[PATCH net 0/5] mptcp: avoid dup NL events and propagate error

[PATCH net 0/5] mptcp: avoid dup NL events and propagate error

[Matthieu Baerts (NGI0)]

Here are two fixes affecting the MPTCP Netlink events with their tests:

- Patches 1 & 2: a subflow closed NL event was visible multiple times in
  some specific conditions. A fix for v5.12.

- Patches 3 & 4: subflow closed NL events never contained the error
  code, even when expected. A fix for v5.11.

Plus an extra fix:

- Patch 5: fix a false positive with the "signal addresses race test"
  subtest when validating the MPTCP Join selftest on a v5.15.y stable
  kernel.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Matthieu Baerts (NGI0) (5):
      mptcp: avoid dup SUB_CLOSED events after disconnect
      selftests: mptcp: check no dup close events after error
      mptcp: only reset subflow errors when propagated
      selftests: mptcp: check subflow errors in close events
      selftests: mptcp: join: fix local endp not being tracked

 net/mptcp/protocol.c                            | 13 ++--
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 81 ++++++++++++++++++++++---
 2 files changed, 81 insertions(+), 13 deletions(-)
---
base-commit: e9acda52fd2ee0cdca332f996da7a95c5fd25294
change-id: 20260127-net-mptcp-dup-nl-events-64f970f274b0

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>

[PATCH net 1/5] mptcp: avoid dup SUB_CLOSED events after disconnect

[Matthieu Baerts (NGI0)]

In case of subflow disconnect(), which can also happen with the first
subflow in case of errors like timeout or reset, mptcp_subflow_ctx_reset
will reset most fields from the mptcp_subflow_context structure,
including close_event_done. Then, when another subflow is closed, yet
another SUB_CLOSED event for the disconnected initial subflow is sent.
Because of the previous reset, there are no source address and
destination port.

A solution is then to also check the subflow's local id: it shouldn't be
negative anyway.

Another solution would be not to reset subflow->close_event_done at
disconnect time, but when reused. But then, probably the whole reset
could be done when being reused. Let's not change this logic, similar
to TCP with tcp_disconnect().

Fixes: d82809b6c5f2 ("mptcp: avoid duplicated SUB_CLOSED events")
Cc: stable@vger.kernel.org
Reported-by: Marco Angaroni <marco.angaroni@italtel.com>
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/603
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index f505b780f713..e32ae594b4ef 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2598,8 +2598,8 @@ void mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	struct sk_buff *skb;
 
-	/* The first subflow can already be closed and still in the list */
-	if (subflow->close_event_done)
+	/* The first subflow can already be closed or disconnected */
+	if (subflow->close_event_done || READ_ONCE(subflow->local_id) < 0)
 		return;
 
 	subflow->close_event_done = true;

-- 
2.51.0

[PATCH net 2/5] selftests: mptcp: check no dup close events after error

[Matthieu Baerts (NGI0)]

This validates the previous commit: subflow closed events are re-sent
with less info when the initial subflow is disconnected after an error
and each time a subflow is closed after that.

In this new test, the userspace PM is involved because that's how it was
discovered, but it is not specific to it. The initial subflow is
terminated with a RESET, and that will cause the subflow disconnect.
Then, a new subflow is initiated, but also got rejected, which cause a
second subflow closed event, but not a third one.

While at it, in case of failure to get the expected amount of events,
the events are printed.

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: d82809b6c5f2 ("mptcp: avoid duplicated SUB_CLOSED events")
Cc: stable@vger.kernel.org
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 51 +++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index b2e6e548f796..1765714a1e2f 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -3872,11 +3872,32 @@ chk_evt_nr()
 	count=$(grep -cw "type:${evt}" "${evts}")
 	if [ "${count}" != "${exp}" ]; then
 		fail_test "got ${count} events, expected ${exp}"
+		cat "${evts}"
 	else
 		print_ok
 	fi
 }
 
+# $1: ns ; $2: event type ; $3: expected count
+wait_event()
+{
+	local ns="${1}"
+	local evt_name="${2}"
+	local exp="${3}"
+
+	local evt="${!evt_name}"
+	local evts="${evts_ns1}"
+	local count
+
+	[ "${ns}" == "ns2" ] && evts="${evts_ns2}"
+
+	for _ in $(seq 100); do
+		count=$(grep -cw "type:${evt}" "${evts}")
+		[ "${count}" -ge "${exp}" ] && break
+		sleep 0.1
+	done
+}
+
 userspace_tests()
 {
 	# userspace pm type prevents add_addr
@@ -4085,6 +4106,36 @@ userspace_tests()
 		kill_events_pids
 		mptcp_lib_kill_group_wait $tests_pid
 	fi
+
+	# userspace pm no duplicated spurious close events after an error
+	if reset_with_events "userspace pm no dup close events after error" &&
+	   continue_if mptcp_lib_has_file '/proc/sys/net/mptcp/pm_type'; then
+		set_userspace_pm $ns2
+		pm_nl_set_limits $ns1 0 2
+		{ timeout_test=120 test_linkfail=128 speed=slow \
+			run_tests $ns1 $ns2 10.0.1.1 & } 2>/dev/null
+		local tests_pid=$!
+		wait_event ns2 MPTCP_LIB_EVENT_ESTABLISHED 1
+		userspace_pm_add_sf $ns2 10.0.3.2 20
+		chk_mptcp_info subflows 1 subflows 1
+		chk_subflows_total 2 2
+
+		# force quick loss
+		ip netns exec $ns2 sysctl -q net.ipv4.tcp_syn_retries=1
+		if ip netns exec "${ns1}" ${iptables} -A INPUT -s "10.0.1.2" \
+		      -p tcp --tcp-option 30 -j REJECT --reject-with tcp-reset &&
+		   ip netns exec "${ns2}" ${iptables} -A INPUT -d "10.0.1.2" \
+		      -p tcp --tcp-option 30 -j REJECT --reject-with tcp-reset; then
+			wait_event ns2 MPTCP_LIB_EVENT_SUB_CLOSED 1
+			wait_event ns1 MPTCP_LIB_EVENT_SUB_CLOSED 1
+			chk_subflows_total 1 1
+			userspace_pm_add_sf $ns2 10.0.1.2 0
+			wait_event ns2 MPTCP_LIB_EVENT_SUB_CLOSED 2
+			chk_evt_nr ns2 MPTCP_LIB_EVENT_SUB_CLOSED 2
+		fi
+		kill_events_pids
+		mptcp_lib_kill_group_wait $tests_pid
+	fi
 }
 
 endpoint_tests()

-- 
2.51.0

[PATCH net 3/5] mptcp: only reset subflow errors when propagated

[Matthieu Baerts (NGI0)]

Some subflow socket errors need to be reported to the MPTCP socket: the
initial subflow connect (MP_CAPABLE), and the ones from the fallback
sockets. The others are not propagated.

The issue is that sock_error() was used to retrieve the error, which was
also resetting the sk_err field. Because of that, when notifying the
userspace about subflow close events later on from the MPTCP worker, the
ssk->sk_err field was always 0.

Now, the error (sk_err) is only reset when propagating it to the msk.

Fixes: 15cc10453398 ("mptcp: deliver ssk errors to msk")
Cc: stable@vger.kernel.org
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index e32ae594b4ef..8d3233667418 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -821,11 +821,8 @@ static bool __mptcp_ofo_queue(struct mptcp_sock *msk)
 
 static bool __mptcp_subflow_error_report(struct sock *sk, struct sock *ssk)
 {
-	int err = sock_error(ssk);
 	int ssk_state;
-
-	if (!err)
-		return false;
+	int err;
 
 	/* only propagate errors on fallen-back sockets or
 	 * on MPC connect
@@ -833,6 +830,10 @@ static bool __mptcp_subflow_error_report(struct sock *sk, struct sock *ssk)
 	if (sk->sk_state != TCP_SYN_SENT && !__mptcp_check_fallback(mptcp_sk(sk)))
 		return false;
 
+	err = sock_error(ssk);
+	if (!err)
+		return false;
+
 	/* We need to propagate only transition to CLOSE state.
 	 * Orphaned socket will see such state change via
 	 * subflow_sched_work_if_closed() and that path will properly

-- 
2.51.0

[PATCH net 4/5] selftests: mptcp: check subflow errors in close events

[Matthieu Baerts (NGI0)]

This validates the previous commit: subflow closed events should contain
an error field when a subflow got closed with an error, e.g. reset or
timeout.

For this test, the chk_evt_nr helper has been extended to check
attributes in the matched events.

In this test, the 2 subflow closed events should have an error.

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: 15cc10453398 ("mptcp: deliver ssk errors to msk")
Cc: stable@vger.kernel.org
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 1765714a1e2f..3fc29201362a 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -3847,21 +3847,28 @@ userspace_pm_chk_get_addr()
 	fi
 }
 
-# $1: ns ; $2: event type ; $3: count
+# $1: ns ; $2: event type ; $3: count ; [ $4: attr ; $5: attr count ]
 chk_evt_nr()
 {
 	local ns=${1}
 	local evt_name="${2}"
 	local exp="${3}"
+	local attr="${4}"
+	local attr_exp="${5}"
 
 	local evts="${evts_ns1}"
 	local evt="${!evt_name}"
+	local attr_name
 	local count
 
+	if [ -n "${attr}" ]; then
+		attr_name=", ${attr}: ${attr_exp}"
+	fi
+
 	evt_name="${evt_name:16}" # without MPTCP_LIB_EVENT_
 	[ "${ns}" == "ns2" ] && evts="${evts_ns2}"
 
-	print_check "event ${ns} ${evt_name} (${exp})"
+	print_check "event ${ns} ${evt_name} (${exp}${attr_name})"
 
 	if [[ "${evt_name}" = "LISTENER_"* ]] &&
 	   ! mptcp_lib_kallsyms_has "mptcp_event_pm_listener$"; then
@@ -3873,6 +3880,16 @@ chk_evt_nr()
 	if [ "${count}" != "${exp}" ]; then
 		fail_test "got ${count} events, expected ${exp}"
 		cat "${evts}"
+		return
+	elif [ -z "${attr}" ]; then
+		print_ok
+		return
+	fi
+
+	count=$(grep -w "type:${evt}" "${evts}" | grep -c ",${attr}:")
+	if [ "${count}" != "${attr_exp}" ]; then
+		fail_test "got ${count} event attributes, expected ${attr_exp}"
+		grep -w "type:${evt}" "${evts}"
 	else
 		print_ok
 	fi
@@ -4131,7 +4148,7 @@ userspace_tests()
 			chk_subflows_total 1 1
 			userspace_pm_add_sf $ns2 10.0.1.2 0
 			wait_event ns2 MPTCP_LIB_EVENT_SUB_CLOSED 2
-			chk_evt_nr ns2 MPTCP_LIB_EVENT_SUB_CLOSED 2
+			chk_evt_nr ns2 MPTCP_LIB_EVENT_SUB_CLOSED 2 error 2
 		fi
 		kill_events_pids
 		mptcp_lib_kill_group_wait $tests_pid

-- 
2.51.0

[PATCH net 5/5] selftests: mptcp: join: fix local endp not being tracked

[Matthieu Baerts (NGI0)]

When running this mptcp_join.sh selftest on older kernel versions not
supporting local endpoints tracking, this test fails because 3 MP_JOIN
ACKs have been received, while only 2 were expected.

It is not clear why only 2 MP_JOIN ACKs were expected on old kernel
versions, while 3 MP_JOIN SYN and SYN+ACK were expected. When testing on
the v5.15.197 kernel, 3 MP_JOIN ACKs are seen, which is also what is
expected in the selftests included in this kernel version, see commit
f4480eaad489 ("selftests: mptcp: add missing join check").

Switch the expected MP_JOIN ACKs to 3. While at it, move this
chk_join_nr helper out of the special condition for older kernel
versions as it is now the same as with more recent ones. Also, invert
the condition to be more logical: what's expected on newer kernel
versions having such helper first.

Fixes: d4c81bbb8600 ("selftests: mptcp: join: support local endpoint being tracked or not")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 3fc29201362a..e70d3420954f 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -2329,17 +2329,16 @@ signal_address_tests()
 		ip netns exec $ns1 sysctl -q net.mptcp.add_addr_timeout=1
 		speed=slow \
 			run_tests $ns1 $ns2 10.0.1.1
+		chk_join_nr 3 3 3
 
 		# It is not directly linked to the commit introducing this
 		# symbol but for the parent one which is linked anyway.
-		if ! mptcp_lib_kallsyms_has "mptcp_pm_subflow_check_next$"; then
-			chk_join_nr 3 3 2
-			chk_add_nr 4 4
-		else
-			chk_join_nr 3 3 3
+		if mptcp_lib_kallsyms_has "mptcp_pm_subflow_check_next$"; then
 			# the server will not signal the address terminating
 			# the MPC subflow
 			chk_add_nr 3 3
+		else
+			chk_add_nr 4 4
 		fi
 	fi
 }

-- 
2.51.0

Re: [PATCH net 0/5] mptcp: avoid dup NL events and propagate error

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 27 Jan 2026 20:27:22 +0100 you wrote:
> Here are two fixes affecting the MPTCP Netlink events with their tests:
> 
> - Patches 1 & 2: a subflow closed NL event was visible multiple times in
>   some specific conditions. A fix for v5.12.
> 
> - Patches 3 & 4: subflow closed NL events never contained the error
>   code, even when expected. A fix for v5.11.
> 
> [...]

Here is the summary with links:
  - [net,1/5] mptcp: avoid dup SUB_CLOSED events after disconnect
    https://git.kernel.org/netdev/net/c/280d654324e3
  - [net,2/5] selftests: mptcp: check no dup close events after error
    https://git.kernel.org/netdev/net/c/8467458dfa61
  - [net,3/5] mptcp: only reset subflow errors when propagated
    https://git.kernel.org/netdev/net/c/dccf46179ddd
  - [net,4/5] selftests: mptcp: check subflow errors in close events
    https://git.kernel.org/netdev/net/c/2ef9e3a3845d
  - [net,5/5] selftests: mptcp: join: fix local endp not being tracked
    https://git.kernel.org/netdev/net/c/c5d5ecf21fdd

You are awesome, thank you!
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