[IPV6]: Ensure to have hop-by-hop options in our header of &sk_buff.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/exthdrs.c

@@ -489,6 +489,18 @@ int ipv6_parse_hopopts(struct sk_buff *skb, int nhoff)
 {
 	struct inet6_skb_parm *opt = IP6CB(skb);
 
+	/*
+	 * skb->nh.raw is equal to skb->data, and
+	 * skb->h.raw - skb->nh.raw is always equal to
+	 * sizeof(struct ipv6hdr) by definition of
+	 * hop-by-hop options.
+	 */
+	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr) + 8) ||
+	    !pskb_may_pull(skb, sizeof(struct ipv6hdr) + ((skb->h.raw[1] + 1) << 3))) {
+		kfree_skb(skb);
+		return -1;
+	}
+
 	opt->hop = sizeof(struct ipv6hdr);
 	if (ip6_parse_tlv(tlvprochopopt_lst, skb)) {
 		skb->h.raw += (skb->h.raw[1]+1)<<3;