selftests: net: test for lwtunnel dst ref loops

As recently specified by commit 0ea09cb ("docs: netdev: add a note
on selftest posting") in net-next, the selftest is therefore shipped in
this series. However, this selftest does not really test this series. It
needs this series to avoid crashing the kernel. What it really tests,
thanks to kmemleak, is what was fixed by the following commits:
- commit c71a192 ("net: ipv6: fix dst refleaks in rpl, seg6 and
ioam6 lwtunnels")
- commit 92191dd ("net: ipv6: fix dst ref loops in rpl, seg6 and
ioam6 lwtunnels")
- commit c64a072 ("net: ipv6: fix dst ref loop on input in seg6
lwt")
- commit 13e55fb ("net: ipv6: fix dst ref loop on input in rpl
lwt")
- commit 0e7633d ("net: ipv6: fix dst ref loop in ila lwtunnel")
- commit 5da15a9 ("net: ipv6: fix missing dst ref drop in ila
lwtunnel")

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Link: https://patch.msgid.link/20250314120048.12569-4-justin.iurman@uliege.be
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

tools/testing/selftests/net/Makefile

@@ -101,6 +101,7 @@ TEST_PROGS += vlan_bridge_binding.sh
 TEST_PROGS += bpf_offload.py
 TEST_PROGS += ipv6_route_update_soft_lockup.sh
 TEST_PROGS += busy_poll_test.sh
+TEST_PROGS += lwt_dst_cache_ref_loop.sh
 
 # YNL files, must be before "include ..lib.mk"
 YNL_GEN_FILES := busy_poller netlink-dumps

tools/testing/selftests/net/config

@@ -107,3 +107,5 @@ CONFIG_XFRM_INTERFACE=m
 CONFIG_XFRM_USER=m
 CONFIG_IP_NF_MATCH_RPFILTER=m
 CONFIG_IP6_NF_MATCH_RPFILTER=m
+CONFIG_IPV6_ILA=m
+CONFIG_IPV6_RPL_LWTUNNEL=y

tools/testing/selftests/net/lwt_dst_cache_ref_loop.sh

@@ -0,0 +1,246 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Author: Justin Iurman <justin.iurman@uliege.be>
+#
+# WARNING
+# -------
+# This is just a dummy script that triggers encap cases with possible dst cache
+# reference loops in affected lwt users (see list below). Some cases are
+# pathological configurations for simplicity, others are valid. Overall, we
+# don't want this issue to happen, no matter what. In order to catch any
+# reference loops, kmemleak MUST be used. The results alone are always blindly
+# successful, don't rely on them. Note that the following tests may crash the
+# kernel if the fix to prevent lwtunnel_{input|output|xmit}() reentry loops is
+# not present.
+#
+# Affected lwt users so far (please update accordingly if needed):
+#  - ila_lwt (output only)
+#  - ioam6_iptunnel (output only)
+#  - rpl_iptunnel (both input and output)
+#  - seg6_iptunnel (both input and output)
+
+source lib.sh
+
+check_compatibility()
+{
+	setup_ns tmp_node &>/dev/null
+	if [ $? != 0 ]; then
+		echo "SKIP: Cannot create netns."
+		exit $ksft_skip
+	fi
+
+	ip link add name veth0 netns $tmp_node type veth \
+		peer name veth1 netns $tmp_node &>/dev/null
+	local ret=$?
+
+	ip -netns $tmp_node link set veth0 up &>/dev/null
+	ret=$((ret + $?))
+
+	ip -netns $tmp_node link set veth1 up &>/dev/null
+	ret=$((ret + $?))
+
+	if [ $ret != 0 ]; then
+		echo "SKIP: Cannot configure links."
+		cleanup_ns $tmp_node
+		exit $ksft_skip
+	fi
+
+	lsmod 2>/dev/null | grep -q "ila"
+	ila_lsmod=$?
+	[ $ila_lsmod != 0 ] && modprobe ila &>/dev/null
+
+	ip -netns $tmp_node route add 2001:db8:1::/64 \
+		encap ila 1:2:3:4 csum-mode no-action ident-type luid \
+			hook-type output \
+		dev veth0 &>/dev/null
+
+	ip -netns $tmp_node route add 2001:db8:2::/64 \
+		encap ioam6 trace prealloc type 0x800000 ns 0 size 4 \
+		dev veth0 &>/dev/null
+
+	ip -netns $tmp_node route add 2001:db8:3::/64 \
+		encap rpl segs 2001:db8:3::1 dev veth0 &>/dev/null
+
+	ip -netns $tmp_node route add 2001:db8:4::/64 \
+		encap seg6 mode inline segs 2001:db8:4::1 dev veth0 &>/dev/null
+
+	ip -netns $tmp_node -6 route 2>/dev/null | grep -q "encap ila"
+	skip_ila=$?
+
+	ip -netns $tmp_node -6 route 2>/dev/null | grep -q "encap ioam6"
+	skip_ioam6=$?
+
+	ip -netns $tmp_node -6 route 2>/dev/null | grep -q "encap rpl"
+	skip_rpl=$?
+
+	ip -netns $tmp_node -6 route 2>/dev/null | grep -q "encap seg6"
+	skip_seg6=$?
+
+	cleanup_ns $tmp_node
+}
+
+setup()
+{
+	setup_ns alpha beta gamma &>/dev/null
+
+	ip link add name veth-alpha netns $alpha type veth \
+		peer name veth-betaL netns $beta &>/dev/null
+
+	ip link add name veth-betaR netns $beta type veth \
+		peer name veth-gamma netns $gamma &>/dev/null
+
+	ip -netns $alpha link set veth-alpha name veth0 &>/dev/null
+	ip -netns $beta link set veth-betaL name veth0 &>/dev/null
+	ip -netns $beta link set veth-betaR name veth1 &>/dev/null
+	ip -netns $gamma link set veth-gamma name veth0 &>/dev/null
+
+	ip -netns $alpha addr add 2001:db8:1::2/64 dev veth0 &>/dev/null
+	ip -netns $alpha link set veth0 up &>/dev/null
+	ip -netns $alpha link set lo up &>/dev/null
+	ip -netns $alpha route add 2001:db8:2::/64 \
+		via 2001:db8:1::1 dev veth0 &>/dev/null
+
+	ip -netns $beta addr add 2001:db8:1::1/64 dev veth0 &>/dev/null
+	ip -netns $beta addr add 2001:db8:2::1/64 dev veth1 &>/dev/null
+	ip -netns $beta link set veth0 up &>/dev/null
+	ip -netns $beta link set veth1 up &>/dev/null
+	ip -netns $beta link set lo up &>/dev/null
+	ip -netns $beta route del 2001:db8:2::/64
+	ip -netns $beta route add 2001:db8:2::/64 dev veth1
+	ip netns exec $beta \
+		sysctl -wq net.ipv6.conf.all.forwarding=1 &>/dev/null
+
+	ip -netns $gamma addr add 2001:db8:2::2/64 dev veth0 &>/dev/null
+	ip -netns $gamma link set veth0 up &>/dev/null
+	ip -netns $gamma link set lo up &>/dev/null
+	ip -netns $gamma route add 2001:db8:1::/64 \
+		via 2001:db8:2::1 dev veth0 &>/dev/null
+
+	sleep 1
+
+	ip netns exec $alpha ping6 -c 5 -W 1 2001:db8:2::2 &>/dev/null
+	if [ $? != 0 ]; then
+		echo "SKIP: Setup failed."
+		exit $ksft_skip
+	fi
+
+	sleep 1
+}
+
+cleanup()
+{
+	cleanup_ns $alpha $beta $gamma
+	[ $ila_lsmod != 0 ] && modprobe -r ila &>/dev/null
+}
+
+run_ila()
+{
+	if [ $skip_ila != 0 ]; then
+		echo "SKIP: ila (output)"
+		return
+	fi
+
+	ip -netns $beta route del 2001:db8:2::/64
+	ip -netns $beta route add 2001:db8:2:0:0:0:0:2/128 \
+		encap ila 2001:db8:2:0 csum-mode no-action ident-type luid \
+			hook-type output \
+		dev veth1 &>/dev/null
+	sleep 1
+
+	echo "TEST: ila (output)"
+	ip netns exec $beta ping6 -c 2 -W 1 2001:db8:2::2 &>/dev/null
+	sleep 1
+
+	ip -netns $beta route del 2001:db8:2:0:0:0:0:2/128
+	ip -netns $beta route add 2001:db8:2::/64 dev veth1
+	sleep 1
+}
+
+run_ioam6()
+{
+	if [ $skip_ioam6 != 0 ]; then
+		echo "SKIP: ioam6 (output)"
+		return
+	fi
+
+	ip -netns $beta route change 2001:db8:2::/64 \
+		encap ioam6 trace prealloc type 0x800000 ns 1 size 4 \
+		dev veth1 &>/dev/null
+	sleep 1
+
+	echo "TEST: ioam6 (output)"
+	ip netns exec $beta ping6 -c 2 -W 1 2001:db8:2::2 &>/dev/null
+	sleep 1
+}
+
+run_rpl()
+{
+	if [ $skip_rpl != 0 ]; then
+		echo "SKIP: rpl (input)"
+		echo "SKIP: rpl (output)"
+		return
+	fi
+
+	ip -netns $beta route change 2001:db8:2::/64 \
+		encap rpl segs 2001:db8:2::2 \
+		dev veth1 &>/dev/null
+	sleep 1
+
+	echo "TEST: rpl (input)"
+	ip netns exec $alpha ping6 -c 2 -W 1 2001:db8:2::2 &>/dev/null
+	sleep 1
+
+	echo "TEST: rpl (output)"
+	ip netns exec $beta ping6 -c 2 -W 1 2001:db8:2::2 &>/dev/null
+	sleep 1
+}
+
+run_seg6()
+{
+	if [ $skip_seg6 != 0 ]; then
+		echo "SKIP: seg6 (input)"
+		echo "SKIP: seg6 (output)"
+		return
+	fi
+
+	ip -netns $beta route change 2001:db8:2::/64 \
+		encap seg6 mode inline segs 2001:db8:2::2 \
+		dev veth1 &>/dev/null
+	sleep 1
+
+	echo "TEST: seg6 (input)"
+	ip netns exec $alpha ping6 -c 2 -W 1 2001:db8:2::2 &>/dev/null
+	sleep 1
+
+	echo "TEST: seg6 (output)"
+	ip netns exec $beta ping6 -c 2 -W 1 2001:db8:2::2 &>/dev/null
+	sleep 1
+}
+
+run()
+{
+	run_ila
+	run_ioam6
+	run_rpl
+	run_seg6
+}
+
+if [ "$(id -u)" -ne 0 ]; then
+	echo "SKIP: Need root privileges."
+	exit $ksft_skip
+fi
+
+if [ ! -x "$(command -v ip)" ]; then
+	echo "SKIP: Could not run test without ip tool."
+	exit $ksft_skip
+fi
+
+check_compatibility
+
+trap cleanup EXIT
+
+setup
+run
+
+exit $ksft_pass