mptcp: fix recent failed backports (20260919)

The following patches could not be applied without conflicts in this tree:

- 2b0f561f21b2 ("mptcp: avoid unneeded actions on subflow reset")
- 42064de57fb8 ("mptcp: close race between scheduler and state change")

I backported the following commit to avoid conflicts:

- c3349a22c200 ("mptcp: consolidate subflow cleanup")

Conflicts (if any) have been resolved, and documented in each patch.

Paolo Abeni (3):
mptcp: consolidate subflow cleanup
mptcp: avoid unneeded actions on subflow reset
mptcp: close race between scheduler and state change

 net/mptcp/protocol.c | 10 ++++++----
 net/mptcp/protocol.h |  3 ++-
 net/mptcp/subflow.c  | 46 ++++++++++++++++++++++++++++----------------
 3 files changed, 37 insertions(+), 22 deletions(-)

2.55.0

From: Paolo Abeni <[email protected]>

commit c3349a22c2002947d29a98a77bfb36d97cfbfac1 upstream.

Consolidate all the cleanup actions requiring the worker in a single helper and ensure the dummy data fin creation for fallback socket is performed only when the tcp rx queue is empty.

There are no functional changes intended, but this will simplify the next patch, when the tcp rx queue spooling could be delayed at release_cb time.

Stable-dep-of: 2b0f561f21b2 ("mptcp: avoid unneeded actions on subflow reset") [ Note: also remove struct mptcp_sock *msk from subflow_state_change: it
is no longer used after this modification. ]

---
 net/mptcp/subflow.c | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

index eed5b90bf5a0..07cdb162b709 100644
@@ -1159,7 +1159,12 @@ static void mptcp_subflow_discard_data(struct sock *ssk, struct sk_buff *skb,
 		subflow->map_valid = 0;
 }
 
-/* sched mptcp worker to remove the subflow if no more data is pending */
+static bool subflow_is_done(const struct sock *sk)
+{
+	return sk->sk_shutdown & RCV_SHUTDOWN || sk->sk_state == TCP_CLOSE;
+}
+
+/* sched mptcp worker for subflow cleanup if no more data is pending */
 static void subflow_sched_work_if_closed(struct mptcp_sock *msk, struct sock *ssk)
 {
 	struct sock *sk = (struct sock *)msk;

@@ -1169,8 +1174,18 @@ static void subflow_sched_work_if_closed(struct mptcp_sock *msk, struct sock *ss
 		    inet_sk_state_load(sk) != TCP_ESTABLISHED)))
 		return;
 
-	if (skb_queue_empty(&ssk->sk_receive_queue) &&
-	    !test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags))
+	if (!skb_queue_empty(&ssk->sk_receive_queue))
+		return;
+
+	if (!test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags))
+		mptcp_schedule_work(sk);
+
+	/* when the fallback subflow closes the rx side, trigger a 'dummy'
+	 * ingress data fin, so that the msk state will follow along
+	 */
+	if (__mptcp_check_fallback(msk) && subflow_is_done(ssk) &&
+	    msk->first == ssk &&
+	    mptcp_update_rcv_data_fin(msk, READ_ONCE(msk->ack_seq), true))
 		mptcp_schedule_work(sk);
 }
 

@@ -1688,20 +1703,13 @@ static void __subflow_state_change(struct sock *sk)
 	rcu_read_unlock();
 }
 
-static bool subflow_is_done(const struct sock *sk)
-{
-	return sk->sk_shutdown & RCV_SHUTDOWN || sk->sk_state == TCP_CLOSE;
-}
-
 static void subflow_state_change(struct sock *sk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 	struct sock *parent = subflow->conn;
-	struct mptcp_sock *msk;
 
 	__subflow_state_change(sk);
 
-	msk = mptcp_sk(parent);
 	/* as recvmsg() does not acquire the subflow socket for ssk selection
 	 * a fin packet carrying a DSS can be unnoticed if we don't trigger
 	 * the data available machinery here.

@@ -1712,13 +1720,6 @@ static void subflow_state_change(struct sock *sk)
 		subflow_error_report(sk);
 
 	subflow_sched_work_if_closed(mptcp_sk(parent), sk);
-
-	/* when the fallback subflow closes the rx side, trigger a 'dummy'
-	 * ingress data fin, so that the msk state will follow along
-	 */
-	if (__mptcp_check_fallback(msk) && subflow_is_done(sk) && msk->first == sk &&
-	    mptcp_update_rcv_data_fin(msk, READ_ONCE(msk->ack_seq), true))
-		mptcp_schedule_work(parent);
 }
 
 void mptcp_subflow_queue_clean(struct sock *listener_sk, struct sock *listener_ssk)

2.55.0

I guess I would have quickly seen that in the mptcp_connect*.sh tests.

Cheers,
Matt

Sponsored by the NGI0 Core fund.

This is a note to let you know that I've just added the patch titled

mptcp: consolidate subflow cleanup

to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mptcp-consolidate-subflow-cleanup.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From [email protected] Sat Sep 19 22:13:14 2026
From: "Matthieu Baerts (NGI0)" <[email protected]>
Date: Sat, 19 Sep 2026 22:12:54 +0200
Subject: mptcp: consolidate subflow cleanup
To: [email protected], [email protected], [email protected]
Cc: Paolo Abeni <[email protected]>, [email protected], Mat Martineau <[email protected]>, "Matthieu Baerts (NGI0)" <[email protected]>, Jakub Kicinski <[email protected]>
Message-ID: <[email protected]>

From: Paolo Abeni <[email protected]>

commit c3349a22c2002947d29a98a77bfb36d97cfbfac1 upstream.

Consolidate all the cleanup actions requiring the worker in a single helper and ensure the dummy data fin creation for fallback socket is performed only when the tcp rx queue is empty.

There are no functional changes intended, but this will simplify the next patch, when the tcp rx queue spooling could be delayed at release_cb time.

Stable-dep-of: 2b0f561f21b2 ("mptcp: avoid unneeded actions on subflow reset") [ Note: also remove struct mptcp_sock *msk from subflow_state_change: it
is no longer used after this modification. ]

---
 net/mptcp/subflow.c |   35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

@@ -1159,7 +1159,12 @@ out:
 		subflow->map_valid = 0;
 }
 
-/* sched mptcp worker to remove the subflow if no more data is pending */
+static bool subflow_is_done(const struct sock *sk)
+{
+	return sk->sk_shutdown & RCV_SHUTDOWN || sk->sk_state == TCP_CLOSE;
+}
+
+/* sched mptcp worker for subflow cleanup if no more data is pending */
 static void subflow_sched_work_if_closed(struct mptcp_sock *msk, struct sock *ssk)
 {
 	struct sock *sk = (struct sock *)msk;

@@ -1169,8 +1174,18 @@ static void subflow_sched_work_if_closed
 		    inet_sk_state_load(sk) != TCP_ESTABLISHED)))
 		return;
 
-	if (skb_queue_empty(&ssk->sk_receive_queue) &&
-	    !test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags))
+	if (!skb_queue_empty(&ssk->sk_receive_queue))
+		return;
+
+	if (!test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags))
+		mptcp_schedule_work(sk);
+
+	/* when the fallback subflow closes the rx side, trigger a 'dummy'
+	 * ingress data fin, so that the msk state will follow along
+	 */
+	if (__mptcp_check_fallback(msk) && subflow_is_done(ssk) &&
+	    msk->first == ssk &&
+	    mptcp_update_rcv_data_fin(msk, READ_ONCE(msk->ack_seq), true))
 		mptcp_schedule_work(sk);
 }
 

@@ -1688,20 +1703,13 @@ static void __subflow_state_change(struc
 	rcu_read_unlock();
 }
 
-static bool subflow_is_done(const struct sock *sk)
-{
-	return sk->sk_shutdown & RCV_SHUTDOWN || sk->sk_state == TCP_CLOSE;
-}
-
 static void subflow_state_change(struct sock *sk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 	struct sock *parent = subflow->conn;
-	struct mptcp_sock *msk;
 
 	__subflow_state_change(sk);
 
-	msk = mptcp_sk(parent);
 	/* as recvmsg() does not acquire the subflow socket for ssk selection
 	 * a fin packet carrying a DSS can be unnoticed if we don't trigger
 	 * the data available machinery here.

@@ -1712,13 +1720,6 @@ static void subflow_state_change(struct
 		subflow_error_report(sk);
 
 	subflow_sched_work_if_closed(mptcp_sk(parent), sk);
-
-	/* when the fallback subflow closes the rx side, trigger a 'dummy'
-	 * ingress data fin, so that the msk state will follow along
-	 */
-	if (__mptcp_check_fallback(msk) && subflow_is_done(sk) && msk->first == sk &&
-	    mptcp_update_rcv_data_fin(msk, READ_ONCE(msk->ack_seq), true))
-		mptcp_schedule_work(parent);
 }
 
 void mptcp_subflow_queue_clean(struct sock *listener_sk, struct sock *listener_ssk)

Patches currently in stable-queue which might be from [email protected] are

queue-6.1/selftests-mptcp-fix-an-uaf-in-mptcp_connect.c.patch queue-6.1/mptcp-syncookies-remember-the-request-backup-flag.patch queue-6.1/mptcp-close-race-between-scheduler-and-state-change.patch queue-6.1/mptcp-avoid-unneeded-actions-on-subflow-reset.patch queue-6.1/mptcp-options-handle-mpc-data-csum-reqd-no-csum.patch queue-6.1/mptcp-consolidate-subflow-cleanup.patch queue-6.1/mptcp-subflow-no-need-to-copy-thmac-during-ulp_clone.patch

From: Paolo Abeni <[email protected]>

commit 2b0f561f21b27c40c91ea4975268a06092bd7e9c upstream.

Once in a blue moon, the mptcp receive path can recursively call mptcp_data_ready() via state change under unlucky error conditions, and then try to hold the data lock again.

Break the recursion loop explicitly checking for the exceptional condition.

Add a new flag instead of using an existing one like 'closing', to exit early in subflow_state_change(), and explicitly flush the RX queue at reset time.

This avoids unneeded processing to check for available data -- calling get_mapping_status() and more on a dying subflow -- but also in error reporting and worker scheduling.

Note that we must consume the currently peeked skb before invoking mptcp_dss_corruption to avoid consuming it again after the eventual reset has freed it.

[ Note: conflict in protocol.c, because commit e0ca4057e0ec ("mptcp:
micro-optimize __mptcp_move_skb()") is not in this version, and is part of a consequent rx path refactor. The conflict is in the context, and is easy to resolve, "done = true" can be moved along without consequences.
Also a conflict in protocol.h, because __unused is at a different number. Decrement the one from this version and add the new flag above. The context is also a bit different with data_avail being an enum, but that's without consequences here. ]

---
 net/mptcp/protocol.c |  6 +++---
 net/mptcp/protocol.h |  3 ++-
 net/mptcp/subflow.c  | 11 +++++++++++
 3 files changed, 16 insertions(+), 4 deletions(-)

index 2ce20884d730..ab83cf46a8c3 100644
@@ -754,13 +754,13 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 				mptcp_dss_corruption(msk, ssk);
 			}
 		} else {
+			sk_eat_skb(ssk, skb);
+			done = true;
+
 			if (unlikely(!fin)) {
 				DEBUG_NET_WARN_ON_ONCE(1);
 				mptcp_dss_corruption(msk, ssk);
 			}
-
-			sk_eat_skb(ssk, skb);
-			done = true;
 		}
 
 		WRITE_ONCE(tp->copied_seq, seq);

index e835028fc4e5..1de257b86839 100644
@@ -492,7 +492,8 @@ struct mptcp_subflow_context {
 		stale : 1,	    /* unable to snd/rcv data, do not use for xmit */
 		valid_csum_seen : 1,        /* at least one csum validated */
 		close_event_done : 1,       /* has done the post-closed part */
-		__unused : 9;
+		resetting : 1,	    /* subflow is resetting */
+		__unused : 8;
 	enum mptcp_data_avail data_avail;
 	bool	pm_listener;	    /* a listener managed by the kernel PM? */
 	u32	remote_nonce;

index 07cdb162b709..cc62681d6ea8 100644
@@ -379,6 +379,10 @@ void mptcp_subflow_reset(struct sock *ssk)
 	/* must hold: tcp_done() could drop last reference on parent */
 	sock_hold(sk);
 
+	subflow->resetting = 1;
+
+	/* No need to delay the actual close for to-be discarded data. */
+	__skb_queue_purge(&ssk->sk_receive_queue);
 	tcp_send_active_reset(ssk, GFP_ATOMIC);
 	tcp_done(ssk);
 	if (!test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &mptcp_sk(sk)->flags))

@@ -1710,6 +1714,13 @@ static void subflow_state_change(struct sock *sk)
 
 	__subflow_state_change(sk);
 
+	/* Rx queue processing is unneeded, error reporting will take place at
+	 * __mptcp_close_ssk() time and subflow reset can't happen in case of
+	 * fallback: subflow_sched_work_if_closed() would be a no-op.
+	 */
+	if (subflow->resetting)
+		return;
+
 	/* as recvmsg() does not acquire the subflow socket for ssk selection
 	 * a fin packet carrying a DSS can be unnoticed if we don't trigger
 	 * the data available machinery here.

2.55.0

This is a note to let you know that I've just added the patch titled

mptcp: avoid unneeded actions on subflow reset

to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mptcp-avoid-unneeded-actions-on-subflow-reset.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From [email protected] Sat Sep 19 22:13:16 2026
From: "Matthieu Baerts (NGI0)" <[email protected]>
Date: Sat, 19 Sep 2026 22:12:55 +0200
Subject: mptcp: avoid unneeded actions on subflow reset
To: [email protected], [email protected], [email protected]
Cc: Paolo Abeni <[email protected]>, [email protected], Xinyang Ge <[email protected]>, "Matthieu Baerts (NGI0)" <[email protected]>, Jakub Kicinski <[email protected]>
Message-ID: <[email protected]>

From: Paolo Abeni <[email protected]>

commit 2b0f561f21b27c40c91ea4975268a06092bd7e9c upstream.

Once in a blue moon, the mptcp receive path can recursively call mptcp_data_ready() via state change under unlucky error conditions, and then try to hold the data lock again.

Break the recursion loop explicitly checking for the exceptional condition.

Add a new flag instead of using an existing one like 'closing', to exit early in subflow_state_change(), and explicitly flush the RX queue at reset time.

This avoids unneeded processing to check for available data -- calling get_mapping_status() and more on a dying subflow -- but also in error reporting and worker scheduling.

Note that we must consume the currently peeked skb before invoking mptcp_dss_corruption to avoid consuming it again after the eventual reset has freed it.

[ Note: conflict in protocol.c, because commit e0ca4057e0ec ("mptcp:
micro-optimize __mptcp_move_skb()") is not in this version, and is part of a consequent rx path refactor. The conflict is in the context, and is easy to resolve, "done = true" can be moved along without consequences.
Also a conflict in protocol.h, because __unused is at a different number. Decrement the one from this version and add the new flag above. The context is also a bit different with data_avail being an enum, but that's without consequences here. ]

---
 net/mptcp/protocol.c |    6 +++---
 net/mptcp/protocol.h |    3 ++-
 net/mptcp/subflow.c  |   11 +++++++++++
 3 files changed, 16 insertions(+), 4 deletions(-)

@@ -754,13 +754,13 @@ static bool __mptcp_move_skbs_from_subfl
 				mptcp_dss_corruption(msk, ssk);
 			}
 		} else {
+			sk_eat_skb(ssk, skb);
+			done = true;
+
 			if (unlikely(!fin)) {
 				DEBUG_NET_WARN_ON_ONCE(1);
 				mptcp_dss_corruption(msk, ssk);
 			}
-
-			sk_eat_skb(ssk, skb);
-			done = true;
 		}
 
 		WRITE_ONCE(tp->copied_seq, seq);

@@ -492,7 +492,8 @@ struct mptcp_subflow_context {
 		stale : 1,	    /* unable to snd/rcv data, do not use for xmit */
 		valid_csum_seen : 1,        /* at least one csum validated */
 		close_event_done : 1,       /* has done the post-closed part */
-		__unused : 9;
+		resetting : 1,	    /* subflow is resetting */
+		__unused : 8;
 	enum mptcp_data_avail data_avail;
 	bool	pm_listener;	    /* a listener managed by the kernel PM? */
 	u32	remote_nonce;

@@ -379,6 +379,10 @@ void mptcp_subflow_reset(struct sock *ss
 	/* must hold: tcp_done() could drop last reference on parent */
 	sock_hold(sk);
 
+	subflow->resetting = 1;
+
+	/* No need to delay the actual close for to-be discarded data. */
+	__skb_queue_purge(&ssk->sk_receive_queue);
 	tcp_send_active_reset(ssk, GFP_ATOMIC);
 	tcp_done(ssk);
 	if (!test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &mptcp_sk(sk)->flags))

@@ -1710,6 +1714,13 @@ static void subflow_state_change(struct
 
 	__subflow_state_change(sk);
 
+	/* Rx queue processing is unneeded, error reporting will take place at
+	 * __mptcp_close_ssk() time and subflow reset can't happen in case of
+	 * fallback: subflow_sched_work_if_closed() would be a no-op.
+	 */
+	if (subflow->resetting)
+		return;
+
 	/* as recvmsg() does not acquire the subflow socket for ssk selection
 	 * a fin packet carrying a DSS can be unnoticed if we don't trigger
 	 * the data available machinery here.

Patches currently in stable-queue which might be from [email protected] are

queue-6.1/selftests-mptcp-fix-an-uaf-in-mptcp_connect.c.patch queue-6.1/mptcp-syncookies-remember-the-request-backup-flag.patch queue-6.1/mptcp-close-race-between-scheduler-and-state-change.patch queue-6.1/mptcp-avoid-unneeded-actions-on-subflow-reset.patch queue-6.1/mptcp-options-handle-mpc-data-csum-reqd-no-csum.patch queue-6.1/mptcp-consolidate-subflow-cleanup.patch queue-6.1/mptcp-subflow-no-need-to-copy-thmac-during-ulp_clone.patch

From: Paolo Abeni <[email protected]>

commit 42064de57fb83231fcc89663a94885f228a1ee53 upstream.

The mptcp scheduler may race with subflow sockets state change: data transmission on the selected socket may fail and a later release could try to use mss_now reset to 0 for a divide operation.

Address the issue by explicitly checking for the critical scenario.

---
 net/mptcp/protocol.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

index ab83cf46a8c3..ca78add7670d 100644
@@ -1636,7 +1636,9 @@ static struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk)
 
 static void mptcp_push_release(struct sock *ssk, struct mptcp_sendmsg_info *info)
 {
-	tcp_push(ssk, 0, info->mss_now, tcp_sk(ssk)->nonagle, info->size_goal);
+	if (info->mss_now)
+		tcp_push(ssk, 0, info->mss_now, tcp_sk(ssk)->nonagle,
+			 info->size_goal);
 	release_sock(ssk);
 }
 

2.55.0

This is a note to let you know that I've just added the patch titled

mptcp: close race between scheduler and state change

to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mptcp-close-race-between-scheduler-and-state-change.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From [email protected] Sat Sep 19 22:13:35 2026
From: "Matthieu Baerts (NGI0)" <[email protected]>
Date: Sat, 19 Sep 2026 22:12:56 +0200
Subject: mptcp: close race between scheduler and state change
To: [email protected], [email protected], [email protected]
Cc: Paolo Abeni <[email protected]>, [email protected], Shardul Bankar <[email protected]>, Xinyang Ge <[email protected]>, "Matthieu Baerts (NGI0)" <[email protected]>, Jakub Kicinski <[email protected]>
Message-ID: <[email protected]>

From: Paolo Abeni <[email protected]>

commit 42064de57fb83231fcc89663a94885f228a1ee53 upstream.

The mptcp scheduler may race with subflow sockets state change: data transmission on the selected socket may fail and a later release could try to use mss_now reset to 0 for a divide operation.

Address the issue by explicitly checking for the critical scenario.

---
 net/mptcp/protocol.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

@@ -1636,7 +1636,9 @@ static struct sock *mptcp_subflow_get_se
 
 static void mptcp_push_release(struct sock *ssk, struct mptcp_sendmsg_info *info)
 {
-	tcp_push(ssk, 0, info->mss_now, tcp_sk(ssk)->nonagle, info->size_goal);
+	if (info->mss_now)
+		tcp_push(ssk, 0, info->mss_now, tcp_sk(ssk)->nonagle,
+			 info->size_goal);
 	release_sock(ssk);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-6.1/selftests-mptcp-fix-an-uaf-in-mptcp_connect.c.patch queue-6.1/mptcp-syncookies-remember-the-request-backup-flag.patch queue-6.1/mptcp-close-race-between-scheduler-and-state-change.patch queue-6.1/mptcp-avoid-unneeded-actions-on-subflow-reset.patch queue-6.1/mptcp-options-handle-mpc-data-csum-reqd-no-csum.patch queue-6.1/mptcp-consolidate-subflow-cleanup.patch queue-6.1/mptcp-subflow-no-need-to-copy-thmac-during-ulp_clone.patch