Date: Mon, 8 Jan 2018 10:55:56 -0800 From: Mahesh Bandewar (महेश बंडेवार) <maheshb@...gle.com> To: "Serge E. Hallyn" <serge@...lyn.com> Cc: James Morris <james.l.morris@...cle.com>, 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>, Mahesh Bandewar <mahesh@...dewar.net> Subject: Re: [PATCHv3 0/2] capability controlled user-namespaces On Mon, Jan 8, 2018 at 10:36 AM, Serge E. Hallyn <serge@...lyn.com> wrote: > Quoting Mahesh Bandewar (महेश बंडेवार) (maheshb@...gle.com): >> On Mon, Jan 8, 2018 at 10:11 AM, Serge E. Hallyn <serge@...lyn.com> wrote: >> > Quoting Mahesh Bandewar (महेश बंडेवार) (maheshb@...gle.com): >> >> On Mon, Jan 8, 2018 at 7:47 AM, Serge E. Hallyn <serge@...lyn.com> wrote: >> >> > Quoting James Morris (james.l.morris@...cle.com): >> >> >> On Mon, 8 Jan 2018, Serge E. Hallyn wrote: >> >> >> I meant in terms of "marking" a user ns as "controlled" type -- it's >> >> >> unnecessary jargon from an end user point of view. >> >> > >> >> > Ah, yes, that was my point in >> >> > >> >> > http://lkml.iu.edu/hypermail/linux/kernel/1711.1/01845.html >> >> > and >> >> > http://lkml.iu.edu/hypermail/linux/kernel/1711.1/02276.html >> >> > >> >> >> This may happen internally but don't make it a special case with a >> >> >> different name and don't bother users with internal concepts: simply >> >> >> implement capability whitelists with the default having equivalent >> > >> > So the challenge is to have unprivileged users be contained, while >> > allowing trusted workloads in containers created by a root user to >> > bypass the restriction. >> > >> > Now, the current proposal actually doesn't support a root user starting >> > an application that it doesn't quite trust in such a way that it *is* >> > subject to the whitelist. >> >> Well, this is not hard since root process can spawn another process >> and loose privileges before creating user-ns to be controlled by the >> whitelist. > > It would have to drop cap_sys_admin for the container to be marked as > "controlled", which may prevent the container runtime from properly starting > the container. > Yes, but that's a conflict of trusted operations (that requires SYS_ADMIN) and untrusted processes it may spawn. >> You need an ability to preserve the creation of user-namespaces that >> exhibit 'the uncontrolled behavior' and only trusted/privileged (root) >> user should have it which is maintained here. >> >> > Which is unfortunate. But apart from using >> > ptags or a cgroup, I can't think of a good way to get us everything we >> > want: >> > >> > 1. unprivileged users always restricted >> > 2. existing unprivileged containers become restricted when whitelist >> > is enabled >> > 3. privileged users are able to create containers which are not restricted >> >> all this is achieved by the patch-set without any changes to the >> application with the above knob. >> >> > 4. privileged users are able to create containers which *are* restricted >> > >> With this patch-set; the root user process can fork another process >> with less privileges before creating a user-ns if the exec-ed process >> cannot be trusted. So there is a way with little modification as >> opposed to nothing available at this moment for this scenario.
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