[PATCH net-next 00/11] mptcp: misc. features for v7.3

[PATCH net-next 00/11] mptcp: misc. features for v7.3

[Matthieu Baerts (NGI0)]

This series contains a few independent new features, and small fixes for
net-next:

- Patch 1: Add WARN_ON_ONCE guards around extra_subflows to catch issues
  with this counter, similar to what is done with other PM counters.

- Patches 2-3: Follow-up patches to remove data_ack field from struct
  mptcp_ext -- now unused after recent fixes -- and makes a userspace PM
  helper static.

- Patch 4: Honour tcp_rto_{min_us,max_ms} sysctls for MPTCP-level
  retransmit timers like with DATA_FIN's and fallback timeout.

- Patches 5-6: Add per-event MIB counters for MPTCP_RST_EMPTCP resets to
  help to spot such situations in production.

- Patches 7-9: Small pcap-related improvements in the selftests.

- Patch 10: Fix compiler warning in the selftests.

- Patch 11: Avoid a buffer overflow when misusing the mptcp_diag tool
  from the selftests.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Geliang Tang (2):
      mptcp: remove unused data_ack from struct mptcp_ext
      selftests: mptcp: fix const qualifier warnings in strchr usage

Jiangshan Yi (1):
      selftests: mptcp: diag: fix stack buffer overflow in get_subflow_info()

Kalpan Jani (1):
      mptcp: honour configured min/max RTO in retransmit paths

Matthieu Baerts (NGI0) (4):
      mptcp: pm: userspace: make remove_addr_entry static
      selftests: mptcp: connect: test name in pcap file
      selftests: mptcp: simult_flow: test name in pcap file
      selftests: mptcp: pcap: drop most of the payload

Shardul Bankar (2):
      mptcp: add per-event MIB counters for MPTCP_RST_EMPTCP resets
      selftests: mptcp: check per-event MPTCP_RST_EMPTCP counters

Tao Cui (1):
      mptcp: pm: add WARN_ON_ONCE guards on extra_subflows underflow

 include/net/mptcp.h                                |  4 -
 include/trace/events/mptcp.h                       |  6 +-
 net/mptcp/mib.c                                    |  7 ++
 net/mptcp/mib.h                                    |  7 ++
 net/mptcp/pm.c                                     |  3 +-
 net/mptcp/pm_userspace.c                           |  7 +-
 net/mptcp/protocol.c                               | 23 +++++-
 net/mptcp/protocol.h                               |  5 +-
 net/mptcp/subflow.c                                | 10 +++
 tools/testing/selftests/net/mptcp/mptcp_connect.c  |  4 +-
 tools/testing/selftests/net/mptcp/mptcp_connect.sh |  8 +-
 tools/testing/selftests/net/mptcp/mptcp_diag.c     |  3 +-
 tools/testing/selftests/net/mptcp/mptcp_join.sh    | 95 +++++++++++++++++++++-
 tools/testing/selftests/net/mptcp/simult_flows.sh  | 11 ++-
 14 files changed, 163 insertions(+), 30 deletions(-)
---
base-commit: ac155a26750a595703e7dadff84735456d75a479
change-id: 20260810-net-next-mptcp-misc-feat-7-3-b066d1e2d57a

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

[PATCH net-next 01/11] mptcp: pm: add WARN_ON_ONCE guards on extra_subflows underflow

[Matthieu Baerts (NGI0)]

From: Tao Cui <cuitao@kylinos.cn>

extra_subflows is a u8 counter that can underflow if a decrement races
with or precedes an increment. While the recently fixed userspace PM
subflow creation path eliminated the primary cause, add defensive
WARN_ON_ONCE guards at both decrement sites to catch any remaining edge
cases rather than silently wrapping to 255.

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm.c       | 3 ++-
 net/mptcp/protocol.h | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index d1f73c3e39fa..8b68868255c5 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -670,7 +670,8 @@ void mptcp_pm_subflow_check_next(struct mptcp_sock *msk,
 	if (mptcp_pm_is_userspace(msk)) {
 		if (update_subflows) {
 			spin_lock_bh(&pm->lock);
-			pm->extra_subflows--;
+			if (!WARN_ON_ONCE(pm->extra_subflows == 0))
+				pm->extra_subflows--;
 			spin_unlock_bh(&pm->lock);
 		}
 		return;
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index b3af3462bdd1..20627e12c113 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -1254,7 +1254,8 @@ u8 mptcp_pm_get_limit_extra_subflows(const struct mptcp_sock *msk);
 /* called under PM lock */
 static inline void __mptcp_pm_close_subflow(struct mptcp_sock *msk)
 {
-	if (--msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk))
+	if (!WARN_ON_ONCE(msk->pm.extra_subflows == 0) &&
+	    --msk->pm.extra_subflows < mptcp_pm_get_limit_extra_subflows(msk))
 		WRITE_ONCE(msk->pm.accept_subflow, true);
 }
 

-- 
2.53.0

[PATCH net-next 02/11] mptcp: remove unused data_ack from struct mptcp_ext

[Matthieu Baerts (NGI0)]

From: Geliang Tang <tanggeliang@kylinos.cn>

The data_ack and data_ack32 fields in struct mptcp_ext are no longer used
anywhere. Remove them from the structure and update mptcp_dump_mpext()
trace helper accordingly. Drop the data_ack field from the trace entry
and the corresponding output in TP_printk().

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
To: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: linux-trace-kernel@vger.kernel.org
---
 include/net/mptcp.h          | 4 ----
 include/trace/events/mptcp.h | 6 ++----
 2 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 71b9fc5a5796..485d55b66ea6 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -19,10 +19,6 @@ struct seq_file;
 
 /* MPTCP sk_buff extension data */
 struct mptcp_ext {
-	union {
-		u64	data_ack;
-		u32	data_ack32;
-	};
 	u64		data_seq;
 	u32		subflow_seq;
 	u16		data_len;
diff --git a/include/trace/events/mptcp.h b/include/trace/events/mptcp.h
index 04521acba483..22882bd03459 100644
--- a/include/trace/events/mptcp.h
+++ b/include/trace/events/mptcp.h
@@ -75,7 +75,6 @@ DECLARE_EVENT_CLASS(mptcp_dump_mpext,
 	TP_ARGS(mpext),
 
 	TP_STRUCT__entry(
-		__field(u64, data_ack)
 		__field(u64, data_seq)
 		__field(u32, subflow_seq)
 		__field(u16, data_len)
@@ -94,7 +93,6 @@ DECLARE_EVENT_CLASS(mptcp_dump_mpext,
 	),
 
 	TP_fast_assign(
-		__entry->data_ack = mpext->ack64 ? mpext->data_ack : mpext->data_ack32;
 		__entry->data_seq = mpext->data_seq;
 		__entry->subflow_seq = mpext->subflow_seq;
 		__entry->data_len = mpext->data_len;
@@ -112,8 +110,8 @@ DECLARE_EVENT_CLASS(mptcp_dump_mpext,
 		__entry->infinite_map = mpext->infinite_map;
 	),
 
-	TP_printk("data_ack=%llu data_seq=%llu subflow_seq=%u data_len=%u csum=%x use_map=%u dsn64=%u data_fin=%u use_ack=%u ack64=%u mpc_map=%u frozen=%u reset_transient=%u reset_reason=%u csum_reqd=%u infinite_map=%u",
-		  __entry->data_ack, __entry->data_seq,
+	TP_printk("data_seq=%llu subflow_seq=%u data_len=%u csum=%x use_map=%u dsn64=%u data_fin=%u use_ack=%u ack64=%u mpc_map=%u frozen=%u reset_transient=%u reset_reason=%u csum_reqd=%u infinite_map=%u",
+		  __entry->data_seq,
 		  __entry->subflow_seq, __entry->data_len,
 		  __entry->csum, __entry->use_map,
 		  __entry->dsn64, __entry->data_fin,

-- 
2.53.0

Re: [PATCH net-next 02/11] mptcp: remove unused data_ack from struct mptcp_ext

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [Medium] When transmitting an MPTCP DATA_FIN DSS option without a data payload (e.g., on a pure ACK), the stack-allocated `opts.mptcp.ext_copy.csum` is left uninitialized. If MPTCP checksums are enabled, this uninitialized memory is written to the TCP header, leaking 2 bytes of kernel stack memory over the network.
--

--- Patch [2]: [PATCH net-next 02/11] mptcp: remove unused data_ack from struct mptcp_ext ---
commit 5596db7582bd748ad6320aef70bbdd448c28de36
Author: Geliang Tang <geliang@kernel.org>

mptcp: remove unused data_ack from struct mptcp_ext
    
The data_ack and data_ack32 fields in struct mptcp_ext are no longer used
anywhere. Remove them from the structure and update mptcp_dump_mpext()
trace helper accordingly. Drop the data_ack field from the trace entry
and the corresponding output in TP_printk().

> diff --git a/include/net/mptcp.h b/include/net/mptcp.h
> index 71b9fc5a57963..485d55b66ea67 100644
> --- a/include/net/mptcp.h
> +++ b/include/net/mptcp.h
> @@ -19,10 +19,6 @@ struct seq_file;
>  
>  /* MPTCP sk_buff extension data */
>  struct mptcp_ext {
> -	union {
> -		u64	data_ack;
> -		u32	data_ack32;
> -	};
>  	u64		data_seq;
>  	u32		subflow_seq;
>  	u16		data_len;

[Severity: Medium]
This is a pre-existing issue, but does this structure leave the csum field
uninitialized on the stack under certain conditions?

When transmitting an MPTCP DATA_FIN DSS option without a data payload (e.g.,
on a pure ACK), the stack-allocated opts structure in 
net/ipv4/tcp_output.c:__tcp_transmit_skb() is not fully zeroed:

    struct tcp_out_options opts;

If mpext is NULL, net/mptcp/options.c:mptcp_established_options_dss() only
clears the bitfield flags:

    /* Zero `use_ack` and `use_map` flags with one shot. */
    memset(&opts->ext_copy.flags, 0, sizeof(opts->ext_copy.flags));

This leaves opts->ext_copy.csum uninitialized. The code then passes this to
net/mptcp/options.c:mptcp_write_data_fin(), which populates fields like
data_fin and data_seq but fails to initialize the csum field.

Finally, in net/mptcp/options.c:mptcp_write_options(), it reads the
uninitialized csum when writing the TCP header:

    put_len_csum(mpext->data_len,
                 (mpext->data_len ? mptcp_make_csum(mpext) : 0),
                 ptr);

Could this uninitialized struct memory result in leaking 2 bytes of kernel
stack memory over the network when MPTCP checksums are enabled?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260812-net-next-mptcp-misc-feat-7-3-v1-0-1905a818f6cb@kernel.org?part=2

[PATCH net-next 03/11] mptcp: pm: userspace: make remove_addr_entry static

[Matthieu Baerts (NGI0)]

Only used in pm_userspace.c.

While at it, use the mptcp_userspace_pm_ prefix, like most functions in
this file: that makes it clear it is specific to this userspace PM.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/pm_userspace.c | 7 ++++---
 net/mptcp/protocol.h     | 2 --
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index 2203cc2d2748..b94fbb483bf9 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -281,8 +281,9 @@ static int mptcp_userspace_pm_remove_id_zero_address(struct mptcp_sock *msk)
 	return err;
 }
 
-void mptcp_pm_remove_addr_entry(struct mptcp_sock *msk,
-				struct mptcp_pm_addr_entry *entry)
+static void
+mptcp_userspace_pm_remove_addr_entry(struct mptcp_sock *msk,
+				     struct mptcp_pm_addr_entry *entry)
 {
 	struct mptcp_rm_list alist = { .nr = 0 };
 	int anno_nr = 0;
@@ -340,7 +341,7 @@ int mptcp_pm_nl_remove_doit(struct sk_buff *skb, struct genl_info *info)
 	list_del_rcu(&match->list);
 	spin_unlock_bh(&msk->pm.lock);
 
-	mptcp_pm_remove_addr_entry(msk, match);
+	mptcp_userspace_pm_remove_addr_entry(msk, match);
 
 	release_sock(sk);
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 20627e12c113..06a107d4e839 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -1149,8 +1149,6 @@ int mptcp_pm_announce_addr(struct mptcp_sock *msk,
 			   const struct mptcp_addr_info *addr,
 			   bool echo);
 int mptcp_pm_remove_addr(struct mptcp_sock *msk, const struct mptcp_rm_list *rm_list);
-void mptcp_pm_remove_addr_entry(struct mptcp_sock *msk,
-				struct mptcp_pm_addr_entry *entry);
 
 /* the default path manager, used in mptcp_pm_unregister */
 extern struct mptcp_pm_ops mptcp_pm_kernel;

-- 
2.53.0

[PATCH net-next 04/11] mptcp: honour configured min/max RTO in retransmit paths

[Matthieu Baerts (NGI0)]

From: Kalpan Jani <kalpan.jani@mpiricsoftware.com>

The MPTCP-level retransmit timers (DATA_FIN retransmissions and the
fallback timeout) used the hard-coded TCP_RTO_MIN / TCP_RTO_MAX
constants, ignoring the tcp_rto_min_us and tcp_rto_max_ms sysctls.

Make them follow the sysctls instead: seed icsk_rto_min / icsk_rto_max
on the MPTCP socket from the per-netns sysctls in __mptcp_init_sock()
-- the msk does not go through tcp_init_sock(), so these fields would
otherwise stay zero -- and read them directly where the constants were
used:

- mptcp_set_datafin_timeout(): both the backoff cap computation and
  the resulting timer_ival. The two sysctls are validated
  independently, so rto_min > rto_max is a valid configuration; keep
  a max_t() guard so ilog2() is never called with 0.

- __mptcp_set_timeout(): the fallback when no subflow timeout is
  available.

The icsk fields are read directly instead of using the
tcp_rto_min()/tcp_rto_max() helpers: the MPTCP socket does not perform
routing lookups in these paths, so the rto_min route metric checked by
tcp_rto_min() can never apply here. The TCP_RTO_MIN_US /
TCP_RTO_MAX_MS socket options are not supported by MPTCP setsockopt()
either; this can be revisited if they get supported on MPTCP sockets.

The remaining uses of TCP_RTO_MAX in net/mptcp/ctrl.c (default
add_addr_timeout) and net/mptcp/subflow.c (MP_FAIL timeout) are
intentionally left unchanged: they use the constant as a default
duration, not as an RTO bound on a retransmit timer.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/618
Signed-off-by: Kalpan Jani <kalpan.jani@mpiricsoftware.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index ec874d2ead6a..8f074d757743 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -581,17 +581,23 @@ static bool mptcp_pending_data_fin(struct sock *sk, u64 *seq)
 static void mptcp_set_datafin_timeout(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
+	u32 rto_min = READ_ONCE(icsk->icsk_rto_min);
+	u32 rto_max = READ_ONCE(icsk->icsk_rto_max);
 	u32 retransmits;
 
+	/* The sysctls are validated independently: rto_min > rto_max is
+	 * possible, guard against ilog2(0).
+	 */
 	retransmits = min_t(u32, icsk->icsk_retransmits,
-			    ilog2(TCP_RTO_MAX / TCP_RTO_MIN));
+			    ilog2(max_t(u32, rto_max / rto_min, 1)));
 
-	mptcp_sk(sk)->timer_ival = TCP_RTO_MIN << retransmits;
+	mptcp_sk(sk)->timer_ival = rto_min << retransmits;
 }
 
 static void __mptcp_set_timeout(struct sock *sk, long tout)
 {
-	mptcp_sk(sk)->timer_ival = tout > 0 ? tout : TCP_RTO_MIN;
+	mptcp_sk(sk)->timer_ival = tout > 0 ? tout :
+				   READ_ONCE(inet_csk(sk)->icsk_rto_min);
 }
 
 static long mptcp_timeout_from_subflow(const struct mptcp_subflow_context *subflow)
@@ -3161,7 +3167,9 @@ static void mptcp_worker(struct work_struct *work)
 
 static void __mptcp_init_sock(struct sock *sk)
 {
+	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct net *net = sock_net(sk);
 
 	INIT_LIST_HEAD(&msk->conn_list);
 	INIT_LIST_HEAD(&msk->join_list);
@@ -3170,7 +3178,13 @@ static void __mptcp_init_sock(struct sock *sk)
 	INIT_WORK(&msk->work, mptcp_worker);
 	msk->out_of_order_queue = RB_ROOT;
 	msk->first_pending = NULL;
-	msk->timer_ival = TCP_RTO_MIN;
+
+	/* msk does not go through tcp_init_sock(); seed RTO bounds. */
+	icsk->icsk_rto_min =
+		usecs_to_jiffies(READ_ONCE(net->ipv4.sysctl_tcp_rto_min_us));
+	icsk->icsk_rto_max =
+		msecs_to_jiffies(READ_ONCE(net->ipv4.sysctl_tcp_rto_max_ms));
+	msk->timer_ival = icsk->icsk_rto_min;
 	msk->scaling_ratio = TCP_DEFAULT_SCALING_RATIO;
 	msk->backlog_len = 0;
 	mptcp_init_rtt_est(msk);

-- 
2.53.0

[PATCH net-next 05/11] mptcp: add per-event MIB counters for MPTCP_RST_EMPTCP resets

[Matthieu Baerts (NGI0)]

From: Shardul Bankar <shardul.b@mpiricsoftware.com>

MPTCP_RST_EMPTCP (reset reason 1) is used as a catch-all for several
distinct error conditions across subflow setup, authentication, and
data-path validation.  The existing MPRstTx/MPRstRx counters only
track aggregate reset volume, making it difficult to diagnose which
code path is triggering subflow resets in production.

Add per-event MIB counters covering each MPTCP_RST_EMPTCP use site
that is not already covered by an existing counter, named after the
underlying event or condition rather than the reset action:

  MD5SigReset           MD5SIG enabled on listener (incompatible)
  MPJoinSynAckNoMPJoin  SYN/ACK missing MP_JOIN option
  MPJoinAckNoMPJoin     server-side ACK missing MP_JOIN option
                          (fallback path, MPJoin required)
  MPJoinAckNoCtx        server-side ACK with no subflow context
  MPJoinNoIdFound       MP_JOIN with a valid token but no PM local ID
  DssReset              data mapping invalid (also fires on
                          MAPPING_NODSS / EMIDDLEBOX path)
  MPJoinNotEstablished  JOIN attempted on a not-fully-established msk

MPJoinNoIdFound covers the second half of the no-msk MP_JOIN reset:
the existing MPJoinNoTokenFound (MPTCP_MIB_JOINNOTOKEN) only counts the
missing-token case in subflow_token_join_request(), while a JOIN that
carries a valid token but for which the path manager returns no local
id reaches the same MPTCP_RST_EMPTCP in subflow_check_req() uncounted.

The aggregate MPRstTx/MPRstRx counters are unchanged.

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/511
Signed-off-by: Shardul Bankar <shardul.b@mpiricsoftware.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/mib.c      |  7 +++++++
 net/mptcp/mib.h      |  7 +++++++
 net/mptcp/protocol.c |  1 +
 net/mptcp/subflow.c  | 10 ++++++++++
 4 files changed, 25 insertions(+)

diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c
index 2569385bab7c..608cb568897c 100644
--- a/net/mptcp/mib.c
+++ b/net/mptcp/mib.c
@@ -21,14 +21,19 @@ static const struct snmp_mib mptcp_snmp_list[] = {
 	SNMP_MIB_ITEM("MPFallbackTokenInit", MPTCP_MIB_TOKENFALLBACKINIT),
 	SNMP_MIB_ITEM("MPTCPRetrans", MPTCP_MIB_RETRANSSEGS),
 	SNMP_MIB_ITEM("MPJoinNoTokenFound", MPTCP_MIB_JOINNOTOKEN),
+	SNMP_MIB_ITEM("MPJoinNoIdFound", MPTCP_MIB_MPJOINNOIDFOUND),
 	SNMP_MIB_ITEM("MPJoinSynRx", MPTCP_MIB_JOINSYNRX),
 	SNMP_MIB_ITEM("MPJoinSynBackupRx", MPTCP_MIB_JOINSYNBACKUPRX),
 	SNMP_MIB_ITEM("MPJoinSynAckRx", MPTCP_MIB_JOINSYNACKRX),
 	SNMP_MIB_ITEM("MPJoinSynAckBackupRx", MPTCP_MIB_JOINSYNACKBACKUPRX),
 	SNMP_MIB_ITEM("MPJoinSynAckHMacFailure", MPTCP_MIB_JOINSYNACKMAC),
+	SNMP_MIB_ITEM("MPJoinSynAckNoMPJoin", MPTCP_MIB_MPJOINSYNACKNOMPJOIN),
 	SNMP_MIB_ITEM("MPJoinAckRx", MPTCP_MIB_JOINACKRX),
 	SNMP_MIB_ITEM("MPJoinAckHMacFailure", MPTCP_MIB_JOINACKMAC),
+	SNMP_MIB_ITEM("MPJoinAckNoMPJoin", MPTCP_MIB_MPJOINACKNOMPJOIN),
+	SNMP_MIB_ITEM("MPJoinAckNoCtx", MPTCP_MIB_MPJOINACKNOCTX),
 	SNMP_MIB_ITEM("MPJoinRejected", MPTCP_MIB_JOINREJECTED),
+	SNMP_MIB_ITEM("MPJoinNotEstablished", MPTCP_MIB_MPJOINNOTESTABLISHED),
 	SNMP_MIB_ITEM("MPJoinSynTx", MPTCP_MIB_JOINSYNTX),
 	SNMP_MIB_ITEM("MPJoinSynTxCreatSkErr", MPTCP_MIB_JOINSYNTXCREATSKERR),
 	SNMP_MIB_ITEM("MPJoinSynTxBindErr", MPTCP_MIB_JOINSYNTXBINDERR),
@@ -81,7 +86,9 @@ static const struct snmp_mib mptcp_snmp_list[] = {
 	SNMP_MIB_ITEM("Blackhole", MPTCP_MIB_BLACKHOLE),
 	SNMP_MIB_ITEM("MPCapableDataFallback", MPTCP_MIB_MPCAPABLEDATAFALLBACK),
 	SNMP_MIB_ITEM("MD5SigFallback", MPTCP_MIB_MD5SIGFALLBACK),
+	SNMP_MIB_ITEM("MD5SigReset", MPTCP_MIB_MD5SIGRESET),
 	SNMP_MIB_ITEM("DssFallback", MPTCP_MIB_DSSFALLBACK),
+	SNMP_MIB_ITEM("DssReset", MPTCP_MIB_DSSRESET),
 	SNMP_MIB_ITEM("SimultConnectFallback", MPTCP_MIB_SIMULTCONNFALLBACK),
 	SNMP_MIB_ITEM("FallbackFailed", MPTCP_MIB_FALLBACKFAILED),
 	SNMP_MIB_ITEM("WinProbe", MPTCP_MIB_WINPROBE),
diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
index 3a3425e258a7..1ebdb55e9534 100644
--- a/net/mptcp/mib.h
+++ b/net/mptcp/mib.h
@@ -16,14 +16,19 @@ enum linux_mptcp_mib_field {
 	MPTCP_MIB_TOKENFALLBACKINIT,	/* Could not init/allocate token */
 	MPTCP_MIB_RETRANSSEGS,		/* Segments retransmitted at the MPTCP-level */
 	MPTCP_MIB_JOINNOTOKEN,		/* Received MP_JOIN but the token was not found */
+	MPTCP_MIB_MPJOINNOIDFOUND,	/* Received MP_JOIN but no local ID was found */
 	MPTCP_MIB_JOINSYNRX,		/* Received a SYN + MP_JOIN */
 	MPTCP_MIB_JOINSYNBACKUPRX,	/* Received a SYN + MP_JOIN + backup flag */
 	MPTCP_MIB_JOINSYNACKRX,		/* Received a SYN/ACK + MP_JOIN */
 	MPTCP_MIB_JOINSYNACKBACKUPRX,	/* Received a SYN/ACK + MP_JOIN + backup flag */
 	MPTCP_MIB_JOINSYNACKMAC,	/* HMAC was wrong on SYN/ACK + MP_JOIN */
+	MPTCP_MIB_MPJOINSYNACKNOMPJOIN,	/* MP_RST: missing MP_JOIN in SYN/ACK */
 	MPTCP_MIB_JOINACKRX,		/* Received an ACK + MP_JOIN */
 	MPTCP_MIB_JOINACKMAC,		/* HMAC was wrong on ACK + MP_JOIN */
+	MPTCP_MIB_MPJOINACKNOMPJOIN,	/* MP_RST: missing MP_JOIN in ACK */
+	MPTCP_MIB_MPJOINACKNOCTX,	/* MP_RST: no subflow context on ACK */
 	MPTCP_MIB_JOINREJECTED,		/* The PM rejected the JOIN request */
+	MPTCP_MIB_MPJOINNOTESTABLISHED,	/* MP_RST: JOIN on not-fully-established msk */
 	MPTCP_MIB_JOINSYNTX,		/* Sending a SYN + MP_JOIN */
 	MPTCP_MIB_JOINSYNTXCREATSKERR,	/* Not able to create a socket when sending a SYN + MP_JOIN */
 	MPTCP_MIB_JOINSYNTXBINDERR,	/* Not able to bind() the address when sending a SYN + MP_JOIN */
@@ -84,7 +89,9 @@ enum linux_mptcp_mib_field {
 					 * established packet
 					 */
 	MPTCP_MIB_MD5SIGFALLBACK,	/* Conflicting TCP option enabled */
+	MPTCP_MIB_MD5SIGRESET,		/* MP_RST: MD5SIG enabled on listener */
 	MPTCP_MIB_DSSFALLBACK,		/* Bad or missing DSS */
+	MPTCP_MIB_DSSRESET,		/* MP_RST: bad data mapping */
 	MPTCP_MIB_SIMULTCONNFALLBACK,	/* Simultaneous connect */
 	MPTCP_MIB_FALLBACKFAILED,	/* Can't fallback due to msk status */
 	MPTCP_MIB_WINPROBE,		/* MPTCP-level zero window probe */
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 8f074d757743..b474d03620a7 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -4002,6 +4002,7 @@ bool mptcp_finish_join(struct sock *ssk)
 
 	/* mptcp socket already closing? */
 	if (!mptcp_is_fully_established(parent)) {
+		MPTCP_INC_STATS(sock_net(parent), MPTCP_MIB_MPJOINNOTESTABLISHED);
 		subflow->reset_reason = MPTCP_RST_EMPTCP;
 		return false;
 	}
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index e1f20ff8fdb4..af81ad5e699d 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -96,6 +96,7 @@ static struct mptcp_sock *subflow_token_join_request(struct request_sock *req)
 
 	local_id = mptcp_pm_get_local_id(msk, (struct sock_common *)req);
 	if (local_id < 0) {
+		SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPJOINNOIDFOUND);
 		sock_put((struct sock *)msk);
 		return NULL;
 	}
@@ -160,6 +161,7 @@ static int subflow_check_req(struct request_sock *req,
 	 * TCP option space.
 	 */
 	if (rcu_access_pointer(tcp_sk(sk_listener)->md5sig_info)) {
+		MPTCP_INC_STATS(sock_net(sk_listener), MPTCP_MIB_MD5SIGRESET);
 		subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
 		return -EINVAL;
 	}
@@ -563,6 +565,7 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 		u8 hmac[SHA256_DIGEST_SIZE];
 
 		if (!(mp_opt.suboptions & OPTION_MPTCP_MPJ_SYNACK)) {
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPJOINSYNACKNOMPJOIN);
 			subflow->reset_reason = MPTCP_RST_EMPTCP;
 			goto do_reset;
 		}
@@ -865,6 +868,12 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
 		 */
 		if (!ctx || fallback) {
 			if (fallback_is_fatal) {
+				if (!ctx)
+					MPTCP_INC_STATS(sock_net(sk),
+							MPTCP_MIB_MPJOINACKNOCTX);
+				else
+					MPTCP_INC_STATS(sock_net(sk),
+							MPTCP_MIB_MPJOINACKNOMPJOIN);
 				subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
 				goto dispose_child;
 			}
@@ -1416,6 +1425,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
 			 * subflow_error_report() will introduce the appropriate barriers
 			 */
 			subflow->reset_transient = 0;
+			MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSRESET);
 			subflow->reset_reason = status == MAPPING_NODSS ?
 						MPTCP_RST_EMIDDLEBOX :
 						MPTCP_RST_EMPTCP;

-- 
2.53.0

[PATCH net-next 06/11] selftests: mptcp: check per-event MPTCP_RST_EMPTCP counters

[Matthieu Baerts (NGI0)]

From: Shardul Bankar <shardul.b@mpiricsoftware.com>

Add named env-var expectations for each per-event MPTCP_RST_EMPTCP
counter, matching the pattern used by the existing JOIN/RST checks.
Each defaults to 0 and is checked silently on success; a mismatch prints
a check line and fails the test.  Counters absent from the running
kernel are skipped silently so older kernels do not false-fail.

The JOIN-related counters (MPJoinSynAckNoMPJoin, MPJoinAckNoMPJoin,
MPJoinAckNoCtx, MPJoinNotEstablished, MPJoinNoIdFound) are checked in
chk_join_nr() on fixed namespaces; the two remaining reset counters
(MD5SigReset, DssReset) stay in chk_rst_nr().

Add a test at the end of signal_address_tests that triggers
MPJoinSynAckNoMPJoin: ns1 signals an address that is already bound on
the client (ns2), where a TCP-only mptcp_connect listener is started.
The client's MP_JOIN routes locally to the TCP listener, which responds
with a plain SYN/ACK without the MP_JOIN option, and the new counter
increments on the client side.

Other per-event counters (MD5SigReset, MPJoinAckNoMPJoin, MPJoinAckNoCtx,
DssReset, MPJoinNotEstablished, MPJoinNoIdFound) are not currently
reachable from mptcp_join.sh; the env-var hooks are in place for future
tests to set expectations explicitly.

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Shardul Bankar <shardul.b@mpiricsoftware.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
To: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 93 +++++++++++++++++++++++++
 1 file changed, 93 insertions(+)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 7dc91fac4917..9b9fb3de9da3 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -75,6 +75,14 @@ unset join_syn_tx
 unset join_create_err
 unset join_bind_err
 unset join_connect_err
+unset join_synack_no_mpjoin
+unset join_ack_no_mpjoin
+unset join_ack_no_ctx
+unset join_not_established
+unset join_no_id_found
+
+unset rst_md5sig
+unset rst_dss
 
 unset fb_ns1
 unset fb_ns2
@@ -1353,6 +1361,8 @@ chk_rst_nr()
 	local rst_tx=$1
 	local rst_rx=$2
 	local ns_invert=${3:-""}
+	local md5sig=${rst_md5sig:-0}
+	local dss=${rst_dss:-0}
 	local count
 	local ns_tx=$ns1
 	local ns_rx=$ns2
@@ -1389,6 +1399,21 @@ chk_rst_nr()
 	else
 		print_ok
 	fi
+
+	# MPTCP_RST_EMPTCP reset-event counters; default 0, gated on
+	# availability.  Fixed namespaces: MD5SigReset fires on the listener
+	# (server), DssReset on the data receiver (client).
+	count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMD5SigReset")
+	if [ -n "$count" ] && [ "$count" != "$md5sig" ]; then
+		print_check "MD5SigReset"
+		fail_test "got $count MD5SigReset expected $md5sig"
+	fi
+
+	count=$(mptcp_lib_get_counter ${ns2} "MPTcpExtDssReset")
+	if [ -n "$count" ] && [ "$count" != "$dss" ]; then
+		print_check "DssReset"
+		fail_test "got $count DssReset expected $dss"
+	fi
 }
 
 chk_infi_nr()
@@ -1587,6 +1612,11 @@ chk_join_nr()
 	local rst_nr=${join_rst_nr:-0}
 	local infi_nr=${join_infi_nr:-0}
 	local corrupted_pkts=${join_corrupted_pkts:-0}
+	local synack_no_mpjoin=${join_synack_no_mpjoin:-0}
+	local ack_no_mpjoin=${join_ack_no_mpjoin:-0}
+	local ack_no_ctx=${join_ack_no_ctx:-0}
+	local not_established=${join_not_established:-0}
+	local no_id_found=${join_no_id_found:-0}
 	local rc=${KSFT_PASS}
 	local count
 	local with_cookie
@@ -1655,6 +1685,44 @@ chk_join_nr()
 		fail_test "got $count JOIN[s] syn rejected expected $syn_rej"
 	fi
 
+	# Per-event MPTCP_RST_EMPTCP JOIN counters; default 0, gated on
+	# availability.  Fixed namespaces: the *SynAck* one fires on the
+	# client receiving the SYN/ACK, the others on the server.
+	count=$(mptcp_lib_get_counter ${ns2} "MPTcpExtMPJoinSynAckNoMPJoin")
+	if [ -n "$count" ] && [ "$count" != "$synack_no_mpjoin" ]; then
+		rc=${KSFT_FAIL}
+		print_check "synack no mpjoin"
+		fail_test "got $count JOIN[s] synack no mpjoin expected $synack_no_mpjoin"
+	fi
+
+	count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinAckNoMPJoin")
+	if [ -n "$count" ] && [ "$count" != "$ack_no_mpjoin" ]; then
+		rc=${KSFT_FAIL}
+		print_check "ack no mpjoin"
+		fail_test "got $count JOIN[s] ack no mpjoin expected $ack_no_mpjoin"
+	fi
+
+	count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinAckNoCtx")
+	if [ -n "$count" ] && [ "$count" != "$ack_no_ctx" ]; then
+		rc=${KSFT_FAIL}
+		print_check "ack no ctx"
+		fail_test "got $count JOIN[s] ack no ctx expected $ack_no_ctx"
+	fi
+
+	count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinNotEstablished")
+	if [ -n "$count" ] && [ "$count" != "$not_established" ]; then
+		rc=${KSFT_FAIL}
+		print_check "join not established"
+		fail_test "got $count JOIN[s] not established expected $not_established"
+	fi
+
+	count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinNoIdFound")
+	if [ -n "$count" ] && [ "$count" != "$no_id_found" ]; then
+		rc=${KSFT_FAIL}
+		print_check "join no id found"
+		fail_test "got $count JOIN[s] no id found expected $no_id_found"
+	fi
+
 	print_results "join Rx" ${rc}
 
 	join_syn_tx="${join_syn_tx:-${syn_nr}}" \
@@ -2359,6 +2427,31 @@ signal_address_tests()
 			chk_add_nr 4 4
 		fi
 	fi
+
+	# signalled address belongs to the client, where a TCP-only
+	# listener is bound at it: the client's MP_JOIN routes locally
+	# to the listener and receives a SYN/ACK without MP_JOIN.
+	# MPJoinSynAckNoMPJoin increments on the client side.
+	if reset "signal address, TCP-only listener on client"; then
+		local extra_bind
+		local port
+
+		pm_nl_set_limits $ns1 0 1
+		pm_nl_set_limits $ns2 1 1
+		pm_nl_add_endpoint $ns1 10.0.2.2 flags signal
+
+		port=$(get_port)
+		ip netns exec ${ns2} ./mptcp_connect -l -t -1 -p "$port" \
+			-s TCP 10.0.2.2 &
+		extra_bind=$!
+		mptcp_lib_wait_local_port_listen "$ns2" "$port"
+
+		run_tests $ns1 $ns2 10.0.1.1
+		join_synack_no_mpjoin=1 join_syn_tx=1 \
+			chk_join_nr 0 0 0
+
+		kill ${extra_bind} 2>/dev/null
+	fi
 }
 
 laminar_endp_tests()

-- 
2.53.0

[PATCH net-next 07/11] selftests: mptcp: connect: test name in pcap file

[Matthieu Baerts (NGI0)]

Even if the pcap prefix is printed in the test, it is clearer if this
prefix also include the test name: mptcp_connect.

With this, it is easily possible to find out which pcap was produced by
which test, and easily delete the right ones.

Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
To: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/net/mptcp/mptcp_connect.sh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.sh b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
index d158678fa6ab..5befd8584a4d 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_connect.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
@@ -212,8 +212,8 @@ if $checksum; then
 fi
 
 if $capture; then
-	rndh="${ns1:4}"
-	mptcp_lib_pr_info "Packet capture files will have this prefix: ${rndh}-"
+	capprefix="mptcp_connect-${ns1:4}"
+	mptcp_lib_pr_info "pcap will have this prefix: ${capprefix}-"
 fi
 
 set_ethtool_flags() {
@@ -372,7 +372,7 @@ do_transfer()
 			capuser="-Z $SUDO_USER"
 		fi
 
-		local capfile="${rndh}-${connector_ns:0:3}-${listener_ns:0:3}-${cl_proto}-${srv_proto}-${connect_addr}-${port}"
+		local capfile="${capprefix}-${connector_ns:0:3}-${listener_ns:0:3}-${cl_proto}-${srv_proto}-${connect_addr}-${port}"
 		local capopt="-i any -s 65535 -B 32768 ${capuser}"
 
 		ip netns exec ${listener_ns} tcpdump ${capopt} \

-- 
2.53.0

[PATCH net-next 08/11] selftests: mptcp: simult_flow: test name in pcap file

[Matthieu Baerts (NGI0)]

To be able to easily find out which pcap was produced by which test, the
selftest name is now added to the pcap file, similar to the other tests.

While at it, print the prefix name to be able to find which capture
files have been produced by which test after several runs. This prefix
was not printed anywhere before.

Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
To: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/net/mptcp/simult_flows.sh | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/simult_flows.sh b/tools/testing/selftests/net/mptcp/simult_flows.sh
index 7b9aabe10170..d723261bdc62 100755
--- a/tools/testing/selftests/net/mptcp/simult_flows.sh
+++ b/tools/testing/selftests/net/mptcp/simult_flows.sh
@@ -24,6 +24,7 @@ small=""
 sout=""
 cout=""
 capout=""
+capprefix=""
 size=0
 
 usage() {
@@ -70,6 +71,11 @@ setup()
 
 	mptcp_lib_ns_init ns1 ns2 ns3
 
+	if $capture; then
+		capprefix="simult_flows-${ns1:4}"
+		mptcp_lib_pr_info "pcap will have this prefix: ${capprefix}-"
+	fi
+
 	ip link add ns1eth1 netns "$ns1" type veth peer name ns2eth1 netns "$ns2"
 	ip link add ns1eth2 netns "$ns1" type veth peer name ns2eth2 netns "$ns2"
 	ip link add ns2eth3 netns "$ns2" type veth peer name ns3eth1 netns "$ns3"
@@ -136,14 +142,13 @@ do_transfer()
 
 	if $capture; then
 		local capuser
-		local rndh="${ns1:4}"
 		if [ -z $SUDO_USER ] ; then
 			capuser=""
 		else
 			capuser="-Z $SUDO_USER"
 		fi
 
-		local capfile="${rndh}-${port}"
+		local capfile="${capprefix}-${port}"
 		local capopt="-i any -s 65535 -B 32768 ${capuser}"
 
 		ip netns exec ${ns3}  tcpdump ${capopt} -w "${capfile}-listener.pcap"  >> "${capout}" 2>&1 &

-- 
2.53.0

[PATCH net-next 09/11] selftests: mptcp: pcap: drop most of the payload

[Matthieu Baerts (NGI0)]

Limit the size of each captured packet to 108B (IPv4 only) or 128B (a
mix of v4 and v6): this should drop most of the payload that is
generally not needed when debugging an issue.

8 bytes are left in this payload, to be able to inspect the beginning,
just in case.

Please also note that generally, this payload is usually mostly filled
with 0, except at the end. This reduces the .pcap sizes, and reduce IO
usage, which helps debugging issues.

Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
To: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/net/mptcp/mptcp_connect.sh | 2 +-
 tools/testing/selftests/net/mptcp/mptcp_join.sh    | 2 +-
 tools/testing/selftests/net/mptcp/simult_flows.sh  | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.sh b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
index 5befd8584a4d..7a2a851fa0ad 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_connect.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
@@ -373,7 +373,7 @@ do_transfer()
 		fi
 
 		local capfile="${capprefix}-${connector_ns:0:3}-${listener_ns:0:3}-${cl_proto}-${srv_proto}-${connect_addr}-${port}"
-		local capopt="-i any -s 65535 -B 32768 ${capuser}"
+		local capopt="-i any -s 128 -B 32768 ${capuser}"
 
 		ip netns exec ${listener_ns} tcpdump ${capopt} \
 			-w "${capfile}-listener.pcap" >> "${capout}" 2>&1 &
diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 9b9fb3de9da3..18ce7136a2b0 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -979,7 +979,7 @@ cond_start_capture()
 		capfile=$(printf "mp_join-%02u-%s.pcap" "$MPTCP_LIB_TEST_COUNTER" "$ns")
 
 		echo "Capturing traffic for test $MPTCP_LIB_TEST_COUNTER into $capfile"
-		ip netns exec "$ns" tcpdump -i any -s 65535 -B 32768 $capuser -w "$capfile" > "$capout" 2>&1 &
+		ip netns exec "$ns" tcpdump -i any -s 128 -B 32768 $capuser -w "$capfile" > "$capout" 2>&1 &
 		cappid=$!
 
 		sleep 1
diff --git a/tools/testing/selftests/net/mptcp/simult_flows.sh b/tools/testing/selftests/net/mptcp/simult_flows.sh
index d723261bdc62..3ea3d1efe32e 100755
--- a/tools/testing/selftests/net/mptcp/simult_flows.sh
+++ b/tools/testing/selftests/net/mptcp/simult_flows.sh
@@ -149,7 +149,7 @@ do_transfer()
 		fi
 
 		local capfile="${capprefix}-${port}"
-		local capopt="-i any -s 65535 -B 32768 ${capuser}"
+		local capopt="-i any -s 108 -B 32768 ${capuser}"
 
 		ip netns exec ${ns3}  tcpdump ${capopt} -w "${capfile}-listener.pcap"  >> "${capout}" 2>&1 &
 		local cappid_listener=$!

-- 
2.53.0

[PATCH net-next 10/11] selftests: mptcp: fix const qualifier warnings in strchr usage

[Matthieu Baerts (NGI0)]

From: Geliang Tang <tanggeliang@kylinos.cn>

In mptcp_connect.c, strchr() returns a pointer to a character within
the input string, which is declared as const char *. Assigning this
return value to a non-const char * discards the const qualifier,
triggering compiler warnings:

 make: Entering directory 'tools/testing/selftests/net/mptcp'
   CC       mptcp_connect
 mptcp_connect.c: In function 'parse_cmsg_types':
 mptcp_connect.c:1267:22: warning: initialization discards 'const'
	qualifier from pointer target type [-Wdiscarded-qualifiers]
  1267 |         char *next = strchr(type, ',');
       |                      ^~~~~~
 mptcp_connect.c: In function 'parse_setsock_options':
 mptcp_connect.c:1295:22: warning: initialization discards 'const'
	qualifier from pointer target type [-Wdiscarded-qualifiers]
  1295 |         char *next = strchr(name, ',');
       |                      ^~~~~~
 make: Leaving directory 'tools/testing/selftests/net/mptcp'

Fix these warnings by declaring the 'next' variable as const char *,
as it is only used for read-only parsing.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
To: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/net/mptcp/mptcp_connect.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.c b/tools/testing/selftests/net/mptcp/mptcp_connect.c
index cbe573c4ab3a..ea4cb6c1bd5e 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_connect.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_connect.c
@@ -1264,7 +1264,7 @@ static void apply_cmsg_types(int fd, const struct cfg_cmsg_types *cmsg)
 
 static void parse_cmsg_types(const char *type)
 {
-	char *next = strchr(type, ',');
+	const char *next = strchr(type, ',');
 	unsigned int len = 0;
 
 	cfg_cmsg_types.cmsg_enabled = 1;
@@ -1292,7 +1292,7 @@ static void parse_cmsg_types(const char *type)
 
 static void parse_setsock_options(const char *name)
 {
-	char *next = strchr(name, ',');
+	const char *next = strchr(name, ',');
 	unsigned int len = 0;
 
 	if (next) {

-- 
2.53.0

[PATCH net-next 11/11] selftests: mptcp: diag: fix stack buffer overflow in get_subflow_info()

[Matthieu Baerts (NGI0)]

From: Jiangshan Yi <yijiangshan@kylinos.cn>

get_subflow_info() parses the subflow address string with:

	char saddr[64], daddr[64];

	ret = sscanf(subflow_addrs, "%[^:]:%d %[^:]:%d",
		     saddr, &sport, daddr, &dport);

The subflow_addrs buffer holds up to 1024 bytes and is taken directly
from the command line ("-c" argument). The "%[^:]" conversions have no
maximum field width, so if the address substring before the ':' exceeds
63 bytes, sscanf() writes past the end of the 64-byte saddr/daddr stack
buffers. This overflows the stack, corrupting adjacent stack data such
as the saved return address, and can crash the tool or lead to
out-of-bounds writes controlled by user-supplied input.

Bound both string conversions to the destination buffer size by adding
an explicit maximum field width of 63 (leaving room for the terminating
NUL), so at most 63 bytes are written into each 64-byte buffer:

	ret = sscanf(subflow_addrs, "%63[^:]:%d %63[^:]:%d",
		     saddr, &sport, daddr, &dport);

The subflow address can be passed in argument, so fixing this is helpful
when the tool is manually used.

Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Jiangshan Yi <yijiangshan@kylinos.cn>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
To: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/net/mptcp/mptcp_diag.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_diag.c b/tools/testing/selftests/net/mptcp/mptcp_diag.c
index 5e222ba977e4..3b8d2c8a6216 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_diag.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_diag.c
@@ -377,7 +377,8 @@ static void get_subflow_info(char *subflow_addrs)
 	int ret;
 	int fd;
 
-	ret = sscanf(subflow_addrs, "%[^:]:%d %[^:]:%d", saddr, &sport, daddr, &dport);
+	ret = sscanf(subflow_addrs, "%63[^:]:%d %63[^:]:%d",
+		     saddr, &sport, daddr, &dport);
 	if (ret != 4)
 		die_perror("IP PORT Pairs has style problems!");
 

-- 
2.53.0

Re: [PATCH net-next 00/11] mptcp: misc. features for v7.3

[Matthieu Baerts]

Hello,

On 12/08/2026 16:55, Matthieu Baerts (NGI0) wrote:
> This series contains a few independent new features, and small fixes for
> net-next:

I checked Sashiko [1] and Clashiko [2] reviews, and here below is a
brief summary. TL;DR: I don't think a v2 is needed, and follow-up
patches fixing pre-existing issues will be sent separately.

[1]
https://sashiko.dev/#/patchset/20260812-net-next-mptcp-misc-feat-7-3-v1-0-1905a818f6cb@kernel.org
[2]
https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260812-net-next-mptcp-misc-feat-7-3-v1-0-1905a818f6cb@kernel.org
> - Patch 1: Add WARN_ON_ONCE guards around extra_subflows to catch issues
>   with this counter, similar to what is done with other PM counters.

Pre-existing issues: fixes will be sent to net.

> - Patches 2-3: Follow-up patches to remove data_ack field from struct
>   mptcp_ext -- now unused after recent fixes -- and makes a userspace PM
>   helper static.

Pre-existing issue: a fix will be sent to net.

> - Patch 4: Honour tcp_rto_{min_us,max_ms} sysctls for MPTCP-level
>   retransmit timers like with DATA_FIN's and fallback timeout.

Not needed: suggesting adding extra checks if the TCP RTO max and min
sysctl are misconfigured (min > max). There is already a check in the
code to avoid a division by 0. The rest is similar to TCP.

> - Patches 5-6: Add per-event MIB counters for MPTCP_RST_EMPTCP resets to
>   help to spot such situations in production.

Patch 5: some imprecisions in the commit message, not worth a respin I
think. Plus a suggestion of adding an extra increment, but it is for a
different case, so no.

Patch 6: no need to handle the only test where the server initiates the
subflow → the goal is to check that globally these counters are not
unexpetedly incremented. Maybe MPJoinNotEstablished could be checked on
the other side as well, but this shouldn't happen with the current
selftests, and this addition can come in a follow-up patch.

> - Patches 7-9: Small pcap-related improvements in the selftests.

Patch 7: no need to differenciate the mptcp_connect_*.sh which are only
there for the CI. Someone doing the debugging and asking for pcaps will
use mptcp_connect.sh

> - Patch 10: Fix compiler warning in the selftests.

pre-existing, and not really an issue: the selftests don't try to trick
mptcp_connect

> - Patch 11: Avoid a buffer overflow when misusing the mptcp_diag tool
>   from the selftests.

Small typo in the commit message, not worth a respin I think. Plus yes
it is a fix, but not worth being backported: can be a bug when this tool
designed for the selftest is used manually with a wrong address (which
is written in the commit message). Plus pre-existing issues that are not
worth fixing in a follow-up patch for this selftest tool.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.