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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 AEA8CC32753 for ; Thu, 15 Aug 2019 00:36:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 704EA2133F for ; Thu, 15 Aug 2019 00:36:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="A1xFdzx3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728864AbfHOAgJ (ORCPT ); Wed, 14 Aug 2019 20:36:09 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:33297 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726490AbfHOAgI (ORCPT ); Wed, 14 Aug 2019 20:36:08 -0400 Received: by mail-pg1-f196.google.com with SMTP id n190so485575pgn.0; Wed, 14 Aug 2019 17:36:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=Ox1a+VYIewcAFQ4OELZh4Q4lPxZBMpjjQSeyyCBfAt4=; b=A1xFdzx3J2IXK/YfLZxOnTYElXzObtSe6u3KhDmJDc8TgZ+VnTSTh61oqnbyUPy+Cy lxSU8sPqGQaTsvXMI7wtAtOB0Sn7PAYrUgHtwso47YnJSvKoYnyTdq2J7aRGfMDrhUwt ImQ/5f0aeYBF4P9VrX74i1K2sPgmIeb/CqsgC8xCwJymBWzn5SaBCFA5Xqoow6Q9Px/z 7VG1XvyMm7L+ucKqVH8FYqLJg8hrjQOj/q0H8rmCSewXpul7vGKTXAEljSgTiEBnQtfW Jo3QDU/1IYquFf5cC+pqFebJOJauI0Ht+0cbnfwUOrUqas8HYYfE2/Jqz1Ey34hVxPz7 gB6w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=Ox1a+VYIewcAFQ4OELZh4Q4lPxZBMpjjQSeyyCBfAt4=; b=koMb44YADjpgWsgj8LCkZ271dQv4xFUZBYWoA6nu98MKPxnUUMFg8Vl2Zv4kW9hiMj 7p1oLu9epoy6n9b5HJTberjrBuGSWmS5oWz9IbIELruLI9wWrdo8BdVEqfUMqZ/Vkwn7 HMUhazGKAXlKS1XSoDuwzOls73yokMNbqOi+5X7bkflaOXwyn/Q9tWJXZ33eqcLu7VDX LLmq5dbqLd/QsNEsHh7Gjx7tNeL1yHcS+50KlmbV+5Pao9SiTOlV0qAkJwssDZ0U+Ek3 7tE7bYPy3XUa9rt+9M9lYiIjiaZYtlEuZvSTcnqtyWzjD7aihuiktR6Nfh3wXa3DNL8m nqAA== X-Gm-Message-State: APjAAAWOEOJeoIOGfO5eqLmvxj7QUUdVdfSADrpGcR2TtbmUsvI62Vxx kZF/Zpq5VrL5MloYipA8vZkxTEb/ X-Google-Smtp-Source: APXvYqzyqVrWOuZQ7tt8Apmsd9fEcv9DPHmv1boZGITqn9Jjg9JKSj2CKRgIubY7ay+Lz4swzKpT4A== X-Received: by 2002:a62:8281:: with SMTP id w123mr2742961pfd.36.1565829367438; Wed, 14 Aug 2019 17:36:07 -0700 (PDT) Received: from ast-mbp.dhcp.thefacebook.com ([2620:10d:c090:180::d35d]) by smtp.gmail.com with ESMTPSA id g19sm1117977pfh.27.2019.08.14.17.36.05 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Aug 2019 17:36:06 -0700 (PDT) Date: Wed, 14 Aug 2019 17:36:04 -0700 From: Alexei Starovoitov To: Andy Lutomirski 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 Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Message-ID: <20190815003602.yp3udcr5mtgw6qrv@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> <20190814233335.37t4zfsiswrpd4d6@ast-mbp.dhcp.thefacebook.com> <317422C3-ACE3-42A7-A287-7B8FEE12E33A@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <317422C3-ACE3-42A7-A287-7B8FEE12E33A@amacapital.net> User-Agent: NeoMutt/20180223 Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Aug 14, 2019 at 04:59:18PM -0700, Andy Lutomirski wrote: > > > > On Aug 14, 2019, at 4:33 PM, Alexei Starovoitov wrote: > > > >> On Wed, Aug 14, 2019 at 03:30:51PM -0700, Andy Lutomirski wrote: > >> > >> > >>>> On Aug 14, 2019, at 3:05 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 'unprivileged 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 controls. > >>> > >>> 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 box. > >>> cap_net_admin is very much privileged. Just 'less privileged' than root. > >>> Same thing for cap_bpf. > >> > >> The new pseudo-capability in this patch set is absurdly broad. I’ve proposed some finer-grained divisions in this thread. Do you have comments on them? > > > > Initially I agreed that it's probably too broad, but then realized > > that they're perfect as-is. There is no need to partition further. > > > >>> 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. > >> > >> What for? If there’s a CAP_BPF, then why do you want /dev/bpf? Especially if you define it to do the same thing. > > > > Indeed, ambient capabilities should work for all cases. > > > >> No, I’m not. I have no objection at all if you try to come up with a clear definition of what the capability checks do and what it means to grant a new permission to a task. Changing *all* of the capable checks is needlessly broad. > > > > There are not that many bits left. I prefer to consume single CAP_BPF bit. > > All capable(CAP_SYS_ADMIN) checks in kernel/bpf/ will become CAP_BPF. > > This is no-brainer. > > > > The only question is whether few cases of CAP_NET_ADMIN in kernel/bpf/ > > should be extended to CAP_BPF or not. > > imo devmap and xskmap can stay CAP_NET_ADMIN, > > but cgroup bpf attach/detach should be either CAP_NET_ADMIN or CAP_BPF. > > Initially cgroup-bpf hooks were limited to networking. > > It's no longer the case. Requiring NET_ADMIN there make little sense now. > > > > Cgroup bpf attach/detach, with the current API, gives very strong control over the whole system, and it will just get stronger as bpf gains features. Making it CAP_BPF means that you will never have the ability to make CAP_BPF safe to give to anything other than an extremely highly trusted process. Unsafe pointers are similar. 'never to less trusted process' ? why do you think so? I don't see a problem adding /dev/bpf/foo in the future and make things more granular. There is no such use case today. Hence I don't want to spend time and design something without clear use case in mind. > Do new programs really need the by_id calls? yes. Lorenz gave an example earlier. map-in-map returns map_id. To operate on that map by_id is needed.