This is a note to let you know that I've just added the patch titled
USB: cdc-acm: fix racy tty buffer accesses
to the 5.4-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:
usb-cdc-acm-fix-racy-tty-buffer-accesses.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 65a205e6113506e69a503b61d97efec43fc10fd7 Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@xxxxxxxxxx>
Date: Wed, 29 Sep 2021 11:09:36 +0200
Subject: USB: cdc-acm: fix racy tty buffer accesses
From: Johan Hovold <johan@xxxxxxxxxx>
commit 65a205e6113506e69a503b61d97efec43fc10fd7 upstream.
A recent change that started reporting break events to the line
discipline caused the tty-buffer insertions to no longer be serialised
by inserting events also from the completion handler for the interrupt
endpoint.
Completion calls for distinct endpoints are not guaranteed to be
serialised. For example, in case a host-controller driver uses
bottom-half completion, the interrupt and bulk-in completion handlers
can end up running in parallel on two CPUs (high-and low-prio tasklets,
respectively) thereby breaking the tty layer's single producer
assumption.
Fix this by holding the read lock also when inserting characters from
the bulk endpoint.
Fixes: 08dff274edda ("cdc-acm: fix BREAK rx code path adding necessary calls")
Cc: stable@xxxxxxxxxxxxxxx
Acked-by: Oliver Neukum <oneukum@xxxxxxxx>
Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210929090937.7410-2-johan@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/usb/class/cdc-acm.c | 5 +++++
1 file changed, 5 insertions(+)
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -474,11 +474,16 @@ static int acm_submit_read_urbs(struct a
static void acm_process_read_urb(struct acm *acm, struct urb *urb)
{
+ unsigned long flags;
+
if (!urb->actual_length)
return;
+ spin_lock_irqsave(&acm->read_lock, flags);
tty_insert_flip_string(&acm->port, urb->transfer_buffer,
urb->actual_length);
+ spin_unlock_irqrestore(&acm->read_lock, flags);
+
tty_flip_buffer_push(&acm->port);
}
Patches currently in stable-queue which might be from johan@xxxxxxxxxx are
queue-5.4/usb-cdc-acm-fix-break-reporting.patch
queue-5.4/usb-cdc-acm-fix-racy-tty-buffer-accesses.patch
