linux-kernel - Re: [PATCH bpf-next v2 01/28] bpf: add new is_sys_admin_prog

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Message-ID: <CAPhsuW5yitrNMvbx3s=K+a5JDrAj1=F=qWfwVLBPFn+w0EypJg@mail.gmail.com>
Date:   Mon, 7 Mar 2022 10:26:12 -0800
From:   Song Liu <song@...nel.org>
To:     Sean Young <sean@...s.org>
Cc:     Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Joe Stringer <joe@...ium.io>,
        Tero Kristo <tero.kristo@...ux.intel.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 01/28] bpf: add new is_sys_admin_prog_type() helper

On Sat, Mar 5, 2022 at 8:58 AM Sean Young <sean@...s.org> wrote:
>
> On Sat, Mar 05, 2022 at 11:07:04AM +0100, Benjamin Tissoires wrote:
> > On Sat, Mar 5, 2022 at 12:12 AM Song Liu <song@...nel.org> wrote:
> > >
> > > On Fri, Mar 4, 2022 at 9:30 AM Benjamin Tissoires
> > > <benjamin.tissoires@...hat.com> wrote:
> > > >
> > > > LIRC_MODE2 does not really need net_admin capability, but only sys_admin.
> > > >
> > > > Extract a new helper for it, it will be also used for the HID bpf
> > > > implementation.
> > > >
> > > > Cc: Sean Young <sean@...s.org>
> > > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > > >
> > > > ---
> > > >
> > > > new in v2
> > > > ---
> > > >  kernel/bpf/syscall.c | 14 +++++++++++++-
> > > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > > > index db402ebc5570..cc570891322b 100644
> > > > --- a/kernel/bpf/syscall.c
> > > > +++ b/kernel/bpf/syscall.c
> > > > @@ -2165,7 +2165,6 @@ static bool is_net_admin_prog_type(enum bpf_prog_type prog_type)
> > > >         case BPF_PROG_TYPE_LWT_SEG6LOCAL:
> > > >         case BPF_PROG_TYPE_SK_SKB:
> > > >         case BPF_PROG_TYPE_SK_MSG:
> > > > -       case BPF_PROG_TYPE_LIRC_MODE2:
> > > >         case BPF_PROG_TYPE_FLOW_DISSECTOR:
> > > >         case BPF_PROG_TYPE_CGROUP_DEVICE:
> > > >         case BPF_PROG_TYPE_CGROUP_SOCK:
> > > > @@ -2202,6 +2201,17 @@ static bool is_perfmon_prog_type(enum bpf_prog_type prog_type)
> > > >         }
> > > >  }
> > > >
> > > > +static bool is_sys_admin_prog_type(enum bpf_prog_type prog_type)
> > > > +{
> > > > +       switch (prog_type) {
> > > > +       case BPF_PROG_TYPE_LIRC_MODE2:
> > > > +       case BPF_PROG_TYPE_EXT: /* extends any prog */
> > > > +               return true;
> > > > +       default:
> > > > +               return false;
> > > > +       }
> > > > +}
> > >
> > > I am not sure whether we should do this. This is a behavior change, that may
> > > break some user space. Also, BPF_PROG_TYPE_EXT is checked in
> > > is_perfmon_prog_type(), and this change will make that case useless.
> >
> > Sure, I can drop it from v3 and make this function appear for HID only.
>
> For BPF_PROG_TYPE_LIRC_MODE2, I don't think this change will break userspace.
> This is called from ir-keytable(1) which is called from udev. It should have
> all the necessary permissions.
>
> In addition, the vast majority IR decoders are non-bpf. bpf ir decoders have
> very few users at the moment.
>
> I am working on completely new userspace tooling which will make extensive
> use of bpf ir decoding with full lircd and IRP compatibility, but this is not
> finished yet (see https://github.com/seanyoung/cir).

Thanks for these information. I guess change for BPF_PROG_TYPE_LIRC_MODE2
is ok then. Would you mind ack or review this change (either current version or
a later version)?

Thanks,
Song