usb: hub: add check for unsupported bus topology

We can't allow hubs on the 7th tier as they would allow
devices on the 8th tier.

Signed-off-by: Felipe Balbi <[e-mail]>
Cc: Alan Stern <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/core/devices.c

···
 #include "usb.h"
 #include "hcd.h"
 
-#define MAX_TOPO_LEVEL		6
-
 /* Define ALLOW_SERIAL_NUMBER if you want to see the serial number of devices */
 #define ALLOW_SERIAL_NUMBER
 

drivers/usb/core/hcd.h

···
 
 #include <linux/rwsem.h>
 
+#define MAX_TOPO_LEVEL		6
+
 /* This file contains declarations of usbcore internals that are mostly
  * used or exposed by Host Controller Drivers.
  */

drivers/usb/core/hub.c

···
 	desc = intf->cur_altsetting;
 	hdev = interface_to_usbdev(intf);
 
+	if (hdev->level == MAX_TOPO_LEVEL) {
+		dev_err(&intf->dev, "Unsupported bus topology: "
+				"hub nested too deep\n");
+		return -E2BIG;
+	}
+
 #ifdef	CONFIG_USB_OTG_BLACKLIST_HUB
 	if (hdev->parent) {
 		dev_warn(&intf->dev, "ignoring external hub\n");