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

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Date:	Wed, 13 Aug 2008 13:03:36 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Mimi Zohar <zohar@...ibm.com>, serue@...ux.vnet.ibm.com,
	Christoph Hellwig <hch@...radead.org>,
	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Randy Dunlap <randy.dunlap@...cle.com>, safford@...son.ibm.com,
	sailer@...son.ibm.com, Stephen Smalley <sds@...ho.nsa.gov>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH 3/4] integrity: Linux Integrity Module(LIM)

On Mon, 2008-08-11 at 14:56 -0500, Serge E. Hallyn wrote: 
> Quoting Mimi Zohar (zohar@...ibm.com):
> > serue@...ux.vnet.ibm.com wrote on 08/11/2008 01:02:55 PM:
> > 
> > > Quoting Mimi Zohar (zohar@...ibm.com):
> > > > Christoph Hellwig <hch@...radead.org> wrote on 08/09/2008 02:53:40 PM:
> > > > > >  int vfs_permission(struct nameidata *nd, int mask)
> > > > > >  {
> > > > > > -   return inode_permission(nd->path.dentry->d_inode, mask);
> > > > > > +   int retval;
> > > > > > +
> > > > > > +   retval = inode_permission(nd->path.dentry->d_inode, mask);
> > > > > > +   if (retval)
> > > > > > +      return retval;
> > > > > > +   return integrity_inode_permission(NULL, &nd->path,
> > > > > > +                 mask & (MAY_READ | MAY_WRITE |
> > > > > > +                    MAY_EXEC));
> > > > > >  }
> > > > > > 
> > > > > >  /**
> > > > > > @@ -306,7 +314,14 @@ int vfs_permission(struct nameidata *nd,
> > > > > >   */
> > > > > >  int file_permission(struct file *file, int mask)
> > > > > >  {
> > > > > > -   return inode_permission(file->f_path.dentry->d_inode, mask);
> > > > > > +   int retval;
> > > > > > +
> > > > > > +   retval = inode_permission(file->f_path.dentry->d_inode, mask);
> > > > > > +   if (retval)
> > > > > > +      return retval;
> > > > > > +   return integrity_inode_permission(file, NULL,
> > > > > > +                 mask & (MAY_READ | MAY_WRITE |
> > > > > > +                    MAY_EXEC));
> > > > > 
> > > > > Please put your hook into inode_permission.  Note that in inode
> > > > > permission and lots of callers there is no path available so don't 
> > pass
> > > > > it.  Please pass the full MAY_FOO mask for new interfaces and do
> > > > > filtering that won't break if new ones are introduced.
> > > > 
> > > > We started out with the integrity_inode_permission() hook call in 
> > > > inode_permission(), but because of the removal of the nameidata 
> > > > parameter in the last merge, based on discussions
> > > > http://marc.info/?l=linux-security-module&m=121797845308246&w=2,
> > > > the call to integrity_inode_permission() was moved up to the caller,
> > > > where either a file or path are available.  Any suggestions?
> > > 
> > > Mimi, can you explain exactly (and concisely) what you are doing with
> > > the pathname?
> > 
> > IMA maintains a list of hash values of system sensitive files loaded 
> > into the run-time of the system and extends a PCR with the hash value. 
> > In order to calculate this hash value, IMA requires access to either
> > the file or the path, which currently is not accessible in 
> > inode_permission().
> 
> So the usual question is, if I've done	
> 	ln -s /etc/shadow /tmp/shadow
> will IMA do the right thing if I'm opening /tmp/shadow?  Or will it only
> catch any writes I've done the next time someone (i.e. passwd) opens
> /etc/shadow?

It will measure the right thing, as the measurement is based on the dentry
contained within the file/path structures, not names.  File names in IMA 
are only used as a hint in the measurement hash list.

Mimi

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