Re: [PATCH net-next V2 3/3] tun: add eBPF based queue selection method

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

On Tue, Oct 31, 2017 at 7:32 PM, Jason Wang <jasowang@redhat.com> wrote:
> This patch introduces an eBPF based queue selection method based on
> the flow steering policy ops. Userspace could load an eBPF program
> through TUNSETSTEERINGEBPF. This gives much more flexibility compare
> to simple but hard coded policy in kernel.
>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> +static int tun_set_steering_ebpf(struct tun_struct *tun, void __user *data)
> +{
> +       struct bpf_prog *prog;
> +       u32 fd;
> +
> +       if (copy_from_user(&fd, data, sizeof(fd)))
> +               return -EFAULT;
> +
> +       prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SOCKET_FILTER);

If the idea is to allow guests to pass BPF programs down to the host,
you may want to define a new program type that is more restrictive than
socket filter.

The external functions allowed for socket filters (sk_filter_func_proto)
are relatively few (compared to, say, clsact), but may still leak host
information to a guest. More importantly, guest security considerations
limits how we can extend socket filters later.