From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, FREEMAIL_REPLYTO_END_DIGIT,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 615B6C433FF for ; Thu, 15 Aug 2019 11:25:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0AB352064A for ; Thu, 15 Aug 2019 11:25:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=protonmail.ch header.i=@protonmail.ch header.b="EX6yYuIf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729157AbfHOLZF (ORCPT ); Thu, 15 Aug 2019 07:25:05 -0400 Received: from mail-40135.protonmail.ch ([185.70.40.135]:11257 "EHLO mail-40135.protonmail.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725875AbfHOLZF (ORCPT ); Thu, 15 Aug 2019 07:25:05 -0400 Date: Thu, 15 Aug 2019 11:24:54 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.ch; s=default; t=1565868301; bh=iAtcP7FshA2GtR0+YOCUr2f4BggVvEAXCTScdeBsrvc=; h=Date:To:From:Cc:Reply-To:Subject:In-Reply-To:References: Feedback-ID:From; b=EX6yYuIfxAu8/7RblrN9Ataw3CyhPC60P1i7RpPAEYWwjtvTkeyKzrxBDSxkEMVOG g4O0QTbSKL4QqMjkJ4VwK83123YG5yl6bLkCnl11spEFo/UPte1Ra0fB2js6OCTVSV FUWHQkrJiPxFCzWcSRaGfPcn9vJfbOV2+kiQ/Q2I= To: Alexei Starovoitov From: Jordan Glover Cc: Andy Lutomirski , Daniel Colascione , Song Liu , Kees Cook , Networking , bpf , Alexei Starovoitov , Daniel Borkmann , Kernel Team , Lorenz Bauer , Jann Horn , Greg KH , Linux API , LSM List Reply-To: Jordan Glover Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Message-ID: In-Reply-To: <20190814220545.co5pucyo5jk3weiv@ast-mbp.dhcp.thefacebook.com> References: <20190806011134.p5baub5l3t5fkmou@ast-mbp> <20190813215823.3sfbakzzjjykyng2@ast-mbp> <20190814005737.4qg6wh4a53vmso2v@ast-mbp> <20190814220545.co5pucyo5jk3weiv@ast-mbp.dhcp.thefacebook.com> Feedback-ID: QEdvdaLhFJaqnofhWA-dldGwsuoeDdDw7vz0UPs8r8sanA3bIt8zJdf4aDqYKSy4gJuZ0WvFYJtvq21y6ge_uQ==:Ext:ProtonMail MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Wednesday, August 14, 2019 10:05 PM, Alexei Starovoitov wrote: > On Wed, Aug 14, 2019 at 10:51:23AM -0700, Andy Lutomirski wrote: > > > If eBPF is genuinely not usable by programs that are not fully trusted > > by the admin, then no kernel changes at all are needed. Programs that > > want to reduce their own privileges can easily fork() a privileged > > subprocess or run a little helper to which they delegate BPF > > operations. This is far more flexible than anything that will ever be > > in the kernel because it allows the helper to verify that the rest of > > the program is doing exactly what it's supposed to and restrict eBPF > > operations to exactly the subset that is needed. So a container > > manager or network manager that drops some provilege could have a > > little bpf-helper that manages its BPF XDP, firewalling, etc > > configuration. The two processes would talk over a socketpair. > > there were three projects that tried to delegate bpf operations. > All of them failed. > bpf operational workflow is much more complex than you're imagining. > fork() also doesn't work for all cases. > I gave this example before: consider multiple systemd-like deamons > that need to do bpf operations that want to pass this 'bpf capability' > to other deamons written by other teams. Some of them will start > non-root, but still need to do bpf. They will be rpm installed > and live upgraded while running. > We considered to make systemd such centralized bpf delegation > authority too. It didn't work. bpf in kernel grows quickly. > libbpf part grows independently. llvm keeps evolving. > All of them are being changed while system overall has to stay > operational. Centralized approach breaks apart. > > > The interesting cases you're talking about really do involved > > unprivileged or less privileged eBPF, though. Let's see: > > systemd --user: systemd --user is not privileged at all. There's no > > issue of reducing privilege, since systemd --user doesn't have any > > privilege to begin with. But systemd supports some eBPF features, and > > presumably it would like to support them in the systemd --user case. > > This is unprivileged eBPF. > > Let's disambiguate the terminology. > This /dev/bpf patch set started as describing the feature as 'unprivilege= d bpf'. > I think that was a mistake. > Let's call systemd-like deamon usage of bpf 'less privileged bpf'. > This is not unprivileged. > 'unprivileged bpf' is what sysctl kernel.unprivileged_bpf_disabled contro= ls. > > There is a huge difference between the two. > I'm against extending 'unprivileged bpf' even a bit more than what it is > today for many reasons mentioned earlier. > The /dev/bpf is about 'less privileged'. > Less privileged than root. We need to split part of full root capability > into bpf capability. So that most of the root can be dropped. > This is very similar to what cap_net_admin does. > cap_net_amdin can bring down eth0 which is just as bad as crashing the bo= x. > cap_net_admin is very much privileged. Just 'less privileged' than root. > Same thing for cap_bpf. > > May be we should do both cap_bpf and /dev/bpf to make it clear that > this is the same thing. Two interfaces to achieve the same result. > systemd --user processes aren't "less privileged". The are COMPLETELY unpri= vileged. Granting them cap_bpf is the same as granting it to every other unprivilege= d user process. Also unprivileged user process can start systemd --user process wi= th any command they like. Jordan