/*
 * security/tomoyo/gc.c
 *
 * 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;
        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".
 *
 * @element: Pointer to "struct list_head".
 *
 * Returns nothing.
 */
static void tomoyo_del_transition_control(struct list_head *element)
{
        struct tomoyo_transition_control *ptr =
                container_of(element, typeof(*ptr), head.list);
        tomoyo_put_name(ptr->domainname);
        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 =
                container_of(element, typeof(*ptr), head.list);
        tomoyo_put_name(ptr->original_name);
        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 =
                container_of(element, typeof(*ptr), head.list);
        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:
                {
                        struct tomoyo_path_acl *entry
                                = container_of(acl, typeof(*entry), head);
                        tomoyo_put_name_union(&entry->name);
                }
                break;
        case TOMOYO_TYPE_PATH2_ACL:
                {
                        struct tomoyo_path2_acl *entry
                                = container_of(acl, typeof(*entry), head);
                        tomoyo_put_name_union(&entry->name1);
                        tomoyo_put_name_union(&entry->name2);
                }
                break;
        case TOMOYO_TYPE_PATH_NUMBER_ACL:
                {
                        struct tomoyo_path_number_acl *entry
                                = container_of(acl, typeof(*entry), head);
                        tomoyo_put_name_union(&entry->name);
                        tomoyo_put_number_union(&entry->number);
                }
                break;
        case TOMOYO_TYPE_MKDEV_ACL:
                {
                        struct tomoyo_mkdev_acl *entry
                                = container_of(acl, typeof(*entry), head);
                        tomoyo_put_name_union(&entry->name);
                        tomoyo_put_number_union(&entry->mode);
                        tomoyo_put_number_union(&entry->major);
                        tomoyo_put_number_union(&entry->minor);
                }
                break;
        case TOMOYO_TYPE_MOUNT_ACL:
                {
                        struct tomoyo_mount_acl *entry
                                = container_of(acl, typeof(*entry), head);
                        tomoyo_put_name_union(&entry->dev_name);
                        tomoyo_put_name_union(&entry->dir_name);
                        tomoyo_put_name_union(&entry->fs_type);
                        tomoyo_put_number_union(&entry->flags);
                }
                break;
        }
}

/**
 * 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 =
                container_of(element, typeof(*domain), list);
        struct tomoyo_acl_info *acl;
        struct tomoyo_acl_info *tmp;
        /*
         * 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;
}

/**
 * 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), 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 =
                container_of(element, typeof(*member), head.list);
        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), 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);
}

/**
 * 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) {
                if (!member->is_deleted)
                        continue;
                if (!tomoyo_add_to_gc(id, &member->list))
                        return false;
        }
        return true;
}

/**
 * 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, list, list) {
                if (!acl->is_deleted)
                        continue;
                if (!tomoyo_add_to_gc(TOMOYO_ID_ACL, &acl->list))
                        return false;
        }
        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;
        idx = tomoyo_read_lock();
        {
                struct tomoyo_domain_info *domain;
                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;
                        /*
                         * 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_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;
                        }
                }
        }
        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(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)
{
        /* Garbage collector thread is exclusive. */
        static DEFINE_MUTEX(tomoyo_gc_mutex);
        if (!mutex_trylock(&tomoyo_gc_mutex))
                goto out;
        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;

                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);
                }
                spin_unlock(&tomoyo_io_buffer_list_lock);
        }
        mutex_unlock(&tomoyo_gc_mutex);
out:
        /* This acts as do_exit(0). */
        return 0;
}

/**
 * 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)
{
        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);
        }
}