Date:	Tue, 24 Feb 2009 18:36:59 -0500
From:	Paul Moore <paul.moore@...com>
To:	etienne <etienne.basset@...ericable.fr>
Cc:	Casey Schaufler <casey@...aufler-ca.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH][SMACK] add a socket_post_accept hook to fix netlabel issues with labeled TCP servers V1

On Tuesday 24 February 2009 05:59:59 pm etienne wrote:
> Paul Moore wrote:
> > On Tuesday 24 February 2009 05:20:42 pm etienne wrote:
> >> Paul Moore wrote:
> >>> On Tuesday 24 February 2009 04:28:24 pm etienne wrote:
> >>>>  /**
> >>>> + * smack_socket_post_access - post access check
> >>>> + * @sock: the socket
> >>>> + * @newsock : the grafted sock
> >>>> + *
> >>>> + * we have to match client IP against smack_host_label()
> >>>> + */
> >>>> +static void  smack_socket_post_accept(struct socket *sock, struct
> >>>> socket *newsock) +{
> >>>> +	char *hostsp;
> >>>> +	struct sockaddr_storage address;
> >>>> +	struct sockaddr_in *sin;
> >>>> +	struct sockaddr_in6 *sin6;
> >>>> +	struct in6_addr *addr6;
> >>>> +	struct socket_smack *ssp = newsock->sk->sk_security;
> >>>> +	int len;
> >>>> +
> >>>> +	if (sock->sk == NULL)
> >>>> +		return;
> >>>> +
> >>>> +	/* sockets can listen on both IPv4 & IPv6,
> >>>> +	   and fallback to V4 if client is V4 */
> >>>> +	if  (newsock->sk->sk_family != AF_INET && newsock->sk->sk_family !=
> >>>> AF_INET6) +		return;
> >>>> +
> >>>> +	/* get the client IP address **/
> >>>> +	newsock->ops->getname(newsock, (struct sockaddr *)&address, &len,
> >>>> 2); +
> >>>> +	switch (newsock->sk->sk_family) {
> >>>> +	case AF_INET:
> >>>> +		sin = (struct sockaddr_in *)&address;
> >>>> +		break;
> >>>> +	case AF_INET6:
> >>>> +		sin6  = (struct sockaddr_in6 *)&address;
> >>>> +		addr6 = &sin6->sin6_addr;
> >>>> +		/* if a V4 client connects to a V6 listening server,
> >>>> +		 * we will get a IPV6_ADDR_MAPPED mapped address here
> >>>> +		 * we have to handle this case too
> >>>> +		 * the test below is ipv6_addr_type()== IPV6_ADDR_MAPPED
> >>>> +		 * without the requirement to have IPv6 compiled in
> >>>> +		 */
> >>>> +		if ((addr6->s6_addr32[0] | addr6->s6_addr32[1]) == 0 &&
> >>>> +				addr6->s6_addr32[2] == htonl(0x0000ffff)) {
> >>>> +			__be32 addr = sin6->sin6_addr.s6_addr32[3];
> >>>> +			__be16 port = sin6->sin6_port;
> >>>> +			sin = (struct sockaddr_in *)&address;
> >>>> +			sin->sin_family = AF_INET;
> >>>> +			sin->sin_port = port;
> >>>> +			sin->sin_addr.s_addr = addr;
> >>>> +		} else {
> >>>> +			/* standard IPv6, we'll send unlabeled */
> >>>> +			smack_netlabel(newsock->sk, SMACK_UNLABELED_SOCKET);
> >>>> +			return;
> >>>> +		}
> >>>> +		break;
> >>>> +	default:
> >>>> +		/** not possible to be there **/
> >>>> +		return;
> >>>> +	}
> >>>> +	/* so, is there a label for the source IP **/
> >>>> +	hostsp = smack_host_label(sin);
> >>>> +
> >>>> +	if (hostsp == NULL) {
> >>>> +		if (ssp->smk_labeled != SMACK_CIPSO_SOCKET)
> >>>> +			smack_netlabel(newsock->sk, SMACK_CIPSO_SOCKET);
> >>>> +		return;
> >>>> +	}
> >>>> +	if (ssp->smk_labeled != SMACK_UNLABELED_SOCKET)
> >>>> +		smack_netlabel(newsock->sk, SMACK_UNLABELED_SOCKET);
> >>>> +	return;
> >>>> +}
> >>>
> >>> NAK, you can't ignore return values like that.
> >>>
> >>> I'm sorry I didn't get a chance to respond to your email from this
> >>> morning, but the problem with the post_accept() hook is that you can't
> >>> fail in this hook.  There has been a _lot_ of discussion about this
> >>> over the past couple of years on the LSM list.  You should check the
> >>> archives for all the details but the main problem is that the
> >>> post_accept() hook is too late to deny the incoming connection so you
> >>> can't reject the connection at that point in any sane manner.
> >>
> >> well, i don't want to reject the connection here :)
> >>
> >>> I think I'm going to draft a patch to remove the post_accept()
> >>> hook since no one in-tree is using it and it's existence seems to cause
> >>> more problems than it solves.
> >>>
> >>> Now, I understand that your patch doesn't actually enforce any access
> >>> controls but it does call smack_netlabel() in several places and that
> >>> function can fail
> >>
> >> The smack_netlabel(newsock->sk, SMACK_CIPSO_SOCKET) can failed, but has
> >> no interest in this function (because the socket has already be
> >> SMACK_CIPSO_SOCKET labeled by the policy) I can remove it.
> >>
> >> but smack_netlabel(SMACK_UNLABELED_SOCKET) cannot fail, and that's what
> >> i'm interested in could this make the patch acceptable?
> >
> > Please elaborate a bit more on how you would intend a user to configure
> > and make use of this.  Also, in what cases would you remove the NetLabel
> > from a socket?  What cases would you keep it?
>
> well, i think it is simple : let's say i want to run a "smack-labelled
> server" (apache, vsftpd, ...) clients connect from internet,  so the server
> admin/user  will want to add a "0.0.0.0/0 @" entry in netlabel that will
> _fail_ because the server will send back "labeled" packets.

I had to go back and look at the address based labeling patches, I had somehow 
forgotten that the single label support in Smack can only be used for removing 
labels, not adding them.  With that in mind your approach should work although 
you will still get really bizarre behavior in the following case:

 * Service not running at the ambient label
 * Only address based label loaded into Smack is "0.0.0.0/0 @" (everything
   unlabeled)
 * Client connects to service using labeled networking

If you and Casey can live with labeled connection suddenly becoming unlabeled 
(I doubt the remote host will deal with it very gracefully) then go for it.

-- 
paul moore
linux @ hp

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