[PATCH net 2/2] act_ct: support asymmetric conntrack

[Aaron Conole]

The act_ct TC module shares a common conntrack and NAT infrastructure
exposed via netfilter.  It's possible that a packet needs both SNAT and
DNAT manipulation, due to e.g. tuple collision.  Netfilter can support
this because it runs through the NAT table twice - once on ingress and
again after egress.  The act_ct action doesn't have such capability.

Like netfilter hook infrastructure, we should run through NAT twice to
keep the symmetry.

Fixes: b57dc7c13ea9 ("net/sched: Introduce action ct")

Signed-off-by: Aaron Conole <aconole@xxxxxxxxxx>
---
 net/sched/act_ct.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
index fcc46025e790..f3232a00970f 100644
--- a/net/sched/act_ct.c
+++ b/net/sched/act_ct.c
@@ -329,6 +329,7 @@ static int tcf_ct_act_nat(struct sk_buff *skb,
 			  bool commit)
 {
 #if IS_ENABLED(CONFIG_NF_NAT)
+	int err;
 	enum nf_nat_manip_type maniptype;
 
 	if (!(ct_action & TCA_CT_ACT_NAT))
@@ -359,7 +360,17 @@ static int tcf_ct_act_nat(struct sk_buff *skb,
 		return NF_ACCEPT;
 	}
 
-	return ct_nat_execute(skb, ct, ctinfo, range, maniptype);
+	err = ct_nat_execute(skb, ct, ctinfo, range, maniptype);
+	if (err == NF_ACCEPT &&
+	    ct->status & IPS_SRC_NAT && ct->status & IPS_DST_NAT) {
+		if (maniptype == NF_NAT_MANIP_SRC)
+			maniptype = NF_NAT_MANIP_DST;
+		else
+			maniptype = NF_NAT_MANIP_SRC;
+
+		err = ct_nat_execute(skb, ct, ctinfo, range, maniptype);
+	}
+	return err;
 #else
 	return NF_ACCEPT;
 #endif
-- 
2.21.0