static unsigned int selinux_ip_postroute(struct sk_buff *skb, int ifindex,
					 u16 family)
{
	u32 secmark_perm;
	u32 peer_sid;
	struct sock *sk;
	struct common_audit_data ad;
	struct lsm_network_audit net = {0,};
	char *addrp;
	u8 secmark_active;
	u8 peerlbl_active;

	/* If any sort of compatibility mode is enabled then handoff processing
	 * to the selinux_ip_postroute_compat() function to deal with the
	 * special handling.  We do this in an attempt to keep this function
	 * as fast and as clean as possible. */
	if (!selinux_policycap_netpeer)
		return selinux_ip_postroute_compat(skb, ifindex, family);

	secmark_active = selinux_secmark_enabled();
	peerlbl_active = selinux_peerlbl_enabled();
	if (!secmark_active && !peerlbl_active)
		return NF_ACCEPT;

	sk = skb->sk;

#ifdef CONFIG_XFRM
	/* If skb->dst->xfrm is non-NULL then the packet is undergoing an IPsec
	 * packet transformation so allow the packet to pass without any checks
	 * since we'll have another chance to perform access control checks
	 * when the packet is on it's final way out.
	 * NOTE: there appear to be some IPv6 multicast cases where skb->dst
	 *       is NULL, in this case go ahead and apply access control.
	 * NOTE: if this is a local socket (skb->sk != NULL) that is in the
	 *       TCP listening state we cannot wait until the XFRM processing
	 *       is done as we will miss out on the SA label if we do;
	 *       unfortunately, this means more work, but it is only once per
	 *       connection. */
	if (skb_dst(skb) != NULL && skb_dst(skb)->xfrm != NULL &&
	    !(sk != NULL && sk->sk_state == TCP_LISTEN))
		return NF_ACCEPT;
#endif

	if (sk == NULL) {
		/* Without an associated socket the packet is either coming
		 * from the kernel or it is being forwarded; check the packet
		 * to determine which and if the packet is being forwarded
		 * query the packet directly to determine the security label. */
		if (skb->skb_iif) {
			secmark_perm = PACKET__FORWARD_OUT;
			if (selinux_skb_peerlbl_sid(skb, family, &peer_sid))
				return NF_DROP;
		} else {
			secmark_perm = PACKET__SEND;
			peer_sid = SECINITSID_KERNEL;
		}
	} else if (sk->sk_state == TCP_LISTEN) {
		/* Locally generated packet but the associated socket is in the
		 * listening state which means this is a SYN-ACK packet.  In
		 * this particular case the correct security label is assigned
		 * to the connection/request_sock but unfortunately we can't
		 * query the request_sock as it isn't queued on the parent
		 * socket until after the SYN-ACK packet is sent; the only
		 * viable choice is to regenerate the label like we do in
		 * selinux_inet_conn_request().  See also selinux_ip_output()
		 * for similar problems. */
		u32 skb_sid;
		struct sk_security_struct *sksec = sk->sk_security;
		if (selinux_skb_peerlbl_sid(skb, family, &skb_sid))
			return NF_DROP;
		/* At this point, if the returned skb peerlbl is SECSID_NULL
		 * and the packet has been through at least one XFRM
		 * transformation then we must be dealing with the "final"
		 * form of labeled IPsec packet; since we've already applied
		 * all of our access controls on this packet we can safely
		 * pass the packet. */
		if (skb_sid == SECSID_NULL) {
			switch (family) {
			case PF_INET:
				if (IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED)
					return NF_ACCEPT;
				break;
			case PF_INET6:
				if (IP6CB(skb)->flags & IP6SKB_XFRM_TRANSFORMED)
					return NF_ACCEPT;
			default:
				return NF_DROP_ERR(-ECONNREFUSED);
			}
		}
		if (selinux_conn_sid(sksec->sid, skb_sid, &peer_sid))
			return NF_DROP;
		secmark_perm = PACKET__SEND;
	} else {
		/* Locally generated packet, fetch the security label from the
		 * associated socket. */
		struct sk_security_struct *sksec = sk->sk_security;
		peer_sid = sksec->sid;
		secmark_perm = PACKET__SEND;
	}

	ad.type = LSM_AUDIT_DATA_NET;
	ad.u.net = &net;
	ad.u.net->netif = ifindex;
	ad.u.net->family = family;
	if (selinux_parse_skb(skb, &ad, &addrp, 0, NULL))
		return NF_DROP;

	if (secmark_active)
		if (avc_has_perm(peer_sid, skb->secmark,
				 SECCLASS_PACKET, secmark_perm, &ad))
			return NF_DROP_ERR(-ECONNREFUSED);

	if (peerlbl_active) {
		u32 if_sid;
		u32 node_sid;

		if (sel_netif_sid(ifindex, &if_sid))
			return NF_DROP;
		if (avc_has_perm(peer_sid, if_sid,
				 SECCLASS_NETIF, NETIF__EGRESS, &ad))
			return NF_DROP_ERR(-ECONNREFUSED);

		if (sel_netnode_sid(addrp, family, &node_sid))
			return NF_DROP;
		if (avc_has_perm(peer_sid, node_sid,
				 SECCLASS_NODE, NODE__SENDTO, &ad))
			return NF_DROP_ERR(-ECONNREFUSED);
	}

	return NF_ACCEPT;
}
Unknown