Root/security/keys/gc.c

Source at commit be977234bfb4a6dca8a39e7c52165e4cd536ad71 created 9 years 5 months ago.
By Lars-Peter Clausen, jz4740: Fix compile error
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}
223

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