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Date:   Mon, 26 Jun 2023 07:52:02 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Jan Beulich <jbeulich@suse.com>,
        Zhang Shurong <zhang_shurong@foxmail.com>
Cc:     xen-devel@lists.xenproject.org, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org, jgross@suse.com
Subject: Re: [PATCH] xen: fix potential shift out-of-bounds in
 xenhcd_hub_control()
Message-ID: <2023062628-shame-ebook-56f2@gregkh>
References: <tencent_15DD79B42AD8A0D64A7CDC24D4FE6C85800A@qq.com>
 <1c8ff405-2bfe-37ff-42ba-aa4f81853475@suse.com>
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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