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                 queue_work(system_nrt_wq, &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  * Some key's cleanup time was met after it expired, so we need to get the
  76  * reaper to go through a cycle finding expired keys.
  77  */
  78 static void key_gc_timer_func(unsigned long data)
  79 {
  80         kenter("");
  81         key_gc_next_run = LONG_MAX;
  82         set_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags);
  83         queue_work(system_nrt_wq, &key_gc_work);
  84 }
  85
  86 /*
  87  * wait_on_bit() sleep function for uninterruptible waiting
  88  */
  89 static int key_gc_wait_bit(void *flags)
  90 {
  91         schedule();
  92         return 0;
  93 }
  94
  95 /*
  96  * Reap keys of dead type.
  97  *
  98  * We use three flags to make sure we see three complete cycles of the garbage
  99  * collector: the first to mark keys of that type as being dead, the second to
 100  * collect dead links and the third to clean up the dead keys.  We have to be
 101  * careful as there may already be a cycle in progress.
 102  *
 103  * The caller must be holding key_types_sem.
 104  */
 105 void key_gc_keytype(struct key_type *ktype)
 106 {
 107         kenter("%s", ktype->name);
 108
 109         key_gc_dead_keytype = ktype;
 110         set_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
 111         smp_mb();
 112         set_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags);
 113
 114         kdebug("schedule");
 115         queue_work(system_nrt_wq, &key_gc_work);
 116
 117         kdebug("sleep");
 118         wait_on_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE, key_gc_wait_bit,
 119                     TASK_UNINTERRUPTIBLE);
 120
 121         key_gc_dead_keytype = NULL;
 122         kleave("");
 123 }
 124
 125 /*
 126  * Garbage collect pointers from a keyring.
 127  *
 128  * Not called with any locks held.  The keyring's key struct will not be
 129  * deallocated under us as only our caller may deallocate it.
 130  */
 131 static void key_gc_keyring(struct key *keyring, time_t limit)
 132 {
 133         struct keyring_list *klist;
 134         struct key *key;
 135         int loop;
 136
 137         kenter("%x", key_serial(keyring));
 138
 139         if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 140                 goto dont_gc;
 141
 142         /* scan the keyring looking for dead keys */
 143         rcu_read_lock();
 144         klist = rcu_dereference(keyring->payload.subscriptions);
 145         if (!klist)
 146                 goto unlock_dont_gc;
 147
 148         loop = klist->nkeys;
 149         smp_rmb();
 150         for (loop--; loop >= 0; loop--) {
 151                 key = klist->keys[loop];
 152                 if (test_bit(KEY_FLAG_DEAD, &key->flags) ||
 153                     (key->expiry > 0 && key->expiry <= limit))
 154                         goto do_gc;
 155         }
 156
 157 unlock_dont_gc:
 158         rcu_read_unlock();
 159 dont_gc:
 160         kleave(" [no gc]");
 161         return;
 162
 163 do_gc:
 164         rcu_read_unlock();
 165
 166         keyring_gc(keyring, limit);
 167         kleave(" [gc]");
 168 }
 169
 170 /*
 171  * Garbage collect an unreferenced, detached key
 172  */
 173 static noinline void key_gc_unused_key(struct key *key)
 174 {
 175         key_check(key);
 176
 177         security_key_free(key);
 178
 179         /* deal with the user's key tracking and quota */
 180         if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
 181                 spin_lock(&key->user->lock);
 182                 key->user->qnkeys--;
 183                 key->user->qnbytes -= key->quotalen;
 184                 spin_unlock(&key->user->lock);
 185         }
 186
 187         atomic_dec(&key->user->nkeys);
 188         if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 189                 atomic_dec(&key->user->nikeys);
 190
 191         key_user_put(key->user);
 192
 193         /* now throw away the key memory */
 194         if (key->type->destroy)
 195                 key->type->destroy(key);
 196
 197         kfree(key->description);
 198
 199 #ifdef KEY_DEBUGGING
 200         key->magic = KEY_DEBUG_MAGIC_X;
 201 #endif
 202         kmem_cache_free(key_jar, key);
 203 }
 204
 205 /*
 206  * Garbage collector for unused keys.
 207  *
 208  * This is done in process context so that we don't have to disable interrupts
 209  * all over the place.  key_put() schedules this rather than trying to do the
 210  * cleanup itself, which means key_put() doesn't have to sleep.
 211  */
 212 static void key_garbage_collector(struct work_struct *work)
 213 {
 214         static u8 gc_state;             /* Internal persistent state */
 215 #define KEY_GC_REAP_AGAIN       0x01    /* - Need another cycle */
 216 #define KEY_GC_REAPING_LINKS    0x02    /* - We need to reap links */
 217 #define KEY_GC_SET_TIMER        0x04    /* - We need to restart the timer */
 218 #define KEY_GC_REAPING_DEAD_1   0x10    /* - We need to mark dead keys */
 219 #define KEY_GC_REAPING_DEAD_2   0x20    /* - We need to reap dead key links */
 220 #define KEY_GC_REAPING_DEAD_3   0x40    /* - We need to reap dead keys */
 221 #define KEY_GC_FOUND_DEAD_KEY   0x80    /* - We found at least one dead key */
 222
 223         struct rb_node *cursor;
 224         struct key *key;
 225         time_t new_timer, limit;
 226
 227         kenter("[%lx,%x]", key_gc_flags, gc_state);
 228
 229         limit = current_kernel_time().tv_sec;
 230         if (limit > key_gc_delay)
 231                 limit -= key_gc_delay;
 232         else
 233                 limit = key_gc_delay;
 234
 235         /* Work out what we're going to be doing in this pass */
 236         gc_state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2;
 237         gc_state <<= 1;
 238         if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags))
 239                 gc_state |= KEY_GC_REAPING_LINKS | KEY_GC_SET_TIMER;
 240
 241         if (test_and_clear_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags))
 242                 gc_state |= KEY_GC_REAPING_DEAD_1;
 243         kdebug("new pass %x", gc_state);
 244
 245         new_timer = LONG_MAX;
 246
 247         /* As only this function is permitted to remove things from the key
 248          * serial tree, if cursor is non-NULL then it will always point to a
 249          * valid node in the tree - even if lock got dropped.
 250          */
 251         spin_lock(&key_serial_lock);
 252         cursor = rb_first(&key_serial_tree);
 253
 254 continue_scanning:
 255         while (cursor) {
 256                 key = rb_entry(cursor, struct key, serial_node);
 257                 cursor = rb_next(cursor);
 258
 259                 if (atomic_read(&key->usage) == 0)
 260                         goto found_unreferenced_key;
 261
 262                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) {
 263                         if (key->type == key_gc_dead_keytype) {
 264                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 265                                 set_bit(KEY_FLAG_DEAD, &key->flags);
 266                                 key->perm = 0;
 267                                 goto skip_dead_key;
 268                         }
 269                 }
 270
 271                 if (gc_state & KEY_GC_SET_TIMER) {
 272                         if (key->expiry > limit && key->expiry < new_timer) {
 273                                 kdebug("will expire %x in %ld",
 274                                        key_serial(key), key->expiry - limit);
 275                                 new_timer = key->expiry;
 276                         }
 277                 }
 278
 279                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2))
 280                         if (key->type == key_gc_dead_keytype)
 281                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 282
 283                 if ((gc_state & KEY_GC_REAPING_LINKS) ||
 284                     unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) {
 285                         if (key->type == &key_type_keyring)
 286                                 goto found_keyring;
 287                 }
 288
 289                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3))
 290                         if (key->type == key_gc_dead_keytype)
 291                                 goto destroy_dead_key;
 292
 293         skip_dead_key:
 294                 if (spin_is_contended(&key_serial_lock) || need_resched())
 295                         goto contended;
 296         }
 297
 298 contended:
 299         spin_unlock(&key_serial_lock);
 300
 301 maybe_resched:
 302         if (cursor) {
 303                 cond_resched();
 304                 spin_lock(&key_serial_lock);
 305                 goto continue_scanning;
 306         }
 307
 308         /* We've completed the pass.  Set the timer if we need to and queue a
 309          * new cycle if necessary.  We keep executing cycles until we find one
 310          * where we didn't reap any keys.
 311          */
 312         kdebug("pass complete");
 313
 314         if (gc_state & KEY_GC_SET_TIMER && new_timer != (time_t)LONG_MAX) {
 315                 new_timer += key_gc_delay;
 316                 key_schedule_gc(new_timer);
 317         }
 318
 319         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) {
 320                 /* Make sure everyone revalidates their keys if we marked a
 321                  * bunch as being dead and make sure all keyring ex-payloads
 322                  * are destroyed.
 323                  */
 324                 kdebug("dead sync");
 325                 synchronize_rcu();
 326         }
 327
 328         if (unlikely(gc_state & (KEY_GC_REAPING_DEAD_1 |
 329                                  KEY_GC_REAPING_DEAD_2))) {
 330                 if (!(gc_state & KEY_GC_FOUND_DEAD_KEY)) {
 331                         /* No remaining dead keys: short circuit the remaining
 332                          * keytype reap cycles.
 333                          */
 334                         kdebug("dead short");
 335                         gc_state &= ~(KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2);
 336                         gc_state |= KEY_GC_REAPING_DEAD_3;
 337                 } else {
 338                         gc_state |= KEY_GC_REAP_AGAIN;
 339                 }
 340         }
 341
 342         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) {
 343                 kdebug("dead wake");
 344                 smp_mb();
 345                 clear_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
 346                 wake_up_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE);
 347         }
 348
 349         if (gc_state & KEY_GC_REAP_AGAIN)
 350                 queue_work(system_nrt_wq, &key_gc_work);
 351         kleave(" [end %x]", gc_state);
 352         return;
 353
 354         /* We found an unreferenced key - once we've removed it from the tree,
 355          * we can safely drop the lock.
 356          */
 357 found_unreferenced_key:
 358         kdebug("unrefd key %d", key->serial);
 359         rb_erase(&key->serial_node, &key_serial_tree);
 360         spin_unlock(&key_serial_lock);
 361
 362         key_gc_unused_key(key);
 363         gc_state |= KEY_GC_REAP_AGAIN;
 364         goto maybe_resched;
 365
 366         /* We found a keyring and we need to check the payload for links to
 367          * dead or expired keys.  We don't flag another reap immediately as we
 368          * have to wait for the old payload to be destroyed by RCU before we
 369          * can reap the keys to which it refers.
 370          */
 371 found_keyring:
 372         spin_unlock(&key_serial_lock);
 373         kdebug("scan keyring %d", key->serial);
 374         key_gc_keyring(key, limit);
 375         goto maybe_resched;
 376
 377         /* We found a dead key that is still referenced.  Reset its type and
 378          * destroy its payload with its semaphore held.
 379          */
 380 destroy_dead_key:
 381         spin_unlock(&key_serial_lock);
 382         kdebug("destroy key %d", key->serial);
 383         down_write(&key->sem);
 384         key->type = &key_type_dead;
 385         if (key_gc_dead_keytype->destroy)
 386                 key_gc_dead_keytype->destroy(key);
 387         memset(&key->payload, KEY_DESTROY, sizeof(key->payload));
 388         up_write(&key->sem);
 389         goto maybe_resched;
 390 }