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 9E45DC3A589 for ; Thu, 15 Aug 2019 17:29:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 65B4A2064A for ; Thu, 15 Aug 2019 17:29:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="gFc99nv7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730531AbfHOR3C (ORCPT ); Thu, 15 Aug 2019 13:29:02 -0400 Received: from mail-pg1-f193.google.com ([209.85.215.193]:37772 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726203AbfHOR3C (ORCPT ); Thu, 15 Aug 2019 13:29:02 -0400 Received: by mail-pg1-f193.google.com with SMTP id d1so989421pgp.4; Thu, 15 Aug 2019 10:29:01 -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:in-reply-to:user-agent; bh=FKRKDbU9S4M5oykmChG6j3tcdYNbDh8DcchmeEeC/cM=; b=gFc99nv7p3ZVWxUmr/LNI6Qe2AMMWiYtv3qR70vS6g9di4iWwJE70RltZUXZXx4EY/ YK0FTCBv4ybf6DyPHtg2wkFOb8D/OecQxRRr6c/JdJWrZXMh3gOKb/fUq4vhVtWmic06 s4/WXyczXn1rcG2w5O+0NJqf/IhuKo9ILKiLt4/gGcuyYGQz+H2iuCUuaDxvRXlu9HFe 0/Nnp1KjEgs3Tfim6WPCh9PxjzN0oxdZWShrgigBs3HTPGtJaLzgco+XegfIz6V195e7 2lNFPG7RStnIZiwDYPlLsWh1FCfWommugB0DbnWYNarIjsLCAJolZZ2FfXHUvSXS+kZD 08nA== 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:in-reply-to:user-agent; bh=FKRKDbU9S4M5oykmChG6j3tcdYNbDh8DcchmeEeC/cM=; b=Q0Z1t+OOuL1PdQZ8SOD/zlzdv/f2a2OH9fvIbbVe6+vHTpgkuzjXeN3UybS2HZw753 SJUuRs42o2NWZtjwYmaTn0etSqwhU8aVoy16NEUjR86LtFHuW+asGbdLozyJEHIz4lpR lZHad3ADTNo+wM2U1LBijCBfs5HB4mWuD3wuUoyeC06JdBPH0KJKs+amC76FdbjfNhgq HpPlTlYaOKetyF56bq4mIUjo0+SGkyyWZuF15bga01qc7gfFfFxkZT5UzHmI2GyGcPU+ quQ9Mo8VOeSWTemcRoOLKvONbIbRWKi01wnnTUHaRhUMlqptwCrkNpHAzyAEhk+7CYx9 6qwQ== X-Gm-Message-State: APjAAAULOdwxE8Z4rfX/E5iaNQ7Kltn//KlwSpOzXxZgobNaazDrGZ+7 BarYdDtNhZ5+pRfrHjqgK14= X-Google-Smtp-Source: APXvYqwu7xZzO2Wk+NqvTdSS/nAjz6TALfbZn2ytrJWT5JTYy0nYbx3JzfquRelt3ZoUGhJ+qHAVCQ== X-Received: by 2002:a17:90a:b30e:: with SMTP id d14mr3104375pjr.26.1565890140860; Thu, 15 Aug 2019 10:29:00 -0700 (PDT) Received: from ast-mbp.dhcp.thefacebook.com ([2620:10d:c090:200::e9c1]) by smtp.gmail.com with ESMTPSA id g2sm4919678pfq.88.2019.08.15.10.28.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Aug 2019 10:28:59 -0700 (PDT) Date: Thu, 15 Aug 2019 10:28:58 -0700 From: Alexei Starovoitov To: 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 Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Message-ID: <20190815172856.yoqvgu2yfrgbkowu@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180223 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Aug 15, 2019 at 11:24:54AM +0000, Jordan Glover wrote: > 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 '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. > > > > 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 unprivileged. > Granting them cap_bpf is the same as granting it to every other unprivileged user > process. Also unprivileged user process can start systemd --user process with any > command they like. systemd itself is trusted. It's the same binary whether it runs as pid=1 or as pid=123. One of the use cases is to make IPAddressDeny= work with --user. Subset of that feature already works with AmbientCapabilities=CAP_NET_ADMIN. CAP_BPF is a natural step in the same direction.