netdev - Re: [PATCH RFC net-next 07/14] bpf: expand BPF syscall with program load/unload

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Date:	Sat, 28 Jun 2014 08:35:51 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Alexei Starovoitov <ast@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next 07/14] bpf: expand BPF syscall with program load/unload

On Sat, Jun 28, 2014 at 8:21 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Sat, Jun 28, 2014 at 12:26:14AM -0700, Alexei Starovoitov wrote:
>> On Fri, Jun 27, 2014 at 11:28 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> > On Fri, Jun 27, 2014 at 11:12 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
>> > If you want to add GPL-only functions in the future, that would be one
>> > thing.  But if someone writes a nice eBPF compiler, and someone else
>> > writes a little program that filters on network packets, I see no
>> > reason to claim that the little program is a derivative work of the
>> > kernel and therefore must be GPL.
>>
>> I think we have to draw a line somewhere. Say, tomorrow I want
>> to modify libpcap to emit eBPF based on existing tcpdump syntax.
>> Would it mean that tcpdump filter strings are GPLed? Definitely not,
>> since they existed before and can function without new libpcap.
>> But if I write a new packet filtering program in C, compile it
>> using LLVM->eBPF and call into in-kernel helper functions
>> (like bpf_map_lookup_elem()),  I think it's exactly the derivative work.
>> It's analogous to kernel modules. If module wants to call
>> export_symbol_gpl() functions, it needs to be GPLed. Here all helper
>> functions are GPL. So we just have a blank check for eBPF program.
>
> I agree, these eBFP programs should be GPL-compatible licensed as well.

I think I'd be happy with an export_symbol_gpl analogue.  I might
argue that bpf_map_lookup_elem shouldn't be gpl-only, though.
Something like "look up the uid that opened a port," on the other
hand, maybe should be.

--Andy
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