1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Key garbage collector
3 *
4 * Copyright (C) 2009-2011 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8#include <linux/slab.h>
9#include <linux/security.h>
10#include <keys/keyring-type.h>
11#include "internal.h"
12
13/*
14 * Delay between key revocation/expiry in seconds
15 */
16unsigned key_gc_delay = 5 * 60;
17
18/*
19 * Reaper for unused keys.
20 */
21static void key_garbage_collector(struct work_struct *work);
22DECLARE_WORK(key_gc_work, key_garbage_collector);
23
24/*
25 * Reaper for links from keyrings to dead keys.
26 */
27static void key_gc_timer_func(struct timer_list *);
28static DEFINE_TIMER(key_gc_timer, key_gc_timer_func);
29
30static time64_t key_gc_next_run = TIME64_MAX;
31static struct key_type *key_gc_dead_keytype;
32
33static unsigned long key_gc_flags;
34#define KEY_GC_KEY_EXPIRED 0 /* A key expired and needs unlinking */
35#define KEY_GC_REAP_KEYTYPE 1 /* A keytype is being unregistered */
36#define KEY_GC_REAPING_KEYTYPE 2 /* Cleared when keytype reaped */
37
38
39/*
40 * Any key whose type gets unregistered will be re-typed to this if it can't be
41 * immediately unlinked.
42 */
43struct key_type key_type_dead = {
44 .name = ".dead",
45};
46
47/*
48 * Schedule a garbage collection run.
49 * - time precision isn't particularly important
50 */
51void key_schedule_gc(time64_t gc_at)
52{
53 unsigned long expires;
54 time64_t now = ktime_get_real_seconds();
55
56 kenter("%lld", gc_at - now);
57
58 if (gc_at <= now || test_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags)) {
59 kdebug("IMMEDIATE");
60 schedule_work(work: &key_gc_work);
61 } else if (gc_at < key_gc_next_run) {
62 kdebug("DEFERRED");
63 key_gc_next_run = gc_at;
64 expires = jiffies + (gc_at - now) * HZ;
65 mod_timer(timer: &key_gc_timer, expires);
66 }
67}
68
69/*
70 * Set the expiration time on a key.
71 */
72void key_set_expiry(struct key *key, time64_t expiry)
73{
74 key->expiry = expiry;
75 if (expiry != TIME64_MAX) {
76 if (!(key->type->flags & KEY_TYPE_INSTANT_REAP))
77 expiry += key_gc_delay;
78 key_schedule_gc(gc_at: expiry);
79 }
80}
81
82/*
83 * Schedule a dead links collection run.
84 */
85void key_schedule_gc_links(void)
86{
87 set_bit(KEY_GC_KEY_EXPIRED, addr: &key_gc_flags);
88 schedule_work(work: &key_gc_work);
89}
90
91/*
92 * Some key's cleanup time was met after it expired, so we need to get the
93 * reaper to go through a cycle finding expired keys.
94 */
95static void key_gc_timer_func(struct timer_list *unused)
96{
97 kenter("");
98 key_gc_next_run = TIME64_MAX;
99 key_schedule_gc_links();
100}
101
102/*
103 * Reap keys of dead type.
104 *
105 * We use three flags to make sure we see three complete cycles of the garbage
106 * collector: the first to mark keys of that type as being dead, the second to
107 * collect dead links and the third to clean up the dead keys. We have to be
108 * careful as there may already be a cycle in progress.
109 *
110 * The caller must be holding key_types_sem.
111 */
112void key_gc_keytype(struct key_type *ktype)
113{
114 kenter("%s", ktype->name);
115
116 key_gc_dead_keytype = ktype;
117 set_bit(KEY_GC_REAPING_KEYTYPE, addr: &key_gc_flags);
118 smp_mb();
119 set_bit(KEY_GC_REAP_KEYTYPE, addr: &key_gc_flags);
120
121 kdebug("schedule");
122 schedule_work(work: &key_gc_work);
123
124 kdebug("sleep");
125 wait_on_bit(word: &key_gc_flags, KEY_GC_REAPING_KEYTYPE,
126 TASK_UNINTERRUPTIBLE);
127
128 key_gc_dead_keytype = NULL;
129 kleave("");
130}
131
132/*
133 * Garbage collect a list of unreferenced, detached keys
134 */
135static noinline void key_gc_unused_keys(struct list_head *keys)
136{
137 while (!list_empty(head: keys)) {
138 struct key *key =
139 list_entry(keys->next, struct key, graveyard_link);
140 short state = key->state;
141
142 list_del(entry: &key->graveyard_link);
143
144 kdebug("- %u", key->serial);
145 key_check(key);
146
147#ifdef CONFIG_KEY_NOTIFICATIONS
148 remove_watch_list(wlist: key->watchers, id: key->serial);
149 key->watchers = NULL;
150#endif
151
152 /* Throw away the key data if the key is instantiated */
153 if (state == KEY_IS_POSITIVE && key->type->destroy)
154 key->type->destroy(key);
155
156 security_key_free(key);
157
158 atomic_dec(v: &key->user->nkeys);
159 if (state != KEY_IS_UNINSTANTIATED)
160 atomic_dec(v: &key->user->nikeys);
161
162 key_user_put(user: key->user);
163 key_put_tag(tag: key->domain_tag);
164 kfree(objp: key->description);
165
166 memzero_explicit(s: key, count: sizeof(*key));
167 kmem_cache_free(s: key_jar, objp: key);
168 }
169}
170
171/*
172 * Garbage collector for unused keys.
173 *
174 * This is done in process context so that we don't have to disable interrupts
175 * all over the place. key_put() schedules this rather than trying to do the
176 * cleanup itself, which means key_put() doesn't have to sleep.
177 */
178static void key_garbage_collector(struct work_struct *work)
179{
180 static LIST_HEAD(graveyard);
181 static u8 gc_state; /* Internal persistent state */
182#define KEY_GC_REAP_AGAIN 0x01 /* - Need another cycle */
183#define KEY_GC_REAPING_LINKS 0x02 /* - We need to reap links */
184#define KEY_GC_REAPING_DEAD_1 0x10 /* - We need to mark dead keys */
185#define KEY_GC_REAPING_DEAD_2 0x20 /* - We need to reap dead key links */
186#define KEY_GC_REAPING_DEAD_3 0x40 /* - We need to reap dead keys */
187#define KEY_GC_FOUND_DEAD_KEY 0x80 /* - We found at least one dead key */
188
189 struct rb_node *cursor;
190 struct key *key;
191 time64_t new_timer, limit, expiry;
192
193 kenter("[%lx,%x]", key_gc_flags, gc_state);
194
195 limit = ktime_get_real_seconds();
196
197 /* Work out what we're going to be doing in this pass */
198 gc_state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2;
199 gc_state <<= 1;
200 if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, addr: &key_gc_flags))
201 gc_state |= KEY_GC_REAPING_LINKS;
202
203 if (test_and_clear_bit(KEY_GC_REAP_KEYTYPE, addr: &key_gc_flags))
204 gc_state |= KEY_GC_REAPING_DEAD_1;
205 kdebug("new pass %x", gc_state);
206
207 new_timer = TIME64_MAX;
208
209 /* As only this function is permitted to remove things from the key
210 * serial tree, if cursor is non-NULL then it will always point to a
211 * valid node in the tree - even if lock got dropped.
212 */
213 spin_lock(lock: &key_serial_lock);
214 cursor = rb_first(root: &key_serial_tree);
215
216continue_scanning:
217 while (cursor) {
218 key = rb_entry(cursor, struct key, serial_node);
219 cursor = rb_next(cursor);
220
221 if (!test_bit_acquire(KEY_FLAG_USER_ALIVE, &key->flags)) {
222 /* Clobber key->user after final put seen. */
223 goto found_unreferenced_key;
224 }
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, addr: &key->flags);
230 key->perm = 0;
231 goto skip_dead_key;
232 } else if (key->type == &key_type_keyring &&
233 key->restrict_link) {
234 goto found_restricted_keyring;
235 }
236 }
237
238 expiry = key->expiry;
239 if (expiry != TIME64_MAX) {
240 if (!(key->type->flags & KEY_TYPE_INSTANT_REAP))
241 expiry += key_gc_delay;
242 if (expiry > limit && expiry < new_timer) {
243 kdebug("will expire %x in %lld",
244 key_serial(key), key->expiry - limit);
245 new_timer = key->expiry;
246 }
247 }
248
249 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2))
250 if (key->type == key_gc_dead_keytype)
251 gc_state |= KEY_GC_FOUND_DEAD_KEY;
252
253 if ((gc_state & KEY_GC_REAPING_LINKS) ||
254 unlikely(gc_state & KEY_GC_REAPING_DEAD_2)) {
255 if (key->type == &key_type_keyring)
256 goto found_keyring;
257 }
258
259 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3))
260 if (key->type == key_gc_dead_keytype)
261 goto destroy_dead_key;
262
263 skip_dead_key:
264 if (spin_is_contended(lock: &key_serial_lock) || need_resched())
265 goto contended;
266 }
267
268contended:
269 spin_unlock(lock: &key_serial_lock);
270
271maybe_resched:
272 if (cursor) {
273 cond_resched();
274 spin_lock(lock: &key_serial_lock);
275 goto continue_scanning;
276 }
277
278 /* We've completed the pass. Set the timer if we need to and queue a
279 * new cycle if necessary. We keep executing cycles until we find one
280 * where we didn't reap any keys.
281 */
282 kdebug("pass complete");
283
284 if (new_timer != TIME64_MAX) {
285 new_timer += key_gc_delay;
286 key_schedule_gc(gc_at: new_timer);
287 }
288
289 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_2) ||
290 !list_empty(head: &graveyard)) {
291 /* Make sure that all pending keyring payload destructions are
292 * fulfilled and that people aren't now looking at dead or
293 * dying keys that they don't have a reference upon or a link
294 * to.
295 */
296 kdebug("gc sync");
297 synchronize_rcu();
298 }
299
300 if (!list_empty(head: &graveyard)) {
301 kdebug("gc keys");
302 key_gc_unused_keys(keys: &graveyard);
303 }
304
305 if (unlikely(gc_state & (KEY_GC_REAPING_DEAD_1 |
306 KEY_GC_REAPING_DEAD_2))) {
307 if (!(gc_state & KEY_GC_FOUND_DEAD_KEY)) {
308 /* No remaining dead keys: short circuit the remaining
309 * keytype reap cycles.
310 */
311 kdebug("dead short");
312 gc_state &= ~(KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2);
313 gc_state |= KEY_GC_REAPING_DEAD_3;
314 } else {
315 gc_state |= KEY_GC_REAP_AGAIN;
316 }
317 }
318
319 if (unlikely(gc_state & KEY_GC_REAPING_DEAD_3)) {
320 kdebug("dead wake");
321 smp_mb();
322 clear_bit(KEY_GC_REAPING_KEYTYPE, addr: &key_gc_flags);
323 wake_up_bit(word: &key_gc_flags, KEY_GC_REAPING_KEYTYPE);
324 }
325
326 if (gc_state & KEY_GC_REAP_AGAIN)
327 schedule_work(work: &key_gc_work);
328 kleave(" [end %x]", gc_state);
329 return;
330
331 /* We found an unreferenced key - once we've removed it from the tree,
332 * we can safely drop the lock.
333 */
334found_unreferenced_key:
335 kdebug("unrefd key %d", key->serial);
336 rb_erase(&key->serial_node, &key_serial_tree);
337 spin_unlock(lock: &key_serial_lock);
338
339 list_add_tail(new: &key->graveyard_link, head: &graveyard);
340 gc_state |= KEY_GC_REAP_AGAIN;
341 goto maybe_resched;
342
343 /* We found a restricted keyring and need to update the restriction if
344 * it is associated with the dead key type.
345 */
346found_restricted_keyring:
347 spin_unlock(lock: &key_serial_lock);
348 keyring_restriction_gc(keyring: key, dead_type: key_gc_dead_keytype);
349 goto maybe_resched;
350
351 /* We found a keyring and we need to check the payload for links to
352 * dead or expired keys. We don't flag another reap immediately as we
353 * have to wait for the old payload to be destroyed by RCU before we
354 * can reap the keys to which it refers.
355 */
356found_keyring:
357 spin_unlock(lock: &key_serial_lock);
358 keyring_gc(keyring: key, limit);
359 goto maybe_resched;
360
361 /* We found a dead key that is still referenced. Reset its type and
362 * destroy its payload with its semaphore held.
363 */
364destroy_dead_key:
365 spin_unlock(lock: &key_serial_lock);
366 kdebug("destroy key %d", key->serial);
367 down_write(sem: &key->sem);
368 key->type = &key_type_dead;
369 if (key_gc_dead_keytype->destroy)
370 key_gc_dead_keytype->destroy(key);
371 memset(&key->payload, KEY_DESTROY, sizeof(key->payload));
372 up_write(sem: &key->sem);
373 goto maybe_resched;
374}
375

source code of linux/security/keys/gc.c