selftests: add IPv4 unicast extensions tests

Add selftests for kernel behavior with regard to various classes of
unallocated/reserved IPv4 addresses, checking whether or not these
addresses can be assigned as unicast addresses on links and used in
routing.

Expect the current kernel behavior at the time of this patch. That is:

* 0/8 and 240/4 may be used as unicast, with the exceptions of 0.0.0.0
  and 255.255.255.255;
* the lowest address in a subnet may only be used as a broadcast address;
* 127/8 may not be used as unicast (the route_localnet option, which is
  disabled by default, still leaves it treated slightly specially);
* 224/4 may not be used as unicast.

Signed-off-by: Seth David Schoen <schoen@loyalty.org>
Suggested-by: John Gilmore <gnu@toad.com>
Acked-by: Dave Taht <dave.taht@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20210126040834.GR24989@frotz.zork.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/Makefile

@@ -22,6 +22,7 @@ TEST_PROGS += devlink_port_split.py
 TEST_PROGS += drop_monitor_tests.sh
 TEST_PROGS += vrf_route_leaking.sh
 TEST_PROGS += bareudp.sh
+TEST_PROGS += unicast_extensions.sh
 TEST_PROGS_EXTENDED := in_netns.sh
 TEST_GEN_FILES =  socket nettest
 TEST_GEN_FILES += psock_fanout psock_tpacket msg_zerocopy reuseport_addr_any

tools/testing/selftests/net/unicast_extensions.sh

@@ -0,0 +1,228 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# By Seth Schoen (c) 2021, for the IPv4 Unicast Extensions Project
+# Thanks to David Ahern for help and advice on nettest modifications.
+#
+# Self-tests for IPv4 address extensions: the kernel's ability to accept
+# certain traditionally unused or unallocated IPv4 addresses. For each kind
+# of address, we test for interface assignment, ping, TCP, and forwarding.
+# Must be run as root (to manipulate network namespaces and virtual
+# interfaces).
+#
+# Things we test for here:
+#
+# * Currently the kernel accepts addresses in 0/8 and 240/4 as valid.
+#
+# * Notwithstanding that, 0.0.0.0 and 255.255.255.255 cannot be assigned.
+#
+# * Currently the kernel DOES NOT accept unicast use of the lowest
+#   address in an IPv4 subnet (e.g. 192.168.100.0/32 in 192.168.100.0/24).
+#   This is treated as a second broadcast address, for compatibility
+#   with 4.2BSD (!).
+#
+# * Currently the kernel DOES NOT accept unicast use of any of 127/8.
+#
+# * Currently the kernel DOES NOT accept unicast use of any of 224/4.
+#
+# These tests provide an easy way to flip the expected result of any
+# of these behaviors for testing kernel patches that change them.
+
+# nettest can be run from PATH or from same directory as this selftest
+if ! which nettest >/dev/null; then
+	PATH=$PWD:$PATH
+	if ! which nettest >/dev/null; then
+		echo "'nettest' command not found; skipping tests"
+		exit 0
+	fi
+fi
+
+result=0
+
+hide_output(){ exec 3>&1 4>&2 >/dev/null 2>/dev/null; }
+show_output(){ exec >&3 2>&4; }
+
+show_result(){
+	if [ $1 -eq 0 ]; then
+		printf "TEST: %-60s  [ OK ]\n" "${2}"
+	else
+		printf "TEST: %-60s  [FAIL]\n" "${2}"
+		result=1
+	fi
+}
+
+_do_segmenttest(){
+	# Perform a simple set of link tests between a pair of
+	# IP addresses on a shared (virtual) segment, using
+	# ping and nettest.
+	# foo --- bar
+	# Arguments: ip_a ip_b prefix_length test_description
+	#
+	# Caller must set up foo-ns and bar-ns namespaces
+	# containing linked veth devices foo and bar,
+	# respectively.
+
+	ip -n foo-ns address add $1/$3 dev foo || return 1
+	ip -n foo-ns link set foo up || return 1
+	ip -n bar-ns address add $2/$3 dev bar || return 1
+	ip -n bar-ns link set bar up || return 1
+
+	ip netns exec foo-ns timeout 2 ping -c 1 $2 || return 1
+	ip netns exec bar-ns timeout 2 ping -c 1 $1 || return 1
+
+	nettest -B -N bar-ns -O foo-ns -r $1 || return 1
+	nettest -B -N foo-ns -O bar-ns -r $2 || return 1
+
+	return 0
+}
+
+_do_route_test(){
+	# Perform a simple set of gateway tests.
+	#
+	# [foo] <---> [foo1]-[bar1] <---> [bar]   /prefix
+	#  host          gateway          host
+	#
+	# Arguments: foo_ip foo1_ip bar1_ip bar_ip prefix_len test_description
+	# Displays test result and returns success or failure.
+
+	# Caller must set up foo-ns, bar-ns, and router-ns
+	# containing linked veth devices foo-foo1, bar1-bar
+	# (foo in foo-ns, foo1 and bar1 in router-ns, and
+	# bar in bar-ns).
+
+	ip -n foo-ns address add $1/$5 dev foo || return 1
+	ip -n foo-ns link set foo up || return 1
+	ip -n foo-ns route add default via $2 || return 1
+	ip -n bar-ns address add $4/$5 dev bar || return 1
+	ip -n bar-ns link set bar up || return 1
+	ip -n bar-ns route add default via $3 || return 1
+	ip -n router-ns address add $2/$5 dev foo1 || return 1
+	ip -n router-ns link set foo1 up || return 1
+	ip -n router-ns address add $3/$5 dev bar1 || return 1
+	ip -n router-ns link set bar1 up || return 1
+
+	echo 1 | ip netns exec router-ns tee /proc/sys/net/ipv4/ip_forward
+
+	ip netns exec foo-ns timeout 2 ping -c 1 $2 || return 1
+	ip netns exec foo-ns timeout 2 ping -c 1 $4 || return 1
+	ip netns exec bar-ns timeout 2 ping -c 1 $3 || return 1
+	ip netns exec bar-ns timeout 2 ping -c 1 $1 || return 1
+
+	nettest -B -N bar-ns -O foo-ns -r $1 || return 1
+	nettest -B -N foo-ns -O bar-ns -r $4 || return 1
+
+	return 0
+}
+
+segmenttest(){
+	# Sets up veth link and tries to connect over it.
+	# Arguments: ip_a ip_b prefix_len test_description
+	hide_output
+	ip netns add foo-ns
+	ip netns add bar-ns
+	ip link add foo netns foo-ns type veth peer name bar netns bar-ns
+
+	test_result=0
+	_do_segmenttest "$@" || test_result=1
+
+	ip netns pids foo-ns | xargs -r kill -9
+	ip netns pids bar-ns | xargs -r kill -9
+	ip netns del foo-ns
+	ip netns del bar-ns
+	show_output
+
+	# inverted tests will expect failure instead of success
+	[ -n "$expect_failure" ] && test_result=`expr 1 - $test_result`
+
+	show_result $test_result "$4"
+}
+
+route_test(){
+	# Sets up a simple gateway and tries to connect through it.
+	# [foo] <---> [foo1]-[bar1] <---> [bar]   /prefix
+	# Arguments: foo_ip foo1_ip bar1_ip bar_ip prefix_len test_description
+	# Returns success or failure.
+
+	hide_output
+	ip netns add foo-ns
+	ip netns add bar-ns
+	ip netns add router-ns
+	ip link add foo netns foo-ns type veth peer name foo1 netns router-ns
+	ip link add bar netns bar-ns type veth peer name bar1 netns router-ns
+
+	test_result=0
+	_do_route_test "$@" || test_result=1
+
+	ip netns pids foo-ns | xargs -r kill -9
+	ip netns pids bar-ns | xargs -r kill -9
+	ip netns pids router-ns | xargs -r kill -9
+	ip netns del foo-ns
+	ip netns del bar-ns
+	ip netns del router-ns
+
+	show_output
+
+	# inverted tests will expect failure instead of success
+	[ -n "$expect_failure" ] && test_result=`expr 1 - $test_result`
+	show_result $test_result "$6"
+}
+
+echo "###########################################################################"
+echo "Unicast address extensions tests (behavior of reserved IPv4 addresses)"
+echo "###########################################################################"
+#
+# Test support for 240/4
+segmenttest 240.1.2.1   240.1.2.4    24 "assign and ping within 240/4 (1 of 2) (is allowed)"
+segmenttest 250.100.2.1 250.100.30.4 16 "assign and ping within 240/4 (2 of 2) (is allowed)"
+#
+# Test support for 0/8
+segmenttest 0.1.2.17    0.1.2.23  24 "assign and ping within 0/8 (1 of 2) (is allowed)"
+segmenttest 0.77.240.17 0.77.2.23 16 "assign and ping within 0/8 (2 of 2) (is allowed)"
+#
+# Even 255.255/16 is OK!
+segmenttest 255.255.3.1 255.255.50.77 16 "assign and ping inside 255.255/16 (is allowed)"
+#
+# Or 255.255.255/24
+segmenttest 255.255.255.1 255.255.255.254 24 "assign and ping inside 255.255.255/24 (is allowed)"
+#
+# Routing between different networks
+route_test 240.5.6.7 240.5.6.1  255.1.2.1    255.1.2.3      24 "route between 240.5.6/24 and 255.1.2/24 (is allowed)"
+route_test 0.200.6.7 0.200.38.1 245.99.101.1 245.99.200.111 16 "route between 0.200/16 and 245.99/16 (is allowed)"
+#
+# ==============================================
+# ==== TESTS THAT CURRENTLY EXPECT FAILURE =====
+# ==============================================
+expect_failure=true
+# It should still not be possible to use 0.0.0.0 or 255.255.255.255
+# as a unicast address.  Thus, these tests expect failure.
+segmenttest 0.0.1.5       0.0.0.0         16 "assigning 0.0.0.0 (is forbidden)"
+segmenttest 255.255.255.1 255.255.255.255 16 "assigning 255.255.255.255 (is forbidden)"
+#
+# Test support for not having all of 127 be loopback
+# Currently Linux does not allow this, so this should fail too
+segmenttest 127.99.4.5 127.99.4.6 16 "assign and ping inside 127/8 (is forbidden)"
+#
+# Test support for lowest address
+# Currently Linux does not allow this, so this should fail too
+segmenttest 5.10.15.20 5.10.15.0 24 "assign and ping lowest address (is forbidden)"
+#
+# Routing using lowest address as a gateway/endpoint
+# Currently Linux does not allow this, so this should fail too
+route_test 192.168.42.1 192.168.42.0 9.8.7.6 9.8.7.0 24 "routing using lowest address (is forbidden)"
+#
+# Test support for unicast use of class D
+# Currently Linux does not allow this, so this should fail too
+segmenttest 225.1.2.3 225.1.2.200 24 "assign and ping class D address (is forbidden)"
+#
+# Routing using class D as a gateway
+route_test 225.1.42.1 225.1.42.2 9.8.7.6 9.8.7.1 24 "routing using class D (is forbidden)"
+#
+# Routing using 127/8
+# Currently Linux does not allow this, so this should fail too
+route_test 127.99.2.3 127.99.2.4 200.1.2.3 200.1.2.4 24 "routing using 127/8 (is forbidden)"
+#
+unset expect_failure
+# =====================================================
+# ==== END OF TESTS THAT CURRENTLY EXPECT FAILURE =====
+# =====================================================
+exit ${result}