linux-kernel - Re: [PATCH 5/9] Make use of permissions, returned by kobj

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Message-Id: <1205328432.23866.233.camel@moss-spartans.epoch.ncsc.mil>
Date:	Wed, 12 Mar 2008 09:27:12 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Pavel Emelyanov <xemul@...nvz.org>, Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, menage@...gle.com,
	sukadev@...ibm.com, Al Viro <viro@...iv.linux.org.uk>,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 5/9] Make use of permissions, returned by kobj_lookup


On Wed, 2008-03-12 at 09:18 -0400, Stephen Smalley wrote:
> On Wed, 2008-03-12 at 08:09 -0500, Serge E. Hallyn wrote:
> > Quoting Pavel Emelyanov (xemul@...nvz.org):
> > > Greg KH wrote:
> > > > On Tue, Mar 11, 2008 at 12:57:55PM +0300, Pavel Emelyanov wrote:
> > > >> Besides, I've measured some things - the lat_syscall test for open from 
> > > >> lmbench test suite and the nptl perf test. Here are the results:
> > > >>
> > > >>         sec     nosec
> > > >> open    3.0980s  3.0709s
> > > >> nptl    2.7746s  2.7710s
> > > >>
> > > >> So we have 0.88% loss in open and ~0.15% with nptl. I know, this is not that
> > > >> much, but it is noticeable. Besides, this is only two tests, digging deeper
> > > >> may reveal more.
> > > > 
> > > > I think that is in the noise of sampling if you run that test many more
> > > > times.
> > > 
> > > These numbers are average values of 20 runs of each test. I didn't
> > > provide the measurement accuracy, but the abs(open.sec - open.nosec)
> > > is greater than it.
> > > 
> > > >> Let alone the fact that simply turning the CONFIG_SECURITY to 'y' puts +8Kb 
> > > >> to the vmlinux...
> > > >>
> > > >> I think, I finally agree with you and Al Viro, that the kobj mapper is 
> > > >> not the right place to put the filtering, but taking the above numbers 
> > > >> into account, can we put the "hooks" into the #else /* CONFIG_SECURITY */
> > > >> versions of security_inode_permission/security_file_permission/etc?
> > > > 
> > > > Ask the security module interface maintainers about this, not me :)
> > > 
> > > OK :) Thanks for your time, Greg.
> > > 
> > > So, Serge, since you already have a LSM-based version, maybe you can
> > > change it with the proposed "fix" and send it to LSM maintainers for
> > > review?
> > 
> > To take the point of view of someone who neither wants containers nor
> > LSM but just a fast box,
> > 
> > you're asking me to introduce LSM hooks for the !SECURITY case?  :)
> > 
> > I can give it a shot, but I expect some complaints.  Now at least the
> > _mknod hook shouldn't be a hotpath,  and I suppose I can add yet
> > an #ifdef inside the !SECURITY version of security_inode_permission().
> > I still expect some complaints though.  I'll send something soon.
> 
> Not sure I'm following the plot here, but please don't do anything that
> will prohibit the use of containers/namespaces with security modules
> like SELinux/Smack.  Yes, that's a legitimate use case, and there will
> be people who will want to do that - they serve different but
> complementary purposes (containers are _not_ a substitute for MAC).  We
> don't want them to be exclusive of one another.

Also, note that "real" device labeling and access control (i.e. bind a
label to a device in the kernel irrespective of what device node is used
to access it so that a process that can create any device nodes at all
can't effectively bypass all device access controls just by creating an
arbitrary node to any device in a type accessible to it) is already
called out on our kernel todo list for SELinux, and contributions there
would be welcome.  

-- 
Stephen Smalley
National Security Agency

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