linux-kernel - Re: [kernel-hardening] [PATCH 0/2] capability controlled user-namespaces

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Message-ID: <CAF2d9jgkKtKUnO6vH1QNLynQs5rh3rhHOFSA9gVNo4KRnBdECg@mail.gmail.com>
Date:   Thu, 19 Oct 2017 09:15:06 -0700
From:   Mahesh Bandewar (महेश बंडेवार) 
        <maheshb@...gle.com>
To:     "Serge E. Hallyn" <serge@...lyn.com>
Cc:     Mahesh Bandewar <mahesh@...dewar.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        Kernel-hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [kernel-hardening] [PATCH 0/2] capability controlled user-namespaces

On Mon, Oct 2, 2017 at 11:12 AM, Mahesh Bandewar (महेश बंडेवार)
<maheshb@...gle.com> wrote:
> On Mon, Oct 2, 2017 at 10:14 AM, Serge E. Hallyn <serge@...lyn.com> wrote:
>> Quoting Mahesh Bandewar (mahesh@...dewar.net):
>>> From: Mahesh Bandewar <maheshb@...gle.com>
>>>
>>> [Same as the previous RFC series sent on 9/21]
>>>
>>> TL;DR version
>>> -------------
>>> Creating a sandbox environment with namespaces is challenging
>>> considering what these sandboxed processes can engage into. e.g.
>>> CVE-2017-6074, CVE-2017-7184, CVE-2017-7308 etc. just to name few.
>>> Current form of user-namespaces, however, if changed a bit can allow
>>> us to create a sandbox environment without locking down user-
>>> namespaces.
>>>
>>> Detailed version
>>> ----------------
>>
>> Hi,
>>
>> still struggling with how I feel about the idea in general.
>>
>> So is the intent mainly that if/when there comes an 0-day which allows
>> users with CAP_NET_ADMIN in any namespace to gain privilege on the host,
>> then this can be used as a stop-gap measure until there is a proper fix?
>>
> Thank for looking at this Serge.
>
> Yes, but at the same time it's not just limited to NET_ADMIN but could
> be any of the current capabilities.
>
>> Otherwise, do you have any guidance for how people should use this?
>>
>> IMO it should be heavily discouraged to use this tool as a regular
>> day to day configuration, as I'm not sure there is any "educated"
>> decision to be made, even by those who are in the know, about what
>> to put in this set.
>>
> I think that really depends on the environment. e.g. in certain
> sandboxes third-part / semi-trusted workload is executed where network
> resource is not used. In that environment I can easily take off
> NET_ADMIN and NET_RAW without affecting anything there. At the same
> time I wont have to worry about 0-day related to these two
> capabilities. I would say the Admins at these places are in the best
> place to decide what they can take-off safely and what they cannot.
> Even if they decide not to take-off anything, having a tool at hand to
> gain control is important when the next 0-day strikes us that can be
> exploited using any of the currently used capabilities.
>
> However, you are absolutely right in terms of using it as a stop-gap
> measure to protect environment until it's fixed and the capability in
> question can not be safely taken off permanently without hampering
> operations.
>
> thanks,
> --mahesh..
>
> [...]

friendly ping.