From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Date: Wed, 31 Jul 2019 12:09:27 -0700 Message-ID: References: <20190627201923.2589391-1-songliubraving@fb.com> <20190627201923.2589391-2-songliubraving@fb.com> <21894f45-70d8-dfca-8c02-044f776c5e05@kernel.org> <3C595328-3ABE-4421-9772-8D41094A4F57@fb.com> <0DE7F23E-9CD2-4F03-82B5-835506B59056@fb.com> <201907021115.DCD56BBABB@keescook> <4A7A225A-6C23-4C0F-9A95-7C6C56B281ED@fb.com> <514D5453-0AEE-420F-AEB6-3F4F58C62E7E@fb.com> <1DE886F3-3982-45DE-B545-67AD6A4871AB@amacapital.net> <7F51F8B8-CF4C-4D82-AAE1-F0F28951DB7F@fb.com> <77354A95-4107-41A7-8936-D144F01C3CA4@fb.com> <369476A8-4CE1-43DA-9239-06437C0384C7@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: Sender: netdev-owner@vger.kernel.org To: Song Liu Cc: Andy Lutomirski , Kees Cook , Networking , bpf , Alexei Starovoitov , Daniel Borkmann , Kernel Team , Lorenz Bauer , Jann Horn , Greg KH , Linux API , LSM List List-Id: linux-api@vger.kernel.org On Wed, Jul 31, 2019 at 1:10 AM Song Liu wrote: > > > > > On Jul 30, 2019, at 1:24 PM, Andy Lutomirski wrote: > > > > On Mon, Jul 29, 2019 at 10:07 PM Song Liu wrote: > >> > >> Hi Andy, > >> > >>> On Jul 27, 2019, at 11:20 AM, Song Liu wrote: > >>> > >>> Hi Andy, > >>> > >>> > > [...] > > >>> > >> > >> I would like more comments on this. > >> > >> Currently, bpf permission is more or less "root or nothing", which we > >> would like to change. > >> > >> The short term goal is to separate bpf from root, in other words, it is > >> "all or nothing". Special user space utilities, such as systemd, would > >> benefit from this. Once this is implemented, systemd can call sys_bpf() > >> when it is not running as root. > > > > As generally nasty as Linux capabilities are, this sounds like a good > > use for CAP_BPF_ADMIN. > > I actually agree CAP_BPF_ADMIN makes sense. The hard part is to make > existing tools (setcap, getcap, etc.) and libraries aware of the new CAP. It's been done before -- it's not that hard. IMO the main tricky bit would be try be somewhat careful about defining exactly what CAP_BPF_ADMIN does. > > I don't see why you need to invent a whole new mechanism for this. > > The entire cgroup ecosystem outside bpf() does just fine using the > > write permission on files in cgroupfs to control access. Why can't > > bpf() do the same thing? > > It is easier to use write permission for BPF_PROG_ATTACH. But it is > not easy to do the same for other bpf commands: BPF_PROG_LOAD and > BPF_MAP_*. A lot of these commands don't have target concept. Maybe > we should have target concept for all these commands. But that is a > much bigger project. OTOH, "all or nothing" model allows all these > commands at once. For BPF_PROG_LOAD, I admit I've never understood why permission is required at all. I think that CAP_SYS_ADMIN or similar should be needed to get is_priv in the verifier, but I think that should mainly be useful for tracing, and that requires lots of privilege anyway. BPF_MAP_* is probably the trickiest part. One solution would be some kind of bpffs, but I'm sure other solutions are possible.