1 files changed, 461 insertions, 90 deletions

diff --git a/security/tomoyo/gc.c b/security/tomoyo/gc.c
index a877e4c..ae135fb 100644
--- a/security/tomoyo/gc.c
+++ b/security/tomoyo/gc.c
@@ -1,58 +1,205 @@
 /*
  * security/tomoyo/gc.c
  *
- * Implementation of the Domain-Based Mandatory Access Control.
- *
- * Copyright (C) 2005-2010  NTT DATA CORPORATION
- *
+ * Copyright (C) 2005-2011  NTT DATA CORPORATION
  */
 
 #include "common.h"
 #include <linux/kthread.h>
 #include <linux/slab.h>
 
+/* The list for "struct tomoyo_io_buffer". */
+static LIST_HEAD(tomoyo_io_buffer_list);
+/* Lock for protecting tomoyo_io_buffer_list. */
+static DEFINE_SPINLOCK(tomoyo_io_buffer_list_lock);
+
+/* Size of an element. */
+static const u8 tomoyo_element_size[TOMOYO_MAX_POLICY] = {
+	[TOMOYO_ID_GROUP] = sizeof(struct tomoyo_group),
+	[TOMOYO_ID_PATH_GROUP] = sizeof(struct tomoyo_path_group),
+	[TOMOYO_ID_NUMBER_GROUP] = sizeof(struct tomoyo_number_group),
+	[TOMOYO_ID_AGGREGATOR] = sizeof(struct tomoyo_aggregator),
+	[TOMOYO_ID_TRANSITION_CONTROL] =
+	sizeof(struct tomoyo_transition_control),
+	[TOMOYO_ID_MANAGER] = sizeof(struct tomoyo_manager),
+	/* [TOMOYO_ID_CONDITION] = "struct tomoyo_condition"->size, */
+	/* [TOMOYO_ID_NAME] = "struct tomoyo_name"->size, */
+	/* [TOMOYO_ID_ACL] =
+	   tomoyo_acl_size["struct tomoyo_acl_info"->type], */
+	[TOMOYO_ID_DOMAIN] = sizeof(struct tomoyo_domain_info),
+};
+
+/* Size of a domain ACL element. */
+static const u8 tomoyo_acl_size[] = {
+	[TOMOYO_TYPE_PATH_ACL] = sizeof(struct tomoyo_path_acl),
+	[TOMOYO_TYPE_PATH2_ACL] = sizeof(struct tomoyo_path2_acl),
+	[TOMOYO_TYPE_PATH_NUMBER_ACL] = sizeof(struct tomoyo_path_number_acl),
+	[TOMOYO_TYPE_MKDEV_ACL] = sizeof(struct tomoyo_mkdev_acl),
+	[TOMOYO_TYPE_MOUNT_ACL] = sizeof(struct tomoyo_mount_acl),
+};
+
+/**
+ * tomoyo_struct_used_by_io_buffer - Check whether the list element is used by /sys/kernel/security/tomoyo/ users or not.
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns true if @element is used by /sys/kernel/security/tomoyo/ users,
+ * false otherwise.
+ */
+static bool tomoyo_struct_used_by_io_buffer(const struct list_head *element)
+{
+	struct tomoyo_io_buffer *head;
+	bool in_use = false;
+
+	spin_lock(&tomoyo_io_buffer_list_lock);
+	list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
+		head->users++;
+		spin_unlock(&tomoyo_io_buffer_list_lock);
+		if (mutex_lock_interruptible(&head->io_sem)) {
+			in_use = true;
+			goto out;
+		}
+		if (head->r.domain == element || head->r.group == element ||
+		    head->r.acl == element || &head->w.domain->list == element)
+			in_use = true;
+		mutex_unlock(&head->io_sem);
+out:
+		spin_lock(&tomoyo_io_buffer_list_lock);
+		head->users--;
+		if (in_use)
+			break;
+	}
+	spin_unlock(&tomoyo_io_buffer_list_lock);
+	return in_use;
+}
+
+/**
+ * tomoyo_name_used_by_io_buffer - Check whether the string is used by /sys/kernel/security/tomoyo/ users or not.
+ *
+ * @string: String to check.
+ * @size:   Memory allocated for @string .
+ *
+ * Returns true if @string is used by /sys/kernel/security/tomoyo/ users,
+ * false otherwise.
+ */
+static bool tomoyo_name_used_by_io_buffer(const char *string,
+					  const size_t size)
+{
+	struct tomoyo_io_buffer *head;
+	bool in_use = false;
+
+	spin_lock(&tomoyo_io_buffer_list_lock);
+	list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
+		int i;
+		head->users++;
+		spin_unlock(&tomoyo_io_buffer_list_lock);
+		if (mutex_lock_interruptible(&head->io_sem)) {
+			in_use = true;
+			goto out;
+		}
+		for (i = 0; i < TOMOYO_MAX_IO_READ_QUEUE; i++) {
+			const char *w = head->r.w[i];
+			if (w < string || w > string + size)
+				continue;
+			in_use = true;
+			break;
+		}
+		mutex_unlock(&head->io_sem);
+out:
+		spin_lock(&tomoyo_io_buffer_list_lock);
+		head->users--;
+		if (in_use)
+			break;
+	}
+	spin_unlock(&tomoyo_io_buffer_list_lock);
+	return in_use;
+}
+
+/* Structure for garbage collection. */
 struct tomoyo_gc {
 	struct list_head list;
-	int type;
+	enum tomoyo_policy_id type;
+	size_t size;
 	struct list_head *element;
 };
-static LIST_HEAD(tomoyo_gc_queue);
-static DEFINE_MUTEX(tomoyo_gc_mutex);
+/* List of entries to be deleted. */
+static LIST_HEAD(tomoyo_gc_list);
+/* Length of tomoyo_gc_list. */
+static int tomoyo_gc_list_len;
 
-/* Caller holds tomoyo_policy_lock mutex. */
+/**
+ * tomoyo_add_to_gc - Add an entry to to be deleted list.
+ *
+ * @type:    One of values in "enum tomoyo_policy_id".
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns true on success, false otherwise.
+ *
+ * Caller holds tomoyo_policy_lock mutex.
+ *
+ * Adding an entry needs kmalloc(). Thus, if we try to add thousands of
+ * entries at once, it will take too long time. Thus, do not add more than 128
+ * entries per a scan. But to be able to handle worst case where all entries
+ * are in-use, we accept one more entry per a scan.
+ *
+ * If we use singly linked list using "struct list_head"->prev (which is
+ * LIST_POISON2), we can avoid kmalloc().
+ */
 static bool tomoyo_add_to_gc(const int type, struct list_head *element)
 {
 	struct tomoyo_gc *entry = kzalloc(sizeof(*entry), GFP_ATOMIC);
 	if (!entry)
 		return false;
 	entry->type = type;
+	if (type == TOMOYO_ID_ACL)
+		entry->size = tomoyo_acl_size[
+			      container_of(element,
+					   typeof(struct tomoyo_acl_info),
+					   list)->type];
+	else if (type == TOMOYO_ID_NAME)
+		entry->size = strlen(container_of(element,
+						  typeof(struct tomoyo_name),
+						  head.list)->entry.name) + 1;
+	else if (type == TOMOYO_ID_CONDITION)
+		entry->size =
+			container_of(element, typeof(struct tomoyo_condition),
+				     head.list)->size;
+	else
+		entry->size = tomoyo_element_size[type];
 	entry->element = element;
-	list_add(&entry->list, &tomoyo_gc_queue);
+	list_add(&entry->list, &tomoyo_gc_list);
 	list_del_rcu(element);
-	return true;
+	return tomoyo_gc_list_len++ < 128;
 }
 
-static void tomoyo_del_allow_read(struct list_head *element)
-{
-	struct tomoyo_readable_file *ptr =
-		container_of(element, typeof(*ptr), head.list);
-	tomoyo_put_name(ptr->filename);
-}
-
-static void tomoyo_del_file_pattern(struct list_head *element)
-{
-	struct tomoyo_no_pattern *ptr =
-		container_of(element, typeof(*ptr), head.list);
-	tomoyo_put_name(ptr->pattern);
-}
-
-static void tomoyo_del_no_rewrite(struct list_head *element)
+/**
+ * tomoyo_element_linked_by_gc - Validate next element of an entry.
+ *
+ * @element: Pointer to an element.
+ * @size:    Size of @element in byte.
+ *
+ * Returns true if @element is linked by other elements in the garbage
+ * collector's queue, false otherwise.
+ */
+static bool tomoyo_element_linked_by_gc(const u8 *element, const size_t size)
 {
-	struct tomoyo_no_rewrite *ptr =
-		container_of(element, typeof(*ptr), head.list);
-	tomoyo_put_name(ptr->pattern);
+	struct tomoyo_gc *p;
+	list_for_each_entry(p, &tomoyo_gc_list, list) {
+		const u8 *ptr = (const u8 *) p->element->next;
+		if (ptr < element || element + size < ptr)
+			continue;
+		return true;
+	}
+	return false;
 }
 
+/**
+ * tomoyo_del_transition_control - Delete members in "struct tomoyo_transition_control".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
 static void tomoyo_del_transition_control(struct list_head *element)
 {
 	struct tomoyo_transition_control *ptr =
@@ -61,6 +208,13 @@ static void tomoyo_del_transition_control(struct list_head *element)
 	tomoyo_put_name(ptr->program);
 }
 
+/**
+ * tomoyo_del_aggregator - Delete members in "struct tomoyo_aggregator".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
 static void tomoyo_del_aggregator(struct list_head *element)
 {
 	struct tomoyo_aggregator *ptr =
@@ -69,6 +223,13 @@ static void tomoyo_del_aggregator(struct list_head *element)
 	tomoyo_put_name(ptr->aggregated_name);
 }
 
+/**
+ * tomoyo_del_manager - Delete members in "struct tomoyo_manager".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
 static void tomoyo_del_manager(struct list_head *element)
 {
 	struct tomoyo_manager *ptr =
@@ -76,10 +237,18 @@ static void tomoyo_del_manager(struct list_head *element)
 	tomoyo_put_name(ptr->manager);
 }
 
+/**
+ * tomoyo_del_acl - Delete members in "struct tomoyo_acl_info".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
 static void tomoyo_del_acl(struct list_head *element)
 {
 	struct tomoyo_acl_info *acl =
 		container_of(element, typeof(*acl), list);
+	tomoyo_put_condition(acl->cond);
 	switch (acl->type) {
 	case TOMOYO_TYPE_PATH_ACL:
 		{
@@ -127,6 +296,13 @@ static void tomoyo_del_acl(struct list_head *element)
 	}
 }
 
+/**
+ * tomoyo_del_domain - Delete members in "struct tomoyo_domain_info".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns true if deleted, false otherwise.
+ */
 static bool tomoyo_del_domain(struct list_head *element)
 {
 	struct tomoyo_domain_info *domain =
@@ -165,13 +341,65 @@ static bool tomoyo_del_domain(struct list_head *element)
 	return true;
 }
 
+/**
+ * tomoyo_del_condition - Delete members in "struct tomoyo_condition".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
+void tomoyo_del_condition(struct list_head *element)
+{
+	struct tomoyo_condition *cond = container_of(element, typeof(*cond),
+						     head.list);
+	const u16 condc = cond->condc;
+	const u16 numbers_count = cond->numbers_count;
+	const u16 names_count = cond->names_count;
+	const u16 argc = cond->argc;
+	const u16 envc = cond->envc;
+	unsigned int i;
+	const struct tomoyo_condition_element *condp
+		= (const struct tomoyo_condition_element *) (cond + 1);
+	struct tomoyo_number_union *numbers_p
+		= (struct tomoyo_number_union *) (condp + condc);
+	struct tomoyo_name_union *names_p
+		= (struct tomoyo_name_union *) (numbers_p + numbers_count);
+	const struct tomoyo_argv *argv
+		= (const struct tomoyo_argv *) (names_p + names_count);
+	const struct tomoyo_envp *envp
+		= (const struct tomoyo_envp *) (argv + argc);
+	for (i = 0; i < numbers_count; i++)
+		tomoyo_put_number_union(numbers_p++);
+	for (i = 0; i < names_count; i++)
+		tomoyo_put_name_union(names_p++);
+	for (i = 0; i < argc; argv++, i++)
+		tomoyo_put_name(argv->value);
+	for (i = 0; i < envc; envp++, i++) {
+		tomoyo_put_name(envp->name);
+		tomoyo_put_name(envp->value);
+	}
+}
 
+/**
+ * tomoyo_del_name - Delete members in "struct tomoyo_name".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
 static void tomoyo_del_name(struct list_head *element)
 {
 	const struct tomoyo_name *ptr =
-		container_of(element, typeof(*ptr), list);
+		container_of(element, typeof(*ptr), head.list);
 }
 
+/**
+ * tomoyo_del_path_group - Delete members in "struct tomoyo_path_group".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
 static void tomoyo_del_path_group(struct list_head *element)
 {
 	struct tomoyo_path_group *member =
@@ -179,20 +407,43 @@ static void tomoyo_del_path_group(struct list_head *element)
 	tomoyo_put_name(member->member_name);
 }
 
+/**
+ * tomoyo_del_group - Delete "struct tomoyo_group".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
 static void tomoyo_del_group(struct list_head *element)
 {
 	struct tomoyo_group *group =
-		container_of(element, typeof(*group), list);
+		container_of(element, typeof(*group), head.list);
 	tomoyo_put_name(group->group_name);
 }
 
+/**
+ * tomoyo_del_number_group - Delete members in "struct tomoyo_number_group".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
 static void tomoyo_del_number_group(struct list_head *element)
 {
 	struct tomoyo_number_group *member =
 		container_of(element, typeof(*member), head.list);
 }
 
-static bool tomoyo_collect_member(struct list_head *member_list, int id)
+/**
+ * tomoyo_collect_member - Delete elements with "struct tomoyo_acl_head".
+ *
+ * @id:          One of values in "enum tomoyo_policy_id".
+ * @member_list: Pointer to "struct list_head".
+ *
+ * Returns true if some elements are deleted, false otherwise.
+ */
+static bool tomoyo_collect_member(const enum tomoyo_policy_id id,
+				  struct list_head *member_list)
 {
 	struct tomoyo_acl_head *member;
 	list_for_each_entry(member, member_list, list) {
@@ -201,13 +452,20 @@ static bool tomoyo_collect_member(struct list_head *member_list, int id)
 		if (!tomoyo_add_to_gc(id, &member->list))
 			return false;
 	}
-        return true;
+	return true;
 }
 
-static bool tomoyo_collect_acl(struct tomoyo_domain_info *domain)
+/**
+ * tomoyo_collect_acl - Delete elements in "struct tomoyo_domain_info".
+ *
+ * @list: Pointer to "struct list_head".
+ *
+ * Returns true if some elements are deleted, false otherwise.
+ */
+static bool tomoyo_collect_acl(struct list_head *list)
 {
 	struct tomoyo_acl_info *acl;
-	list_for_each_entry(acl, &domain->acl_info_list, list) {
+	list_for_each_entry(acl, list, list) {
 		if (!acl->is_deleted)
 			continue;
 		if (!tomoyo_add_to_gc(TOMOYO_ID_ACL, &acl->list))
@@ -216,19 +474,24 @@ static bool tomoyo_collect_acl(struct tomoyo_domain_info *domain)
 	return true;
 }
 
+/**
+ * tomoyo_collect_entry - Scan lists for deleted elements.
+ *
+ * Returns nothing.
+ */
 static void tomoyo_collect_entry(void)
 {
 	int i;
+	enum tomoyo_policy_id id;
+	struct tomoyo_policy_namespace *ns;
+	int idx;
 	if (mutex_lock_interruptible(&tomoyo_policy_lock))
 		return;
-	for (i = 0; i < TOMOYO_MAX_POLICY; i++) {
-		if (!tomoyo_collect_member(&tomoyo_policy_list[i], i))
-			goto unlock;
-	}
+	idx = tomoyo_read_lock();
 	{
 		struct tomoyo_domain_info *domain;
 		list_for_each_entry_rcu(domain, &tomoyo_domain_list, list) {
-			if (!tomoyo_collect_acl(domain))
+			if (!tomoyo_collect_acl(&domain->acl_info_list))
 				goto unlock;
 			if (!domain->is_deleted || atomic_read(&domain->users))
 				continue;
@@ -241,48 +504,93 @@ static void tomoyo_collect_entry(void)
 				goto unlock;
 		}
 	}
-	for (i = 0; i < TOMOYO_MAX_HASH; i++) {
-		struct tomoyo_name *ptr;
-		list_for_each_entry_rcu(ptr, &tomoyo_name_list[i], list) {
-			if (atomic_read(&ptr->users))
-				continue;
-			if (!tomoyo_add_to_gc(TOMOYO_ID_NAME, &ptr->list))
+	list_for_each_entry_rcu(ns, &tomoyo_namespace_list, namespace_list) {
+		for (id = 0; id < TOMOYO_MAX_POLICY; id++)
+			if (!tomoyo_collect_member(id, &ns->policy_list[id]))
 				goto unlock;
+		for (i = 0; i < TOMOYO_MAX_ACL_GROUPS; i++)
+			if (!tomoyo_collect_acl(&ns->acl_group[i]))
+				goto unlock;
+		for (i = 0; i < TOMOYO_MAX_GROUP; i++) {
+			struct list_head *list = &ns->group_list[i];
+			struct tomoyo_group *group;
+			switch (i) {
+			case 0:
+				id = TOMOYO_ID_PATH_GROUP;
+				break;
+			default:
+				id = TOMOYO_ID_NUMBER_GROUP;
+				break;
+			}
+			list_for_each_entry(group, list, head.list) {
+				if (!tomoyo_collect_member
+				    (id, &group->member_list))
+					goto unlock;
+				if (!list_empty(&group->member_list) ||
+				    atomic_read(&group->head.users))
+					continue;
+				if (!tomoyo_add_to_gc(TOMOYO_ID_GROUP,
+						      &group->head.list))
+					goto unlock;
+			}
 		}
 	}
-	for (i = 0; i < TOMOYO_MAX_GROUP; i++) {
-		struct list_head *list = &tomoyo_group_list[i];
-		int id;
-		struct tomoyo_group *group;
-		switch (i) {
-		case 0:
-			id = TOMOYO_ID_PATH_GROUP;
-			break;
-		default:
-			id = TOMOYO_ID_NUMBER_GROUP;
-			break;
-		}
-		list_for_each_entry(group, list, list) {
-			if (!tomoyo_collect_member(&group->member_list, id))
-				goto unlock;
-			if (!list_empty(&group->member_list) ||
-			    atomic_read(&group->users))
+	id = TOMOYO_ID_CONDITION;
+	for (i = 0; i < TOMOYO_MAX_HASH + 1; i++) {
+		struct list_head *list = !i ?
+			&tomoyo_condition_list : &tomoyo_name_list[i - 1];
+		struct tomoyo_shared_acl_head *ptr;
+		list_for_each_entry(ptr, list, list) {
+			if (atomic_read(&ptr->users))
 				continue;
-			if (!tomoyo_add_to_gc(TOMOYO_ID_GROUP, &group->list))
+			if (!tomoyo_add_to_gc(id, &ptr->list))
 				goto unlock;
 		}
+		id = TOMOYO_ID_NAME;
 	}
- unlock:
+unlock:
+	tomoyo_read_unlock(idx);
 	mutex_unlock(&tomoyo_policy_lock);
 }
 
-static void tomoyo_kfree_entry(void)
+/**
+ * tomoyo_kfree_entry - Delete entries in tomoyo_gc_list.
+ *
+ * Returns true if some entries were kfree()d, false otherwise.
+ */
+static bool tomoyo_kfree_entry(void)
 {
 	struct tomoyo_gc *p;
 	struct tomoyo_gc *tmp;
+	bool result = false;
 
-	list_for_each_entry_safe(p, tmp, &tomoyo_gc_queue, list) {
+	list_for_each_entry_safe(p, tmp, &tomoyo_gc_list, list) {
 		struct list_head *element = p->element;
+
+		/*
+		 * list_del_rcu() in tomoyo_add_to_gc() guarantees that the
+		 * list element became no longer reachable from the list which
+		 * the element was originally on (e.g. tomoyo_domain_list).
+		 * Also, synchronize_srcu() in tomoyo_gc_thread() guarantees
+		 * that the list element became no longer referenced by syscall
+		 * users.
+		 *
+		 * However, there are three users which may still be using the
+		 * list element. We need to defer until all of these users
+		 * forget the list element.
+		 *
+		 * Firstly, defer until "struct tomoyo_io_buffer"->r.{domain,
+		 * group,acl} and "struct tomoyo_io_buffer"->w.domain forget
+		 * the list element.
+		 */
+		if (tomoyo_struct_used_by_io_buffer(element))
+			continue;
+		/*
+		 * Secondly, defer until all other elements in the
+		 * tomoyo_gc_list list forget the list element.
+		 */
+		if (tomoyo_element_linked_by_gc((const u8 *) element, p->size))
+			continue;
 		switch (p->type) {
 		case TOMOYO_ID_TRANSITION_CONTROL:
 			tomoyo_del_transition_control(element);
@@ -290,19 +598,21 @@ static void tomoyo_kfree_entry(void)
 		case TOMOYO_ID_AGGREGATOR:
 			tomoyo_del_aggregator(element);
 			break;
-		case TOMOYO_ID_GLOBALLY_READABLE:
-			tomoyo_del_allow_read(element);
-			break;
-		case TOMOYO_ID_PATTERN:
-			tomoyo_del_file_pattern(element);
-			break;
-		case TOMOYO_ID_NO_REWRITE:
-			tomoyo_del_no_rewrite(element);
-			break;
 		case TOMOYO_ID_MANAGER:
 			tomoyo_del_manager(element);
 			break;
+		case TOMOYO_ID_CONDITION:
+			tomoyo_del_condition(element);
+			break;
 		case TOMOYO_ID_NAME:
+			/*
+			 * Thirdly, defer until all "struct tomoyo_io_buffer"
+			 * ->r.w[] forget the list element.
+			 */
+			if (tomoyo_name_used_by_io_buffer(
+			    container_of(element, typeof(struct tomoyo_name),
+					 head.list)->entry.name, p->size))
+				continue;
 			tomoyo_del_name(element);
 			break;
 		case TOMOYO_ID_ACL:
@@ -321,34 +631,95 @@ static void tomoyo_kfree_entry(void)
 		case TOMOYO_ID_NUMBER_GROUP:
 			tomoyo_del_number_group(element);
 			break;
+		case TOMOYO_MAX_POLICY:
+			break;
 		}
 		tomoyo_memory_free(element);
 		list_del(&p->list);
 		kfree(p);
+		tomoyo_gc_list_len--;
+		result = true;
 	}
+	return result;
 }
 
+/**
+ * tomoyo_gc_thread - Garbage collector thread function.
+ *
+ * @unused: Unused.
+ *
+ * In case OOM-killer choose this thread for termination, we create this thread
+ * as a short live thread whenever /sys/kernel/security/tomoyo/ interface was
+ * close()d.
+ *
+ * Returns 0.
+ */
 static int tomoyo_gc_thread(void *unused)
 {
+	/* Garbage collector thread is exclusive. */
+	static DEFINE_MUTEX(tomoyo_gc_mutex);
+	if (!mutex_trylock(&tomoyo_gc_mutex))
+		goto out;
 	daemonize("GC for TOMOYO");
-	if (mutex_trylock(&tomoyo_gc_mutex)) {
-		int i;
-		for (i = 0; i < 10; i++) {
-			tomoyo_collect_entry();
-			if (list_empty(&tomoyo_gc_queue))
-				break;
-			synchronize_srcu(&tomoyo_ss);
-			tomoyo_kfree_entry();
+	do {
+		tomoyo_collect_entry();
+		if (list_empty(&tomoyo_gc_list))
+			break;
+		synchronize_srcu(&tomoyo_ss);
+	} while (tomoyo_kfree_entry());
+	{
+		struct tomoyo_io_buffer *head;
+		struct tomoyo_io_buffer *tmp;
+
+		spin_lock(&tomoyo_io_buffer_list_lock);
+		list_for_each_entry_safe(head, tmp, &tomoyo_io_buffer_list,
+					 list) {
+			if (head->users)
+				continue;
+			list_del(&head->list);
+			kfree(head->read_buf);
+			kfree(head->write_buf);
+			kfree(head);
 		}
-		mutex_unlock(&tomoyo_gc_mutex);
+		spin_unlock(&tomoyo_io_buffer_list_lock);
 	}
-	do_exit(0);
+	mutex_unlock(&tomoyo_gc_mutex);
+out:
+	/* This acts as do_exit(0). */
+	return 0;
 }
 
-void tomoyo_run_gc(void)
+/**
+ * tomoyo_notify_gc - Register/unregister /sys/kernel/security/tomoyo/ users.
+ *
+ * @head:        Pointer to "struct tomoyo_io_buffer".
+ * @is_register: True if register, false if unregister.
+ *
+ * Returns nothing.
+ */
+void tomoyo_notify_gc(struct tomoyo_io_buffer *head, const bool is_register)
 {
-	struct task_struct *task = kthread_create(tomoyo_gc_thread, NULL,
-						  "GC for TOMOYO");
-	if (!IS_ERR(task))
-		wake_up_process(task);
+	bool is_write = false;
+
+	spin_lock(&tomoyo_io_buffer_list_lock);
+	if (is_register) {
+		head->users = 1;
+		list_add(&head->list, &tomoyo_io_buffer_list);
+	} else {
+		is_write = head->write_buf != NULL;
+		if (!--head->users) {
+			list_del(&head->list);
+			kfree(head->read_buf);
+			kfree(head->write_buf);
+			kfree(head);
+		}
+	}
+	spin_unlock(&tomoyo_io_buffer_list_lock);
+	if (is_write) {
+		struct task_struct *task = kthread_create(tomoyo_gc_thread,
+							  NULL,
+							  "GC for TOMOYO");
+		if (!IS_ERR(task))
+			wake_up_process(task);
+	}
 }