net/sched: act_ct: fix err check for nf_conntrack_confirm

The confirm operation should be checked. If there are any failed,
the packet should be dropped like in ovs and netfilter.

Fixes: b57dc7c1 ("net/sched: Introduce action ct")
Signed-off-by: Nwenxu <wenxu@ucloud.cn>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/act_ct.c

@@ -1026,7 +1026,8 @@ static int tcf_ct_act(struct sk_buff *skb, const struct tc_action *a,
 		/* This will take care of sending queued events
 		 * even if the connection is already confirmed.
 		 */
-		nf_conntrack_confirm(skb);
+		if (nf_conntrack_confirm(skb) != NF_ACCEPT)
+			goto drop;
 	}
 
 	if (!skip_add)