Re: [PATCH] usb: host: max3421: Fix shift-out-of-bounds in max3421_hub_control()

[Greg Kroah-Hartman]

On Sun, May 17, 2026 at 02:19:07PM -0400, Seungjin Bae wrote:
> 2026년 5월 17일 (일) 오전 1:49, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>님이 작성:
> >
> > On Sat, May 16, 2026 at 08:01:46PM -0400, pip-izony wrote:
> > > From: Seungjin Bae <eeodqql09@xxxxxxxxx>
> > >
> > > So if a malicious userspace task with access to the root hub via
> > > /dev/bus/usb/.../001 issues a USBDEVFS_CONTROL ioctl with `wValue`
> > > greater than or equal to 32, the left shift operation invokes
> > > shift-out-of-bounds undefined behavior. This results in arbitrary
> > > bit corruption of `port_status`, including the normally-immutable
> > > change bits, which can bypass internal state checks and confuse the
> > > hub status.
> > >
> > > Fix this by rejecting requests whose `value` exceeds the shift width
> > > before performing the shift.
> > >
> > > Fixes: 2d53139f3162 ("Add support for using a MAX3421E chip as a host driver.")
> > > Signed-off-by: Seungjin Bae <eeodqql09@xxxxxxxxx>
> > > ---
> > >  drivers/usb/host/max3421-hcd.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/drivers/usb/host/max3421-hcd.c b/drivers/usb/host/max3421-hcd.c
> > > index 0e17c988d36a..3d6b351dcb1a 100644
> > > --- a/drivers/usb/host/max3421-hcd.c
> > > +++ b/drivers/usb/host/max3421-hcd.c
> > > @@ -1694,6 +1694,8 @@ max3421_hub_control(struct usb_hcd *hcd, u16 type_req, u16 value, u16 index,
> > >                                               !pdata->vbus_active_level);
> > >                       fallthrough;
> > >               default:
> > > +                     if (value >= 32)
> > > +                             goto error;
> >
> > Cool, what tool found this?  I've been running some static checkers and
> > I don't think it turned this one up yet.
> >
> > thanks,
> >
> > greg k-h
> 
> Thanks for your interest!
> 
> It's a KLEE-based symbolic execution tool I've been developing for
> kernel drivers. It's still a work in progress, but I'd be happy to
> share more details and the tool itself once it's in better shape.

As per our documentation, you MUST document the fact that you are using
a tool to find/fix things.  Please fix up our newly submitted patches to
include that information.

thanks,

greg k-h