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Date:   Thu, 8 Mar 2018 17:20:48 -0800
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     Kees Cook <keescook@chromium.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Djalal Harouni <tixxdz@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "David S. Miller" <davem@davemloft.net>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        "Luis R. Rodriguez" <mcgrof@kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, kernel-team@fb.com,
        Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH net-next] modules: allow modprobe load regular elf
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Message-ID: <20180309012046.6kcivmzzkap3a4xc@ast-mbp>
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On Fri, Mar 09, 2018 at 12:59:36AM +0000, Andy Lutomirski wrote:
> 
> Alexei, can you give an example use case?  I'm sure it's upthread
> somewhere, but I'm having trouble finding it.

at the time of iptable's setsockopt() the kernel will do
err = request_module("bpfilter");
once.
The rough POC code:
https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git/tree/net/ipv4/bpfilter/sockopt.c?h=ipt_bpf#n25

> Also, I just tested this concept a bit.  Depmod invoked explicitly on
> an ET_EXEC with a.ko extension gets mad, but depmod -a on a kernel
> that has a "module" like that seems to work fine.  Go figure.

right. that's with the current patch.
In v2 I require .modinfo section to make sure license is specified,
but depmod still not very happy:
$ depmod /lib/modules/`uname -r`/kernel/net/bpfilter/bpfilter.ko
depmod: ERROR: Bad version passed /lib/modules/4.16.0-rc4-00799-g1716f0aa3039-dirty/kernel/net/bpfilter/bpfilter.ko
I'm not sure it's worth to silence it, since
as you noticed 'depmod -a' works.