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_check(keyring->payload.subscriptions,
  81                                       lockdep_is_held(&key_serial_lock));
  82         if (!klist)
  83                 goto dont_gc;
  84
  85         for (loop = klist->nkeys - 1; loop >= 0; loop--) {
  86                 key = klist->keys[loop];
  87                 if (test_bit(KEY_FLAG_DEAD, &key->flags) ||
  88                     (key->expiry > 0 && key->expiry <= limit))
  89                         goto do_gc;
  90         }
  91
  92 dont_gc:
  93         kleave(" = false");
  94         return false;
  95
  96 do_gc:
  97         key_gc_cursor = keyring->serial;
  98         key_get(keyring);
  99         spin_unlock(&key_serial_lock);
 100         keyring_gc(keyring, limit);
 101         key_put(keyring);
 102         kleave(" = true");
 103         return true;
 104 }
 105
 106 /*
 107  * Garbage collector for keys
 108  * - this involves scanning the keyrings for dead, expired and revoked keys
 109  *   that have overstayed their welcome
 110  */
 111 static void key_garbage_collector(struct work_struct *work)
 112 {
 113         struct rb_node *rb;
 114         key_serial_t cursor;
 115         struct key *key, *xkey;
 116         time_t new_timer = LONG_MAX, limit, now;
 117
 118         now = current_kernel_time().tv_sec;
 119         kenter("[%x,%ld]", key_gc_cursor, key_gc_new_timer - now);
 120
 121         if (test_and_set_bit(0, &key_gc_executing)) {
 122                 key_schedule_gc(current_kernel_time().tv_sec + 1);
 123                 kleave(" [busy; deferring]");
 124                 return;
 125         }
 126
 127         limit = now;
 128         if (limit > key_gc_delay)
 129                 limit -= key_gc_delay;
 130         else
 131                 limit = key_gc_delay;
 132
 133         spin_lock(&key_serial_lock);
 134
 135         if (unlikely(RB_EMPTY_ROOT(&key_serial_tree))) {
 136                 spin_unlock(&key_serial_lock);
 137                 clear_bit(0, &key_gc_executing);
 138                 return;
 139         }
 140
 141         cursor = key_gc_cursor;
 142         if (cursor < 0)
 143                 cursor = 0;
 144         if (cursor > 0)
 145                 new_timer = key_gc_new_timer;
 146         else
 147                 key_gc_again = false;
 148
 149         /* find the first key above the cursor */
 150         key = NULL;
 151         rb = key_serial_tree.rb_node;
 152         while (rb) {
 153                 xkey = rb_entry(rb, struct key, serial_node);
 154                 if (cursor < xkey->serial) {
 155                         key = xkey;
 156                         rb = rb->rb_left;
 157                 } else if (cursor > xkey->serial) {
 158                         rb = rb->rb_right;
 159                 } else {
 160                         rb = rb_next(rb);
 161                         if (!rb)
 162                                 goto reached_the_end;
 163                         key = rb_entry(rb, struct key, serial_node);
 164                         break;
 165                 }
 166         }
 167
 168         if (!key)
 169                 goto reached_the_end;
 170
 171         /* trawl through the keys looking for keyrings */
 172         for (;;) {
 173                 if (key->expiry > limit && key->expiry < new_timer) {
 174                         kdebug("will expire %x in %ld",
 175                                key_serial(key), key->expiry - limit);
 176                         new_timer = key->expiry;
 177                 }
 178
 179                 if (key->type == &key_type_keyring &&
 180                     key_gc_keyring(key, limit))
 181                         /* the gc had to release our lock so that the keyring
 182                          * could be modified, so we have to get it again */
 183                         goto gc_released_our_lock;
 184
 185                 rb = rb_next(&key->serial_node);
 186                 if (!rb)
 187                         goto reached_the_end;
 188                 key = rb_entry(rb, struct key, serial_node);
 189         }
 190
 191 gc_released_our_lock:
 192         kdebug("gc_released_our_lock");
 193         key_gc_new_timer = new_timer;
 194         key_gc_again = true;
 195         clear_bit(0, &key_gc_executing);
 196         schedule_work(&key_gc_work);
 197         kleave(" [continue]");
 198         return;
 199
 200         /* when we reach the end of the run, we set the timer for the next one */
 201 reached_the_end:
 202         kdebug("reached_the_end");
 203         spin_unlock(&key_serial_lock);
 204         key_gc_new_timer = new_timer;
 205         key_gc_cursor = 0;
 206         clear_bit(0, &key_gc_executing);
 207
 208         if (key_gc_again) {
 209                 /* there may have been a key that expired whilst we were
 210                  * scanning, so if we discarded any links we should do another
 211                  * scan */
 212                 new_timer = now + 1;
 213                 key_schedule_gc(new_timer);
 214         } else if (new_timer < LONG_MAX) {
 215                 new_timer += key_gc_delay;
 216                 key_schedule_gc(new_timer);
 217         }
 218         kleave(" [end]");
 219 }