selftets: seg6: disable rp_filter by default in srv6_end_dt4_l3vpn_test

On some distributions, the rp_filter is automatically set (=1) by
default on a netdev basis (also on VRFs).
In an SRv6 End.DT4 behavior, decapsulated IPv4 packets are routed using
the table associated with the VRF bound to that tunnel. During lookup
operations, the rp_filter can lead to packet loss when activated on the
VRF.
Therefore, we chose to make this selftest more robust by explicitly
disabling the rp_filter during tests (as it is automatically set by some
Linux distributions).

Fixes: 2195444 ("selftests: add selftest for the SRv6 End.DT4 behavior")
Reported-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Andrea Mayer <andrea.mayer@uniroma2.it>
Tested-by: Hangbin Liu <liuhangbin@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/srv6_end_dt4_l3vpn_test.sh

@@ -258,6 +258,12 @@ setup_hs()
 
 	# set the networking for the host
 	ip netns add ${hsname}
+
+	# disable the rp_filter otherwise the kernel gets confused about how
+	# to route decap ipv4 packets.
+	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.all.rp_filter=0
+	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.default.rp_filter=0
+
 	ip -netns ${hsname} link add veth0 type veth peer name ${rtveth}
 	ip -netns ${hsname} link set ${rtveth} netns ${rtname}
 	ip -netns ${hsname} addr add ${IPv4_HS_NETWORK}.${hs}/24 dev veth0
@@ -276,11 +282,6 @@ setup_hs()
 
 	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.${rtveth}.proxy_arp=1
 
-	# disable the rp_filter otherwise the kernel gets confused about how
-	# to route decap ipv4 packets.
-	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.all.rp_filter=0
-	ip netns exec ${rtname} sysctl -wq net.ipv4.conf.${rtveth}.rp_filter=0
-
 	ip netns exec ${rtname} sh -c "echo 1 > /proc/sys/net/vrf/strict_mode"
 }