netdev - Re: Clarification on bpftool dual licensing

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Message-ID: <0b80c79b-de0c-931c-262d-4da6e2add9f9@iogearbox.net>
Date:   Tue, 16 Nov 2021 11:16:50 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Martin Kelly <martin.kelly@...wdstrike.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kernel-team@...com" <kernel-team@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Andrii Nakryiko <andrii@...nel.org>
Subject: Re: Clarification on bpftool dual licensing

On 11/15/21 7:20 PM, Martin Kelly wrote:
> Hi,
> 
> I have a question regarding the dual licensing provision of bpftool. I
> understand that bpftool can be distributed as either GPL 2.0 or BSD 2-clause.
> That said, bpftool can also auto-generate BPF code that gets specified inline
> in the skeleton header file, and it's possible that the BPF code generated is
> GPL. What I'm wondering is what happens if bpftool generates GPL-licensed BPF
> code inside the skeleton header, so that you get a header like this:
> 
> something.skel.h:
> /* this file is BSD 2-clause, by nature of dual licensing */

Fwiw, the generated header contains an SPDX identifier:

  /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
  /* THIS FILE IS AUTOGENERATED! */

> /* THIS FILE IS AUTOGENERATED! */
> 
> /* standard skeleton definitions */
> 
> ...
> 
> s->data_sz = XXX;
> s->data = (void *)"\
> <eBPF bytecode, produced by GPL 2.0 sources, specified in binary>
> ";
> 
> My guess is that, based on the choice to dual-license bpftool, the header is
> meant to still be BSD 2-clause, and the s->data inline code's GPL license is
> not meant to change the licensing of the header itself, but I wanted to
> double-check, especially as I am not a lawyer. If this is indeed the intent,
> is there any opposition to a patch clarifying this more explicitly in
> Documentation/bpf/bpf_licensing.rst?

Not a lawyer either, but my interpretation is that this point related to "packaging"
of BPF programs from the bpf_licensing.rst would apply here (given this is what it
does after all):

   Packaging BPF programs with user space applications
   ===================================================

   Generally, proprietary-licensed applications and GPL licensed BPF programs
   written for the Linux kernel in the same package can co-exist because they are
   separate executable processes. This applies to both cBPF and eBPF programs.