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

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Mimi Zohar (zohar@us.ibm.com):
> serue@linux.vnet.ibm.com wrote on 08/11/2008 01:02:55 PM:
> 
> > Quoting Mimi Zohar (zohar@us.ibm.com):
> > > Christoph Hellwig <hch@infradead.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?

thanks,
-serge