netfilter: xt_iprange: Incorrect xt_iprange boundary check for IPv6

iprange_ipv6_sub was substracting 2 unsigned ints and then casting
the result to int to find out whether they are lt, eq or gt each
other, this doesn't work if the full 32 bits of each part
can be used in IPv6 addresses. Patch should remedy that without
significant performance penalties. Also number of ntohl
calls can be reduced this way (Jozsef Kadlecsik).
Signed-off-by: Thomas Jacob <jacob@internet24.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/netfilter/xt_iprange.c

@@ -53,15 +53,13 @@ iprange_mt4(const struct sk_buff *skb, struct xt_action_param *par)
 }
 
 static inline int
-iprange_ipv6_sub(const struct in6_addr *a, const struct in6_addr *b)
+iprange_ipv6_lt(const struct in6_addr *a, const struct in6_addr *b)
 {
 	unsigned int i;
-	int r;
 
 	for (i = 0; i < 4; ++i) {
-		r = ntohl(a->s6_addr32[i]) - ntohl(b->s6_addr32[i]);
-		if (r != 0)
-			return r;
+		if (a->s6_addr32[i] != b->s6_addr32[i])
+			return ntohl(a->s6_addr32[i]) < ntohl(b->s6_addr32[i]);
 	}
 
 	return 0;
@@ -75,15 +73,15 @@ iprange_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 	bool m;
 
 	if (info->flags & IPRANGE_SRC) {
-		m  = iprange_ipv6_sub(&iph->saddr, &info->src_min.in6) < 0;
-		m |= iprange_ipv6_sub(&iph->saddr, &info->src_max.in6) > 0;
+		m  = iprange_ipv6_lt(&iph->saddr, &info->src_min.in6);
+		m |= iprange_ipv6_lt(&info->src_max.in6, &iph->saddr);
 		m ^= !!(info->flags & IPRANGE_SRC_INV);
 		if (m)
 			return false;
 	}
 	if (info->flags & IPRANGE_DST) {
-		m  = iprange_ipv6_sub(&iph->daddr, &info->dst_min.in6) < 0;
-		m |= iprange_ipv6_sub(&iph->daddr, &info->dst_max.in6) > 0;
+		m  = iprange_ipv6_lt(&iph->daddr, &info->dst_min.in6);
+		m |= iprange_ipv6_lt(&info->dst_max.in6, &iph->daddr);
 		m ^= !!(info->flags & IPRANGE_DST_INV);
 		if (m)
 			return false;