linux-kernel - [PATCH 4.18 15/34] cdc-acm: do not reset notification buffer index upon urb unlinking

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Date:   Thu,  8 Nov 2018 13:52:44 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tobias Herzog <t-herzog@....de>,
        Oliver Neukum <oneukum@...e.com>
Subject: [PATCH 4.18 15/34] cdc-acm: do not reset notification buffer index upon urb unlinking

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tobias Herzog <t-herzog@....de>

commit dae3ddba36f8c337fb59cef07d564da6fc9b7551 upstream.

Resetting the write index of the notification buffer on urb unlink (e.g.
closing a cdc-acm device from userspace) may lead to wrong interpretation
of further received notifications, in case the index is not 0 when urb
unlink happens (i.e. when parts of a notification already have been
transferred). On the device side there is no "reset" of the notification
transimission and thus we would get out of sync with the device.

Signed-off-by: Tobias Herzog <t-herzog@....de>
Acked-by: Oliver Neukum <oneukum@...e.com>
Cc: stable <stable@...r.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/usb/class/cdc-acm.c |    1 -
 1 file changed, 1 deletion(-)

--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -354,7 +354,6 @@ static void acm_ctrl_irq(struct urb *urb
 	case -ENOENT:
 	case -ESHUTDOWN:
 		/* this urb is terminated, clean up */
-		acm->nb_index = 0;
 		dev_dbg(&acm->control->dev,
 			"%s - urb shutting down with status: %d\n",
 			__func__, status);