[NETFILTER]: conntrack: don't call helpers for related ICMP messages

None of the existing helpers expects to get called for related ICMP
packets and some even drop them if they can't parse them.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/ip_conntrack_standalone.c

@@ -417,7 +417,7 @@ static unsigned int ip_conntrack_help(unsigned int hooknum,
 
 	/* This is where we call the helper: as the packet goes out. */
 	ct = ip_conntrack_get(*pskb, &ctinfo);
-	if (ct && ct->helper) {
+	if (ct && ct->helper && ctinfo != IP_CT_RELATED + IP_CT_IS_REPLY) {
 		unsigned int ret;
 		ret = ct->helper->help(pskb, ct, ctinfo);
 		if (ret != NF_ACCEPT)

net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c

@@ -145,7 +145,7 @@ static unsigned int ipv4_conntrack_help(unsigned int hooknum,
 
 	/* This is where we call the helper: as the packet goes out. */
 	ct = nf_ct_get(*pskb, &ctinfo);
-	if (!ct)
+	if (!ct || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY)
 		return NF_ACCEPT;
 
 	help = nfct_help(ct);

net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c

@@ -189,7 +189,7 @@ static unsigned int ipv6_confirm(unsigned int hooknum,
 
 	/* This is where we call the helper: as the packet goes out. */
 	ct = nf_ct_get(*pskb, &ctinfo);
-	if (!ct)
+	if (!ct || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY)
 		goto out;
 
 	help = nfct_help(ct);