seg6: fix skb transport_header after decap_and_validate()

in the receive path (more precisely in ip6_rcv_core()) the
skb->transport_header is set to skb->network_header + sizeof(*hdr). As a
consequence, after routing operations, destination input expects to find
skb->transport_header correctly set to the next protocol (or extension
header) that follows the network protocol. However, decap behaviors (DX*,
DT*) remove the outer IPv6 and SRH extension and do not set again the
skb->transport_header pointer correctly. For this reason, the patch sets
the skb->transport_header to the skb->network_header + sizeof(hdr) in each
DX* and DT* behavior.
Signed-off-by: Andrea Mayer <andrea.mayer@uniroma2.it>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/seg6_local.c

@@ -341,6 +341,8 @@ static int input_action_end_dx6(struct sk_buff *skb,
 	if (!ipv6_addr_any(&slwt->nh6))
 		nhaddr = &slwt->nh6;
 
+	skb_set_transport_header(skb, sizeof(struct ipv6hdr));
+
 	seg6_lookup_nexthop(skb, nhaddr, 0);
 
 	return dst_input(skb);
@@ -370,6 +372,8 @@ static int input_action_end_dx4(struct sk_buff *skb,
 
 	skb_dst_drop(skb);
 
+	skb_set_transport_header(skb, sizeof(struct iphdr));
+
 	err = ip_route_input(skb, nhaddr, iph->saddr, 0, skb->dev);
 	if (err)
 		goto drop;
@@ -390,6 +394,8 @@ static int input_action_end_dt6(struct sk_buff *skb,
 	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
 		goto drop;
 
+	skb_set_transport_header(skb, sizeof(struct ipv6hdr));
+
 	seg6_lookup_nexthop(skb, NULL, slwt->table);
 
 	return dst_input(skb);