net: shy netns_ok check

Failure to pass netns_ok check is SILENT, except some MIB counter is
incremented somewhere.

And adding "netns_ok = 1" (after long head-scratching session) is
usually the last step in making some protocol netns-ready...
Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ip_input.c

@@ -209,9 +209,17 @@ static int ip_local_deliver_finish(struct sk_buff *skb)
 
 		hash = protocol & (MAX_INET_PROTOS - 1);
 		ipprot = rcu_dereference(inet_protos[hash]);
-		if (ipprot != NULL && (net == &init_net || ipprot->netns_ok)) {
+		if (ipprot != NULL) {
 			int ret;
 
+			if (!net_eq(net, &init_net) && !ipprot->netns_ok) {
+				if (net_ratelimit())
+					printk("%s: proto %d isn't netns-ready\n",
+						__func__, protocol);
+				kfree_skb(skb);
+				goto out;
+			}
+
 			if (!ipprot->no_policy) {
 				if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb)) {
 					kfree_skb(skb);