ipv6: xfrm: dereference inner ipv6 header if encapsulated

In xfrm6_local_error use inner_header if the packet was encapsulated.

Cc: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>

net/ipv6/xfrm6_output.c

@@ -59,10 +59,12 @@ static void xfrm6_local_rxpmtu(struct sk_buff *skb, u32 mtu)
 void xfrm6_local_error(struct sk_buff *skb, u32 mtu)
 {
 	struct flowi6 fl6;
+	const struct ipv6hdr *hdr;
 	struct sock *sk = skb->sk;
 
+	hdr = skb->encapsulation ? inner_ipv6_hdr(skb) : ipv6_hdr(skb);
 	fl6.fl6_dport = inet_sk(sk)->inet_dport;
-	fl6.daddr = ipv6_hdr(skb)->daddr;
+	fl6.daddr = hdr->daddr;
 
 	ipv6_local_error(sk, EMSGSIZE, &fl6, mtu);
 }