linux/security/keys/gc.c
David Howells cf8304e8f3 KEYS: Fix RCU handling in key_gc_keyring()
key_gc_keyring() needs to either hold the RCU read lock or hold the keyring
semaphore if it's going to scan the keyring's list.  Given that it only needs
to read the key list, and it's doing so under a spinlock, the RCU read lock is
the thing to use.

Furthermore, the RCU check added in e7b0a61b79 is
incorrect as holding the spinlock on key_serial_lock is not grounds for
assuming a keyring's pointer list can be read safely.  Instead, a simple
rcu_dereference() inside of the previously mentioned RCU read lock is what we
want.

Reported-by: Serge E. Hallyn <serue@us.ibm.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
2010-05-05 11:39:23 +10:00

222 lines
5.2 KiB
C

/* 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
* - 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]");
}