FAILED: patch "[PATCH] mptcp: close subflow when receiving TCP+FIN" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org>.

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 f09b0ad55a1196f5891663f8888463c0541059cb
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024083037-germproof-omnivore-ecf0@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

f09b0ad55a11 ("mptcp: close subflow when receiving TCP+FIN")
a5cb752b1257 ("mptcp: use mptcp_schedule_work instead of open-coding it")

thanks,

greg k-h

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

From f09b0ad55a1196f5891663f8888463c0541059cb Mon Sep 17 00:00:00 2001
From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>
Date: Mon, 26 Aug 2024 19:11:18 +0200
Subject: [PATCH] mptcp: close subflow when receiving TCP+FIN

When a peer decides to close one subflow in the middle of a connection
having multiple subflows, the receiver of the first FIN should accept
that, and close the subflow on its side as well. If not, the subflow
will stay half closed, and would even continue to be used until the end
of the MPTCP connection or a reset from the network.

The issue has not been seen before, probably because the in-kernel
path-manager always sends a RM_ADDR before closing the subflow. Upon the
reception of this RM_ADDR, the other peer will initiate the closure on
its side as well. On the other hand, if the RM_ADDR is lost, or if the
path-manager of the other peer only closes the subflow without sending a
RM_ADDR, the subflow would switch to TCP_CLOSE_WAIT, but that's it,
leaving the subflow half-closed.

So now, when the subflow switches to the TCP_CLOSE_WAIT state, and if
the MPTCP connection has not been closed before with a DATA_FIN, the
kernel owning the subflow schedules its worker to initiate the closure
on its side as well.

This issue can be easily reproduced with packetdrill, as visible in [1],
by creating an additional subflow, injecting a FIN+ACK before sending
the DATA_FIN, and expecting a FIN+ACK in return.

Fixes: 40947e13997a ("mptcp: schedule worker when subflow is closed")
Cc: stable@vger.kernel.org
Link: https://github.com/multipath-tcp/packetdrill/pull/154 [1]
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240826-net-mptcp-close-extra-sf-fin-v1-1-905199fe1172@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 0d536b183a6c..151e82e2ff2e 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2533,8 +2533,11 @@ static void __mptcp_close_subflow(struct sock *sk)
 
 	mptcp_for_each_subflow_safe(msk, subflow, tmp) {
 		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+		int ssk_state = inet_sk_state_load(ssk);
 
-		if (inet_sk_state_load(ssk) != TCP_CLOSE)
+		if (ssk_state != TCP_CLOSE &&
+		    (ssk_state != TCP_CLOSE_WAIT ||
+		     inet_sk_state_load(sk) != TCP_ESTABLISHED))
 			continue;
 
 		/* 'subflow_data_ready' will re-sched once rx queue is empty */
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index a21c712350c3..4834e7fc2fb6 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1255,12 +1255,16 @@ static void mptcp_subflow_discard_data(struct sock *ssk, struct sk_buff *skb,
 /* sched mptcp worker to remove the subflow if no more data is pending */
 static void subflow_sched_work_if_closed(struct mptcp_sock *msk, struct sock *ssk)
 {
-	if (likely(ssk->sk_state != TCP_CLOSE))
+	struct sock *sk = (struct sock *)msk;
+
+	if (likely(ssk->sk_state != TCP_CLOSE &&
+		   (ssk->sk_state != TCP_CLOSE_WAIT ||
+		    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))
-		mptcp_schedule_work((struct sock *)msk);
+		mptcp_schedule_work(sk);
 }
 
 static bool subflow_can_fallback(struct mptcp_subflow_context *subflow)