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From:   Kees Cook <keescook@chromium.org>
Date:   Tue, 9 Apr 2019 09:54:20 -0700
Message-ID: <CAGXu5j+hW4NPihH+LmvCRxpNdHJDh=KD=k2FtFx51Ay8=vSdgA@mail.gmail.com>
Subject: Re: [PATCH v3 bpf-next 02/21] bpf: Sysctl hook
To:     Andrey Ignatov <rdna@fb.com>
Cc:     Network Development <netdev@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Roman Gushchin <guro@fb.com>, kernel-team <kernel-team@fb.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        Jann Horn <jannh@google.com>,
        =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <mic@digikod.net>
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On Fri, Apr 5, 2019 at 12:36 PM Andrey Ignatov <rdna@fb.com> wrote:
> Containerized applications may run as root and it may create problems
> for whole host. Specifically such applications may change a sysctl and
> affect applications in other containers.
>
> Furthermore in existing infrastructure it may not be possible to just
> completely disable writing to sysctl, instead such a process should be
> gradual with ability to log what sysctl are being changed by a
> container, investigate, limit the set of writable sysctl to currently
> used ones (so that new ones can not be changed) and eventually reduce
> this set to zero.

Actual-root-in-a-container is pretty powerful. What about module
loading, or /dev files? Instead of sysctl-specific hooks, what about
VFS hooks, which would be able to cover all file-based APIs. This is
what, for example, Landlock was working on doing (also with eBPF).

-- 
Kees Cook