usb: typec: class: Fix NULL pointer access

Concurrent calls to typec_partner_unlink_device can lead to a NULL pointer
dereference. This patch adds a mutex to protect USB device pointers and
prevent this issue. The same mutex protects both the device pointers and
the partner device registration.

Cc: [e-mail]
Fixes: 59de2a56d127 ("usb: typec: Link enumerated USB devices with Type-C partner")
Signed-off-by: Andrei Kuchynski <[e-mail]>
Reviewed-by: Benson Leung <[e-mail]>
Reviewed-by: Heikki Krogerus <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/typec/class.c

···
 		partner->usb_mode = USB_MODE_USB3;
 	}
 
+	mutex_lock(&port->partner_link_lock);
 	ret = device_register(&partner->dev);
 	if (ret) {
 		dev_err(&port->dev, "failed to register partner (%d)\n", ret);
···
 		typec_partner_link_device(partner, port->usb2_dev);
 	if (port->usb3_dev)
 		typec_partner_link_device(partner, port->usb3_dev);
+	mutex_unlock(&port->partner_link_lock);
 
 	return partner;
 }
···
 
 	port = to_typec_port(partner->dev.parent);
 
+	mutex_lock(&port->partner_link_lock);
 	if (port->usb2_dev)
 		typec_partner_unlink_device(partner, port->usb2_dev);
 	if (port->usb3_dev)
 		typec_partner_unlink_device(partner, port->usb3_dev);
 
 	device_unregister(&partner->dev);
+	mutex_unlock(&port->partner_link_lock);
 }
 EXPORT_SYMBOL_GPL(typec_unregister_partner);
 
···
 static void typec_partner_attach(struct typec_connector *con, struct device *dev)
 {
 	struct typec_port *port = container_of(con, struct typec_port, con);
-	struct typec_partner *partner = typec_get_partner(port);
+	struct typec_partner *partner;
 	struct usb_device *udev = to_usb_device(dev);
 	enum usb_mode usb_mode;
 
+	mutex_lock(&port->partner_link_lock);
 	if (udev->speed < USB_SPEED_SUPER) {
 		usb_mode = USB_MODE_USB2;
 		port->usb2_dev = dev;
···
 		port->usb3_dev = dev;
 	}
 
+	partner = typec_get_partner(port);
 	if (partner) {
 		typec_partner_set_usb_mode(partner, usb_mode);
 		typec_partner_link_device(partner, dev);
 		put_device(&partner->dev);
 	}
+	mutex_unlock(&port->partner_link_lock);
 }
 
 static void typec_partner_deattach(struct typec_connector *con, struct device *dev)
 {
 	struct typec_port *port = container_of(con, struct typec_port, con);
-	struct typec_partner *partner = typec_get_partner(port);
+	struct typec_partner *partner;
 
+	mutex_lock(&port->partner_link_lock);
+	partner = typec_get_partner(port);
 	if (partner) {
 		typec_partner_unlink_device(partner, dev);
 		put_device(&partner->dev);
···
 		port->usb2_dev = NULL;
 	else if (port->usb3_dev == dev)
 		port->usb3_dev = NULL;
+	mutex_unlock(&port->partner_link_lock);
 }
 
 /**
···
 
 	ida_init(&port->mode_ids);
 	mutex_init(&port->port_type_lock);
+	mutex_init(&port->partner_link_lock);
 
 	port->id = id;
 	port->ops = cap->ops;

drivers/usb/typec/class.h

···
 	enum typec_port_type		port_type;
 	enum usb_mode			usb_mode;
 	struct mutex			port_type_lock;
+	struct mutex			partner_link_lock;
 
 	enum typec_orientation		orientation;
 	struct typec_switch		*sw;