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

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Message-ID: <CAGXu5j+B4wgT3ovynAxa1zwCeROfN5zK45tL1FUnFh0sg8M5AA@mail.gmail.com>
Date:   Thu, 8 Mar 2018 17:44:11 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Djalal Harouni <tixxdz@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        LKML <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 Thu, Mar 8, 2018 at 5:38 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Thu, Mar 8, 2018 at 4:59 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>
>> Also, I don't see how this is any more exploitable than any other
>> init_module().
>
> Absolutely. If Kees doesn't trust the files to be loaded, an
> executable - even if it's running with root privileges and in the
> initns - is still fundamentally weaker than a kernel module.
>
> So I don't understand the security argument AT ALL. It's nonsensical.
> The executable loading does all the same security checks that the
> module loading does, including the signing check.
>
> And the whole point is that we can now do things with building and
> loading a ebpf rule instead of having a full module.

My concerns are mostly about crossing namespaces. If a container
triggers an autoload, the result runs in the init_ns. So, really,
there's nothing new from my perspective, except that it's in userspace
instead of in the kernel.

Perhaps it's an orthogonal concern.

-Kees

-- 
Kees Cook
Pixel Security