linux-kernel - Re: [PATCH 3/4] integrity: Linux Integrity Module(LIM)

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Date:	Wed, 13 Aug 2008 13:03:23 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Mimi Zohar <zohar@...ibm.com>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Al Viro <viro@...IV.linux.org.uk>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	James Morris <jmorris@...ei.org>,
	Randy Dunlap <randy.dunlap@...cle.com>, safford@...son.ibm.com,
	serue@...ux.vnet.ibm.com, sailer@...son.ibm.com
Subject: Re: [PATCH 3/4] integrity: Linux Integrity Module(LIM)

On Tue, 2008-08-12 at 16:19 -0500, Serge E. Hallyn wrote: 
> Quoting Christoph Hellwig (hch@...radead.org):
> > On Mon, Aug 11, 2008 at 12:02:55PM -0500, Serge E. Hallyn wrote:
> > > > > Sorry, but I don't think we can bloat the inode even further for this.
> > > > 
> > > > The original version of IMA was LSM based, using i_security. Based
> > > > on discussions on the LSM mailing list, it was decided that the LSM hooks
> > > > were meant only for access control.  During the same time frame, there 
> > > > was a lot of work done in stacking LSM modules and i_security, but that
> > > > approach was dropped. It was suggested that we define a separate set of
> > > > hooks for integrity, which this patch set provides. Caching integrity 
> > > > results is an important aspect. Any suggestions in lieu of defining 
> > > > i_integrity?
> > > 
> > > The i_integrity is only bloating the inode if LIM is enabled.  Surely
> > > that beats having LIM define its own hash table and locking to track
> > > integrity labels on inodes?  Do you have another suggestion?
> > > 
> > > Or is the concern about having more #ifdefs in the struct inode
> > > definition?
> > 
> > No, the concern is over bloating the inode for a rather academic fringe
> > feature.  As this comes from IBM I'm pretty sure someone will pressure
> > the big distro to turn it on.
> 
> By default??  I should hope not...
> 
> Note that these are all not loadable modules.  So presumably either it's
> in the kernel and enforcing, or it's not there.
> 
> > And inode growth is a concern for
> > fileserving or other inode heavy workload.  Mimi mentioned this is just
> > a cache of information, so consider using something like XFS's mru cache
> > which is used for something similar where the xfs_inode was kept small
> > despite a very niche feature needing a cache attached to the inode:
> > 
> > 	fs/xfs/xfs_mru_cache.c
> 
> ok, so basically as I said above
> 
> > > ... having LIM define its own hash table and locking to track
> > > integrity labels on inodes?
> 
> :)
> 
> But then that is in fact the better way to go if there can be a lot
> of inodes with i_integrity=NULL.  It looks like IMA always allocates
> something, but if I understand the idea behind templates correctly,
> that isn't necessarily always the case.
> 
> thanks,
> -serge

IMA has a two stage initialization, one at security_initcall() and 
another at late_initcall(), when the tpm is available, to make sure 
that all inode's i_integrity are allocated.  

Multiple templates can register themselves with LIM, but only one
integrity provider, such as IMA, can register itself at a time. So
hypothetically, other integrity providers could be implemented 
without a need for i_integrity.

Mimi

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