Re: [PATCH] usb:host: fix divide-by-zero in function fhci_queue_urb

zhuyan (M)
2019-04-17T15:33:25Z

On Wed, 17 Apr 2019, 9:45 -400, Alan Stern wrote:
> On Wed, 17 Apr 2019, zhuyan (M) wrote:
> > On Tue, 16 Apr 2019 11:07:56 -0400, Alan Stern wrote:
> > > On Tue, 16 Apr 2019, zhuyan (M) wrote:
> > > > On Tue, 16 Apr 2019 at 11:45:45 +0200, Greg KH wrote:
> > > > > On Tue, Apr 09, 2019 at 10:37:12PM +0800, zhuyan wrote:
> > > > > > In function fhci_queue_urb, the divisor of expression
> > > > > > (urb->transfer_buffer_length % usb_maxpacket(urb->dev,
> > > > > > urb->pipe,
> > > > > > usb_pipeout(urb->pipe))) may be zero.
> > > > >
> > > > > How can you hit that?
> > > > >
> > > > > > When it is zero, unexpected results may occur, so it is
> > > > > > necessary to ensure that the divisor is not zero.
> > > > > >
> > > > > > Signed-off-by: zhuyan <zhuyan34@huawei.com>
> > > > >
> > > > > I need a "Full" name here, not just a single name. Whatever you use to sign documents is good.
> > > > >
> > > > > thanks,
> > > > >
> > > > > greg k-h
> > > >
> > > > In function usb_maxpacket, when ep is NULL, its return value is 0.
> > >
> > > fhci_queue_urb() shouldn't use urb->pipe to compute the maxpacket
> > > size anyway. It should use usb_endpoint_maxp(&urb->ep->desc).
> >
> > Currently, fhci_queue_urb(), call usb_maxpacket() multiple times to
> > calculate the maxpacket size. The usb_maxpacket() will call
> > usb_endpoint_maxp() to compute the maxpacket size.
>
> I know that. What fhci_queue_urb() is doing is wrong. You should change
> it: Make it call usb_endpoint_maxp directly instead of calling usb_maxpacket.

ok, I will resubmit a patch to repair it.

Best wish to you!
zhuyan