ipv6: raw: fix icmpv6_filter()

icmpv6_filter() should not modify its input, or else its caller
would need to recompute ipv6_hdr() if skb->head is reallocated.

Use skb_header_pointer() instead of pskb_may_pull() and
change the prototype to make clear both sk and skb are const.

Also, if icmpv6 header cannot be found, do not deliver the packet,
as we do in IPv4.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/raw.c

@@ -107,21 +107,20 @@ found:
  *	0 - deliver
  *	1 - block
  */
-static __inline__ int icmpv6_filter(struct sock *sk, struct sk_buff *skb)
+static int icmpv6_filter(const struct sock *sk, const struct sk_buff *skb)
 {
-	struct icmp6hdr *icmph;
-	struct raw6_sock *rp = raw6_sk(sk);
+	struct icmp6hdr *_hdr;
+	const struct icmp6hdr *hdr;
 
-	if (pskb_may_pull(skb, sizeof(struct icmp6hdr))) {
-		__u32 *data = &rp->filter.data[0];
-		int bit_nr;
+	hdr = skb_header_pointer(skb, skb_transport_offset(skb),
+				 sizeof(_hdr), &_hdr);
+	if (hdr) {
+		const __u32 *data = &raw6_sk(sk)->filter.data[0];
+		unsigned int type = hdr->icmp6_type;
 
-		icmph = (struct icmp6hdr *) skb->data;
-		bit_nr = icmph->icmp6_type;
-
-		return (data[bit_nr >> 5] & (1 << (bit_nr & 31))) != 0;
+		return (data[type >> 5] & (1U << (type & 31))) != 0;
 	}
-	return 0;
+	return 1;
 }
 
 #if defined(CONFIG_IPV6_MIP6) || defined(CONFIG_IPV6_MIP6_MODULE)