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?
> }
>
> - 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);
>
>
