netdev - Re: [PATCH bpf-next 1/4] xdp: Support specifying expected existing program when attaching XDP

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Message-ID: <CAEf4BzYuxS6VEy2S9OOdmXmsg=dXU2svSqpCsNdNzGjn-AHfHg@mail.gmail.com>
Date:   Fri, 27 Mar 2020 13:10:26 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Lorenz Bauer <lmb@...udflare.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Andrey Ignatov <rdna@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/4] xdp: Support specifying expected existing
 program when attaching XDP

On Fri, Mar 27, 2020 at 9:12 AM David Ahern <dsahern@...il.com> wrote:
>
> On 3/27/20 5:06 AM, Lorenz Bauer wrote:
> > However, this behaviour concerns me. It's like Windows not
> > letting you delete a file while an application has it opened, which just leads
> > to randomly killing programs until you find the right one. It's frustrating
> > and counter productive.
> >
> > You're taking power away from the operator. In your deployment scenario
> > this might make sense, but I think it's a really bad model in general. If I am
> > privileged I need to be able to exercise that privilege. This means that if
> > there is a netdevice in my network namespace, and I have CAP_NET_ADMIN
> > or whatever, I can break the association.
> >
> > So, to be constructive: I'd prefer bpf_link to replace a netlink attachment and
> > vice versa. If you need to restrict control, use network namespaces
> > to hide the devices, instead of hiding the bpffs.
>
> I had a thought yesterday along similar lines: bpf_link is about
> ownership and preventing "accidental" deletes. What's the observability
> wrt to learning who owns a program at a specific attach point and can
> that ever be hidden.

We are talking about adding LINK_QUERY command that will return
attached BPF program and ifindex or cgroup (or whatever else) that it
is attached to.

If it's about which applications holds open FD to bpf_link, it's the
same problem as with any other FD, I'm not sure there is a
well-defined solution to this problem. Using drgn script to get this
is one possible solution that can be implemented today without
extending any of kernel APIs.