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From:   Paul Moore <paul@paul-moore.com>
Date:   Mon, 8 Aug 2022 15:16:16 -0400
Message-ID: <CAHC9VhS3udhEecVYVvHm=tuqiPGh034-xPqXYtFjBk23+p-Szg@mail.gmail.com>
Subject: Re: [PATCH v4 0/4] Introduce security_create_user_ns()
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Frederick Lawler <fred@cloudflare.com>, kpsingh@kernel.org,
        revest@chromium.org, jackmanb@chromium.org, ast@kernel.org,
        daniel@iogearbox.net, andrii@kernel.org, kafai@fb.com,
        songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com,
        jmorris@namei.org, serge@hallyn.com,
        stephen.smalley.work@gmail.com, eparis@parisplace.org,
        shuah@kernel.org, brauner@kernel.org, casey@schaufler-ca.com,
        bpf@vger.kernel.org, linux-security-module@vger.kernel.org,
        selinux@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        kernel-team@cloudflare.com, cgzones@googlemail.com,
        karl@bigbadwolfsecurity.com
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On Mon, Aug 8, 2022 at 2:56 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
> Paul Moore <paul@paul-moore.com> writes:
> > On Mon, Aug 1, 2022 at 10:56 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
> >> Frederick Lawler <fred@cloudflare.com> writes:
> >>
> >> > While creating a LSM BPF MAC policy to block user namespace creation, we
> >> > used the LSM cred_prepare hook because that is the closest hook to prevent
> >> > a call to create_user_ns().
> >>
> >> Re-nack for all of the same reasons.
> >> AKA This can only break the users of the user namespace.
> >>
> >> Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>
> >>
> >> You aren't fixing what your problem you are papering over it by denying
> >> access to the user namespace.
> >>
> >> Nack Nack Nack.
> >>
> >> Stop.
> >>
> >> Go back to the drawing board.
> >>
> >> Do not pass go.
> >>
> >> Do not collect $200.
> >
> > If you want us to take your comments seriously Eric, you need to
> > provide the list with some constructive feedback that would allow
> > Frederick to move forward with a solution to the use case that has
> > been proposed.  You response above may be many things, but it is
> > certainly not that.
>
> I did provide constructive feedback.  My feedback to his problem
> was to address the real problem of bugs in the kernel.

We've heard from several people who have use cases which require
adding LSM-level access controls and observability to user namespace
creation.  This is the problem we are trying to solve here; if you do
not like the approach proposed in this patchset please suggest another
implementation that allows LSMs visibility into user namespace
creation.

-- 
paul-moore.com