Date:   Thu, 9 Dec 2021 16:06:55 +0100
From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Michal =?utf-8?Q?Koutn=C3=BD?= <mkoutny@suse.com>
Cc:     Tejun Heo <tj@kernel.org>,
        Linus Torvalds <torvalds@linuxfoundation.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        Kees Cook <keescook@chromium.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jim Newsome <jnewsome@torproject.org>,
        Alexey Gladkov <legion@kernel.org>,
        Security Officers <security@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Jann Horn <jannh@google.com>
Subject: Re: [PATCH] exit: Retain nsproxy for exit_task_work() work entries
Message-ID: <20211209150655.zqm77gmteu436xvb@wittgenstein>
References: <20211208180501.11969-1-mkoutny@suse.com>
 <87sfv3540t.fsf@email.froward.int.ebiederm.org>
 <YbECHjMLPEHO0vqA@slm.duckdns.org>
 <CAHk-=wjcWEYSEVKvowUA0yEeDM279Zg-ptM_SsCMxmRSPJHjAw@mail.gmail.com>
 <YbEMPal0sKkk0+Tl@slm.duckdns.org>
 <YbE6yvMav5Xtp5HO@slm.duckdns.org>
 <20211209134419.GA17186@blackbody.suse.cz>
 <20211209140826.kc2xvvwxrdrwmrtj@wittgenstein>
 <20211209144700.GC63648@blackbody.suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <20211209144700.GC63648@blackbody.suse.cz>
Precedence: bulk

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@ubuntu.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.