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: NFelipe Balbi <felipe.balbi@nokia.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/devices.c

@@ -61,8 +61,6 @@
 #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

@@ -21,6 +21,8 @@
 
 #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

@@ -1051,6 +1051,12 @@ static int hub_probe(struct usb_interface *intf, const struct usb_device_id *id)
 	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");