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  * wait_on_bit() sleep function for uninterruptible waiting
  96  */
  97 static int key_gc_wait_bit(void *flags)
  98 {
  99         schedule();
 100         return 0;
 101 }
 102
 103 /*
 104  * Reap keys of dead type.
 105  *
 106  * We use three flags to make sure we see three complete cycles of the garbage
 107  * collector: the first to mark keys of that type as being dead, the second to
 108  * collect dead links and the third to clean up the dead keys.  We have to be
 109  * careful as there may already be a cycle in progress.
 110  *
 111  * The caller must be holding key_types_sem.
 112  */
 113 void key_gc_keytype(struct key_type *ktype)
 114 {
 115         kenter("%s", ktype->name);
 116
 117         key_gc_dead_keytype = ktype;
 118         set_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
 119         smp_mb();
 120         set_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags);
 121
 122         kdebug("schedule");
 123         schedule_work(&key_gc_work);
 124
 125         kdebug("sleep");
 126         wait_on_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE, key_gc_wait_bit,
 127                     TASK_UNINTERRUPTIBLE);
 128
 129         key_gc_dead_keytype = NULL;
 130         kleave("");
 131 }
 132
 133 /*
 134  * Garbage collect pointers from a keyring.
 135  *
 136  * Not called with any locks held.  The keyring's key struct will not be
 137  * deallocated under us as only our caller may deallocate it.
 138  */
 139 static void key_gc_keyring(struct key *keyring, time_t limit)
 140 {
 141         struct keyring_list *klist;
 142         int loop;
 143
 144         kenter("%x", key_serial(keyring));
 145
 146         if (keyring->flags & ((1 << KEY_FLAG_INVALIDATED) |
 147                               (1 << KEY_FLAG_REVOKED)))
 148                 goto dont_gc;
 149
 150         /* scan the keyring looking for dead keys */
 151         rcu_read_lock();
 152         klist = rcu_dereference(keyring->payload.subscriptions);
 153         if (!klist)
 154                 goto unlock_dont_gc;
 155
 156         loop = klist->nkeys;
 157         smp_rmb();
 158         for (loop--; loop >= 0; loop--) {
 159                 struct key *key = rcu_dereference(klist->keys[loop]);
 160                 if (key_is_dead(key, limit))
 161                         goto do_gc;
 162         }
 163
 164 unlock_dont_gc:
 165         rcu_read_unlock();
 166 dont_gc:
 167         kleave(" [no gc]");
 168         return;
 169
 170 do_gc:
 171         rcu_read_unlock();
 172
 173         keyring_gc(keyring, limit);
 174         kleave(" [gc]");
 175 }
 176
 177 /*
 178  * Garbage collect a list of unreferenced, detached keys
 179  */
 180 static noinline void key_gc_unused_keys(struct list_head *keys)
 181 {
 182         while (!list_empty(keys)) {
 183                 struct key *key =
 184                         list_entry(keys->next, struct key, graveyard_link);
 185                 list_del(&key->graveyard_link);
 186
 187                 kdebug("- %u", key->serial);
 188                 key_check(key);
 189
 190                 security_key_free(key);
 191
 192                 /* deal with the user's key tracking and quota */
 193                 if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
 194                         spin_lock(&key->user->lock);
 195                         key->user->qnkeys--;
 196                         key->user->qnbytes -= key->quotalen;
 197                         spin_unlock(&key->user->lock);
 198                 }
 199
 200                 atomic_dec(&key->user->nkeys);
 201                 if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 202                         atomic_dec(&key->user->nikeys);
 203
 204                 key_user_put(key->user);
 205
 206                 /* now throw away the key memory */
 207                 if (key->type->destroy)
 208                         key->type->destroy(key);
 209
 210                 kfree(key->description);
 211
 212 #ifdef KEY_DEBUGGING
 213                 key->magic = KEY_DEBUG_MAGIC_X;
 214 #endif
 215                 kmem_cache_free(key_jar, key);
 216         }
 217 }
 218
 219 /*
 220  * Garbage collector for unused keys.
 221  *
 222  * This is done in process context so that we don't have to disable interrupts
 223  * all over the place.  key_put() schedules this rather than trying to do the
 224  * cleanup itself, which means key_put() doesn't have to sleep.
 225  */
 226 static void key_garbage_collector(struct work_struct *work)
 227 {
 228         static LIST_HEAD(graveyard);
 229         static u8 gc_state;             /* Internal persistent state */
 230 #define KEY_GC_REAP_AGAIN       0x01    /* - Need another cycle */
 231 #define KEY_GC_REAPING_LINKS    0x02    /* - We need to reap links */
 232 #define KEY_GC_SET_TIMER        0x04    /* - We need to restart the timer */
 233 #define KEY_GC_REAPING_DEAD_1   0x10    /* - We need to mark dead keys */
 234 #define KEY_GC_REAPING_DEAD_2   0x20    /* - We need to reap dead key links */
 235 #define KEY_GC_REAPING_DEAD_3   0x40    /* - We need to reap dead keys */
 236 #define KEY_GC_FOUND_DEAD_KEY   0x80    /* - We found at least one dead key */
 237
 238         struct rb_node *cursor;
 239         struct key *key;
 240         time_t new_timer, limit;
 241
 242         kenter("[%lx,%x]", key_gc_flags, gc_state);
 243
 244         limit = current_kernel_time().tv_sec;
 245         if (limit > key_gc_delay)
 246                 limit -= key_gc_delay;
 247         else
 248                 limit = key_gc_delay;
 249
 250         /* Work out what we're going to be doing in this pass */
 251         gc_state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2;
 252         gc_state <<= 1;
 253         if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags))
 254                 gc_state |= KEY_GC_REAPING_LINKS | KEY_GC_SET_TIMER;
 255
 256         if (test_and_clear_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags))
 257                 gc_state |= KEY_GC_REAPING_DEAD_1;
 258         kdebug("new pass %x", gc_state);
 259
 260         new_timer = LONG_MAX;
 261
 262         /* As only this function is permitted to remove things from the key
 263          * serial tree, if cursor is non-NULL then it will always point to a
 264          * valid node in the tree - even if lock got dropped.
 265          */
 266         spin_lock(&key_serial_lock);
 267         cursor = rb_first(&key_serial_tree);
 268
 269 continue_scanning:
 270         while (cursor) {
 271                 key = rb_entry(cursor, struct key, serial_node);
 272                 cursor = rb_next(cursor);
 273
 274                 if (atomic_read(&key->usage) == 0)
 275                         goto found_unreferenced_key;
 276
 277                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) {
 278                         if (key->type == key_gc_dead_keytype) {
 279                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 280                                 set_bit(KEY_FLAG_DEAD, &key->flags);
 281                                 key->perm = 0;
 282                                 goto skip_dead_key;
 283                         }
 284                 }
 285
 286                 if (gc_state & KEY_GC_SET_TIMER) {
 287                         if (key->expiry > limit && key->expiry < new_timer) {
 288                                 kdebug("will expire %x in %ld",
 289                                        key_serial(key), key->expiry - limit);
 290                                 new_timer = key->expiry;
 291                         }
 292                 }
 293
 294                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2))
 295                         if (key->type == key_gc_dead_keytype)
 296                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 297
 298                 if ((gc_state & KEY_GC_REAPING_LINKS) ||
 299                     unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) {
 300                         if (key->type == &key_type_keyring)
 301                                 goto found_keyring;
 302                 }
 303
 304                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3))
 305                         if (key->type == key_gc_dead_keytype)
 306                                 goto destroy_dead_key;
 307
 308         skip_dead_key:
 309                 if (spin_is_contended(&key_serial_lock) || need_resched())
 310                         goto contended;
 311         }
 312
 313 contended:
 314         spin_unlock(&key_serial_lock);
 315
 316 maybe_resched:
 317         if (cursor) {
 318                 cond_resched();
 319                 spin_lock(&key_serial_lock);
 320                 goto continue_scanning;
 321         }
 322
 323         /* We've completed the pass.  Set the timer if we need to and queue a
 324          * new cycle if necessary.  We keep executing cycles until we find one
 325          * where we didn't reap any keys.
 326          */
 327         kdebug("pass complete");
 328
 329         if (gc_state & KEY_GC_SET_TIMER && new_timer != (time_t)LONG_MAX) {
 330                 new_timer += key_gc_delay;
 331                 key_schedule_gc(new_timer);
 332         }
 333
 334         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2) ||
 335             !list_empty(&graveyard)) {
 336                 /* Make sure that all pending keyring payload destructions are
 337                  * fulfilled and that people aren't now looking at dead or
 338                  * dying keys that they don't have a reference upon or a link
 339                  * to.
 340                  */
 341                 kdebug("gc sync");
 342                 synchronize_rcu();
 343         }
 344
 345         if (!list_empty(&graveyard)) {
 346                 kdebug("gc keys");
 347                 key_gc_unused_keys(&graveyard);
 348         }
 349
 350         if (unlikely(gc_state & (KEY_GC_REAPING_DEAD_1 |
 351                                  KEY_GC_REAPING_DEAD_2))) {
 352                 if (!(gc_state & KEY_GC_FOUND_DEAD_KEY)) {
 353                         /* No remaining dead keys: short circuit the remaining
 354                          * keytype reap cycles.
 355                          */
 356                         kdebug("dead short");
 357                         gc_state &= ~(KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2);
 358                         gc_state |= KEY_GC_REAPING_DEAD_3;
 359                 } else {
 360                         gc_state |= KEY_GC_REAP_AGAIN;
 361                 }
 362         }
 363
 364         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) {
 365                 kdebug("dead wake");
 366                 smp_mb();
 367                 clear_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
 368                 wake_up_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE);
 369         }
 370
 371         if (gc_state & KEY_GC_REAP_AGAIN)
 372                 schedule_work(&key_gc_work);
 373         kleave(" [end %x]", gc_state);
 374         return;
 375
 376         /* We found an unreferenced key - once we've removed it from the tree,
 377          * we can safely drop the lock.
 378          */
 379 found_unreferenced_key:
 380         kdebug("unrefd key %d", key->serial);
 381         rb_erase(&key->serial_node, &key_serial_tree);
 382         spin_unlock(&key_serial_lock);
 383
 384         list_add_tail(&key->graveyard_link, &graveyard);
 385         gc_state |= KEY_GC_REAP_AGAIN;
 386         goto maybe_resched;
 387
 388         /* We found a keyring and we need to check the payload for links to
 389          * dead or expired keys.  We don't flag another reap immediately as we
 390          * have to wait for the old payload to be destroyed by RCU before we
 391          * can reap the keys to which it refers.
 392          */
 393 found_keyring:
 394         spin_unlock(&key_serial_lock);
 395         kdebug("scan keyring %d", key->serial);
 396         key_gc_keyring(key, limit);
 397         goto maybe_resched;
 398
 399         /* We found a dead key that is still referenced.  Reset its type and
 400          * destroy its payload with its semaphore held.
 401          */
 402 destroy_dead_key:
 403         spin_unlock(&key_serial_lock);
 404         kdebug("destroy key %d", key->serial);
 405         down_write(&key->sem);
 406         key->type = &key_type_dead;
 407         if (key_gc_dead_keytype->destroy)
 408                 key_gc_dead_keytype->destroy(key);
 409         memset(&key->payload, KEY_DESTROY, sizeof(key->payload));
 410         up_write(&key->sem);
 411         goto maybe_resched;
 412 }