[PATCH v2 3/4] 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 "new_id" attributes must first be removed to prevent new
ids from being added and triggering a probe of the USB driver after it
has been deregistered.

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/bus.c        |  4 ++++
 drivers/usb/serial/usb-serial.c | 21 ++++++++++++++++++---
 include/linux/usb/serial.h      |  1 +
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/serial/bus.c b/drivers/usb/serial/bus.c
index 295c61afa44c..ea1fe5d1e449 100644
--- a/drivers/usb/serial/bus.c
+++ b/drivers/usb/serial/bus.c
@@ -169,3 +169,7 @@ void usb_serial_bus_deregister(struct usb_serial_driver *driver)
 	free_dynids(driver);
 }
 
+void usb_serial_bus_remove_new_id(struct usb_serial_driver *driver)
+{
+	driver_remove_file(&driver->driver, &driver_attr_new_id);
+}
diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index a4fbc849c0fa..11a0ed6d6546 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -1469,7 +1469,7 @@ int __usb_serial_register_drivers(struct usb_serial_driver *const serial_drivers
 {
 	int rc;
 	struct usb_driver *udriver;
-	struct usb_serial_driver * const *sd;
+	struct usb_serial_driver * const *sd, * const *s;
 
 	/*
 	 * udriver must be registered before any of the serial drivers,
@@ -1522,9 +1522,11 @@ int __usb_serial_register_drivers(struct usb_serial_driver *const serial_drivers
 	return 0;
 
 err_deregister_drivers:
+	for (s = serial_drivers; s < sd; ++s)
+		usb_serial_bus_remove_new_id(*s);
+	usb_deregister(udriver);
 	while (sd-- > serial_drivers)
 		usb_serial_deregister(*sd);
-	usb_deregister(udriver);
 err_free_driver:
 	kfree(udriver);
 	return rc;
@@ -1542,10 +1544,23 @@ EXPORT_SYMBOL_GPL(__usb_serial_register_drivers);
 void usb_serial_deregister_drivers(struct usb_serial_driver *const serial_drivers[])
 {
 	struct usb_driver *udriver = (*serial_drivers)->usb_driver;
+	struct usb_serial_driver * const *sd;
+
+	/*
+	 * udriver must be deregistered before the serial drivers so that
+	 * I/O is stopped before unbinding the ports.
+	 *
+	 * Remove the new_id attributes to prevent ids from being added and
+	 * triggering a probe of udriver after it has been deregistered.
+	 */
+	for (sd = serial_drivers; *sd; ++sd)
+		usb_serial_bus_remove_new_id(*sd);
+
+	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);
diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index 534e6650e2aa..ab0a32a90629 100644
--- a/include/linux/usb/serial.h
+++ b/include/linux/usb/serial.h
@@ -381,6 +381,7 @@ void usb_serial_handle_dcd_change(struct usb_serial_port *usb_port,
 
 int usb_serial_bus_register(struct usb_serial_driver *device);
 void usb_serial_bus_deregister(struct usb_serial_driver *device);
+void usb_serial_bus_remove_new_id(struct usb_serial_driver *driver);
 
 extern const struct bus_type usb_serial_bus_type;
 extern struct tty_driver *usb_serial_tty_driver;
-- 
2.54.0