// SPDX-License-Identifier: GPL-2.0
/* Copyright (C) B.A.T.M.A.N. contributors:
 *
 * Antonio Quartulli
 */

#include "distributed-arp-table.h"
#include "main.h"

#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/byteorder/generic.h>
#include <linux/container_of.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/etherdevice.h>
#include <linux/gfp.h>
#include <linux/if_arp.h>
#include <linux/if_ether.h>
#include <linux/if_vlan.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/jiffies.h>
#include <linux/kref.h>
#include <linux/list.h>
#include <linux/netlink.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/stddef.h>
#include <linux/string.h>
#include <linux/udp.h>
#include <linux/unaligned.h>
#include <linux/workqueue.h>
#include <net/arp.h>
#include <net/genetlink.h>
#include <net/netlink.h>
#include <uapi/linux/batman_adv.h>

#include "bridge_loop_avoidance.h"
#include "hard-interface.h"
#include "hash.h"
#include "log.h"
#include "netlink.h"
#include "originator.h"
#include "send.h"
#include "translation-table.h"
#include "tvlv.h"

enum batadv_bootpop {
        BATADV_BOOTREPLY        = 2,
};

enum batadv_boothtype {
        BATADV_HTYPE_ETHERNET   = 1,
};

enum batadv_dhcpoptioncode {
        BATADV_DHCP_OPT_PAD             = 0,
        BATADV_DHCP_OPT_MSG_TYPE        = 53,
        BATADV_DHCP_OPT_END             = 255,
};

enum batadv_dhcptype {
        BATADV_DHCPACK          = 5,
};

/* { 99, 130, 83, 99 } */
#define BATADV_DHCP_MAGIC 1669485411

struct batadv_dhcp_packet {
        __u8 op;
        __u8 htype;
        __u8 hlen;
        __u8 hops;
        __be32 xid;
        __be16 secs;
        __be16 flags;
        __be32 ciaddr;
        __be32 yiaddr;
        __be32 siaddr;
        __be32 giaddr;
        __u8 chaddr[16];
        __u8 sname[64];
        __u8 file[128];
        __be32 magic;
        /* __u8 options[]; */
};

#define BATADV_DHCP_YIADDR_LEN sizeof(((struct batadv_dhcp_packet *)0)->yiaddr)
#define BATADV_DHCP_CHADDR_LEN sizeof(((struct batadv_dhcp_packet *)0)->chaddr)

static void batadv_dat_purge(struct work_struct *work);

/**
 * batadv_dat_start_timer() - initialise the DAT periodic worker
 * @bat_priv: the bat priv with all the mesh interface information
 */
static void batadv_dat_start_timer(struct batadv_priv *bat_priv)
{
        queue_delayed_work(batadv_event_workqueue, &bat_priv->dat.work,
                           msecs_to_jiffies(10000));
}

/**
 * batadv_dat_entry_release() - release dat_entry from lists and queue for free
 *  after rcu grace period
 * @ref: kref pointer of the dat_entry
 */
static void batadv_dat_entry_release(struct kref *ref)
{
        struct batadv_dat_entry *dat_entry;

        dat_entry = container_of(ref, struct batadv_dat_entry, refcount);

        kfree_rcu(dat_entry, rcu);
}

/**
 * batadv_dat_entry_put() - decrement the dat_entry refcounter and possibly
 *  release it
 * @dat_entry: dat_entry to be free'd
 */
static void batadv_dat_entry_put(struct batadv_dat_entry *dat_entry)
{
        if (!dat_entry)
                return;

        kref_put(&dat_entry->refcount, batadv_dat_entry_release);
}

/**
 * batadv_dat_to_purge() - check whether a dat_entry has to be purged or not
 * @dat_entry: the entry to check
 *
 * Return: true if the entry has to be purged now, false otherwise.
 */
static bool batadv_dat_to_purge(struct batadv_dat_entry *dat_entry)
{
        return batadv_has_timed_out(dat_entry->last_update,
                                    BATADV_DAT_ENTRY_TIMEOUT);
}

/**
 * __batadv_dat_purge() - delete entries from the DAT local storage
 * @bat_priv: the bat priv with all the mesh interface information
 * @to_purge: function in charge to decide whether an entry has to be purged or
 *            not. This function takes the dat_entry as argument and has to
 *            returns a boolean value: true is the entry has to be deleted,
 *            false otherwise
 *
 * Loops over each entry in the DAT local storage and deletes it if and only if
 * the to_purge function passed as argument returns true.
 */
static void __batadv_dat_purge(struct batadv_priv *bat_priv,
                               bool (*to_purge)(struct batadv_dat_entry *))
{
        spinlock_t *list_lock; /* protects write access to the hash lists */
        struct batadv_dat_entry *dat_entry;
        struct hlist_node *node_tmp;
        struct hlist_head *head;
        u32 i;

        if (!bat_priv->dat.hash)
                return;

        for (i = 0; i < bat_priv->dat.hash->size; i++) {
                head = &bat_priv->dat.hash->table[i];
                list_lock = &bat_priv->dat.hash->list_locks[i];

                spin_lock_bh(list_lock);
                hlist_for_each_entry_safe(dat_entry, node_tmp, head,
                                          hash_entry) {
                        /* if a helper function has been passed as parameter,
                         * ask it if the entry has to be purged or not
                         */
                        if (to_purge && !to_purge(dat_entry))
                                continue;

                        hlist_del_rcu(&dat_entry->hash_entry);
                        batadv_dat_entry_put(dat_entry);
                }
                spin_unlock_bh(list_lock);
        }
}

/**
 * batadv_dat_purge() - periodic task that deletes old entries from the local
 *  DAT hash table
 * @work: kernel work struct
 */
static void batadv_dat_purge(struct work_struct *work)
{
        struct delayed_work *delayed_work;
        struct batadv_priv_dat *priv_dat;
        struct batadv_priv *bat_priv;

        delayed_work = to_delayed_work(work);
        priv_dat = container_of(delayed_work, struct batadv_priv_dat, work);
        bat_priv = container_of(priv_dat, struct batadv_priv, dat);

        __batadv_dat_purge(bat_priv, batadv_dat_to_purge);
        batadv_dat_start_timer(bat_priv);
}

/**
 * batadv_compare_dat() - comparing function used in the local DAT hash table
 * @node: node in the local table
 * @data2: second object to compare the node to
 *
 * Return: true if the two entries are the same, false otherwise.
 */
static bool batadv_compare_dat(const struct hlist_node *node, const void *data2)
{
        const void *data1 = container_of(node, struct batadv_dat_entry,
                                         hash_entry);

        return memcmp(data1, data2, sizeof(__be32)) == 0;
}

/**
 * batadv_arp_hw_src() - extract the hw_src field from an ARP packet
 * @skb: ARP packet
 * @hdr_size: size of the possible header before the ARP packet
 *
 * Return: the value of the hw_src field in the ARP packet.
 */
static u8 *batadv_arp_hw_src(struct sk_buff *skb, int hdr_size)
{
        u8 *addr;

        addr = (u8 *)(skb->data + hdr_size);
        addr += ETH_HLEN + sizeof(struct arphdr);

        return addr;
}

/**
 * batadv_arp_ip_src() - extract the ip_src field from an ARP packet
 * @skb: ARP packet
 * @hdr_size: size of the possible header before the ARP packet
 *
 * Return: the value of the ip_src field in the ARP packet.
 */
static __be32 batadv_arp_ip_src(struct sk_buff *skb, int hdr_size)
{
        return *(__force __be32 *)(batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN);
}

/**
 * batadv_arp_hw_dst() - extract the hw_dst field from an ARP packet
 * @skb: ARP packet
 * @hdr_size: size of the possible header before the ARP packet
 *
 * Return: the value of the hw_dst field in the ARP packet.
 */
static u8 *batadv_arp_hw_dst(struct sk_buff *skb, int hdr_size)
{
        return batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN + 4;
}

/**
 * batadv_arp_ip_dst() - extract the ip_dst field from an ARP packet
 * @skb: ARP packet
 * @hdr_size: size of the possible header before the ARP packet
 *
 * Return: the value of the ip_dst field in the ARP packet.
 */
static __be32 batadv_arp_ip_dst(struct sk_buff *skb, int hdr_size)
{
        u8 *dst = batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN * 2 + 4;

        return *(__force __be32 *)dst;
}

/**
 * batadv_hash_dat() - compute the hash value for an IP address
 * @data: data to hash
 * @size: size of the hash table
 *
 * Return: the selected index in the hash table for the given data.
 */
static u32 batadv_hash_dat(const void *data, u32 size)
{
        u32 hash = 0;
        const struct batadv_dat_entry *dat = data;
        const unsigned char *key;
        __be16 vid;
        u32 i;

        key = (__force const unsigned char *)&dat->ip;
        for (i = 0; i < sizeof(dat->ip); i++) {
                hash += key[i];
                hash += (hash << 10);
                hash ^= (hash >> 6);
        }

        vid = htons(dat->vid);
        key = (__force const unsigned char *)&vid;
        for (i = 0; i < sizeof(dat->vid); i++) {
                hash += key[i];
                hash += (hash << 10);
                hash ^= (hash >> 6);
        }

        hash += (hash << 3);
        hash ^= (hash >> 11);
        hash += (hash << 15);

        return hash % size;
}

/**
 * batadv_dat_entry_hash_find() - look for a given dat_entry in the local hash
 * table
 * @bat_priv: the bat priv with all the mesh interface information
 * @ip: search key
 * @vid: VLAN identifier
 *
 * Return: the dat_entry if found, NULL otherwise.
 */
static struct batadv_dat_entry *
batadv_dat_entry_hash_find(struct batadv_priv *bat_priv, __be32 ip,
                           unsigned short vid)
{
        struct hlist_head *head;
        struct batadv_dat_entry to_find, *dat_entry, *dat_entry_tmp = NULL;
        struct batadv_hashtable *hash = bat_priv->dat.hash;
        u32 index;

        if (!hash)
                return NULL;

        to_find.ip = ip;
        to_find.vid = vid;

        index = batadv_hash_dat(&to_find, hash->size);
        head = &hash->table[index];

        rcu_read_lock();
        hlist_for_each_entry_rcu(dat_entry, head, hash_entry) {
                if (dat_entry->ip != ip)
                        continue;

                if (!kref_get_unless_zero(&dat_entry->refcount))
                        continue;

                dat_entry_tmp = dat_entry;
                break;
        }
        rcu_read_unlock();

        return dat_entry_tmp;
}

/**
 * batadv_dat_entry_add() - add a new dat entry or update it if already exists
 * @bat_priv: the bat priv with all the mesh interface information
 * @ip: ipv4 to add/edit
 * @mac_addr: mac address to assign to the given ipv4
 * @vid: VLAN identifier
 */
static void batadv_dat_entry_add(struct batadv_priv *bat_priv, __be32 ip,
                                 u8 *mac_addr, unsigned short vid)
{
        struct batadv_dat_entry *dat_entry;
        int hash_added;

        dat_entry = batadv_dat_entry_hash_find(bat_priv, ip, vid);
        /* if this entry is already known, just update it */
        if (dat_entry) {
                if (!batadv_compare_eth(dat_entry->mac_addr, mac_addr))
                        ether_addr_copy(dat_entry->mac_addr, mac_addr);
                dat_entry->last_update = jiffies;
                batadv_dbg(BATADV_DBG_DAT, bat_priv,
                           "Entry updated: %pI4 %pM (vid: %d)\n",
                           &dat_entry->ip, dat_entry->mac_addr,
                           batadv_print_vid(vid));
                goto out;
        }

        dat_entry = kmalloc_obj(*dat_entry, GFP_ATOMIC);
        if (!dat_entry)
                goto out;

        dat_entry->ip = ip;
        dat_entry->vid = vid;
        ether_addr_copy(dat_entry->mac_addr, mac_addr);
        dat_entry->last_update = jiffies;
        kref_init(&dat_entry->refcount);

        kref_get(&dat_entry->refcount);
        hash_added = batadv_hash_add(bat_priv->dat.hash, batadv_compare_dat,
                                     batadv_hash_dat, dat_entry,
                                     &dat_entry->hash_entry);

        if (unlikely(hash_added != 0)) {
                /* remove the reference for the hash */
                batadv_dat_entry_put(dat_entry);
                goto out;
        }

        batadv_dbg(BATADV_DBG_DAT, bat_priv, "New entry added: %pI4 %pM (vid: %d)\n",
                   &dat_entry->ip, dat_entry->mac_addr, batadv_print_vid(vid));

out:
        batadv_dat_entry_put(dat_entry);
}

#ifdef CONFIG_BATMAN_ADV_DEBUG

/**
 * batadv_dbg_arp() - print a debug message containing all the ARP packet
 *  details
 * @bat_priv: the bat priv with all the mesh interface information
 * @skb: ARP packet
 * @hdr_size: size of the possible header before the ARP packet
 * @msg: message to print together with the debugging information
 */
static void batadv_dbg_arp(struct batadv_priv *bat_priv, struct sk_buff *skb,
                           int hdr_size, char *msg)
{
        struct batadv_unicast_4addr_packet *unicast_4addr_packet;
        struct batadv_bcast_packet *bcast_pkt;
        u8 *orig_addr;
        __be32 ip_src, ip_dst;

        if (msg)
                batadv_dbg(BATADV_DBG_DAT, bat_priv, "%s\n", msg);

        ip_src = batadv_arp_ip_src(skb, hdr_size);
        ip_dst = batadv_arp_ip_dst(skb, hdr_size);
        batadv_dbg(BATADV_DBG_DAT, bat_priv,
                   "ARP MSG = [src: %pM-%pI4 dst: %pM-%pI4]\n",
                   batadv_arp_hw_src(skb, hdr_size), &ip_src,
                   batadv_arp_hw_dst(skb, hdr_size), &ip_dst);

        if (hdr_size < sizeof(struct batadv_unicast_packet))
                return;

        unicast_4addr_packet = (struct batadv_unicast_4addr_packet *)skb->data;

        switch (unicast_4addr_packet->u.packet_type) {
        case BATADV_UNICAST:
                batadv_dbg(BATADV_DBG_DAT, bat_priv,
                           "* encapsulated within a UNICAST packet\n");
                break;
        case BATADV_UNICAST_4ADDR:
                batadv_dbg(BATADV_DBG_DAT, bat_priv,
                           "* encapsulated within a UNICAST_4ADDR packet (src: %pM)\n",
                           unicast_4addr_packet->src);
                switch (unicast_4addr_packet->subtype) {
                case BATADV_P_DAT_DHT_PUT:
                        batadv_dbg(BATADV_DBG_DAT, bat_priv, "* type: DAT_DHT_PUT\n");
                        break;
                case BATADV_P_DAT_DHT_GET:
                        batadv_dbg(BATADV_DBG_DAT, bat_priv, "* type: DAT_DHT_GET\n");
                        break;
                case BATADV_P_DAT_CACHE_REPLY:
                        batadv_dbg(BATADV_DBG_DAT, bat_priv,
                                   "* type: DAT_CACHE_REPLY\n");
                        break;
                case BATADV_P_DATA:
                        batadv_dbg(BATADV_DBG_DAT, bat_priv, "* type: DATA\n");
                        break;
                default:
                        batadv_dbg(BATADV_DBG_DAT, bat_priv, "* type: Unknown (%u)!\n",
                                   unicast_4addr_packet->u.packet_type);
                }
                break;
        case BATADV_BCAST:
                bcast_pkt = (struct batadv_bcast_packet *)unicast_4addr_packet;
                orig_addr = bcast_pkt->orig;
                batadv_dbg(BATADV_DBG_DAT, bat_priv,
                           "* encapsulated within a BCAST packet (src: %pM)\n",
                           orig_addr);
                break;
        default:
                batadv_dbg(BATADV_DBG_DAT, bat_priv,
                           "* encapsulated within an unknown packet type (0x%x)\n",
                           unicast_4addr_packet->u.packet_type);
        }
}

#else

static void batadv_dbg_arp(struct batadv_priv *bat_priv, struct sk_buff *skb,
                           int hdr_size, char *msg)
{
}

#endif /* CONFIG_BATMAN_ADV_DEBUG */

/**
 * batadv_is_orig_node_eligible() - check whether a node can be a DHT candidate
 * @res: the array with the already selected candidates
 * @select: number of already selected candidates
 * @tmp_max: address of the currently evaluated node
 * @max: current round max address
 * @last_max: address of the last selected candidate
 * @candidate: orig_node under evaluation
 * @max_orig_node: last selected candidate
 *
 * Return: true if the node has been elected as next candidate or false
 * otherwise.
 */
static bool batadv_is_orig_node_eligible(struct batadv_dat_candidate *res,
                                         int select, batadv_dat_addr_t tmp_max,
                                         batadv_dat_addr_t max,
                                         batadv_dat_addr_t last_max,
                                         struct batadv_orig_node *candidate,
                                         struct batadv_orig_node *max_orig_node)
{
        bool ret = false;
        int j;

        /* check if orig node candidate is running DAT */
        if (!test_bit(BATADV_ORIG_CAPA_HAS_DAT, &candidate->capabilities))
                goto out;

        /* Check if this node has already been selected... */
        for (j = 0; j < select; j++)
                if (res[j].orig_node == candidate)
                        break;
        /* ..and possibly skip it */
        if (j < select)
                goto out;
        /* sanity check: has it already been selected? This should not happen */
        if (tmp_max > last_max)
                goto out;
        /* check if during this iteration an originator with a closer dht
         * address has already been found
         */
        if (tmp_max < max)
                goto out;
        /* this is an hash collision with the temporary selected node. Choose
         * the one with the lowest address
         */
        if (tmp_max == max && max_orig_node &&
            batadv_compare_eth(candidate->orig, max_orig_node->orig))
                goto out;

        ret = true;
out:
        return ret;
}

/**
 * batadv_choose_next_candidate() - select the next DHT candidate
 * @bat_priv: the bat priv with all the mesh interface information
 * @cands: candidates array
 * @select: number of candidates already present in the array
 * @ip_key: key to look up in the DHT
 * @last_max: pointer where the address of the selected candidate will be saved
 */
static void batadv_choose_next_candidate(struct batadv_priv *bat_priv,
                                         struct batadv_dat_candidate *cands,
                                         int select, batadv_dat_addr_t ip_key,
                                         batadv_dat_addr_t *last_max)
{
        batadv_dat_addr_t max = 0;
        batadv_dat_addr_t tmp_max = 0;
        struct batadv_orig_node *orig_node, *max_orig_node = NULL;
        struct batadv_hashtable *hash = bat_priv->orig_hash;
        struct hlist_head *head;
        int i;

        /* if no node is eligible as candidate, leave the candidate type as
         * NOT_FOUND
         */
        cands[select].type = BATADV_DAT_CANDIDATE_NOT_FOUND;

        /* iterate over the originator list and find the node with the closest
         * dat_address which has not been selected yet
         */
        for (i = 0; i < hash->size; i++) {
                head = &hash->table[i];

                rcu_read_lock();
                hlist_for_each_entry_rcu(orig_node, head, hash_entry) {
                        /* the dht space is a ring using unsigned addresses */
                        tmp_max = BATADV_DAT_ADDR_MAX - orig_node->dat_addr +
                                  ip_key;

                        if (!batadv_is_orig_node_eligible(cands, select,
                                                          tmp_max, max,
                                                          *last_max, orig_node,
                                                          max_orig_node))
                                continue;

                        if (!kref_get_unless_zero(&orig_node->refcount))
                                continue;

                        max = tmp_max;
                        batadv_orig_node_put(max_orig_node);
                        max_orig_node = orig_node;
                }
                rcu_read_unlock();
        }
        if (max_orig_node) {
                cands[select].type = BATADV_DAT_CANDIDATE_ORIG;
                cands[select].orig_node = max_orig_node;
                batadv_dbg(BATADV_DBG_DAT, bat_priv,
                           "dat_select_candidates() %d: selected %pM addr=%u dist=%u\n",
                           select, max_orig_node->orig, max_orig_node->dat_addr,
                           max);
        }
        *last_max = max;
}

/**
 * batadv_dat_select_candidates() - select the nodes which the DHT message has
 *  to be sent to
 * @bat_priv: the bat priv with all the mesh interface information
 * @ip_dst: ipv4 to look up in the DHT
 * @vid: VLAN identifier
 *
 * An originator O is selected if and only if its DHT_ID value is one of three
 * closest values (from the LEFT, with wrap around if needed) then the hash
 * value of the key. ip_dst is the key.
 *
 * Return: the candidate array of size BATADV_DAT_CANDIDATE_NUM.
 */
static struct batadv_dat_candidate *
batadv_dat_select_candidates(struct batadv_priv *bat_priv, __be32 ip_dst,
                             unsigned short vid)
{
        int select;
        batadv_dat_addr_t last_max = BATADV_DAT_ADDR_MAX, ip_key;
        struct batadv_dat_candidate *res;
        struct batadv_dat_entry dat;

        if (!bat_priv->orig_hash)
                return NULL;

        res = kmalloc_objs(*res, BATADV_DAT_CANDIDATES_NUM, GFP_ATOMIC);
        if (!res)
                return NULL;

        dat.ip = ip_dst;
        dat.vid = vid;
        ip_key = (batadv_dat_addr_t)batadv_hash_dat(&dat,
                                                    BATADV_DAT_ADDR_MAX);

        batadv_dbg(BATADV_DBG_DAT, bat_priv,
                   "%s(): IP=%pI4 hash(IP)=%u\n", __func__, &ip_dst,
                   ip_key);

        for (select = 0; select < BATADV_DAT_CANDIDATES_NUM; select++)
                batadv_choose_next_candidate(bat_priv, res, select, ip_key,
                                             &last_max);

        return res;
}

/**
 * batadv_dat_forward_data() - copy and send payload to the selected candidates
 * @bat_priv: the bat priv with all the mesh interface information
 * @skb: payload to send
 * @ip: the DHT key
 * @vid: VLAN identifier
 * @packet_subtype: unicast4addr packet subtype to use
 *
 * This function copies the skb with pskb_copy() and is sent as a unicast packet
 * to each of the selected candidates.
 *
 * Return: true if the packet is sent to at least one candidate, false
 * otherwise.
 */
static bool batadv_dat_forward_data(struct batadv_priv *bat_priv,
                                    struct sk_buff *skb, __be32 ip,
                                    unsigned short vid, int packet_subtype)
{
        int i;
        bool ret = false;
        int send_status;
        struct batadv_neigh_node *neigh_node = NULL;
        struct sk_buff *tmp_skb;
        struct batadv_dat_candidate *cand;

        cand = batadv_dat_select_candidates(bat_priv, ip, vid);
        if (!cand)
                return ret;

        batadv_dbg(BATADV_DBG_DAT, bat_priv, "DHT_SEND for %pI4\n", &ip);

        for (i = 0; i < BATADV_DAT_CANDIDATES_NUM; i++) {
                if (cand[i].type == BATADV_DAT_CANDIDATE_NOT_FOUND)
                        continue;

                neigh_node = batadv_orig_router_get(cand[i].orig_node,
                                                    BATADV_IF_DEFAULT);
                if (!neigh_node)
                        goto free_orig;

                tmp_skb = pskb_copy_for_clone(skb, GFP_ATOMIC);
                if (!batadv_send_skb_prepare_unicast_4addr(bat_priv, tmp_skb,
                                                           cand[i].orig_node,
                                                           packet_subtype)) {
                        kfree_skb(tmp_skb);
                        goto free_neigh;
                }

                send_status = batadv_send_unicast_skb(tmp_skb, neigh_node);
                if (send_status == NET_XMIT_SUCCESS) {
                        /* count the sent packet */
                        switch (packet_subtype) {
                        case BATADV_P_DAT_DHT_GET:
                                batadv_inc_counter(bat_priv,
                                                   BATADV_CNT_DAT_GET_TX);
                                break;
                        case BATADV_P_DAT_DHT_PUT:
                                batadv_inc_counter(bat_priv,
                                                   BATADV_CNT_DAT_PUT_TX);
                                break;
                        }

                        /* packet sent to a candidate: return true */
                        ret = true;
                }
free_neigh:
                batadv_neigh_node_put(neigh_node);
free_orig:
                batadv_orig_node_put(cand[i].orig_node);
        }

        kfree(cand);
        return ret;
}

/**
 * batadv_dat_tvlv_container_update() - update the dat tvlv container after dat
 *  setting change
 * @bat_priv: the bat priv with all the mesh interface information
 */
static void batadv_dat_tvlv_container_update(struct batadv_priv *bat_priv)
{
        char dat_mode;

        dat_mode = atomic_read(&bat_priv->distributed_arp_table);

        switch (dat_mode) {
        case 0:
                batadv_tvlv_container_unregister(bat_priv, BATADV_TVLV_DAT, 1);
                break;
        case 1:
                batadv_tvlv_container_register(bat_priv, BATADV_TVLV_DAT, 1,
                                               NULL, 0);
                break;
        }
}

/**
 * batadv_dat_status_update() - update the dat tvlv container after dat
 *  setting change
 * @net_dev: the mesh interface net device
 */
void batadv_dat_status_update(struct net_device *net_dev)
{
        struct batadv_priv *bat_priv = netdev_priv(net_dev);

        batadv_dat_tvlv_container_update(bat_priv);
}

/**
 * batadv_dat_tvlv_ogm_handler_v1() - process incoming dat tvlv container
 * @bat_priv: the bat priv with all the mesh interface information
 * @orig: the orig_node of the ogm
 * @flags: flags indicating the tvlv state (see batadv_tvlv_handler_flags)
 * @tvlv_value: tvlv buffer containing the gateway data
 * @tvlv_value_len: tvlv buffer length
 */
static void batadv_dat_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
                                           struct batadv_orig_node *orig,
                                           u8 flags,
                                           void *tvlv_value, u16 tvlv_value_len)
{
        if (flags & BATADV_TVLV_HANDLER_OGM_CIFNOTFND)
                clear_bit(BATADV_ORIG_CAPA_HAS_DAT, &orig->capabilities);
        else
                set_bit(BATADV_ORIG_CAPA_HAS_DAT, &orig->capabilities);
}

/**
 * batadv_dat_hash_free() - free the local DAT hash table
 * @bat_priv: the bat priv with all the mesh interface information
 */
static void batadv_dat_hash_free(struct batadv_priv *bat_priv)
{
        if (!bat_priv->dat.hash)
                return;

        __batadv_dat_purge(bat_priv, NULL);

        batadv_hash_destroy(bat_priv->dat.hash);

        bat_priv->dat.hash = NULL;
}

/**
 * batadv_dat_init() - initialise the DAT internals
 * @bat_priv: the bat priv with all the mesh interface information
 *
 * Return: 0 in case of success, a negative error code otherwise
 */
int batadv_dat_init(struct batadv_priv *bat_priv)
{
        if (bat_priv->dat.hash)
                return 0;

        bat_priv->dat.hash = batadv_hash_new(1024);

        if (!bat_priv->dat.hash)
                return -ENOMEM;

        INIT_DELAYED_WORK(&bat_priv->dat.work, batadv_dat_purge);
        batadv_dat_start_timer(bat_priv);

        batadv_tvlv_handler_register(bat_priv, batadv_dat_tvlv_ogm_handler_v1,
                                     NULL, NULL, BATADV_TVLV_DAT, 1,
                                     BATADV_TVLV_HANDLER_OGM_CIFNOTFND);
        batadv_dat_tvlv_container_update(bat_priv);
        return 0;
}

/**
 * batadv_dat_free() - free the DAT internals
 * @bat_priv: the bat priv with all the mesh interface information
 */
void batadv_dat_free(struct batadv_priv *bat_priv)
{
        batadv_tvlv_container_unregister(bat_priv, BATADV_TVLV_DAT, 1);
        batadv_tvlv_handler_unregister(bat_priv, BATADV_TVLV_DAT, 1);

        cancel_delayed_work_sync(&bat_priv->dat.work);

        batadv_dat_hash_free(bat_priv);
}

/**
 * batadv_dat_cache_dump_entry() - dump one entry of the DAT cache table to a
 *  netlink socket
 * @msg: buffer for the message
 * @portid: netlink port
 * @cb: Control block containing additional options
 * @dat_entry: entry to dump
 *
 * Return: 0 or error code.
 */
static int
batadv_dat_cache_dump_entry(struct sk_buff *msg, u32 portid,
                            struct netlink_callback *cb,
                            struct batadv_dat_entry *dat_entry)
{
        int msecs;
        void *hdr;

        hdr = genlmsg_put(msg, portid, cb->nlh->nlmsg_seq,
                          &batadv_netlink_family, NLM_F_MULTI,
                          BATADV_CMD_GET_DAT_CACHE);
        if (!hdr)
                return -ENOBUFS;

        genl_dump_check_consistent(cb, hdr);

        msecs = jiffies_to_msecs(jiffies - dat_entry->last_update);

        if (nla_put_in_addr(msg, BATADV_ATTR_DAT_CACHE_IP4ADDRESS,
                            dat_entry->ip) ||
            nla_put(msg, BATADV_ATTR_DAT_CACHE_HWADDRESS, ETH_ALEN,
                    dat_entry->mac_addr) ||
            nla_put_u16(msg, BATADV_ATTR_DAT_CACHE_VID, dat_entry->vid) ||
            nla_put_u32(msg, BATADV_ATTR_LAST_SEEN_MSECS, msecs)) {
                genlmsg_cancel(msg, hdr);
                return -EMSGSIZE;
        }

        genlmsg_end(msg, hdr);
        return 0;
}

/**
 * batadv_dat_cache_dump_bucket() - dump one bucket of the DAT cache table to
 *  a netlink socket
 * @msg: buffer for the message
 * @portid: netlink port
 * @cb: Control block containing additional options
 * @hash: hash to dump
 * @bucket: bucket index to dump
 * @idx_skip: How many entries to skip
 *
 * Return: 0 or error code.
 */
static int
batadv_dat_cache_dump_bucket(struct sk_buff *msg, u32 portid,
                             struct netlink_callback *cb,
                             struct batadv_hashtable *hash, unsigned int bucket,
                             int *idx_skip)
{
        struct batadv_dat_entry *dat_entry;
        int idx = 0;

        spin_lock_bh(&hash->list_locks[bucket]);
        cb->seq = atomic_read(&hash->generation) << 1 | 1;

        hlist_for_each_entry(dat_entry, &hash->table[bucket], hash_entry) {
                if (idx < *idx_skip)
                        goto skip;

                if (batadv_dat_cache_dump_entry(msg, portid, cb, dat_entry)) {
                        spin_unlock_bh(&hash->list_locks[bucket]);
                        *idx_skip = idx;

                        return -EMSGSIZE;
                }

skip:
                idx++;
        }
        spin_unlock_bh(&hash->list_locks[bucket]);

        return 0;
}

/**
 * batadv_dat_cache_dump() - dump DAT cache table to a netlink socket
 * @msg: buffer for the message
 * @cb: callback structure containing arguments
 *
 * Return: message length.
 */
int batadv_dat_cache_dump(struct sk_buff *msg, struct netlink_callback *cb)
{
        struct batadv_hard_iface *primary_if = NULL;
        int portid = NETLINK_CB(cb->skb).portid;
        struct net_device *mesh_iface;
        struct batadv_hashtable *hash;
        struct batadv_priv *bat_priv;
        int bucket = cb->args[0];
        int idx = cb->args[1];
        int ret = 0;

        mesh_iface = batadv_netlink_get_meshif(cb);
        if (IS_ERR(mesh_iface))
                return PTR_ERR(mesh_iface);

        bat_priv = netdev_priv(mesh_iface);
        hash = bat_priv->dat.hash;

        primary_if = batadv_primary_if_get_selected(bat_priv);
        if (!primary_if || primary_if->if_status != BATADV_IF_ACTIVE) {
                ret = -ENOENT;
                goto out;
        }

        while (bucket < hash->size) {
                if (batadv_dat_cache_dump_bucket(msg, portid, cb, hash, bucket,
                                                 &idx))
                        break;

                bucket++;
                idx = 0;
        }

        cb->args[0] = bucket;
        cb->args[1] = idx;

        ret = msg->len;

out:
        batadv_hardif_put(primary_if);

        dev_put(mesh_iface);

        return ret;
}

/**
 * batadv_arp_get_type() - parse an ARP packet and gets the type
 * @bat_priv: the bat priv with all the mesh interface information
 * @skb: packet to analyse
 * @hdr_size: size of the possible header before the ARP packet in the skb
 *
 * Return: the ARP type if the skb contains a valid ARP packet, 0 otherwise.
 */
static u16 batadv_arp_get_type(struct batadv_priv *bat_priv,
                               struct sk_buff *skb, int hdr_size)
{
        struct arphdr *arphdr;
        struct ethhdr *ethhdr;
        __be32 ip_src, ip_dst;
        u8 *hw_src, *hw_dst;
        u16 type = 0;

        /* pull the ethernet header */
        if (unlikely(!pskb_may_pull(skb, hdr_size + ETH_HLEN)))
                goto out;

        ethhdr = (struct ethhdr *)(skb->data + hdr_size);

        if (ethhdr->h_proto != htons(ETH_P_ARP))
                goto out;

        /* pull the ARP payload */
        if (unlikely(!pskb_may_pull(skb, hdr_size + ETH_HLEN +
                                    arp_hdr_len(skb->dev))))
                goto out;

        arphdr = (struct arphdr *)(skb->data + hdr_size + ETH_HLEN);

        /* check whether the ARP packet carries a valid IP information */
        if (arphdr->ar_hrd != htons(ARPHRD_ETHER))
                goto out;

        if (arphdr->ar_pro != htons(ETH_P_IP))
                goto out;

        if (arphdr->ar_hln != ETH_ALEN)
                goto out;

        if (arphdr->ar_pln != 4)
                goto out;

        /* Check for bad reply/request. If the ARP message is not sane, DAT
         * will simply ignore it
         */
        ip_src = batadv_arp_ip_src(skb, hdr_size);
        ip_dst = batadv_arp_ip_dst(skb, hdr_size);
        if (ipv4_is_loopback(ip_src) || ipv4_is_multicast(ip_src) ||
            ipv4_is_loopback(ip_dst) || ipv4_is_multicast(ip_dst) ||
            ipv4_is_zeronet(ip_src) || ipv4_is_lbcast(ip_src) ||
            ipv4_is_zeronet(ip_dst) || ipv4_is_lbcast(ip_dst))
                goto out;

        hw_src = batadv_arp_hw_src(skb, hdr_size);
        if (is_zero_ether_addr(hw_src) || is_multicast_ether_addr(hw_src))
                goto out;

        /* don't care about the destination MAC address in ARP requests */
        if (arphdr->ar_op != htons(ARPOP_REQUEST)) {
                hw_dst = batadv_arp_hw_dst(skb, hdr_size);
                if (is_zero_ether_addr(hw_dst) ||
                    is_multicast_ether_addr(hw_dst))
                        goto out;
        }

        type = ntohs(arphdr->ar_op);
out:
        return type;
}

/**
 * batadv_dat_get_vid() - extract the VLAN identifier from skb if any
 * @skb: the buffer containing the packet to extract the VID from
 * @hdr_size: the size of the batman-adv header encapsulating the packet
 *
 * Return: If the packet embedded in the skb is vlan tagged this function
 * returns the VID with the BATADV_VLAN_HAS_TAG flag. Otherwise BATADV_NO_FLAGS
 * is returned.
 */
static unsigned short batadv_dat_get_vid(struct sk_buff *skb, int *hdr_size)
{
        unsigned short vid;

        vid = batadv_get_vid(skb, *hdr_size);

        /* ARP parsing functions jump forward of hdr_size + ETH_HLEN.
         * If the header contained in the packet is a VLAN one (which is longer)
         * hdr_size is updated so that the functions will still skip the
         * correct amount of bytes.
         */
        if (vid & BATADV_VLAN_HAS_TAG)
                *hdr_size += VLAN_HLEN;

        return vid;
}

/**
 * batadv_dat_arp_create_reply() - create an ARP Reply
 * @bat_priv: the bat priv with all the mesh interface information
 * @ip_src: ARP sender IP
 * @ip_dst: ARP target IP
 * @hw_src: Ethernet source and ARP sender MAC
 * @hw_dst: Ethernet destination and ARP target MAC
 * @vid: VLAN identifier (optional, set to zero otherwise)
 *
 * Creates an ARP Reply from the given values, optionally encapsulated in a
 * VLAN header.
 *
 * Return: An skb containing an ARP Reply.
 */
static struct sk_buff *
batadv_dat_arp_create_reply(struct batadv_priv *bat_priv, __be32 ip_src,
                            __be32 ip_dst, u8 *hw_src, u8 *hw_dst,
                            unsigned short vid)
{
        struct sk_buff *skb;

        skb = arp_create(ARPOP_REPLY, ETH_P_ARP, ip_dst, bat_priv->mesh_iface,
                         ip_src, hw_dst, hw_src, hw_dst);
        if (!skb)
                return NULL;

        skb_reset_mac_header(skb);

        if (vid & BATADV_VLAN_HAS_TAG)
                skb = vlan_insert_tag(skb, htons(ETH_P_8021Q),
                                      vid & VLAN_VID_MASK);

        return skb;
}

/**
 * batadv_dat_snoop_outgoing_arp_request() - snoop the ARP request and try to
 * answer using DAT
 * @bat_priv: the bat priv with all the mesh interface information
 * @skb: packet to check
 *
 * Return: true if the message has been sent to the dht candidates, false
 * otherwise. In case of a positive return value the message has to be enqueued
 * to permit the fallback.
 */
bool batadv_dat_snoop_outgoing_arp_request(struct batadv_priv *bat_priv,
                                           struct sk_buff *skb)
{
        u16 type = 0;
        __be32 ip_dst, ip_src;
        u8 *hw_src;
        bool ret = false;
        struct batadv_dat_entry *dat_entry = NULL;
        struct sk_buff *skb_new;
        struct net_device *mesh_iface = bat_priv->mesh_iface;
        int hdr_size = 0;
        unsigned short vid;

        if (!atomic_read(&bat_priv->distributed_arp_table))
                goto out;

        vid = batadv_dat_get_vid(skb, &hdr_size);

        type = batadv_arp_get_type(bat_priv, skb, hdr_size);
        /* If the node gets an ARP_REQUEST it has to send a DHT_GET unicast
         * message to the selected DHT candidates
         */
        if (type != ARPOP_REQUEST)
                goto out;

        batadv_dbg_arp(bat_priv, skb, hdr_size, "Parsing outgoing ARP REQUEST");

        ip_src = batadv_arp_ip_src(skb, hdr_size);
        hw_src = batadv_arp_hw_src(skb, hdr_size);
        ip_dst = batadv_arp_ip_dst(skb, hdr_size);

        batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);

        dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_dst, vid);
        if (dat_entry) {
                /* If the ARP request is destined for a local client the local
                 * client will answer itself. DAT would only generate a
                 * duplicate packet.
                 *
                 * Moreover, if the mesh-interface is enslaved into a bridge, an
                 * additional DAT answer may trigger kernel warnings about
                 * a packet coming from the wrong port.
                 */
                if (batadv_is_my_client(bat_priv, dat_entry->mac_addr, vid)) {
                        ret = true;
                        goto out;
                }

                /* If BLA is enabled, only send ARP replies if we have claimed
                 * the destination for the ARP request or if no one else of
                 * the backbone gws belonging to our backbone has claimed the
                 * destination.
                 */
                if (!batadv_bla_check_claim(bat_priv,
                                            dat_entry->mac_addr, vid)) {
                        batadv_dbg(BATADV_DBG_DAT, bat_priv,
                                   "Device %pM claimed by another backbone gw. Don't send ARP reply!",
                                   dat_entry->mac_addr);
                        ret = true;
                        goto out;
                }

                skb_new = batadv_dat_arp_create_reply(bat_priv, ip_dst, ip_src,
                                                      dat_entry->mac_addr,
                                                      hw_src, vid);
                if (!skb_new)
                        goto out;

                skb_new->protocol = eth_type_trans(skb_new, mesh_iface);

                batadv_inc_counter(bat_priv, BATADV_CNT_RX);
                batadv_add_counter(bat_priv, BATADV_CNT_RX_BYTES,
                                   skb->len + ETH_HLEN + hdr_size);

                netif_rx(skb_new);
                batadv_dbg(BATADV_DBG_DAT, bat_priv, "ARP request replied locally\n");
                ret = true;
        } else {
                /* Send the request to the DHT */
                ret = batadv_dat_forward_data(bat_priv, skb, ip_dst, vid,
                                              BATADV_P_DAT_DHT_GET);
        }
out:
        batadv_dat_entry_put(dat_entry);
        return ret;
}

/**
 * batadv_dat_snoop_incoming_arp_request() - snoop the ARP request and try to
 * answer using the local DAT storage
 * @bat_priv: the bat priv with all the mesh interface information
 * @skb: packet to check
 * @hdr_size: size of the encapsulation header
 *
 * Return: true if the request has been answered, false otherwise.
 */
bool batadv_dat_snoop_incoming_arp_request(struct batadv_priv *bat_priv,
                                           struct sk_buff *skb, int hdr_size)
{
        u16 type;
        __be32 ip_src, ip_dst;
        u8 *hw_src;
        struct sk_buff *skb_new;
        struct batadv_dat_entry *dat_entry = NULL;
        bool ret = false;
        unsigned short vid;
        int err;

        if (!atomic_read(&bat_priv->distributed_arp_table))
                goto out;

        vid = batadv_dat_get_vid(skb, &hdr_size);

        type = batadv_arp_get_type(bat_priv, skb, hdr_size);
        if (type != ARPOP_REQUEST)
                goto out;

        hw_src = batadv_arp_hw_src(skb, hdr_size);
        ip_src = batadv_arp_ip_src(skb, hdr_size);
        ip_dst = batadv_arp_ip_dst(skb, hdr_size);

        batadv_dbg_arp(bat_priv, skb, hdr_size, "Parsing incoming ARP REQUEST");

        batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);

        dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_dst, vid);
        if (!dat_entry)
                goto out;

        skb_new = batadv_dat_arp_create_reply(bat_priv, ip_dst, ip_src,
                                              dat_entry->mac_addr, hw_src, vid);
        if (!skb_new)
                goto out;

        /* To preserve backwards compatibility, the node has choose the outgoing
         * format based on the incoming request packet type. The assumption is
         * that a node not using the 4addr packet format doesn't support it.
         */
        if (hdr_size == sizeof(struct batadv_unicast_4addr_packet))
                err = batadv_send_skb_via_tt_4addr(bat_priv, skb_new,
                                                   BATADV_P_DAT_CACHE_REPLY,
                                                   NULL, vid);
        else
                err = batadv_send_skb_via_tt(bat_priv, skb_new, NULL, vid);

        if (err != NET_XMIT_DROP) {
                batadv_inc_counter(bat_priv, BATADV_CNT_DAT_CACHED_REPLY_TX);
                ret = true;
        }
out:
        batadv_dat_entry_put(dat_entry);
        if (ret)
                kfree_skb(skb);
        return ret;
}

/**
 * batadv_dat_snoop_outgoing_arp_reply() - snoop the ARP reply and fill the DHT
 * @bat_priv: the bat priv with all the mesh interface information
 * @skb: packet to check
 */
void batadv_dat_snoop_outgoing_arp_reply(struct batadv_priv *bat_priv,
                                         struct sk_buff *skb)
{
        u16 type;
        __be32 ip_src, ip_dst;
        u8 *hw_src, *hw_dst;
        int hdr_size = 0;
        unsigned short vid;

        if (!atomic_read(&bat_priv->distributed_arp_table))
                return;

        vid = batadv_dat_get_vid(skb, &hdr_size);

        type = batadv_arp_get_type(bat_priv, skb, hdr_size);
        if (type != ARPOP_REPLY)
                return;

        batadv_dbg_arp(bat_priv, skb, hdr_size, "Parsing outgoing ARP REPLY");

        hw_src = batadv_arp_hw_src(skb, hdr_size);
        ip_src = batadv_arp_ip_src(skb, hdr_size);
        hw_dst = batadv_arp_hw_dst(skb, hdr_size);
        ip_dst = batadv_arp_ip_dst(skb, hdr_size);

        batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);
        batadv_dat_entry_add(bat_priv, ip_dst, hw_dst, vid);

        /* Send the ARP reply to the candidates for both the IP addresses that
         * the node obtained from the ARP reply
         */
        batadv_dat_forward_data(bat_priv, skb, ip_src, vid,
                                BATADV_P_DAT_DHT_PUT);
        batadv_dat_forward_data(bat_priv, skb, ip_dst, vid,
                                BATADV_P_DAT_DHT_PUT);
}

/**
 * batadv_dat_snoop_incoming_arp_reply() - snoop the ARP reply and fill the
 *  local DAT storage only
 * @bat_priv: the bat priv with all the mesh interface information
 * @skb: packet to check
 * @hdr_size: size of the encapsulation header
 *
 * Return: true if the packet was snooped and consumed by DAT. False if the
 * packet has to be delivered to the interface
 */
bool batadv_dat_snoop_incoming_arp_reply(struct batadv_priv *bat_priv,
                                         struct sk_buff *skb, int hdr_size)
{
        struct batadv_dat_entry *dat_entry = NULL;
        u16 type;
        __be32 ip_src, ip_dst;
        u8 *hw_src, *hw_dst;
        bool dropped = false;
        unsigned short vid;

        if (!atomic_read(&bat_priv->distributed_arp_table))
                goto out;

        vid = batadv_dat_get_vid(skb, &hdr_size);

        type = batadv_arp_get_type(bat_priv, skb, hdr_size);
        if (type != ARPOP_REPLY)
                goto out;

        batadv_dbg_arp(bat_priv, skb, hdr_size, "Parsing incoming ARP REPLY");

        hw_src = batadv_arp_hw_src(skb, hdr_size);
        ip_src = batadv_arp_ip_src(skb, hdr_size);
        hw_dst = batadv_arp_hw_dst(skb, hdr_size);
        ip_dst = batadv_arp_ip_dst(skb, hdr_size);

        /* If ip_dst is already in cache and has the right mac address,
         * drop this frame if this ARP reply is destined for us because it's
         * most probably an ARP reply generated by another node of the DHT.
         * We have most probably received already a reply earlier. Delivering
         * this frame would lead to doubled receive of an ARP reply.
         */
        dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_src, vid);
        if (dat_entry && batadv_compare_eth(hw_src, dat_entry->mac_addr)) {
                batadv_dbg(BATADV_DBG_DAT, bat_priv, "Doubled ARP reply removed: ARP MSG = [src: %pM-%pI4 dst: %pM-%pI4]; dat_entry: %pM-%pI4\n",
                           hw_src, &ip_src, hw_dst, &ip_dst,
                           dat_entry->mac_addr, &dat_entry->ip);
                dropped = true;
        }

        /* Update our internal cache with both the IP addresses the node got
         * within the ARP reply
         */
        batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);
        batadv_dat_entry_add(bat_priv, ip_dst, hw_dst, vid);

        if (dropped)
                goto out;

        /* If BLA is enabled, only forward ARP replies if we have claimed the
         * source of the ARP reply or if no one else of the same backbone has
         * already claimed that client. This prevents that different gateways
         * to the same backbone all forward the ARP reply leading to multiple
         * replies in the backbone.
         */
        if (!batadv_bla_check_claim(bat_priv, hw_src, vid)) {
                batadv_dbg(BATADV_DBG_DAT, bat_priv,
                           "Device %pM claimed by another backbone gw. Drop ARP reply.\n",
                           hw_src);
                dropped = true;
                goto out;
        }

        /* if this REPLY is directed to a client of mine, let's deliver the
         * packet to the interface
         */
        dropped = !batadv_is_my_client(bat_priv, hw_dst, vid);

        /* if this REPLY is sent on behalf of a client of mine, let's drop the
         * packet because the client will reply by itself
         */
        dropped |= batadv_is_my_client(bat_priv, hw_src, vid);
out:
        if (dropped)
                kfree_skb(skb);
        batadv_dat_entry_put(dat_entry);
        /* if dropped == false -> deliver to the interface */
        return dropped;
}

/**
 * batadv_dat_check_dhcp_ipudp() - check skb for IP+UDP headers valid for DHCP
 * @skb: the packet to check
 * @ip_src: a buffer to store the IPv4 source address in
 *
 * Checks whether the given skb has an IP and UDP header valid for a DHCP
 * message from a DHCP server. And if so, stores the IPv4 source address in
 * the provided buffer.
 *
 * Return: True if valid, false otherwise.
 */
static bool
batadv_dat_check_dhcp_ipudp(struct sk_buff *skb, __be32 *ip_src)
{
        unsigned int offset = skb_network_offset(skb);
        struct udphdr *udphdr, _udphdr;
        struct iphdr *iphdr, _iphdr;

        iphdr = skb_header_pointer(skb, offset, sizeof(_iphdr), &_iphdr);
        if (!iphdr || iphdr->version != 4 || iphdr->ihl * 4 < sizeof(_iphdr))
                return false;

        if (iphdr->protocol != IPPROTO_UDP)
                return false;

        offset += iphdr->ihl * 4;
        skb_set_transport_header(skb, offset);

        udphdr = skb_header_pointer(skb, offset, sizeof(_udphdr), &_udphdr);
        if (!udphdr || udphdr->source != htons(67))
                return false;

        *ip_src = get_unaligned(&iphdr->saddr);

        return true;
}

/**
 * batadv_dat_check_dhcp() - examine packet for valid DHCP message
 * @skb: the packet to check
 * @proto: ethernet protocol hint (behind a potential vlan)
 * @ip_src: a buffer to store the IPv4 source address in
 *
 * Checks whether the given skb is a valid DHCP packet. And if so, stores the
 * IPv4 source address in the provided buffer.
 *
 * Caller needs to ensure that the skb network header is set correctly.
 *
 * Return: If skb is a valid DHCP packet, then returns its op code
 * (e.g. BOOTREPLY vs. BOOTREQUEST). Otherwise returns -EINVAL.
 */
static int
batadv_dat_check_dhcp(struct sk_buff *skb, __be16 proto, __be32 *ip_src)
{
        __be32 *magic, _magic;
        unsigned int offset;
        struct {
                __u8 op;
                __u8 htype;
                __u8 hlen;
                __u8 hops;
        } *dhcp_h, _dhcp_h;

        if (proto != htons(ETH_P_IP))
                return -EINVAL;

        if (!batadv_dat_check_dhcp_ipudp(skb, ip_src))
                return -EINVAL;

        offset = skb_transport_offset(skb) + sizeof(struct udphdr);
        if (skb->len < offset + sizeof(struct batadv_dhcp_packet))
                return -EINVAL;

        dhcp_h = skb_header_pointer(skb, offset, sizeof(_dhcp_h), &_dhcp_h);
        if (!dhcp_h || dhcp_h->htype != BATADV_HTYPE_ETHERNET ||
            dhcp_h->hlen != ETH_ALEN)
                return -EINVAL;

        offset += offsetof(struct batadv_dhcp_packet, magic);

        magic = skb_header_pointer(skb, offset, sizeof(_magic), &_magic);
        if (!magic || get_unaligned(magic) != htonl(BATADV_DHCP_MAGIC))
                return -EINVAL;

        return dhcp_h->op;
}

/**
 * batadv_dat_get_dhcp_message_type() - get message type of a DHCP packet
 * @skb: the DHCP packet to parse
 *
 * Iterates over the DHCP options of the given DHCP packet to find a
 * DHCP Message Type option and parse it.
 *
 * Caller needs to ensure that the given skb is a valid DHCP packet and
 * that the skb transport header is set correctly.
 *
 * Return: The found DHCP message type value, if found. -EINVAL otherwise.
 */
static int batadv_dat_get_dhcp_message_type(struct sk_buff *skb)
{
        unsigned int offset = skb_transport_offset(skb) + sizeof(struct udphdr);
        u8 *type, _type;
        struct {
                u8 type;
                u8 len;
        } *tl, _tl;

        offset += sizeof(struct batadv_dhcp_packet);

        while ((tl = skb_header_pointer(skb, offset, sizeof(_tl), &_tl))) {
                if (tl->type == BATADV_DHCP_OPT_MSG_TYPE)
                        break;

                if (tl->type == BATADV_DHCP_OPT_END)
                        break;

                if (tl->type == BATADV_DHCP_OPT_PAD)
                        offset++;
                else
                        offset += tl->len + sizeof(_tl);
        }

        /* Option Overload Code not supported */
        if (!tl || tl->type != BATADV_DHCP_OPT_MSG_TYPE ||
            tl->len != sizeof(_type))
                return -EINVAL;

        offset += sizeof(_tl);

        type = skb_header_pointer(skb, offset, sizeof(_type), &_type);
        if (!type)
                return -EINVAL;

        return *type;
}

/**
 * batadv_dat_dhcp_get_yiaddr() - get yiaddr from a DHCP packet
 * @skb: the DHCP packet to parse
 * @buf: a buffer to store the yiaddr in
 *
 * Caller needs to ensure that the given skb is a valid DHCP packet and
 * that the skb transport header is set correctly.
 *
 * Return: True on success, false otherwise.
 */
static bool batadv_dat_dhcp_get_yiaddr(struct sk_buff *skb, __be32 *buf)
{
        unsigned int offset = skb_transport_offset(skb) + sizeof(struct udphdr);
        __be32 *yiaddr;

        offset += offsetof(struct batadv_dhcp_packet, yiaddr);
        yiaddr = skb_header_pointer(skb, offset, BATADV_DHCP_YIADDR_LEN, buf);

        if (!yiaddr)
                return false;

        if (yiaddr != buf)
                *buf = get_unaligned(yiaddr);

        return true;
}

/**
 * batadv_dat_get_dhcp_chaddr() - get chaddr from a DHCP packet
 * @skb: the DHCP packet to parse
 * @buf: a buffer to store the chaddr in
 *
 * Caller needs to ensure that the given skb is a valid DHCP packet and
 * that the skb transport header is set correctly.
 *
 * Return: True on success, false otherwise
 */
static bool batadv_dat_get_dhcp_chaddr(struct sk_buff *skb, u8 *buf)
{
        unsigned int offset = skb_transport_offset(skb) + sizeof(struct udphdr);
        u8 *chaddr;

        offset += offsetof(struct batadv_dhcp_packet, chaddr);
        chaddr = skb_header_pointer(skb, offset, BATADV_DHCP_CHADDR_LEN, buf);

        if (!chaddr)
                return false;

        if (chaddr != buf)
                memcpy(buf, chaddr, BATADV_DHCP_CHADDR_LEN);

        return true;
}

/**
 * batadv_dat_put_dhcp() - puts addresses from a DHCP packet into the DHT and
 *  DAT cache
 * @bat_priv: the bat priv with all the mesh interface information
 * @chaddr: the DHCP client MAC address
 * @yiaddr: the DHCP client IP address
 * @hw_dst: the DHCP server MAC address
 * @ip_dst: the DHCP server IP address
 * @vid: VLAN identifier
 *
 * Adds given MAC/IP pairs to the local DAT cache and propagates them further
 * into the DHT.
 *
 * For the DHT propagation, client MAC + IP will appear as the ARP Reply
 * transmitter (and hw_dst/ip_dst as the target).
 */
static void batadv_dat_put_dhcp(struct batadv_priv *bat_priv, u8 *chaddr,
                                __be32 yiaddr, u8 *hw_dst, __be32 ip_dst,
                                unsigned short vid)
{
        struct sk_buff *skb;

        skb = batadv_dat_arp_create_reply(bat_priv, yiaddr, ip_dst, chaddr,
                                          hw_dst, vid);
        if (!skb)
                return;

        skb_set_network_header(skb, ETH_HLEN);

        batadv_dat_entry_add(bat_priv, yiaddr, chaddr, vid);
        batadv_dat_entry_add(bat_priv, ip_dst, hw_dst, vid);

        batadv_dat_forward_data(bat_priv, skb, yiaddr, vid,
                                BATADV_P_DAT_DHT_PUT);
        batadv_dat_forward_data(bat_priv, skb, ip_dst, vid,
                                BATADV_P_DAT_DHT_PUT);

        consume_skb(skb);

        batadv_dbg(BATADV_DBG_DAT, bat_priv,
                   "Snooped from outgoing DHCPACK (server address): %pI4, %pM (vid: %i)\n",
                   &ip_dst, hw_dst, batadv_print_vid(vid));
        batadv_dbg(BATADV_DBG_DAT, bat_priv,
                   "Snooped from outgoing DHCPACK (client address): %pI4, %pM (vid: %i)\n",
                   &yiaddr, chaddr, batadv_print_vid(vid));
}

/**
 * batadv_dat_check_dhcp_ack() - examine packet for valid DHCP message
 * @skb: the packet to check
 * @proto: ethernet protocol hint (behind a potential vlan)
 * @ip_src: a buffer to store the IPv4 source address in
 * @chaddr: a buffer to store the DHCP Client Hardware Address in
 * @yiaddr: a buffer to store the DHCP Your IP Address in
 *
 * Checks whether the given skb is a valid DHCPACK. And if so, stores the
 * IPv4 server source address (ip_src), client MAC address (chaddr) and client
 * IPv4 address (yiaddr) in the provided buffers.
 *
 * Caller needs to ensure that the skb network header is set correctly.
 *
 * Return: True if the skb is a valid DHCPACK. False otherwise.
 */
static bool
batadv_dat_check_dhcp_ack(struct sk_buff *skb, __be16 proto, __be32 *ip_src,
                          u8 *chaddr, __be32 *yiaddr)
{
        int type;

        type = batadv_dat_check_dhcp(skb, proto, ip_src);
        if (type != BATADV_BOOTREPLY)
                return false;

        type = batadv_dat_get_dhcp_message_type(skb);
        if (type != BATADV_DHCPACK)
                return false;

        if (!batadv_dat_dhcp_get_yiaddr(skb, yiaddr))
                return false;

        if (!batadv_dat_get_dhcp_chaddr(skb, chaddr))
                return false;

        return true;
}

/**
 * batadv_dat_snoop_outgoing_dhcp_ack() - snoop DHCPACK and fill DAT with it
 * @bat_priv: the bat priv with all the mesh interface information
 * @skb: the packet to snoop
 * @proto: ethernet protocol hint (behind a potential vlan)
 * @vid: VLAN identifier
 *
 * This function first checks whether the given skb is a valid DHCPACK. If
 * so then its source MAC and IP as well as its DHCP Client Hardware Address
 * field and DHCP Your IP Address field are added to the local DAT cache and
 * propagated into the DHT.
 *
 * Caller needs to ensure that the skb mac and network headers are set
 * correctly.
 */
void batadv_dat_snoop_outgoing_dhcp_ack(struct batadv_priv *bat_priv,
                                        struct sk_buff *skb,
                                        __be16 proto,
                                        unsigned short vid)
{
        u8 chaddr[BATADV_DHCP_CHADDR_LEN];
        __be32 ip_src, yiaddr;

        if (!atomic_read(&bat_priv->distributed_arp_table))
                return;

        if (!batadv_dat_check_dhcp_ack(skb, proto, &ip_src, chaddr, &yiaddr))
                return;

        batadv_dat_put_dhcp(bat_priv, chaddr, yiaddr, eth_hdr(skb)->h_source,
                            ip_src, vid);
}

/**
 * batadv_dat_snoop_incoming_dhcp_ack() - snoop DHCPACK and fill DAT cache
 * @bat_priv: the bat priv with all the mesh interface information
 * @skb: the packet to snoop
 * @hdr_size: header size, up to the tail of the batman-adv header
 *
 * This function first checks whether the given skb is a valid DHCPACK. If
 * so then its source MAC and IP as well as its DHCP Client Hardware Address
 * field and DHCP Your IP Address field are added to the local DAT cache.
 */
void batadv_dat_snoop_incoming_dhcp_ack(struct batadv_priv *bat_priv,
                                        struct sk_buff *skb, int hdr_size)
{
        u8 chaddr[BATADV_DHCP_CHADDR_LEN];
        struct ethhdr *ethhdr;
        __be32 ip_src, yiaddr;
        unsigned short vid;
        __be16 proto;
        u8 *hw_src;

        if (!atomic_read(&bat_priv->distributed_arp_table))
                return;

        if (unlikely(!pskb_may_pull(skb, hdr_size + ETH_HLEN)))
                return;

        ethhdr = (struct ethhdr *)(skb->data + hdr_size);
        skb_set_network_header(skb, hdr_size + ETH_HLEN);
        proto = ethhdr->h_proto;

        if (!batadv_dat_check_dhcp_ack(skb, proto, &ip_src, chaddr, &yiaddr))
                return;

        hw_src = ethhdr->h_source;
        vid = batadv_dat_get_vid(skb, &hdr_size);

        batadv_dat_entry_add(bat_priv, yiaddr, chaddr, vid);
        batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);

        batadv_dbg(BATADV_DBG_DAT, bat_priv,
                   "Snooped from incoming DHCPACK (server address): %pI4, %pM (vid: %i)\n",
                   &ip_src, hw_src, batadv_print_vid(vid));
        batadv_dbg(BATADV_DBG_DAT, bat_priv,
                   "Snooped from incoming DHCPACK (client address): %pI4, %pM (vid: %i)\n",
                   &yiaddr, chaddr, batadv_print_vid(vid));
}

/**
 * batadv_dat_drop_broadcast_packet() - check if an ARP request has to be
 *  dropped (because the node has already obtained the reply via DAT) or not
 * @bat_priv: the bat priv with all the mesh interface information
 * @forw_packet: the broadcast packet
 *
 * Return: true if the node can drop the packet, false otherwise.
 */
bool batadv_dat_drop_broadcast_packet(struct batadv_priv *bat_priv,
                                      struct batadv_forw_packet *forw_packet)
{
        u16 type;
        __be32 ip_dst;
        struct batadv_dat_entry *dat_entry = NULL;
        bool ret = false;
        int hdr_size = sizeof(struct batadv_bcast_packet);
        unsigned short vid;

        if (!atomic_read(&bat_priv->distributed_arp_table))
                goto out;

        /* If this packet is an ARP_REQUEST and the node already has the
         * information that it is going to ask, then the packet can be dropped
         */
        if (batadv_forw_packet_is_rebroadcast(forw_packet))
                goto out;

        vid = batadv_dat_get_vid(forw_packet->skb, &hdr_size);

        type = batadv_arp_get_type(bat_priv, forw_packet->skb, hdr_size);
        if (type != ARPOP_REQUEST)
                goto out;

        ip_dst = batadv_arp_ip_dst(forw_packet->skb, hdr_size);
        dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_dst, vid);
        /* check if the node already got this entry */
        if (!dat_entry) {
                batadv_dbg(BATADV_DBG_DAT, bat_priv,
                           "ARP Request for %pI4: fallback\n", &ip_dst);
                goto out;
        }

        batadv_dbg(BATADV_DBG_DAT, bat_priv,
                   "ARP Request for %pI4: fallback prevented\n", &ip_dst);
        ret = true;

out:
        batadv_dat_entry_put(dat_entry);
        return ret;
}