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 10:26:29 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Miklos Szeredi <miklos@...redi.hu>
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

On Wed, 2007-04-18 at 16:03 +0200, Miklos Szeredi wrote:
> > 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.

Cheers
  Trond

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