linux-kernel - Re: [PATCH 08/14] NFSv4: Add label recommended attribute and NFSv4 flags

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Date:	Fri, 03 Apr 2009 07:29:00 -0400
From:	"David P. Quigley" <dpquigl@...ho.nsa.gov>
To:	James Morris <jmorris@...ei.org>
Cc:	hch@...radead.org, viro@...iv.linux.org.uk, casey@...aufler-ca.com,
	sds@...ho.nsa.gov, "Matthew N. Dodd" <matthew.dodd@...rta.com>,
	trond.myklebust@....uio.no, bfields@...ldses.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
	labeled-nfs@...ux-nfs.org
Subject: Re: [PATCH 08/14] NFSv4: Add label recommended attribute and NFSv4
 flags

On Fri, 2009-04-03 at 19:31 +1100, James Morris wrote:
> On Wed, 26 Nov 2008, David P. Quigley wrote:
> 
> > diff --git a/include/linux/nfs4.h b/include/linux/nfs4.h
> > index ea03667..144eacf 100644
> > --- a/include/linux/nfs4.h
> > +++ b/include/linux/nfs4.h
> > @@ -21,6 +21,7 @@
> >  #define NFS4_FHSIZE		128
> >  #define NFS4_MAXPATHLEN		PATH_MAX
> >  #define NFS4_MAXNAMLEN		NAME_MAX
> > +#define NFS4_MAXLABELLEN	4096
> 
> I can't recall if this has been discussed before, but why is the label 
> length limited to this value?
> 
> SELinux on-disk labels can be up to 64KB in size (XATTR_SIZE_MAX), and I'd 
> like to ensure that we don't end up with an unnecessary disk vs. network 
> label size incompatibility.
> 
> While it seems unlikely that SELinux (and other forms of MAC) security 
> labels would currently exceed 4K, we don't know how SELinux might be 
> extended in the future, and should avoid limiting label flexibility 
> beyond existing constraints.
> 
> 
> - James

Also there is nothing in the specification that limits it to 4k. This is
a specific implementation detail of the Linux prototype and can be
changed at a later date if necessary without having to modify any
documents. 

Dave

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