linux-kernel - Re: [PATCH bpf] Revert "bpf: program: Refuse non-O_RDWR flags in BPF_OBJ

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Date:   Thu, 24 Jun 2021 17:13:44 -0700
From:   Maciej Żenczykowski <zenczykowski@...il.com>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linux Network Development Mailing List 
        <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        BPF Mailing List <bpf@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Greg Kroah-Hartman <gregkh@...gle.com>
Subject: Re: [PATCH bpf] Revert "bpf: program: Refuse non-O_RDWR flags in BPF_OBJ_GET"

Reposting since apparently my reply only went to Lorenz.

On Wed, Jun 23, 2021 at 1:45 AM Lorenz Bauer <lmb@...udflare.com> wrote:
>
> On Fri, 18 Jun 2021 at 11:55, Maciej Żenczykowski
> <zenczykowski@...il.com> wrote:
> >
> > From: Maciej Żenczykowski <maze@...gle.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:frameworks/libs/net/common/native/bpf_syscall_wrappers/include/BpfSyscallWrappers.h;drc=7005c764be23d31fa1d69e826b4a2f6689a8c81e;l=124
>
> 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...??)