Re: [PATCH net-next 2/4] packet: add eBPF fanout mode

[Willem de Bruijn <willemb@google.com>]

> [ @Willem: RH email doesn't exist anymore, I took it out, otherwise
>   every reply gets a bounce. ;) ]

Sorry for using the wrong address, Daniel.

>> Also instead of:
>>   #define PACKET_FANOUT_BPF        6
>>   #define PACKET_FANOUT_EBPF        7
>>
>> I would call them FANOUT_CBPF and FANOUT_EBPF to be unambiguous.
>> This is how bpf manpage distinguishes them.
>
> We have SO_ATTACH_FILTER and SO_ATTACH_BPF, could also be
> analogous for fanout, if we want to be consistent with the API?
>
> But C/E prefix seems okay too, how you want ...

I don't feel very strongly, either. But CBPF/EBPF is a bit more
descriptive, so let's do that.

> Btw, in case someone sets sock_flag(sk, SOCK_FILTER_LOCKED),
> perhaps we should also apply it on fanout?

Good point. With classic bpf, packet access control is fully
enforced in per-socket filters, but playing with load balancing
filters could allow an adversary to infer some information
about the dropped packets*. With eBPF and maps, access
is even more direct. Let's support locking of fanout filters in
place.

I intend to test the existing socket flag. No need to add a
separate flag for the fanout group, as far as I can see.


(*) I noticed that a similar unintended effect also causes the
PACKET_FANOUT_LB selftest to be flaky: filters on the
sockets ensure that the test only reads expected packets.
But, all traffic makes it through packet_rcv_fanout. Packets
that are later dropped by sk_filter have already incremented
rr_cur. Worst case, with 2 sockets and each accepted packet
interleaved with a dropped packet, all packets are queued on
only one socket. Test flakiness is fixed, e.g., by running in a
private network namespace. The implementation behavior
may be unexpected in other, production, environments.