linux-kernel - Re: [PATCH] exit: Retain nsproxy for exit_task

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Date:   Thu, 9 Dec 2021 16:06:55 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Tejun Heo <tj@...nel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Kees Cook <keescook@...omium.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jim Newsome <jnewsome@...project.org>,
        Alexey Gladkov <legion@...nel.org>,
        Security Officers <security@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH] exit: Retain nsproxy for exit_task_work() work entries

On Thu, Dec 09, 2021 at 03:47:00PM +0100, Michal Koutný wrote:
> On Thu, Dec 09, 2021 at 03:08:26PM +0100, Christian Brauner <christian.brauner@...ntu.com> wrote:
> > send_sig() isn't used that was changed in response to a review. I'm
> > confused. 
> 
> Sorry for ambiguity, I meant this instance [1].

Sure, seems good.

> 
> > Kill and freeze only do time permission checking at open. Why would you
> > introduce another write time check?
>  
> Let's have a cgroup G with tasks t1,...,tn (run by user u) and some
> monitoring tasks m1,...,mk belonging to a different user v != u.
> 
> Currently u can kill also the tasks of v -- I'm not sure if that's
> intentional. My argument would apply if it wasn't -- it'd be suscebtible

That was discussed and is intentional and is supposed to mirror the
behavior of cgroup.freeze. Delegated killing was supposed to work and
was one use-case.