selftests: netfilter: add ebtables broute test case

ebtables -t broute allows to redirect packets in a way that
they get pushed up the stack, even if the interface is part
of a bridge.

In case of IP packets to non-local address, this means
those IP packets are routed instead of bridged-forwarded, just
as if the bridge would not have existed.

Expected test output is:
PASS: netns connectivity: ns1 and ns2 can reach each other
PASS: ns1/ns2 connectivity with active broute rule
PASS: ns1/ns2 connectivity with active broute rule and bridge forward drop
Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

tools/testing/selftests/netfilter/Makefile

 # SPDX-License-Identifier: GPL-2.0
 # Makefile for netfilter selftests
 
-TEST_PROGS := nft_trans_stress.sh nft_nat.sh
+TEST_PROGS := nft_trans_stress.sh nft_nat.sh bridge_brouter.sh
 
 include ../lib.mk

tools/testing/selftests/netfilter/bridge_brouter.sh

+#!/bin/bash
+#
+# This test is for bridge 'brouting', i.e. make some packets being routed
+# rather than getting bridged even though they arrive on interface that is
+# part of a bridge.
+
+#           eth0    br0     eth0
+# setup is: ns1 <-> ns0 <-> ns2
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+ret=0
+
+ebtables -V > /dev/null 2>&1
+if [ $? -ne 0 ];then
+	echo "SKIP: Could not run test without ebtables"
+	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 ns0
+ip netns add ns1
+ip netns add ns2
+
+ip link add veth0 netns ns0 type veth peer name eth0 netns ns1
+if [ $? -ne 0 ]; then
+	echo "SKIP: Can't create veth device"
+	exit $ksft_skip
+fi
+ip link add veth1 netns ns0 type veth peer name eth0 netns ns2
+
+ip -net ns0 link set lo up
+ip -net ns0 link set veth0 up
+ip -net ns0 link set veth1 up
+
+ip -net ns0 link add br0 type bridge
+if [ $? -ne 0 ]; then
+	echo "SKIP: Can't create bridge br0"
+	exit $ksft_skip
+fi
+
+ip -net ns0 link set veth0 master br0
+ip -net ns0 link set veth1 master br0
+ip -net ns0 link set br0 up
+ip -net ns0 addr add 10.0.0.1/24 dev br0
+
+# place both in same subnet, ns1 and ns2 connected via ns0:br0
+for i in 1 2; do
+  ip -net ns$i link set lo up
+  ip -net ns$i link set eth0 up
+  ip -net ns$i addr add 10.0.0.1$i/24 dev eth0
+done
+
+test_ebtables_broute()
+{
+	local cipt
+
+	# redirect is needed so the dstmac is rewritten to the bridge itself,
+	# ip stack won't process OTHERHOST (foreign unicast mac) packets.
+	ip netns exec ns0 ebtables -t broute -A BROUTING -p ipv4 --ip-protocol icmp -j redirect --redirect-target=DROP
+	if [ $? -ne 0 ]; then
+		echo "SKIP: Could not add ebtables broute redirect rule"
+		return $ksft_skip
+	fi
+
+	# ping netns1, expected to not work (ip forwarding is off)
+	ip netns exec ns1 ping -q -c 1 10.0.0.12 > /dev/null 2>&1
+	if [ $? -eq 0 ]; then
+		echo "ERROR: ping works, should have failed" 1>&2
+		return 1
+	fi
+
+	# enable forwarding on both interfaces.
+	# neither needs an ip address, but at least the bridge needs
+	# an ip address in same network segment as ns1 and ns2 (ns0
+	# needs to be able to determine route for to-be-forwarded packet).
+	ip netns exec ns0 sysctl -q net.ipv4.conf.veth0.forwarding=1
+	ip netns exec ns0 sysctl -q net.ipv4.conf.veth1.forwarding=1
+
+	sleep 1
+
+	ip netns exec ns1 ping -q -c 1 10.0.0.12 > /dev/null
+	if [ $? -ne 0 ]; then
+		echo "ERROR: ping did not work, but it should (broute+forward)" 1>&2
+		return 1
+	fi
+
+	echo "PASS: ns1/ns2 connectivity with active broute rule"
+	ip netns exec ns0 ebtables -t broute -F
+
+	# ping netns1, expected to work (frames are bridged)
+	ip netns exec ns1 ping -q -c 1 10.0.0.12 > /dev/null
+	if [ $? -ne 0 ]; then
+		echo "ERROR: ping did not work, but it should (bridged)" 1>&2
+		return 1
+	fi
+
+	ip netns exec ns0 ebtables -t filter -A FORWARD -p ipv4 --ip-protocol icmp -j DROP
+
+	# ping netns1, expected to not work (DROP in bridge forward)
+	ip netns exec ns1 ping -q -c 1 10.0.0.12 > /dev/null 2>&1
+	if [ $? -eq 0 ]; then
+		echo "ERROR: ping works, should have failed (icmp forward drop)" 1>&2
+		return 1
+	fi
+
+	# re-activate brouter
+	ip netns exec ns0 ebtables -t broute -A BROUTING -p ipv4 --ip-protocol icmp -j redirect --redirect-target=DROP
+
+	ip netns exec ns2 ping -q -c 1 10.0.0.11 > /dev/null
+	if [ $? -ne 0 ]; then
+		echo "ERROR: ping did not work, but it should (broute+forward 2)" 1>&2
+		return 1
+	fi
+
+	echo "PASS: ns1/ns2 connectivity with active broute rule and bridge forward drop"
+	return 0
+}
+
+# test basic connectivity
+ip netns exec ns1 ping -c 1 -q 10.0.0.12 > /dev/null
+if [ $? -ne 0 ]; then
+    echo "ERROR: Could not reach ns2 from ns1" 1>&2
+    ret=1
+fi
+
+ip netns exec ns2 ping -c 1 -q 10.0.0.11 > /dev/null
+if [ $? -ne 0 ]; then
+    echo "ERROR: Could not reach ns1 from ns2" 1>&2
+    ret=1
+fi
+
+if [ $ret -eq 0 ];then
+    echo "PASS: netns connectivity: ns1 and ns2 can reach each other"
+fi
+
+test_ebtables_broute
+ret=$?
+for i in 0 1 2; do ip netns del ns$i;done
+
+exit $ret