security/keys/gc.c

   1 /* Key garbage collector
   2  *
   3  * Copyright (C) 2009-2011 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 <linux/slab.h>
  14 #include <linux/security.h>
  15 #include <keys/keyring-type.h>
  16 #include "internal.h"
  17
  18 /*
  19  * Delay between key revocation/expiry in seconds
  20  */
  21 unsigned key_gc_delay = 5 * 60;
  22
  23 /*
  24  * Reaper for unused keys.
  25  */
  26 static void key_garbage_collector(struct work_struct *work);
  27 DECLARE_WORK(key_gc_work, key_garbage_collector);
  28
  29 /*
  30  * Reaper for links from keyrings to dead keys.
  31  */
  32 static void key_gc_timer_func(unsigned long);
  33 static DEFINE_TIMER(key_gc_timer, key_gc_timer_func, 0, 0);
  34
  35 static time_t key_gc_next_run = LONG_MAX;
  36 static struct key_type *key_gc_dead_keytype;
  37
  38 static unsigned long key_gc_flags;
  39 #define KEY_GC_KEY_EXPIRED      0       /* A key expired and needs unlinking */
  40 #define KEY_GC_REAP_KEYTYPE     1       /* A keytype is being unregistered */
  41 #define KEY_GC_REAPING_KEYTYPE  2       /* Cleared when keytype reaped */
  42
  43
  44 /*
  45  * Any key whose type gets unregistered will be re-typed to this if it can't be
  46  * immediately unlinked.
  47  */
  48 struct key_type key_type_dead = {
  49         .name = ".dead",
  50 };
  51
  52 /*
  53  * Schedule a garbage collection run.
  54  * - time precision isn't particularly important
  55  */
  56 void key_schedule_gc(time_t gc_at)
  57 {
  58         unsigned long expires;
  59         time_t now = current_kernel_time().tv_sec;
  60
  61         kenter("%ld", gc_at - now);
  62
  63         if (gc_at <= now || test_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags)) {
  64                 kdebug("IMMEDIATE");
  65                 schedule_work(&key_gc_work);
  66         } else if (gc_at < key_gc_next_run) {
  67                 kdebug("DEFERRED");
  68                 key_gc_next_run = gc_at;
  69                 expires = jiffies + (gc_at - now) * HZ;
  70                 mod_timer(&key_gc_timer, expires);
  71         }
  72 }
  73
  74 /*
  75  * Schedule a dead links collection run.
  76  */
  77 void key_schedule_gc_links(void)
  78 {
  79         set_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags);
  80         schedule_work(&key_gc_work);
  81 }
  82
  83 /*
  84  * Some key's cleanup time was met after it expired, so we need to get the
  85  * reaper to go through a cycle finding expired keys.
  86  */
  87 static void key_gc_timer_func(unsigned long data)
  88 {
  89         kenter("");
  90         key_gc_next_run = LONG_MAX;
  91         key_schedule_gc_links();
  92 }
  93
  94 /*
  95  * Reap keys of dead type.
  96  *
  97  * We use three flags to make sure we see three complete cycles of the garbage
  98  * collector: the first to mark keys of that type as being dead, the second to
  99  * collect dead links and the third to clean up the dead keys.  We have to be
 100  * careful as there may already be a cycle in progress.
 101  *
 102  * The caller must be holding key_types_sem.
 103  */
 104 void key_gc_keytype(struct key_type *ktype)
 105 {
 106         kenter("%s", ktype->name);
 107
 108         key_gc_dead_keytype = ktype;
 109         set_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
 110         smp_mb();
 111         set_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags);
 112
 113         kdebug("schedule");
 114         schedule_work(&key_gc_work);
 115
 116         kdebug("sleep");
 117         wait_on_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE,
 118                     TASK_UNINTERRUPTIBLE);
 119
 120         key_gc_dead_keytype = NULL;
 121         kleave("");
 122 }
 123
 124 /*
 125  * Garbage collect a list of unreferenced, detached keys
 126  */
 127 static noinline void key_gc_unused_keys(struct list_head *keys)
 128 {
 129         while (!list_empty(keys)) {
 130                 struct key *key =
 131                         list_entry(keys->next, struct key, graveyard_link);
 132                 short state = key->state;
 133
 134                 list_del(&key->graveyard_link);
 135
 136                 kdebug("- %u", key->serial);
 137                 key_check(key);
 138
 139                 /* Throw away the key data if the key is instantiated */
 140                 if (state == KEY_IS_POSITIVE && key->type->destroy)
 141                         key->type->destroy(key);
 142
 143                 security_key_free(key);
 144
 145                 /* deal with the user's key tracking and quota */
 146                 if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
 147                         spin_lock(&key->user->lock);
 148                         key->user->qnkeys--;
 149                         key->user->qnbytes -= key->quotalen;
 150                         spin_unlock(&key->user->lock);
 151                 }
 152
 153                 atomic_dec(&key->user->nkeys);
 154                 if (state != KEY_IS_UNINSTANTIATED)
 155                         atomic_dec(&key->user->nikeys);
 156
 157                 key_user_put(key->user);
 158
 159                 kfree(key->description);
 160
 161 #ifdef KEY_DEBUGGING
 162                 key->magic = KEY_DEBUG_MAGIC_X;
 163 #endif
 164                 kmem_cache_free(key_jar, key);
 165         }
 166 }
 167
 168 /*
 169  * Garbage collector for unused keys.
 170  *
 171  * This is done in process context so that we don't have to disable interrupts
 172  * all over the place.  key_put() schedules this rather than trying to do the
 173  * cleanup itself, which means key_put() doesn't have to sleep.
 174  */
 175 static void key_garbage_collector(struct work_struct *work)
 176 {
 177         static LIST_HEAD(graveyard);
 178         static u8 gc_state;             /* Internal persistent state */
 179 #define KEY_GC_REAP_AGAIN       0x01    /* - Need another cycle */
 180 #define KEY_GC_REAPING_LINKS    0x02    /* - We need to reap links */
 181 #define KEY_GC_SET_TIMER        0x04    /* - We need to restart the timer */
 182 #define KEY_GC_REAPING_DEAD_1   0x10    /* - We need to mark dead keys */
 183 #define KEY_GC_REAPING_DEAD_2   0x20    /* - We need to reap dead key links */
 184 #define KEY_GC_REAPING_DEAD_3   0x40    /* - We need to reap dead keys */
 185 #define KEY_GC_FOUND_DEAD_KEY   0x80    /* - We found at least one dead key */
 186
 187         struct rb_node *cursor;
 188         struct key *key;
 189         time_t new_timer, limit;
 190
 191         kenter("[%lx,%x]", key_gc_flags, gc_state);
 192
 193         limit = current_kernel_time().tv_sec;
 194         if (limit > key_gc_delay)
 195                 limit -= key_gc_delay;
 196         else
 197                 limit = key_gc_delay;
 198
 199         /* Work out what we're going to be doing in this pass */
 200         gc_state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2;
 201         gc_state <<= 1;
 202         if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags))
 203                 gc_state |= KEY_GC_REAPING_LINKS | KEY_GC_SET_TIMER;
 204
 205         if (test_and_clear_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags))
 206                 gc_state |= KEY_GC_REAPING_DEAD_1;
 207         kdebug("new pass %x", gc_state);
 208
 209         new_timer = LONG_MAX;
 210
 211         /* As only this function is permitted to remove things from the key
 212          * serial tree, if cursor is non-NULL then it will always point to a
 213          * valid node in the tree - even if lock got dropped.
 214          */
 215         spin_lock(&key_serial_lock);
 216         cursor = rb_first(&key_serial_tree);
 217
 218 continue_scanning:
 219         while (cursor) {
 220                 key = rb_entry(cursor, struct key, serial_node);
 221                 cursor = rb_next(cursor);
 222
 223                 if (atomic_read(&key->usage) == 0)
 224                         goto found_unreferenced_key;
 225
 226                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) {
 227                         if (key->type == key_gc_dead_keytype) {
 228                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 229                                 set_bit(KEY_FLAG_DEAD, &key->flags);
 230                                 key->perm = 0;
 231                                 goto skip_dead_key;
 232                         }
 233                 }
 234
 235                 if (gc_state & KEY_GC_SET_TIMER) {
 236                         if (key->expiry > limit && key->expiry < new_timer) {
 237                                 kdebug("will expire %x in %ld",
 238                                        key_serial(key), key->expiry - limit);
 239                                 new_timer = key->expiry;
 240                         }
 241                 }
 242
 243                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2))
 244                         if (key->type == key_gc_dead_keytype)
 245                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 246
 247                 if ((gc_state & KEY_GC_REAPING_LINKS) ||
 248                     unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) {
 249                         if (key->type == &key_type_keyring)
 250                                 goto found_keyring;
 251                 }
 252
 253                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3))
 254                         if (key->type == key_gc_dead_keytype)
 255                                 goto destroy_dead_key;
 256
 257         skip_dead_key:
 258                 if (spin_is_contended(&key_serial_lock) || need_resched())
 259                         goto contended;
 260         }
 261
 262 contended:
 263         spin_unlock(&key_serial_lock);
 264
 265 maybe_resched:
 266         if (cursor) {
 267                 cond_resched();
 268                 spin_lock(&key_serial_lock);
 269                 goto continue_scanning;
 270         }
 271
 272         /* We've completed the pass.  Set the timer if we need to and queue a
 273          * new cycle if necessary.  We keep executing cycles until we find one
 274          * where we didn't reap any keys.
 275          */
 276         kdebug("pass complete");
 277
 278         if (gc_state & KEY_GC_SET_TIMER && new_timer != (time_t)LONG_MAX) {
 279                 new_timer += key_gc_delay;
 280                 key_schedule_gc(new_timer);
 281         }
 282
 283         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2) ||
 284             !list_empty(&graveyard)) {
 285                 /* Make sure that all pending keyring payload destructions are
 286                  * fulfilled and that people aren't now looking at dead or
 287                  * dying keys that they don't have a reference upon or a link
 288                  * to.
 289                  */
 290                 kdebug("gc sync");
 291                 synchronize_rcu();
 292         }
 293
 294         if (!list_empty(&graveyard)) {
 295                 kdebug("gc keys");
 296                 key_gc_unused_keys(&graveyard);
 297         }
 298
 299         if (unlikely(gc_state & (KEY_GC_REAPING_DEAD_1 |
 300                                  KEY_GC_REAPING_DEAD_2))) {
 301                 if (!(gc_state & KEY_GC_FOUND_DEAD_KEY)) {
 302                         /* No remaining dead keys: short circuit the remaining
 303                          * keytype reap cycles.
 304                          */
 305                         kdebug("dead short");
 306                         gc_state &= ~(KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2);
 307                         gc_state |= KEY_GC_REAPING_DEAD_3;
 308                 } else {
 309                         gc_state |= KEY_GC_REAP_AGAIN;
 310                 }
 311         }
 312
 313         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) {
 314                 kdebug("dead wake");
 315                 smp_mb();
 316                 clear_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
 317                 wake_up_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE);
 318         }
 319
 320         if (gc_state & KEY_GC_REAP_AGAIN)
 321                 schedule_work(&key_gc_work);
 322         kleave(" [end %x]", gc_state);
 323         return;
 324
 325         /* We found an unreferenced key - once we've removed it from the tree,
 326          * we can safely drop the lock.
 327          */
 328 found_unreferenced_key:
 329         kdebug("unrefd key %d", key->serial);
 330         rb_erase(&key->serial_node, &key_serial_tree);
 331         spin_unlock(&key_serial_lock);
 332
 333         list_add_tail(&key->graveyard_link, &graveyard);
 334         gc_state |= KEY_GC_REAP_AGAIN;
 335         goto maybe_resched;
 336
 337         /* We found a keyring and we need to check the payload for links to
 338          * dead or expired keys.  We don't flag another reap immediately as we
 339          * have to wait for the old payload to be destroyed by RCU before we
 340          * can reap the keys to which it refers.
 341          */
 342 found_keyring:
 343         spin_unlock(&key_serial_lock);
 344         keyring_gc(key, limit);
 345         goto maybe_resched;
 346
 347         /* We found a dead key that is still referenced.  Reset its type and
 348          * destroy its payload with its semaphore held.
 349          */
 350 destroy_dead_key:
 351         spin_unlock(&key_serial_lock);
 352         kdebug("destroy key %d", key->serial);
 353         down_write(&key->sem);
 354         key->type = &key_type_dead;
 355         if (key_gc_dead_keytype->destroy)
 356                 key_gc_dead_keytype->destroy(key);
 357         memset(&key->payload, KEY_DESTROY, sizeof(key->payload));
 358         up_write(&key->sem);
 359         goto maybe_resched;
 360 }