netdev - Re: [PATCH resend 1/2] capability: introduce sysctl for controlled user-ns capability whitelist

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Date:   Thu, 9 Nov 2017 22:30:10 -0600
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Mahesh Bandewar
         (महेश बंडेवार) <maheshb@...gle.com>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        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: [PATCH resend 1/2] capability: introduce sysctl for controlled
 user-ns capability whitelist

Quoting Mahesh Bandewar (महेश बंडेवार) (maheshb@...gle.com):
...
> >>
> >>  ==============================================================
> >>
> >> +controlled_userns_caps_whitelist
> >> +
> >> +Capability mask that is whitelisted for "controlled" user namespaces.
> >> +Any capability that is missing from this mask will not be allowed to
> >> +any process that is attached to a controlled-userns. e.g. if CAP_NET_RAW
> >> +is not part of this mask, then processes running inside any controlled
> >> +userns's will not be allowed to perform action that needs CAP_NET_RAW
> >> +capability. However, processes that are attached to a parent user-ns
> >> +hierarchy that is *not* controlled and has CAP_NET_RAW can continue
> >> +performing those actions. User-namespaces are marked "controlled" at
> >> +the time of their creation based on the capabilities of the creator.
> >> +A process that does not have CAP_SYS_ADMIN will create user-namespaces
> >> +that are controlled.
> >
> > Hm.  I think that's fine (the way 'controlled' user namespaces are
> > defined), but that is design decision in itself, and should perhaps be
> > discussed.
> >
> > Did you consider other ways?  What about using CAP_SETPCAP?
> >
> I did try other ways e.g. using another bounding-set etc. but
> eventually settled with this approach because of main two properties -

No, I meant did you try other ways of defining a controlled user
namespace, other than one which is created by a task lacking
CAP_SYS_ADMIN?

...

> >> +The value is expressed as two comma separated hex words (u32). This
> >
> > Why comma separated?  whitespace ok?  Leading 0x ok?  What is the
> > default at boot?  (Obviously the patch tells me, I'm asking for it
> > to be spelled out in the doc)
> >
> I tried multiple ways including representing capabilities in
> string/name form for better readability but didn't want to add
> additional complexities of dealing with strings and possible
> string-related-issues for this. Also didn't want to reinvent the new
> form so settled with something that is widely used (cpu
> bounding/affinity/irq mapping etc.) and is capable of handling growing
> bit set (currently 37 but possibly more later).

Ok, thanks.