linux-kernel - Re: [PATCH] bpf: lirc program type should not require SYS_CAP

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Date:   Fri, 14 Apr 2023 08:39:13 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Sean Young <sean@...s.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        linux-media@...r.kernel.org
Subject: Re: [PATCH] bpf: lirc program type should not require SYS_CAP_ADMIN

On Fri, Apr 14, 2023 at 3:58 AM Sean Young <sean@...s.org> wrote:
>
> On Thu, Apr 13, 2023 at 04:54:21PM -0700, Alexei Starovoitov wrote:
> > On Thu, Apr 13, 2023 at 1:28 AM Sean Young <sean@...s.org> wrote:
> > >
> > > On Wed, Apr 12, 2023 at 04:14:05PM -0700, Alexei Starovoitov wrote:
> > > > On Tue, Apr 11, 2023 at 8:45 AM Sean Young <sean@...s.org> wrote:
> > > > >
> > > > > Make it possible to load lirc program type with just CAP_BPF.
> > > >
> > > > Is it safe?
> > > > If the user can load with just CAP_BPF the FD to the prog and target_fd
> > > > will allow attach as well.
> > >
> > > Exactly, that's the $1m question of course.
> > >
> > > I think it's safe from a lirc perspective because you need to be able to
> > > open the /dev/lirc0 device in the first place; if you can open it, you
> > > alter all sorts of lirc receiving options already. Changing the IR protocol
> > > decoder is no different in that perspective.
> > >
> > > The other side of course, is it save to load a bpf lirc program as a normal
> > > user. I don't see any issue with this; I guess this depends on whether the
> > > subset of functions in lirc_mode2_func_proto() is safe. I am hoping that
> > > the expert opinion everyone here can help answer that question.
> >
> > That part is fine under CAP_BPF.
> > I don't know how lirc devices are typically setup.
> > If they need root to open them
> > then why bother relaxing bpf loading part?
>
> I'd like to get a point where /dev/lircN can have the same permissions as
> for example /dev/videoN devices: group read/write, so that local users
> don't have to become root to use them.
>
> Without relaxing the bpf side, this seems like a chicken and egg problem
> (tiktaalik and egg?).
>
> Also - the CAP_NET_ADMIN requirement seems completely arbitrary compared
> to other program types.

Yeah. Agree. Could you respin with all these additional details
explaining the motivation and driver permission model?