Message-ID: <1364698027.2580.243.camel@falcor1.watson.ibm.com>
Subject: Re: [PATCH 13/14] NFSD: Server implementation of MAC Labeling
From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: David Quigley <dpquigl@davequigley.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>,
        Steve Dickson <steved@redhat.com>,
        Trond Myklebust <trond.myklebust@netapp.com>,
        "J. Bruce Fields" <bfields@redhat.com>,
        "David P. Quigley" <dpquigl@tycho.nsa.gov>,
        Linux NFS list <linux-nfs@vger.kernel.org>,
        Linux Security List <linux-security-module@vger.kernel.org>,
        SELinux List <selinux@tycho.nsa.gov>
Date: Sat, 30 Mar 2013 22:47:07 -0400
In-Reply-To: <001ff69afd411b0318d7122bf07bd218@countercultured.net>
References: <1364478845-29796-1-git-send-email-SteveD@redhat.com>
	 <1364478845-29796-14-git-send-email-SteveD@redhat.com>
	 <20130328161444.GF7080@fieldses.org> <51550C03.1000107@davequigley.com>
	 <20130329144050.GB22307@fieldses.org>
	 <001ff69afd411b0318d7122bf07bd218@countercultured.net>
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Sender: linux-nfs-owner@vger.kernel.org

On Fri, 2013-03-29 at 10:49 -0400, David Quigley wrote:
> On 03/29/2013 10:40, J. Bruce Fields wrote:
> > On Thu, Mar 28, 2013 at 11:35:31PM -0400, Dave Quigley wrote:
> >> On 3/28/2013 12:14 PM, J. Bruce Fields wrote:
> >> >On Thu, Mar 28, 2013 at 09:54:04AM -0400, Steve Dickson wrote:
> >> >>From: David Quigley <dpquigl@davequigley.com>
> >> >>
> >> >>This patch adds the ability to encode and decode file labels on 
> >> the server for
> >> >>the purpose of sending them to the client and also to process 
> >> label change
> >> >>requests from the client.
> >> >>
> >> >>Signed-off-by: Matthew N. Dodd <Matthew.Dodd@sparta.com>
> >> >>Signed-off-by: Miguel Rodel Felipe <Rodel_FM@dsi.a-star.edu.sg>
> >> >>Signed-off-by: Phua Eu Gene <PHUA_Eu_Gene@dsi.a-star.edu.sg>
> >> >>Signed-off-by: Khin Mi Mi Aung <Mi_Mi_AUNG@dsi.a-star.edu.sg>
> >> >>---
> >> >>  fs/nfsd/nfs4proc.c |  41 +++++++++++++++++++
> >> >>  fs/nfsd/nfs4xdr.c  | 116 
> >> ++++++++++++++++++++++++++++++++++++++++++++++++++---
> >> >>  fs/nfsd/nfsd.h     |   6 ++-
> >> >>  fs/nfsd/vfs.c      |  29 ++++++++++++++
> >> >>  fs/nfsd/vfs.h      |   2 +
> >> >>  fs/nfsd/xdr4.h     |   3 ++
> >> >>  6 files changed, 191 insertions(+), 6 deletions(-)
> >> >>
> >> >>diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> >> >>index ae73175..bb17589 100644
> >> >>--- a/fs/nfsd/nfs4proc.c
> >> >>+++ b/fs/nfsd/nfs4proc.c
> >> >>@@ -42,6 +42,36 @@
> >> >>  #include "current_stateid.h"
> >> >>  #include "netns.h"
> >> >>
> >> >>+#ifdef CONFIG_NFSD_V4_SECURITY_LABEL
> >> >>+#include <linux/security.h>
> >> >>+
> >> >>+static inline void
> >> >>+nfsd4_security_inode_setsecctx(struct svc_fh *resfh, struct 
> >> nfs4_label *label, u32 *bmval)
> >> >>+{
> >> >>+	struct inode *inode = resfh->fh_dentry->d_inode;
> >> >>+	int status;
> >> >>+
> >> >>+	mutex_lock(&inode->i_mutex);
> >> >>+	status = security_inode_setsecctx(resfh->fh_dentry,
> >> >>+		label->label, label->len);
> >> >>+	mutex_unlock(&inode->i_mutex);
> >> >>+
> >> >>+	if (status)
> >> >>+		/*
> >> >>+		 * We should probably fail the whole open at this point,
> >> >>+		 * but we've already created or opened the file, so it's
> >> >>+		 * too late; So this seems the least of evils:
> >> >>+		 */
> >> >>+		bmval[2] &= ~FATTR4_WORD2_SECURITY_LABEL;
> >> >
> >> >Is there any way to avoid this?
> >> >
> >> >How does the vfs open code handle this?  It has to be able to set a
> >> >security contexts atomically on open(O_CREAT), doesn't it?
> >> >
> >>
> >> I believe the way this is handled is that the inode is created and
> >> labeled and then only after that is it bound to the namespace.
> >> Because of that ordering we can fail and release the inode without
> >> it ever having a dentry in the namespace.
> >
> > Grepping around....  Looks like that's done by
> > security_inode_init_security(), from the filesystem's create method.
> >
> > So we'd need to be able to pass something down to there.
> >
> > Is the current client actually expected to use this?  (So are we 
> > going
> > to see a lot of opens that set the label?)
> >
> > --b.
> 
> I don't have all the code infront of me but we have a different hook to 
> do that. The call to nfsd4_security_inode_setsecctx is supposed to be 
> used from the setattr handlers to do the equivalent of a setxattr on the 
> file over NFS. The actual creation gets done with something like 
> security_dentry_init_security which should be in an earlier patch. I'd 
> have to look more clearly at the code to find out. 

Anytime an EVM 'protected' xattr is created/modified/deleted, EVM needs
to be called to calculate and write the 'security.evm' hmac.  It looks
like the security_inode_setsecctx() hook is missing the EVM call.
Instead of writing the LSM label, immediately followed by the EVM label,
security_inode_init_security() creates the list of xattrs to be written.
Only then, it calls the fs to write them.  I would think that
security_inode_setsecctx() would need to do something similar.

thanks,

Mimi

> Also where did we 
> come up with 128 for label length? The SELinux code assumes a starting 
> point of 255 and goes up from there as needed. The MLS policies will 
> definitely exceed a 128 byte label.