Re: [PATCH] xen: fix potential shift out-of-bounds in xenhcd_hub_control()

[Greg KH]

On Mon, Jun 26, 2023 at 07:48:05AM +0200, Jan Beulich wrote:
> On 25.06.2023 18:42, Zhang Shurong wrote:
> > --- a/drivers/usb/host/xen-hcd.c
> > +++ b/drivers/usb/host/xen-hcd.c
> > @@ -456,6 +456,8 @@ static int xenhcd_hub_control(struct usb_hcd *hcd, __u16 typeReq, __u16 wValue,
> >  			info->ports[wIndex - 1].c_connection = false;
> >  			fallthrough;
> >  		default:
> > +			if (wValue >= 32)
> > +				goto error;
> >  			info->ports[wIndex - 1].status &= ~(1 << wValue);
> 
> Even 31 is out of bounds (as in: UB) as long as it's 1 here rather
> than 1u.

Why isn't the caller fixed so this type of value could never be passed
to the hub_control callback?

thanks,

greg k-h