From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Smalley <sds@tycho.nsa.gov>
Subject: Re: [PATCH 6/7] SELinux: The copy-up operation must have read permission
 on the lower file
Date: Wed, 05 Nov 2014 11:43:21 -0500
Message-ID: <545A53A9.4060009@tycho.nsa.gov>
References: <20141105154217.2555.578.stgit@warthog.procyon.org.uk> <20141105154318.2555.7052.stgit@warthog.procyon.org.uk>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Return-path: <linux-unionfs-owner@vger.kernel.org>
Received: from emvm-gh1-uea08.nsa.gov ([63.239.67.9]:56934 "EHLO
	emvm-gh1-uea08.nsa.gov" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754749AbaKEQqv (ORCPT
	<rfc822;linux-unionfs@vger.kernel.org>);
	Wed, 5 Nov 2014 11:46:51 -0500
In-Reply-To: <20141105154318.2555.7052.stgit@warthog.procyon.org.uk>
Sender: linux-unionfs-owner@vger.kernel.org
List-Id: linux-unionfs@vger.kernel.org
To: David Howells <dhowells@redhat.com>, linux-unionfs@vger.kernel.org, selinux@tycho.nsa.gov
Cc: linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org

On 11/05/2014 10:43 AM, David Howells wrote:
> The copy-up operation must have read permission on the lower file for the task
> that caused the copy-up.  This helps prevent overlayfs from being used to
> access something it shouldn't.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> ---
> 
>  security/selinux/hooks.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index f43f07fdc028..57f9c641779f 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3144,7 +3144,8 @@ static void selinux_inode_getsecid(const struct inode *inode, u32 *secid)
>  
>  static int selinux_inode_copy_up(struct dentry *src, struct dentry *dst)
>  {
> -	return 0;
> +	const struct cred *cred = current_cred();
> +	return dentry_has_perm(cred, src, FILE__OPEN | FILE__READ);
>  }

Won't this get checked anyway when overlayfs calls vfs helpers to open
the source and those vfs helpers call the security hooks and apply the
usual checks?

Or, if not, where do you check permissions for the destination?