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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 AAABAC32753 for ; Tue, 13 Aug 2019 23:06:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 763012070D for ; Tue, 13 Aug 2019 23:06:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565737576; bh=UYu26GUQAaKNlccIn4jPZ2pz2hbDX6W5aP6WZ+L37CI=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=jQgsOA41UrndEZMr5hn6XVT0c1xn7OKeZuHaoY9BqmLShO8uTzg9R21aXgkmaQ26N 556G9IiuVjms/eBdJuzha62M0daqYAIYB7OuE+DGbD9Sf6GkCXD+VZLOZ+EIFp2VZI OTQGkWJ65BCs5quqUlUqXaRmOG1PbB+Ec5an/a9o= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727425AbfHMXGP (ORCPT ); Tue, 13 Aug 2019 19:06:15 -0400 Received: from mail.kernel.org ([198.145.29.99]:34196 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727412AbfHMXGP (ORCPT ); Tue, 13 Aug 2019 19:06:15 -0400 Received: from mail-wm1-f42.google.com (mail-wm1-f42.google.com [209.85.128.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6C26420874 for ; Tue, 13 Aug 2019 23:06:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565737573; bh=UYu26GUQAaKNlccIn4jPZ2pz2hbDX6W5aP6WZ+L37CI=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=y0d/aeA/oHe7Ek9Oh0h0yfiYACeb5Phg6xTSU1ohEkYF/bR32GSZS2EapOSxaweNi UusU+zxqOPAy6AcE5QacsqFQf8lH8PQZ4g28vhaMjjn//bb9r20NBhrO/DVTjsMK3B H6NHRXiaNrBdqOT8uleZa79VQrgww+EOSzM7Tnus= Received: by mail-wm1-f42.google.com with SMTP id i63so2811446wmg.4 for ; Tue, 13 Aug 2019 16:06:13 -0700 (PDT) X-Gm-Message-State: APjAAAXQIWVZ1ydiaFSqhv6NtYyAdvpmP7Kd+mUZv4TGHFbqskcHTV5u ESqvqP6jAyV2vOeG2K4PGGuBwllS5NFNhadojaxNdg== X-Google-Smtp-Source: APXvYqzgctiSJ0eW17obIPLwzTtaflh0LjZKHtQoMzK/pi06oFlrGOU2Do83ItsTLqtVbfPkz5Pqf+2slTU2GsNMazE= X-Received: by 2002:a7b:c4d2:: with SMTP id g18mr5105868wmk.79.1565737571802; Tue, 13 Aug 2019 16:06:11 -0700 (PDT) MIME-Version: 1.0 References: <5A2FCD7E-7F54-41E5-BFAE-BB9494E74F2D@fb.com> <20190805192122.laxcaz75k4vxdspn@ast-mbp> <20190806011134.p5baub5l3t5fkmou@ast-mbp> <20190813215823.3sfbakzzjjykyng2@ast-mbp> In-Reply-To: <20190813215823.3sfbakzzjjykyng2@ast-mbp> From: Andy Lutomirski Date: Tue, 13 Aug 2019 16:06:00 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf To: Alexei Starovoitov Cc: Andy Lutomirski , Song Liu , Kees Cook , Networking , bpf , Alexei Starovoitov , Daniel Borkmann , Kernel Team , Lorenz Bauer , Jann Horn , Greg KH , Linux API , LSM List Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Tue, Aug 13, 2019 at 2:58 PM Alexei Starovoitov wrote: > > On Tue, Aug 06, 2019 at 10:24:25PM -0700, Andy Lutomirski wrote: > > > > > > Inside containers and inside nested containers we need to start processes > > > that will use bpf. All of the processes are trusted. > > > > Trusted by whom? In a non-nested container, the container manager > > *might* be trusted by the outside world. In a *nested* container, > > unless the inner container management is controlled from outside the > > outer container, it's not trusted. I don't know much about how > > Facebook's containers work, but the LXC/LXD/Podman world is moving > > very strongly toward user namespaces and maximally-untrusted > > containers, and I think bpf() should work in that context. > > agree that containers (namespaces) reduce amount of trust necessary > for apps to run, but the end goal is not security though. > Linux has become a single user system. > If user can ssh into the host they can become root. > If arbitrary code can run on the host it will be break out of any sandbox. I would argue that this is a reasonable assumption to make if you're designing a system using Linux, but it's not a valid assumption to make as kernel developers. Otherwise we should just give everyone CAP_SYS_ADMIN and call it a day. There really is a difference between root and non-root. > Containers are not providing the level of security that is enough > to run arbitrary code. VMs can do it better, but cpu bugs don't make it easy. > Containers are used to make production systems safer. > Some people call it more 'secure', but it's clearly not secure for > arbitrary code and that is what kernel.unprivileged_bpf_disabled allows. > When we say 'unprivileged bpf' we really mean arbitrary malicious bpf program. > It's been a constant source of pain. The constant blinding, randomization, > verifier speculative analysis, all spectre v1, v2, v4 mitigations > are simply not worth it. It's a lot of complex kernel code without users. Seccomp really will want eBPF some day, and it should work without privilege. Maybe it should be a restricted subset of eBPF, and Spectre will always be an issue until dramatically better hardware shows up, but I think people will want the ability for regular programs to load eBPF seccomp programs. > Hence I prefer this /dev/bpf mechanism to be as simple a possible. > The applications that will use it are going to be just as trusted as systemd. I still don't understand your systemd example. systemd --users is not trusted systemwide in any respect. The main PID 1 systemd is root. No matter how you dice it, granting a user systemd instance extra bpf access is tantamount to granting the user extra bpf access in general. It sounds to me like you're thinking of eBPF as a feature a bit like unprivileged user namespaces: *in principle*, it's supposed to be safe to give any unprivileged process the ability to use it, and you consider security flaws in it to be bugs worth fixing. But you think it's a large attack surface and that most unprivileged programs shouldn't be allowed to use it. Is that reasonable? > > > > To solve your concern of bypassing all capable checks... > > > How about we do /dev/bpf/full_verifier first? > > > It will replace capable() checks in the verifier only. > > > > I'm not convinced that "in the verifier" is the right distinction. > > Telling administrators that some setting lets certain users bypass > > bpf() verifier checks doesn't have a clear enough meaning. > > linux is a single user system. there are no administrators any more. > No doubt, folks will disagree, but that game is over. > At least on bpf side it's done. > > > I propose, > > instead, that the current capable() checks be divided into three > > categories: > > I don't see a use case for these categories. > All bpf programs extend the kernel in some way. > The kernel vs user is one category. > Conceptually CAP_BPF is enough. It would be similar to CAP_NET_ADMIN. > When application has CAP_NET_ADMIN it covers all of networking knobs. > There is no use case that would warrant fine grain CAP_ROUTE_ADMIN, > CAP_ETHTOOL_ADMIN, CAP_ETH0_ADMIN, etc. > Similarly CAP_BPF as the only knob is enough. > The only disadvantage of CAP_BPF is that it's not possible to > pass it from one systemd-like daemon to another systemd-like daemon. > Hence /dev/bpf idea and passing file descriptor. > > > This type of thing actually fits quite nicely into an idea I've been > > thinking about for a while called "implicit rights". In very brief > > summary, there would be objects called /dev/rights/xyz, where xyz is > > the same of a "right". If there is a readable object of the right > > type at the literal path "/dev/rights/xyz", then you have right xyz. > > There's a bit more flexibility on top of this. BPF could use > > /dev/rights/bpf/maptypes/lpm and > > /dev/rights/bpf/verifier/bounded_loops, for example. Other non-BPF > > use cases include a biggie: > > /dev/rights/namespace/create_unprivileged_userns. > > /dev/rights/bind_port/80 would be nice, too. > > The concept of "implicit rights" is very nice and I'm sure it will > be a good fit somewhere, but I don't see why use it in bpf space. > There is no use case for fine grain partition of bpf features. >