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From:   Kees Cook <keescook@chromium.org>
Date:   Tue, 13 Feb 2018 13:32:26 -0800
Message-ID: <CAGXu5jLS2dzCjZOKa-W4kUdOPoJkRAq5Rsw1t5jX99v34yaoQw@mail.gmail.com>
Subject: Re: [RFC 3/3] seccomp: add a way to get a listener fd from ptrace
To:     Tycho Andersen <tycho@tycho.ws>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Linux Containers <containers@lists.linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Oleg Nesterov <oleg@redhat.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        "Serge E . Hallyn" <serge@hallyn.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Tyler Hicks <tyhicks@canonical.com>,
        Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
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On Sun, Feb 4, 2018 at 2:49 AM, Tycho Andersen <tycho@tycho.ws> wrote:
> As an alternative to SECCOMP_FILTER_FLAG_GET_LISTENER, perhaps a ptrace()
> version which can acquire filters is useful. There are at least two reasons
> this is preferable, even though it uses ptrace:
>
> 1. You can control tasks that aren't cooperating with you
> 2. You can control tasks whose filters block sendmsg() and socket(); if the
>    task installs a filter which blocks these calls, there's no way with
>    SECCOMP_FILTER_FLAG_GET_LISTENER to get the fd out to the privileged task.

I got worried for a second that this would get us into a many-to-many
state, but I see init_listener enforces a single listener per filter.
Whew. Seems legit. :)

-Kees

-- 
Kees Cook
Pixel Security