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

[Willem de Bruijn]

On Fri, Nov 3, 2017 at 5:56 PM, Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
> On Tue, Oct 31, 2017 at 7:32 PM, Jason Wang <jasowang@xxxxxxxxxx> 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@xxxxxxxxxx>
>> ---
>> +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.

Unless the idea is for the hypervisor to prepared the BPF based on a
limited set of well defined modes that the guest can configure. Then
socket filters are fine, as the BPF is prepared by a regular host process.