USB: usbip: fix nonconforming hub descriptor

commit ec963b41 upstream.

Fix up the root-hub descriptor to accommodate the variable-length
DeviceRemovable and PortPwrCtrlMask fields, while marking all ports as
removable (and leaving the reserved bit zero unset).

Also add a build-time constraint on VHCI_HC_PORTS which must never be
greater than USB_MAXCHILDREN (but this was only enforced through a
KConfig constant).

This specifically fixes the descriptor layout whenever VHCI_HC_PORTS is
greater than seven (default is 8).

Fixes: 04679b34 ("Staging: USB/IP: add client driver")
Cc: Takahiro Hirofuchi <hirofuchi@users.sourceforge.net>
Cc: Valentina Manea <valentina.manea.m@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2:
 - s/VHCI_HC_PORTS/VHCI_NPORTS/
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/staging/usbip/vhci_hcd.c

@@ -248,14 +248,19 @@ static int vhci_hub_status(struct usb_hcd *hcd, char *buf)
 /* See hub_configure in hub.c */
 static inline void hub_descriptor(struct usb_hub_descriptor *desc)
 {
+	int width;
+
 	memset(desc, 0, sizeof(*desc));
 	desc->bDescriptorType = 0x29;
-	desc->bDescLength = 9;
 	desc->wHubCharacteristics = (__force __u16)
 		(__constant_cpu_to_le16(0x0001));
+
 	desc->bNbrPorts = VHCI_NPORTS;
-	desc->u.hs.DeviceRemovable[0] = 0xff;
-	desc->u.hs.DeviceRemovable[1] = 0xff;
+	BUILD_BUG_ON(VHCI_NPORTS > USB_MAXCHILDREN);
+	width = desc->bNbrPorts / 8 + 1;
+	desc->bDescLength = USB_DT_HUB_NONVAR_SIZE + 2 * width;
+	memset(&desc->u.hs.DeviceRemovable[0], 0, width);
+	memset(&desc->u.hs.DeviceRemovable[width], 0xff, width);
 }
 
 static int vhci_hub_control(struct usb_hcd *hcd, u16 typeReq, u16 wValue,