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David Howells5d135442009-09-02 09:14:00 +01001/* Key garbage collector
2 *
David Howells0c061b52011-08-22 14:09:36 +01003 * Copyright (C) 2009-2011 Red Hat, Inc. All Rights Reserved.
David Howells5d135442009-09-02 09:14:00 +01004 * 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>
David Howells8bc16de2011-08-22 14:09:11 +010013#include <linux/slab.h>
14#include <linux/security.h>
David Howells5d135442009-09-02 09:14:00 +010015#include <keys/keyring-type.h>
16#include "internal.h"
17
18/*
19 * Delay between key revocation/expiry in seconds
20 */
21unsigned key_gc_delay = 5 * 60;
22
23/*
David Howells8bc16de2011-08-22 14:09:11 +010024 * Reaper for unused keys.
25 */
David Howells0c061b52011-08-22 14:09:36 +010026static void key_garbage_collector(struct work_struct *work);
27DECLARE_WORK(key_gc_work, key_garbage_collector);
David Howells8bc16de2011-08-22 14:09:11 +010028
29/*
30 * Reaper for links from keyrings to dead keys.
David Howells5d135442009-09-02 09:14:00 +010031 */
32static void key_gc_timer_func(unsigned long);
David Howells5d135442009-09-02 09:14:00 +010033static DEFINE_TIMER(key_gc_timer, key_gc_timer_func, 0, 0);
David Howells0c061b52011-08-22 14:09:36 +010034
David Howells5d135442009-09-02 09:14:00 +010035static time_t key_gc_next_run = LONG_MAX;
David Howells0c061b52011-08-22 14:09:36 +010036static struct key_type *key_gc_dead_keytype;
37
38static 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 */
48struct key_type key_type_dead = {
49 .name = "dead",
50};
David Howells5d135442009-09-02 09:14:00 +010051
52/*
David Howells973c9f42011-01-20 16:38:33 +000053 * Schedule a garbage collection run.
54 * - time precision isn't particularly important
David Howells5d135442009-09-02 09:14:00 +010055 */
56void 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
David Howells0c061b52011-08-22 14:09:36 +010063 if (gc_at <= now || test_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags)) {
64 kdebug("IMMEDIATE");
Tejun Heo3b07e9c2012-08-20 14:51:24 -070065 schedule_work(&key_gc_work);
David Howells5d135442009-09-02 09:14:00 +010066 } else if (gc_at < key_gc_next_run) {
David Howells0c061b52011-08-22 14:09:36 +010067 kdebug("DEFERRED");
68 key_gc_next_run = gc_at;
David Howells5d135442009-09-02 09:14:00 +010069 expires = jiffies + (gc_at - now) * HZ;
70 mod_timer(&key_gc_timer, expires);
71 }
72}
73
74/*
David Howellsfd758152012-05-11 10:56:56 +010075 * Schedule a dead links collection run.
76 */
77void key_schedule_gc_links(void)
78{
79 set_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags);
Tejun Heo3b07e9c2012-08-20 14:51:24 -070080 schedule_work(&key_gc_work);
David Howellsfd758152012-05-11 10:56:56 +010081}
82
83/*
David Howells0c061b52011-08-22 14:09:36 +010084 * 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.
David Howells5d135442009-09-02 09:14:00 +010086 */
87static void key_gc_timer_func(unsigned long data)
88{
89 kenter("");
90 key_gc_next_run = LONG_MAX;
David Howellsfd758152012-05-11 10:56:56 +010091 key_schedule_gc_links();
David Howells5d135442009-09-02 09:14:00 +010092}
93
94/*
David Howells0c061b52011-08-22 14:09:36 +010095 * 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 */
104void 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");
Tejun Heo3b07e9c2012-08-20 14:51:24 -0700114 schedule_work(&key_gc_work);
David Howells0c061b52011-08-22 14:09:36 +0100115
116 kdebug("sleep");
NeilBrown74316202014-07-07 15:16:04 +1000117 wait_on_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE,
David Howells0c061b52011-08-22 14:09:36 +0100118 TASK_UNINTERRUPTIBLE);
119
120 key_gc_dead_keytype = NULL;
121 kleave("");
122}
123
David Howells5d135442009-09-02 09:14:00 +0100124/*
David Howells65d87fe2012-05-11 10:56:56 +0100125 * Garbage collect a list of unreferenced, detached keys
David Howells5d135442009-09-02 09:14:00 +0100126 */
David Howells65d87fe2012-05-11 10:56:56 +0100127static noinline void key_gc_unused_keys(struct list_head *keys)
David Howells5d135442009-09-02 09:14:00 +0100128{
David Howells65d87fe2012-05-11 10:56:56 +0100129 while (!list_empty(keys)) {
130 struct key *key =
131 list_entry(keys->next, struct key, graveyard_link);
132 list_del(&key->graveyard_link);
David Howells8bc16de2011-08-22 14:09:11 +0100133
David Howells65d87fe2012-05-11 10:56:56 +0100134 kdebug("- %u", key->serial);
135 key_check(key);
David Howells8bc16de2011-08-22 14:09:11 +0100136
David Howellsf05819d2015-10-15 17:21:37 +0100137 /* Throw away the key data if the key is instantiated */
138 if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags) &&
139 !test_bit(KEY_FLAG_NEGATIVE, &key->flags) &&
140 key->type->destroy)
David Howells94c45542015-09-25 16:30:08 +0100141 key->type->destroy(key);
142
David Howells65d87fe2012-05-11 10:56:56 +0100143 security_key_free(key);
David Howells8bc16de2011-08-22 14:09:11 +0100144
David Howells65d87fe2012-05-11 10:56:56 +0100145 /* 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 }
David Howells8bc16de2011-08-22 14:09:11 +0100152
David Howells65d87fe2012-05-11 10:56:56 +0100153 atomic_dec(&key->user->nkeys);
154 if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
155 atomic_dec(&key->user->nikeys);
David Howells8bc16de2011-08-22 14:09:11 +0100156
Sasha Levina3a87842014-12-29 09:39:01 -0500157 key_user_put(key->user);
158
David Howells65d87fe2012-05-11 10:56:56 +0100159 kfree(key->description);
David Howells8bc16de2011-08-22 14:09:11 +0100160
161#ifdef KEY_DEBUGGING
David Howells65d87fe2012-05-11 10:56:56 +0100162 key->magic = KEY_DEBUG_MAGIC_X;
David Howells8bc16de2011-08-22 14:09:11 +0100163#endif
David Howells65d87fe2012-05-11 10:56:56 +0100164 kmem_cache_free(key_jar, key);
165 }
David Howells0c061b52011-08-22 14:09:36 +0100166}
David Howells8bc16de2011-08-22 14:09:11 +0100167
David Howells0c061b52011-08-22 14:09:36 +0100168/*
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 */
175static void key_garbage_collector(struct work_struct *work)
176{
David Howells65d87fe2012-05-11 10:56:56 +0100177 static LIST_HEAD(graveyard);
David Howells0c061b52011-08-22 14:09:36 +0100178 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
218continue_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
262contended:
263 spin_unlock(&key_serial_lock);
264
265maybe_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
David Howells65d87fe2012-05-11 10:56:56 +0100283 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.
David Howells0c061b52011-08-22 14:09:36 +0100289 */
David Howells65d87fe2012-05-11 10:56:56 +0100290 kdebug("gc sync");
David Howells0c061b52011-08-22 14:09:36 +0100291 synchronize_rcu();
292 }
293
David Howells65d87fe2012-05-11 10:56:56 +0100294 if (!list_empty(&graveyard)) {
295 kdebug("gc keys");
296 key_gc_unused_keys(&graveyard);
297 }
298
David Howells0c061b52011-08-22 14:09:36 +0100299 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)
Tejun Heo3b07e9c2012-08-20 14:51:24 -0700321 schedule_work(&key_gc_work);
David Howells0c061b52011-08-22 14:09:36 +0100322 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 */
328found_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
David Howells65d87fe2012-05-11 10:56:56 +0100333 list_add_tail(&key->graveyard_link, &graveyard);
David Howells0c061b52011-08-22 14:09:36 +0100334 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 */
342found_keyring:
343 spin_unlock(&key_serial_lock);
David Howells62fe3182013-11-14 13:02:31 +0000344 keyring_gc(key, limit);
David Howells0c061b52011-08-22 14:09:36 +0100345 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 */
350destroy_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;
David Howells8bc16de2011-08-22 14:09:11 +0100360}