On Thu, 17 Aug 2017 11:46:10 -0700 John Fastabend <john.fastab...@gmail.com>
wrote:
> On 08/17/2017 09:22 AM, Jesper Dangaard Brouer wrote:
> > The return error code need to be included in the tracepoint
> > xdp:xdp_redirect, else its not possible to distinguish successful or
> > failed XDP_REDIRECT transmits.
> >
> > XDP have no queuing mechanism. Thus, it is fairly easily to overrun a
> > NIC transmit queue. The eBPF program invoking helpers (bpf_redirect
> > or bpf_redirect_map) to redirect a packet doesn't get any feedback
> > whether the packet was actually transmitted.
> >
> > Info on failed transmits in the tracepoint xdp:xdp_redirect, is
> > interesting as this opens for providing a feedback-loop to the
> > receiving XDP program.
> >
> > Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
> > ---
>
> [...]
>
> > @@ -2532,12 +2535,14 @@ int xdp_do_redirect(struct net_device *dev, struct
> > xdp_buff *xdp,
> > ri->map = NULL;
> > if (unlikely(!fwd)) {
> > bpf_warn_invalid_xdp_redirect(index);
> > - return -EINVAL;
> > + err = -EINVAL;
> > + goto out;
>
> It doesn't look like there is a check in trace_xdp_redirect to
> avoid dereferencing a NULL fwd pointer here (*to in trace code
> path). Did I miss something?
Nice that you spotted this in your review, but the __string() macro
used in trace code already takes case of this, see output:
xdp:xdp_redirect: prog=39cf08f65683838a from=ixgbe2 to=(null) action=REDIRECT
err=-22
> > }
> >
> > - trace_xdp_redirect(dev, fwd, xdp_prog, XDP_REDIRECT);
> > -
> > - return __bpf_tx_xdp(fwd, NULL, xdp, 0);
> > + err = __bpf_tx_xdp(fwd, NULL, xdp, 0);
> > +out:
> > + trace_xdp_redirect(dev, fwd, xdp_prog, XDP_REDIRECT, err);
> > + return err;
> > }
> > EXPORT_SYMBOL_GPL(xdp_do_redirect);
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
