linux-kernel - Re: [PATCH] xen: fix potential shift out-of-bounds in xenhcd_hub

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Date:   Sun, 6 Aug 2023 11:15:51 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Zhang Shurong <zhang_shurong@...mail.com>, jgross@...e.com,
        xen-devel@...ts.xenproject.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen: fix potential shift out-of-bounds in
 xenhcd_hub_control()

On Sun, Aug 06, 2023 at 04:27:27PM +0200, Greg KH wrote:
> 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.

It's not feasible to fix all the callers, because the calls can come 
from userspace via usbfs.

Alan Stern