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diff --git a/tools/testing/selftests/net/unicast_extensions.sh b/tools/testing/selftests/net/unicast_extensions.sh
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+#!/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.
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+# 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 $ksft_skip
+	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)"
+#
+# Test support for lowest address ending in .0
+segmenttest 5.10.15.20 5.10.15.0 24 "assign and ping lowest address (/24)"
+#
+# Test support for lowest address not ending in .0
+segmenttest 192.168.101.192 192.168.101.193 26 "assign and ping lowest address (/26)"
+#
+# Routing using lowest address as a gateway/endpoint
+route_test 192.168.42.1 192.168.42.0 9.8.7.6 9.8.7.0 24 "routing using lowest address"
+#
+# ==============================================
+# ==== 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 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}