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[PATCH 4.14 20/31] cdc-acm: fix race between reset and control messaging




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

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

From: Oliver Neukum <oneukum@xxxxxxxx>

commit 9397940ed812b942c520e0c25ed4b2c64d57e8b9 upstream.

If a device splits up a control message and a reset() happens
between the parts, the message is lost and already recieved parts
must be dropped.

Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
Fixes: 1aba579f3cf51 ("cdc-acm: handle read pipe errors")
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1654,6 +1654,7 @@ static int acm_pre_reset(struct usb_inte
 	struct acm *acm = usb_get_intfdata(intf);
 
 	clear_bit(EVENT_RX_STALL, &acm->flags);
+	acm->nb_index = 0; /* pending control transfers are lost */
 
 	return 0;
 }