usb: gadget: android: Save/restore ep0 completion function

The android_setup() function currently gives the f_accessory
setup function first opportunity to handle control requests
in order to support Android Open Accessory (AOA) hosts. That
function makes use of cdev->req and overrides its completion
function, but not in all cases. Thus, if a later request uses
the same request pointer but doesn't (re)set req->complete it
could result in the wrong completion function being called and
causing invalid memory access.

One way to fix this would be to explicitly set req->complete in
all cases but that might require auditing all function drivers
that have ep0 handling. Instead, note that the composite device
had already initially set cdev->req->complete and simply cache
and restore that pointer at the start of android_setup().

Change-Id: I33bcd17bd20687a349d537d1013b52a2afef6996
Signed-off-by: Jack Pham <[email protected]>

drivers/usb/gadget/android.c

@@ -90,6 +90,9 @@ struct android_dev {
 	struct usb_composite_dev *cdev;
 	struct device *dev;
 
+	void (*setup_complete)(struct usb_ep *ep,
+				struct usb_request *req);
+
 	bool enabled;
 	int disable_depth;
 	struct mutex mutex;
@@ -1312,6 +1315,9 @@ static int android_bind(struct usb_composite_dev *cdev)
 	struct usb_gadget	*gadget = cdev->gadget;
 	int			id, ret;
 
+	/* Save the default handler */
+	dev->setup_complete = cdev->req->complete;
+
 	/*
 	 * Start disconnected. Userspace will connect the gadget once
 	 * it is done configuring the functions.
@@ -1378,6 +1384,7 @@ android_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *c)
 
 	req->zero = 0;
 	req->length = 0;
+	req->complete = dev->setup_complete;
 	gadget->ep0->driver_data = cdev;
 
 	list_for_each_entry(f, &dev->enabled_functions, enabled_list) {