aboutsummaryrefslogtreecommitdiff
path: root/security/keys/gc.c
blob: 89df6b5f203c534c64fffd3fc0547f611dedebea (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
/* Key garbage collector
 *
 * Copyright (C) 2009 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

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

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

/*
 * Reaper
 */
static void key_gc_timer_func(unsigned long);
static void key_garbage_collector(struct work_struct *);
static DEFINE_TIMER(key_gc_timer, key_gc_timer_func, 0, 0);
static DECLARE_WORK(key_gc_work, key_garbage_collector);
static key_serial_t key_gc_cursor; /* the last key the gc considered */
static bool key_gc_again;
static unsigned long key_gc_executing;
static time_t key_gc_next_run = LONG_MAX;
static time_t key_gc_new_timer;

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

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

	if (gc_at <= now) {
		schedule_work(&key_gc_work);
	} else if (gc_at < key_gc_next_run) {
		expires = jiffies + (gc_at - now) * HZ;
		mod_timer(&key_gc_timer, expires);
	}
}

/*
 * The garbage collector timer kicked off
 */
static void key_gc_timer_func(unsigned long data)
{
	kenter("");
	key_gc_next_run = LONG_MAX;
	schedule_work(&key_gc_work);
}

/*
 * Garbage collect pointers from a keyring.
 *
 * Return true if we altered the keyring.
 */
static bool key_gc_keyring(struct key *keyring, time_t limit)
	__releases(key_serial_lock)
{
	struct keyring_list *klist;
	struct key *key;
	int loop;

	kenter("%x", key_serial(keyring));

	if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
		goto dont_gc;

	/* scan the keyring looking for dead keys */
	rcu_read_lock();
	klist = rcu_dereference(keyring->payload.subscriptions);
	if (!klist)
		goto unlock_dont_gc;

	for (loop = klist->nkeys - 1; loop >= 0; loop--) {
		key = klist->keys[loop];
		if (test_bit(KEY_FLAG_DEAD, &key->flags) ||
		    (key->expiry > 0 && key->expiry <= limit))
			goto do_gc;
	}

unlock_dont_gc:
	rcu_read_unlock();
dont_gc:
	kleave(" = false");
	return false;

do_gc:
	rcu_read_unlock();
	key_gc_cursor = keyring->serial;
	key_get(keyring);
	spin_unlock(&key_serial_lock);
	keyring_gc(keyring, limit);
	key_put(keyring);
	kleave(" = true");
	return true;
}

/*
 * Garbage collector for keys.  This involves scanning the keyrings for dead,
 * expired and revoked keys that have overstayed their welcome
 */
static void key_garbage_collector(struct work_struct *work)
{
	struct rb_node *rb;
	key_serial_t cursor;
	struct key *key, *xkey;
	time_t new_timer = LONG_MAX, limit, now;

	now = current_kernel_time().tv_sec;
	kenter("[%x,%ld]", key_gc_cursor, key_gc_new_timer - now);

	if (test_and_set_bit(0, &key_gc_executing)) {
		key_schedule_gc(current_kernel_time().tv_sec + 1);
		kleave(" [busy; deferring]");
		return;
	}

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

	spin_lock(&key_serial_lock);

	if (unlikely(RB_EMPTY_ROOT(&key_serial_tree))) {
		spin_unlock(&key_serial_lock);
		clear_bit(0, &key_gc_executing);
		return;
	}

	cursor = key_gc_cursor;
	if (cursor < 0)
		cursor = 0;
	if (cursor > 0)
		new_timer = key_gc_new_timer;
	else
		key_gc_again = false;

	/* find the first key above the cursor */
	key = NULL;
	rb = key_serial_tree.rb_node;
	while (rb) {
		xkey = rb_entry(rb, struct key, serial_node);
		if (cursor < xkey->serial) {
			key = xkey;
			rb = rb->rb_left;
		} else if (cursor > xkey->serial) {
			rb = rb->rb_right;
		} else {
			rb = rb_next(rb);
			if (!rb)
				goto reached_the_end;
			key = rb_entry(rb, struct key, serial_node);
			break;
		}
	}

	if (!key)
		goto reached_the_end;

	/* trawl through the keys looking for keyrings */
	for (;;) {
		if (key->expiry > limit && key->expiry < new_timer) {
			kdebug("will expire %x in %ld",
			       key_serial(key), key->expiry - limit);
			new_timer = key->expiry;
		}

		if (key->type == &key_type_keyring &&
		    key_gc_keyring(key, limit))
			/* the gc had to release our lock so that the keyring
			 * could be modified, so we have to get it again */
			goto gc_released_our_lock;

		rb = rb_next(&key->serial_node);
		if (!rb)
			goto reached_the_end;
		key = rb_entry(rb, struct key, serial_node);
	}

gc_released_our_lock:
	kdebug("gc_released_our_lock");
	key_gc_new_timer = new_timer;
	key_gc_again = true;
	clear_bit(0, &key_gc_executing);
	schedule_work(&key_gc_work);
	kleave(" [continue]");
	return;

	/* when we reach the end of the run, we set the timer for the next one */
reached_the_end:
	kdebug("reached_the_end");
	spin_unlock(&key_serial_lock);
	key_gc_new_timer = new_timer;
	key_gc_cursor = 0;
	clear_bit(0, &key_gc_executing);

	if (key_gc_again) {
		/* there may have been a key that expired whilst we were
		 * scanning, so if we discarded any links we should do another
		 * scan */
		new_timer = now + 1;
		key_schedule_gc(new_timer);
	} else if (new_timer < LONG_MAX) {
		new_timer += key_gc_delay;
		key_schedule_gc(new_timer);
	}
	kleave(" [end]");
}