[PATCH 6.1.y] selftests: mptcp: join: check RM_ADDR not sent over same subflow

[Sasha Levin <sashal@kernel.org>]

From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>

[ Upstream commit 560edd99b5f58b2d4bbe3c8e51e1eed68d887b0e ]

This validates the previous commit: RM_ADDR were sent over the first
found active subflow which could be the same as the one being removed.
It is more likely to loose this notification.

For this check, RM_ADDR are explicitly dropped when trying to send them
over the initial subflow, when removing the endpoint attached to it. If
it is dropped, the test will complain because some RM_ADDR have not been
received.

Note that only the RM_ADDR are dropped, to allow the linked subflow to
be quickly and cleanly closed. To only drop those RM_ADDR, a cBPF byte
code is used. If the IPTables commands fail, that's OK, the tests will
continue to pass, but not validate this part. This can be ignored:
another subtest fully depends on such command, and will be marked as
skipped.

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: 8dd5efb1f91b ("mptcp: send ack for rm_addr")
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/20260303-net-mptcp-misc-fixes-7-0-rc2-v1-3-4b5462b6f016@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ adapted chk_subflow_nr calls to include extra empty first argument ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 .../testing/selftests/net/mptcp/mptcp_join.sh | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 5a40e09e8374c..80497053fe2f4 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -64,6 +64,24 @@ CBPF_MPTCP_SUBOPTION_ADD_ADDR="14,
 			       6 0 0 65535,
 			       6 0 0 0"
 
+# IPv4: TCP hdr of 48B, a first suboption of 12B (DACK8), the RM_ADDR suboption
+# generated using "nfbpf_compile '(ip[32] & 0xf0) == 0xc0 && ip[53] == 0x0c &&
+#				  (ip[66] & 0xf0) == 0x40'"
+CBPF_MPTCP_SUBOPTION_RM_ADDR="13,
+			      48 0 0 0,
+			      84 0 0 240,
+			      21 0 9 64,
+			      48 0 0 32,
+			      84 0 0 240,
+			      21 0 6 192,
+			      48 0 0 53,
+			      21 0 4 12,
+			      48 0 0 66,
+			      84 0 0 240,
+			      21 0 1 64,
+			      6 0 0 65535,
+			      6 0 0 0"
+
 init_partial()
 {
 	capout=$(mktemp)
@@ -3455,6 +3473,14 @@ endpoint_tests()
 		wait_mpj $ns2
 		chk_subflow_nr "" "after no reject" 3
 
+		# To make sure RM_ADDR are sent over a different subflow, but
+		# allow the rest to quickly and cleanly close the subflow
+		local ipt=1
+		ip netns exec "${ns2}" ${iptables} -I OUTPUT -s "10.0.1.2" \
+			-p tcp -m tcp --tcp-option 30 \
+			-m bpf --bytecode \
+			"$CBPF_MPTCP_SUBOPTION_RM_ADDR" \
+			-j DROP || ipt=0
 		local i
 		for i in $(seq 3); do
 			pm_nl_del_endpoint $ns2 1 10.0.1.2
@@ -3465,6 +3491,7 @@ endpoint_tests()
 			wait_mpj $ns2
 			chk_subflow_nr "" "after re-add id 0 ($i)" 3
 		done
+		[ ${ipt} = 1 ] && ip netns exec "${ns2}" ${iptables} -D OUTPUT 1
 
 		kill_wait "${tests_pid}"
 		kill_events_pids
@@ -3514,9 +3541,18 @@ endpoint_tests()
 		wait_mpj $ns2
 		chk_subflow_nr "" "after re-add" 3
 
+		# To make sure RM_ADDR are sent over a different subflow, but
+		# allow the rest to quickly and cleanly close the subflow
+		local ipt=1
+		ip netns exec "${ns1}" ${iptables} -I OUTPUT -s "10.0.1.1" \
+			-p tcp -m tcp --tcp-option 30 \
+			-m bpf --bytecode \
+			"$CBPF_MPTCP_SUBOPTION_RM_ADDR" \
+			-j DROP || ipt=0
 		pm_nl_del_endpoint $ns1 42 10.0.1.1
 		sleep 0.5
 		chk_subflow_nr "" "after delete ID 0" 2
+		[ ${ipt} = 1 ] && ip netns exec "${ns1}" ${iptables} -D OUTPUT 1
 
 		pm_nl_add_endpoint $ns1 10.0.1.1 id 99 flags signal
 		wait_mpj $ns2
-- 
2.51.0