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

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Date:   Fri, 20 Mar 2020 09:48:34 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Yonghong Song <yhs@...com>, Alexei Starovoitov <ast@...nel.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        Andrii Nakryiko <andriin@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Andrey Ignatov <rdna@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/4] xdp: Support specifying expected existing program when attaching XDP

Yonghong Song <yhs@...com> writes:

> On 3/19/20 6:13 AM, Toke Høiland-Jørgensen wrote:
>> From: Toke Høiland-Jørgensen <toke@...hat.com>
>> 
>> While it is currently possible for userspace to specify that an existing
>> XDP program should not be replaced when attaching to an interface, there is
>> no mechanism to safely replace a specific XDP program with another.
>> 
>> This patch adds a new netlink attribute, IFLA_XDP_EXPECTED_FD, which can be
>> set along with IFLA_XDP_FD. If set, the kernel will check that the program
>> currently loaded on the interface matches the expected one, and fail the
>> operation if it does not. This corresponds to a 'cmpxchg' memory operation.
>
> The patch set itself looks good to me. But previously there is a
> discussion regarding a potential similar functionality through bpf_link.
> I guess maintainers (Alexei and Daniel) need to weigh in as some
> future vision is involved.

Right, sure. See my reply to Jakub for why I went ahead with this
anyway.

-Toke