Patched in Tegra support.

1 files changed, 305 insertions, 235 deletions

diff --git a/security/tomoyo/gc.c b/security/tomoyo/gc.c
index 986a6a75686..ae135fbbbe9 100644
--- a/security/tomoyo/gc.c
+++ b/security/tomoyo/gc.c
@@ -8,26 +8,36 @@
 #include <linux/kthread.h>
 #include <linux/slab.h>
 
-/**
- * tomoyo_memory_free - Free memory for elements.
- *
- * @ptr:  Pointer to allocated memory.
- *
- * Returns nothing.
- *
- * Caller holds tomoyo_policy_lock mutex.
- */
-static inline void tomoyo_memory_free(void *ptr)
-{
-        tomoyo_memory_used[TOMOYO_MEMORY_POLICY] -= ksize(ptr);
-        kfree(ptr);
-}
-
 /* 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.
  *
@@ -45,11 +55,15 @@ static bool tomoyo_struct_used_by_io_buffer(const struct list_head *element)
         list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
                 head->users++;
                 spin_unlock(&tomoyo_io_buffer_list_lock);
-                mutex_lock(&head->io_sem);
+                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)
@@ -63,14 +77,15 @@ static bool tomoyo_struct_used_by_io_buffer(const struct list_head *element)
  * 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)
+static bool tomoyo_name_used_by_io_buffer(const char *string,
+                                          const size_t size)
 {
         struct tomoyo_io_buffer *head;
-        const size_t size = strlen(string) + 1;
         bool in_use = false;
 
         spin_lock(&tomoyo_io_buffer_list_lock);
@@ -78,7 +93,10 @@ static bool tomoyo_name_used_by_io_buffer(const char *string)
                 int i;
                 head->users++;
                 spin_unlock(&tomoyo_io_buffer_list_lock);
-                mutex_lock(&head->io_sem);
+                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)
@@ -87,6 +105,7 @@ static bool tomoyo_name_used_by_io_buffer(const char *string)
                         break;
                 }
                 mutex_unlock(&head->io_sem);
+out:
                 spin_lock(&tomoyo_io_buffer_list_lock);
                 head->users--;
                 if (in_use)
@@ -96,6 +115,84 @@ static bool tomoyo_name_used_by_io_buffer(const char *string)
         return in_use;
 }
 
+/* Structure for garbage collection. */
+struct tomoyo_gc {
+        struct list_head list;
+        enum tomoyo_policy_id type;
+        size_t size;
+        struct list_head *element;
+};
+/* List of entries to be deleted. */
+static LIST_HEAD(tomoyo_gc_list);
+/* Length of tomoyo_gc_list. */
+static int tomoyo_gc_list_len;
+
+/**
+ * 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_list);
+        list_del_rcu(element);
+        return tomoyo_gc_list_len++ < 128;
+}
+
+/**
+ * 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_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".
  *
@@ -103,7 +200,7 @@ static bool tomoyo_name_used_by_io_buffer(const char *string)
  *
  * Returns nothing.
  */
-static inline void tomoyo_del_transition_control(struct list_head *element)
+static void tomoyo_del_transition_control(struct list_head *element)
 {
         struct tomoyo_transition_control *ptr =
                 container_of(element, typeof(*ptr), head.list);
@@ -118,7 +215,7 @@ static inline void tomoyo_del_transition_control(struct list_head *element)
  *
  * Returns nothing.
  */
-static inline void tomoyo_del_aggregator(struct list_head *element)
+static void tomoyo_del_aggregator(struct list_head *element)
 {
         struct tomoyo_aggregator *ptr =
                 container_of(element, typeof(*ptr), head.list);
@@ -133,7 +230,7 @@ static inline void tomoyo_del_aggregator(struct list_head *element)
  *
  * Returns nothing.
  */
-static inline void tomoyo_del_manager(struct list_head *element)
+static void tomoyo_del_manager(struct list_head *element)
 {
         struct tomoyo_manager *ptr =
                 container_of(element, typeof(*ptr), head.list);
@@ -196,38 +293,6 @@ static void tomoyo_del_acl(struct list_head *element)
                         tomoyo_put_number_union(&entry->flags);
                 }
                 break;
-        case TOMOYO_TYPE_ENV_ACL:
-                {
-                        struct tomoyo_env_acl *entry =
-                                container_of(acl, typeof(*entry), head);
-
-                        tomoyo_put_name(entry->env);
-                }
-                break;
-        case TOMOYO_TYPE_INET_ACL:
-                {
-                        struct tomoyo_inet_acl *entry =
-                                container_of(acl, typeof(*entry), head);
-
-                        tomoyo_put_group(entry->address.group);
-                        tomoyo_put_number_union(&entry->port);
-                }
-                break;
-        case TOMOYO_TYPE_UNIX_ACL:
-                {
-                        struct tomoyo_unix_acl *entry =
-                                container_of(acl, typeof(*entry), head);
-
-                        tomoyo_put_name_union(&entry->name);
-                }
-                break;
-        case TOMOYO_TYPE_MANUAL_TASK_ACL:
-                {
-                        struct tomoyo_task_acl *entry =
-                                container_of(acl, typeof(*entry), head);
-                        tomoyo_put_name(entry->domainname);
-                }
-                break;
         }
 }
 
@@ -236,26 +301,44 @@ static void tomoyo_del_acl(struct list_head *element)
  *
  * @element: Pointer to "struct list_head".
  *
- * Returns nothing.
- *
- * Caller holds tomoyo_policy_lock mutex.
+ * Returns true if deleted, false otherwise.
  */
-static inline void tomoyo_del_domain(struct list_head *element)
+static bool tomoyo_del_domain(struct list_head *element)
 {
         struct tomoyo_domain_info *domain =
                 container_of(element, typeof(*domain), list);
         struct tomoyo_acl_info *acl;
         struct tomoyo_acl_info *tmp;
         /*
-         * Since this domain is referenced from neither
-         * "struct tomoyo_io_buffer" nor "struct cred"->security, we can delete
-         * elements without checking for is_deleted flag.
+         * Since we don't protect whole execve() operation using SRCU,
+         * we need to recheck domain->users at this point.
+         *
+         * (1) Reader starts SRCU section upon execve().
+         * (2) Reader traverses tomoyo_domain_list and finds this domain.
+         * (3) Writer marks this domain as deleted.
+         * (4) Garbage collector removes this domain from tomoyo_domain_list
+         *     because this domain is marked as deleted and used by nobody.
+         * (5) Reader saves reference to this domain into
+         *     "struct linux_binprm"->cred->security .
+         * (6) Reader finishes SRCU section, although execve() operation has
+         *     not finished yet.
+         * (7) Garbage collector waits for SRCU synchronization.
+         * (8) Garbage collector kfree() this domain because this domain is
+         *     used by nobody.
+         * (9) Reader finishes execve() operation and restores this domain from
+         *     "struct linux_binprm"->cred->security.
+         *
+         * By updating domain->users at (5), we can solve this race problem
+         * by rechecking domain->users at (8).
          */
+        if (atomic_read(&domain->users))
+                return false;
         list_for_each_entry_safe(acl, tmp, &domain->acl_info_list, list) {
                 tomoyo_del_acl(&acl->list);
                 tomoyo_memory_free(acl);
         }
         tomoyo_put_name(domain->domainname);
+        return true;
 }
 
 /**
@@ -304,9 +387,10 @@ void tomoyo_del_condition(struct list_head *element)
  *
  * Returns nothing.
  */
-static inline void tomoyo_del_name(struct list_head *element)
+static void tomoyo_del_name(struct list_head *element)
 {
-        /* Nothing to do. */
+        const struct tomoyo_name *ptr =
+                container_of(element, typeof(*ptr), head.list);
 }
 
 /**
@@ -316,7 +400,7 @@ static inline void tomoyo_del_name(struct list_head *element)
  *
  * Returns nothing.
  */
-static inline void tomoyo_del_path_group(struct list_head *element)
+static void tomoyo_del_path_group(struct list_head *element)
 {
         struct tomoyo_path_group *member =
                 container_of(element, typeof(*member), head.list);
@@ -330,7 +414,7 @@ static inline void tomoyo_del_path_group(struct list_head *element)
  *
  * Returns nothing.
  */
-static inline void tomoyo_del_group(struct list_head *element)
+static void tomoyo_del_group(struct list_head *element)
 {
         struct tomoyo_group *group =
                 container_of(element, typeof(*group), head.list);
@@ -338,128 +422,16 @@ static inline void tomoyo_del_group(struct list_head *element)
 }
 
 /**
- * tomoyo_del_address_group - Delete members in "struct tomoyo_address_group".
- *
- * @element: Pointer to "struct list_head".
- *
- * Returns nothing.
- */
-static inline void tomoyo_del_address_group(struct list_head *element)
-{
-        /* Nothing to do. */
-}
-
-/**
  * tomoyo_del_number_group - Delete members in "struct tomoyo_number_group".
  *
  * @element: Pointer to "struct list_head".
  *
  * Returns nothing.
  */
-static inline void tomoyo_del_number_group(struct list_head *element)
+static void tomoyo_del_number_group(struct list_head *element)
 {
-        /* Nothing to do. */
-}
-
-/**
- * tomoyo_try_to_gc - Try to kfree() an entry.
- *
- * @type:    One of values in "enum tomoyo_policy_id".
- * @element: Pointer to "struct list_head".
- *
- * Returns nothing.
- *
- * Caller holds tomoyo_policy_lock mutex.
- */
-static void tomoyo_try_to_gc(const enum tomoyo_policy_id type,
-                             struct list_head *element)
-{
-        /*
-         * __list_del_entry() 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() guarantees that the
-         * list element became no longer referenced by syscall users.
-         */
-        __list_del_entry(element);
-        mutex_unlock(&tomoyo_policy_lock);
-        synchronize_srcu(&tomoyo_ss);
-        /*
-         * However, there are two users which may still be using the list
-         * element. We need to defer until both users forget this element.
-         *
-         * Don't kfree() until "struct tomoyo_io_buffer"->r.{domain,group,acl}
-         * and "struct tomoyo_io_buffer"->w.domain forget this element.
-         */
-        if (tomoyo_struct_used_by_io_buffer(element))
-                goto reinject;
-        switch (type) {
-        case TOMOYO_ID_TRANSITION_CONTROL:
-                tomoyo_del_transition_control(element);
-                break;
-        case TOMOYO_ID_MANAGER:
-                tomoyo_del_manager(element);
-                break;
-        case TOMOYO_ID_AGGREGATOR:
-                tomoyo_del_aggregator(element);
-                break;
-        case TOMOYO_ID_GROUP:
-                tomoyo_del_group(element);
-                break;
-        case TOMOYO_ID_PATH_GROUP:
-                tomoyo_del_path_group(element);
-                break;
-        case TOMOYO_ID_ADDRESS_GROUP:
-                tomoyo_del_address_group(element);
-                break;
-        case TOMOYO_ID_NUMBER_GROUP:
-                tomoyo_del_number_group(element);
-                break;
-        case TOMOYO_ID_CONDITION:
-                tomoyo_del_condition(element);
-                break;
-        case TOMOYO_ID_NAME:
-                /*
-                 * Don't kfree() until all "struct tomoyo_io_buffer"->r.w[]
-                 * forget this element.
-                 */
-                if (tomoyo_name_used_by_io_buffer
-                    (container_of(element, typeof(struct tomoyo_name),
-                                  head.list)->entry.name))
-                        goto reinject;
-                tomoyo_del_name(element);
-                break;
-        case TOMOYO_ID_ACL:
-                tomoyo_del_acl(element);
-                break;
-        case TOMOYO_ID_DOMAIN:
-                /*
-                 * Don't kfree() until all "struct cred"->security forget this
-                 * element.
-                 */
-                if (atomic_read(&container_of
-                                (element, typeof(struct tomoyo_domain_info),
-                                 list)->users))
-                        goto reinject;
-                break;
-        case TOMOYO_MAX_POLICY:
-                break;
-        }
-        mutex_lock(&tomoyo_policy_lock);
-        if (type == TOMOYO_ID_DOMAIN)
-                tomoyo_del_domain(element);
-        tomoyo_memory_free(element);
-        return;
-reinject:
-        /*
-         * We can safely reinject this element here bacause
-         * (1) Appending list elements and removing list elements are protected
-         *     by tomoyo_policy_lock mutex.
-         * (2) Only this function removes list elements and this function is
-         *     exclusively executed by tomoyo_gc_mutex mutex.
-         * are true.
-         */
-        mutex_lock(&tomoyo_policy_lock);
-        list_add_rcu(element, element->prev);
+        struct tomoyo_number_group *member =
+                container_of(element, typeof(*member), head.list);
 }
 
 /**
@@ -468,19 +440,19 @@ reinject:
  * @id:          One of values in "enum tomoyo_policy_id".
  * @member_list: Pointer to "struct list_head".
  *
- * Returns nothing.
+ * Returns true if some elements are deleted, false otherwise.
  */
-static void tomoyo_collect_member(const enum tomoyo_policy_id id,
+static bool tomoyo_collect_member(const enum tomoyo_policy_id id,
                                   struct list_head *member_list)
 {
         struct tomoyo_acl_head *member;
-        struct tomoyo_acl_head *tmp;
-        list_for_each_entry_safe(member, tmp, member_list, list) {
+        list_for_each_entry(member, member_list, list) {
                 if (!member->is_deleted)
                         continue;
-                member->is_deleted = TOMOYO_GC_IN_PROGRESS;
-                tomoyo_try_to_gc(id, &member->list);
+                if (!tomoyo_add_to_gc(id, &member->list))
+                        return false;
         }
+        return true;
 }
 
 /**
@@ -488,22 +460,22 @@ static void tomoyo_collect_member(const enum tomoyo_policy_id id,
  *
  * @list: Pointer to "struct list_head".
  *
- * Returns nothing.
+ * Returns true if some elements are deleted, false otherwise.
  */
-static void tomoyo_collect_acl(struct list_head *list)
+static bool tomoyo_collect_acl(struct list_head *list)
 {
         struct tomoyo_acl_info *acl;
-        struct tomoyo_acl_info *tmp;
-        list_for_each_entry_safe(acl, tmp, list, list) {
+        list_for_each_entry(acl, list, list) {
                 if (!acl->is_deleted)
                         continue;
-                acl->is_deleted = TOMOYO_GC_IN_PROGRESS;
-                tomoyo_try_to_gc(TOMOYO_ID_ACL, &acl->list);
+                if (!tomoyo_add_to_gc(TOMOYO_ID_ACL, &acl->list))
+                        return false;
         }
+        return true;
 }
 
 /**
- * tomoyo_collect_entry - Try to kfree() deleted elements.
+ * tomoyo_collect_entry - Scan lists for deleted elements.
  *
  * Returns nothing.
  */
@@ -512,82 +484,174 @@ static void tomoyo_collect_entry(void)
         int i;
         enum tomoyo_policy_id id;
         struct tomoyo_policy_namespace *ns;
-        mutex_lock(&tomoyo_policy_lock);
+        int idx;
+        if (mutex_lock_interruptible(&tomoyo_policy_lock))
+                return;
+        idx = tomoyo_read_lock();
         {
                 struct tomoyo_domain_info *domain;
-                struct tomoyo_domain_info *tmp;
-                list_for_each_entry_safe(domain, tmp, &tomoyo_domain_list,
-                                         list) {
-                        tomoyo_collect_acl(&domain->acl_info_list);
+                list_for_each_entry_rcu(domain, &tomoyo_domain_list, list) {
+                        if (!tomoyo_collect_acl(&domain->acl_info_list))
+                                goto unlock;
                         if (!domain->is_deleted || atomic_read(&domain->users))
                                 continue;
-                        tomoyo_try_to_gc(TOMOYO_ID_DOMAIN, &domain->list);
+                        /*
+                         * Nobody is referring this domain. But somebody may
+                         * refer this domain after successful execve().
+                         * We recheck domain->users after SRCU synchronization.
+                         */
+                        if (!tomoyo_add_to_gc(TOMOYO_ID_DOMAIN, &domain->list))
+                                goto unlock;
                 }
         }
-        list_for_each_entry(ns, &tomoyo_namespace_list, namespace_list) {
+        list_for_each_entry_rcu(ns, &tomoyo_namespace_list, namespace_list) {
                 for (id = 0; id < TOMOYO_MAX_POLICY; id++)
-                        tomoyo_collect_member(id, &ns->policy_list[id]);
+                        if (!tomoyo_collect_member(id, &ns->policy_list[id]))
+                                goto unlock;
                 for (i = 0; i < TOMOYO_MAX_ACL_GROUPS; i++)
-                        tomoyo_collect_acl(&ns->acl_group[i]);
-        }
-        {
-                struct tomoyo_shared_acl_head *ptr;
-                struct tomoyo_shared_acl_head *tmp;
-                list_for_each_entry_safe(ptr, tmp, &tomoyo_condition_list,
-                                         list) {
-                        if (atomic_read(&ptr->users) > 0)
-                                continue;
-                        atomic_set(&ptr->users, TOMOYO_GC_IN_PROGRESS);
-                        tomoyo_try_to_gc(TOMOYO_ID_CONDITION, &ptr->list);
-                }
-        }
-        list_for_each_entry(ns, &tomoyo_namespace_list, namespace_list) {
+                        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;
-                        struct tomoyo_group *tmp;
                         switch (i) {
                         case 0:
                                 id = TOMOYO_ID_PATH_GROUP;
                                 break;
-                        case 1:
-                                id = TOMOYO_ID_NUMBER_GROUP;
-                                break;
                         default:
-                                id = TOMOYO_ID_ADDRESS_GROUP;
+                                id = TOMOYO_ID_NUMBER_GROUP;
                                 break;
                         }
-                        list_for_each_entry_safe(group, tmp, list, head.list) {
-                                tomoyo_collect_member(id, &group->member_list);
+                        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) > 0)
+                                    atomic_read(&group->head.users))
                                         continue;
-                                atomic_set(&group->head.users,
-                                           TOMOYO_GC_IN_PROGRESS);
-                                tomoyo_try_to_gc(TOMOYO_ID_GROUP,
-                                                 &group->head.list);
+                                if (!tomoyo_add_to_gc(TOMOYO_ID_GROUP,
+                                                      &group->head.list))
+                                        goto unlock;
                         }
                 }
         }
-        for (i = 0; i < TOMOYO_MAX_HASH; i++) {
-                struct list_head *list = &tomoyo_name_list[i];
+        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;
-                struct tomoyo_shared_acl_head *tmp;
-                list_for_each_entry_safe(ptr, tmp, list, list) {
-                        if (atomic_read(&ptr->users) > 0)
+                list_for_each_entry(ptr, list, list) {
+                        if (atomic_read(&ptr->users))
                                 continue;
-                        atomic_set(&ptr->users, TOMOYO_GC_IN_PROGRESS);
-                        tomoyo_try_to_gc(TOMOYO_ID_NAME, &ptr->list);
+                        if (!tomoyo_add_to_gc(id, &ptr->list))
+                                goto unlock;
                 }
+                id = TOMOYO_ID_NAME;
         }
+unlock:
+        tomoyo_read_unlock(idx);
         mutex_unlock(&tomoyo_policy_lock);
 }
 
 /**
+ * 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_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);
+                        break;
+                case TOMOYO_ID_AGGREGATOR:
+                        tomoyo_del_aggregator(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:
+                        tomoyo_del_acl(element);
+                        break;
+                case TOMOYO_ID_DOMAIN:
+                        if (!tomoyo_del_domain(element))
+                                continue;
+                        break;
+                case TOMOYO_ID_PATH_GROUP:
+                        tomoyo_del_path_group(element);
+                        break;
+                case TOMOYO_ID_GROUP:
+                        tomoyo_del_group(element);
+                        break;
+                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)
@@ -596,7 +660,13 @@ static int tomoyo_gc_thread(void *unused)
         static DEFINE_MUTEX(tomoyo_gc_mutex);
         if (!mutex_trylock(&tomoyo_gc_mutex))
                 goto out;
-        tomoyo_collect_entry();
+        daemonize("GC for TOMOYO");
+        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;