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

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Date:   Thu, 13 Apr 2023 16:54:21 -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 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?