netdev - Re: [PATCH bpf 1/2] bpf: enforce that struct

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Message-ID: <20210325181552.ottuv7shqgfwxlsg@kafai-mbp.dhcp.thefacebook.com>
Date:   Thu, 25 Mar 2021 11:15:52 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Clark Williams <williams@...hat.com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf 1/2] bpf: enforce that struct_ops programs be GPL-only

On Thu, Mar 25, 2021 at 04:40:33PM +0100, Toke Høiland-Jørgensen wrote:
> With the introduction of the struct_ops program type, it became possible to
> implement kernel functionality in BPF, making it viable to use BPF in place
> of a regular kernel module for these particular operations.
> 
> Thus far, the only user of this mechanism is for implementing TCP
> congestion control algorithms. These are clearly marked as GPL-only when
> implemented as modules (as seen by the use of EXPORT_SYMBOL_GPL for
> tcp_register_congestion_control()), so it seems like an oversight that this
> was not carried over to BPF implementations. And sine this is the only user
> of the struct_ops mechanism, just enforcing GPL-only for the struct_ops
> program type seems like the simplest way to fix this.
> 
> Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf")
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  kernel/bpf/verifier.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 44e4ec1640f1..48dd0c0f087c 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -12166,6 +12166,11 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env)
>  		return -ENOTSUPP;
>  	}
>  
> +	if (!prog->gpl_compatible) {
> +		verbose(env, "struct ops programs must have a GPL compatible license\n");
> +		return -EINVAL;
> +	}
> +
Thanks for the patch.

A nit.  Instead of sitting in between of the attach_btf_id check
and expected_attach_type check, how about moving it to the beginning
of this function.  Checking attach_btf_id and expected_attach_type
would make more sense to be done next to each other as in the current
code.

Acked-by: Martin KaFai Lau <kafai@...com>