cdc-acm: do not reset notification buffer index upon urb unlinking

BugLink: https://bugs.launchpad.net/bugs/1836654
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@gmx.de>
Acked-by: Oliver Neukum <oneukum@suse.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index e04e72ef712a92abf305c8129361d5eaf702549e..e9679815c7218806b7fd7537d87c9dc771ce2546 100644 (file)
--- 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);