text: /* Copyright (C) 2009-2017  B.A.T.M.A.N. contributors:
   *
   * Marek Lindner
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of version 2 of the GNU General Public
   * License as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, see <http://www.gnu.org/licenses/>.
   */
  
  #include "gateway_client.h"
  #include "main.h"
  
  #include <linux/atomic.h>
  #include <linux/byteorder/generic.h>
  #include <linux/errno.h>
  #include <linux/etherdevice.h>
  #include <linux/fs.h>
  #include <linux/if_ether.h>
  #include <linux/if_vlan.h>
  #include <linux/in.h>
  #include <linux/ip.h>
  #include <linux/ipv6.h>
  #include <linux/kernel.h>
  #include <linux/kref.h>
  #include <linux/list.h>
  #include <linux/netdevice.h>
  #include <linux/netlink.h>
  #include <linux/rculist.h>
  #include <linux/rcupdate.h>
  #include <linux/seq_file.h>
  #include <linux/skbuff.h>
  #include <linux/slab.h>
  #include <linux/spinlock.h>
  #include <linux/stddef.h>
  #include <linux/udp.h>
  #include <net/sock.h>
  #include <uapi/linux/batman_adv.h>
  
  #include "gateway_common.h"
  #include "hard-interface.h"
  #include "log.h"
  #include "netlink.h"
  #include "originator.h"
  #include "packet.h"
  #include "routing.h"
  #include "soft-interface.h"
  #include "sysfs.h"
  #include "translation-table.h"
  
  /* These are the offsets of the "hw type" and "hw address length" in the dhcp
   * packet starting at the beginning of the dhcp header
   */
  #define BATADV_DHCP_HTYPE_OFFSET	1
  #define BATADV_DHCP_HLEN_OFFSET		2
  /* Value of htype representing Ethernet */
  #define BATADV_DHCP_HTYPE_ETHERNET	0x01
  /* This is the offset of the "chaddr" field in the dhcp packet starting at the
   * beginning of the dhcp header
   */
  #define BATADV_DHCP_CHADDR_OFFSET	28
  
  /**
   * batadv_gw_node_release - release gw_node from lists and queue for free after
   *  rcu grace period
   * @ref: kref pointer of the gw_node
   */
  static void batadv_gw_node_release(struct kref *ref)
  {
  	struct batadv_gw_node *gw_node;
  
  	gw_node = container_of(ref, struct batadv_gw_node, refcount);
  
  	batadv_orig_node_put(gw_node->orig_node);
  	kfree_rcu(gw_node, rcu);
  }
  
  /**
   * batadv_gw_node_put - decrement the gw_node refcounter and possibly release it
   * @gw_node: gateway node to free
   */
  void batadv_gw_node_put(struct batadv_gw_node *gw_node)
  {
  	kref_put(&gw_node->refcount, batadv_gw_node_release);
  }
  
  struct batadv_gw_node *
  batadv_gw_get_selected_gw_node(struct batadv_priv *bat_priv)
  {
  	struct batadv_gw_node *gw_node;
  
  	rcu_read_lock();
  	gw_node = rcu_dereference(bat_priv->gw.curr_gw);
  	if (!gw_node)
  		goto out;
  
  	if (!kref_get_unless_zero(&gw_node->refcount))
  		gw_node = NULL;
  
  out:
  	rcu_read_unlock();
  	return gw_node;
  }
  
  struct batadv_orig_node *
  batadv_gw_get_selected_orig(struct batadv_priv *bat_priv)
  {
  	struct batadv_gw_node *gw_node;
  	struct batadv_orig_node *orig_node = NULL;
  
  	gw_node = batadv_gw_get_selected_gw_node(bat_priv);
  	if (!gw_node)
  		goto out;
  
  	rcu_read_lock();
  	orig_node = gw_node->orig_node;
  	if (!orig_node)
  		goto unlock;
  
  	if (!kref_get_unless_zero(&orig_node->refcount))
  		orig_node = NULL;
  
  unlock:
  	rcu_read_unlock();
  out:
  	if (gw_node)
  		batadv_gw_node_put(gw_node);
  	return orig_node;
  }
  
  static void batadv_gw_select(struct batadv_priv *bat_priv,
  			     struct batadv_gw_node *new_gw_node)
  {
  	struct batadv_gw_node *curr_gw_node;
  
  	spin_lock_bh(&bat_priv->gw.list_lock);
  
  	if (new_gw_node)
  		kref_get(&new_gw_node->refcount);
  
  	curr_gw_node = rcu_dereference_protected(bat_priv->gw.curr_gw, 1);
  	rcu_assign_pointer(bat_priv->gw.curr_gw, new_gw_node);
  
  	if (curr_gw_node)
  		batadv_gw_node_put(curr_gw_node);
  
  	spin_unlock_bh(&bat_priv->gw.list_lock);
  }
  
  /**
   * batadv_gw_reselect - force a gateway reselection
   * @bat_priv: the bat priv with all the soft interface information
   *
   * Set a flag to remind the GW component to perform a new gateway reselection.
   * However this function does not ensure that the current gateway is going to be
   * deselected. The reselection mechanism may elect the same gateway once again.
   *
   * This means that invoking batadv_gw_reselect() does not guarantee a gateway
   * change and therefore a uevent is not necessarily expected.
   */
  void batadv_gw_reselect(struct batadv_priv *bat_priv)
  {
  	atomic_set(&bat_priv->gw.reselect, 1);
  }
  
  /**
   * batadv_gw_check_client_stop - check if client mode has been switched off
   * @bat_priv: the bat priv with all the soft interface information
   *
   * This function assumes the caller has checked that the gw state *is actually
   * changing*. This function is not supposed to be called when there is no state
   * change.
   */
  void batadv_gw_check_client_stop(struct batadv_priv *bat_priv)
  {
  	struct batadv_gw_node *curr_gw;
  
  	if (atomic_read(&bat_priv->gw.mode) != BATADV_GW_MODE_CLIENT)
  		return;
  
  	curr_gw = batadv_gw_get_selected_gw_node(bat_priv);
  	if (!curr_gw)
  		return;
  
  	/* deselect the current gateway so that next time that client mode is
  	 * enabled a proper GW_ADD event can be sent
  	 */
  	batadv_gw_select(bat_priv, NULL);
  
  	/* if batman-adv is switching the gw client mode off and a gateway was
  	 * already selected, send a DEL uevent
  	 */
  	batadv_throw_uevent(bat_priv, BATADV_UEV_GW, BATADV_UEV_DEL, NULL);
  
  	batadv_gw_node_put(curr_gw);
  }
  
  void batadv_gw_election(struct batadv_priv *bat_priv)
  {
  	struct batadv_gw_node *curr_gw = NULL;
  	struct batadv_gw_node *next_gw = NULL;
  	struct batadv_neigh_node *router = NULL;
  	struct batadv_neigh_ifinfo *router_ifinfo = NULL;
  	char gw_addr[18] = { '\0' };
  
  	if (atomic_read(&bat_priv->gw.mode) != BATADV_GW_MODE_CLIENT)
  		goto out;
  
  	if (!bat_priv->algo_ops->gw.get_best_gw_node)
  		goto out;
  
  	curr_gw = batadv_gw_get_selected_gw_node(bat_priv);
  
  	if (!batadv_atomic_dec_not_zero(&bat_priv->gw.reselect) && curr_gw)
  		goto out;
  
  	/* if gw.reselect is set to 1 it means that a previous call to
  	 * gw.is_eligible() said that we have a new best GW, therefore it can
  	 * now be picked from the list and selected
  	 */
  	next_gw = bat_priv->algo_ops->gw.get_best_gw_node(bat_priv);
  
  	if (curr_gw == next_gw)
  		goto out;
  
  	if (next_gw) {
  		sprintf(gw_addr, "%pM", next_gw->orig_node->orig);
  
  		router = batadv_orig_router_get(next_gw->orig_node,
  						BATADV_IF_DEFAULT);
  		if (!router) {
  			batadv_gw_reselect(bat_priv);
  			goto out;
  		}
  
  		router_ifinfo = batadv_neigh_ifinfo_get(router,
  							BATADV_IF_DEFAULT);
  		if (!router_ifinfo) {
  			batadv_gw_reselect(bat_priv);
  			goto out;
  		}
  	}
  
  	if ((curr_gw) && (!next_gw)) {
  		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
  			   "Removing selected gateway - no gateway in range\n");
  		batadv_throw_uevent(bat_priv, BATADV_UEV_GW, BATADV_UEV_DEL,
  				    NULL);
  	} else if ((!curr_gw) && (next_gw)) {
  		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
  			   "Adding route to gateway %pM (bandwidth: %u.%u/%u.%u MBit, tq: %i)\n",
  			   next_gw->orig_node->orig,
  			   next_gw->bandwidth_down / 10,
  			   next_gw->bandwidth_down % 10,
  			   next_gw->bandwidth_up / 10,
  			   next_gw->bandwidth_up % 10,
  			   router_ifinfo->bat_iv.tq_avg);
  		batadv_throw_uevent(bat_priv, BATADV_UEV_GW, BATADV_UEV_ADD,
  				    gw_addr);
  	} else {
  		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
  			   "Changing route to gateway %pM (bandwidth: %u.%u/%u.%u MBit, tq: %i)\n",
  			   next_gw->orig_node->orig,
  			   next_gw->bandwidth_down / 10,
  			   next_gw->bandwidth_down % 10,
  			   next_gw->bandwidth_up / 10,
  			   next_gw->bandwidth_up % 10,
  			   router_ifinfo->bat_iv.tq_avg);
  		batadv_throw_uevent(bat_priv, BATADV_UEV_GW, BATADV_UEV_CHANGE,
  				    gw_addr);
  	}
  
  	batadv_gw_select(bat_priv, next_gw);
  
  out:
  	if (curr_gw)
  		batadv_gw_node_put(curr_gw);
  	if (next_gw)
  		batadv_gw_node_put(next_gw);
  	if (router)
  		batadv_neigh_node_put(router);
  	if (router_ifinfo)
  		batadv_neigh_ifinfo_put(router_ifinfo);
  }
  
  void batadv_gw_check_election(struct batadv_priv *bat_priv,
  			      struct batadv_orig_node *orig_node)
  {
  	struct batadv_orig_node *curr_gw_orig;
  
  	/* abort immediately if the routing algorithm does not support gateway
  	 * election
  	 */
  	if (!bat_priv->algo_ops->gw.is_eligible)
  		return;
  
  	curr_gw_orig = batadv_gw_get_selected_orig(bat_priv);
  	if (!curr_gw_orig)
  		goto reselect;
  
  	/* this node already is the gateway */
  	if (curr_gw_orig == orig_node)
  		goto out;
  
  	if (!bat_priv->algo_ops->gw.is_eligible(bat_priv, curr_gw_orig,
  						orig_node))
  		goto out;
  
  reselect:
  	batadv_gw_reselect(bat_priv);
  out:
  	if (curr_gw_orig)
  		batadv_orig_node_put(curr_gw_orig);
  }
  
  /**
   * batadv_gw_node_add - add gateway node to list of available gateways
   * @bat_priv: the bat priv with all the soft interface information
   * @orig_node: originator announcing gateway capabilities
   * @gateway: announced bandwidth information
   */
  static void batadv_gw_node_add(struct batadv_priv *bat_priv,
  			       struct batadv_orig_node *orig_node,
  			       struct batadv_tvlv_gateway_data *gateway)
  {
  	struct batadv_gw_node *gw_node;
  
  	if (gateway->bandwidth_down == 0)
  		return;
  
  	gw_node = kzalloc(sizeof(*gw_node), GFP_ATOMIC);
  	if (!gw_node)
  		return;
  
  	kref_init(&gw_node->refcount);
  	INIT_HLIST_NODE(&gw_node->list);
  	kref_get(&orig_node->refcount);
  	gw_node->orig_node = orig_node;
  	gw_node->bandwidth_down = ntohl(gateway->bandwidth_down);
  	gw_node->bandwidth_up = ntohl(gateway->bandwidth_up);
  
  	spin_lock_bh(&bat_priv->gw.list_lock);
  	kref_get(&gw_node->refcount);
  	hlist_add_head_rcu(&gw_node->list, &bat_priv->gw.gateway_list);
  	spin_unlock_bh(&bat_priv->gw.list_lock);
  
  	batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
  		   "Found new gateway %pM -> gw bandwidth: %u.%u/%u.%u MBit\n",
  		   orig_node->orig,
  		   ntohl(gateway->bandwidth_down) / 10,
  		   ntohl(gateway->bandwidth_down) % 10,
  		   ntohl(gateway->bandwidth_up) / 10,
  		   ntohl(gateway->bandwidth_up) % 10);
  
  	/* don't return reference to new gw_node */
  	batadv_gw_node_put(gw_node);
  }
  
  /**
   * batadv_gw_node_get - retrieve gateway node from list of available gateways
   * @bat_priv: the bat priv with all the soft interface information
   * @orig_node: originator announcing gateway capabilities
   *
   * Return: gateway node if found or NULL otherwise.
   */
  struct batadv_gw_node *batadv_gw_node_get(struct batadv_priv *bat_priv,
  					  struct batadv_orig_node *orig_node)
  {
  	struct batadv_gw_node *gw_node_tmp, *gw_node = NULL;
  
  	rcu_read_lock();
  	hlist_for_each_entry_rcu(gw_node_tmp, &bat_priv->gw.gateway_list,
  				 list) {
  		if (gw_node_tmp->orig_node != orig_node)
  			continue;
  
  		if (!kref_get_unless_zero(&gw_node_tmp->refcount))
  			continue;
  
  		gw_node = gw_node_tmp;
  		break;
  	}
  	rcu_read_unlock();
  
  	return gw_node;
  }
  
  /**
   * batadv_gw_node_update - update list of available gateways with changed
   *  bandwidth information
   * @bat_priv: the bat priv with all the soft interface information
   * @orig_node: originator announcing gateway capabilities
   * @gateway: announced bandwidth information
   */
  void batadv_gw_node_update(struct batadv_priv *bat_priv,
  			   struct batadv_orig_node *orig_node,
  			   struct batadv_tvlv_gateway_data *gateway)
  {
  	struct batadv_gw_node *gw_node, *curr_gw = NULL;
  
  	gw_node = batadv_gw_node_get(bat_priv, orig_node);
  	if (!gw_node) {
  		batadv_gw_node_add(bat_priv, orig_node, gateway);
  		goto out;
  	}
  
  	if ((gw_node->bandwidth_down == ntohl(gateway->bandwidth_down)) &&
  	    (gw_node->bandwidth_up == ntohl(gateway->bandwidth_up)))
  		goto out;
  
  	batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
  		   "Gateway bandwidth of originator %pM changed from %u.%u/%u.%u MBit to %u.%u/%u.%u MBit\n",
  		   orig_node->orig,
  		   gw_node->bandwidth_down / 10,
  		   gw_node->bandwidth_down % 10,
  		   gw_node->bandwidth_up / 10,
  		   gw_node->bandwidth_up % 10,
  		   ntohl(gateway->bandwidth_down) / 10,
  		   ntohl(gateway->bandwidth_down) % 10,
  		   ntohl(gateway->bandwidth_up) / 10,
  		   ntohl(gateway->bandwidth_up) % 10);
  
  	gw_node->bandwidth_down = ntohl(gateway->bandwidth_down);
  	gw_node->bandwidth_up = ntohl(gateway->bandwidth_up);
  
  	if (ntohl(gateway->bandwidth_down) == 0) {
  		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
  			   "Gateway %pM removed from gateway list\n",
  			   orig_node->orig);
  
  		/* Note: We don't need a NULL check here, since curr_gw never
  		 * gets dereferenced.
  		 */
  		spin_lock_bh(&bat_priv->gw.list_lock);
  		if (!hlist_unhashed(&gw_node->list)) {
  			hlist_del_init_rcu(&gw_node->list);
  			batadv_gw_node_put(gw_node);
  		}
  		spin_unlock_bh(&bat_priv->gw.list_lock);
  
  		curr_gw = batadv_gw_get_selected_gw_node(bat_priv);
  		if (gw_node == curr_gw)
  			batadv_gw_reselect(bat_priv);
  
  		if (curr_gw)
  			batadv_gw_node_put(curr_gw);
  	}
  
  out:
  	if (gw_node)
  		batadv_gw_node_put(gw_node);
  }
  
  void batadv_gw_node_delete(struct batadv_priv *bat_priv,
  			   struct batadv_orig_node *orig_node)
  {
  	struct batadv_tvlv_gateway_data gateway;
  
  	gateway.bandwidth_down = 0;
  	gateway.bandwidth_up = 0;
  
  	batadv_gw_node_update(bat_priv, orig_node, &gateway);
  }
  
  void batadv_gw_node_free(struct batadv_priv *bat_priv)
  {
  	struct batadv_gw_node *gw_node;
  	struct hlist_node *node_tmp;
  
  	spin_lock_bh(&bat_priv->gw.list_lock);
  	hlist_for_each_entry_safe(gw_node, node_tmp,
  				  &bat_priv->gw.gateway_list, list) {
  		hlist_del_init_rcu(&gw_node->list);
  		batadv_gw_node_put(gw_node);
  	}
  	spin_unlock_bh(&bat_priv->gw.list_lock);
  }
  
  #ifdef CONFIG_BATMAN_ADV_DEBUGFS
  int batadv_gw_client_seq_print_text(struct seq_file *seq, void *offset)
  {
  	struct net_device *net_dev = (struct net_device *)seq->private;
  	struct batadv_priv *bat_priv = netdev_priv(net_dev);
  	struct batadv_hard_iface *primary_if;
  
  	primary_if = batadv_seq_print_text_primary_if_get(seq);
  	if (!primary_if)
  		return 0;
  
  	seq_printf(seq, "[B.A.T.M.A.N. adv %s, MainIF/MAC: %s/%pM (%s %s)]\n",
  		   BATADV_SOURCE_VERSION, primary_if->net_dev->name,
  		   primary_if->net_dev->dev_addr, net_dev->name,
  		   bat_priv->algo_ops->name);
  
  	batadv_hardif_put(primary_if);
  
  	if (!bat_priv->algo_ops->gw.print) {
  		seq_puts(seq,
  			 "No printing function for this routing protocol\n");
  		return 0;
  	}
  
  	bat_priv->algo_ops->gw.print(bat_priv, seq);
  
  	return 0;
  }
  #endif
  
  /**
   * batadv_gw_dump - Dump gateways into a message
   * @msg: Netlink message to dump into
   * @cb: Control block containing additional options
   *
   * Return: Error code, or length of message
   */
  int batadv_gw_dump(struct sk_buff *msg, struct netlink_callback *cb)
  {
  	struct batadv_hard_iface *primary_if = NULL;
  	struct net *net = sock_net(cb->skb->sk);
  	struct net_device *soft_iface;
  	struct batadv_priv *bat_priv;
  	int ifindex;
  	int ret;
  
  	ifindex = batadv_netlink_get_ifindex(cb->nlh,
  					     BATADV_ATTR_MESH_IFINDEX);
  	if (!ifindex)
  		return -EINVAL;
  
  	soft_iface = dev_get_by_index(net, ifindex);
  	if (!soft_iface || !batadv_softif_is_valid(soft_iface)) {
  		ret = -ENODEV;
  		goto out;
  	}
  
  	bat_priv = netdev_priv(soft_iface);
  
  	primary_if = batadv_primary_if_get_selected(bat_priv);
  	if (!primary_if || primary_if->if_status != BATADV_IF_ACTIVE) {
  		ret = -ENOENT;
  		goto out;
  	}
  
  	if (!bat_priv->algo_ops->gw.dump) {
  		ret = -EOPNOTSUPP;
  		goto out;
  	}
  
  	bat_priv->algo_ops->gw.dump(msg, cb, bat_priv);
  
  	ret = msg->len;
  
  out:
  	if (primary_if)
  		batadv_hardif_put(primary_if);
  	if (soft_iface)
  		dev_put(soft_iface);
  
  	return ret;
  }
  
  /**
   * batadv_gw_dhcp_recipient_get - check if a packet is a DHCP message
   * @skb: the packet to check
   * @header_len: a pointer to the batman-adv header size
   * @chaddr: buffer where the client address will be stored. Valid
   *  only if the function returns BATADV_DHCP_TO_CLIENT
   *
   * This function may re-allocate the data buffer of the skb passed as argument.
   *
   * Return:
   * - BATADV_DHCP_NO if the packet is not a dhcp message or if there was an error
   *   while parsing it
   * - BATADV_DHCP_TO_SERVER if this is a message going to the DHCP server
   * - BATADV_DHCP_TO_CLIENT if this is a message going to a DHCP client
   */
  enum batadv_dhcp_recipient
  batadv_gw_dhcp_recipient_get(struct sk_buff *skb, unsigned int *header_len,
  			     u8 *chaddr)
  {
  	enum batadv_dhcp_recipient ret = BATADV_DHCP_NO;
  	struct ethhdr *ethhdr;
  	struct iphdr *iphdr;
  	struct ipv6hdr *ipv6hdr;
  	struct udphdr *udphdr;
  	struct vlan_ethhdr *vhdr;
  	int chaddr_offset;
  	__be16 proto;
  	u8 *p;
  
  	/* check for ethernet header */
  	if (!pskb_may_pull(skb, *header_len + ETH_HLEN))
  		return BATADV_DHCP_NO;
  
  	ethhdr = eth_hdr(skb);
  	proto = ethhdr->h_proto;
  	*header_len += ETH_HLEN;
  
  	/* check for initial vlan header */
  	if (proto == htons(ETH_P_8021Q)) {
  		if (!pskb_may_pull(skb, *header_len + VLAN_HLEN))
  			return BATADV_DHCP_NO;
  
  		vhdr = vlan_eth_hdr(skb);
  		proto = vhdr->h_vlan_encapsulated_proto;
  		*header_len += VLAN_HLEN;
  	}
  
  	/* check for ip header */
  	switch (proto) {
  	case htons(ETH_P_IP):
  		if (!pskb_may_pull(skb, *header_len + sizeof(*iphdr)))
  			return BATADV_DHCP_NO;
  
  		iphdr = (struct iphdr *)(skb->data + *header_len);
  		*header_len += iphdr->ihl * 4;
  
  		/* check for udp header */
  		if (iphdr->protocol != IPPROTO_UDP)
  			return BATADV_DHCP_NO;
  
  		break;
  	case htons(ETH_P_IPV6):
  		if (!pskb_may_pull(skb, *header_len + sizeof(*ipv6hdr)))
  			return BATADV_DHCP_NO;
  
  		ipv6hdr = (struct ipv6hdr *)(skb->data + *header_len);
  		*header_len += sizeof(*ipv6hdr);
  
  		/* check for udp header */
  		if (ipv6hdr->nexthdr != IPPROTO_UDP)
  			return BATADV_DHCP_NO;
  
  		break;
  	default:
  		return BATADV_DHCP_NO;
  	}
  
  	if (!pskb_may_pull(skb, *header_len + sizeof(*udphdr)))
  		return BATADV_DHCP_NO;
  
  	udphdr = (struct udphdr *)(skb->data + *header_len);
  	*header_len += sizeof(*udphdr);
  
  	/* check for bootp port */
  	switch (proto) {
  	case htons(ETH_P_IP):
  		if (udphdr->dest == htons(67))
  			ret = BATADV_DHCP_TO_SERVER;
  		else if (udphdr->source == htons(67))
  			ret = BATADV_DHCP_TO_CLIENT;
  		break;
  	case htons(ETH_P_IPV6):
  		if (udphdr->dest == htons(547))
  			ret = BATADV_DHCP_TO_SERVER;
  		else if (udphdr->source == htons(547))
  			ret = BATADV_DHCP_TO_CLIENT;
  		break;
  	}
  
  	chaddr_offset = *header_len + BATADV_DHCP_CHADDR_OFFSET;
  	/* store the client address if the message is going to a client */
  	if (ret == BATADV_DHCP_TO_CLIENT &&
  	    pskb_may_pull(skb, chaddr_offset + ETH_ALEN)) {
  		/* check if the DHCP packet carries an Ethernet DHCP */
  		p = skb->data + *header_len + BATADV_DHCP_HTYPE_OFFSET;
  		if (*p != BATADV_DHCP_HTYPE_ETHERNET)
  			return BATADV_DHCP_NO;
  
  		/* check if the DHCP packet carries a valid Ethernet address */
  		p = skb->data + *header_len + BATADV_DHCP_HLEN_OFFSET;
  		if (*p != ETH_ALEN)
  			return BATADV_DHCP_NO;
  
  		ether_addr_copy(chaddr, skb->data + chaddr_offset);
  	}
  
  	return ret;
  }
  
  /**
   * batadv_gw_out_of_range - check if the dhcp request destination is the best gw
   * @bat_priv: the bat priv with all the soft interface information
   * @skb: the outgoing packet
   *
   * Check if the skb is a DHCP request and if it is sent to the current best GW
   * server. Due to topology changes it may be the case that the GW server
   * previously selected is not the best one anymore.
   *
   * This call might reallocate skb data.
   * Must be invoked only when the DHCP packet is going TO a DHCP SERVER.
   *
   * Return: true if the packet destination is unicast and it is not the best gw,
   * false otherwise.
   */
  bool batadv_gw_out_of_range(struct batadv_priv *bat_priv,
  			    struct sk_buff *skb)
  {
  	struct batadv_neigh_node *neigh_curr = NULL;
  	struct batadv_neigh_node *neigh_old = NULL;
  	struct batadv_orig_node *orig_dst_node = NULL;
  	struct batadv_gw_node *gw_node = NULL;
  	struct batadv_gw_node *curr_gw = NULL;
  	struct batadv_neigh_ifinfo *curr_ifinfo, *old_ifinfo;
  	struct ethhdr *ethhdr = (struct ethhdr *)skb->data;
  	bool out_of_range = false;
  	u8 curr_tq_avg;
  	unsigned short vid;
  
  	vid = batadv_get_vid(skb, 0);
  
  	if (is_multicast_ether_addr(ethhdr->h_dest))
  		goto out;
  
  	orig_dst_node = batadv_transtable_search(bat_priv, ethhdr->h_source,
  						 ethhdr->h_dest, vid);
  	if (!orig_dst_node)
  		goto out;
  
  	gw_node = batadv_gw_node_get(bat_priv, orig_dst_node);
  	if (!gw_node)
  		goto out;
  
  	switch (atomic_read(&bat_priv->gw.mode)) {
  	case BATADV_GW_MODE_SERVER:
  		/* If we are a GW then we are our best GW. We can artificially
  		 * set the tq towards ourself as the maximum value
  		 */
  		curr_tq_avg = BATADV_TQ_MAX_VALUE;
  		break;
  	case BATADV_GW_MODE_CLIENT:
  		curr_gw = batadv_gw_get_selected_gw_node(bat_priv);
  		if (!curr_gw)
  			goto out;
  
  		/* packet is going to our gateway */
  		if (curr_gw->orig_node == orig_dst_node)
  			goto out;
  
  		/* If the dhcp packet has been sent to a different gw,
  		 * we have to evaluate whether the old gw is still
  		 * reliable enough
  		 */
  		neigh_curr = batadv_find_router(bat_priv, curr_gw->orig_node,
  						NULL);
  		if (!neigh_curr)
  			goto out;
  
  		curr_ifinfo = batadv_neigh_ifinfo_get(neigh_curr,
  						      BATADV_IF_DEFAULT);
  		if (!curr_ifinfo)
  			goto out;
  
  		curr_tq_avg = curr_ifinfo->bat_iv.tq_avg;
  		batadv_neigh_ifinfo_put(curr_ifinfo);
  
  		break;
  	case BATADV_GW_MODE_OFF:
  	default:
  		goto out;
  	}
  
  	neigh_old = batadv_find_router(bat_priv, orig_dst_node, NULL);
  	if (!neigh_old)
  		goto out;
  
  	old_ifinfo = batadv_neigh_ifinfo_get(neigh_old, BATADV_IF_DEFAULT);
  	if (!old_ifinfo)
  		goto out;
  
  	if ((curr_tq_avg - old_ifinfo->bat_iv.tq_avg) > BATADV_GW_THRESHOLD)
  		out_of_range = true;
  	batadv_neigh_ifinfo_put(old_ifinfo);
  
  out:
  	if (orig_dst_node)
  		batadv_orig_node_put(orig_dst_node);
  	if (curr_gw)
  		batadv_gw_node_put(curr_gw);
  	if (gw_node)
  		batadv_gw_node_put(gw_node);
  	if (neigh_old)
  		batadv_neigh_node_put(neigh_old);
  	if (neigh_curr)
  		batadv_neigh_node_put(neigh_curr);
  	return out_of_range;
  }
  