Date: Mon, 25 Jan 2016 10:51:49 -0800 From: Kees Cook <keescook@...omium.org> To: Andy Lutomirski <luto@...capital.net> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Andrew Morton <akpm@...ux-foundation.org>, Al Viro <viro@...iv.linux.org.uk>, Richard Weinberger <richard@....at>, Robert Święcki <robert@...ecki.net>, Dmitry Vyukov <dvyukov@...gle.com>, David Howells <dhowells@...hat.com>, Miklos Szeredi <mszeredi@...e.cz>, Kostya Serebryany <kcc@...gle.com>, Alexander Potapenko <glider@...gle.com>, Eric Dumazet <edumazet@...gle.com>, Sasha Levin <sasha.levin@...cle.com>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to be disabled On Sun, Jan 24, 2016 at 2:22 PM, Andy Lutomirski <luto@...capital.net> wrote: > On Fri, Jan 22, 2016 at 7:02 PM, Eric W. Biederman > <ebiederm@...ssion.com> wrote: >> Kees Cook <keescook@...omium.org> writes: >> >>> There continues to be unexpected side-effects and security exposures >>> via CLONE_NEWUSER. For many end-users running distro kernels with >>> CONFIG_USER_NS enabled, there is no way to disable this feature when >>> desired. As such, this creates a sysctl to restrict CLONE_NEWUSER so >>> admins not running containers or Chrome can avoid the risks of this >>> feature. >> >> I don't actually think there do continue to be unexpected side-effects >> and security exposures with CLONE_NEWUSER. It takes a while for all of >> the fixes to trickle out to distros. At most what I have seen recently >> are problems with other kernel interfaces being amplified with user >> namespaces. AKA the current mess with devpts, and the unexpected >> issues with bind mounts in mount namespaces. >> > >> >> So to keep this productive. Please tell me about the threat model >> you envision, and how you envision knobs in the kernel being used to >> counter those threats. > > I consider the ability to use CLONE_NEWUSER to acquire CAP_NET_ADMIN > over /any/ network namespace and to thus access the network > configuration API to be a huge risk. For example, unprivileged users > can program iptables. I'll eat my hat if there are no privilege > escalations in there. (They can't request module loading, but still.) Should I consider this an Ack for the patch? :) -Kees -- Kees Cook Chrome OS & Brillo Security
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