netfilter: ip6tables: mark malformed IPv6 extension headers for hotdrop

The ah, hbh and rt matches check that the fixed extension header is
present, then use the header length field to derive the advertised
extension header length for matching.

For the ah match, add the missing advertised-length check. For hbh
and rt, update the existing advertised-length checks. In all three
cases, set hotdrop to true before returning false when the advertised
extension header length exceeds the available skb data.

Returning false treats the packet as a rule mismatch. Set hotdrop to
true and drop malformed packets so they cannot bypass rules intended
to drop packets with these IPv6 extension headers.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Zhixing Chen <running910@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>

net/ipv6/netfilter/ip6t_ah.c

@@ -56,6 +56,11 @@ static bool ah_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 	}
 
 	hdrlen = ipv6_authlen(ah);
+	if (skb->len - ptr < hdrlen) {
+		/* Packet smaller than its length field */
+		par->hotdrop = true;
+		return false;
+	}
 
 	pr_debug("IPv6 AH LEN %u %u ", hdrlen, ah->hdrlen);
 	pr_debug("RES %04X ", ah->reserved);

net/ipv6/netfilter/ip6t_hbh.c

@@ -75,6 +75,7 @@ hbh_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 	hdrlen = ipv6_optlen(oh);
 	if (skb->len - ptr < hdrlen) {
 		/* Packet smaller than it's length field */
+		par->hotdrop = true;
 		return false;
 	}
 

net/ipv6/netfilter/ip6t_rt.c

@@ -56,7 +56,8 @@ static bool rt_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 
 	hdrlen = ipv6_optlen(rh);
 	if (skb->len - ptr < hdrlen) {
-		/* Pcket smaller than its length field */
+		/* Packet smaller than its length field */
+		par->hotdrop = true;
 		return false;
 	}