linux-kernel - Re: plan9 semantics on Linux

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Message-ID: <2050418.Dl5pXkWGsk@blindfold>
Date:   Wed, 14 Feb 2018 15:19:24 +0100
From:   Richard Weinberger <richard@...ma-star.at>
To:     Enrico Weigelt <lkml@...ux.net>
Cc:     Aleksa Sarai <asarai@...e.de>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: plan9 semantics on Linux - mount namespaces

Am Mittwoch, 14. Februar 2018, 15:03:55 CET schrieb Enrico Weigelt:
> On 14.02.2018 13:53, Richard Weinberger wrote:
> > It does what you ask it for. > Also see the --setgroups switch.> AFAICT
> > --setgroups=deny is the new
> default, then your command line should just> work. Maybe your unshare
> tool is too old.
> Also doesn't help:
> 
> daemon@...habox:~ unshare -U -r --setgroups=deny
> unshare: can't open '/proc/self/setgroups': Permission denied

Works here(tm).
Can you debug it? Maybe we miss something obvious.
 
> >> What I'd like to achieve is that processes can manipulate their private
> >> >> namespace at will and mount other filesystems (primarily 9p and
> fuse).>>>> For that, I need to get rid of setuid (and per-file caps) for
> these>> private namespaces.>
> 
> > This is exactly why we have the user namespace.
> > In the user namespace you can create your own mount namespace and do
> > (almost) whatever you want.
> 
> What's the exact relation between user and mnt namespace ?
> Why do I need an own user ns for private mnt ns ? (except for the suid
> bit, which I wanna get rid of anyways).

mount related system calls are root-only. Therefore you need the user 
namespace to become a root in your own little world. :)

Thanks,
//richard

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