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

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Date:   Thu, 19 Mar 2020 15:52:36 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     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>,
        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

On Thu, 19 Mar 2020 14:13:13 +0100 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.
> 
> A new companion flag, XDP_FLAGS_EXPECT_FD, is also added to explicitly
> request checking of the EXPECTED_FD attribute. This is needed for userspace
> to discover whether the kernel supports the new attribute.
> 
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>

I didn't know we wanted to go ahead with this...

If we do please run this thru checkpatch, set .strict_start_type, and
make the expected fd unsigned. A negative expected fd makes no sense.