net sched: ipt action fix late binding

This was broken and is fixed with this patch.

//add an ipt action and give it an instance id of 1
sudo tc actions add action ipt -j mark --set-mark 2 index 1
//create a filter which binds to ipt action id 1
sudo tc filter add dev $DEV parent ffff: protocol ip prio 1 u32\
match ip dst 17.0.0.1/32 flowid 1:10 action ipt index 1

Message before bug fix was:
RTNETLINK answers: Invalid argument
We have an error talking to the kernel
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_ipt.c

@@ -96,7 +96,7 @@ static int __tcf_ipt_init(struct tc_action_net *tn, struct nlattr *nla,
 	struct tcf_ipt *ipt;
 	struct xt_entry_target *td, *t;
 	char *tname;
-	int ret = 0, err;
+	int ret = 0, err, exists = 0;
 	u32 hook = 0;
 	u32 index = 0;
 
@@ -107,18 +107,23 @@ static int __tcf_ipt_init(struct tc_action_net *tn, struct nlattr *nla,
 	if (err < 0)
 		return err;
 
-	if (tb[TCA_IPT_HOOK] == NULL)
-		return -EINVAL;
-	if (tb[TCA_IPT_TARG] == NULL)
+	if (tb[TCA_IPT_INDEX] != NULL)
+		index = nla_get_u32(tb[TCA_IPT_INDEX]);
+
+	exists = tcf_hash_check(tn, index, a, bind);
+	if (exists && bind)
+		return 0;
+
+	if (tb[TCA_IPT_HOOK] == NULL || tb[TCA_IPT_TARG] == NULL) {
+		if (exists)
+			tcf_hash_release(a, bind);
 		return -EINVAL;
+	}
 
 	td = (struct xt_entry_target *)nla_data(tb[TCA_IPT_TARG]);
 	if (nla_len(tb[TCA_IPT_TARG]) < td->u.target_size)
 		return -EINVAL;
 
-	if (tb[TCA_IPT_INDEX] != NULL)
-		index = nla_get_u32(tb[TCA_IPT_INDEX]);
-
 	if (!tcf_hash_check(tn, index, a, bind)) {
 		ret = tcf_hash_create(tn, index, est, a, sizeof(*ipt), bind,
 				      false);