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

[Zhang Shurong <zhang_shurong@xxxxxxxxxxx>]

在 2023年6月26日星期一 CST 下午1:52:02，您写道：
> 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
Although I'm not knowledgeable about the USB subsystem, I've observed that not 
all driver code that implements hub_control callback performs a shift 
operation on wValue, and not all shift operations among them cause problems. 
Therefore, I've decided to fix this issue within each driver itself.

For example, in r8a66597_hub_control, it will first check whether wValue is 
valid (always < 31) before the shift operation. In case of an invalid number, 
the code would execute the error branch instead of the shift operation.

switch (wValue) {
case USB_PORT_FEAT_ENABLE:
        rh->port &= ~USB_PORT_STAT_POWER;
        break;
case USB_PORT_FEAT_SUSPEND:
        break;
case USB_PORT_FEAT_POWER:
        r8a66597_port_power(r8a66597, port, 0);
        break;
case USB_PORT_FEAT_C_ENABLE:
case USB_PORT_FEAT_C_SUSPEND:
case USB_PORT_FEAT_C_CONNECTION:
case USB_PORT_FEAT_C_OVER_CURRENT:
case USB_PORT_FEAT_C_RESET:
        break;
default:
        goto error;
}
rh->port &= ~(1 << wValue);