>From c3b9dfbcf35ea38a3dce22daf7450fc23c620aea Mon Sep 17 00:00:00 2001 From: Pablo Neira Ayuso Date: Mon, 11 Jul 2016 17:28:54 +0200 Subject: [PATCH] netfilter: conntrack: skip clash resolution if nat is in place The clash resolution is not easy to apply if the NAT table is registered. Even if no NAT rules are installed, the nul-binding ensures that a unique tuple is used, thus, the packet that loses race gets a different source port number, as described by: http://marc.info/?l=netfilter-devel&m=146818011604484&w=2 Clash resolution with NAT is also problematic if addresses/port range ports are used since the conntrack that wins race may describe a different mangling that we may have earlier applied to the packet via nf_nat_setup_info(). Fixes: 71d8c47fc653 ("netfilter: conntrack: introduce clash resolution on insertion race") Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_core.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index e0e9c9a..2b0f80a 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -657,6 +657,7 @@ static int nf_ct_resolve_clash(struct net *net, struct sk_buff *skb, l4proto = __nf_ct_l4proto_find(nf_ct_l3num(ct), nf_ct_protonum(ct)); if (l4proto->allow_clash && + !nfct_nat(ct) && !nf_ct_is_dying(ct) && atomic_inc_not_zero(&ct->ct_general.use)) { nf_ct_acct_merge(ct, ctinfo, (struct nf_conn *)skb->nfct); -- 2.1.4