From: Jordan Glover <Golden_Miller83@protonmail.ch>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>,
Daniel Colascione <dancol@google.com>,
Song Liu <songliubraving@fb.com>,
Kees Cook <keescook@chromium.org>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <Kernel-team@fb.com>,
Lorenz Bauer <lmb@cloudflare.com>, Jann Horn <jannh@google.com>,
Greg KH <gregkh@linuxfoundation.org>,
Linux API <linux-api@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf
Date: Thu, 15 Aug 2019 18:43:06 +0000 [thread overview]
Message-ID: <eHOd0IhIGMCitkKOPHlXyhVUNtZQ7lj3A1dmxkDQ2ky2tbzfAv1Yp5ZoO3fNXr3GQ3HrEiMNy_n6dncrbVkvUjakh1VCx0vi0nUkNB_PE0Q=@protonmail.ch> (raw)
In-Reply-To: <20190815172856.yoqvgu2yfrgbkowu@ast-mbp.dhcp.thefacebook.com>
On Thursday, August 15, 2019 5:28 PM, Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:
> On Thu, Aug 15, 2019 at 11:24:54AM +0000, Jordan Glover wrote:
>
> > On Wednesday, August 14, 2019 10:05 PM, Alexei Starovoitov alexei.starovoitov@gmail.com 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.
The point was that systemd will run any arbitrary command you'll throw at it and you want
to automatically attach CAP_BPF to it. AmbientCapabilities is not valid option for
systemd --user instance (otherwise it would be nuts).
I think we may have misunderstanding here. Did you mean systemd "system" service with
"User=xxx" option instead of "systemd --user" service? It would make sense then.
next prev parent reply other threads:[~2019-08-15 18:43 UTC|newest]
Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-27 20:19 [PATCH v2 bpf-next 0/4] sys_bpf() access control via /dev/bpf Song Liu
2019-06-27 20:19 ` [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access " Song Liu
2019-06-27 23:40 ` Andy Lutomirski
2019-06-27 23:42 ` Andy Lutomirski
2019-06-28 10:28 ` Christian Brauner
2019-06-28 9:05 ` Lorenz Bauer
2019-06-28 19:04 ` Song Liu
2019-06-30 0:12 ` Andy Lutomirski
2019-07-01 9:03 ` Song Liu
2019-07-02 1:59 ` Andy Lutomirski
2019-07-02 18:24 ` Kees Cook
2019-07-02 21:32 ` Andy Lutomirski
2019-07-02 23:48 ` Song Liu
2019-07-22 20:53 ` Song Liu
2019-07-23 10:45 ` Lorenz Bauer
2019-07-23 15:11 ` Andy Lutomirski
2019-07-23 22:56 ` Song Liu
2019-07-24 1:40 ` Andy Lutomirski
2019-07-24 6:30 ` Song Liu
2019-07-27 18:20 ` Song Liu
2019-07-30 5:07 ` Song Liu
2019-07-30 20:24 ` Andy Lutomirski
2019-07-31 8:10 ` Song Liu
2019-07-31 19:09 ` Andy Lutomirski
2019-08-02 7:21 ` Song Liu
2019-08-04 22:16 ` Andy Lutomirski
2019-08-05 0:08 ` Andy Lutomirski
2019-08-05 5:47 ` Andy Lutomirski
2019-08-05 7:36 ` Song Liu
2019-08-05 17:23 ` Andy Lutomirski
2019-08-05 19:21 ` Alexei Starovoitov
2019-08-05 21:25 ` Andy Lutomirski
2019-08-05 22:21 ` Andy Lutomirski
2019-08-06 1:11 ` Alexei Starovoitov
2019-08-07 5:24 ` Andy Lutomirski
2019-08-07 9:03 ` Lorenz Bauer
2019-08-07 13:52 ` Andy Lutomirski
2019-08-13 21:58 ` Alexei Starovoitov
2019-08-13 22:26 ` Daniel Colascione
2019-08-13 23:24 ` Andy Lutomirski
2019-08-13 23:06 ` Andy Lutomirski
2019-08-14 0:57 ` Alexei Starovoitov
2019-08-14 17:51 ` Andy Lutomirski
2019-08-14 22:05 ` Alexei Starovoitov
2019-08-14 22:30 ` Andy Lutomirski
2019-08-14 23:33 ` Alexei Starovoitov
2019-08-14 23:59 ` Andy Lutomirski
2019-08-15 0:36 ` Alexei Starovoitov
2019-08-15 11:24 ` Jordan Glover
2019-08-15 17:28 ` Alexei Starovoitov
2019-08-15 18:36 ` Andy Lutomirski
2019-08-15 23:08 ` Alexei Starovoitov
2019-08-16 9:34 ` Jordan Glover
2019-08-16 9:59 ` Thomas Gleixner
2019-08-16 11:33 ` Jordan Glover
2019-08-16 19:52 ` Alexei Starovoitov
2019-08-16 20:28 ` Thomas Gleixner
2019-08-17 15:02 ` Alexei Starovoitov
2019-08-17 15:44 ` Andy Lutomirski
2019-08-19 9:15 ` Thomas Gleixner
2019-08-19 17:27 ` Alexei Starovoitov
2019-08-19 17:38 ` Andy Lutomirski
2019-08-15 18:43 ` Jordan Glover [this message]
2019-08-15 19:46 ` Kees Cook
2019-08-15 23:46 ` Alexei Starovoitov
2019-08-16 0:54 ` Andy Lutomirski
2019-08-16 5:56 ` Song Liu
2019-08-16 21:45 ` Alexei Starovoitov
2019-08-16 22:22 ` Christian Brauner
2019-08-17 15:08 ` Alexei Starovoitov
2019-08-17 15:16 ` Christian Brauner
2019-08-17 15:36 ` Alexei Starovoitov
2019-08-17 15:42 ` Christian Brauner
2019-08-22 14:17 ` Daniel Borkmann
2019-08-22 15:16 ` Andy Lutomirski
2019-08-22 15:17 ` RFC: very rough draft of a bpf permission model Andy Lutomirski
2019-08-22 23:26 ` Alexei Starovoitov
2019-08-23 23:09 ` Andy Lutomirski
2019-08-26 22:36 ` Alexei Starovoitov
2019-08-27 0:05 ` Andy Lutomirski
2019-08-27 0:34 ` Alexei Starovoitov
2019-08-22 22:48 ` [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Alexei Starovoitov
2019-07-30 20:20 ` Andy Lutomirski
2019-07-31 7:44 ` Song Liu
2019-06-28 9:01 ` Lorenz Bauer
2019-06-28 19:10 ` Song Liu
2019-07-01 9:34 ` Lorenz Bauer
2019-07-02 19:22 ` Andrii Nakryiko
2019-07-03 7:28 ` Greg KH
2019-06-27 20:19 ` [PATCH v2 bpf-next 2/4] bpf: sync tools/include/uapi/linux/bpf.h Song Liu
2019-06-27 20:19 ` [PATCH v2 bpf-next 3/4] libbpf: add libbpf_[enable|disable]_sys_bpf() Song Liu
2019-06-27 20:19 ` [PATCH v2 bpf-next 4/4] bpftool: use libbpf_[enable|disable]_sys_bpf() Song Liu
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