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>
