netfilter: nat: really support inet nat without l3 address

When no l3 address is given, priv->family is set to NFPROTO_INET and
the evaluation function isn't called.

Call it too so l4-only rewrite can work.
Also add a test case for this.

Fixes: a33f387ecd5aa ("netfilter: nft_nat: allow to specify layer 4 protocol NAT only")
Reported-by: Yi Chen <[e-mail]>
Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nft_nat.c

···
 {
 	const struct nft_nat *priv = nft_expr_priv(expr);
 
-	if (priv->family == nft_pf(pkt))
+	if (priv->family == nft_pf(pkt) ||
+	    priv->family == NFPROTO_INET)
 		nft_nat_eval(expr, regs, pkt);
 }
 

tools/testing/selftests/netfilter/nft_nat.sh

···
 	return $lret
 }
 
+test_local_dnat_portonly()
+{
+	local family=$1
+	local daddr=$2
+	local lret=0
+	local sr_s
+	local sr_r
+
+ip netns exec "$ns0" nft -f /dev/stdin <<EOF
+table $family nat {
+	chain output {
+		type nat hook output priority 0; policy accept;
+		meta l4proto tcp dnat to :2000
+
+	}
+}
+EOF
+	if [ $? -ne 0 ]; then
+		if [ $family = "inet" ];then
+			echo "SKIP: inet port test"
+			test_inet_nat=false
+			return
+		fi
+		echo "SKIP: Could not add $family dnat hook"
+		return
+	fi
+
+	echo SERVER-$family | ip netns exec "$ns1" timeout 5 socat -u STDIN TCP-LISTEN:2000 &
+	sc_s=$!
+
+	result=$(ip netns exec "$ns0" timeout 1 socat TCP:$daddr:2000 STDOUT)
+
+	if [ "$result" = "SERVER-inet" ];then
+		echo "PASS: inet port rewrite without l3 address"
+	else
+		echo "ERROR: inet port rewrite"
+		ret=1
+	fi
+}
 
 test_masquerade6()
 {
···
 reset_counters
 test_local_dnat ip
 test_local_dnat6 ip6
+
+reset_counters
+test_local_dnat_portonly inet 10.0.1.99
+
 reset_counters
 $test_inet_nat && test_local_dnat inet
 $test_inet_nat && test_local_dnat6 inet