netdev - Re: [PATCH nf-next] netfilter: xt

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Date:   Tue, 6 Dec 2016 00:00:55 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
        daniel@...earbox.net, Willem de Bruijn <willemb@...gle.com>,
        Florian Westphal <fw@...len.de>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH nf-next] netfilter: xt_bpf: support ebpf

On Mon, Dec 05, 2016 at 11:34:15PM +0100, Pablo Neira Ayuso wrote:
> On Mon, Dec 05, 2016 at 10:30:01PM +0100, Florian Westphal wrote:
> > Eric Dumazet <eric.dumazet@...il.com> wrote:
> > > On Mon, 2016-12-05 at 15:28 -0500, Willem de Bruijn wrote:
> > > > From: Willem de Bruijn <willemb@...gle.com>
> > > > 
> > > > Add support for attaching an eBPF object by file descriptor.
> > > > 
> > > > The iptables binary can be called with a path to an elf object or a
> > > > pinned bpf object. Also pass the mode and path to the kernel to be
> > > > able to return it later for iptables dump and save.
> > > > 
> > > > Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> > > > ---
> > > 
> > > Assuming there is no simple way to get variable matchsize in iptables,
> > > this looks good to me, thanks.
> > 
> > It should be possible by setting kernel .matchsize to ~0 which
> > suppresses strict size enforcement.
> > 
> > Its currently only used by ebt_among, but this should work for any xtables
> > module.
> 
> This is likely going to trigger a large rewrite of the core userspace
> iptables codebase, and likely going to pull part of the mess we have
> in ebtables into iptables. So I'd prefer not to follow this path.

So this variable path is there to annotate what userspace claims that
is the file that contains the bpf blob that was loaded, actually this
is irrelevant to the kernel, so this is just there to dump it back
when iptables-save it is called. Just a side note, one could set
anything there from userspace, point somewhere else actually...

Well anyway, going back to the path problem to keep it simple: Why
don't just trim this down to something smaller, are you really
expecting to reach PATH_MAX in your usecase?