On Thu, Sep 21, 2017 at 10:17:03AM -0400, Alan Stern wrote:
> On Thu, 21 Sep 2017, Dan Carpenter wrote:
>
> > There used to be an integer overflow check in proc_do_submiturb() but
> > it accidentally got removed. We need to put it back. The
>
> The removal was deliberate, not accidental. :-)
>
> > uurb->buffer_length variable is a signed integer and it's controlled by
> > the user. It can lead to an integer overflow when we do:
> >
> > num_sgs = DIV_ROUND_UP(uurb->buffer_length, USB_SG_SIZE);
>
> Sorry, I don't understand. How can division by 16384 lead to an
> integer overflow?
It looks like this when you unwrap the macro:
num_sgs = (uurb->buffer_length + USB_SG_SIZE - 1) / USB_SG_SIZE;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This first addition can overflow.
regards,
dan carpenter
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