netfilter: cttimeout: fix use after free error when delete netns
In general, when we want to delete a netns, cttimeout_net_exit will
be called before ipt_unregister_table, i.e. before ctnl_timeout_put.
But after call kfree_rcu in cttimeout_net_exit, we will still decrease
the timeout object's refcnt in ctnl_timeout_put, this is incorrect,
and will cause a use after free error.
It is easy to reproduce this problem:
# while : ; do
ip netns add xxx
ip netns exec xxx nfct add timeout testx inet icmp timeout 200
ip netns exec xxx iptables -t raw -p icmp -I OUTPUT -j CT --timeout testx
ip netns del xxx
done
=======================================================================
BUG kmalloc-96 (Tainted: G B E ): Poison overwritten
-----------------------------------------------------------------------
INFO: 0xffff88002b5161e8-0xffff88002b5161e8. First byte 0x6a instead of
0x6b
INFO: Allocated in cttimeout_new_timeout+0xd4/0x240 [nfnetlink_cttimeout]
age=104 cpu=0 pid=3330
___slab_alloc+0x4da/0x540
__slab_alloc+0x20/0x40
__kmalloc+0x1c8/0x240
cttimeout_new_timeout+0xd4/0x240 [nfnetlink_cttimeout]
nfnetlink_rcv_msg+0x21a/0x230 [nfnetlink]
[ ... ]
So only when the refcnt decreased to 0, we call kfree_rcu to free the
timeout object. And like nfnetlink_acct do, use atomic_cmpxchg to
avoid race between ctnl_timeout_try_del and ctnl_timeout_put.
Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c
index 4cdcd96..68216cd 100644
--- a/net/netfilter/nfnetlink_cttimeout.c
+++ b/net/netfilter/nfnetlink_cttimeout.c
@@ -330,16 +330,16 @@
{
int ret = 0;
- /* we want to avoid races with nf_ct_timeout_find_get. */
- if (atomic_dec_and_test(&timeout->refcnt)) {
+ /* We want to avoid races with ctnl_timeout_put. So only when the
+ * current refcnt is 1, we decrease it to 0.
+ */
+ if (atomic_cmpxchg(&timeout->refcnt, 1, 0) == 1) {
/* We are protected by nfnl mutex. */
list_del_rcu(&timeout->head);
nf_ct_l4proto_put(timeout->l4proto);
ctnl_untimeout(net, timeout);
kfree_rcu(timeout, rcu_head);
} else {
- /* still in use, restore reference counter. */
- atomic_inc(&timeout->refcnt);
ret = -EBUSY;
}
return ret;
@@ -543,7 +543,9 @@
static void ctnl_timeout_put(struct ctnl_timeout *timeout)
{
- atomic_dec(&timeout->refcnt);
+ if (atomic_dec_and_test(&timeout->refcnt))
+ kfree_rcu(timeout, rcu_head);
+
module_put(THIS_MODULE);
}
#endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
@@ -591,7 +593,9 @@
list_for_each_entry_safe(cur, tmp, &net->nfct_timeout_list, head) {
list_del_rcu(&cur->head);
nf_ct_l4proto_put(cur->l4proto);
- kfree_rcu(cur, rcu_head);
+
+ if (atomic_dec_and_test(&cur->refcnt))
+ kfree_rcu(cur, rcu_head);
}
}