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 a list of unreferenced, detached keys
 135  */
 136 static noinline void key_gc_unused_keys(struct list_head *keys)
 137 {
 138         while (!list_empty(keys)) {
 139                 struct key *key =
 140                         list_entry(keys->next, struct key, graveyard_link);
 141                 list_del(&key->graveyard_link);
 142
 143                 kdebug("- %u", key->serial);
 144                 key_check(key);
 145
 146                 security_key_free(key);
 147
 148                 /* deal with the user's key tracking and quota */
 149                 if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
 150                         spin_lock(&key->user->lock);
 151                         key->user->qnkeys--;
 152                         key->user->qnbytes -= key->quotalen;
 153                         spin_unlock(&key->user->lock);
 154                 }
 155
 156                 atomic_dec(&key->user->nkeys);
 157                 if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 158                         atomic_dec(&key->user->nikeys);
 159
 160                 key_user_put(key->user);
 161
 162                 /* now throw away the key memory */
 163                 if (key->type->destroy)
 164                         key->type->destroy(key);
 165
 166                 kfree(key->description);
 167
 168 #ifdef KEY_DEBUGGING
 169                 key->magic = KEY_DEBUG_MAGIC_X;
 170 #endif
 171                 kmem_cache_free(key_jar, key);
 172         }
 173 }
 174
 175 /*
 176  * Garbage collector for unused keys.
 177  *
 178  * This is done in process context so that we don't have to disable interrupts
 179  * all over the place.  key_put() schedules this rather than trying to do the
 180  * cleanup itself, which means key_put() doesn't have to sleep.
 181  */
 182 static void key_garbage_collector(struct work_struct *work)
 183 {
 184         static LIST_HEAD(graveyard);
 185         static u8 gc_state;             /* Internal persistent state */
 186 #define KEY_GC_REAP_AGAIN       0x01    /* - Need another cycle */
 187 #define KEY_GC_REAPING_LINKS    0x02    /* - We need to reap links */
 188 #define KEY_GC_SET_TIMER        0x04    /* - We need to restart the timer */
 189 #define KEY_GC_REAPING_DEAD_1   0x10    /* - We need to mark dead keys */
 190 #define KEY_GC_REAPING_DEAD_2   0x20    /* - We need to reap dead key links */
 191 #define KEY_GC_REAPING_DEAD_3   0x40    /* - We need to reap dead keys */
 192 #define KEY_GC_FOUND_DEAD_KEY   0x80    /* - We found at least one dead key */
 193
 194         struct rb_node *cursor;
 195         struct key *key;
 196         time_t new_timer, limit;
 197
 198         kenter("[%lx,%x]", key_gc_flags, gc_state);
 199
 200         limit = current_kernel_time().tv_sec;
 201         if (limit > key_gc_delay)
 202                 limit -= key_gc_delay;
 203         else
 204                 limit = key_gc_delay;
 205
 206         /* Work out what we're going to be doing in this pass */
 207         gc_state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2;
 208         gc_state <<= 1;
 209         if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags))
 210                 gc_state |= KEY_GC_REAPING_LINKS | KEY_GC_SET_TIMER;
 211
 212         if (test_and_clear_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags))
 213                 gc_state |= KEY_GC_REAPING_DEAD_1;
 214         kdebug("new pass %x", gc_state);
 215
 216         new_timer = LONG_MAX;
 217
 218         /* As only this function is permitted to remove things from the key
 219          * serial tree, if cursor is non-NULL then it will always point to a
 220          * valid node in the tree - even if lock got dropped.
 221          */
 222         spin_lock(&key_serial_lock);
 223         cursor = rb_first(&key_serial_tree);
 224
 225 continue_scanning:
 226         while (cursor) {
 227                 key = rb_entry(cursor, struct key, serial_node);
 228                 cursor = rb_next(cursor);
 229
 230                 if (atomic_read(&key->usage) == 0)
 231                         goto found_unreferenced_key;
 232
 233                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) {
 234                         if (key->type == key_gc_dead_keytype) {
 235                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 236                                 set_bit(KEY_FLAG_DEAD, &key->flags);
 237                                 key->perm = 0;
 238                                 goto skip_dead_key;
 239                         }
 240                 }
 241
 242                 if (gc_state & KEY_GC_SET_TIMER) {
 243                         if (key->expiry > limit && key->expiry < new_timer) {
 244                                 kdebug("will expire %x in %ld",
 245                                        key_serial(key), key->expiry - limit);
 246                                 new_timer = key->expiry;
 247                         }
 248                 }
 249
 250                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2))
 251                         if (key->type == key_gc_dead_keytype)
 252                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 253
 254                 if ((gc_state & KEY_GC_REAPING_LINKS) ||
 255                     unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) {
 256                         if (key->type == &key_type_keyring)
 257                                 goto found_keyring;
 258                 }
 259
 260                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3))
 261                         if (key->type == key_gc_dead_keytype)
 262                                 goto destroy_dead_key;
 263
 264         skip_dead_key:
 265                 if (spin_is_contended(&key_serial_lock) || need_resched())
 266                         goto contended;
 267         }
 268
 269 contended:
 270         spin_unlock(&key_serial_lock);
 271
 272 maybe_resched:
 273         if (cursor) {
 274                 cond_resched();
 275                 spin_lock(&key_serial_lock);
 276                 goto continue_scanning;
 277         }
 278
 279         /* We've completed the pass.  Set the timer if we need to and queue a
 280          * new cycle if necessary.  We keep executing cycles until we find one
 281          * where we didn't reap any keys.
 282          */
 283         kdebug("pass complete");
 284
 285         if (gc_state & KEY_GC_SET_TIMER && new_timer != (time_t)LONG_MAX) {
 286                 new_timer += key_gc_delay;
 287                 key_schedule_gc(new_timer);
 288         }
 289
 290         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2) ||
 291             !list_empty(&graveyard)) {
 292                 /* Make sure that all pending keyring payload destructions are
 293                  * fulfilled and that people aren't now looking at dead or
 294                  * dying keys that they don't have a reference upon or a link
 295                  * to.
 296                  */
 297                 kdebug("gc sync");
 298                 synchronize_rcu();
 299         }
 300
 301         if (!list_empty(&graveyard)) {
 302                 kdebug("gc keys");
 303                 key_gc_unused_keys(&graveyard);
 304         }
 305
 306         if (unlikely(gc_state & (KEY_GC_REAPING_DEAD_1 |
 307                                  KEY_GC_REAPING_DEAD_2))) {
 308                 if (!(gc_state & KEY_GC_FOUND_DEAD_KEY)) {
 309                         /* No remaining dead keys: short circuit the remaining
 310                          * keytype reap cycles.
 311                          */
 312                         kdebug("dead short");
 313                         gc_state &= ~(KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2);
 314                         gc_state |= KEY_GC_REAPING_DEAD_3;
 315                 } else {
 316                         gc_state |= KEY_GC_REAP_AGAIN;
 317                 }
 318         }
 319
 320         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) {
 321                 kdebug("dead wake");
 322                 smp_mb();
 323                 clear_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
 324                 wake_up_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE);
 325         }
 326
 327         if (gc_state & KEY_GC_REAP_AGAIN)
 328                 schedule_work(&key_gc_work);
 329         kleave(" [end %x]", gc_state);
 330         return;
 331
 332         /* We found an unreferenced key - once we've removed it from the tree,
 333          * we can safely drop the lock.
 334          */
 335 found_unreferenced_key:
 336         kdebug("unrefd key %d", key->serial);
 337         rb_erase(&key->serial_node, &key_serial_tree);
 338         spin_unlock(&key_serial_lock);
 339
 340         list_add_tail(&key->graveyard_link, &graveyard);
 341         gc_state |= KEY_GC_REAP_AGAIN;
 342         goto maybe_resched;
 343
 344         /* We found a keyring and we need to check the payload for links to
 345          * dead or expired keys.  We don't flag another reap immediately as we
 346          * have to wait for the old payload to be destroyed by RCU before we
 347          * can reap the keys to which it refers.
 348          */
 349 found_keyring:
 350         spin_unlock(&key_serial_lock);
 351         keyring_gc(key, limit);
 352         goto maybe_resched;
 353
 354         /* We found a dead key that is still referenced.  Reset its type and
 355          * destroy its payload with its semaphore held.
 356          */
 357 destroy_dead_key:
 358         spin_unlock(&key_serial_lock);
 359         kdebug("destroy key %d", key->serial);
 360         down_write(&key->sem);
 361         key->type = &key_type_dead;
 362         if (key_gc_dead_keytype->destroy)
 363                 key_gc_dead_keytype->destroy(key);
 364         memset(&key->payload, KEY_DESTROY, sizeof(key->payload));
 365         up_write(&key->sem);
 366         goto maybe_resched;
 367 }