RE: [PATCH net-next v02 1/2] af_packet: allow fanout_add when socket is not RUNNING

[Gur Stavi <gur.stavi@huawei.com>]

> 
> If we don't care about opening up fanout groups to ETH_P_NONE, then
> patch v2 seems sufficient. If explicitly blocking this, the ENXIO
> return can be added, but ideally without touching the other lines.

I don't think that allowing ETH_P_NONE is relevant.
In my opinion the 2 options that should be considered to fail
fanout_add are:
1. Testing proto == 0
2. Testing proto == 0 || ifindex == -1

The only corner case that is caught by [2] and missed by [1] is
the "unlisted" case during do_bind. It is such a rare case that
probably no one will ever encounter bind "unlisted" followed by
FANOUT_ADD. And this is not a dangerous corner case that leads to
system crash.

However, being a purist, I see the major goal of code review to promote
correctness by identifying corner cases while improving style is a
secondary priority. Since we did identify this corner case in our
discussion I think we should still use [2].
I don't consider the code complex. In fact, to me, the ifindex clause
is a more understandable direct reason for failure than the proto which
is indirect. Having the ifindex clause helps figuring out the proto
clause.