linux-kernel - Re: [patch 0/8] unprivileged mount syscall

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Message-ID: <20070409143802.GB4891@sergelap.austin.ibm.com>
Date:	Mon, 9 Apr 2007 09:38:02 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	containers@...ts.osdl.org, util-linux-ng@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 0/8] unprivileged mount syscall

Quoting Miklos Szeredi (miklos@...redi.hu):
> > > This patchset adds support for keeping mount ownership information in
> > > the kernel, and allow unprivileged mount(2) and umount(2) in certain
> > > cases.
> > 
> > No replies, huh?
> 
> All we need is a comment from Andrew, and the replies come flooding in ;)
> 
> > My knowledge of the code which you're touching is not strong, and my spare
> > reviewing capacity is not high.  And this work does need close review by
> > people who are familar with the code which you're changing.
> > 
> > So could I suggest that you go for a dig through the git history, identify
> > some individuals who look like they know this code, then do a resend,
> > cc'ing those people?  Please also cc linux-kernel on that resend.
> 
> OK.
> 
> > > One thing that is missing from this series is the ability to restrict
> > > user mounts to private namespaces.  The reason is that private
> > > namespaces have still not gained the momentum and support needed for
> > > painless user experience.  So such a feature would not yet get enough
> > > attention and testing.  However adding such an optional restriction
> > > can be done with minimal changes in the future, once private
> > > namespaces have matured.
> > 
> > I suspect the people who developed and maintain nsproxy would disagree ;)
> 
> Well, they better show me some working and simple-to-use userspace
> code, because I've not seen anything like that related to mount
> namespaces.

If you mean to test/exploit them, see
http://lxc.sourceforge.net/patches/2.6.20/2.6.20-lxc8/broken-out/tests/

Compile the ns_exec.c program and do

	ns_exec -m /bin/sh

to get a shell in a new mounts namespace.

> pam_namespace.so is one example of a non-working, but probably-not-too-
> hard-to-fix one.

Non-working?  I sure hope the one used for LSPP certification is
working...  As is the ugly version I wrote 18 mounts ago and use on my
laptop.

> I'm just saying this is not yet something that Joe Blow would just
> enable by ticking a box in their desktop setup wizard, and it would
> all work flawlessly thereafter.  There's still a _long_ way towards
> that, and mostly in userspace.

I'm not sure there's a that long a way to go, but clearly we need to be
showing users what they can do, or they'll never work their way towards
there.

For instance, as you say, a user admin gui with a checkmark and text
boxes saying 'enter new namespace on login', 'create private /tmp',
and 'create private dmcrypted /home' would be trivial right now.

-serge
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