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netfilter: conntrack: skip clash resolution if nat is in place

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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: 71d8c47fc6 ("netfilter: conntrack: introduce clash resolution on insertion race")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Tested-by: Marc Dionne <marc.c.dionne@gmail.com>
This commit is contained in:
Pablo Neira Ayuso 2016-07-11 17:28:54 +02:00
parent 4edfa9d0bf
commit 590b52e10d
1 changed files with 1 additions and 0 deletions
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net/netfilter/nf_conntrack_core.c
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@ -646,6 +646,7 @@ 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);