selftests: netfilter: test nat port clash resolution interaction with tcp early demux

Convert Antonio Ojeas bug reproducer to a kselftest.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

tools/testing/selftests/netfilter/Makefile

@@ -4,7 +4,7 @@
 TEST_PROGS := nft_trans_stress.sh nft_nat.sh bridge_brouter.sh \
 	conntrack_icmp_related.sh nft_flowtable.sh ipvs.sh \
 	nft_concat_range.sh nft_conntrack_helper.sh \
-	nft_queue.sh nft_meta.sh \
+	nft_queue.sh nft_meta.sh nf_nat_edemux.sh \
 	ipip-conntrack-mtu.sh
 
 LDLIBS = -lmnl

tools/testing/selftests/netfilter/nf_nat_edemux.sh

@@ -0,0 +1,99 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Test NAT source port clash resolution
+#
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+ret=0
+
+sfx=$(mktemp -u "XXXXXXXX")
+ns1="ns1-$sfx"
+ns2="ns2-$sfx"
+
+cleanup()
+{
+	ip netns del $ns1
+	ip netns del $ns2
+}
+
+iperf3 -v > /dev/null 2>&1
+if [ $? -ne 0 ];then
+	echo "SKIP: Could not run test without iperf3"
+	exit $ksft_skip
+fi
+
+iptables --version > /dev/null 2>&1
+if [ $? -ne 0 ];then
+	echo "SKIP: Could not run test without iptables"
+	exit $ksft_skip
+fi
+
+ip -Version > /dev/null 2>&1
+if [ $? -ne 0 ];then
+	echo "SKIP: Could not run test without ip tool"
+	exit $ksft_skip
+fi
+
+ip netns add "$ns1"
+if [ $? -ne 0 ];then
+	echo "SKIP: Could not create net namespace $ns1"
+	exit $ksft_skip
+fi
+
+trap cleanup EXIT
+
+ip netns add $ns2
+
+# Connect the namespaces using a veth pair
+ip link add name veth2 type veth peer name veth1
+ip link set netns $ns1 dev veth1
+ip link set netns $ns2 dev veth2
+
+ip netns exec $ns1 ip link set up dev lo
+ip netns exec $ns1 ip link set up dev veth1
+ip netns exec $ns1 ip addr add 192.168.1.1/24 dev veth1
+
+ip netns exec $ns2 ip link set up dev lo
+ip netns exec $ns2 ip link set up dev veth2
+ip netns exec $ns2 ip addr add 192.168.1.2/24 dev veth2
+
+# Create a server in one namespace
+ip netns exec $ns1 iperf3 -s > /dev/null 2>&1 &
+iperfs=$!
+
+# Restrict source port to just one so we don't have to exhaust
+# all others.
+ip netns exec $ns2 sysctl -q net.ipv4.ip_local_port_range="10000 10000"
+
+# add a virtual IP using DNAT
+ip netns exec $ns2 iptables -t nat -A OUTPUT -d 10.96.0.1/32 -p tcp --dport 443 -j DNAT --to-destination 192.168.1.1:5201
+
+# ... and route it to the other namespace
+ip netns exec $ns2 ip route add 10.96.0.1 via 192.168.1.1
+
+sleep 1
+
+# add a persistent connection from the other namespace
+ip netns exec $ns2 nc -q 10 -w 10 192.168.1.1 5201 > /dev/null &
+
+sleep 1
+
+# ip daddr:dport will be rewritten to 192.168.1.1 5201
+# NAT must reallocate source port 10000 because
+# 192.168.1.2:10000 -> 192.168.1.1:5201 is already in use
+echo test | ip netns exec $ns2 nc -w 3 -q 3 10.96.0.1 443 >/dev/null
+ret=$?
+
+kill $iperfs
+
+# Check nc can connect to 10.96.0.1:443 (aka 192.168.1.1:5201).
+if [ $ret -eq 0 ]; then
+	echo "PASS: nc can connect via NAT'd address"
+else
+	echo "FAIL: nc cannot connect via NAT'd address"
+	exit 1
+fi
+
+exit 0