security/keys/gc.c

   1 /* Key garbage collector
   2  *
   3  * Copyright (C) 2009 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <keys/keyring-type.h>
  14 #include "internal.h"
  15
  16 /*
  17  * Delay between key revocation/expiry in seconds
  18  */
  19 unsigned key_gc_delay = 5 * 60;
  20
  21 /*
  22  * Reaper
  23  */
  24 static void key_gc_timer_func(unsigned long);
  25 static void key_garbage_collector(struct work_struct *);
  26 static DEFINE_TIMER(key_gc_timer, key_gc_timer_func, 0, 0);
  27 static DECLARE_WORK(key_gc_work, key_garbage_collector);
  28 static key_serial_t key_gc_cursor; /* the last key the gc considered */
  29 static bool key_gc_again;
  30 static unsigned long key_gc_executing;
  31 static time_t key_gc_next_run = LONG_MAX;
  32 static time_t key_gc_new_timer;
  33
  34 /*
  35  * Schedule a garbage collection run
  36  * - precision isn't particularly important
  37  */
  38 void key_schedule_gc(time_t gc_at)
  39 {
  40         unsigned long expires;
  41         time_t now = current_kernel_time().tv_sec;
  42
  43         kenter("%ld", gc_at - now);
  44
  45         if (gc_at <= now) {
  46                 schedule_work(&key_gc_work);
  47         } else if (gc_at < key_gc_next_run) {
  48                 expires = jiffies + (gc_at - now) * HZ;
  49                 mod_timer(&key_gc_timer, expires);
  50         }
  51 }
  52
  53 /*
  54  * The garbage collector timer kicked off
  55  */
  56 static void key_gc_timer_func(unsigned long data)
  57 {
  58         kenter("");
  59         key_gc_next_run = LONG_MAX;
  60         schedule_work(&key_gc_work);
  61 }
  62
  63 /*
  64  * Garbage collect pointers from a keyring
  65  * - return true if we altered the keyring
  66  */
  67 static bool key_gc_keyring(struct key *keyring, time_t limit)
  68         __releases(key_serial_lock)
  69 {
  70         struct keyring_list *klist;
  71         struct key *key;
  72         int loop;
  73
  74         kenter("%x", key_serial(keyring));
  75
  76         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
  77                 goto dont_gc;
  78
  79         /* scan the keyring looking for dead keys */
  80         klist = rcu_dereference(keyring->payload.subscriptions);
  81         if (!klist)
  82                 goto dont_gc;
  83
  84         for (loop = klist->nkeys - 1; loop >= 0; loop--) {
  85                 key = klist->keys[loop];
  86                 if (test_bit(KEY_FLAG_DEAD, &key->flags) ||
  87                     (key->expiry > 0 && key->expiry <= limit))
  88                         goto do_gc;
  89         }
  90
  91 dont_gc:
  92         kleave(" = false");
  93         return false;
  94
  95 do_gc:
  96         key_gc_cursor = keyring->serial;
  97         key_get(keyring);
  98         spin_unlock(&key_serial_lock);
  99         keyring_gc(keyring, limit);
 100         key_put(keyring);
 101         kleave(" = true");
 102         return true;
 103 }
 104
 105 /*
 106  * Garbage collector for keys
 107  * - this involves scanning the keyrings for dead, expired and revoked keys
 108  *   that have overstayed their welcome
 109  */
 110 static void key_garbage_collector(struct work_struct *work)
 111 {
 112         struct rb_node *rb;
 113         key_serial_t cursor;
 114         struct key *key, *xkey;
 115         time_t new_timer = LONG_MAX, limit, now;
 116
 117         now = current_kernel_time().tv_sec;
 118         kenter("[%x,%ld]", key_gc_cursor, key_gc_new_timer - now);
 119
 120         if (test_and_set_bit(0, &key_gc_executing)) {
 121                 key_schedule_gc(current_kernel_time().tv_sec + 1);
 122                 kleave(" [busy; deferring]");
 123                 return;
 124         }
 125
 126         limit = now;
 127         if (limit > key_gc_delay)
 128                 limit -= key_gc_delay;
 129         else
 130                 limit = key_gc_delay;
 131
 132         spin_lock(&key_serial_lock);
 133
 134         if (unlikely(RB_EMPTY_ROOT(&key_serial_tree))) {
 135                 spin_unlock(&key_serial_lock);
 136                 clear_bit(0, &key_gc_executing);
 137                 return;
 138         }
 139
 140         cursor = key_gc_cursor;
 141         if (cursor < 0)
 142                 cursor = 0;
 143         if (cursor > 0)
 144                 new_timer = key_gc_new_timer;
 145         else
 146                 key_gc_again = false;
 147
 148         /* find the first key above the cursor */
 149         key = NULL;
 150         rb = key_serial_tree.rb_node;
 151         while (rb) {
 152                 xkey = rb_entry(rb, struct key, serial_node);
 153                 if (cursor < xkey->serial) {
 154                         key = xkey;
 155                         rb = rb->rb_left;
 156                 } else if (cursor > xkey->serial) {
 157                         rb = rb->rb_right;
 158                 } else {
 159                         rb = rb_next(rb);
 160                         if (!rb)
 161                                 goto reached_the_end;
 162                         key = rb_entry(rb, struct key, serial_node);
 163                         break;
 164                 }
 165         }
 166
 167         if (!key)
 168                 goto reached_the_end;
 169
 170         /* trawl through the keys looking for keyrings */
 171         for (;;) {
 172                 if (key->expiry > limit && key->expiry < new_timer) {
 173                         kdebug("will expire %x in %ld",
 174                                key_serial(key), key->expiry - limit);
 175                         new_timer = key->expiry;
 176                 }
 177
 178                 if (key->type == &key_type_keyring &&
 179                     key_gc_keyring(key, limit))
 180                         /* the gc had to release our lock so that the keyring
 181                          * could be modified, so we have to get it again */
 182                         goto gc_released_our_lock;
 183
 184                 rb = rb_next(&key->serial_node);
 185                 if (!rb)
 186                         goto reached_the_end;
 187                 key = rb_entry(rb, struct key, serial_node);
 188         }
 189
 190 gc_released_our_lock:
 191         kdebug("gc_released_our_lock");
 192         key_gc_new_timer = new_timer;
 193         key_gc_again = true;
 194         clear_bit(0, &key_gc_executing);
 195         schedule_work(&key_gc_work);
 196         kleave(" [continue]");
 197         return;
 198
 199         /* when we reach the end of the run, we set the timer for the next one */
 200 reached_the_end:
 201         kdebug("reached_the_end");
 202         spin_unlock(&key_serial_lock);
 203         key_gc_new_timer = new_timer;
 204         key_gc_cursor = 0;
 205         clear_bit(0, &key_gc_executing);
 206
 207         if (key_gc_again) {
 208                 /* there may have been a key that expired whilst we were
 209                  * scanning, so if we discarded any links we should do another
 210                  * scan */
 211                 new_timer = now + 1;
 212                 key_schedule_gc(new_timer);
 213         } else if (new_timer < LONG_MAX) {
 214                 new_timer += key_gc_delay;
 215                 key_schedule_gc(new_timer);
 216         }
 217         kleave(" [end]");
 218 }