linux-kernel - Re: [RFC] Add option to mount only a pids subset

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Message-ID: <20170330214523.GA13761@comp-core-i7-2640m-0182e6>
Date:   Thu, 30 Mar 2017 23:45:23 +0200
From:   Alexey Gladkov <gladkov.alexey@...il.com>
To:     Djalal Harouni <tixxdz@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Vasiliy Kulikov <segoon@...nwall.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...allels.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "Dmitry V. Levin" <ldv@...linux.org>, Jann Horn <jann@...jh.net>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>,
        Miklos Szeredi <miklos@...redi.hu>
Subject: Re: [RFC] Add option to mount only a pids subset

On Sun, Mar 26, 2017 at 09:03:33AM +0200, Djalal Harouni wrote:
> (Cc'ed Kees and Jann for the procfs stacking issue)
> 
> > I completely agree with you that it looks wrong when options of one
> > mountpoint affect the others mountpoints.
> >
> >> I'm not sure if that's the right approach, it is still buggy, however
> >> seems that your patch also stores the mount option inside the
> >> pid_namespace which may get propagated to all mounts inside same pidns
> >> ?
> >
> > I don't store 'pidonly' option in my current patch. I mean in:
> > https://lkml.org/lkml/2017/3/20/363
> >
> > I parse options twice at first mount of procfs. It happens before
> > the mounting /proc in userspace.
> >
> > I know it's bad, but I couldn't find place to store this option.
> 
> Ok, then maybe that approach of having a procfs struct holder instead
> of using pid namespace may help!

I deside to stop doing my patch. I talked with a few people and found out
that the overlayfs doesn't feel very well if on the lower level filesystem
appear/disappear files.

In addition with the pidfs isn't so simple. Separate the root will lead to
a doubling of memory consumption and restrictions on the filesystem operations
level can easily be skipped.

It means that even I can do this pidfs (or pid subset in /proc), it
will be pointless.

-- 
Rgrds, legion