[PATCH 6.1.y 0/3] mptcp: fix recent failed backports (20260919)

[PATCH 6.1.y 0/3] mptcp: fix recent failed backports (20260919)

[Matthieu Baerts (NGI0)]

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

[PATCH 6.1.y 1/3] mptcp: consolidate subflow cleanup

[Matthieu Baerts (NGI0)]

From: Paolo Abeni <pabeni@redhat.com>

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.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250218-net-next-mptcp-rx-path-refactor-v1-1-4a47d90d7998@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/subflow.c | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index eed5b90bf5a0..07cdb162b709 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -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

[PATCH 6.1.y 2/3] mptcp: avoid unneeded actions on subflow reset

[Matthieu Baerts (NGI0)]

From: Paolo Abeni <pabeni@redhat.com>

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.

Fixes: e32d262c89e2 ("mptcp: handle consistently DSS corruption")
Cc: stable@vger.kernel.org
Reported-by: Xinyang Ge <xinyang@anthropic.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260917-net-mptcp-misc-fixes-7-3-rc4-v2-1-0cf5c72667c8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ 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. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.c |  6 +++---
 net/mptcp/protocol.h |  3 ++-
 net/mptcp/subflow.c  | 11 +++++++++++
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 2ce20884d730..ab83cf46a8c3 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -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);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index e835028fc4e5..1de257b86839 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -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;
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 07cdb162b709..cc62681d6ea8 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -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

[PATCH 6.1.y 3/3] mptcp: close race between scheduler and state change

[Matthieu Baerts (NGI0)]

From: Paolo Abeni <pabeni@redhat.com>

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.

Fixes: c886d70286bf ("mptcp: do not queue data on closed subflows")
Cc: stable@vger.kernel.org
Reported-by: Shardul Bankar <shardul.b@mpiricsoftware.com>
Reported-by: Xinyang Ge <xinyang@anthropic.com>
Closes: https://lore.kernel.org/20260525194828.1137119-1-shardul.b@mpiricsoftware.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260917-net-mptcp-misc-fixes-7-3-rc4-v2-2-0cf5c72667c8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index ab83cf46a8c3..ca78add7670d 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -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