From: Andy Lutomirski <firstname.lastname@example.org> To: Alexei Starovoitov <email@example.com> Cc: Andy Lutomirski <firstname.lastname@example.org>, Daniel Colascione <email@example.com>, Song Liu <firstname.lastname@example.org>, Kees Cook <email@example.com>, Networking <firstname.lastname@example.org>, bpf <email@example.com>, Alexei Starovoitov <firstname.lastname@example.org>, Daniel Borkmann <email@example.com>, Kernel Team <Kernelfirstname.lastname@example.org>, Lorenz Bauer <email@example.com>, Jann Horn <firstname.lastname@example.org>, Greg KH <email@example.com>, Linux API <firstname.lastname@example.org>, LSM List <email@example.com> Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Date: Wed, 14 Aug 2019 15:30:51 -0700 Message-ID: <AD211133-EA60-4B91-AB1B-201713F50AB2@amacapital.net> (raw) In-Reply-To: <firstname.lastname@example.org> > On Aug 14, 2019, at 3:05 PM, Alexei Starovoitov <email@example.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. 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? > > 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. > >> Seccomp. Seccomp already uses cBPF, which is a form of BPF although >> it doesn't involve the bpf() syscall. There are some seccomp >> proposals in the works that will want some stuff from eBPF. In > > I'm afraid these proposals won't go anywhere. Can you explain why? > >> So it's a bit of a chicken-and-egg situation. There aren't major >> unprivileged eBPF users because the kernel support isn't there. > > As I said before there are zero known use cases of 'unprivileged bpf'. > > If I understand you correctly you're refusing to accept that > 'less privileged bpf' is a valid use case while pushing for extending > scope of 'unprivileged'. 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.
next prev parent reply index Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <firstname.lastname@example.org> [not found] ` <email@example.com> [not found] ` <firstname.lastname@example.org> [not found] ` <3C595328-3ABE-4421-9772-8D41094A4F57@fb.com> [not found] ` <CALCETrWBnH4Q43POU8cQ7YMjb9LioK28FDEQf7aHZbdf1eBZWg@mail.gmail.com> [not found] ` <0DE7F23E-9CD2-4F03-82B5-835506B59056@fb.com> [not found] ` <CALCETrWBWbNFJvsTCeUchu3BZJ3SH3dvtXLUB2EhnPrzFfsLNA@mail.gmail.com> [not found] ` <201907021115.DCD56BBABB@keescook> [not found] ` <CALCETrXTta26CTtEDnzvtd03-WOGdXcnsAogP8JjLkcj4-mHvg@mail.gmail.com> [not found] ` <4A7A225A-6C23-4C0F-9A95-7C6C56B281ED@fb.com> [not found] ` <CALCETrX2bMnwC6_t4b_G-hzJSfMPrkK4YKs5ebcecv2LJ0rt3w@mail.gmail.com> [not found] ` <514D5453-0AEE-420F-AEB6-3F4F58C62E7E@fb.com> [not found] ` <1DE886F3-3982-45DE-B545-67AD6A4871AB@amacapital.net> [not found] ` <7F51F8B8-CF4C-4D82-AAE1-F0F28951DB7F@fb.com> [not found] ` <77354A95-4107-41A7-8936-D144F01C3CA4@fb.com> [not found] ` <369476A8-4CE1-43DA-9239-06437C0384C7@fb.com> 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 [this message] 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 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
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