linux-kernel - Re: [PATCH v5 next 1/5] modules:capabilities: add request_module

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Date:   Wed, 29 Nov 2017 11:28:52 -0600
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Theodore Ts'o <tytso@....edu>, David Miller <davem@...emloft.net>,
        gnomes@...rguk.ukuu.org.uk, keescook@...omium.org,
        mcgrof@...nel.org, tixxdz@...il.com, luto@...nel.org,
        akpm@...ux-foundation.org, james.l.morris@...cle.com,
        ben.hutchings@...ethink.co.uk, solar@...nwall.com,
        serge@...lyn.com, jeyu@...nel.org, rusty@...tcorp.com.au,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, corbet@....net,
        mingo@...nel.org, netdev@...r.kernel.org, peterz@...radead.org,
        torvalds@...ux-foundation.org
Subject: Re: [PATCH v5 next 1/5] modules:capabilities: add
 request_module_cap()

Quoting Theodore Ts'o (tytso@....edu):
> Half the problem here is that with containers, people are changing the
> security model, because they want to let untrusted users have "root",
> without really having "root".  Part of the fundamental problem is that
> there are some well-meaning, but fundamentally misguided people, who
> have been asserting: "Containers are just as secure as VM's".
> 
> Well, they are not.  And the sooner people get past this, the better
> off they'll be....

Just to be clear, module loading requires - and must always continue to
require - CAP_SYS_MODULE against the initial user namespace.  Containers
in user namespaces do not have that.

I don't believe anyone has ever claimed that containers which are not in
a user namespace are in any way secure.

(And as for the other claim, I'd prefer to stick to "VMs are in most
cases as insecure as properly configured containers" :)

-serge