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

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Aug 06, 2023 at 10:11:43PM +0800, Zhang Shurong wrote:
> 在 2023年7月1日星期六 CST 下午11:51:43，Zhang Shurong 写道：
> > 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);
> 
> Hi there. I apologize for reaching out once more. I'm feeling a bit puzzled 
> about what my next step should be. I'm unsure whether I should rewrite this 
> patch or attempt to address the issue at the caller level.

Try addressing it at the caller level first please.  If that somehow
does not work, then we will take a patch series that fixes all of the
host controller drivers at once.

thanks,

greg k-h