summaryrefslogtreecommitdiff
path: root/security/keys/gc.c
blob: 48c3e124c2729bcaf198841b381d56b096a6cc89 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
// SPDX-License-Identifier: GPL-2.0-or-later
/* Key garbage collector
 *
 * Copyright (C) 2009-2011 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 */

#include <linux/slab.h>
#include <linux/security.h>
#include <keys/keyring-type.h>
#include "internal.h"

/*
 * Delay between key revocation/expiry in seconds
 */
unsigned key_gc_delay = 5 * 60;

/*
 * Reaper for unused keys.
 */
static void key_garbage_collector(struct work_struct *work);
DECLARE_WORK(key_gc_work, key_garbage_collector);

/*
 * Reaper for links from keyrings to dead keys.
 */
static void key_gc_timer_func(struct timer_list *);
static DEFINE_TIMER(key_gc_timer, key_gc_timer_func);

static time64_t key_gc_next_run = TIME64_MAX;
static struct key_type *key_gc_dead_keytype;

static unsigned long key_gc_flags;
#define KEY_GC_KEY_EXPIRED	0	/* A key expired and needs unlinking */
#define KEY_GC_REAP_KEYTYPE	1	/* A keytype is being unregistered */
#define KEY_GC_REAPING_KEYTYPE	2	/* Cleared when keytype reaped */


/*
 * Any key whose type gets unregistered will be re-typed to this if it can't be
 * immediately unlinked.
 */
struct key_type key_type_dead = {
	.name = ".dead",
};

/*
 * Schedule a garbage collection run.
 * - time precision isn't particularly important
 */
void key_schedule_gc(time64_t gc_at)
{
	unsigned long expires;
	time64_t now = ktime_get_real_seconds();

	kenter("%lld", gc_at - now);

	if (gc_at <= now || test_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags)) {
		kdebug("IMMEDIATE");
		schedule_work(&key_gc_work);
	} else if (gc_at < key_gc_next_run) {
		kdebug("DEFERRED");
		key_gc_next_run = gc_at;
		expires = jiffies + (gc_at - now) * HZ;
		mod_timer(&key_gc_timer, expires);
	}
}

/*
 * Schedule a dead links collection run.
 */
void key_schedule_gc_links(void)
{
	set_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags);
	schedule_work(&key_gc_work);
}

/*
 * Some key's cleanup time was met after it expired, so we need to get the
 * reaper to go through a cycle finding expired keys.
 */
static void key_gc_timer_func(struct timer_list *unused)
{
	kenter("");
	key_gc_next_run = TIME64_MAX;
	key_schedule_gc_links();
}

/*
 * Reap keys of dead type.
 *
 * We use three flags to make sure we see three complete cycles of the garbage
 * collector: the first to mark keys of that type as being dead, the second to
 * collect dead links and the third to clean up the dead keys.  We have to be
 * careful as there may already be a cycle in progress.
 *
 * The caller must be holding key_types_sem.
 */
void key_gc_keytype(struct key_type *ktype)
{
	kenter("%s", ktype->name);

	key_gc_dead_keytype = ktype;
	set_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
	smp_mb();
	set_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags);

	kdebug("schedule");
	schedule_work(&key_gc_work);

	kdebug("sleep");
	wait_on_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE,
		    TASK_UNINTERRUPTIBLE);

	key_gc_dead_keytype = NULL;
	kleave("");
}

/*
 * Garbage collect a list of unreferenced, detached keys
 */
static noinline void key_gc_unused_keys(struct list_head *keys)
{
	while (!list_empty(keys)) {
		struct key *key =
			list_entry(keys->next, struct key, graveyard_link);
		short state = key->state;

		list_del(&key->graveyard_link);

		kdebug("- %u", key->serial);
		key_check(key);

		/* Throw away the key data if the key is instantiated */
		if (state == KEY_IS_POSITIVE && key->type->destroy)
			key->type->destroy(key);

		security_key_free(key);

		/* deal with the user's key tracking and quota */
		if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
			spin_lock(&key->user->lock);
			key->user->qnkeys--;
			key->user->qnbytes -= key->quotalen;
			spin_unlock(&key->user->lock);
		}

		atomic_dec(&key->user->nkeys);
		if (state != KEY_IS_UNINSTANTIATED)
			atomic_dec(&key->user->nikeys);

		key_user_put(key->user);
		key_put_tag(key->domain_tag);
		key_put_acl(rcu_access_pointer(key->acl));
		kfree(key->description);

		memzero_explicit(key, sizeof(*key));
		kmem_cache_free(key_jar, key);
	}
}

/*
 * Garbage collector for unused keys.
 *
 * This is done in process context so that we don't have to disable interrupts
 * all over the place.  key_put() schedules this rather than trying to do the
 * cleanup itself, which means key_put() doesn't have to sleep.
 */
static void key_garbage_collector(struct work_struct *work)
{
	static LIST_HEAD(graveyard);
	static u8 gc_state;		/* Internal persistent state */
#define KEY_GC_REAP_AGAIN	0x01	/* - Need another cycle */
#define KEY_GC_REAPING_LINKS	0x02	/* - We need to reap links */
#define KEY_GC_SET_TIMER	0x04	/* - We need to restart the timer */
#define KEY_GC_REAPING_DEAD_1	0x10	/* - We need to mark dead keys */
#define KEY_GC_REAPING_DEAD_2	0x20	/* - We need to reap dead key links */
#define KEY_GC_REAPING_DEAD_3	0x40	/* - We need to reap dead keys */
#define KEY_GC_FOUND_DEAD_KEY	0x80	/* - We found at least one dead key */

	struct rb_node *cursor;
	struct key *key;
	time64_t new_timer, limit;

	kenter("[%lx,%x]", key_gc_flags, gc_state);

	limit = ktime_get_real_seconds();
	if (limit > key_gc_delay)
		limit -= key_gc_delay;
	else
		limit = key_gc_delay;

	/* Work out what we're going to be doing in this pass */
	gc_state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2;
	gc_state <<= 1;
	if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags))
		gc_state |= KEY_GC_REAPING_LINKS | KEY_GC_SET_TIMER;

	if (test_and_clear_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags))
		gc_state |= KEY_GC_REAPING_DEAD_1;
	kdebug("new pass %x", gc_state);

	new_timer = TIME64_MAX;

	/* As only this function is permitted to remove things from the key
	 * serial tree, if cursor is non-NULL then it will always point to a
	 * valid node in the tree - even if lock got dropped.
	 */
	spin_lock(&key_serial_lock);
	cursor = rb_first(&key_serial_tree);

continue_scanning:
	while (cursor) {
		key = rb_entry(cursor, struct key, serial_node);
		cursor = rb_next(cursor);

		if (refcount_read(&key->usage) == 0)
			goto found_unreferenced_key;

		if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) {
			if (key->type == key_gc_dead_keytype) {
				gc_state |= KEY_GC_FOUND_DEAD_KEY;
				set_bit(KEY_FLAG_DEAD, &key->flags);
				goto skip_dead_key;
			} else if (key->type == &key_type_keyring &&
				   key->restrict_link) {
				goto found_restricted_keyring;
			}
		}

		if (gc_state & KEY_GC_SET_TIMER) {
			if (key->expiry > limit && key->expiry < new_timer) {
				kdebug("will expire %x in %lld",
				       key_serial(key), key->expiry - limit);
				new_timer = key->expiry;
			}
		}

		if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2))
			if (key->type == key_gc_dead_keytype)
				gc_state |= KEY_GC_FOUND_DEAD_KEY;

		if ((gc_state & KEY_GC_REAPING_LINKS) ||
		    unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) {
			if (key->type == &key_type_keyring)
				goto found_keyring;
		}

		if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3))
			if (key->type == key_gc_dead_keytype)
				goto destroy_dead_key;

	skip_dead_key:
		if (spin_is_contended(&key_serial_lock) || need_resched())
			goto contended;
	}

contended:
	spin_unlock(&key_serial_lock);

maybe_resched:
	if (cursor) {
		cond_resched();
		spin_lock(&key_serial_lock);
		goto continue_scanning;
	}

	/* We've completed the pass.  Set the timer if we need to and queue a
	 * new cycle if necessary.  We keep executing cycles until we find one
	 * where we didn't reap any keys.
	 */
	kdebug("pass complete");

	if (gc_state & KEY_GC_SET_TIMER && new_timer != (time64_t)TIME64_MAX) {
		new_timer += key_gc_delay;
		key_schedule_gc(new_timer);
	}

	if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2) ||
	    !list_empty(&graveyard)) {
		/* Make sure that all pending keyring payload destructions are
		 * fulfilled and that people aren't now looking at dead or
		 * dying keys that they don't have a reference upon or a link
		 * to.
		 */
		kdebug("gc sync");
		synchronize_rcu();
	}

	if (!list_empty(&graveyard)) {
		kdebug("gc keys");
		key_gc_unused_keys(&graveyard);
	}

	if (unlikely(gc_state & (KEY_GC_REAPING_DEAD_1 |
				 KEY_GC_REAPING_DEAD_2))) {
		if (!(gc_state & KEY_GC_FOUND_DEAD_KEY)) {
			/* No remaining dead keys: short circuit the remaining
			 * keytype reap cycles.
			 */
			kdebug("dead short");
			gc_state &= ~(KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2);
			gc_state |= KEY_GC_REAPING_DEAD_3;
		} else {
			gc_state |= KEY_GC_REAP_AGAIN;
		}
	}

	if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) {
		kdebug("dead wake");
		smp_mb();
		clear_bit(KEY_GC_REAPING_KEYTYPE, &key_gc_flags);
		wake_up_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE);
	}

	if (gc_state & KEY_GC_REAP_AGAIN)
		schedule_work(&key_gc_work);
	kleave(" [end %x]", gc_state);
	return;

	/* We found an unreferenced key - once we've removed it from the tree,
	 * we can safely drop the lock.
	 */
found_unreferenced_key:
	kdebug("unrefd key %d", key->serial);
	rb_erase(&key->serial_node, &key_serial_tree);
	spin_unlock(&key_serial_lock);

	list_add_tail(&key->graveyard_link, &graveyard);
	gc_state |= KEY_GC_REAP_AGAIN;
	goto maybe_resched;

	/* We found a restricted keyring and need to update the restriction if
	 * it is associated with the dead key type.
	 */
found_restricted_keyring:
	spin_unlock(&key_serial_lock);
	keyring_restriction_gc(key, key_gc_dead_keytype);
	goto maybe_resched;

	/* We found a keyring and we need to check the payload for links to
	 * dead or expired keys.  We don't flag another reap immediately as we
	 * have to wait for the old payload to be destroyed by RCU before we
	 * can reap the keys to which it refers.
	 */
found_keyring:
	spin_unlock(&key_serial_lock);
	keyring_gc(key, limit);
	goto maybe_resched;

	/* We found a dead key that is still referenced.  Reset its type and
	 * destroy its payload with its semaphore held.
	 */
destroy_dead_key:
	spin_unlock(&key_serial_lock);
	kdebug("destroy key %d", key->serial);
	down_write(&key->sem);
	key->type = &key_type_dead;
	if (key_gc_dead_keytype->destroy)
		key_gc_dead_keytype->destroy(key);
	memset(&key->payload, KEY_DESTROY, sizeof(key->payload));
	up_write(&key->sem);
	goto maybe_resched;
}