linux-kernel - Re: [Devel] Re: [patch 05/10] add "permit user mounts in new namespace" clone flag

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Date:	Wed, 18 Apr 2007 17:06:33 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	trond.myklebust@....uio.no
CC:	ebiederm@...ssion.com, serue@...ibm.com, linuxram@...ibm.com,
	linux-fsdevel@...r.kernel.org, viro@....linux.org.uk,
	containers@...ts.osdl.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Devel] Re: [patch 05/10] add "permit user mounts in new
	namespace" clone flag

> > > Don't forget that almost all mount flags are per-superblock. How are you
> > > planning on dealing with the case that one user mounts a filesystem
> > > read-only, while another is trying to mount the same one read-write?
> > 
> > Yeah, I forgot, the per-mount read-only patches are not yet in.
> > 
> > That doesn't really change my agrument though.  _If_ the flag is per
> > mount, then it makes sense to be able to change it on a master and not
> > on a slave.  If mount flags are propagated, this is not possible.
> 
> Read-only isn't the only issue. On something like NFS, there are flags
> to set the security flavour, turn on/off encryption etc.
> 
> If I mount your home directory using no encryption in my namespace, for
> instance, then neither you nor the administrator will be able to turn it
> on afterwards in yours without first unmounting it from mine so that the
> superblock is destroyed.

OK, that's interesting, but I fail to grasp the relevance of this to
unprivileged mounts.

Or are you thinking of unprivileged NFS mounts?  Well, think again,
because that involves _much_ more than it seems at first glance.

Miklos
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