("append %hu/%hu/%hu",
946 		       klist->delkey, klist->nkeys, klist->maxkeys);
947 
948 		RCU_INIT_POINTER(klist->keys[klist->delkey], key);
949 		smp_wmb();
950 		klist->nkeys++;
951 	}
952 }
953 
954 /*
955  * Finish linking a key into to a keyring.
956  *
957  * Must be called with __key_link_begin() having being called.
958  */
__key_link_end(struct key * keyring,struct key_type * type,unsigned long prealloc)959 void __key_link_end(struct key *keyring, struct key_type *type,
960 		    unsigned long prealloc)
961 	__releases(&keyring->sem)
962 	__releases(&keyring_serialise_link_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  */
key_link(struct key * keyring,struct key * key)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  */
key_unlink(struct key * keyring,struct key * key)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  */
keyring_clear_rcu_disposal(struct rcu_head * rcu)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  */
keyring_clear(struct key * keyring)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  */
keyring_revoke(struct key * keyring)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  */
keyring_gc(struct key * keyring,time_t limit)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