x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 1990 insertions, 0 deletions

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
new file mode 100644
index 000000000..011cfdc47
--- /dev/null
+++ b/net/batman-adv/distributed-arp-table.c
@@ -0,0 +1,1990 @@
+// 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/bug.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 - BOOTP/DHCP message op codes
+ */
+enum batadv_bootpop {
+	/** @BATADV_BOOTREPLY: server-to-client reply */
+	BATADV_BOOTREPLY	= 2,
+};
+
+/**
+ * enum batadv_boothtype - BOOTP/DHCP hardware address types
+ */
+enum batadv_boothtype {
+	/** @BATADV_HTYPE_ETHERNET: Ethernet (10Mb) */
+	BATADV_HTYPE_ETHERNET	= 1,
+};
+
+/**
+ * enum batadv_dhcpoptioncode - DHCP option codes relevant for batman-adv DAT
+ */
+enum batadv_dhcpoptioncode {
+	/** @BATADV_DHCP_OPT_PAD: pad option */
+	BATADV_DHCP_OPT_PAD		= 0,
+
+	/** @BATADV_DHCP_OPT_MSG_TYPE: DHCP message type option */
+	BATADV_DHCP_OPT_MSG_TYPE	= 53,
+
+	/** @BATADV_DHCP_OPT_END: end of options marker */
+	BATADV_DHCP_OPT_END		= 255,
+};
+
+/**
+ * enum batadv_dhcptype - DHCP message types relevant for batman-adv DAT
+ */
+enum batadv_dhcptype {
+	/** @BATADV_DHCPACK: DHCPACK message */
+	BATADV_DHCPACK		= 5,
+};
+
+/* { 99, 130, 83, 99 } */
+#define BATADV_DHCP_MAGIC 1669485411
+
+/**
+ * struct batadv_dhcp_packet - BOOTP/DHCP packet header
+ * @op: message op code / message type
+ * @htype: hardware address type
+ * @hlen: hardware address length
+ * @hops: number of relay hops
+ * @xid: transaction identifier
+ * @secs: seconds elapsed since client started trying to boot
+ * @flags: BOOTP/DHCP flags
+ * @ciaddr: client IP address
+ * @yiaddr: "your" (client) IP address as assigned by the server
+ * @siaddr: IP address of next server to use in bootstrap
+ * @giaddr: relay agent IP address
+ * @chaddr: client hardware address
+ * @sname: optional server host name
+ * @file: boot file name
+ * @magic: BOOTP/DHCP magic cookie identifying the start of options
+ */
+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[]; */
+};
+
+/**
+ * struct batadv_dhcp_header - minimal BOOTP/DHCP packet header
+ */
+struct batadv_dhcp_header {
+	/** @op: message op code / message type */
+	__u8 op;
+
+	/** @htype: hardware address type */
+	__u8 htype;
+
+	/** @hlen: hardware address length */
+	__u8 hlen;
+
+	/** @hops: number of relay hops */
+	__u8 hops;
+};
+
+/**
+ * struct batadv_dhcp_option_header - BOOTP/DHCP option header
+ */
+struct batadv_dhcp_option_header {
+	/** @type: type of option */
+	__u8 type;
+
+	/** @len: length of option */
+	__u8 len;
+};
+
+#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 struct batadv_dat_entry *entry1;
+	const struct batadv_dat_entry *entry2;
+
+	entry1 = container_of(node, struct batadv_dat_entry, hash_entry);
+	entry2 = data2;
+
+	return entry1->ip == entry2->ip && entry1->vid == entry2->vid;
+}
+
+/**
+ * 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)
+{
+	u8 *src = batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN;
+	__be32 *ip = (__force __be32 *)src;
+
+	return get_unaligned(ip);
+}
+
+/**
+ * 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;
+	__be32 *ip = (__force __be32 *)dst;
+
+	return get_unaligned(ip);
+}
+
+/**
+ * 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)
+{
+	const struct batadv_dat_entry *dat = data;
+	const unsigned char *key;
+	u32 hash = 0;
+	__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 batadv_hashtable *hash = bat_priv->dat.hash;
+	struct batadv_dat_entry *dat_entry_tmp = NULL;
+	struct batadv_dat_entry *dat_entry;
+	struct batadv_dat_entry to_find;
+	struct hlist_head *head;
+	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 (dat_entry->vid != vid)
+			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)
+{
+	u64 u64_mac = ether_addr_to_u64(mac_addr);
+	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) {
+		atomic64_set(&dat_entry->mac_addr, u64_mac);
+
+		dat_entry->last_update = jiffies;
+		batadv_dbg(BATADV_DBG_DAT, bat_priv,
+			   "Entry updated: %pI4 %pM (vid: %d)\n",
+			   &dat_entry->ip, 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;
+	atomic64_set(&dat_entry->mac_addr, u64_mac);
+	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, 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;
+	__be32 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 &&
+	    memcmp(candidate->orig, max_orig_node->orig, ETH_ALEN) >= 0)
+		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)
+{
+	struct batadv_hashtable *hash = bat_priv->orig_hash;
+	struct batadv_orig_node *max_orig_node = NULL;
+	struct batadv_orig_node *orig_node;
+	batadv_dat_addr_t tmp_max = 0;
+	batadv_dat_addr_t max = 0;
+	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)
+{
+	batadv_dat_addr_t last_max = BATADV_DAT_ADDR_MAX;
+	struct batadv_dat_candidate *res;
+	struct batadv_dat_entry dat;
+	batadv_dat_addr_t ip_key;
+	int select;
+
+	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)
+{
+	struct batadv_neigh_node *neigh_node = NULL;
+	struct batadv_dat_candidate *cand;
+	struct sk_buff *tmp_skb;
+	bool ret = false;
+	int send_status;
+	int i;
+
+	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 (!tmp_skb)
+			goto free_neigh;
+
+		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 = READ_ONCE(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);
+
+	disable_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)
+{
+	u8 mac[ETH_ALEN];
+	u64 u64_mac;
+	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);
+	u64_mac = atomic64_read(&dat_entry->mac_addr);
+	u64_to_ether_addr(u64_mac, mac);
+
+	if (nla_put_in_addr(msg, BATADV_ATTR_DAT_CACHE_IP4ADDRESS,
+			    dat_entry->ip) ||
+	    nla_put(msg, BATADV_ATTR_DAT_CACHE_HWADDRESS, ETH_ALEN, mac) ||
+	    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
+ *
+ * Warning: This function may reallocate the skb data buffer via
+ * pskb_may_pull()/... Any pointer into the skb data (e.g. obtained from skb->data
+ * or eth_hdr()) before this call must be considered invalid afterwards and has
+ * to be reacquired.
+ *
+ * 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;
+	__be32 ip_dst;
+	u16 type = 0;
+	u8 *hw_src;
+	u8 *hw_dst;
+
+	/* 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
+ *
+ * The caller must ensure that at least @hdr_size + ETH_HLEN bytes are
+ * accessible after skb->data.
+ *
+ * Warning: This function calls batadv_get_vid() and may therefore reallocate
+ * the skb data buffer. Any pointer into the skb data (e.g. obtained from
+ * skb->data or eth_hdr()) before this call must be considered invalid
+ * afterwards and has to be reacquired.
+ *
+ * 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
+ *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid()/.... Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
+ * 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)
+{
+	struct net_device *mesh_iface = bat_priv->mesh_iface;
+	struct batadv_dat_entry *dat_entry = NULL;
+	struct sk_buff *skb_new;
+	unsigned short vid;
+	bool ret = false;
+	u8 mac[ETH_ALEN];
+	int hdr_size = 0;
+	__be32 ip_dst;
+	__be32 ip_src;
+	u16 type = 0;
+	u64 u64_mac;
+	u8 *hw_src;
+
+	if (!READ_ONCE(bat_priv->distributed_arp_table))
+		goto out;
+
+	/* first, find out the vid. */
+	if (!pskb_may_pull(skb, hdr_size + ETH_HLEN))
+		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) {
+		u64_mac = atomic64_read(&dat_entry->mac_addr);
+		u64_to_ether_addr(u64_mac, mac);
+
+		/* 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, mac, 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, mac, vid)) {
+			batadv_dbg(BATADV_DBG_DAT, bat_priv,
+				   "Device %pM claimed by another backbone gw. Don't send ARP reply!",
+				   mac);
+			ret = true;
+			goto out;
+		}
+
+		skb_new = batadv_dat_arp_create_reply(bat_priv, ip_dst, ip_src,
+						      mac, 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
+ *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid()/... Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
+ * 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)
+{
+	struct batadv_dat_entry *dat_entry = NULL;
+	struct sk_buff *skb_new;
+	unsigned short vid;
+	bool ret = false;
+	u8 mac[ETH_ALEN];
+	__be32 ip_src;
+	__be32 ip_dst;
+	u64 u64_mac;
+	u8 *hw_src;
+	u16 type;
+	int err;
+
+	if (!READ_ONCE(bat_priv->distributed_arp_table))
+		goto out;
+
+	/* first, find out the vid. */
+	if (!pskb_may_pull(skb, hdr_size + ETH_HLEN))
+		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;
+
+	u64_mac = atomic64_read(&dat_entry->mac_addr);
+	u64_to_ether_addr(u64_mac, mac);
+
+	skb_new = batadv_dat_arp_create_reply(bat_priv, ip_dst, ip_src,
+					      mac, hw_src, vid);
+	if (!skb_new)
+		goto out;
+
+	err = batadv_send_skb_via_tt_4addr(bat_priv, skb_new,
+					   BATADV_P_DAT_CACHE_REPLY,
+					   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
+ *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid()/... Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ */
+void batadv_dat_snoop_outgoing_arp_reply(struct batadv_priv *bat_priv,
+					 struct sk_buff *skb)
+{
+	unsigned short vid;
+	int hdr_size = 0;
+	__be32 ip_src;
+	__be32 ip_dst;
+	u8 *hw_src;
+	u8 *hw_dst;
+	u16 type;
+
+	if (!READ_ONCE(bat_priv->distributed_arp_table))
+		return;
+
+	/* first, find out the vid. */
+	if (!pskb_may_pull(skb, hdr_size + ETH_HLEN))
+		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
+ *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid()/... Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
+ * 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;
+	bool dropped = false;
+	unsigned short vid;
+	u8 mac[ETH_ALEN];
+	__be32 ip_src;
+	__be32 ip_dst;
+	u64 u64_mac;
+	u8 *hw_src;
+	u8 *hw_dst;
+	u16 type;
+
+	if (!READ_ONCE(bat_priv->distributed_arp_table))
+		goto out;
+
+	/* first, find out the vid. */
+	if (!pskb_may_pull(skb, hdr_size + ETH_HLEN))
+		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) {
+		u64_mac = atomic64_read(&dat_entry->mac_addr);
+		u64_to_ether_addr(u64_mac, mac);
+
+		if (batadv_compare_eth(hw_src, mac)) {
+			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,
+				   mac, &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;
+	struct udphdr _udphdr;
+	struct iphdr *iphdr;
+	struct 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)
+{
+	struct batadv_dhcp_header *dhcp_h;
+	struct batadv_dhcp_header _dhcp_h;
+	unsigned int offset;
+	__be32 *magic;
+	__be32 _magic;
+
+	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);
+	struct batadv_dhcp_option_header *tl;
+	struct batadv_dhcp_option_header _tl;
+	u8 *type;
+	u8 _type;
+
+	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;
+	__be32 yiaddr;
+
+	if (!READ_ONCE(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.
+ *
+ * Warning: This function may reallocate the skb data buffer via
+ * pskb_may_pull()/batadv_dat_get_vid()/... Any pointer into the skb data
+ * (e.g.obtained from skb->data or eth_hdr()) before this call must be
+ * considered invalid afterwards and has to be reacquired.
+ */
+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;
+	unsigned short vid;
+	int hdr_size_tmp;
+	__be32 ip_src;
+	__be32 yiaddr;
+	__be16 proto;
+	u8 *hw_src;
+
+	if (!READ_ONCE(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;
+
+	hdr_size_tmp = hdr_size;
+	vid = batadv_dat_get_vid(skb, &hdr_size_tmp);
+	ethhdr = (struct ethhdr *)(skb->data + hdr_size);
+	hw_src = ethhdr->h_source;
+
+	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
+ *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid()/... Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
+ * 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)
+{
+	int hdr_size = sizeof(struct batadv_bcast_packet);
+	struct batadv_dat_entry *dat_entry = NULL;
+	unsigned short vid;
+	bool ret = false;
+	__be32 ip_dst;
+	u16 type;
+
+	if (!READ_ONCE(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;
+
+	/* first, find out the vid. */
+	if (!pskb_may_pull(forw_packet->skb, hdr_size + ETH_HLEN))
+		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;
+}