linux-kernel - Re: Potential issues (security and otherwise) with the current cgroup-bpf API

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Message-ID: <CALCETrUWhus3givcEOLxEmKhOcYGpWnuADXTJTfbVP1HcUmQQA@mail.gmail.com>
Date:   Sat, 4 Feb 2017 09:10:57 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Ahern <dsahern@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Daniel Mack <daniel@...que.org>,
        Mickaël Salaün <mic@...ikod.net>,
        Kees Cook <keescook@...omium.org>, Jann Horn <jann@...jh.net>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Graf <tgraf@...g.ch>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Linux API <linux-api@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: Potential issues (security and otherwise) with the current
 cgroup-bpf API

On Fri, Feb 3, 2017 at 3:21 PM, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> On Fri, Feb 03, 2017 at 01:07:39PM -0800, Andy Lutomirski wrote:
>>
>> Is there any plan to address this?  If not, I'll try to write that
>> patch this weekend.
>
> yes. I'm working on 'disallow program override' flag.
> It got stalled, because netns discussion got stalled.
> Later today will send a patch for dev_id+inode and
> will continue on the flag patch.
>

Would it make sense to try to document what your proposal does before
writing the code?  I don't yet see how to get semantics that are both
simple and sensible with a "disallow override" flag.

I *do* see how to get simple, sensible semantics with an approach
where all the programs in scope for the cgroup in question get called.
If needed, I can imagine a special "overridable" program that would
not be run if the socket in question is bound to a descendent cgroup
that also has an "overridable" program but would still let all the
normal hierarchical programs in scope get called.