netdev - Re: [PATCH net-next] modules: allow modprobe load regular elf binaries

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Date:   Tue, 6 Mar 2018 11:12:24 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     David Miller <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH net-next] modules: allow modprobe load regular elf binaries

On Mon, Mar 5, 2018 at 5:34 PM, Alexei Starovoitov <ast@...nel.org> wrote:
> As the first step in development of bpfilter project [1] the request_module()
> code is extended to allow user mode helpers to be invoked. Idea is that
> user mode helpers are built as part of the kernel build and installed as
> traditional kernel modules with .ko file extension into distro specified
> location, such that from a distribution point of view, they are no different
> than regular kernel modules. Thus, allow request_module() logic to load such
> user mode helper (umh) modules via:
[,,]

I like this, but I have one request: can we make sure that this action
is visible in the system messages?

When we load a regular module, at least it shows in lsmod afterwards,
although I have a few times wanted to really see module load as an
event in the logs too.

When we load a module that just executes a user program, and there is
no sign of it in the module list, I think we *really* need to make
that event show to the admin some way.

.. and yes, maybe we'll need to rate-limit the messages, and maybe it
turns out that I'm entirely wrong and people will hate the messages
after they get used to the concept of these pseudo-modules, but
particularly for the early implementation when this is a new thing, I
really want a message like

     executed user process xyz-abc as a pseudo-module

or something in dmesg.

I do *not* want this to be a magical way to hide things.

                  Linus