linux-kernel - Re: [PATCH] proc: allow killing processes via file descriptors

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Date:   Tue, 20 Nov 2018 07:21:47 +1100
From:   Aleksa Sarai <cyphar@...har.com>
To:     Daniel Colascione <dancol@...gle.com>
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Christian Brauner <christian@...uner.io>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        open list <linux-kernel@...r.kernel.org>,
        Serge Hallyn <serge@...lyn.com>, Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Tim Murray <timmurray@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Jan Engelhardt <jengelh@...i.de>,
        Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH] proc: allow killing processes via file descriptors

On 2018-11-19, Daniel Colascione <dancol@...gle.com> wrote:
> > I wonder how fast it would be holding a pid with another open()ed fd.
> > And then you need to read comm (or how you filter whom to kill).
> > It seems to me that procfs will be even slower with this safe-way.
> > But I might misunderstand the idea, excuses.
> >
> > So, I just wanted to gently remind about procfs with netlink socket[1].
> 
> We discussed netlink was extensively on the thread about
> /proc/pid/kill. For numerous reasons, it's not suitable for
> fundamental process management. We really need an FD-based interface
> to processes, just like we have FD-based interfaces to other resource
> types. We need something consistent and reliable, not an abuse of a
> monitoring interface.

Another significant problem with using netlink for something like this
is that (as its name suggest) it's tied to network namespaces and not
pid namespaces so you wouldn't reasonably be able to use the API inside
a container. Using an fd side-steps the problem somewhat (though this
just gave me an idea -- I will add it to the other thread).

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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