selftests: mptcp: validate MPJoinRejected counter

The parent commit adds this new counter, incremented when receiving a
connection request, if the PM didn't allow the creation of new subflows.

Most of the time, it is then kept at 0, except when the PM limits cause
the receiver side to reject new MPJoin connections. This is the case in
the following tests:

 - single subflow, limited by server
 - multiple subflows, limited by server
 - subflows limited by server w cookies
 - userspace pm type rejects join
 - userspace pm type prevents mp_prio

Simply set join_syn_rej=1 when checking the MPJoin counters for these
tests.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250413-net-next-mptcp-sched-mib-sft-misc-v2-6-0f83a4350150@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index befa66f..b8af653 100755 (executable)
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -62,6 +62,7 @@ unset sflags
 unset fastclose
 unset fullmesh
 unset speed
+unset join_syn_rej
 unset join_csum_ns1
 unset join_csum_ns2
 unset join_fail_nr
@@ -1403,6 +1404,7 @@ chk_join_nr()
        local syn_nr=$1
        local syn_ack_nr=$2
        local ack_nr=$3
+       local syn_rej=${join_syn_rej:-0}
        local csum_ns1=${join_csum_ns1:-0}
        local csum_ns2=${join_csum_ns2:-0}
        local fail_nr=${join_fail_nr:-0}
@@ -1468,6 +1470,15 @@ chk_join_nr()
                fail_test "got $count JOIN[s] ack HMAC failure expected 0"
        fi
 
+       count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinRejected")
+       if [ -z "$count" ]; then
+               rc=${KSFT_SKIP}
+       elif [ "$count" != "$syn_rej" ]; then
+               rc=${KSFT_FAIL}
+               print_check "syn rejected"
+               fail_test "got $count JOIN[s] syn rejected expected $syn_rej"
+       fi
+
        print_results "join Rx" ${rc}
 
        join_syn_tx="${join_syn_tx:-${syn_nr}}" \
@@ -1963,7 +1974,8 @@ subflows_tests()
                pm_nl_set_limits $ns2 0 1
                pm_nl_add_endpoint $ns2 10.0.3.2 flags subflow
                run_tests $ns1 $ns2 10.0.1.1
-               chk_join_nr 1 1 0
+               join_syn_rej=1 \
+                       chk_join_nr 1 1 0
        fi
 
        # subflow
@@ -1992,7 +2004,8 @@ subflows_tests()
                pm_nl_add_endpoint $ns2 10.0.3.2 flags subflow
                pm_nl_add_endpoint $ns2 10.0.2.2 flags subflow
                run_tests $ns1 $ns2 10.0.1.1
-               chk_join_nr 2 2 1
+               join_syn_rej=1 \
+                       chk_join_nr 2 2 1
        fi
 
        # single subflow, dev
@@ -3061,7 +3074,8 @@ syncookies_tests()
                pm_nl_add_endpoint $ns2 10.0.3.2 flags subflow
                pm_nl_add_endpoint $ns2 10.0.2.2 flags subflow
                run_tests $ns1 $ns2 10.0.1.1
-               chk_join_nr 2 1 1
+               join_syn_rej=1 \
+                       chk_join_nr 2 1 1
        fi
 
        # test signal address with cookies
@@ -3545,7 +3559,8 @@ userspace_tests()
                pm_nl_set_limits $ns2 1 1
                pm_nl_add_endpoint $ns2 10.0.3.2 flags subflow
                run_tests $ns1 $ns2 10.0.1.1
-               chk_join_nr 1 1 0
+               join_syn_rej=1 \
+                       chk_join_nr 1 1 0
        fi
 
        # userspace pm type does not send join
@@ -3568,7 +3583,8 @@ userspace_tests()
                pm_nl_add_endpoint $ns2 10.0.3.2 flags subflow
                sflags=backup speed=slow \
                        run_tests $ns1 $ns2 10.0.1.1
-               chk_join_nr 1 1 0
+               join_syn_rej=1 \
+                       chk_join_nr 1 1 0
                chk_prio_nr 0 0 0 0
        fi