linux-kernel - Re: [RFC] cgroups: implement device whitelist lsm (v2)

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Date:	Fri, 14 Mar 2008 08:58:17 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	James Morris <jmorris@...ei.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org, Greg KH <greg@...ah.com>,
	Stephen Smalley <sds@...ch.ncsc.mil>,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [RFC] cgroups: implement device whitelist lsm (v2)

Quoting Pavel Emelyanov (xemul@...nvz.org):
> Serge E. Hallyn wrote:
> > Quoting James Morris (jmorris@...ei.org):
> >> On Thu, 13 Mar 2008, Serge E. Hallyn wrote:
> >>
> >>> Quoting James Morris (jmorris@...ei.org):
> >>>> On Thu, 13 Mar 2008, Serge E. Hallyn wrote:
> >>>>
> >>>>> True, but while this change simplifies the code a bit, the semantics
> >>>>> seem more muddled - devcg will be enforcing when CONFIG_CGROUP_DEV=y
> >>>>> and:
> >>>>>
> >>>>> 	SECURITY=n or
> >>>>> 	rootplug is enabled
> >>>>> 	capabilities is enabled
> >>>>> 	smack is enabled
> >>>>> 	selinux+capabilities is enabled
> >>>> Well, this is how real systems are going to be deployed.
> >>> Sorry, do you mean with capabilities?
> >> Yes.
> >>
> >> All Fedora, RHEL, CentOS etc. ship with SELinux+capabilities.  I can't 
> >> imagine not enabling them on other kernels.
> >>
> >>>> It becomes confusing, IMHO, if you have to change which secondary LSM you 
> >>>> stack with SELinux to enable a cgroup feature.
> >>> So you're saying selinux without capabilities should still be able to
> >>> use dev_cgroup?  (Just making sure I understand right)
> >> Nope, SELinux always stacks with capabilities, so havng the cgroup hooks 
> >> in capabilities makes sense (rather than having us change the secondary 
> >> stacking LSM just to enable a feature).
> > 
> > Oh, ok.
> > 
> > Will let the patch stand until Pavel and Greg comment then.
> 
> Well, I saw your previous patch, that was implemented as just another
> LSM module and I liked it except for the LSM dependency.

James and Stephen agree with your LSM qualms.  I suppose we could add
cgroups next to the lsm hooks.  I suspect Paul Menage would complain
about that (Paul?), and I do think it's silly as they are security
questions, not group tracking questions, but if it's what people want
I can send out a new patch next week.

> Since this version can happily work w/o LSM, I like it too :)

In an earlier version I asked whether you had any experience with usual
# rules per container.  Do you have an idea?  Right now the whitelist is
a straight list we search through linearly.  If # rules is generally
tiny then I'm inclined to keep it that way...

thanks,
-serge
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