net_sched: fix a NULL pointer deref in ipt action

The net pointer in struct xt_tgdtor_param is not explicitly
initialized therefore is still NULL when dereferencing it.
So we have to find a way to pass the correct net pointer to
ipt_destroy_target().

The best way I find is just saving the net pointer inside the per
netns struct tcf_idrinfo, which could make this patch smaller.

Fixes: 0c66dc1ea3f0 ("netfilter: conntrack: register hooks in netns when needed by ruleset")
Reported-and-tested-by: itugrok@yahoo.com
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/act_ipt.c b/net/sched/act_ipt.c
index ce2c30a..214a03d 100644
--- a/net/sched/act_ipt.c
+++ b/net/sched/act_ipt.c
@@ -61,12 +61,13 @@ static int ipt_init_target(struct net *net, struct xt_entry_target *t,
 	return 0;
 }
 
-static void ipt_destroy_target(struct xt_entry_target *t)
+static void ipt_destroy_target(struct xt_entry_target *t, struct net *net)
 {
 	struct xt_tgdtor_param par = {
 		.target   = t->u.kernel.target,
 		.targinfo = t->data,
 		.family   = NFPROTO_IPV4,
+		.net      = net,
 	};
 	if (par.target->destroy != NULL)
 		par.target->destroy(&par);
@@ -78,7 +79,7 @@ static void tcf_ipt_release(struct tc_action *a)
 	struct tcf_ipt *ipt = to_ipt(a);
 
 	if (ipt->tcfi_t) {
-		ipt_destroy_target(ipt->tcfi_t);
+		ipt_destroy_target(ipt->tcfi_t, a->idrinfo->net);
 		kfree(ipt->tcfi_t);
 	}
 	kfree(ipt->tcfi_tname);
@@ -180,7 +181,7 @@ static int __tcf_ipt_init(struct net *net, unsigned int id, struct nlattr *nla,
 
 	spin_lock_bh(&ipt->tcf_lock);
 	if (ret != ACT_P_CREATED) {
-		ipt_destroy_target(ipt->tcfi_t);
+		ipt_destroy_target(ipt->tcfi_t, net);
 		kfree(ipt->tcfi_tname);
 		kfree(ipt->tcfi_t);
 	}
@@ -350,7 +351,7 @@ static __net_init int ipt_init_net(struct net *net)
 {
 	struct tc_action_net *tn = net_generic(net, ipt_net_id);
 
-	return tc_action_net_init(tn, &act_ipt_ops);
+	return tc_action_net_init(net, tn, &act_ipt_ops);
 }
 
 static void __net_exit ipt_exit_net(struct list_head *net_list)
@@ -399,7 +400,7 @@ static __net_init int xt_init_net(struct net *net)
 {
 	struct tc_action_net *tn = net_generic(net, xt_net_id);
 
-	return tc_action_net_init(tn, &act_xt_ops);
+	return tc_action_net_init(net, tn, &act_xt_ops);
 }
 
 static void __net_exit xt_exit_net(struct list_head *net_list)