linux-hardening - Re: [PATCH] capabilities: new kernel.ns_modules

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Date:   Mon, 15 Aug 2022 10:33:28 +0200
From:   Vegard Nossum <vegard.nossum@...cle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        Serge Hallyn <serge@...lyn.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        linux-hardening@...r.kernel.org, John Haxby <john.haxby@...cle.com>
Subject: Re: [PATCH] capabilities: new kernel.ns_modules_allowed sysctl


On 8/12/22 20:48, Kees Cook wrote:
> On Wed, Aug 10, 2022 at 10:25:17AM +0200, Vegard Nossum wrote:
>>
>> On 8/10/22 00:56, Kees Cook wrote:
>>> On Tue, Aug 09, 2022 at 08:52:29PM +0200, Vegard Nossum wrote:
>>>> Creating a new user namespace grants you the ability to reach a lot of code
>>>> (including loading certain kernel modules) that would otherwise be out of
>>>> reach of an attacker. We can reduce the attack surface and block exploits
>>>> by ensuring that user namespaces cannot trigger module (auto-)loading.
>>>>

[...]

> I agree, it'd be nice to have. I'm just trying to predict what kind of
> push-back there may be.
> 
> Can you address the build failures noted on the thread, and send a v2?

Did just now:

https://lore.kernel.org/all/20220815082753.6088-1-vegard.nossum@oracle.com/

> I
> note that after this patch it looks like all module loading from a userns
> gets logged, regardless of the setting. Is that intended?

Yeah, I thought it was useful to know even when the sysctl was disabled
but I've removed it in v2 so the patch is less intrusive. I guess it can
always be added later if it actually serves a purpose.

Thanks,


Vegard