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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 */
21unsigned key_gc_delay = 5 * 60;
22
23/*
24 * Reaper for unused keys.
25 */
26static void key_garbage_collector(struct work_struct *work);
27DECLARE_WORK(key_gc_work, key_garbage_collector);
28
29/*
30 * Reaper for links from keyrings to dead keys.
31 */
32static void key_gc_timer_func(unsigned long);
33static DEFINE_TIMER(key_gc_timer, key_gc_timer_func, 0, 0);
34
35static time_t key_gc_next_run = LONG_MAX;
36static 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};
51
52/*
53 * Schedule a garbage collection run.
54 * - time precision isn't particularly important
55 */
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
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 */
77void 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 */
87static 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 */
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");
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 */
127static 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 /* 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)
141 key->type->destroy(key);
142
143 security_key_free(key);
144
145 /* 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 }
152
153 atomic_dec(&key->user->nkeys);
154 if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
155 atomic_dec(&key->user->nikeys);
156
157 key_user_put(key->user);
158
159 kfree(key->description);
160
161#ifdef KEY_DEBUGGING
162 key->magic = KEY_DEBUG_MAGIC_X;
163#endif
164 kmem_cache_free(key_jar, key);
165 }
166}
167
168/*
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{
177 static LIST_HEAD(graveyard);
178 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
283 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.
289 */
290 kdebug("gc sync");
291 synchronize_rcu();
292 }
293
294 if (!list_empty(&graveyard)) {
295 kdebug("gc keys");
296 key_gc_unused_keys(&graveyard);
297 }
298
299 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)
321 schedule_work(&key_gc_work);
322 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
333 list_add_tail(&key->graveyard_link, &graveyard);
334 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);
344 keyring_gc(key, limit);
345 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;
360}
1/* Key garbage collector
2 *
3 * Copyright (C) 2009 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 <keys/keyring-type.h>
14#include "internal.h"
15
16/*
17 * Delay between key revocation/expiry in seconds
18 */
19unsigned key_gc_delay = 5 * 60;
20
21/*
22 * Reaper
23 */
24static void key_gc_timer_func(unsigned long);
25static void key_garbage_collector(struct work_struct *);
26static DEFINE_TIMER(key_gc_timer, key_gc_timer_func, 0, 0);
27static DECLARE_WORK(key_gc_work, key_garbage_collector);
28static key_serial_t key_gc_cursor; /* the last key the gc considered */
29static bool key_gc_again;
30static unsigned long key_gc_executing;
31static time_t key_gc_next_run = LONG_MAX;
32static time_t key_gc_new_timer;
33
34/*
35 * Schedule a garbage collection run.
36 * - time precision isn't particularly important
37 */
38void key_schedule_gc(time_t gc_at)
39{
40 unsigned long expires;
41 time_t now = current_kernel_time().tv_sec;
42
43 kenter("%ld", gc_at - now);
44
45 if (gc_at <= now) {
46 schedule_work(&key_gc_work);
47 } else if (gc_at < key_gc_next_run) {
48 expires = jiffies + (gc_at - now) * HZ;
49 mod_timer(&key_gc_timer, expires);
50 }
51}
52
53/*
54 * The garbage collector timer kicked off
55 */
56static void key_gc_timer_func(unsigned long data)
57{
58 kenter("");
59 key_gc_next_run = LONG_MAX;
60 schedule_work(&key_gc_work);
61}
62
63/*
64 * Garbage collect pointers from a keyring.
65 *
66 * Return true if we altered the keyring.
67 */
68static bool key_gc_keyring(struct key *keyring, time_t limit)
69 __releases(key_serial_lock)
70{
71 struct keyring_list *klist;
72 struct key *key;
73 int loop;
74
75 kenter("%x", key_serial(keyring));
76
77 if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
78 goto dont_gc;
79
80 /* scan the keyring looking for dead keys */
81 rcu_read_lock();
82 klist = rcu_dereference(keyring->payload.subscriptions);
83 if (!klist)
84 goto unlock_dont_gc;
85
86 for (loop = klist->nkeys - 1; loop >= 0; loop--) {
87 key = klist->keys[loop];
88 if (test_bit(KEY_FLAG_DEAD, &key->flags) ||
89 (key->expiry > 0 && key->expiry <= limit))
90 goto do_gc;
91 }
92
93unlock_dont_gc:
94 rcu_read_unlock();
95dont_gc:
96 kleave(" = false");
97 return false;
98
99do_gc:
100 rcu_read_unlock();
101 key_gc_cursor = keyring->serial;
102 key_get(keyring);
103 spin_unlock(&key_serial_lock);
104 keyring_gc(keyring, limit);
105 key_put(keyring);
106 kleave(" = true");
107 return true;
108}
109
110/*
111 * Garbage collector for keys. This involves scanning the keyrings for dead,
112 * expired and revoked keys that have overstayed their welcome
113 */
114static void key_garbage_collector(struct work_struct *work)
115{
116 struct rb_node *rb;
117 key_serial_t cursor;
118 struct key *key, *xkey;
119 time_t new_timer = LONG_MAX, limit, now;
120
121 now = current_kernel_time().tv_sec;
122 kenter("[%x,%ld]", key_gc_cursor, key_gc_new_timer - now);
123
124 if (test_and_set_bit(0, &key_gc_executing)) {
125 key_schedule_gc(current_kernel_time().tv_sec + 1);
126 kleave(" [busy; deferring]");
127 return;
128 }
129
130 limit = now;
131 if (limit > key_gc_delay)
132 limit -= key_gc_delay;
133 else
134 limit = key_gc_delay;
135
136 spin_lock(&key_serial_lock);
137
138 if (unlikely(RB_EMPTY_ROOT(&key_serial_tree))) {
139 spin_unlock(&key_serial_lock);
140 clear_bit(0, &key_gc_executing);
141 return;
142 }
143
144 cursor = key_gc_cursor;
145 if (cursor < 0)
146 cursor = 0;
147 if (cursor > 0)
148 new_timer = key_gc_new_timer;
149 else
150 key_gc_again = false;
151
152 /* find the first key above the cursor */
153 key = NULL;
154 rb = key_serial_tree.rb_node;
155 while (rb) {
156 xkey = rb_entry(rb, struct key, serial_node);
157 if (cursor < xkey->serial) {
158 key = xkey;
159 rb = rb->rb_left;
160 } else if (cursor > xkey->serial) {
161 rb = rb->rb_right;
162 } else {
163 rb = rb_next(rb);
164 if (!rb)
165 goto reached_the_end;
166 key = rb_entry(rb, struct key, serial_node);
167 break;
168 }
169 }
170
171 if (!key)
172 goto reached_the_end;
173
174 /* trawl through the keys looking for keyrings */
175 for (;;) {
176 if (key->expiry > limit && key->expiry < new_timer) {
177 kdebug("will expire %x in %ld",
178 key_serial(key), key->expiry - limit);
179 new_timer = key->expiry;
180 }
181
182 if (key->type == &key_type_keyring &&
183 key_gc_keyring(key, limit))
184 /* the gc had to release our lock so that the keyring
185 * could be modified, so we have to get it again */
186 goto gc_released_our_lock;
187
188 rb = rb_next(&key->serial_node);
189 if (!rb)
190 goto reached_the_end;
191 key = rb_entry(rb, struct key, serial_node);
192 }
193
194gc_released_our_lock:
195 kdebug("gc_released_our_lock");
196 key_gc_new_timer = new_timer;
197 key_gc_again = true;
198 clear_bit(0, &key_gc_executing);
199 schedule_work(&key_gc_work);
200 kleave(" [continue]");
201 return;
202
203 /* when we reach the end of the run, we set the timer for the next one */
204reached_the_end:
205 kdebug("reached_the_end");
206 spin_unlock(&key_serial_lock);
207 key_gc_new_timer = new_timer;
208 key_gc_cursor = 0;
209 clear_bit(0, &key_gc_executing);
210
211 if (key_gc_again) {
212 /* there may have been a key that expired whilst we were
213 * scanning, so if we discarded any links we should do another
214 * scan */
215 new_timer = now + 1;
216 key_schedule_gc(new_timer);
217 } else if (new_timer < LONG_MAX) {
218 new_timer += key_gc_delay;
219 key_schedule_gc(new_timer);
220 }
221 kleave(" [end]");
222}