netdev - Re: how is the bpfilter sockopt processing supposed to work

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Message-ID: <CAADnVQ+rD+7fAsLZT4pG7AN4iO7-dQ+3adw0tBhrf8TGbtLjtA@mail.gmail.com>
Date:   Fri, 17 Jul 2020 09:13:07 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Christoph Hellwig <hch@....de>, Stanislav Fomichev <sdf@...gle.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: how is the bpfilter sockopt processing supposed to work

On Thu, Jul 16, 2020 at 10:52 PM Christoph Hellwig <hch@....de> wrote:
>
> Hi Alexei,
>
> I've just been auditing the sockopt code, and bpfilter looks really
> odd.  Both getsockopts and setsockopt eventually end up
> in__bpfilter_process_sockopt, which then passes record to the
> userspace helper containing the address of the optval buffer.
> Which depending on bpf-cgroup might be in user or kernel space.
> But even if it is in userspace it would be in a different process
> than the bpfiler helper.  What makes all this work?

Hmm. Good point. bpfilter assumes user addresses. It will break
if bpf cgroup sockopt messes with it.
We had a different issue with bpf-cgroup-sockopt and iptables in the past.
Probably the easiest way forward is to special case this particular one.
With your new series is there a way to tell in bpfilter_ip_get_sockopt()
whether addr is kernel or user? And if it's the kernel just return with error.