selftests: netfilter: extend flowtable test script with dnat rule

NAT test currently covers snat (masquerade) only.

Also add a dnat rule and then check that a connecting to the
to-be-dnated address will work.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

tools/testing/selftests/netfilter/nft_flowtable.sh

@@ -226,17 +226,19 @@ check_transfer()
 	return 0
 }
 
-test_tcp_forwarding()
+test_tcp_forwarding_ip()
 {
 	local nsa=$1
 	local nsb=$2
+	local dstip=$3
+	local dstport=$4
 	local lret=0
 
 	ip netns exec $nsb nc -w 5 -l -p 12345 < "$ns2in" > "$ns2out" &
 	lpid=$!
 
 	sleep 1
-	ip netns exec $nsa nc -w 4 10.0.2.99 12345 < "$ns1in" > "$ns1out" &
+	ip netns exec $nsa nc -w 4 "$dstip" "$dstport" < "$ns1in" > "$ns1out" &
 	cpid=$!
 
 	sleep 3
@@ -258,6 +260,28 @@ test_tcp_forwarding()
 	return $lret
 }
 
+test_tcp_forwarding()
+{
+	test_tcp_forwarding_ip "$1" "$2" 10.0.2.99 12345
+
+	return $?
+}
+
+test_tcp_forwarding_nat()
+{
+	local lret
+
+	test_tcp_forwarding_ip "$1" "$2" 10.0.2.99 12345
+	lret=$?
+
+	if [ $lret -eq 0 ] ; then
+		test_tcp_forwarding_ip "$1" "$2" 10.6.6.6 1666
+		lret=$?
+	fi
+
+	return $lret
+}
+
 make_file "$ns1in" "ns1"
 make_file "$ns2in" "ns2"
 
@@ -283,14 +307,19 @@ ip -net ns2 route add 192.168.10.1 via 10.0.2.1
 # Same, but with NAT enabled.
 ip netns exec nsr1 nft -f - <<EOF
 table ip nat {
+   chain prerouting {
+      type nat hook prerouting priority 0; policy accept;
+      meta iif "veth0" ip daddr 10.6.6.6 tcp dport 1666 counter dnat ip to 10.0.2.99:12345
+   }
+
    chain postrouting {
       type nat hook postrouting priority 0; policy accept;
-      meta oifname "veth1" masquerade
+      meta oifname "veth1" counter masquerade
    }
 }
 EOF
 
-test_tcp_forwarding ns1 ns2
+test_tcp_forwarding_nat ns1 ns2
 
 if [ $? -eq 0 ] ;then
 	echo "PASS: flow offloaded for ns1/ns2 with NAT"
@@ -313,7 +342,7 @@ fi
 ip netns exec ns1 sysctl net.ipv4.ip_no_pmtu_disc=0 > /dev/null
 ip netns exec ns2 sysctl net.ipv4.ip_no_pmtu_disc=0 > /dev/null
 
-test_tcp_forwarding ns1 ns2
+test_tcp_forwarding_nat ns1 ns2
 if [ $? -eq 0 ] ;then
 	echo "PASS: flow offloaded for ns1/ns2 with NAT and pmtu discovery"
 else