xref: /linux/security/keys/keyring.c (revision 827634added7f38b7d724cab1dccdb2b004c13c3)
1 /* Keyring handling
2  *
3  * Copyright (C) 2004-2005, 2008, 2013 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 <keys/user-type.h>
21 #include <linux/assoc_array_priv.h>
22 #include <linux/uaccess.h>
23 #include "internal.h"
24 
25 /*
26  * When plumbing the depths of the key tree, this sets a hard limit
27  * set on how deep we're willing to go.
28  */
29 #define KEYRING_SEARCH_MAX_DEPTH 6
30 
31 /*
32  * We keep all named keyrings in a hash to speed looking them up.
33  */
34 #define KEYRING_NAME_HASH_SIZE	(1 << 5)
35 
36 /*
37  * We mark pointers we pass to the associative array with bit 1 set if
38  * they're keyrings and clear otherwise.
39  */
40 #define KEYRING_PTR_SUBTYPE	0x2UL
41 
42 static inline bool keyring_ptr_is_keyring(const struct assoc_array_ptr *x)
43 {
44 	return (unsigned long)x & KEYRING_PTR_SUBTYPE;
45 }
46 static inline struct key *keyring_ptr_to_key(const struct assoc_array_ptr *x)
47 {
48 	void *object = assoc_array_ptr_to_leaf(x);
49 	return (struct key *)((unsigned long)object & ~KEYRING_PTR_SUBTYPE);
50 }
51 static inline void *keyring_key_to_ptr(struct key *key)
52 {
53 	if (key->type == &key_type_keyring)
54 		return (void *)((unsigned long)key | KEYRING_PTR_SUBTYPE);
55 	return key;
56 }
57 
58 static struct list_head	keyring_name_hash[KEYRING_NAME_HASH_SIZE];
59 static DEFINE_RWLOCK(keyring_name_lock);
60 
61 static inline unsigned keyring_hash(const char *desc)
62 {
63 	unsigned bucket = 0;
64 
65 	for (; *desc; desc++)
66 		bucket += (unsigned char)*desc;
67 
68 	return bucket & (KEYRING_NAME_HASH_SIZE - 1);
69 }
70 
71 /*
72  * The keyring key type definition.  Keyrings are simply keys of this type and
73  * can be treated as ordinary keys in addition to having their own special
74  * operations.
75  */
76 static int keyring_preparse(struct key_preparsed_payload *prep);
77 static void keyring_free_preparse(struct key_preparsed_payload *prep);
78 static int keyring_instantiate(struct key *keyring,
79 			       struct key_preparsed_payload *prep);
80 static void keyring_revoke(struct key *keyring);
81 static void keyring_destroy(struct key *keyring);
82 static void keyring_describe(const struct key *keyring, struct seq_file *m);
83 static long keyring_read(const struct key *keyring,
84 			 char __user *buffer, size_t buflen);
85 
86 struct key_type key_type_keyring = {
87 	.name		= "keyring",
88 	.def_datalen	= 0,
89 	.preparse	= keyring_preparse,
90 	.free_preparse	= keyring_free_preparse,
91 	.instantiate	= keyring_instantiate,
92 	.revoke		= keyring_revoke,
93 	.destroy	= keyring_destroy,
94 	.describe	= keyring_describe,
95 	.read		= keyring_read,
96 };
97 EXPORT_SYMBOL(key_type_keyring);
98 
99 /*
100  * Semaphore to serialise link/link calls to prevent two link calls in parallel
101  * introducing a cycle.
102  */
103 static DECLARE_RWSEM(keyring_serialise_link_sem);
104 
105 /*
106  * Publish the name of a keyring so that it can be found by name (if it has
107  * one).
108  */
109 static void keyring_publish_name(struct key *keyring)
110 {
111 	int bucket;
112 
113 	if (keyring->description) {
114 		bucket = keyring_hash(keyring->description);
115 
116 		write_lock(&keyring_name_lock);
117 
118 		if (!keyring_name_hash[bucket].next)
119 			INIT_LIST_HEAD(&keyring_name_hash[bucket]);
120 
121 		list_add_tail(&keyring->type_data.link,
122 			      &keyring_name_hash[bucket]);
123 
124 		write_unlock(&keyring_name_lock);
125 	}
126 }
127 
128 /*
129  * Preparse a keyring payload
130  */
131 static int keyring_preparse(struct key_preparsed_payload *prep)
132 {
133 	return prep->datalen != 0 ? -EINVAL : 0;
134 }
135 
136 /*
137  * Free a preparse of a user defined key payload
138  */
139 static void keyring_free_preparse(struct key_preparsed_payload *prep)
140 {
141 }
142 
143 /*
144  * Initialise a keyring.
145  *
146  * Returns 0 on success, -EINVAL if given any data.
147  */
148 static int keyring_instantiate(struct key *keyring,
149 			       struct key_preparsed_payload *prep)
150 {
151 	assoc_array_init(&keyring->keys);
152 	/* make the keyring available by name if it has one */
153 	keyring_publish_name(keyring);
154 	return 0;
155 }
156 
157 /*
158  * Multiply 64-bits by 32-bits to 96-bits and fold back to 64-bit.  Ideally we'd
159  * fold the carry back too, but that requires inline asm.
160  */
161 static u64 mult_64x32_and_fold(u64 x, u32 y)
162 {
163 	u64 hi = (u64)(u32)(x >> 32) * y;
164 	u64 lo = (u64)(u32)(x) * y;
165 	return lo + ((u64)(u32)hi << 32) + (u32)(hi >> 32);
166 }
167 
168 /*
169  * Hash a key type and description.
170  */
171 static unsigned long hash_key_type_and_desc(const struct keyring_index_key *index_key)
172 {
173 	const unsigned level_shift = ASSOC_ARRAY_LEVEL_STEP;
174 	const unsigned long fan_mask = ASSOC_ARRAY_FAN_MASK;
175 	const char *description = index_key->description;
176 	unsigned long hash, type;
177 	u32 piece;
178 	u64 acc;
179 	int n, desc_len = index_key->desc_len;
180 
181 	type = (unsigned long)index_key->type;
182 
183 	acc = mult_64x32_and_fold(type, desc_len + 13);
184 	acc = mult_64x32_and_fold(acc, 9207);
185 	for (;;) {
186 		n = desc_len;
187 		if (n <= 0)
188 			break;
189 		if (n > 4)
190 			n = 4;
191 		piece = 0;
192 		memcpy(&piece, description, n);
193 		description += n;
194 		desc_len -= n;
195 		acc = mult_64x32_and_fold(acc, piece);
196 		acc = mult_64x32_and_fold(acc, 9207);
197 	}
198 
199 	/* Fold the hash down to 32 bits if need be. */
200 	hash = acc;
201 	if (ASSOC_ARRAY_KEY_CHUNK_SIZE == 32)
202 		hash ^= acc >> 32;
203 
204 	/* Squidge all the keyrings into a separate part of the tree to
205 	 * ordinary keys by making sure the lowest level segment in the hash is
206 	 * zero for keyrings and non-zero otherwise.
207 	 */
208 	if (index_key->type != &key_type_keyring && (hash & fan_mask) == 0)
209 		return hash | (hash >> (ASSOC_ARRAY_KEY_CHUNK_SIZE - level_shift)) | 1;
210 	if (index_key->type == &key_type_keyring && (hash & fan_mask) != 0)
211 		return (hash + (hash << level_shift)) & ~fan_mask;
212 	return hash;
213 }
214 
215 /*
216  * Build the next index key chunk.
217  *
218  * On 32-bit systems the index key is laid out as:
219  *
220  *	0	4	5	9...
221  *	hash	desclen	typeptr	desc[]
222  *
223  * On 64-bit systems:
224  *
225  *	0	8	9	17...
226  *	hash	desclen	typeptr	desc[]
227  *
228  * We return it one word-sized chunk at a time.
229  */
230 static unsigned long keyring_get_key_chunk(const void *data, int level)
231 {
232 	const struct keyring_index_key *index_key = data;
233 	unsigned long chunk = 0;
234 	long offset = 0;
235 	int desc_len = index_key->desc_len, n = sizeof(chunk);
236 
237 	level /= ASSOC_ARRAY_KEY_CHUNK_SIZE;
238 	switch (level) {
239 	case 0:
240 		return hash_key_type_and_desc(index_key);
241 	case 1:
242 		return ((unsigned long)index_key->type << 8) | desc_len;
243 	case 2:
244 		if (desc_len == 0)
245 			return (u8)((unsigned long)index_key->type >>
246 				    (ASSOC_ARRAY_KEY_CHUNK_SIZE - 8));
247 		n--;
248 		offset = 1;
249 	default:
250 		offset += sizeof(chunk) - 1;
251 		offset += (level - 3) * sizeof(chunk);
252 		if (offset >= desc_len)
253 			return 0;
254 		desc_len -= offset;
255 		if (desc_len > n)
256 			desc_len = n;
257 		offset += desc_len;
258 		do {
259 			chunk <<= 8;
260 			chunk |= ((u8*)index_key->description)[--offset];
261 		} while (--desc_len > 0);
262 
263 		if (level == 2) {
264 			chunk <<= 8;
265 			chunk |= (u8)((unsigned long)index_key->type >>
266 				      (ASSOC_ARRAY_KEY_CHUNK_SIZE - 8));
267 		}
268 		return chunk;
269 	}
270 }
271 
272 static unsigned long keyring_get_object_key_chunk(const void *object, int level)
273 {
274 	const struct key *key = keyring_ptr_to_key(object);
275 	return keyring_get_key_chunk(&key->index_key, level);
276 }
277 
278 static bool keyring_compare_object(const void *object, const void *data)
279 {
280 	const struct keyring_index_key *index_key = data;
281 	const struct key *key = keyring_ptr_to_key(object);
282 
283 	return key->index_key.type == index_key->type &&
284 		key->index_key.desc_len == index_key->desc_len &&
285 		memcmp(key->index_key.description, index_key->description,
286 		       index_key->desc_len) == 0;
287 }
288 
289 /*
290  * Compare the index keys of a pair of objects and determine the bit position
291  * at which they differ - if they differ.
292  */
293 static int keyring_diff_objects(const void *object, const void *data)
294 {
295 	const struct key *key_a = keyring_ptr_to_key(object);
296 	const struct keyring_index_key *a = &key_a->index_key;
297 	const struct keyring_index_key *b = data;
298 	unsigned long seg_a, seg_b;
299 	int level, i;
300 
301 	level = 0;
302 	seg_a = hash_key_type_and_desc(a);
303 	seg_b = hash_key_type_and_desc(b);
304 	if ((seg_a ^ seg_b) != 0)
305 		goto differ;
306 
307 	/* The number of bits contributed by the hash is controlled by a
308 	 * constant in the assoc_array headers.  Everything else thereafter we
309 	 * can deal with as being machine word-size dependent.
310 	 */
311 	level += ASSOC_ARRAY_KEY_CHUNK_SIZE / 8;
312 	seg_a = a->desc_len;
313 	seg_b = b->desc_len;
314 	if ((seg_a ^ seg_b) != 0)
315 		goto differ;
316 
317 	/* The next bit may not work on big endian */
318 	level++;
319 	seg_a = (unsigned long)a->type;
320 	seg_b = (unsigned long)b->type;
321 	if ((seg_a ^ seg_b) != 0)
322 		goto differ;
323 
324 	level += sizeof(unsigned long);
325 	if (a->desc_len == 0)
326 		goto same;
327 
328 	i = 0;
329 	if (((unsigned long)a->description | (unsigned long)b->description) &
330 	    (sizeof(unsigned long) - 1)) {
331 		do {
332 			seg_a = *(unsigned long *)(a->description + i);
333 			seg_b = *(unsigned long *)(b->description + i);
334 			if ((seg_a ^ seg_b) != 0)
335 				goto differ_plus_i;
336 			i += sizeof(unsigned long);
337 		} while (i < (a->desc_len & (sizeof(unsigned long) - 1)));
338 	}
339 
340 	for (; i < a->desc_len; i++) {
341 		seg_a = *(unsigned char *)(a->description + i);
342 		seg_b = *(unsigned char *)(b->description + i);
343 		if ((seg_a ^ seg_b) != 0)
344 			goto differ_plus_i;
345 	}
346 
347 same:
348 	return -1;
349 
350 differ_plus_i:
351 	level += i;
352 differ:
353 	i = level * 8 + __ffs(seg_a ^ seg_b);
354 	return i;
355 }
356 
357 /*
358  * Free an object after stripping the keyring flag off of the pointer.
359  */
360 static void keyring_free_object(void *object)
361 {
362 	key_put(keyring_ptr_to_key(object));
363 }
364 
365 /*
366  * Operations for keyring management by the index-tree routines.
367  */
368 static const struct assoc_array_ops keyring_assoc_array_ops = {
369 	.get_key_chunk		= keyring_get_key_chunk,
370 	.get_object_key_chunk	= keyring_get_object_key_chunk,
371 	.compare_object		= keyring_compare_object,
372 	.diff_objects		= keyring_diff_objects,
373 	.free_object		= keyring_free_object,
374 };
375 
376 /*
377  * Clean up a keyring when it is destroyed.  Unpublish its name if it had one
378  * and dispose of its data.
379  *
380  * The garbage collector detects the final key_put(), removes the keyring from
381  * the serial number tree and then does RCU synchronisation before coming here,
382  * so we shouldn't need to worry about code poking around here with the RCU
383  * readlock held by this time.
384  */
385 static void keyring_destroy(struct key *keyring)
386 {
387 	if (keyring->description) {
388 		write_lock(&keyring_name_lock);
389 
390 		if (keyring->type_data.link.next != NULL &&
391 		    !list_empty(&keyring->type_data.link))
392 			list_del(&keyring->type_data.link);
393 
394 		write_unlock(&keyring_name_lock);
395 	}
396 
397 	assoc_array_destroy(&keyring->keys, &keyring_assoc_array_ops);
398 }
399 
400 /*
401  * Describe a keyring for /proc.
402  */
403 static void keyring_describe(const struct key *keyring, struct seq_file *m)
404 {
405 	if (keyring->description)
406 		seq_puts(m, keyring->description);
407 	else
408 		seq_puts(m, "[anon]");
409 
410 	if (key_is_instantiated(keyring)) {
411 		if (keyring->keys.nr_leaves_on_tree != 0)
412 			seq_printf(m, ": %lu", keyring->keys.nr_leaves_on_tree);
413 		else
414 			seq_puts(m, ": empty");
415 	}
416 }
417 
418 struct keyring_read_iterator_context {
419 	size_t			qty;
420 	size_t			count;
421 	key_serial_t __user	*buffer;
422 };
423 
424 static int keyring_read_iterator(const void *object, void *data)
425 {
426 	struct keyring_read_iterator_context *ctx = data;
427 	const struct key *key = keyring_ptr_to_key(object);
428 	int ret;
429 
430 	kenter("{%s,%d},,{%zu/%zu}",
431 	       key->type->name, key->serial, ctx->count, ctx->qty);
432 
433 	if (ctx->count >= ctx->qty)
434 		return 1;
435 
436 	ret = put_user(key->serial, ctx->buffer);
437 	if (ret < 0)
438 		return ret;
439 	ctx->buffer++;
440 	ctx->count += sizeof(key->serial);
441 	return 0;
442 }
443 
444 /*
445  * Read a list of key IDs from the keyring's contents in binary form
446  *
447  * The keyring's semaphore is read-locked by the caller.  This prevents someone
448  * from modifying it under us - which could cause us to read key IDs multiple
449  * times.
450  */
451 static long keyring_read(const struct key *keyring,
452 			 char __user *buffer, size_t buflen)
453 {
454 	struct keyring_read_iterator_context ctx;
455 	unsigned long nr_keys;
456 	int ret;
457 
458 	kenter("{%d},,%zu", key_serial(keyring), buflen);
459 
460 	if (buflen & (sizeof(key_serial_t) - 1))
461 		return -EINVAL;
462 
463 	nr_keys = keyring->keys.nr_leaves_on_tree;
464 	if (nr_keys == 0)
465 		return 0;
466 
467 	/* Calculate how much data we could return */
468 	ctx.qty = nr_keys * sizeof(key_serial_t);
469 
470 	if (!buffer || !buflen)
471 		return ctx.qty;
472 
473 	if (buflen > ctx.qty)
474 		ctx.qty = buflen;
475 
476 	/* Copy the IDs of the subscribed keys into the buffer */
477 	ctx.buffer = (key_serial_t __user *)buffer;
478 	ctx.count = 0;
479 	ret = assoc_array_iterate(&keyring->keys, keyring_read_iterator, &ctx);
480 	if (ret < 0) {
481 		kleave(" = %d [iterate]", ret);
482 		return ret;
483 	}
484 
485 	kleave(" = %zu [ok]", ctx.count);
486 	return ctx.count;
487 }
488 
489 /*
490  * Allocate a keyring and link into the destination keyring.
491  */
492 struct key *keyring_alloc(const char *description, kuid_t uid, kgid_t gid,
493 			  const struct cred *cred, key_perm_t perm,
494 			  unsigned long flags, struct key *dest)
495 {
496 	struct key *keyring;
497 	int ret;
498 
499 	keyring = key_alloc(&key_type_keyring, description,
500 			    uid, gid, cred, perm, flags);
501 	if (!IS_ERR(keyring)) {
502 		ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
503 		if (ret < 0) {
504 			key_put(keyring);
505 			keyring = ERR_PTR(ret);
506 		}
507 	}
508 
509 	return keyring;
510 }
511 EXPORT_SYMBOL(keyring_alloc);
512 
513 /*
514  * By default, we keys found by getting an exact match on their descriptions.
515  */
516 bool key_default_cmp(const struct key *key,
517 		     const struct key_match_data *match_data)
518 {
519 	return strcmp(key->description, match_data->raw_data) == 0;
520 }
521 
522 /*
523  * Iteration function to consider each key found.
524  */
525 static int keyring_search_iterator(const void *object, void *iterator_data)
526 {
527 	struct keyring_search_context *ctx = iterator_data;
528 	const struct key *key = keyring_ptr_to_key(object);
529 	unsigned long kflags = key->flags;
530 
531 	kenter("{%d}", key->serial);
532 
533 	/* ignore keys not of this type */
534 	if (key->type != ctx->index_key.type) {
535 		kleave(" = 0 [!type]");
536 		return 0;
537 	}
538 
539 	/* skip invalidated, revoked and expired keys */
540 	if (ctx->flags & KEYRING_SEARCH_DO_STATE_CHECK) {
541 		if (kflags & ((1 << KEY_FLAG_INVALIDATED) |
542 			      (1 << KEY_FLAG_REVOKED))) {
543 			ctx->result = ERR_PTR(-EKEYREVOKED);
544 			kleave(" = %d [invrev]", ctx->skipped_ret);
545 			goto skipped;
546 		}
547 
548 		if (key->expiry && ctx->now.tv_sec >= key->expiry) {
549 			if (!(ctx->flags & KEYRING_SEARCH_SKIP_EXPIRED))
550 				ctx->result = ERR_PTR(-EKEYEXPIRED);
551 			kleave(" = %d [expire]", ctx->skipped_ret);
552 			goto skipped;
553 		}
554 	}
555 
556 	/* keys that don't match */
557 	if (!ctx->match_data.cmp(key, &ctx->match_data)) {
558 		kleave(" = 0 [!match]");
559 		return 0;
560 	}
561 
562 	/* key must have search permissions */
563 	if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM) &&
564 	    key_task_permission(make_key_ref(key, ctx->possessed),
565 				ctx->cred, KEY_NEED_SEARCH) < 0) {
566 		ctx->result = ERR_PTR(-EACCES);
567 		kleave(" = %d [!perm]", ctx->skipped_ret);
568 		goto skipped;
569 	}
570 
571 	if (ctx->flags & KEYRING_SEARCH_DO_STATE_CHECK) {
572 		/* we set a different error code if we pass a negative key */
573 		if (kflags & (1 << KEY_FLAG_NEGATIVE)) {
574 			smp_rmb();
575 			ctx->result = ERR_PTR(key->type_data.reject_error);
576 			kleave(" = %d [neg]", ctx->skipped_ret);
577 			goto skipped;
578 		}
579 	}
580 
581 	/* Found */
582 	ctx->result = make_key_ref(key, ctx->possessed);
583 	kleave(" = 1 [found]");
584 	return 1;
585 
586 skipped:
587 	return ctx->skipped_ret;
588 }
589 
590 /*
591  * Search inside a keyring for a key.  We can search by walking to it
592  * directly based on its index-key or we can iterate over the entire
593  * tree looking for it, based on the match function.
594  */
595 static int search_keyring(struct key *keyring, struct keyring_search_context *ctx)
596 {
597 	if (ctx->match_data.lookup_type == KEYRING_SEARCH_LOOKUP_DIRECT) {
598 		const void *object;
599 
600 		object = assoc_array_find(&keyring->keys,
601 					  &keyring_assoc_array_ops,
602 					  &ctx->index_key);
603 		return object ? ctx->iterator(object, ctx) : 0;
604 	}
605 	return assoc_array_iterate(&keyring->keys, ctx->iterator, ctx);
606 }
607 
608 /*
609  * Search a tree of keyrings that point to other keyrings up to the maximum
610  * depth.
611  */
612 static bool search_nested_keyrings(struct key *keyring,
613 				   struct keyring_search_context *ctx)
614 {
615 	struct {
616 		struct key *keyring;
617 		struct assoc_array_node *node;
618 		int slot;
619 	} stack[KEYRING_SEARCH_MAX_DEPTH];
620 
621 	struct assoc_array_shortcut *shortcut;
622 	struct assoc_array_node *node;
623 	struct assoc_array_ptr *ptr;
624 	struct key *key;
625 	int sp = 0, slot;
626 
627 	kenter("{%d},{%s,%s}",
628 	       keyring->serial,
629 	       ctx->index_key.type->name,
630 	       ctx->index_key.description);
631 
632 #define STATE_CHECKS (KEYRING_SEARCH_NO_STATE_CHECK | KEYRING_SEARCH_DO_STATE_CHECK)
633 	BUG_ON((ctx->flags & STATE_CHECKS) == 0 ||
634 	       (ctx->flags & STATE_CHECKS) == STATE_CHECKS);
635 
636 	if (ctx->index_key.description)
637 		ctx->index_key.desc_len = strlen(ctx->index_key.description);
638 
639 	/* Check to see if this top-level keyring is what we are looking for
640 	 * and whether it is valid or not.
641 	 */
642 	if (ctx->match_data.lookup_type == KEYRING_SEARCH_LOOKUP_ITERATE ||
643 	    keyring_compare_object(keyring, &ctx->index_key)) {
644 		ctx->skipped_ret = 2;
645 		switch (ctx->iterator(keyring_key_to_ptr(keyring), ctx)) {
646 		case 1:
647 			goto found;
648 		case 2:
649 			return false;
650 		default:
651 			break;
652 		}
653 	}
654 
655 	ctx->skipped_ret = 0;
656 
657 	/* Start processing a new keyring */
658 descend_to_keyring:
659 	kdebug("descend to %d", keyring->serial);
660 	if (keyring->flags & ((1 << KEY_FLAG_INVALIDATED) |
661 			      (1 << KEY_FLAG_REVOKED)))
662 		goto not_this_keyring;
663 
664 	/* Search through the keys in this keyring before its searching its
665 	 * subtrees.
666 	 */
667 	if (search_keyring(keyring, ctx))
668 		goto found;
669 
670 	/* Then manually iterate through the keyrings nested in this one.
671 	 *
672 	 * Start from the root node of the index tree.  Because of the way the
673 	 * hash function has been set up, keyrings cluster on the leftmost
674 	 * branch of the root node (root slot 0) or in the root node itself.
675 	 * Non-keyrings avoid the leftmost branch of the root entirely (root
676 	 * slots 1-15).
677 	 */
678 	ptr = ACCESS_ONCE(keyring->keys.root);
679 	if (!ptr)
680 		goto not_this_keyring;
681 
682 	if (assoc_array_ptr_is_shortcut(ptr)) {
683 		/* If the root is a shortcut, either the keyring only contains
684 		 * keyring pointers (everything clusters behind root slot 0) or
685 		 * doesn't contain any keyring pointers.
686 		 */
687 		shortcut = assoc_array_ptr_to_shortcut(ptr);
688 		smp_read_barrier_depends();
689 		if ((shortcut->index_key[0] & ASSOC_ARRAY_FAN_MASK) != 0)
690 			goto not_this_keyring;
691 
692 		ptr = ACCESS_ONCE(shortcut->next_node);
693 		node = assoc_array_ptr_to_node(ptr);
694 		goto begin_node;
695 	}
696 
697 	node = assoc_array_ptr_to_node(ptr);
698 	smp_read_barrier_depends();
699 
700 	ptr = node->slots[0];
701 	if (!assoc_array_ptr_is_meta(ptr))
702 		goto begin_node;
703 
704 descend_to_node:
705 	/* Descend to a more distal node in this keyring's content tree and go
706 	 * through that.
707 	 */
708 	kdebug("descend");
709 	if (assoc_array_ptr_is_shortcut(ptr)) {
710 		shortcut = assoc_array_ptr_to_shortcut(ptr);
711 		smp_read_barrier_depends();
712 		ptr = ACCESS_ONCE(shortcut->next_node);
713 		BUG_ON(!assoc_array_ptr_is_node(ptr));
714 	}
715 	node = assoc_array_ptr_to_node(ptr);
716 
717 begin_node:
718 	kdebug("begin_node");
719 	smp_read_barrier_depends();
720 	slot = 0;
721 ascend_to_node:
722 	/* Go through the slots in a node */
723 	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
724 		ptr = ACCESS_ONCE(node->slots[slot]);
725 
726 		if (assoc_array_ptr_is_meta(ptr) && node->back_pointer)
727 			goto descend_to_node;
728 
729 		if (!keyring_ptr_is_keyring(ptr))
730 			continue;
731 
732 		key = keyring_ptr_to_key(ptr);
733 
734 		if (sp >= KEYRING_SEARCH_MAX_DEPTH) {
735 			if (ctx->flags & KEYRING_SEARCH_DETECT_TOO_DEEP) {
736 				ctx->result = ERR_PTR(-ELOOP);
737 				return false;
738 			}
739 			goto not_this_keyring;
740 		}
741 
742 		/* Search a nested keyring */
743 		if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM) &&
744 		    key_task_permission(make_key_ref(key, ctx->possessed),
745 					ctx->cred, KEY_NEED_SEARCH) < 0)
746 			continue;
747 
748 		/* stack the current position */
749 		stack[sp].keyring = keyring;
750 		stack[sp].node = node;
751 		stack[sp].slot = slot;
752 		sp++;
753 
754 		/* begin again with the new keyring */
755 		keyring = key;
756 		goto descend_to_keyring;
757 	}
758 
759 	/* We've dealt with all the slots in the current node, so now we need
760 	 * to ascend to the parent and continue processing there.
761 	 */
762 	ptr = ACCESS_ONCE(node->back_pointer);
763 	slot = node->parent_slot;
764 
765 	if (ptr && assoc_array_ptr_is_shortcut(ptr)) {
766 		shortcut = assoc_array_ptr_to_shortcut(ptr);
767 		smp_read_barrier_depends();
768 		ptr = ACCESS_ONCE(shortcut->back_pointer);
769 		slot = shortcut->parent_slot;
770 	}
771 	if (!ptr)
772 		goto not_this_keyring;
773 	node = assoc_array_ptr_to_node(ptr);
774 	smp_read_barrier_depends();
775 	slot++;
776 
777 	/* If we've ascended to the root (zero backpointer), we must have just
778 	 * finished processing the leftmost branch rather than the root slots -
779 	 * so there can't be any more keyrings for us to find.
780 	 */
781 	if (node->back_pointer) {
782 		kdebug("ascend %d", slot);
783 		goto ascend_to_node;
784 	}
785 
786 	/* The keyring we're looking at was disqualified or didn't contain a
787 	 * matching key.
788 	 */
789 not_this_keyring:
790 	kdebug("not_this_keyring %d", sp);
791 	if (sp <= 0) {
792 		kleave(" = false");
793 		return false;
794 	}
795 
796 	/* Resume the processing of a keyring higher up in the tree */
797 	sp--;
798 	keyring = stack[sp].keyring;
799 	node = stack[sp].node;
800 	slot = stack[sp].slot + 1;
801 	kdebug("ascend to %d [%d]", keyring->serial, slot);
802 	goto ascend_to_node;
803 
804 	/* We found a viable match */
805 found:
806 	key = key_ref_to_ptr(ctx->result);
807 	key_check(key);
808 	if (!(ctx->flags & KEYRING_SEARCH_NO_UPDATE_TIME)) {
809 		key->last_used_at = ctx->now.tv_sec;
810 		keyring->last_used_at = ctx->now.tv_sec;
811 		while (sp > 0)
812 			stack[--sp].keyring->last_used_at = ctx->now.tv_sec;
813 	}
814 	kleave(" = true");
815 	return true;
816 }
817 
818 /**
819  * keyring_search_aux - Search a keyring tree for a key matching some criteria
820  * @keyring_ref: A pointer to the keyring with possession indicator.
821  * @ctx: The keyring search context.
822  *
823  * Search the supplied keyring tree for a key that matches the criteria given.
824  * The root keyring and any linked keyrings must grant Search permission to the
825  * caller to be searchable and keys can only be found if they too grant Search
826  * to the caller. The possession flag on the root keyring pointer controls use
827  * of the possessor bits in permissions checking of the entire tree.  In
828  * addition, the LSM gets to forbid keyring searches and key matches.
829  *
830  * The search is performed as a breadth-then-depth search up to the prescribed
831  * limit (KEYRING_SEARCH_MAX_DEPTH).
832  *
833  * Keys are matched to the type provided and are then filtered by the match
834  * function, which is given the description to use in any way it sees fit.  The
835  * match function may use any attributes of a key that it wishes to to
836  * determine the match.  Normally the match function from the key type would be
837  * used.
838  *
839  * RCU can be used to prevent the keyring key lists from disappearing without
840  * the need to take lots of locks.
841  *
842  * Returns a pointer to the found key and increments the key usage count if
843  * successful; -EAGAIN if no matching keys were found, or if expired or revoked
844  * keys were found; -ENOKEY if only negative keys were found; -ENOTDIR if the
845  * specified keyring wasn't a keyring.
846  *
847  * In the case of a successful return, the possession attribute from
848  * @keyring_ref is propagated to the returned key reference.
849  */
850 key_ref_t keyring_search_aux(key_ref_t keyring_ref,
851 			     struct keyring_search_context *ctx)
852 {
853 	struct key *keyring;
854 	long err;
855 
856 	ctx->iterator = keyring_search_iterator;
857 	ctx->possessed = is_key_possessed(keyring_ref);
858 	ctx->result = ERR_PTR(-EAGAIN);
859 
860 	keyring = key_ref_to_ptr(keyring_ref);
861 	key_check(keyring);
862 
863 	if (keyring->type != &key_type_keyring)
864 		return ERR_PTR(-ENOTDIR);
865 
866 	if (!(ctx->flags & KEYRING_SEARCH_NO_CHECK_PERM)) {
867 		err = key_task_permission(keyring_ref, ctx->cred, KEY_NEED_SEARCH);
868 		if (err < 0)
869 			return ERR_PTR(err);
870 	}
871 
872 	rcu_read_lock();
873 	ctx->now = current_kernel_time();
874 	if (search_nested_keyrings(keyring, ctx))
875 		__key_get(key_ref_to_ptr(ctx->result));
876 	rcu_read_unlock();
877 	return ctx->result;
878 }
879 
880 /**
881  * keyring_search - Search the supplied keyring tree for a matching key
882  * @keyring: The root of the keyring tree to be searched.
883  * @type: The type of keyring we want to find.
884  * @description: The name of the keyring we want to find.
885  *
886  * As keyring_search_aux() above, but using the current task's credentials and
887  * type's default matching function and preferred search method.
888  */
889 key_ref_t keyring_search(key_ref_t keyring,
890 			 struct key_type *type,
891 			 const char *description)
892 {
893 	struct keyring_search_context ctx = {
894 		.index_key.type		= type,
895 		.index_key.description	= description,
896 		.cred			= current_cred(),
897 		.match_data.cmp		= key_default_cmp,
898 		.match_data.raw_data	= description,
899 		.match_data.lookup_type	= KEYRING_SEARCH_LOOKUP_DIRECT,
900 		.flags			= KEYRING_SEARCH_DO_STATE_CHECK,
901 	};
902 	key_ref_t key;
903 	int ret;
904 
905 	if (type->match_preparse) {
906 		ret = type->match_preparse(&ctx.match_data);
907 		if (ret < 0)
908 			return ERR_PTR(ret);
909 	}
910 
911 	key = keyring_search_aux(keyring, &ctx);
912 
913 	if (type->match_free)
914 		type->match_free(&ctx.match_data);
915 	return key;
916 }
917 EXPORT_SYMBOL(keyring_search);
918 
919 /*
920  * Search the given keyring for a key that might be updated.
921  *
922  * The caller must guarantee that the keyring is a keyring and that the
923  * permission is granted to modify the keyring as no check is made here.  The
924  * caller must also hold a lock on the keyring semaphore.
925  *
926  * Returns a pointer to the found key with usage count incremented if
927  * successful and returns NULL if not found.  Revoked and invalidated keys are
928  * skipped over.
929  *
930  * If successful, the possession indicator is propagated from the keyring ref
931  * to the returned key reference.
932  */
933 key_ref_t find_key_to_update(key_ref_t keyring_ref,
934 			     const struct keyring_index_key *index_key)
935 {
936 	struct key *keyring, *key;
937 	const void *object;
938 
939 	keyring = key_ref_to_ptr(keyring_ref);
940 
941 	kenter("{%d},{%s,%s}",
942 	       keyring->serial, index_key->type->name, index_key->description);
943 
944 	object = assoc_array_find(&keyring->keys, &keyring_assoc_array_ops,
945 				  index_key);
946 
947 	if (object)
948 		goto found;
949 
950 	kleave(" = NULL");
951 	return NULL;
952 
953 found:
954 	key = keyring_ptr_to_key(object);
955 	if (key->flags & ((1 << KEY_FLAG_INVALIDATED) |
956 			  (1 << KEY_FLAG_REVOKED))) {
957 		kleave(" = NULL [x]");
958 		return NULL;
959 	}
960 	__key_get(key);
961 	kleave(" = {%d}", key->serial);
962 	return make_key_ref(key, is_key_possessed(keyring_ref));
963 }
964 
965 /*
966  * Find a keyring with the specified name.
967  *
968  * All named keyrings in the current user namespace are searched, provided they
969  * grant Search permission directly to the caller (unless this check is
970  * skipped).  Keyrings whose usage points have reached zero or who have been
971  * revoked are skipped.
972  *
973  * Returns a pointer to the keyring with the keyring's refcount having being
974  * incremented on success.  -ENOKEY is returned if a key could not be found.
975  */
976 struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
977 {
978 	struct key *keyring;
979 	int bucket;
980 
981 	if (!name)
982 		return ERR_PTR(-EINVAL);
983 
984 	bucket = keyring_hash(name);
985 
986 	read_lock(&keyring_name_lock);
987 
988 	if (keyring_name_hash[bucket].next) {
989 		/* search this hash bucket for a keyring with a matching name
990 		 * that's readable and that hasn't been revoked */
991 		list_for_each_entry(keyring,
992 				    &keyring_name_hash[bucket],
993 				    type_data.link
994 				    ) {
995 			if (!kuid_has_mapping(current_user_ns(), keyring->user->uid))
996 				continue;
997 
998 			if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
999 				continue;
1000 
1001 			if (strcmp(keyring->description, name) != 0)
1002 				continue;
1003 
1004 			if (!skip_perm_check &&
1005 			    key_permission(make_key_ref(keyring, 0),
1006 					   KEY_NEED_SEARCH) < 0)
1007 				continue;
1008 
1009 			/* we've got a match but we might end up racing with
1010 			 * key_cleanup() if the keyring is currently 'dead'
1011 			 * (ie. it has a zero usage count) */
1012 			if (!atomic_inc_not_zero(&keyring->usage))
1013 				continue;
1014 			keyring->last_used_at = current_kernel_time().tv_sec;
1015 			goto out;
1016 		}
1017 	}
1018 
1019 	keyring = ERR_PTR(-ENOKEY);
1020 out:
1021 	read_unlock(&keyring_name_lock);
1022 	return keyring;
1023 }
1024 
1025 static int keyring_detect_cycle_iterator(const void *object,
1026 					 void *iterator_data)
1027 {
1028 	struct keyring_search_context *ctx = iterator_data;
1029 	const struct key *key = keyring_ptr_to_key(object);
1030 
1031 	kenter("{%d}", key->serial);
1032 
1033 	/* We might get a keyring with matching index-key that is nonetheless a
1034 	 * different keyring. */
1035 	if (key != ctx->match_data.raw_data)
1036 		return 0;
1037 
1038 	ctx->result = ERR_PTR(-EDEADLK);
1039 	return 1;
1040 }
1041 
1042 /*
1043  * See if a cycle will will be created by inserting acyclic tree B in acyclic
1044  * tree A at the topmost level (ie: as a direct child of A).
1045  *
1046  * Since we are adding B to A at the top level, checking for cycles should just
1047  * be a matter of seeing if node A is somewhere in tree B.
1048  */
1049 static int keyring_detect_cycle(struct key *A, struct key *B)
1050 {
1051 	struct keyring_search_context ctx = {
1052 		.index_key		= A->index_key,
1053 		.match_data.raw_data	= A,
1054 		.match_data.lookup_type = KEYRING_SEARCH_LOOKUP_DIRECT,
1055 		.iterator		= keyring_detect_cycle_iterator,
1056 		.flags			= (KEYRING_SEARCH_NO_STATE_CHECK |
1057 					   KEYRING_SEARCH_NO_UPDATE_TIME |
1058 					   KEYRING_SEARCH_NO_CHECK_PERM |
1059 					   KEYRING_SEARCH_DETECT_TOO_DEEP),
1060 	};
1061 
1062 	rcu_read_lock();
1063 	search_nested_keyrings(B, &ctx);
1064 	rcu_read_unlock();
1065 	return PTR_ERR(ctx.result) == -EAGAIN ? 0 : PTR_ERR(ctx.result);
1066 }
1067 
1068 /*
1069  * Preallocate memory so that a key can be linked into to a keyring.
1070  */
1071 int __key_link_begin(struct key *keyring,
1072 		     const struct keyring_index_key *index_key,
1073 		     struct assoc_array_edit **_edit)
1074 	__acquires(&keyring->sem)
1075 	__acquires(&keyring_serialise_link_sem)
1076 {
1077 	struct assoc_array_edit *edit;
1078 	int ret;
1079 
1080 	kenter("%d,%s,%s,",
1081 	       keyring->serial, index_key->type->name, index_key->description);
1082 
1083 	BUG_ON(index_key->desc_len == 0);
1084 
1085 	if (keyring->type != &key_type_keyring)
1086 		return -ENOTDIR;
1087 
1088 	down_write(&keyring->sem);
1089 
1090 	ret = -EKEYREVOKED;
1091 	if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
1092 		goto error_krsem;
1093 
1094 	/* serialise link/link calls to prevent parallel calls causing a cycle
1095 	 * when linking two keyring in opposite orders */
1096 	if (index_key->type == &key_type_keyring)
1097 		down_write(&keyring_serialise_link_sem);
1098 
1099 	/* Create an edit script that will insert/replace the key in the
1100 	 * keyring tree.
1101 	 */
1102 	edit = assoc_array_insert(&keyring->keys,
1103 				  &keyring_assoc_array_ops,
1104 				  index_key,
1105 				  NULL);
1106 	if (IS_ERR(edit)) {
1107 		ret = PTR_ERR(edit);
1108 		goto error_sem;
1109 	}
1110 
1111 	/* If we're not replacing a link in-place then we're going to need some
1112 	 * extra quota.
1113 	 */
1114 	if (!edit->dead_leaf) {
1115 		ret = key_payload_reserve(keyring,
1116 					  keyring->datalen + KEYQUOTA_LINK_BYTES);
1117 		if (ret < 0)
1118 			goto error_cancel;
1119 	}
1120 
1121 	*_edit = edit;
1122 	kleave(" = 0");
1123 	return 0;
1124 
1125 error_cancel:
1126 	assoc_array_cancel_edit(edit);
1127 error_sem:
1128 	if (index_key->type == &key_type_keyring)
1129 		up_write(&keyring_serialise_link_sem);
1130 error_krsem:
1131 	up_write(&keyring->sem);
1132 	kleave(" = %d", ret);
1133 	return ret;
1134 }
1135 
1136 /*
1137  * Check already instantiated keys aren't going to be a problem.
1138  *
1139  * The caller must have called __key_link_begin(). Don't need to call this for
1140  * keys that were created since __key_link_begin() was called.
1141  */
1142 int __key_link_check_live_key(struct key *keyring, struct key *key)
1143 {
1144 	if (key->type == &key_type_keyring)
1145 		/* check that we aren't going to create a cycle by linking one
1146 		 * keyring to another */
1147 		return keyring_detect_cycle(keyring, key);
1148 	return 0;
1149 }
1150 
1151 /*
1152  * Link a key into to a keyring.
1153  *
1154  * Must be called with __key_link_begin() having being called.  Discards any
1155  * already extant link to matching key if there is one, so that each keyring
1156  * holds at most one link to any given key of a particular type+description
1157  * combination.
1158  */
1159 void __key_link(struct key *key, struct assoc_array_edit **_edit)
1160 {
1161 	__key_get(key);
1162 	assoc_array_insert_set_object(*_edit, keyring_key_to_ptr(key));
1163 	assoc_array_apply_edit(*_edit);
1164 	*_edit = NULL;
1165 }
1166 
1167 /*
1168  * Finish linking a key into to a keyring.
1169  *
1170  * Must be called with __key_link_begin() having being called.
1171  */
1172 void __key_link_end(struct key *keyring,
1173 		    const struct keyring_index_key *index_key,
1174 		    struct assoc_array_edit *edit)
1175 	__releases(&keyring->sem)
1176 	__releases(&keyring_serialise_link_sem)
1177 {
1178 	BUG_ON(index_key->type == NULL);
1179 	kenter("%d,%s,", keyring->serial, index_key->type->name);
1180 
1181 	if (index_key->type == &key_type_keyring)
1182 		up_write(&keyring_serialise_link_sem);
1183 
1184 	if (edit && !edit->dead_leaf) {
1185 		key_payload_reserve(keyring,
1186 				    keyring->datalen - KEYQUOTA_LINK_BYTES);
1187 		assoc_array_cancel_edit(edit);
1188 	}
1189 	up_write(&keyring->sem);
1190 }
1191 
1192 /**
1193  * key_link - Link a key to a keyring
1194  * @keyring: The keyring to make the link in.
1195  * @key: The key to link to.
1196  *
1197  * Make a link in a keyring to a key, such that the keyring holds a reference
1198  * on that key and the key can potentially be found by searching that keyring.
1199  *
1200  * This function will write-lock the keyring's semaphore and will consume some
1201  * of the user's key data quota to hold the link.
1202  *
1203  * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring,
1204  * -EKEYREVOKED if the keyring has been revoked, -ENFILE if the keyring is
1205  * full, -EDQUOT if there is insufficient key data quota remaining to add
1206  * another link or -ENOMEM if there's insufficient memory.
1207  *
1208  * It is assumed that the caller has checked that it is permitted for a link to
1209  * be made (the keyring should have Write permission and the key Link
1210  * permission).
1211  */
1212 int key_link(struct key *keyring, struct key *key)
1213 {
1214 	struct assoc_array_edit *edit;
1215 	int ret;
1216 
1217 	kenter("{%d,%d}", keyring->serial, atomic_read(&keyring->usage));
1218 
1219 	key_check(keyring);
1220 	key_check(key);
1221 
1222 	if (test_bit(KEY_FLAG_TRUSTED_ONLY, &keyring->flags) &&
1223 	    !test_bit(KEY_FLAG_TRUSTED, &key->flags))
1224 		return -EPERM;
1225 
1226 	ret = __key_link_begin(keyring, &key->index_key, &edit);
1227 	if (ret == 0) {
1228 		kdebug("begun {%d,%d}", keyring->serial, atomic_read(&keyring->usage));
1229 		ret = __key_link_check_live_key(keyring, key);
1230 		if (ret == 0)
1231 			__key_link(key, &edit);
1232 		__key_link_end(keyring, &key->index_key, edit);
1233 	}
1234 
1235 	kleave(" = %d {%d,%d}", ret, keyring->serial, atomic_read(&keyring->usage));
1236 	return ret;
1237 }
1238 EXPORT_SYMBOL(key_link);
1239 
1240 /**
1241  * key_unlink - Unlink the first link to a key from a keyring.
1242  * @keyring: The keyring to remove the link from.
1243  * @key: The key the link is to.
1244  *
1245  * Remove a link from a keyring to a key.
1246  *
1247  * This function will write-lock the keyring's semaphore.
1248  *
1249  * Returns 0 if successful, -ENOTDIR if the keyring isn't a keyring, -ENOENT if
1250  * the key isn't linked to by the keyring or -ENOMEM if there's insufficient
1251  * memory.
1252  *
1253  * It is assumed that the caller has checked that it is permitted for a link to
1254  * be removed (the keyring should have Write permission; no permissions are
1255  * required on the key).
1256  */
1257 int key_unlink(struct key *keyring, struct key *key)
1258 {
1259 	struct assoc_array_edit *edit;
1260 	int ret;
1261 
1262 	key_check(keyring);
1263 	key_check(key);
1264 
1265 	if (keyring->type != &key_type_keyring)
1266 		return -ENOTDIR;
1267 
1268 	down_write(&keyring->sem);
1269 
1270 	edit = assoc_array_delete(&keyring->keys, &keyring_assoc_array_ops,
1271 				  &key->index_key);
1272 	if (IS_ERR(edit)) {
1273 		ret = PTR_ERR(edit);
1274 		goto error;
1275 	}
1276 	ret = -ENOENT;
1277 	if (edit == NULL)
1278 		goto error;
1279 
1280 	assoc_array_apply_edit(edit);
1281 	key_payload_reserve(keyring, keyring->datalen - KEYQUOTA_LINK_BYTES);
1282 	ret = 0;
1283 
1284 error:
1285 	up_write(&keyring->sem);
1286 	return ret;
1287 }
1288 EXPORT_SYMBOL(key_unlink);
1289 
1290 /**
1291  * keyring_clear - Clear a keyring
1292  * @keyring: The keyring to clear.
1293  *
1294  * Clear the contents of the specified keyring.
1295  *
1296  * Returns 0 if successful or -ENOTDIR if the keyring isn't a keyring.
1297  */
1298 int keyring_clear(struct key *keyring)
1299 {
1300 	struct assoc_array_edit *edit;
1301 	int ret;
1302 
1303 	if (keyring->type != &key_type_keyring)
1304 		return -ENOTDIR;
1305 
1306 	down_write(&keyring->sem);
1307 
1308 	edit = assoc_array_clear(&keyring->keys, &keyring_assoc_array_ops);
1309 	if (IS_ERR(edit)) {
1310 		ret = PTR_ERR(edit);
1311 	} else {
1312 		if (edit)
1313 			assoc_array_apply_edit(edit);
1314 		key_payload_reserve(keyring, 0);
1315 		ret = 0;
1316 	}
1317 
1318 	up_write(&keyring->sem);
1319 	return ret;
1320 }
1321 EXPORT_SYMBOL(keyring_clear);
1322 
1323 /*
1324  * Dispose of the links from a revoked keyring.
1325  *
1326  * This is called with the key sem write-locked.
1327  */
1328 static void keyring_revoke(struct key *keyring)
1329 {
1330 	struct assoc_array_edit *edit;
1331 
1332 	edit = assoc_array_clear(&keyring->keys, &keyring_assoc_array_ops);
1333 	if (!IS_ERR(edit)) {
1334 		if (edit)
1335 			assoc_array_apply_edit(edit);
1336 		key_payload_reserve(keyring, 0);
1337 	}
1338 }
1339 
1340 static bool keyring_gc_select_iterator(void *object, void *iterator_data)
1341 {
1342 	struct key *key = keyring_ptr_to_key(object);
1343 	time_t *limit = iterator_data;
1344 
1345 	if (key_is_dead(key, *limit))
1346 		return false;
1347 	key_get(key);
1348 	return true;
1349 }
1350 
1351 static int keyring_gc_check_iterator(const void *object, void *iterator_data)
1352 {
1353 	const struct key *key = keyring_ptr_to_key(object);
1354 	time_t *limit = iterator_data;
1355 
1356 	key_check(key);
1357 	return key_is_dead(key, *limit);
1358 }
1359 
1360 /*
1361  * Garbage collect pointers from a keyring.
1362  *
1363  * Not called with any locks held.  The keyring's key struct will not be
1364  * deallocated under us as only our caller may deallocate it.
1365  */
1366 void keyring_gc(struct key *keyring, time_t limit)
1367 {
1368 	int result;
1369 
1370 	kenter("%x{%s}", keyring->serial, keyring->description ?: "");
1371 
1372 	if (keyring->flags & ((1 << KEY_FLAG_INVALIDATED) |
1373 			      (1 << KEY_FLAG_REVOKED)))
1374 		goto dont_gc;
1375 
1376 	/* scan the keyring looking for dead keys */
1377 	rcu_read_lock();
1378 	result = assoc_array_iterate(&keyring->keys,
1379 				     keyring_gc_check_iterator, &limit);
1380 	rcu_read_unlock();
1381 	if (result == true)
1382 		goto do_gc;
1383 
1384 dont_gc:
1385 	kleave(" [no gc]");
1386 	return;
1387 
1388 do_gc:
1389 	down_write(&keyring->sem);
1390 	assoc_array_gc(&keyring->keys, &keyring_assoc_array_ops,
1391 		       keyring_gc_select_iterator, &limit);
1392 	up_write(&keyring->sem);
1393 	kleave(" [gc]");
1394 }
1395