/* Key garbage collector
 *
 * Copyright (C) 2009 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/module.h>
#include <keys/keyring-type.h>
#include "internal.h"

/*
 * Delay between key revocation/expiry in seconds
 */
unsigned key_gc_delay = 5 * 60;

/*
 * Reaper
 */
static void key_gc_timer_func(unsigned long);
static void key_garbage_collector(struct work_struct *);
static DEFINE_TIMER(key_gc_timer, key_gc_timer_func, 0, 0);
static DECLARE_WORK(key_gc_work, key_garbage_collector);
static key_serial_t key_gc_cursor; /* the last key the gc considered */
static bool key_gc_again;
static unsigned long key_gc_executing;
static time_t key_gc_next_run = LONG_MAX;
static time_t key_gc_new_timer;

/*
 * Schedule a garbage collection run.
 * - time precision isn't particularly important
 */
void key_schedule_gc(time_t gc_at)
{
        unsigned long expires;
        time_t now = current_kernel_time().tv_sec;

        kenter("%ld", gc_at - now);

        if (gc_at <= now) {
                schedule_work(&key_gc_work);
        } else if (gc_at < key_gc_next_run) {
                expires = jiffies + (gc_at - now) * HZ;
                mod_timer(&key_gc_timer, expires);
        }
}

/*
 * The garbage collector timer kicked off
 */
static void key_gc_timer_func(unsigned long data)
{
        kenter("");
        key_gc_next_run = LONG_MAX;
        schedule_work(&key_gc_work);
}

/*
 * Garbage collect pointers from a keyring.
 *
 * Return true if we altered the keyring.
 */
static bool key_gc_keyring(struct key *keyring, time_t limit)
        __releases(key_serial_lock)
{
        struct keyring_list *klist;
        struct key *key;
        int loop;

        kenter("%x", key_serial(keyring));

        if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
                goto dont_gc;

        /* scan the keyring looking for dead keys */
        rcu_read_lock();
        klist = rcu_dereference(keyring->payload.subscriptions);
        if (!klist)
                goto unlock_dont_gc;

        for (loop = klist->nkeys - 1; loop >= 0; loop--) {
                key = klist->keys[loop];
                if (test_bit(KEY_FLAG_DEAD, &key->flags) ||
                    (key->expiry > 0 && key->expiry <= limit))
                        goto do_gc;
        }

unlock_dont_gc:
        rcu_read_unlock();
dont_gc:
        kleave(" = false");
        return false;

do_gc:
        rcu_read_unlock();
        key_gc_cursor = keyring->serial;
        key_get(keyring);
        spin_unlock(&key_serial_lock);
        keyring_gc(keyring, limit);
        key_put(keyring);
        kleave(" = true");
        return true;
}

/*
 * Garbage collector for keys.  This involves scanning the keyrings for dead,
 * expired and revoked keys that have overstayed their welcome
 */
static void key_garbage_collector(struct work_struct *work)
{
        struct rb_node *rb;
        key_serial_t cursor;
        struct key *key, *xkey;
        time_t new_timer = LONG_MAX, limit, now;

        now = current_kernel_time().tv_sec;
        kenter("[%x,%ld]", key_gc_cursor, key_gc_new_timer - now);

        if (test_and_set_bit(0, &key_gc_executing)) {
                key_schedule_gc(current_kernel_time().tv_sec + 1);
                kleave(" [busy; deferring]");
                return;
        }

        limit = now;
        if (limit > key_gc_delay)
                limit -= key_gc_delay;
        else
                limit = key_gc_delay;

        spin_lock(&key_serial_lock);

        if (unlikely(RB_EMPTY_ROOT(&key_serial_tree))) {
                spin_unlock(&key_serial_lock);
                clear_bit(0, &key_gc_executing);
                return;
        }

        cursor = key_gc_cursor;
        if (cursor < 0)
                cursor = 0;
        if (cursor > 0)
                new_timer = key_gc_new_timer;
        else
                key_gc_again = false;

        /* find the first key above the cursor */
        key = NULL;
        rb = key_serial_tree.rb_node;
        while (rb) {
                xkey = rb_entry(rb, struct key, serial_node);
                if (cursor < xkey->serial) {
                        key = xkey;
                        rb = rb->rb_left;
                } else if (cursor > xkey->serial) {
                        rb = rb->rb_right;
                } else {
                        rb = rb_next(rb);
                        if (!rb)
                                goto reached_the_end;
                        key = rb_entry(rb, struct key, serial_node);
                        break;
                }
        }

        if (!key)
                goto reached_the_end;

        /* trawl through the keys looking for keyrings */
        for (;;) {
                if (key->expiry > limit && key->expiry < new_timer) {
                        kdebug("will expire %x in %ld",
                               key_serial(key), key->expiry - limit);
                        new_timer = key->expiry;
                }

                if (key->type == &key_type_keyring &&
                    key_gc_keyring(key, limit))
                        /* the gc had to release our lock so that the keyring
                         * could be modified, so we have to get it again */
                        goto gc_released_our_lock;

                rb = rb_next(&key->serial_node);
                if (!rb)
                        goto reached_the_end;
                key = rb_entry(rb, struct key, serial_node);
        }

gc_released_our_lock:
        kdebug("gc_released_our_lock");
        key_gc_new_timer = new_timer;
        key_gc_again = true;
        clear_bit(0, &key_gc_executing);
        schedule_work(&key_gc_work);
        kleave(" [continue]");
        return;

        /* when we reach the end of the run, we set the timer for the next one */
reached_the_end:
        kdebug("reached_the_end");
        spin_unlock(&key_serial_lock);
        key_gc_new_timer = new_timer;
        key_gc_cursor = 0;
        clear_bit(0, &key_gc_executing);

        if (key_gc_again) {
                /* there may have been a key that expired whilst we were
                 * scanning, so if we discarded any links we should do another
                 * scan */
                new_timer = now + 1;
                key_schedule_gc(new_timer);
        } else if (new_timer < LONG_MAX) {
                new_timer += key_gc_delay;
                key_schedule_gc(new_timer);
        }
        kleave(" [end]");
}