selftests: mptcp: join: test for flush/re-add endpoints

commit e06959e upstream.

After having flushed endpoints that didn't cause the creation of new
subflows, it is important to check endpoints can be re-created, re-using
previously used IDs.

Before the previous commit, the client would not have been able to
re-create the subflow that was previously rejected.

The 'Fixes' tag here below is the same as the one from the previous
commit: this patch here is not fixing anything wrong in the selftests,
but it validates the previous fix for an issue introduced by this commit
ID.

Fixes: 06faa22 ("mptcp: remove multi addresses and subflows in PM")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240819-net-mptcp-pm-reusing-id-v1-6-38035d40de5b@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ No conflicts, but adapt the test to the helpers in this version:
  - run_tests has been modified a few times to reduce the number of
    positional parameters
  - no chk_mptcp_info helper
  - chk_subflow_nr taking an extra parameter
  - kill_tests_wait instead of mptcp_lib_kill_wait ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/testing/selftests/net/mptcp/mptcp_join.sh

@@ -3262,6 +3262,35 @@ userspace_tests()
 		kill_tests_wait
 	fi
 
+	# flush and re-add
+	if reset_with_tcp_filter "flush re-add" ns2 10.0.3.2 REJECT OUTPUT &&
+	   mptcp_lib_kallsyms_has "subflow_rebuild_header$"; then
+		pm_nl_set_limits $ns1 0 2
+		pm_nl_set_limits $ns2 1 2
+		# broadcast IP: no packet for this address will be received on ns1
+		pm_nl_add_endpoint $ns1 224.0.0.1 id 2 flags signal
+		pm_nl_add_endpoint $ns2 10.0.3.2 id 3 flags subflow
+		run_tests $ns1 $ns2 10.0.1.1 4 0 0 speed_20 2>/dev/null &
+		local tests_pid=$!
+
+		wait_attempt_fail $ns2
+		chk_subflow_nr needtitle "before flush" 1
+
+		pm_nl_flush_endpoint $ns2
+		pm_nl_flush_endpoint $ns1
+		wait_rm_addr $ns2 0
+		ip netns exec "${ns2}" ${iptables} -D OUTPUT -s "10.0.3.2" -p tcp -j REJECT
+		pm_nl_add_endpoint $ns2 10.0.3.2 id 3 flags subflow
+		wait_mpj $ns2
+		pm_nl_add_endpoint $ns1 10.0.3.1 id 2 flags signal
+		wait_mpj $ns2
+		kill_wait "${tests_pid}"
+		kill_tests_wait
+
+		chk_join_nr 2 2 2
+		chk_add_nr 2 2
+		chk_rm_nr 1 0 invert
+	fi
 }
 
 endpoint_tests()