linux-kernel - Re: [PATCH][SMACK] add a socket_post_accept hook to fix netlabel issues with labeled TCP servers V1

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Date:	Tue, 24 Feb 2009 17:38:08 -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 05:20:42 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?

-- 
paul moore
linux @ hp

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