Re: [RFC bpf-next v1 3/7] bpf: Support pulling non-linear xdp data

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 25 Aug 2025 22:12:21 -0700 Amery Hung wrote:
> > > +     data_end = xdp->data + len;
> > > +     delta = data_end - xdp->data_end;
> > > +
> > > +     if (delta <= 0)
> > > +             return 0;
> > > +
> > > +     if (unlikely(data_end > data_hard_end))
> > > +             return -EINVAL;  
> >
> > Is this safe against pointers wrapping on 32b systems?
> >  
> 
> You are right. This may be a problem.
> 
> > Maybe it's better to do:
> >
> >          if (unlikely(data_hard_end - xdp->data_end < delta))
> >
> > ?  
> 
> But delta may be negative if the pointer wraps around and then the
> function will still continue. How about adding data_end < xdp->data
> check and reorganizing the checks like this?

You already checked that delta is positive in the previous if (),
so I think it's safe. Admittedly having 3 separate conditions is 
more readable but it's not strictly necessary. Up to you.