FAILED: patch "[PATCH] mptcp: avoid dup SUB_CLOSED events after disconnect" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 280d654324e33f8e6e3641f76764694c7b64c5db
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026020301-griminess-trespass-07fe@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 280d654324e33f8e6e3641f76764694c7b64c5db Mon Sep 17 00:00:00 2001
From: "Matthieu Baerts (NGI0)" <[email protected]>
Date: Tue, 27 Jan 2026 20:27:23 +0100
Subject: [PATCH] mptcp: avoid dup SUB_CLOSED events after disconnect

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().

index f505b780f713..e32ae594b4ef 100644
@@ -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;

From: "Matthieu Baerts (NGI0)" <[email protected]>

[ Upstream commit 280d654324e33f8e6e3641f76764694c7b64c5db ]

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().

---
 net/mptcp/protocol.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 98fd4ffe6f115..43cdf562ff5ea 100644
@@ -2397,8 +2397,8 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 void mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 		     struct mptcp_subflow_context *subflow)
 {
-	/* 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