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

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Date:   Mon, 7 Mar 2022 10:23:36 -0800
From:   Song Liu <song@...nel.org>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     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, Sean Young <sean@...s.org>
Subject: Re: [PATCH bpf-next v2 01/28] bpf: add new is_sys_admin_prog_type() helper

On Sat, Mar 5, 2022 at 2:07 AM Benjamin Tissoires
<benjamin.tissoires@...hat.com> 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.
>
> Regarding BPF_PROG_TYPE_EXT, it was already in both
> is_net_admin_prog_type() and is_perfmon_prog_type(), so I duplicated
> it here, but I agree, given that it's already in the first function
> there, CPA_SYS_ADMIN is already checked.

I think with current code, a user with CAP_BPF, CAP_NET_ADMIN, and
CAP_PERFMON (but not CAP_SYS_ADMIN) can load programs of type
BPF_PROG_TYPE_EXT. But after the patch, the same user will not be
able to do it. Did I misread it? It is not a common case though.