Date: Tue, 26 Jan 2016 17:15:23 +0000 From: Serge Hallyn <serge.hallyn@...ntu.com> To: kernel-hardening@...ts.openwall.com Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Kees Cook <keescook@...omium.org>, 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>, 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> Subject: Re: Re: [PATCH 0/2] sysctl: allow CLONE_NEWUSER to be disabled Quoting Josh Boyer (jwboyer@...oraproject.org): > On Mon, Jan 25, 2016 at 11:57 PM, Eric W. Biederman > <ebiederm@...ssion.com> wrote: > > Kees Cook <keescook@...omium.org> writes: > > > >> On Mon, Jan 25, 2016 at 11:33 AM, Eric W. Biederman > >> <ebiederm@...ssion.com> wrote: > >>> Kees Cook <keescook@...omium.org> writes: > >>>> > >>>> Well, I don't know about less weird, but it would leave a unneeded > >>>> hole in the permission checks. > >>> > >>> To be clear the current patch has my: > >>> > >>> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com> > >>> > >>> The code is buggy, and poorly thought through. Your lack of interest in > >>> fixing the bugs in your patch is distressing. > >> > >> I'm not sure where you see me having a "lack of interest". The > >> existing cap-checking sysctls have a corner-case bug, which is > >> orthogonal to this change. > > > > That certainly doesn't sound like you have any plans to change anything > > there. > > > >>> So broken code, not willing to fix. No. We are not merging this sysctl. > >> > >> I think you're jumping to conclusions. :) > > > > I think I am the maintainer. > > > > What you are proposing is very much something that is only of interst to > > people who are not using user namespaces. It is fatally flawed as > > a way to avoid new attack surfaces for people who don't care as the > > sysctl leaves user namespaces enabled by default. It is fatally flawed > > as remediation to recommend to people to change if a new user namespace > > related but is discovered. Any running process that happens to be > > created while user namespace creation was enabled will continue to > > exist. Effectively a reboot will be required as part of a mitigation. > > Many sysadmins will get that wrong. > > > > I can't possibly see your sysctl as proposed achieving it's goals. A > > person has to be entirely too aware of subtlety and nuance to use it > > effectively. > > 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. thanks, -serge
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