staging: usbip: cleanup and fix of vhci_hub_status

Changed setting the status bits to a byte-oriented approach. Number of
written status bits is now based on VHCI_NPORT, instead of casting
status buffer to a long. This fixes a stack corruption bug on 64-bit
based architectures, and potential byte order / endianness related
issues.

In addition updated function comments, and log statements.

Signed-off-by: Bart Westgeest <bart@elbrys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/usbip/vhci_hcd.c

@@ -178,44 +178,32 @@ void rh_port_disconnect(int rhport)
 	  | USB_PORT_STAT_C_RESET) << 16)
 
 /*
- * This function is almostly the same as dummy_hcd.c:dummy_hub_status() without
- * suspend/resume support. But, it is modified to provide multiple ports.
+ * Returns 0 if the status hasn't changed, or the number of bytes in buf.
+ * Ports are 0-indexed from the HCD point of view,
+ * and 1-indexed from the USB core pointer of view.
  *
  * @buf: a bitmap to show which port status has been changed.
- *  bit  0: reserved or used for another purpose?
+ *  bit  0: reserved
  *  bit  1: the status of port 0 has been changed.
  *  bit  2: the status of port 1 has been changed.
  *  ...
- *  bit  7: the status of port 6 has been changed.
- *  bit  8: the status of port 7 has been changed.
- *  ...
- *  bit 15: the status of port 14 has been changed.
- *
- * So, the maximum number of ports is 31 ( port 0 to port 30) ?
- *
- * The return value is the actual transferred length in byte. If nothing has
- * been changed, return 0. In the case that the number of ports is less than or
- * equal to 6 (VHCI_NPORTS==7), return 1.
- *
  */
 static int vhci_hub_status(struct usb_hcd *hcd, char *buf)
 {
 	struct vhci_hcd	*vhci;
 	unsigned long	flags;
-	int		retval = 0;
-
-	/* the enough buffer is allocated according to USB_MAXCHILDREN */
-	unsigned long	*event_bits = (unsigned long *) buf;
+	int		retval;
 	int		rhport;
 	int		changed = 0;
 
-	*event_bits = 0;
+	retval = DIV_ROUND_UP(VHCI_NPORTS + 1, 8);
+	memset(buf, 0, retval);
 
 	vhci = hcd_to_vhci(hcd);
 
 	spin_lock_irqsave(&vhci->lock, flags);
 	if (!HCD_HW_ACCESSIBLE(hcd)) {
-		usbip_dbg_vhci_rh("hw accessible flag in on?\n");
+		usbip_dbg_vhci_rh("hw accessible flag not on?\n");
 		goto done;
 	}
 
@@ -223,9 +211,9 @@ static int vhci_hub_status(struct usb_hcd *hcd, char *buf)
 	for (rhport = 0; rhport < VHCI_NPORTS; rhport++) {
 		if ((vhci->port_status[rhport] & PORT_C_MASK)) {
 			/* The status of a port has been changed, */
-			usbip_dbg_vhci_rh("port %d is changed\n", rhport);
+			usbip_dbg_vhci_rh("port %d status changed\n", rhport);
 
-			*event_bits |= 1 << (rhport + 1);
+			buf[(rhport + 1) / 8] |= 1 << (rhport + 1) % 8;
 			changed = 1;
 		}
 	}
@@ -235,14 +223,9 @@ static int vhci_hub_status(struct usb_hcd *hcd, char *buf)
 	if (hcd->state == HC_STATE_SUSPENDED)
 		usb_hcd_resume_root_hub(hcd);
 
-	if (changed)
-		retval = 1 + (VHCI_NPORTS / 8);
-	else
-		retval = 0;
-
 done:
 	spin_unlock_irqrestore(&vhci->lock, flags);
-	return retval;
+	return changed ? retval : 0;
 }
 
 /* See hub_configure in hub.c */