[Devel] [PATCH vz10] selftests: mptcp: turn forwarding off in the test namespaces

[Eva Kurchatova <eva.kurchatova@virtuozzo.com>]

A new namespace inherits net.ipv4.ip_forward from the host, so on a host
that routes, so do the namespaces these tests build.

"invalid address, ADD_ADDR timeout" then reports 0 JOINs where it wants
1.  The server announces an unreachable address first and a valid one
after it.  With forwarding on, the SYN to the unreachable address draws
an ICMP error instead of being dropped, so the subflow attempt fails at
once and the next ADD_ADDR retransmission starts another one.  Every
attempt that no longer finds its predecessor bumps add_addr_accepted, so
the unreachable address alone uses up both accepted slots and the valid
address that follows is dropped without ever getting a subflow.

The two tests that do need a router, mptcp_connect.sh and
simult_flows.sh, turn forwarding on themselves for those namespaces, so
switching it off in the common setup is enough.

https://virtuozzo.atlassian.net/browse/VSTOR-139651
Feature: fix selftests
Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
---
 tools/testing/selftests/net/mptcp/mptcp_lib.sh | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_lib.sh b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
index a326f34fc719..43112e1c8c59 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_lib.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_lib.sh
@@ -455,6 +455,13 @@ mptcp_lib_ns_init() {
 	local netns
 	for netns in "${@}"; do
 		ip netns exec "${!netns}" sysctl -q net.mptcp.enabled=1
+		# The tests that need a router enable forwarding themselves,
+		# everywhere else it has to be off: a new namespace inherits
+		# the setting, so on a host that routes, an unreachable
+		# announced address is answered with an ICMP error instead of
+		# being silently dropped.
+		ip netns exec "${!netns}" sysctl -q net.ipv4.ip_forward=0
+		ip netns exec "${!netns}" sysctl -q net.ipv6.conf.all.forwarding=0
 	done
 }
 
-- 
2.55.0