net: ip: make ip_route_input_rcu() return drop reasons

In this commit, we make ip_route_input_rcu() return drop reasons, which
come from ip_route_input_mc() and ip_route_input_slow().

The only caller of ip_route_input_rcu() is ip_route_input_noref(). We
adjust it by making it return -EINVAL on error and ignore the reasons that
ip_route_input_rcu() returns. In the following patch, we will make
ip_route_input_noref() returns the drop reasons.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv4/route.c

@@ -2448,9 +2448,10 @@ ip_route_input_slow(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 }
 
 /* called with rcu_read_lock held */
-static int ip_route_input_rcu(struct sk_buff *skb, __be32 daddr, __be32 saddr,
-			      dscp_t dscp, struct net_device *dev,
-			      struct fib_result *res)
+static enum skb_drop_reason
+ip_route_input_rcu(struct sk_buff *skb, __be32 daddr, __be32 saddr,
+		   dscp_t dscp, struct net_device *dev,
+		   struct fib_result *res)
 {
 	/* Multicast recognition logic is moved from route cache to here.
 	 * The problem was that too many Ethernet cards have broken/missing
@@ -2493,23 +2494,23 @@ static int ip_route_input_rcu(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 			reason = ip_route_input_mc(skb, daddr, saddr, dscp,
 						   dev, our);
 		}
-		return reason ? -EINVAL : 0;
+		return reason;
 	}
 
-	return ip_route_input_slow(skb, daddr, saddr, dscp, dev, res) ? -EINVAL : 0;
+	return ip_route_input_slow(skb, daddr, saddr, dscp, dev, res);
 }
 
 int ip_route_input_noref(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 			 dscp_t dscp, struct net_device *dev)
 {
+	enum skb_drop_reason reason;
 	struct fib_result res;
-	int err;
 
 	rcu_read_lock();
-	err = ip_route_input_rcu(skb, daddr, saddr, dscp, dev, &res);
+	reason = ip_route_input_rcu(skb, daddr, saddr, dscp, dev, &res);
 	rcu_read_unlock();
 
-	return err;
+	return reason ? -EINVAL : 0;
 }
 EXPORT_SYMBOL(ip_route_input_noref);
 
@@ -3321,7 +3322,7 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 		skb->mark	= mark;
 		err = ip_route_input_rcu(skb, dst, src,
 					 inet_dsfield_to_dscp(rtm->rtm_tos),
-					 dev, &res);
+					 dev, &res) ? -EINVAL : 0;
 
 		rt = skb_rtable(skb);
 		if (err == 0 && rt->dst.error)