On 15/09/2016 03:25, Andy Lutomirski wrote: > On Wed, Sep 14, 2016 at 3:11 PM, Mickaël Salaün <m...@digikod.net> wrote: >> >> On 14/09/2016 20:27, Andy Lutomirski wrote: >>> On Wed, Sep 14, 2016 at 12:24 AM, Mickaël Salaün <m...@digikod.net> wrote: >>>> Add a new flag CGRP_NO_NEW_PRIVS for each cgroup. This flag is initially >>>> set for all cgroup except the root. The flag is clear when a new process >>>> without the no_new_privs flags is attached to the cgroup. >>>> >>>> If a cgroup is landlocked, then any new attempt, from an unprivileged >>>> process, to attach a process without no_new_privs to this cgroup will >>>> be denied. >>> >>> Until and unless everyone can agree on a way to properly namespace, >>> delegate, etc cgroups, I think that trying to add unprivileged >>> semantics to cgroups is nuts. Given the big thread about cgroup v2, >>> no-internal-tasks, etc, I just don't see how this approach can be >>> viable. >> >> As far as I can tell, the no_new_privs flag of at task is not related to >> namespaces. The CGRP_NO_NEW_PRIVS flag is only a cache to quickly access >> the no_new_privs property of *tasks* in a cgroup. The semantic is unchanged. >> >> Using cgroup is optional, any task could use the seccomp-based >> landlocking instead. However, for those that want/need to manage a >> security policy in a more dynamic way, using cgroups may make sense. >> >> I though cgroup delegation was OK in the v2, isn't it the case? Do you >> have some links? >> >>> >>> Can we try to make landlock work completely independently of cgroups >>> so that it doesn't get stuck and so that programs can use it without >>> worrying about cgroup v1 vs v2, interactions with cgroup managers, >>> cgroup managers that (supposedly?) will start migrating processes >>> around piecemeal and almost certainly blowing up landlock in the >>> process, etc? >> >> This RFC handle both cgroup and seccomp approaches in a similar way. I >> don't see why building on top of cgroup v2 is a problem. Is there >> security issues with delegation? > > What I mean is: cgroup v2 delegation has a functionality problem. > Tejun says [1]: > > We haven't had to face this decision because cgroup has never properly > supported delegating to applications and the in-use setups where this > happens are custom configurations where there is no boundary between > system and applications and adhoc trial-and-error is good enough a way > to find a working solution. That wiggle room goes away once we > officially open this up to individual applications. > > Unless and until that changes, I think that landlock should stay away > from cgroups. Others could reasonably disagree with me. > > [1] https://lkml.kernel.org/r/20160909225747.ga30...@mtj.duckdns.org >
I don't get the same echo here: https://lkml.kernel.org/r/20160826155026.gd16...@mtj.duckdns.org On 26/08/2016 17:50, Tejun Heo wrote: > Please refer to "2-5. Delegation" of Documentation/cgroup-v2.txt. > Delegation on v1 is broken on both core and specific controller > behaviors and thus discouraged. On v2, delegation should work just > fine. Tejun, could you please clarify if there is still a problem with cgroup v2 delegation? This patch only implement a cache mechanism with the CGRP_NO_NEW_PRIVS flag. If cgroups can group processes correctly, I don't see any (security) issue here. It's the administrator choice to delegate a part of the cgroup management. It's then the delegatee responsibility to correctly put processes in cgroups. This is comparable to a process which is responsible to correctly call seccomp(2). Mickaël
signature.asc
Description: OpenPGP digital signature
