1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * security/tomoyo/gc.c
4  *
5  * Copyright (C) 2005-2011  NTT DATA CORPORATION
6  */
7 
8 #include "common.h"
9 #include <linux/kthread.h>
10 #include <linux/slab.h>
11 
12 /**
13  * tomoyo_memory_free - Free memory for elements.
14  *
15  * @ptr:  Pointer to allocated memory.
16  *
17  * Returns nothing.
18  *
19  * Caller holds tomoyo_policy_lock mutex.
20  */
tomoyo_memory_free(void * ptr)21 static inline void tomoyo_memory_free(void *ptr)
22 {
23 	tomoyo_memory_used[TOMOYO_MEMORY_POLICY] -= ksize(ptr);
24 	kfree(ptr);
25 }
26 
27 /* The list for "struct tomoyo_io_buffer". */
28 static LIST_HEAD(tomoyo_io_buffer_list);
29 /* Lock for protecting tomoyo_io_buffer_list. */
30 static DEFINE_SPINLOCK(tomoyo_io_buffer_list_lock);
31 
32 /**
33  * tomoyo_struct_used_by_io_buffer - Check whether the list element is used by /sys/kernel/security/tomoyo/ users or not.
34  *
35  * @element: Pointer to "struct list_head".
36  *
37  * Returns true if @element is used by /sys/kernel/security/tomoyo/ users,
38  * false otherwise.
39  */
tomoyo_struct_used_by_io_buffer(const struct list_head * element)40 static bool tomoyo_struct_used_by_io_buffer(const struct list_head *element)
41 {
42 	struct tomoyo_io_buffer *head;
43 	bool in_use = false;
44 
45 	spin_lock(&tomoyo_io_buffer_list_lock);
46 	list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
47 		head->users++;
48 		spin_unlock(&tomoyo_io_buffer_list_lock);
49 		mutex_lock(&head->io_sem);
50 		if (head->r.domain == element || head->r.group == element ||
51 		    head->r.acl == element || &head->w.domain->list == element)
52 			in_use = true;
53 		mutex_unlock(&head->io_sem);
54 		spin_lock(&tomoyo_io_buffer_list_lock);
55 		head->users--;
56 		if (in_use)
57 			break;
58 	}
59 	spin_unlock(&tomoyo_io_buffer_list_lock);
60 	return in_use;
61 }
62 
63 /**
64  * tomoyo_name_used_by_io_buffer - Check whether the string is used by /sys/kernel/security/tomoyo/ users or not.
65  *
66  * @string: String to check.
67  *
68  * Returns true if @string is used by /sys/kernel/security/tomoyo/ users,
69  * false otherwise.
70  */
tomoyo_name_used_by_io_buffer(const char * string)71 static bool tomoyo_name_used_by_io_buffer(const char *string)
72 {
73 	struct tomoyo_io_buffer *head;
74 	const size_t size = strlen(string) + 1;
75 	bool in_use = false;
76 
77 	spin_lock(&tomoyo_io_buffer_list_lock);
78 	list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
79 		int i;
80 
81 		head->users++;
82 		spin_unlock(&tomoyo_io_buffer_list_lock);
83 		mutex_lock(&head->io_sem);
84 		for (i = 0; i < TOMOYO_MAX_IO_READ_QUEUE; i++) {
85 			const char *w = head->r.w[i];
86 
87 			if (w < string || w > string + size)
88 				continue;
89 			in_use = true;
90 			break;
91 		}
92 		mutex_unlock(&head->io_sem);
93 		spin_lock(&tomoyo_io_buffer_list_lock);
94 		head->users--;
95 		if (in_use)
96 			break;
97 	}
98 	spin_unlock(&tomoyo_io_buffer_list_lock);
99 	return in_use;
100 }
101 
102 /**
103  * tomoyo_del_transition_control - Delete members in "struct tomoyo_transition_control".
104  *
105  * @element: Pointer to "struct list_head".
106  *
107  * Returns nothing.
108  */
tomoyo_del_transition_control(struct list_head * element)109 static inline void tomoyo_del_transition_control(struct list_head *element)
110 {
111 	struct tomoyo_transition_control *ptr =
112 		container_of(element, typeof(*ptr), head.list);
113 
114 	tomoyo_put_name(ptr->domainname);
115 	tomoyo_put_name(ptr->program);
116 }
117 
118 /**
119  * tomoyo_del_aggregator - Delete members in "struct tomoyo_aggregator".
120  *
121  * @element: Pointer to "struct list_head".
122  *
123  * Returns nothing.
124  */
tomoyo_del_aggregator(struct list_head * element)125 static inline void tomoyo_del_aggregator(struct list_head *element)
126 {
127 	struct tomoyo_aggregator *ptr =
128 		container_of(element, typeof(*ptr), head.list);
129 
130 	tomoyo_put_name(ptr->original_name);
131 	tomoyo_put_name(ptr->aggregated_name);
132 }
133 
134 /**
135  * tomoyo_del_manager - Delete members in "struct tomoyo_manager".
136  *
137  * @element: Pointer to "struct list_head".
138  *
139  * Returns nothing.
140  */
tomoyo_del_manager(struct list_head * element)141 static inline void tomoyo_del_manager(struct list_head *element)
142 {
143 	struct tomoyo_manager *ptr =
144 		container_of(element, typeof(*ptr), head.list);
145 
146 	tomoyo_put_name(ptr->manager);
147 }
148 
149 /**
150  * tomoyo_del_acl - Delete members in "struct tomoyo_acl_info".
151  *
152  * @element: Pointer to "struct list_head".
153  *
154  * Returns nothing.
155  */
tomoyo_del_acl(struct list_head * element)156 static void tomoyo_del_acl(struct list_head *element)
157 {
158 	struct tomoyo_acl_info *acl =
159 		container_of(element, typeof(*acl), list);
160 
161 	tomoyo_put_condition(acl->cond);
162 	switch (acl->type) {
163 	case TOMOYO_TYPE_PATH_ACL:
164 		{
165 			struct tomoyo_path_acl *entry
166 				= container_of(acl, typeof(*entry), head);
167 			tomoyo_put_name_union(&entry->name);
168 		}
169 		break;
170 	case TOMOYO_TYPE_PATH2_ACL:
171 		{
172 			struct tomoyo_path2_acl *entry
173 				= container_of(acl, typeof(*entry), head);
174 			tomoyo_put_name_union(&entry->name1);
175 			tomoyo_put_name_union(&entry->name2);
176 		}
177 		break;
178 	case TOMOYO_TYPE_PATH_NUMBER_ACL:
179 		{
180 			struct tomoyo_path_number_acl *entry
181 				= container_of(acl, typeof(*entry), head);
182 			tomoyo_put_name_union(&entry->name);
183 			tomoyo_put_number_union(&entry->number);
184 		}
185 		break;
186 	case TOMOYO_TYPE_MKDEV_ACL:
187 		{
188 			struct tomoyo_mkdev_acl *entry
189 				= container_of(acl, typeof(*entry), head);
190 			tomoyo_put_name_union(&entry->name);
191 			tomoyo_put_number_union(&entry->mode);
192 			tomoyo_put_number_union(&entry->major);
193 			tomoyo_put_number_union(&entry->minor);
194 		}
195 		break;
196 	case TOMOYO_TYPE_MOUNT_ACL:
197 		{
198 			struct tomoyo_mount_acl *entry
199 				= container_of(acl, typeof(*entry), head);
200 			tomoyo_put_name_union(&entry->dev_name);
201 			tomoyo_put_name_union(&entry->dir_name);
202 			tomoyo_put_name_union(&entry->fs_type);
203 			tomoyo_put_number_union(&entry->flags);
204 		}
205 		break;
206 	case TOMOYO_TYPE_ENV_ACL:
207 		{
208 			struct tomoyo_env_acl *entry =
209 				container_of(acl, typeof(*entry), head);
210 
211 			tomoyo_put_name(entry->env);
212 		}
213 		break;
214 	case TOMOYO_TYPE_INET_ACL:
215 		{
216 			struct tomoyo_inet_acl *entry =
217 				container_of(acl, typeof(*entry), head);
218 
219 			tomoyo_put_group(entry->address.group);
220 			tomoyo_put_number_union(&entry->port);
221 		}
222 		break;
223 	case TOMOYO_TYPE_UNIX_ACL:
224 		{
225 			struct tomoyo_unix_acl *entry =
226 				container_of(acl, typeof(*entry), head);
227 
228 			tomoyo_put_name_union(&entry->name);
229 		}
230 		break;
231 	case TOMOYO_TYPE_MANUAL_TASK_ACL:
232 		{
233 			struct tomoyo_task_acl *entry =
234 				container_of(acl, typeof(*entry), head);
235 
236 			tomoyo_put_name(entry->domainname);
237 		}
238 		break;
239 	}
240 }
241 
242 /**
243  * tomoyo_del_domain - Delete members in "struct tomoyo_domain_info".
244  *
245  * @element: Pointer to "struct list_head".
246  *
247  * Returns nothing.
248  *
249  * Caller holds tomoyo_policy_lock mutex.
250  */
tomoyo_del_domain(struct list_head * element)251 static inline void tomoyo_del_domain(struct list_head *element)
252 {
253 	struct tomoyo_domain_info *domain =
254 		container_of(element, typeof(*domain), list);
255 	struct tomoyo_acl_info *acl;
256 	struct tomoyo_acl_info *tmp;
257 
258 	/*
259 	 * Since this domain is referenced from neither
260 	 * "struct tomoyo_io_buffer" nor "struct cred"->security, we can delete
261 	 * elements without checking for is_deleted flag.
262 	 */
263 	list_for_each_entry_safe(acl, tmp, &domain->acl_info_list, list) {
264 		tomoyo_del_acl(&acl->list);
265 		tomoyo_memory_free(acl);
266 	}
267 	tomoyo_put_name(domain->domainname);
268 }
269 
270 /**
271  * tomoyo_del_condition - Delete members in "struct tomoyo_condition".
272  *
273  * @element: Pointer to "struct list_head".
274  *
275  * Returns nothing.
276  */
tomoyo_del_condition(struct list_head * element)277 void tomoyo_del_condition(struct list_head *element)
278 {
279 	struct tomoyo_condition *cond = container_of(element, typeof(*cond),
280 						     head.list);
281 	const u16 condc = cond->condc;
282 	const u16 numbers_count = cond->numbers_count;
283 	const u16 names_count = cond->names_count;
284 	const u16 argc = cond->argc;
285 	const u16 envc = cond->envc;
286 	unsigned int i;
287 	const struct tomoyo_condition_element *condp
288 		= (const struct tomoyo_condition_element *) (cond + 1);
289 	struct tomoyo_number_union *numbers_p
290 		= (struct tomoyo_number_union *) (condp + condc);
291 	struct tomoyo_name_union *names_p
292 		= (struct tomoyo_name_union *) (numbers_p + numbers_count);
293 	const struct tomoyo_argv *argv
294 		= (const struct tomoyo_argv *) (names_p + names_count);
295 	const struct tomoyo_envp *envp
296 		= (const struct tomoyo_envp *) (argv + argc);
297 
298 	for (i = 0; i < numbers_count; i++)
299 		tomoyo_put_number_union(numbers_p++);
300 	for (i = 0; i < names_count; i++)
301 		tomoyo_put_name_union(names_p++);
302 	for (i = 0; i < argc; argv++, i++)
303 		tomoyo_put_name(argv->value);
304 	for (i = 0; i < envc; envp++, i++) {
305 		tomoyo_put_name(envp->name);
306 		tomoyo_put_name(envp->value);
307 	}
308 }
309 
310 /**
311  * tomoyo_del_name - Delete members in "struct tomoyo_name".
312  *
313  * @element: Pointer to "struct list_head".
314  *
315  * Returns nothing.
316  */
tomoyo_del_name(struct list_head * element)317 static inline void tomoyo_del_name(struct list_head *element)
318 {
319 	/* Nothing to do. */
320 }
321 
322 /**
323  * tomoyo_del_path_group - Delete members in "struct tomoyo_path_group".
324  *
325  * @element: Pointer to "struct list_head".
326  *
327  * Returns nothing.
328  */
tomoyo_del_path_group(struct list_head * element)329 static inline void tomoyo_del_path_group(struct list_head *element)
330 {
331 	struct tomoyo_path_group *member =
332 		container_of(element, typeof(*member), head.list);
333 
334 	tomoyo_put_name(member->member_name);
335 }
336 
337 /**
338  * tomoyo_del_group - Delete "struct tomoyo_group".
339  *
340  * @element: Pointer to "struct list_head".
341  *
342  * Returns nothing.
343  */
tomoyo_del_group(struct list_head * element)344 static inline void tomoyo_del_group(struct list_head *element)
345 {
346 	struct tomoyo_group *group =
347 		container_of(element, typeof(*group), head.list);
348 
349 	tomoyo_put_name(group->group_name);
350 }
351 
352 /**
353  * tomoyo_del_address_group - Delete members in "struct tomoyo_address_group".
354  *
355  * @element: Pointer to "struct list_head".
356  *
357  * Returns nothing.
358  */
tomoyo_del_address_group(struct list_head * element)359 static inline void tomoyo_del_address_group(struct list_head *element)
360 {
361 	/* Nothing to do. */
362 }
363 
364 /**
365  * tomoyo_del_number_group - Delete members in "struct tomoyo_number_group".
366  *
367  * @element: Pointer to "struct list_head".
368  *
369  * Returns nothing.
370  */
tomoyo_del_number_group(struct list_head * element)371 static inline void tomoyo_del_number_group(struct list_head *element)
372 {
373 	/* Nothing to do. */
374 }
375 
376 /**
377  * tomoyo_try_to_gc - Try to kfree() an entry.
378  *
379  * @type:    One of values in "enum tomoyo_policy_id".
380  * @element: Pointer to "struct list_head".
381  *
382  * Returns nothing.
383  *
384  * Caller holds tomoyo_policy_lock mutex.
385  */
tomoyo_try_to_gc(const enum tomoyo_policy_id type,struct list_head * element)386 static void tomoyo_try_to_gc(const enum tomoyo_policy_id type,
387 			     struct list_head *element)
388 {
389 	/*
390 	 * __list_del_entry() guarantees that the list element became no longer
391 	 * reachable from the list which the element was originally on (e.g.
392 	 * tomoyo_domain_list). Also, synchronize_srcu() guarantees that the
393 	 * list element became no longer referenced by syscall users.
394 	 */
395 	__list_del_entry(element);
396 	mutex_unlock(&tomoyo_policy_lock);
397 	synchronize_srcu(&tomoyo_ss);
398 	/*
399 	 * However, there are two users which may still be using the list
400 	 * element. We need to defer until both users forget this element.
401 	 *
402 	 * Don't kfree() until "struct tomoyo_io_buffer"->r.{domain,group,acl}
403 	 * and "struct tomoyo_io_buffer"->w.domain forget this element.
404 	 */
405 	if (tomoyo_struct_used_by_io_buffer(element))
406 		goto reinject;
407 	switch (type) {
408 	case TOMOYO_ID_TRANSITION_CONTROL:
409 		tomoyo_del_transition_control(element);
410 		break;
411 	case TOMOYO_ID_MANAGER:
412 		tomoyo_del_manager(element);
413 		break;
414 	case TOMOYO_ID_AGGREGATOR:
415 		tomoyo_del_aggregator(element);
416 		break;
417 	case TOMOYO_ID_GROUP:
418 		tomoyo_del_group(element);
419 		break;
420 	case TOMOYO_ID_PATH_GROUP:
421 		tomoyo_del_path_group(element);
422 		break;
423 	case TOMOYO_ID_ADDRESS_GROUP:
424 		tomoyo_del_address_group(element);
425 		break;
426 	case TOMOYO_ID_NUMBER_GROUP:
427 		tomoyo_del_number_group(element);
428 		break;
429 	case TOMOYO_ID_CONDITION:
430 		tomoyo_del_condition(element);
431 		break;
432 	case TOMOYO_ID_NAME:
433 		/*
434 		 * Don't kfree() until all "struct tomoyo_io_buffer"->r.w[]
435 		 * forget this element.
436 		 */
437 		if (tomoyo_name_used_by_io_buffer
438 		    (container_of(element, typeof(struct tomoyo_name),
439 				  head.list)->entry.name))
440 			goto reinject;
441 		tomoyo_del_name(element);
442 		break;
443 	case TOMOYO_ID_ACL:
444 		tomoyo_del_acl(element);
445 		break;
446 	case TOMOYO_ID_DOMAIN:
447 		/*
448 		 * Don't kfree() until all "struct cred"->security forget this
449 		 * element.
450 		 */
451 		if (atomic_read(&container_of
452 				(element, typeof(struct tomoyo_domain_info),
453 				 list)->users))
454 			goto reinject;
455 		break;
456 	case TOMOYO_MAX_POLICY:
457 		break;
458 	}
459 	mutex_lock(&tomoyo_policy_lock);
460 	if (type == TOMOYO_ID_DOMAIN)
461 		tomoyo_del_domain(element);
462 	tomoyo_memory_free(element);
463 	return;
464 reinject:
465 	/*
466 	 * We can safely reinject this element here because
467 	 * (1) Appending list elements and removing list elements are protected
468 	 *     by tomoyo_policy_lock mutex.
469 	 * (2) Only this function removes list elements and this function is
470 	 *     exclusively executed by tomoyo_gc_mutex mutex.
471 	 * are true.
472 	 */
473 	mutex_lock(&tomoyo_policy_lock);
474 	list_add_rcu(element, element->prev);
475 }
476 
477 /**
478  * tomoyo_collect_member - Delete elements with "struct tomoyo_acl_head".
479  *
480  * @id:          One of values in "enum tomoyo_policy_id".
481  * @member_list: Pointer to "struct list_head".
482  *
483  * Returns nothing.
484  */
tomoyo_collect_member(const enum tomoyo_policy_id id,struct list_head * member_list)485 static void tomoyo_collect_member(const enum tomoyo_policy_id id,
486 				  struct list_head *member_list)
487 {
488 	struct tomoyo_acl_head *member;
489 	struct tomoyo_acl_head *tmp;
490 
491 	list_for_each_entry_safe(member, tmp, member_list, list) {
492 		if (!member->is_deleted)
493 			continue;
494 		member->is_deleted = TOMOYO_GC_IN_PROGRESS;
495 		tomoyo_try_to_gc(id, &member->list);
496 	}
497 }
498 
499 /**
500  * tomoyo_collect_acl - Delete elements in "struct tomoyo_domain_info".
501  *
502  * @list: Pointer to "struct list_head".
503  *
504  * Returns nothing.
505  */
tomoyo_collect_acl(struct list_head * list)506 static void tomoyo_collect_acl(struct list_head *list)
507 {
508 	struct tomoyo_acl_info *acl;
509 	struct tomoyo_acl_info *tmp;
510 
511 	list_for_each_entry_safe(acl, tmp, list, list) {
512 		if (!acl->is_deleted)
513 			continue;
514 		acl->is_deleted = TOMOYO_GC_IN_PROGRESS;
515 		tomoyo_try_to_gc(TOMOYO_ID_ACL, &acl->list);
516 	}
517 }
518 
519 /**
520  * tomoyo_collect_entry - Try to kfree() deleted elements.
521  *
522  * Returns nothing.
523  */
tomoyo_collect_entry(void)524 static void tomoyo_collect_entry(void)
525 {
526 	int i;
527 	enum tomoyo_policy_id id;
528 	struct tomoyo_policy_namespace *ns;
529 
530 	mutex_lock(&tomoyo_policy_lock);
531 	{
532 		struct tomoyo_domain_info *domain;
533 		struct tomoyo_domain_info *tmp;
534 
535 		list_for_each_entry_safe(domain, tmp, &tomoyo_domain_list,
536 					 list) {
537 			tomoyo_collect_acl(&domain->acl_info_list);
538 			if (!domain->is_deleted || atomic_read(&domain->users))
539 				continue;
540 			tomoyo_try_to_gc(TOMOYO_ID_DOMAIN, &domain->list);
541 		}
542 	}
543 	list_for_each_entry(ns, &tomoyo_namespace_list, namespace_list) {
544 		for (id = 0; id < TOMOYO_MAX_POLICY; id++)
545 			tomoyo_collect_member(id, &ns->policy_list[id]);
546 		for (i = 0; i < TOMOYO_MAX_ACL_GROUPS; i++)
547 			tomoyo_collect_acl(&ns->acl_group[i]);
548 	}
549 	{
550 		struct tomoyo_shared_acl_head *ptr;
551 		struct tomoyo_shared_acl_head *tmp;
552 
553 		list_for_each_entry_safe(ptr, tmp, &tomoyo_condition_list,
554 					 list) {
555 			if (atomic_read(&ptr->users) > 0)
556 				continue;
557 			atomic_set(&ptr->users, TOMOYO_GC_IN_PROGRESS);
558 			tomoyo_try_to_gc(TOMOYO_ID_CONDITION, &ptr->list);
559 		}
560 	}
561 	list_for_each_entry(ns, &tomoyo_namespace_list, namespace_list) {
562 		for (i = 0; i < TOMOYO_MAX_GROUP; i++) {
563 			struct list_head *list = &ns->group_list[i];
564 			struct tomoyo_group *group;
565 			struct tomoyo_group *tmp;
566 
567 			switch (i) {
568 			case 0:
569 				id = TOMOYO_ID_PATH_GROUP;
570 				break;
571 			case 1:
572 				id = TOMOYO_ID_NUMBER_GROUP;
573 				break;
574 			default:
575 				id = TOMOYO_ID_ADDRESS_GROUP;
576 				break;
577 			}
578 			list_for_each_entry_safe(group, tmp, list, head.list) {
579 				tomoyo_collect_member(id, &group->member_list);
580 				if (!list_empty(&group->member_list) ||
581 				    atomic_read(&group->head.users) > 0)
582 					continue;
583 				atomic_set(&group->head.users,
584 					   TOMOYO_GC_IN_PROGRESS);
585 				tomoyo_try_to_gc(TOMOYO_ID_GROUP,
586 						 &group->head.list);
587 			}
588 		}
589 	}
590 	for (i = 0; i < TOMOYO_MAX_HASH; i++) {
591 		struct list_head *list = &tomoyo_name_list[i];
592 		struct tomoyo_shared_acl_head *ptr;
593 		struct tomoyo_shared_acl_head *tmp;
594 
595 		list_for_each_entry_safe(ptr, tmp, list, list) {
596 			if (atomic_read(&ptr->users) > 0)
597 				continue;
598 			atomic_set(&ptr->users, TOMOYO_GC_IN_PROGRESS);
599 			tomoyo_try_to_gc(TOMOYO_ID_NAME, &ptr->list);
600 		}
601 	}
602 	mutex_unlock(&tomoyo_policy_lock);
603 }
604 
605 /**
606  * tomoyo_gc_thread - Garbage collector thread function.
607  *
608  * @unused: Unused.
609  *
610  * Returns 0.
611  */
tomoyo_gc_thread(void * unused)612 static int tomoyo_gc_thread(void *unused)
613 {
614 	/* Garbage collector thread is exclusive. */
615 	static DEFINE_MUTEX(tomoyo_gc_mutex);
616 
617 	if (!mutex_trylock(&tomoyo_gc_mutex))
618 		goto out;
619 	tomoyo_collect_entry();
620 	{
621 		struct tomoyo_io_buffer *head;
622 		struct tomoyo_io_buffer *tmp;
623 
624 		spin_lock(&tomoyo_io_buffer_list_lock);
625 		list_for_each_entry_safe(head, tmp, &tomoyo_io_buffer_list,
626 					 list) {
627 			if (head->users)
628 				continue;
629 			list_del(&head->list);
630 			kfree(head->read_buf);
631 			kfree(head->write_buf);
632 			kfree(head);
633 		}
634 		spin_unlock(&tomoyo_io_buffer_list_lock);
635 	}
636 	mutex_unlock(&tomoyo_gc_mutex);
637 out:
638 	/* This acts as do_exit(0). */
639 	return 0;
640 }
641 
642 /**
643  * tomoyo_notify_gc - Register/unregister /sys/kernel/security/tomoyo/ users.
644  *
645  * @head:        Pointer to "struct tomoyo_io_buffer".
646  * @is_register: True if register, false if unregister.
647  *
648  * Returns nothing.
649  */
tomoyo_notify_gc(struct tomoyo_io_buffer * head,const bool is_register)650 void tomoyo_notify_gc(struct tomoyo_io_buffer *head, const bool is_register)
651 {
652 	bool is_write = false;
653 
654 	spin_lock(&tomoyo_io_buffer_list_lock);
655 	if (is_register) {
656 		head->users = 1;
657 		list_add(&head->list, &tomoyo_io_buffer_list);
658 	} else {
659 		is_write = head->write_buf != NULL;
660 		if (!--head->users) {
661 			list_del(&head->list);
662 			kfree(head->read_buf);
663 			kfree(head->write_buf);
664 			kfree(head);
665 		}
666 	}
667 	spin_unlock(&tomoyo_io_buffer_list_lock);
668 	if (is_write)
669 		kthread_run(tomoyo_gc_thread, NULL, "GC for TOMOYO");
670 }
671