xfrm: fix "disable_policy" on ipv4 early demux

The commit in the "Fixes" tag tried to avoid a case where policy check
is ignored due to dst caching in next hops.

However, when the traffic is locally consumed, the dst may be cached
in a local TCP or UDP socket as part of early demux. In this case the
"disable_policy" flag is not checked as ip_route_input_noref() was only
called before caching, and thus, packets after the initial packet in a
flow will be dropped if not matching policies.

Fix by checking the "disable_policy" flag also when a valid dst is
already available.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216557Reported-by: Monil Patel <monil191989@gmail.com>
Fixes: e6175a2e ("xfrm: fix "disable_policy" flag use when arriving from different devices")
Signed-off-by: Eyal Birger <eyal.birger@gmail.com>

----

v2: use dev instead of skb->dev
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv4/ip_input.c

@@ -366,6 +366,11 @@ static int ip_rcv_finish_core(struct net *net, struct sock *sk,
 					   iph->tos, dev);
 		if (unlikely(err))
 			goto drop_error;
+	} else {
+		struct in_device *in_dev = __in_dev_get_rcu(dev);
+
+		if (in_dev && IN_DEV_ORCONF(in_dev, NOPOLICY))
+			IPCB(skb)->flags |= IPSKB_NOPOLICY;
 	}
 
 #ifdef CONFIG_IP_ROUTE_CLASSID