HID: hidraw: protect hidraw_disconnect() better

The function hidraw_disconnect() only acquires the hidraw minors_lock
when clearing the entry in hidraw_table. However the device_destroy()
call can cause a userland read/write to return with an error. It may
cause the program to release the file descripter before the disconnect
is finished. hidraw_disconnect() has already set hidraw->exist to 0,
which makes hidraw_release() kfree the hidraw structure, which
hidraw_disconnect() continues to access and even tries to kfree again.
Similarly if a hidraw_release() occurs after setting hidraw->exist to 0,
the same thing can happen.

This is fixed by expanding the mutex critical section to cover the whole
function from setting hidraw->exist to 0 to freeing the hidraw
structure, preventing a hidraw_release() from interfering.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Tested-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hidraw.c

@@ -510,13 +510,12 @@ void hidraw_disconnect(struct hid_device *hid)
 {
 	struct hidraw *hidraw = hid->hidraw;
 
+	mutex_lock(&minors_lock);
 	hidraw->exist = 0;
 
 	device_destroy(hidraw_class, MKDEV(hidraw_major, hidraw->minor));
 
-	mutex_lock(&minors_lock);
 	hidraw_table[hidraw->minor] = NULL;
-	mutex_unlock(&minors_lock);
 
 	if (hidraw->open) {
 		hid_hw_close(hid);
@@ -524,6 +523,7 @@ void hidraw_disconnect(struct hid_device *hid)
 	} else {
 		kfree(hidraw);
 	}
+	mutex_unlock(&minors_lock);
 }
 EXPORT_SYMBOL_GPL(hidraw_disconnect);