netdev - Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf

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Date:   Wed, 7 Aug 2019 06:52:36 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Song Liu <songliubraving@...com>,
        Kees Cook <keescook@...omium.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>, Jann Horn <jannh@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux API <linux-api@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf


> On Aug 7, 2019, at 2:03 AM, Lorenz Bauer <lmb@...udflare.com> wrote:
> 
>> On Wed, 7 Aug 2019 at 06:24, Andy Lutomirski <luto@...nel.org> wrote:
>> a) Those that, by design, control privileged operations.  This
>> includes most attach calls, but it also includes allow_ptr_leaks,
>> bpf_probe_read(), and quite a few other things.  It also includes all
>> of the by_id calls, I think, unless some clever modification to the
>> way they worked would isolate different users' objects.  I think that
>> persistent objects can do pretty much everything that by_id users
>> would need, so this isn't a big deal.
> 
> Slightly OT, since this is an implementation question: GET_MAP_FD_BY_ID
> is useful to iterate a nested map. This isn't covered by rights to
> persistent objects,
> so it would need some thought.
> 
> 

A call to get an fd to a map referenced by a map to which you already have an fd seems reasonable to me. The new fd would inherit the old fd’s access mode.