[PATCH 2/2] USB: serial: fix driver deregistration order

USB serial driver modules register one driver for the USB bus and one or
more drivers for the ports on the USB serial bus.

When unloading a driver module, the USB driver must be deregistered
before the USB serial bus drivers so that I/O is stopped before
unbinding the ports to avoid use-after-free in completion handlers
accessing port data.

Note that the order does not matter currently in the registration error
path as the USB driver is not bound until after the USB serial drivers
have been registered.

Fixes: 765e0ba62613 ("usb-serial: new API for driver registration")
Cc: [email protected]	# 3.4
Cc: Alan Stern <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>
---
 drivers/usb/serial/usb-serial.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index a4fbc849c0fa..08a9b6f8cf7d 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -1522,9 +1522,9 @@ int __usb_serial_register_drivers(struct usb_serial_driver *const serial_drivers
 	return 0;
 
 err_deregister_drivers:
+	usb_deregister(udriver);
 	while (sd-- > serial_drivers)
 		usb_serial_deregister(*sd);
-	usb_deregister(udriver);
 err_free_driver:
 	kfree(udriver);
 	return rc;
@@ -1543,9 +1543,15 @@ void usb_serial_deregister_drivers(struct usb_serial_driver *const serial_driver
 {
 	struct usb_driver *udriver = (*serial_drivers)->usb_driver;
 
+	/*
+	 * The USB driver must be deregistered before the USB serial drivers
+	 * so that I/O is stopped before unbinding the ports.
+	 */
+	usb_deregister(udriver);
+
 	for (; *serial_drivers; ++serial_drivers)
 		usb_serial_deregister(*serial_drivers);
-	usb_deregister(udriver);
+
 	kfree(udriver);
 }
 EXPORT_SYMBOL_GPL(usb_serial_deregister_drivers);
-- 
2.54.0