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

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Date:	Mon, 16 Apr 2007 19:50:46 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	linuxram@...ibm.com
CC:	devel@...nvz.org, serue@...ibm.com, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, viro@....linux.org.uk,
	linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [Devel] Re: [patch 05/10] add "permit user mounts in new
	namespace" clone flag

> > > > > Also for bind-mount and remount operations the flag has to be propagated
> > > > > down its propagation tree.  Otherwise a unpriviledged mount in a shared
> > > > > mount wont get reflected in its peers and slaves, leading to unidentical
> > > > > shared-subtrees.
> > > > 
> > > > That's an interesting question.  Do we want shared mounts to be
> > > > totally identical, including mnt_flags?  It doesn't look as if
> > > > do_remount() guarantees that currently.
> > > 
> > > Depends on the semantics of each of the flags. Some flags like of the
> > > read/write flag, would not interfere with the propagation semantics
> > > AFAICT.  But this one certainly seems to interfere.
> > 
> > That depends.  Current patches check the "unprivileged submounts
> > allowed under this mount" flag only on the requested mount and not on
> > the propagated mounts.  Do you see a problem with this?
> 
> Don't see a problem if the flag is propagated to all peers and slave
> mounts. 
> 
> If not, I see a problem. What if the propagated mount has its flag set
> to not do un-priviledged mounts, whereas the requested mount has it
> allowed?

Then the mount is allowed.

It is up to the sysadmin/distro to design set up the propagations in a
way that this is not a problem.

I think it would be much less clear conceptually, if unprivileged
mounting would have to check propagations as well.

Miklos
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