Re: [PATCHv4 bpf-next 1/2] xdp: add a new helper for dev map multicast support

Jesper Dangaard Brouer
2020-06-10T10:22:23Z

On Tue, 26 May 2020 22:05:38 +0800
Hangbin Liu <liuhangbin@gmail.com> wrote:

> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index a51d9fb7a359..ecc5c44a5bab 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
[...]

> +int dev_map_enqueue_multi(struct xdp_buff *xdp, struct net_device *dev_rx,
> + struct bpf_map *map, struct bpf_map *ex_map,
> + bool exclude_ingress)
> +{
> + struct bpf_dtab_netdev *obj = NULL;
> + struct xdp_frame *xdpf, *nxdpf;
> + struct net_device *dev;
> + bool first = true;
> + u32 key, next_key;
> + int err;
> +
> + devmap_get_next_key(map, NULL, &key);
> +
> + xdpf = convert_to_xdp_frame(xdp);
> + if (unlikely(!xdpf))
> + return -EOVERFLOW;
> +
> + for (;;) {
> + switch (map->map_type) {
> + case BPF_MAP_TYPE_DEVMAP:
> + obj = __dev_map_lookup_elem(map, key);
> + break;
> + case BPF_MAP_TYPE_DEVMAP_HASH:
> + obj = __dev_map_hash_lookup_elem(map, key);
> + break;
> + default:
> + break;
> + }
> +
> + if (!obj || dev_in_exclude_map(obj, ex_map,
> + exclude_ingress ? dev_rx->ifindex : 0))
> + goto find_next;
> +
> + dev = obj->dev;
> +
> + if (!dev->netdev_ops->ndo_xdp_xmit)
> + goto find_next;
> +
> + err = xdp_ok_fwd_dev(dev, xdp->data_end - xdp->data);
> + if (unlikely(err))
> + goto find_next;
> +
> + if (!first) {
> + nxdpf = xdpf_clone(xdpf);
> + if (unlikely(!nxdpf))
> + return -ENOMEM;
> +
> + bq_enqueue(dev, nxdpf, dev_rx);
> + } else {
> + bq_enqueue(dev, xdpf, dev_rx);

This looks racy. You enqueue the original frame, and then later
xdpf_clone it. The original frame might have been freed at that point.

> + first = false;
> + }
> +
> +find_next:
> + err = devmap_get_next_key(map, &key, &next_key);
> + if (err)
> + break;
> + key = next_key;
> + }
> +
> + /* didn't find anywhere to forward to, free buf */
> + if (first)
> + xdp_return_frame_rx_napi(xdpf);
> +
> + return 0;
> +}
> +

--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer