ipv6: Store Router Alert option in IP6CB directly.

Router Alert option is very small and we can store the value
itself in the skb.

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

include/linux/ipv6.h

@@ -84,7 +84,7 @@ static inline struct ipv6hdr *ipipv6_hdr(const struct sk_buff *skb)
 
 struct inet6_skb_parm {
 	int			iif;
-	__u16			ra;
+	__be16			ra;
 	__u16			hop;
 	__u16			dst0;
 	__u16			srcrt;
@@ -100,6 +100,7 @@ struct inet6_skb_parm {
 #define IP6SKB_XFRM_TRANSFORMED	1
 #define IP6SKB_FORWARDED	2
 #define IP6SKB_REROUTED		4
+#define IP6SKB_ROUTERALERT	8
 };
 
 #define IP6CB(skb)	((struct inet6_skb_parm*)((skb)->cb))

include/uapi/linux/ipv6.h

@@ -63,6 +63,8 @@ struct ipv6_opt_hdr {
 #define ipv6_destopt_hdr ipv6_opt_hdr
 #define ipv6_hopopt_hdr  ipv6_opt_hdr
 
+/* Router Alert option values (RFC2711) */
+#define IPV6_OPT_ROUTERALERT_MLD	0x0000	/* MLD(RFC2710) */
 
 /*
  *	routing header type 0 (used in cmsghdr struct)

net/ipv6/exthdrs.c

@@ -553,7 +553,8 @@ static bool ipv6_hop_ra(struct sk_buff *skb, int optoff)
 	const unsigned char *nh = skb_network_header(skb);
 
 	if (nh[optoff + 1] == 2) {
-		IP6CB(skb)->ra = optoff;
+		IP6CB(skb)->flags |= IP6SKB_ROUTERALERT;
+		memcpy(&IP6CB(skb)->ra, nh + optoff + 2, sizeof(IP6CB(skb)->ra));
 		return true;
 	}
 	LIMIT_NETDEBUG(KERN_DEBUG "ipv6_hop_ra: wrong RA length %d\n",

net/ipv6/ip6_input.c

@@ -280,17 +280,16 @@ int ip6_mc_input(struct sk_buff *skb)
 		struct inet6_skb_parm *opt = IP6CB(skb);
 
 		/* Check for MLD */
-		if (unlikely(opt->ra)) {
+		if (unlikely(opt->flags & IP6SKB_ROUTERALERT)) {
 			/* Check if this is a mld message */
-			u8 *ptr = skb_network_header(skb) + opt->ra;
 			u8 nexthdr = hdr->nexthdr;
 			__be16 frag_off;
 			int offset;
 
 			/* Check if the value of Router Alert
 			 * is for MLD (0x0000).
 			 */
-			if ((ptr[2] | ptr[3]) == 0) {
+			if (opt->ra == htons(IPV6_OPT_ROUTERALERT_MLD)) {
 				deliver = false;
 
 				if (!ipv6_ext_hdr(nexthdr)) {