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 D05DEC32753 for ; Wed, 14 Aug 2019 23:33:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 95B6F216F4 for ; Wed, 14 Aug 2019 23:33:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="UG9NeAbi" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729001AbfHNXdm (ORCPT ); Wed, 14 Aug 2019 19:33:42 -0400 Received: from mail-pl1-f195.google.com ([209.85.214.195]:39361 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728370AbfHNXdm (ORCPT ); Wed, 14 Aug 2019 19:33:42 -0400 Received: by mail-pl1-f195.google.com with SMTP id z3so310134pln.6; Wed, 14 Aug 2019 16:33:41 -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=64YfvXkywFPm4ZCDH4Fs38E0TxCDMFv/QZ/yXhaRRg4=; b=UG9NeAbiYSVNURFY+JehQV9hg9+mjf3EwuyoyPZ36gfjXx4/NkDW1cRGhBQx4CGVUA qjSzPtNklsZ4xk800TG66QV7/JuiaraofYRu7ZnOirM0IjuvehMLEMF7ISNAqI7JpybR q2CBWG/X0uZP9Y+VrPIQk1xarSpG1JXofPoj3zbOiwKHikWSKmVpkUzhU77fEIewftvz CY0VFN366abCqK3sQTjK/Q5Dk8wi6lVlfePG+AH2KW0+r4eDnRX9aaVKxL+Tf+BcXf4h vx+F4YpLbhXHlkMyVFvR98/igIivtWuPn5idjmfWf6rVKRy+G45zpR0gIKtN8kw8IUa4 KOVQ== 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=64YfvXkywFPm4ZCDH4Fs38E0TxCDMFv/QZ/yXhaRRg4=; b=J0wr8ajk+Nw/DzgFRam9krRH7sITZskFewxQQ49No/8tiAcf3RZxLOWYc+tcj7TKMO 2b4IbjX/DXBfk3DRpwTPEImXbloLzGIQM1F1tER/bMAeAHzF5oPnXqB9oh6KStr55s9l M3abYpS6H2NCXcCsPgufpSkpaRLfUTei/FmZnc6G2IbIL0rga2ctDPqtdRUz2oTLt2mz 7gQxNChYSyD/mleAK9ewN4JzGyci8iHf2W939XcoEpBt/btcI8VKkIbRah0AW1Sv+/Nt rIgF2dDiW5R0AAbICu6Q8S23eE7nB+cPas7up5AkGQyblDduWfUX0azMKEdo0POm83AC EkHA== X-Gm-Message-State: APjAAAWP1gDg6p3x4+huDpH/sfsIVpjzsxK513/811UFSHkLQRzQe/uP 47dM1BlyeOOnc4a0n5TZF88= X-Google-Smtp-Source: APXvYqxjcW3PLBW7DtqzQYovP9O02ccLCvToCZEM0WdTU7mTjM7fpQdxXi2d10oAzZzXC8NodVAUig== X-Received: by 2002:a17:902:b605:: with SMTP id b5mr1720031pls.103.1565825620989; Wed, 14 Aug 2019 16:33:40 -0700 (PDT) Received: from ast-mbp.dhcp.thefacebook.com ([2620:10d:c090:180::d35d]) by smtp.gmail.com with ESMTPSA id q13sm994117pfl.124.2019.08.14.16.33.39 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Aug 2019 16:33:40 -0700 (PDT) Date: Wed, 14 Aug 2019 16:33:38 -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: <20190814233335.37t4zfsiswrpd4d6@ast-mbp.dhcp.thefacebook.com> References: <20190805192122.laxcaz75k4vxdspn@ast-mbp> <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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: NeoMutt/20180223 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: 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.