Date: Wed, 27 Jan 2016 04:27:19 -0600 From: ebiederm@...ssion.com (Eric W. Biederman) To: Kees Cook <keescook@...omium.org> Cc: Serge Hallyn <serge.hallyn@...ntu.com>, "kernel-hardening\@lists.openwall.com" <kernel-hardening@...ts.openwall.com>, Andy Lutomirski <luto@...capital.net>, 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>, Kostya Serebryany <kcc@...gle.com>, Alexander Potapenko <glider@...gle.com>, Eric Dumazet <edumazet@...gle.com>, Sasha Levin <sasha.levin@...cle.com>, "linux-doc\@vger.kernel.org" <linux-doc@...r.kernel.org>, "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to be disabled Kees Cook <keescook@...omium.org> writes: > On Tue, Jan 26, 2016 at 9:15 AM, Serge Hallyn <serge.hallyn@...ntu.com> wrote: >> Quoting Josh Boyer (jwboyer@...oraproject.org): >>> What you're saying is true for the "oh crap" case of a new userns >>> related CVE being found. However, there is the case where sysadmins >>> know for a fact that a set of machines should not allow user >>> namespaces to be enabled. Currently they have 2 choices, 1) use their >> >> Hi - can you give a specific example of this? (Where users really should >> not be able to use them - not where they might not need them) I think >> it'll help the discussion tremendously. Because so far the only good >> arguments I've seen have been about actual bugs in the user namespaces, >> which would not warrant a designed-in permanent disable switch. If >> there are good use cases where such a disable switch will always be >> needed (and compiling out can't satisfy) that'd be helpful. > > My example is a machine in a colo rack serving web pages. A site gets > attacked, and www-data uses user namespaces to continue their attack > to gain root privileges. > > The admin of such a machine could have disabled userns months earlier > and limited the scope of the attack. Of course for the paranoid there is already a mechanism to do this. /sbin/chroot. No new user namespaces are allowed to be created inside of a chroot. Eric
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