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

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Date:	Tue, 12 Aug 2008 15:27:41 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Mimi Zohar <zohar@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	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,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Subject: Re: [PATCH 3/4] integrity: Linux Integrity Module(LIM)

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.  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
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