ipv6: handle Redirect ICMP Message with no Redirected Header option

rfc 4861 says the Redirected Header option is optional, so
the kernel should not drop the Redirect Message that has no
Redirected Header option. In this patch, the function
ip6_redirect_no_header() is introduced to deal with that
condition.

Signed-off-by: Duan Jiong <duanj.fnst@cn.fujitsu.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>

include/net/ip6_route.h

@@ -135,6 +135,8 @@ extern void ip6_update_pmtu(struct sk_buff *skb, struct net *net, __be32 mtu,
 extern void ip6_sk_update_pmtu(struct sk_buff *skb, struct sock *sk,
 			       __be32 mtu);
 extern void ip6_redirect(struct sk_buff *skb, struct net *net, int oif, u32 mark);
+extern void ip6_redirect_no_header(struct sk_buff *skb, struct net *net, int oif,
+				   u32 mark);
 extern void ip6_sk_redirect(struct sk_buff *skb, struct sock *sk);
 
 struct netlink_callback;

net/ipv6/ndisc.c

@@ -1369,8 +1369,10 @@ static void ndisc_redirect_rcv(struct sk_buff *skb)
 	if (!ndisc_parse_options(msg->opt, ndoptlen, &ndopts))
 		return;
 
-	if (!ndopts.nd_opts_rh)
+	if (!ndopts.nd_opts_rh) {
+		ip6_redirect_no_header(skb, dev_net(skb->dev), 0, 0);
 		return;
+	}
 
 	hdr = (u8 *)ndopts.nd_opts_rh;
 	hdr += 8;

net/ipv6/route.c

@@ -1178,6 +1178,27 @@ void ip6_redirect(struct sk_buff *skb, struct net *net, int oif, u32 mark)
 }
 EXPORT_SYMBOL_GPL(ip6_redirect);
 
+void ip6_redirect_no_header(struct sk_buff *skb, struct net *net, int oif,
+			    u32 mark)
+{
+	const struct ipv6hdr *iph = ipv6_hdr(skb);
+	const struct rd_msg *msg = (struct rd_msg *)icmp6_hdr(skb);
+	struct dst_entry *dst;
+	struct flowi6 fl6;
+
+	memset(&fl6, 0, sizeof(fl6));
+	fl6.flowi6_oif = oif;
+	fl6.flowi6_mark = mark;
+	fl6.flowi6_flags = 0;
+	fl6.daddr = msg->dest;
+	fl6.saddr = iph->daddr;
+
+	dst = ip6_route_output(net, NULL, &fl6);
+	if (!dst->error)
+		rt6_do_redirect(dst, NULL, skb);
+	dst_release(dst);
+}
+
 void ip6_sk_redirect(struct sk_buff *skb, struct sock *sk)
 {
 	ip6_redirect(skb, sock_net(sk), sk->sk_bound_dev_if, sk->sk_mark);