1 files changed, 369 insertions, 0 deletions
diff --git a/security/keys/gc.c b/security/keys/gc.c
new file mode 100644
index 000000000..7207e6094
--- /dev/null
+++ b/security/keys/gc.c
@@ -0,0 +1,369 @@
+/* Key garbage collector
+ *
+ * Copyright (C) 2009-2011 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 <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);
+
+		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);
+				key->perm = 0;
+				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;
+}