selftests: mptcp: join: check removing ID 0 endpoint

Removing the endpoint linked to the initial subflow should trigger a
RM_ADDR for the right ID, and the removal of the subflow. That's what is
now being verified in the "delete and re-add" test.

Note that removing the initial subflow will not decrement the 'subflows'
counters, which corresponds to the *additional* subflows. On the other
hand, when the same endpoint is re-added, it will increment this
counter, as it will be seen as an additional subflow this time.

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: 3ad14f54 ("mptcp: more accurate MPC endpoint tracking")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

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

@@ -3572,8 +3572,9 @@ endpoint_tests()
 
 	if reset_with_tcp_filter "delete and 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 0 2
+		pm_nl_set_limits $ns1 0 3
+		pm_nl_set_limits $ns2 0 3
+		pm_nl_add_endpoint $ns2 10.0.1.2 id 1 dev ns2eth1 flags subflow
 		pm_nl_add_endpoint $ns2 10.0.2.2 id 2 dev ns2eth2 flags subflow
 		test_linkfail=4 speed=20 \
 			run_tests $ns1 $ns2 10.0.1.1 &
@@ -3582,17 +3583,17 @@ endpoint_tests()
 		wait_mpj $ns2
 		pm_nl_check_endpoint "creation" \
 			$ns2 10.0.2.2 id 2 flags subflow dev ns2eth2
-		chk_subflow_nr "before delete" 2
+		chk_subflow_nr "before delete id 2" 2
 		chk_mptcp_info subflows 1 subflows 1
 
 		pm_nl_del_endpoint $ns2 2 10.0.2.2
 		sleep 0.5
-		chk_subflow_nr "after delete" 1
+		chk_subflow_nr "after delete id 2" 1
 		chk_mptcp_info subflows 0 subflows 0
 
 		pm_nl_add_endpoint $ns2 10.0.2.2 id 2 dev ns2eth2 flags subflow
 		wait_mpj $ns2
-		chk_subflow_nr "after re-add" 2
+		chk_subflow_nr "after re-add id 2" 2
 		chk_mptcp_info subflows 1 subflows 1
 
 		pm_nl_add_endpoint $ns2 10.0.3.2 id 3 flags subflow
@@ -3607,10 +3608,20 @@ endpoint_tests()
 		chk_subflow_nr "after no reject" 3
 		chk_mptcp_info subflows 2 subflows 2
 
+		pm_nl_del_endpoint $ns2 1 10.0.1.2
+		sleep 0.5
+		chk_subflow_nr "after delete id 0" 2
+		chk_mptcp_info subflows 2 subflows 2 # only decr for additional sf
+
+		pm_nl_add_endpoint $ns2 10.0.1.2 id 1 dev ns2eth1 flags subflow
+		wait_mpj $ns2
+		chk_subflow_nr "after re-add id 0" 3
+		chk_mptcp_info subflows 3 subflows 3
+
 		mptcp_lib_kill_wait $tests_pid
 
-		chk_join_nr 3 3 3
-		chk_rm_nr 1 1
+		chk_join_nr 4 4 4
+		chk_rm_nr 2 2
 	fi
 
 	# remove and re-add