[PATCH 4.19 28/49] openvswitch: handle DNAT tuple collision

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Dumitru Ceara <dceara@redhat.com>

commit 8aa7b526dc0b5dbf40c1b834d76a667ad672a410 upstream.

With multiple DNAT rules it's possible that after destination
translation the resulting tuples collide.

For example, two openvswitch flows:
nw_dst=10.0.0.10,tp_dst=10, actions=ct(commit,table=2,nat(dst=20.0.0.1:20))
nw_dst=10.0.0.20,tp_dst=10, actions=ct(commit,table=2,nat(dst=20.0.0.1:20))

Assuming two TCP clients initiating the following connections:
10.0.0.10:5000->10.0.0.10:10
10.0.0.10:5000->10.0.0.20:10

Both tuples would translate to 10.0.0.10:5000->20.0.0.1:20 causing
nf_conntrack_confirm() to fail because of tuple collision.

Netfilter handles this case by allocating a null binding for SNAT at
egress by default.  Perform the same operation in openvswitch for DNAT
if no explicit SNAT is requested by the user and allocate a null binding
for SNAT for packets in the "original" direction.

Reported-at: https://bugzilla.redhat.com/1877128
Suggested-by: Florian Westphal <fw@strlen.de>
Fixes: 05752523e565 ("openvswitch: Interface with NAT.")
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/openvswitch/conntrack.c |   20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

--- a/net/openvswitch/conntrack.c
+++ b/net/openvswitch/conntrack.c
@@ -899,15 +899,19 @@ static int ovs_ct_nat(struct net *net, s
 	}
 	err = ovs_ct_nat_execute(skb, ct, ctinfo, &info->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;
+	if (err == NF_ACCEPT && ct->status & IPS_DST_NAT) {
+		if (ct->status & IPS_SRC_NAT) {
+			if (maniptype == NF_NAT_MANIP_SRC)
+				maniptype = NF_NAT_MANIP_DST;
+			else
+				maniptype = NF_NAT_MANIP_SRC;
 
-		err = ovs_ct_nat_execute(skb, ct, ctinfo, &info->range,
-					 maniptype);
+			err = ovs_ct_nat_execute(skb, ct, ctinfo, &info->range,
+						 maniptype);
+		} else if (CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) {
+			err = ovs_ct_nat_execute(skb, ct, ctinfo, NULL,
+						 NF_NAT_MANIP_SRC);
+		}
 	}
 
 	/* Mark NAT done if successful and update the flow key. */