[NETFILTER]: introduce skb_header_pointer() to ipv6header match

Signed-off-by: Yasuyuki KOZAKAI <yasuyuki.kozakai@toshiba.co.jp>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/ipv6/netfilter/ip6t_ipv6header.c

@@ -51,7 +51,7 @@ ipv6header_match(const struct sk_buff *skb,
 	temp = 0;
 
         while (ip6t_ext_hdr(nexthdr)) {
-        	struct ipv6_opt_hdr *hdr;
+		struct ipv6_opt_hdr _hdr, *hp;
         	int hdrlen;
 
 		/* Is there enough space for the next ext header? */
@@ -68,15 +68,16 @@ ipv6header_match(const struct sk_buff *skb,
 			break;
 		}
 
-		hdr=(struct ipv6_opt_hdr *)(skb->data+ptr);
+		hp = skb_header_pointer(skb, ptr, sizeof(_hdr), &_hdr);
+		BUG_ON(hp == NULL);
 
 		/* Calculate the header length */
                 if (nexthdr == NEXTHDR_FRAGMENT) {
                         hdrlen = 8;
                 } else if (nexthdr == NEXTHDR_AUTH)
-                        hdrlen = (hdr->hdrlen+2)<<2;
+                        hdrlen = (hp->hdrlen+2)<<2;
                 else
-                        hdrlen = ipv6_optlen(hdr);
+                        hdrlen = ipv6_optlen(hp);
 
 		/* set the flag */
 		switch (nexthdr){
@@ -100,7 +101,7 @@ ipv6header_match(const struct sk_buff *skb,
 				break;
 		}
 
-                nexthdr = hdr->nexthdr;
+                nexthdr = hp->nexthdr;
                 len -= hdrlen;
                 ptr += hdrlen;
 		if (ptr > skb->len)