linux-kernel - Re: [PATCH 3/7] security,overlayfs: Provide security hook for copy up of xattrs for overlay file

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Message-ID: <20160711165659.GC7728@redhat.com>
Date:	Mon, 11 Jul 2016 12:56:59 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Stephen Smalley <sds@...ho.nsa.gov>
Cc:	miklos@...redi.hu, pmoore@...hat.com, casey@...aufler-ca.com,
	linux-kernel@...r.kernel.org, linux-unionfs@...r.kernel.org,
	linux-security-module@...r.kernel.org, dwalsh@...hat.com,
	dhowells@...hat.com, viro@...IV.linux.org.uk,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 3/7] security,overlayfs: Provide security hook for copy
 up of xattrs for overlay file

On Mon, Jul 11, 2016 at 11:31:47AM -0400, Stephen Smalley wrote:
> On 07/08/2016 12:19 PM, Vivek Goyal wrote:
> > Provide a security hook which is called when xattrs of a file are being
> > copied up. This hook is called once for each xattr and LSM can return 0
> > to access the xattr, 1 to reject xattr, -EOPNOTSUPP if none of the lsms
> > claim to know xattr and a negative error code if something went terribly
> > wrong.
> 
> 0 if the security module wants the xattr to be copied up, 1 if the
> security module wants the xattr to be discarded on the copy, -EOPNOTSUPP
> if the security module does not handle/manage the xattr, or a -errno
> upon an error.

Ok, will change the description.

> 
> > 
> > If 0 or -EOPNOTSUPP is returned, xattr will be copied up, if 1 is returned,
> > xattr will not be copied up and if negative error code is returned, copy up
> > will be aborted.
> 
> Not sure I understand the benefit of the 0 vs -EOPNOTSUPP distinction.

I am not sure either. Casey wanted to have four states so I introduced it. 

Thanks
Vivek