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                 list_del(&key->graveyard_link);
 133
 134                 kdebug("- %u", key->serial);
 135                 key_check(key);
 136
 137                 security_key_free(key);
 138
 139                 /* deal with the user's key tracking and quota */
 140                 if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
 141                         spin_lock(&key->user->lock);
 142                         key->user->qnkeys--;
 143                         key->user->qnbytes -= key->quotalen;
 144                         spin_unlock(&key->user->lock);
 145                 }
 146
 147                 atomic_dec(&key->user->nkeys);
 148                 if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 149                         atomic_dec(&key->user->nikeys);
 150
 151                 /* now throw away the key memory */
 152                 if (key->type->destroy)
 153                         key->type->destroy(key);
 154
 155                 key_user_put(key->user);
 156
 157                 kfree(key->description);
 158
 159 #ifdef KEY_DEBUGGING
 160                 key->magic = KEY_DEBUG_MAGIC_X;
 161 #endif
 162                 kmem_cache_free(key_jar, key);
 163         }
 164 }
 165
 166 /*
 167  * Garbage collector for unused keys.
 168  *
 169  * This is done in process context so that we don't have to disable interrupts
 170  * all over the place.  key_put() schedules this rather than trying to do the
 171  * cleanup itself, which means key_put() doesn't have to sleep.
 172  */
 173 static void key_garbage_collector(struct work_struct *work)
 174 {
 175         static LIST_HEAD(graveyard);
 176         static u8 gc_state;             /* Internal persistent state */
 177 #define KEY_GC_REAP_AGAIN       0x01    /* - Need another cycle */
 178 #define KEY_GC_REAPING_LINKS    0x02    /* - We need to reap links */
 179 #define KEY_GC_SET_TIMER        0x04    /* - We need to restart the timer */
 180 #define KEY_GC_REAPING_DEAD_1   0x10    /* - We need to mark dead keys */
 181 #define KEY_GC_REAPING_DEAD_2   0x20    /* - We need to reap dead key links */
 182 #define KEY_GC_REAPING_DEAD_3   0x40    /* - We need to reap dead keys */
 183 #define KEY_GC_FOUND_DEAD_KEY   0x80    /* - We found at least one dead key */
 184
 185         struct rb_node *cursor;
 186         struct key *key;
 187         time_t new_timer, limit;
 188
 189         kenter("[%lx,%x]", key_gc_flags, gc_state);
 190
 191         limit = current_kernel_time().tv_sec;
 192         if (limit > key_gc_delay)
 193                 limit -= key_gc_delay;
 194         else
 195                 limit = key_gc_delay;
 196
 197         /* Work out what we're going to be doing in this pass */
 198         gc_state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2;
 199         gc_state <<= 1;
 200         if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags))
 201                 gc_state |= KEY_GC_REAPING_LINKS | KEY_GC_SET_TIMER;
 202
 203         if (test_and_clear_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags))
 204                 gc_state |= KEY_GC_REAPING_DEAD_1;
 205         kdebug("new pass %x", gc_state);
 206
 207         new_timer = LONG_MAX;
 208
 209         /* As only this function is permitted to remove things from the key
 210          * serial tree, if cursor is non-NULL then it will always point to a
 211          * valid node in the tree - even if lock got dropped.
 212          */
 213         spin_lock(&key_serial_lock);
 214         cursor = rb_first(&key_serial_tree);
 215
 216 continue_scanning:
 217         while (cursor) {
 218                 key = rb_entry(cursor, struct key, serial_node);
 219                 cursor = rb_next(cursor);
 220
 221                 if (atomic_read(&key->usage) == 0)
 222                         goto found_unreferenced_key;
 223
 224                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) {
 225                         if (key->type == key_gc_dead_keytype) {
 226                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 227                                 set_bit(KEY_FLAG_DEAD, &key->flags);
 228                                 key->perm = 0;
 229                                 goto skip_dead_key;
 230                         }
 231                 }
 232
 233                 if (gc_state & KEY_GC_SET_TIMER) {
 234                         if (key->expiry > limit && key->expiry < new_timer) {
 235                                 kdebug("will expire %x in %ld",
 236                                        key_serial(key), key->expiry - limit);
 237                                 new_timer = key->expiry;
 238                         }
 239                 }
 240
 241                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2))
 242                         if (key->type == key_gc_dead_keytype)
 243                                 gc_state |= KEY_GC_FOUND_DEAD_KEY;
 244
 245                 if ((gc_state & KEY_GC_REAPING_LINKS) ||
 246                     unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) {
 247                         if (key->type == &key_type_keyring)
 248                                 goto found_keyring;
 249                 }
 250
 251                 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3))
 252                         if (key->type == key_gc_dead_keytype)
 253                                 goto destroy_dead_key;
 254
 255         skip_dead_key:
 256                 if (spin_is_contended(&key_serial_lock) || need_resched())
 257                         goto contended;
 258         }
 259
 260 contended:
 261         spin_unlock(&key_serial_lock);
 262
 263 maybe_resched:
 264         if (cursor) {
 265                 cond_resched();
 266                 spin_lock(&key_serial_lock);
 267                 goto continue_scanning;
 268         }
 269
 270         /* We've completed the pass.  Set the timer if we need to and queue a
 271          * new cycle if necessary.  We keep executing cycles until we find one
 272          * where we didn't reap any keys.
 273          */
 274         kdebug("pass complete");
 275
 276         if (gc_state & KEY_GC_SET_TIMER && new_timer != (time_t)LONG_MAX) {
 277                 new_timer += key_gc_delay;
 278                 key_schedule_gc(new_timer);
 279         }
 280
 281         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2) ||
 282             !list_empty(&graveyard)) {
 283                 /* Make sure that all pending keyring payload destructions are
 284                  * fulfilled and that people aren't now looking at dead or
 285                  * dying keys that they don't have a reference upon or a link
 286                  * to.
 287                  */
 288                 kdebug("gc sync");
 289                 synchronize_rcu();
 290         }
 291
 292         if (!list_empty(&graveyard)) {
 293                 kdebug("gc keys");
 294                 key_gc_unused_keys(&graveyard);
 295         }
 296
 297         if (unlikely(gc_state & (KEY_GC_REAPING_DEAD_1 |
 298                                  KEY_GC_REAPING_DEAD_2))) {
 299                 if (!(gc_state & KEY_GC_FOUND_DEAD_KEY)) {
 300                         /* No remaining dead keys: short circuit the remaining
 301                          * keytype reap cycles.
 302                          */
 303                         kdebug("dead short");
 304                         gc_state &= ~(KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2);
 305                         gc_state |= KEY_GC_REAPING_DEAD_3;
 306                 } else {
 307                         gc_state |= KEY_GC_REAP_AGAIN;
 308                 }
 309         }
 310
 311         if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) {
 312                 kdebug("dead wake");
 313                 smp_mb();
 314                 clear_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
 315                 wake_up_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE);
 316         }
 317
 318         if (gc_state & KEY_GC_REAP_AGAIN)
 319                 schedule_work(&key_gc_work);
 320         kleave(" [end %x]", gc_state);
 321         return;
 322
 323         /* We found an unreferenced key - once we've removed it from the tree,
 324          * we can safely drop the lock.
 325          */
 326 found_unreferenced_key:
 327         kdebug("unrefd key %d", key->serial);
 328         rb_erase(&key->serial_node, &key_serial_tree);
 329         spin_unlock(&key_serial_lock);
 330
 331         list_add_tail(&key->graveyard_link, &graveyard);
 332         gc_state |= KEY_GC_REAP_AGAIN;
 333         goto maybe_resched;
 334
 335         /* We found a keyring and we need to check the payload for links to
 336          * dead or expired keys.  We don't flag another reap immediately as we
 337          * have to wait for the old payload to be destroyed by RCU before we
 338          * can reap the keys to which it refers.
 339          */
 340 found_keyring:
 341         spin_unlock(&key_serial_lock);
 342         keyring_gc(key, limit);
 343         goto maybe_resched;
 344
 345         /* We found a dead key that is still referenced.  Reset its type and
 346          * destroy its payload with its semaphore held.
 347          */
 348 destroy_dead_key:
 349         spin_unlock(&key_serial_lock);
 350         kdebug("destroy key %d", key->serial);
 351         down_write(&key->sem);
 352         key->type = &key_type_dead;
 353         if (key_gc_dead_keytype->destroy)
 354                 key_gc_dead_keytype->destroy(key);
 355         memset(&key->payload, KEY_DESTROY, sizeof(key->payload));
 356         up_write(&key->sem);
 357         goto maybe_resched;
 358 }