Merging upstream version 6.8.9.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1178 insertions, 0 deletions

diff --git a/net/batman-adv/multicast_forw.c b/net/batman-adv/multicast_forw.c
new file mode 100644
index 0000000000..fafd6ba8c0
--- /dev/null
+++ b/net/batman-adv/multicast_forw.c
@@ -0,0 +1,1178 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) B.A.T.M.A.N. contributors:
+ *
+ * Linus Lüssing
+ */
+
+#include "multicast.h"
+#include "main.h"
+
+#include <linux/bug.h>
+#include <linux/build_bug.h>
+#include <linux/byteorder/generic.h>
+#include <linux/compiler.h>
+#include <linux/errno.h>
+#include <linux/etherdevice.h>
+#include <linux/gfp.h>
+#include <linux/if_ether.h>
+#include <linux/if_vlan.h>
+#include <linux/ipv6.h>
+#include <linux/limits.h>
+#include <linux/netdevice.h>
+#include <linux/rculist.h>
+#include <linux/rcupdate.h>
+#include <linux/skbuff.h>
+#include <linux/stddef.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <uapi/linux/batadv_packet.h>
+
+#include "bridge_loop_avoidance.h"
+#include "originator.h"
+#include "send.h"
+#include "translation-table.h"
+
+#define batadv_mcast_forw_tracker_for_each_dest(dest, num_dests) \
+	for (; num_dests; num_dests--, (dest) += ETH_ALEN)
+
+#define batadv_mcast_forw_tracker_for_each_dest2(dest1, dest2, num_dests) \
+	for (; num_dests; num_dests--, (dest1) += ETH_ALEN, (dest2) += ETH_ALEN)
+
+/**
+ * batadv_mcast_forw_skb_push() - skb_push and memorize amount of pushed bytes
+ * @skb: the skb to push onto
+ * @size: the amount of bytes to push
+ * @len: stores the total amount of bytes pushed
+ *
+ * Performs an skb_push() onto the given skb and adds the amount of pushed bytes
+ * to the given len pointer.
+ *
+ * Return: the return value of the skb_push() call.
+ */
+static void *batadv_mcast_forw_skb_push(struct sk_buff *skb, size_t size,
+					unsigned short *len)
+{
+	*len += size;
+	return skb_push(skb, size);
+}
+
+/**
+ * batadv_mcast_forw_push_padding() - push 2 padding bytes to skb's front
+ * @skb: the skb to push onto
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Pushes two padding bytes to the front of the given skb.
+ *
+ * Return: On success a pointer to the first byte of the two pushed padding
+ * bytes within the skb. NULL otherwise.
+ */
+static char *
+batadv_mcast_forw_push_padding(struct sk_buff *skb, unsigned short *tvlv_len)
+{
+	const int pad_len = 2;
+	char *padding;
+
+	if (skb_headroom(skb) < pad_len)
+		return NULL;
+
+	padding = batadv_mcast_forw_skb_push(skb, pad_len, tvlv_len);
+	memset(padding, 0, pad_len);
+
+	return padding;
+}
+
+/**
+ * batadv_mcast_forw_push_est_padding() - push padding bytes if necessary
+ * @skb: the skb to potentially push the padding onto
+ * @count: the (estimated) number of originators the multicast packet needs to
+ *  be sent to
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * If the number of destination entries is even then this adds two
+ * padding bytes to the end of the tracker TVLV.
+ *
+ * Return: true on success or if no padding is needed, false otherwise.
+ */
+static bool
+batadv_mcast_forw_push_est_padding(struct sk_buff *skb, int count,
+				   unsigned short *tvlv_len)
+{
+	if (!(count % 2) && !batadv_mcast_forw_push_padding(skb, tvlv_len))
+		return false;
+
+	return true;
+}
+
+/**
+ * batadv_mcast_forw_orig_entry() - get orig_node from an hlist node
+ * @node: the hlist node to get the orig_node from
+ * @entry_offset: the offset of the hlist node within the orig_node struct
+ *
+ * Return: The orig_node containing the hlist node on success, NULL on error.
+ */
+static struct batadv_orig_node *
+batadv_mcast_forw_orig_entry(struct hlist_node *node,
+			     size_t entry_offset)
+{
+	/* sanity check */
+	switch (entry_offset) {
+	case offsetof(struct batadv_orig_node, mcast_want_all_ipv4_node):
+	case offsetof(struct batadv_orig_node, mcast_want_all_ipv6_node):
+	case offsetof(struct batadv_orig_node, mcast_want_all_rtr4_node):
+	case offsetof(struct batadv_orig_node, mcast_want_all_rtr6_node):
+		break;
+	default:
+		WARN_ON(1);
+		return NULL;
+	}
+
+	return (struct batadv_orig_node *)((void *)node - entry_offset);
+}
+
+/**
+ * batadv_mcast_forw_push_dest() - push an originator MAC address onto an skb
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the skb to push the destination address onto
+ * @vid: the vlan identifier
+ * @orig_node: the originator node to get the MAC address from
+ * @num_dests: a pointer to store the number of pushed addresses in
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * If the orig_node is a BLA backbone gateway, if there is not enough skb
+ * headroom available or if num_dests is already at its maximum (65535) then
+ * neither the skb nor num_dests is changed. Otherwise the originator's MAC
+ * address is pushed onto the given skb and num_dests incremented by one.
+ *
+ * Return: true if the orig_node is a backbone gateway or if an orig address
+ *  was pushed successfully, false otherwise.
+ */
+static bool batadv_mcast_forw_push_dest(struct batadv_priv *bat_priv,
+					struct sk_buff *skb, unsigned short vid,
+					struct batadv_orig_node *orig_node,
+					unsigned short *num_dests,
+					unsigned short *tvlv_len)
+{
+	BUILD_BUG_ON(sizeof_field(struct batadv_tvlv_mcast_tracker, num_dests)
+		     != sizeof(__be16));
+
+	/* Avoid sending to other BLA gateways - they already got the frame from
+	 * the LAN side we share with them.
+	 * TODO: Refactor to take BLA into account earlier in mode check.
+	 */
+	if (batadv_bla_is_backbone_gw_orig(bat_priv, orig_node->orig, vid))
+		return true;
+
+	if (skb_headroom(skb) < ETH_ALEN || *num_dests == U16_MAX)
+		return false;
+
+	batadv_mcast_forw_skb_push(skb, ETH_ALEN, tvlv_len);
+	ether_addr_copy(skb->data, orig_node->orig);
+	(*num_dests)++;
+
+	return true;
+}
+
+/**
+ * batadv_mcast_forw_push_dests_list() - push originators from list onto an skb
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the skb to push the destination addresses onto
+ * @vid: the vlan identifier
+ * @head: the list to gather originators from
+ * @entry_offset: offset of an hlist node in an orig_node structure
+ * @num_dests: a pointer to store the number of pushed addresses in
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Push the MAC addresses of all originators in the given list onto the given
+ * skb.
+ *
+ * Return: true on success, false otherwise.
+ */
+static int batadv_mcast_forw_push_dests_list(struct batadv_priv *bat_priv,
+					     struct sk_buff *skb,
+					     unsigned short vid,
+					     struct hlist_head *head,
+					     size_t entry_offset,
+					     unsigned short *num_dests,
+					     unsigned short *tvlv_len)
+{
+	struct hlist_node *node;
+	struct batadv_orig_node *orig_node;
+
+	rcu_read_lock();
+	__hlist_for_each_rcu(node, head) {
+		orig_node = batadv_mcast_forw_orig_entry(node, entry_offset);
+		if (!orig_node ||
+		    !batadv_mcast_forw_push_dest(bat_priv, skb, vid, orig_node,
+						 num_dests, tvlv_len)) {
+			rcu_read_unlock();
+			return false;
+		}
+	}
+	rcu_read_unlock();
+
+	return true;
+}
+
+/**
+ * batadv_mcast_forw_push_tt() - push originators with interest through TT
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the skb to push the destination addresses onto
+ * @vid: the vlan identifier
+ * @num_dests: a pointer to store the number of pushed addresses in
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Push the MAC addresses of all originators which have indicated interest in
+ * this multicast packet through the translation table onto the given skb.
+ *
+ * Return: true on success, false otherwise.
+ */
+static bool
+batadv_mcast_forw_push_tt(struct batadv_priv *bat_priv, struct sk_buff *skb,
+			  unsigned short vid, unsigned short *num_dests,
+			  unsigned short *tvlv_len)
+{
+	struct batadv_tt_orig_list_entry *orig_entry;
+
+	struct batadv_tt_global_entry *tt_global;
+	const u8 *addr = eth_hdr(skb)->h_dest;
+
+	/* ok */
+	int ret = true;
+
+	tt_global = batadv_tt_global_hash_find(bat_priv, addr, vid);
+	if (!tt_global)
+		goto out;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(orig_entry, &tt_global->orig_list, list) {
+		if (!batadv_mcast_forw_push_dest(bat_priv, skb, vid,
+						 orig_entry->orig_node,
+						 num_dests, tvlv_len)) {
+			ret = false;
+			break;
+		}
+	}
+	rcu_read_unlock();
+
+	batadv_tt_global_entry_put(tt_global);
+
+out:
+	return ret;
+}
+
+/**
+ * batadv_mcast_forw_push_want_all() - push originators with want-all flag
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the skb to push the destination addresses onto
+ * @vid: the vlan identifier
+ * @num_dests: a pointer to store the number of pushed addresses in
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Push the MAC addresses of all originators which have indicated interest in
+ * this multicast packet through the want-all flag onto the given skb.
+ *
+ * Return: true on success, false otherwise.
+ */
+static bool batadv_mcast_forw_push_want_all(struct batadv_priv *bat_priv,
+					    struct sk_buff *skb,
+					    unsigned short vid,
+					    unsigned short *num_dests,
+					    unsigned short *tvlv_len)
+{
+	struct hlist_head *head = NULL;
+	size_t offset;
+	int ret;
+
+	switch (eth_hdr(skb)->h_proto) {
+	case htons(ETH_P_IP):
+		head = &bat_priv->mcast.want_all_ipv4_list;
+		offset = offsetof(struct batadv_orig_node,
+				  mcast_want_all_ipv4_node);
+		break;
+	case htons(ETH_P_IPV6):
+		head = &bat_priv->mcast.want_all_ipv6_list;
+		offset = offsetof(struct batadv_orig_node,
+				  mcast_want_all_ipv6_node);
+		break;
+	default:
+		return false;
+	}
+
+	ret = batadv_mcast_forw_push_dests_list(bat_priv, skb, vid, head,
+						offset, num_dests, tvlv_len);
+	if (!ret)
+		return false;
+
+	return true;
+}
+
+/**
+ * batadv_mcast_forw_push_want_rtr() - push originators with want-router flag
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the skb to push the destination addresses onto
+ * @vid: the vlan identifier
+ * @num_dests: a pointer to store the number of pushed addresses in
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Push the MAC addresses of all originators which have indicated interest in
+ * this multicast packet through the want-all-rtr flag onto the given skb.
+ *
+ * Return: true on success, false otherwise.
+ */
+static bool batadv_mcast_forw_push_want_rtr(struct batadv_priv *bat_priv,
+					    struct sk_buff *skb,
+					    unsigned short vid,
+					    unsigned short *num_dests,
+					    unsigned short *tvlv_len)
+{
+	struct hlist_head *head = NULL;
+	size_t offset;
+	int ret;
+
+	switch (eth_hdr(skb)->h_proto) {
+	case htons(ETH_P_IP):
+		head = &bat_priv->mcast.want_all_rtr4_list;
+		offset = offsetof(struct batadv_orig_node,
+				  mcast_want_all_rtr4_node);
+		break;
+	case htons(ETH_P_IPV6):
+		head = &bat_priv->mcast.want_all_rtr6_list;
+		offset = offsetof(struct batadv_orig_node,
+				  mcast_want_all_rtr6_node);
+		break;
+	default:
+		return false;
+	}
+
+	ret = batadv_mcast_forw_push_dests_list(bat_priv, skb, vid, head,
+						offset, num_dests, tvlv_len);
+	if (!ret)
+		return false;
+
+	return true;
+}
+
+/**
+ * batadv_mcast_forw_scrape() - remove bytes within skb data
+ * @skb: the skb to remove bytes from
+ * @offset: the offset from the skb data from which to scrape
+ * @len: the amount of bytes to scrape starting from the offset
+ *
+ * Scrapes/removes len bytes from the given skb at the given offset from the
+ * skb data.
+ *
+ * Caller needs to ensure that the region from the skb data's start up
+ * to/including the to be removed bytes are linearized.
+ */
+static void batadv_mcast_forw_scrape(struct sk_buff *skb,
+				     unsigned short offset,
+				     unsigned short len)
+{
+	char *to, *from;
+
+	SKB_LINEAR_ASSERT(skb);
+
+	to = skb_pull(skb, len);
+	from = to - len;
+
+	memmove(to, from, offset);
+}
+
+/**
+ * batadv_mcast_forw_push_scrape_padding() - remove TVLV padding
+ * @skb: the skb to potentially adjust the TVLV's padding on
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Remove two padding bytes from the end of the multicast tracker TVLV,
+ * from before the payload data.
+ *
+ * Caller needs to ensure that the TVLV bytes are linearized.
+ */
+static void batadv_mcast_forw_push_scrape_padding(struct sk_buff *skb,
+						  unsigned short *tvlv_len)
+{
+	const int pad_len = 2;
+
+	batadv_mcast_forw_scrape(skb, *tvlv_len - pad_len, pad_len);
+	*tvlv_len -= pad_len;
+}
+
+/**
+ * batadv_mcast_forw_push_insert_padding() - insert TVLV padding
+ * @skb: the skb to potentially adjust the TVLV's padding on
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Inserts two padding bytes at the end of the multicast tracker TVLV,
+ * before the payload data in the given skb.
+ *
+ * Return: true on success, false otherwise.
+ */
+static bool batadv_mcast_forw_push_insert_padding(struct sk_buff *skb,
+						  unsigned short *tvlv_len)
+{
+	unsigned short offset =	*tvlv_len;
+	char *to, *from = skb->data;
+
+	to = batadv_mcast_forw_push_padding(skb, tvlv_len);
+	if (!to)
+		return false;
+
+	memmove(to, from, offset);
+	memset(to + offset, 0, *tvlv_len - offset);
+	return true;
+}
+
+/**
+ * batadv_mcast_forw_push_adjust_padding() - adjust padding if necessary
+ * @skb: the skb to potentially adjust the TVLV's padding on
+ * @count: the estimated number of originators the multicast packet needs to
+ *  be sent to
+ * @num_dests_pushed: the number of originators that were actually added to the
+ *  multicast packet's tracker TVLV
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Adjusts the padding in the multicast packet's tracker TVLV depending on the
+ * initially estimated amount of destinations versus the amount of destinations
+ * that were actually added to the tracker TVLV.
+ *
+ * If the initial estimate was correct or at least the oddness was the same then
+ * no padding adjustment is performed.
+ * If the initially estimated number was even, so padding was initially added,
+ * but it turned out to be odd then padding is removed.
+ * If the initially estimated number was odd, so no padding was initially added,
+ * but it turned out to be even then padding is added.
+ *
+ * Return: true if no padding adjustment is needed or the adjustment was
+ * successful, false otherwise.
+ */
+static bool
+batadv_mcast_forw_push_adjust_padding(struct sk_buff *skb, int *count,
+				      unsigned short num_dests_pushed,
+				      unsigned short *tvlv_len)
+{
+	int ret = true;
+
+	if (likely((num_dests_pushed % 2) == (*count % 2)))
+		goto out;
+
+	/**
+	 * estimated even number of destinations, but turned out to be odd
+	 * -> remove padding
+	 */
+	if (!(*count % 2) && (num_dests_pushed % 2))
+		batadv_mcast_forw_push_scrape_padding(skb, tvlv_len);
+	/**
+	 * estimated odd number of destinations, but turned out to be even
+	 * -> add padding
+	 */
+	else if ((*count % 2) && (!(num_dests_pushed % 2)))
+		ret = batadv_mcast_forw_push_insert_padding(skb, tvlv_len);
+
+out:
+	*count = num_dests_pushed;
+	return ret;
+}
+
+/**
+ * batadv_mcast_forw_push_dests() - push originator addresses onto an skb
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the skb to push the destination addresses onto
+ * @vid: the vlan identifier
+ * @is_routable: indicates whether the destination is routable
+ * @count: the number of originators the multicast packet needs to be sent to
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Push the MAC addresses of all originators which have indicated interest in
+ * this multicast packet onto the given skb.
+ *
+ * Return: -ENOMEM if there is not enough skb headroom available. Otherwise, on
+ * success 0.
+ */
+static int
+batadv_mcast_forw_push_dests(struct batadv_priv *bat_priv, struct sk_buff *skb,
+			     unsigned short vid, int is_routable, int *count,
+			     unsigned short *tvlv_len)
+{
+	unsigned short num_dests = 0;
+
+	if (!batadv_mcast_forw_push_est_padding(skb, *count, tvlv_len))
+		goto err;
+
+	if (!batadv_mcast_forw_push_tt(bat_priv, skb, vid, &num_dests,
+				       tvlv_len))
+		goto err;
+
+	if (!batadv_mcast_forw_push_want_all(bat_priv, skb, vid, &num_dests,
+					     tvlv_len))
+		goto err;
+
+	if (is_routable &&
+	    !batadv_mcast_forw_push_want_rtr(bat_priv, skb, vid, &num_dests,
+					     tvlv_len))
+		goto err;
+
+	if (!batadv_mcast_forw_push_adjust_padding(skb, count, num_dests,
+						   tvlv_len))
+		goto err;
+
+	return 0;
+err:
+	return -ENOMEM;
+}
+
+/**
+ * batadv_mcast_forw_push_tracker() - push a multicast tracker TVLV header
+ * @skb: the skb to push the tracker TVLV onto
+ * @num_dests: the number of destination addresses to set in the header
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Pushes a multicast tracker TVLV header onto the given skb, including the
+ * generic TVLV header but excluding the destination MAC addresses.
+ *
+ * The provided num_dests value is taken into consideration to set the
+ * num_dests field in the tracker header and to set the appropriate TVLV length
+ * value fields.
+ *
+ * Return: -ENOMEM if there is not enough skb headroom available. Otherwise, on
+ * success 0.
+ */
+static int batadv_mcast_forw_push_tracker(struct sk_buff *skb, int num_dests,
+					  unsigned short *tvlv_len)
+{
+	struct batadv_tvlv_mcast_tracker *mcast_tracker;
+	struct batadv_tvlv_hdr *tvlv_hdr;
+	unsigned int tvlv_value_len;
+
+	if (skb_headroom(skb) < sizeof(*mcast_tracker) + sizeof(*tvlv_hdr))
+		return -ENOMEM;
+
+	tvlv_value_len = sizeof(*mcast_tracker) + *tvlv_len;
+	if (tvlv_value_len + sizeof(*tvlv_hdr) > U16_MAX)
+		return -ENOMEM;
+
+	batadv_mcast_forw_skb_push(skb, sizeof(*mcast_tracker), tvlv_len);
+	mcast_tracker = (struct batadv_tvlv_mcast_tracker *)skb->data;
+	mcast_tracker->num_dests = htons(num_dests);
+
+	skb_reset_network_header(skb);
+
+	batadv_mcast_forw_skb_push(skb, sizeof(*tvlv_hdr), tvlv_len);
+	tvlv_hdr = (struct batadv_tvlv_hdr *)skb->data;
+	tvlv_hdr->type = BATADV_TVLV_MCAST_TRACKER;
+	tvlv_hdr->version = 1;
+	tvlv_hdr->len = htons(tvlv_value_len);
+
+	return 0;
+}
+
+/**
+ * batadv_mcast_forw_push_tvlvs() - push a multicast tracker TVLV onto an skb
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the skb to push the tracker TVLV onto
+ * @vid: the vlan identifier
+ * @is_routable: indicates whether the destination is routable
+ * @count: the number of originators the multicast packet needs to be sent to
+ * @tvlv_len: stores the amount of currently pushed TVLV bytes
+ *
+ * Pushes a multicast tracker TVLV onto the given skb, including the collected
+ * destination MAC addresses and the generic TVLV header.
+ *
+ * Return: -ENOMEM if there is not enough skb headroom available. Otherwise, on
+ * success 0.
+ */
+static int
+batadv_mcast_forw_push_tvlvs(struct batadv_priv *bat_priv, struct sk_buff *skb,
+			     unsigned short vid, int is_routable, int count,
+			     unsigned short *tvlv_len)
+{
+	int ret;
+
+	ret = batadv_mcast_forw_push_dests(bat_priv, skb, vid, is_routable,
+					   &count, tvlv_len);
+	if (ret < 0)
+		return ret;
+
+	ret = batadv_mcast_forw_push_tracker(skb, count, tvlv_len);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+/**
+ * batadv_mcast_forw_push_hdr() - push a multicast packet header onto an skb
+ * @skb: the skb to push the header onto
+ * @tvlv_len: the total TVLV length value to set in the header
+ *
+ * Pushes a batman-adv multicast packet header onto the given skb and sets
+ * the provided total TVLV length value in it.
+ *
+ * Caller needs to ensure enough skb headroom is available.
+ *
+ * Return: -ENOMEM if there is not enough skb headroom available. Otherwise, on
+ * success 0.
+ */
+static int
+batadv_mcast_forw_push_hdr(struct sk_buff *skb, unsigned short tvlv_len)
+{
+	struct batadv_mcast_packet *mcast_packet;
+
+	if (skb_headroom(skb) < sizeof(*mcast_packet))
+		return -ENOMEM;
+
+	skb_push(skb, sizeof(*mcast_packet));
+
+	mcast_packet = (struct batadv_mcast_packet *)skb->data;
+	mcast_packet->version = BATADV_COMPAT_VERSION;
+	mcast_packet->ttl = BATADV_TTL;
+	mcast_packet->packet_type = BATADV_MCAST;
+	mcast_packet->reserved = 0;
+	mcast_packet->tvlv_len = htons(tvlv_len);
+
+	return 0;
+}
+
+/**
+ * batadv_mcast_forw_scrub_dests() - scrub destinations in a tracker TVLV
+ * @bat_priv: the bat priv with all the soft interface information
+ * @comp_neigh: next hop neighbor to scrub+collect destinations for
+ * @dest: start MAC entry in original skb's tracker TVLV
+ * @next_dest: start MAC entry in to be sent skb's tracker TVLV
+ * @num_dests: number of remaining destination MAC entries to iterate over
+ *
+ * This sorts destination entries into either the original batman-adv
+ * multicast packet or the skb (copy) that is going to be sent to comp_neigh
+ * next.
+ *
+ * In preparation for the next, to be (unicast) transmitted batman-adv multicast
+ * packet skb to be sent to the given neighbor node, tries to collect all
+ * originator MAC addresses that have the given neighbor node as their next hop
+ * in the to be transmitted skb (copy), which next_dest points into. That is we
+ * zero all destination entries in next_dest which do not have comp_neigh as
+ * their next hop. And zero all destination entries in the original skb that
+ * would have comp_neigh as their next hop (to avoid redundant transmissions and
+ * duplicated payload later).
+ */
+static void
+batadv_mcast_forw_scrub_dests(struct batadv_priv *bat_priv,
+			      struct batadv_neigh_node *comp_neigh, u8 *dest,
+			      u8 *next_dest, u16 num_dests)
+{
+	struct batadv_neigh_node *next_neigh;
+
+	/* skip first entry, this is what we are comparing with */
+	eth_zero_addr(dest);
+	dest += ETH_ALEN;
+	next_dest += ETH_ALEN;
+	num_dests--;
+
+	batadv_mcast_forw_tracker_for_each_dest2(dest, next_dest, num_dests) {
+		if (is_zero_ether_addr(next_dest))
+			continue;
+
+		/* sanity check, we expect unicast destinations */
+		if (is_multicast_ether_addr(next_dest)) {
+			eth_zero_addr(dest);
+			eth_zero_addr(next_dest);
+			continue;
+		}
+
+		next_neigh = batadv_orig_to_router(bat_priv, next_dest, NULL);
+		if (!next_neigh) {
+			eth_zero_addr(next_dest);
+			continue;
+		}
+
+		if (!batadv_compare_eth(next_neigh->addr, comp_neigh->addr)) {
+			eth_zero_addr(next_dest);
+			batadv_neigh_node_put(next_neigh);
+			continue;
+		}
+
+		/* found an entry for our next packet to transmit, so remove it
+		 * from the original packet
+		 */
+		eth_zero_addr(dest);
+		batadv_neigh_node_put(next_neigh);
+	}
+}
+
+/**
+ * batadv_mcast_forw_shrink_fill() - swap slot with next non-zero destination
+ * @slot: the to be filled zero-MAC destination entry in a tracker TVLV
+ * @num_dests_slot: remaining entries in tracker TVLV from/including slot
+ *
+ * Searches for the next non-zero-MAC destination entry in a tracker TVLV after
+ * the given slot pointer. And if found, swaps it with the zero-MAC destination
+ * entry which the slot points to.
+ *
+ * Return: true if slot was swapped/filled successfully, false otherwise.
+ */
+static bool batadv_mcast_forw_shrink_fill(u8 *slot, u16 num_dests_slot)
+{
+	u16 num_dests_filler;
+	u8 *filler;
+
+	/* sanity check, should not happen */
+	if (!num_dests_slot)
+		return false;
+
+	num_dests_filler = num_dests_slot - 1;
+	filler = slot + ETH_ALEN;
+
+	/* find a candidate to fill the empty slot */
+	batadv_mcast_forw_tracker_for_each_dest(filler, num_dests_filler) {
+		if (is_zero_ether_addr(filler))
+			continue;
+
+		ether_addr_copy(slot, filler);
+		eth_zero_addr(filler);
+		return true;
+	}
+
+	return false;
+}
+
+/**
+ * batadv_mcast_forw_shrink_pack_dests() - pack destinations of a tracker TVLV
+ * @skb: the batman-adv multicast packet to compact destinations in
+ *
+ * Compacts the originator destination MAC addresses in the multicast tracker
+ * TVLV of the given multicast packet. This is done by moving all non-zero
+ * MAC addresses in direction of the skb head and all zero MAC addresses in skb
+ * tail direction, within the multicast tracker TVLV.
+ *
+ * Return: The number of consecutive zero MAC address destinations which are
+ * now at the end of the multicast tracker TVLV.
+ */
+static int batadv_mcast_forw_shrink_pack_dests(struct sk_buff *skb)
+{
+	struct batadv_tvlv_mcast_tracker *mcast_tracker;
+	unsigned char *skb_net_hdr;
+	u16 num_dests_slot;
+	u8 *slot;
+
+	skb_net_hdr = skb_network_header(skb);
+	mcast_tracker = (struct batadv_tvlv_mcast_tracker *)skb_net_hdr;
+	num_dests_slot = ntohs(mcast_tracker->num_dests);
+
+	slot = (u8 *)mcast_tracker + sizeof(*mcast_tracker);
+
+	batadv_mcast_forw_tracker_for_each_dest(slot, num_dests_slot) {
+		/* find an empty slot */
+		if (!is_zero_ether_addr(slot))
+			continue;
+
+		if (!batadv_mcast_forw_shrink_fill(slot, num_dests_slot))
+			/* could not find a filler, so we successfully packed
+			 * and can stop - and must not reduce num_dests_slot!
+			 */
+			break;
+	}
+
+	/* num_dests_slot is now the amount of reduced, zeroed
+	 * destinations at the end of the tracker TVLV
+	 */
+	return num_dests_slot;
+}
+
+/**
+ * batadv_mcast_forw_shrink_align_offset() - get new alignment offset
+ * @num_dests_old: the old, to be updated amount of destination nodes
+ * @num_dests_reduce: the number of destinations that were removed
+ *
+ * Calculates the amount of potential extra alignment offset that is needed to
+ * adjust the TVLV padding after the change in destination nodes.
+ *
+ * Return:
+ *	0: If no change to padding is needed.
+ *	2: If padding needs to be removed.
+ *	-2: If padding needs to be added.
+ */
+static short
+batadv_mcast_forw_shrink_align_offset(unsigned int num_dests_old,
+				      unsigned int num_dests_reduce)
+{
+	/* even amount of removed destinations -> no alignment change */
+	if (!(num_dests_reduce % 2))
+		return 0;
+
+	/* even to odd amount of destinations -> remove padding */
+	if (!(num_dests_old % 2))
+		return 2;
+
+	/* odd to even amount of destinations -> add padding */
+	return -2;
+}
+
+/**
+ * batadv_mcast_forw_shrink_update_headers() - update shrunk mc packet headers
+ * @skb: the batman-adv multicast packet to update headers of
+ * @num_dests_reduce: the number of destinations that were removed
+ *
+ * This updates any fields of a batman-adv multicast packet that are affected
+ * by the reduced number of destinations in the multicast tracket TVLV. In
+ * particular this updates:
+ *
+ * The num_dest field of the multicast tracker TVLV.
+ * The TVLV length field of the according generic TVLV header.
+ * The batman-adv multicast packet's total TVLV length field.
+ *
+ * Return: The offset in skb's tail direction at which the new batman-adv
+ * multicast packet header needs to start.
+ */
+static unsigned int
+batadv_mcast_forw_shrink_update_headers(struct sk_buff *skb,
+					unsigned int num_dests_reduce)
+{
+	struct batadv_tvlv_mcast_tracker *mcast_tracker;
+	struct batadv_mcast_packet *mcast_packet;
+	struct batadv_tvlv_hdr *tvlv_hdr;
+	unsigned char *skb_net_hdr;
+	unsigned int offset;
+	short align_offset;
+	u16 num_dests;
+
+	skb_net_hdr = skb_network_header(skb);
+	mcast_tracker = (struct batadv_tvlv_mcast_tracker *)skb_net_hdr;
+	num_dests = ntohs(mcast_tracker->num_dests);
+
+	align_offset = batadv_mcast_forw_shrink_align_offset(num_dests,
+							     num_dests_reduce);
+	offset = ETH_ALEN * num_dests_reduce + align_offset;
+	num_dests -= num_dests_reduce;
+
+	/* update tracker header */
+	mcast_tracker->num_dests = htons(num_dests);
+
+	/* update tracker's tvlv header's length field */
+	tvlv_hdr = (struct batadv_tvlv_hdr *)(skb_network_header(skb) -
+					      sizeof(*tvlv_hdr));
+	tvlv_hdr->len = htons(ntohs(tvlv_hdr->len) - offset);
+
+	/* update multicast packet header's tvlv length field */
+	mcast_packet = (struct batadv_mcast_packet *)skb->data;
+	mcast_packet->tvlv_len = htons(ntohs(mcast_packet->tvlv_len) - offset);
+
+	return offset;
+}
+
+/**
+ * batadv_mcast_forw_shrink_move_headers() - move multicast headers by offset
+ * @skb: the batman-adv multicast packet to move headers for
+ * @offset: a non-negative offset to move headers by, towards the skb tail
+ *
+ * Moves the batman-adv multicast packet header, its multicast tracker TVLV and
+ * any TVLVs in between by the given offset in direction towards the tail.
+ */
+static void
+batadv_mcast_forw_shrink_move_headers(struct sk_buff *skb, unsigned int offset)
+{
+	struct batadv_tvlv_mcast_tracker *mcast_tracker;
+	unsigned char *skb_net_hdr;
+	unsigned int len;
+	u16 num_dests;
+
+	skb_net_hdr = skb_network_header(skb);
+	mcast_tracker = (struct batadv_tvlv_mcast_tracker *)skb_net_hdr;
+	num_dests = ntohs(mcast_tracker->num_dests);
+	len = skb_network_offset(skb) + sizeof(*mcast_tracker);
+	len += num_dests * ETH_ALEN;
+
+	batadv_mcast_forw_scrape(skb, len, offset);
+}
+
+/**
+ * batadv_mcast_forw_shrink_tracker() - remove zero addresses in a tracker tvlv
+ * @skb: the batman-adv multicast packet to (potentially) shrink
+ *
+ * Removes all destinations with a zero MAC addresses (00:00:00:00:00:00) from
+ * the given batman-adv multicast packet's tracker TVLV and updates headers
+ * accordingly to maintain a valid batman-adv multicast packet.
+ */
+static void batadv_mcast_forw_shrink_tracker(struct sk_buff *skb)
+{
+	unsigned int offset;
+	u16 dests_reduced;
+
+	dests_reduced = batadv_mcast_forw_shrink_pack_dests(skb);
+	if (!dests_reduced)
+		return;
+
+	offset = batadv_mcast_forw_shrink_update_headers(skb, dests_reduced);
+	batadv_mcast_forw_shrink_move_headers(skb, offset);
+}
+
+/**
+ * batadv_mcast_forw_packet() - forward a batman-adv multicast packet
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the received or locally generated batman-adv multicast packet
+ * @local_xmit: indicates that the packet was locally generated and not received
+ *
+ * Parses the tracker TVLV of a batman-adv multicast packet and forwards the
+ * packet as indicated in this TVLV.
+ *
+ * Caller needs to set the skb network header to the start of the multicast
+ * tracker TVLV (excluding the generic TVLV header) and the skb transport header
+ * to the next byte after this multicast tracker TVLV.
+ *
+ * Caller needs to free the skb.
+ *
+ * Return: NET_RX_SUCCESS or NET_RX_DROP on success or a negative error
+ * code on failure. NET_RX_SUCCESS if the received packet is supposed to be
+ * decapsulated and forwarded to the own soft interface, NET_RX_DROP otherwise.
+ */
+static int batadv_mcast_forw_packet(struct batadv_priv *bat_priv,
+				    struct sk_buff *skb, bool local_xmit)
+{
+	struct batadv_tvlv_mcast_tracker *mcast_tracker;
+	struct batadv_neigh_node *neigh_node;
+	unsigned long offset, num_dests_off;
+	struct sk_buff *nexthop_skb;
+	unsigned char *skb_net_hdr;
+	bool local_recv = false;
+	unsigned int tvlv_len;
+	bool xmitted = false;
+	u8 *dest, *next_dest;
+	u16 num_dests;
+	int ret;
+
+	/* (at least) TVLV part needs to be linearized */
+	SKB_LINEAR_ASSERT(skb);
+
+	/* check if num_dests is within skb length */
+	num_dests_off = offsetof(struct batadv_tvlv_mcast_tracker, num_dests);
+	if (num_dests_off > skb_network_header_len(skb))
+		return -EINVAL;
+
+	skb_net_hdr = skb_network_header(skb);
+	mcast_tracker = (struct batadv_tvlv_mcast_tracker *)skb_net_hdr;
+	num_dests = ntohs(mcast_tracker->num_dests);
+
+	dest = (u8 *)mcast_tracker + sizeof(*mcast_tracker);
+
+	/* check if full tracker tvlv is within skb length */
+	tvlv_len = sizeof(*mcast_tracker) + ETH_ALEN * num_dests;
+	if (tvlv_len > skb_network_header_len(skb))
+		return -EINVAL;
+
+	/* invalidate checksum: */
+	skb->ip_summed = CHECKSUM_NONE;
+
+	batadv_mcast_forw_tracker_for_each_dest(dest, num_dests) {
+		if (is_zero_ether_addr(dest))
+			continue;
+
+		/* only unicast originator addresses supported */
+		if (is_multicast_ether_addr(dest)) {
+			eth_zero_addr(dest);
+			continue;
+		}
+
+		if (batadv_is_my_mac(bat_priv, dest)) {
+			eth_zero_addr(dest);
+			local_recv = true;
+			continue;
+		}
+
+		neigh_node = batadv_orig_to_router(bat_priv, dest, NULL);
+		if (!neigh_node) {
+			eth_zero_addr(dest);
+			continue;
+		}
+
+		nexthop_skb = skb_copy(skb, GFP_ATOMIC);
+		if (!nexthop_skb) {
+			batadv_neigh_node_put(neigh_node);
+			return -ENOMEM;
+		}
+
+		offset = dest - skb->data;
+		next_dest = nexthop_skb->data + offset;
+
+		batadv_mcast_forw_scrub_dests(bat_priv, neigh_node, dest,
+					      next_dest, num_dests);
+		batadv_mcast_forw_shrink_tracker(nexthop_skb);
+
+		batadv_inc_counter(bat_priv, BATADV_CNT_MCAST_TX);
+		batadv_add_counter(bat_priv, BATADV_CNT_MCAST_TX_BYTES,
+				   nexthop_skb->len + ETH_HLEN);
+		xmitted = true;
+		ret = batadv_send_unicast_skb(nexthop_skb, neigh_node);
+
+		batadv_neigh_node_put(neigh_node);
+
+		if (ret < 0)
+			return ret;
+	}
+
+	if (xmitted) {
+		if (local_xmit) {
+			batadv_inc_counter(bat_priv, BATADV_CNT_MCAST_TX_LOCAL);
+			batadv_add_counter(bat_priv,
+					   BATADV_CNT_MCAST_TX_LOCAL_BYTES,
+					   skb->len -
+					   skb_transport_offset(skb));
+		} else {
+			batadv_inc_counter(bat_priv, BATADV_CNT_MCAST_FWD);
+			batadv_add_counter(bat_priv, BATADV_CNT_MCAST_FWD_BYTES,
+					   skb->len + ETH_HLEN);
+		}
+	}
+
+	if (local_recv)
+		return NET_RX_SUCCESS;
+	else
+		return NET_RX_DROP;
+}
+
+/**
+ * batadv_mcast_forw_tracker_tvlv_handler() - handle an mcast tracker tvlv
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the received batman-adv multicast packet
+ *
+ * Parses the tracker TVLV of an incoming batman-adv multicast packet and
+ * forwards the packet as indicated in this TVLV.
+ *
+ * Caller needs to set the skb network header to the start of the multicast
+ * tracker TVLV (excluding the generic TVLV header) and the skb transport header
+ * to the next byte after this multicast tracker TVLV.
+ *
+ * Caller needs to free the skb.
+ *
+ * Return: NET_RX_SUCCESS or NET_RX_DROP on success or a negative error
+ * code on failure. NET_RX_SUCCESS if the received packet is supposed to be
+ * decapsulated and forwarded to the own soft interface, NET_RX_DROP otherwise.
+ */
+int batadv_mcast_forw_tracker_tvlv_handler(struct batadv_priv *bat_priv,
+					   struct sk_buff *skb)
+{
+	return batadv_mcast_forw_packet(bat_priv, skb, false);
+}
+
+/**
+ * batadv_mcast_forw_packet_hdrlen() - multicast packet header length
+ * @num_dests: number of destination nodes
+ *
+ * Calculates the total batman-adv multicast packet header length for a given
+ * number of destination nodes (excluding the outer ethernet frame).
+ *
+ * Return: The calculated total batman-adv multicast packet header length.
+ */
+unsigned int batadv_mcast_forw_packet_hdrlen(unsigned int num_dests)
+{
+	/**
+	 * If the number of destination entries is even then we need to add
+	 * two byte padding to the tracker TVLV.
+	 */
+	int padding = (!(num_dests % 2)) ? 2 : 0;
+
+	return padding + num_dests * ETH_ALEN +
+	       sizeof(struct batadv_tvlv_mcast_tracker) +
+	       sizeof(struct batadv_tvlv_hdr) +
+	       sizeof(struct batadv_mcast_packet);
+}
+
+/**
+ * batadv_mcast_forw_expand_head() - expand headroom for an mcast packet
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the multicast packet to send
+ *
+ * Tries to expand an skb's headroom so that its head to tail is 1298
+ * bytes (minimum IPv6 MTU + vlan ethernet header size) large.
+ *
+ * Return: -EINVAL if the given skb's length is too large or -ENOMEM on memory
+ * allocation failure. Otherwise, on success, zero is returned.
+ */
+static int batadv_mcast_forw_expand_head(struct batadv_priv *bat_priv,
+					 struct sk_buff *skb)
+{
+	int hdr_size = VLAN_ETH_HLEN + IPV6_MIN_MTU - skb->len;
+
+	 /* TODO: Could be tightened to actual number of destination nodes?
+	  * But it's tricky, number of destinations might have increased since
+	  * we last checked.
+	  */
+	if (hdr_size < 0) {
+		/* batadv_mcast_forw_mode_check_count() should ensure we do not
+		 * end up here
+		 */
+		WARN_ON(1);
+		return -EINVAL;
+	}
+
+	if (skb_headroom(skb) < hdr_size &&
+	    pskb_expand_head(skb, hdr_size, 0, GFP_ATOMIC) < 0)
+		return -ENOMEM;
+
+	return 0;
+}
+
+/**
+ * batadv_mcast_forw_push() - encapsulate skb in a batman-adv multicast packet
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the multicast packet to encapsulate and send
+ * @vid: the vlan identifier
+ * @is_routable: indicates whether the destination is routable
+ * @count: the number of originators the multicast packet needs to be sent to
+ *
+ * Encapsulates the given multicast packet in a batman-adv multicast packet.
+ * A multicast tracker TVLV with destination originator addresses for any node
+ * that signaled interest in it, that is either via the translation table or the
+ * according want-all flags, is attached accordingly.
+ *
+ * Return: true on success, false otherwise.
+ */
+bool batadv_mcast_forw_push(struct batadv_priv *bat_priv, struct sk_buff *skb,
+			    unsigned short vid, int is_routable, int count)
+{
+	unsigned short tvlv_len = 0;
+	int ret;
+
+	if (batadv_mcast_forw_expand_head(bat_priv, skb) < 0)
+		goto err;
+
+	skb_reset_transport_header(skb);
+
+	ret = batadv_mcast_forw_push_tvlvs(bat_priv, skb, vid, is_routable,
+					   count, &tvlv_len);
+	if (ret < 0)
+		goto err;
+
+	ret = batadv_mcast_forw_push_hdr(skb, tvlv_len);
+	if (ret < 0)
+		goto err;
+
+	return true;
+
+err:
+	if (tvlv_len)
+		skb_pull(skb, tvlv_len);
+
+	return false;
+}
+
+/**
+ * batadv_mcast_forw_mcsend() - send a self prepared batman-adv multicast packet
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the multicast packet to encapsulate and send
+ *
+ * Transmits a batman-adv multicast packet that was locally prepared and
+ * consumes/frees it.
+ *
+ * Return: NET_XMIT_DROP on memory allocation failure. NET_XMIT_SUCCESS
+ * otherwise.
+ */
+int batadv_mcast_forw_mcsend(struct batadv_priv *bat_priv,
+			     struct sk_buff *skb)
+{
+	int ret = batadv_mcast_forw_packet(bat_priv, skb, true);
+
+	if (ret < 0) {
+		kfree_skb(skb);
+		return NET_XMIT_DROP;
+	}
+
+	consume_skb(skb);
+	return NET_XMIT_SUCCESS;
+}