Re: [PATCH net] net: netlink: filter particular protocols from analyzers

[David Miller <davem@davemloft.net>]

From: Daniel Borkmann <dborkman@redhat.com>
Date: Thu,  5 Sep 2013 17:48:47 +0200

> From: Daniel Borkmann <dborkmann@redhat.com>
> 
> Fix finer-grained control and let only a whitelist of allowed netlink
> protocols pass, in our case related to networking. If later on, other
> subsystems decide they want to add their protocol as well to the list
> of allowed protocols they shall simply add it. While at it, we also
> need to tell what protocol is in use otherwise BPF_S_ANC_PROTOCOL can
> not pick it up (as it's not filled out).
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>

This takes away functionality that I'd be more interesting in using,
namely being able to listen to all netlink protocols using one tap.

Seriously, when I first saw this feature, that was the first way I'd
imagine myself using it, as a tcpdump for netlink traffic, all of
it.

If I just want to hear all netlink traffic, don't make me be forced to
know every single NETLINK_* protocol value and have to open that many
sockets just to do so.

It also makes it so that I can't listen to userlevel custom netlink
protocols, another minus of filtering.

At the very least, allow an sk_protocol of zero or similar to have this
meaning of "everything".

I'm not applying this patch, sorry.