Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210618105526.265003-1-zenczykowski@gmail.com> <CACAyw9-UnQODTf+=xEmexpWE6zhYUQfp7go76bEEc_A1rAyd7Q@mail.gmail.com>
In-Reply-To: <CACAyw9-UnQODTf+=xEmexpWE6zhYUQfp7go76bEEc_A1rAyd7Q@mail.gmail.com>
From:   =?UTF-8?Q?Maciej_=C5=BBenczykowski?= <zenczykowski@gmail.com>
Date:   Thu, 24 Jun 2021 17:13:44 -0700
Message-ID: <CAHo-OoyxD=4gYvnrYPwJ_Lyb-JoR6n2Ehvrq6jKoQbmP5JJdpA@mail.gmail.com>
Subject: Re: [PATCH bpf] Revert "bpf: program: Refuse non-O_RDWR flags in BPF_OBJ_GET"
To:     Lorenz Bauer <lmb@cloudflare.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Linux Network Development Mailing List 
        <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        BPF Mailing List <bpf@vger.kernel.org>,
        "David S . Miller" <davem@davemloft.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Greg Kroah-Hartman <gregkh@google.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Reposting since apparently my reply only went to Lorenz.

On Wed, Jun 23, 2021 at 1:45 AM Lorenz Bauer <lmb@cloudflare.com> wrote:
>
> On Fri, 18 Jun 2021 at 11:55, Maciej =C5=BBenczykowski
> <zenczykowski@gmail.com> wrote:
> >
> > From: Maciej =C5=BBenczykowski <maze@google.com>
> >
> > This reverts commit d37300ed182131f1757895a62e556332857417e5.
> >
> > This breaks Android userspace which expects to be able to
> > fetch programs with just read permissions.
> >
> > See: https://cs.android.com/android/platform/superproject/+/master:fram=
eworks/libs/net/common/native/bpf_syscall_wrappers/include/BpfSyscallWrappe=
rs.h;drc=3D7005c764be23d31fa1d69e826b4a2f6689a8c81e;l=3D124
>
> As a follow up, what does Android expect to be able to do with this
> read only FD?

I'm not actually sure of all the use cases, but at a bare minimum:
We use it for iptables xt_bpf, and to attach to cgroup net hooks and
tc bpf hooks.
There's also some still incomplete support for xdp.
There's also non-networking stuff like gpu memory tracking and
tracepoints that I know very little about - probably something perf
related.
So I think the answer is that mostly we expect to be able to attach it
to places (iptables/cgroup/tc/xdp/....others...??)