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, 633 insertions, 0 deletions

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
new file mode 100644
index 000000000..493af3091
--- /dev/null
+++ b/net/batman-adv/fragmentation.c
@@ -0,0 +1,633 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) B.A.T.M.A.N. contributors:
+ *
+ * Martin Hundebøll <martin@hundeboll.net>
+ */
+
+#include "fragmentation.h"
+#include "main.h"
+
+#include <linux/atomic.h>
+#include <linux/bug.h>
+#include <linux/byteorder/generic.h>
+#include <linux/errno.h>
+#include <linux/etherdevice.h>
+#include <linux/gfp.h>
+#include <linux/if_ether.h>
+#include <linux/jiffies.h>
+#include <linux/lockdep.h>
+#include <linux/minmax.h>
+#include <linux/netdevice.h>
+#include <linux/overflow.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <uapi/linux/batadv_packet.h>
+
+#include "hard-interface.h"
+#include "originator.h"
+#include "send.h"
+
+/**
+ * batadv_frag_clear_chain() - delete entries in the fragment buffer chain
+ * @head: head of chain with entries.
+ * @dropped: whether the chain is cleared because all fragments are dropped
+ *
+ * Free fragments in the passed hlist. Should be called with appropriate lock.
+ */
+static void batadv_frag_clear_chain(struct hlist_head *head, bool dropped)
+{
+	struct batadv_frag_list_entry *entry;
+	struct hlist_node *node;
+
+	hlist_for_each_entry_safe(entry, node, head, list) {
+		hlist_del(&entry->list);
+
+		if (dropped)
+			kfree_skb(entry->skb);
+		else
+			consume_skb(entry->skb);
+
+		kfree(entry);
+	}
+}
+
+/**
+ * batadv_frag_purge_orig() - free fragments associated to an orig
+ * @orig_node: originator to free fragments from
+ * @check_cb: optional function to tell if an entry should be purged
+ */
+void batadv_frag_purge_orig(struct batadv_orig_node *orig_node,
+			    bool (*check_cb)(struct batadv_frag_table_entry *))
+{
+	struct batadv_frag_table_entry *chain;
+	u8 i;
+
+	for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
+		chain = &orig_node->fragments[i];
+		spin_lock_bh(&chain->lock);
+
+		if (!check_cb || check_cb(chain)) {
+			batadv_frag_clear_chain(&chain->fragment_list, true);
+			chain->size = 0;
+		}
+
+		spin_unlock_bh(&chain->lock);
+	}
+}
+
+/**
+ * batadv_frag_size_limit() - maximum possible size of packet to be fragmented
+ *
+ * Return: the maximum size of payload that can be fragmented.
+ */
+static size_t batadv_frag_size_limit(void)
+{
+	size_t limit = BATADV_FRAG_MAX_FRAG_SIZE;
+
+	limit -= sizeof(struct batadv_frag_packet);
+	limit *= BATADV_FRAG_MAX_FRAGMENTS;
+
+	return limit;
+}
+
+/**
+ * batadv_frag_init_chain() - check and prepare fragment chain for new fragment
+ * @chain: chain in fragments table to init
+ * @seqno: sequence number of the received fragment
+ *
+ * Make chain ready for a fragment with sequence number "seqno". Delete existing
+ * entries if they have an "old" sequence number.
+ *
+ * Caller must hold chain->lock.
+ *
+ * Return: true if chain is empty and the caller can just insert the new
+ * fragment without searching for the right position.
+ */
+static bool batadv_frag_init_chain(struct batadv_frag_table_entry *chain,
+				   u16 seqno)
+{
+	lockdep_assert_held(&chain->lock);
+
+	if (chain->seqno == seqno)
+		return false;
+
+	if (!hlist_empty(&chain->fragment_list))
+		batadv_frag_clear_chain(&chain->fragment_list, true);
+
+	chain->size = 0;
+	chain->seqno = seqno;
+
+	return true;
+}
+
+/**
+ * batadv_frag_insert_packet() - insert a fragment into a fragment chain
+ * @orig_node: originator that the fragment was received from
+ * @skb: skb to insert
+ * @chain_out: list head to attach complete chains of fragments to
+ *
+ * Insert a new fragment into the reverse ordered chain in the right table
+ * entry. The hash table entry is cleared if "old" fragments exist in it.
+ *
+ * Return: true if skb is buffered, false on error. If the chain has all the
+ * fragments needed to merge the packet, the chain is moved to the passed head
+ * to avoid locking the chain in the table.
+ */
+static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
+				      struct sk_buff *skb,
+				      struct hlist_head *chain_out)
+{
+	struct batadv_frag_list_entry *frag_entry_last = NULL;
+	struct batadv_frag_list_entry *frag_entry_new = NULL;
+	u16 hdr_size = sizeof(struct batadv_frag_packet);
+	struct batadv_frag_list_entry *frag_entry_curr;
+	struct batadv_frag_packet *frag_packet;
+	struct batadv_frag_table_entry *chain;
+	bool overflow = false;
+	bool ret = false;
+	size_t data_len;
+	u8 bucket;
+	u16 seqno;
+
+	/* Linearize packet to avoid linearizing 16 packets in a row when doing
+	 * the later merge. Non-linear merge should be added to remove this
+	 * linearization.
+	 */
+	if (skb_linearize(skb) < 0)
+		goto err;
+
+	frag_packet = (struct batadv_frag_packet *)skb->data;
+	data_len = skb->len - hdr_size;
+	seqno = ntohs(frag_packet->seqno);
+	bucket = seqno % BATADV_FRAG_BUFFER_COUNT;
+
+	frag_entry_new = kmalloc_obj(*frag_entry_new, GFP_ATOMIC);
+	if (!frag_entry_new)
+		goto err;
+
+	frag_entry_new->skb = skb;
+	frag_entry_new->no = frag_packet->no;
+
+	/* Select entry in the "chain table" and delete any prior fragments
+	 * with another sequence number. batadv_frag_init_chain() returns true,
+	 * if the list is empty at return.
+	 */
+	chain = &orig_node->fragments[bucket];
+	spin_lock_bh(&chain->lock);
+	if (batadv_frag_init_chain(chain, seqno)) {
+		hlist_add_head(&frag_entry_new->list, &chain->fragment_list);
+		chain->size = data_len;
+		chain->timestamp = jiffies;
+		chain->total_size = ntohs(frag_packet->total_size);
+		ret = true;
+		goto out;
+	}
+
+	/* Find the position for the new fragment. */
+	hlist_for_each_entry(frag_entry_curr, &chain->fragment_list, list) {
+		/* Drop packet if fragment already exists. */
+		if (frag_entry_curr->no == frag_entry_new->no)
+			goto err_unlock;
+
+		/* Order fragments from highest to lowest. */
+		if (frag_entry_curr->no < frag_entry_new->no) {
+			hlist_add_before(&frag_entry_new->list,
+					 &frag_entry_curr->list);
+
+			if (check_add_overflow(chain->size, data_len,
+					       &chain->size))
+				overflow = true;
+
+			chain->timestamp = jiffies;
+			ret = true;
+			goto out;
+		}
+
+		/* store current entry because it could be the last in list */
+		frag_entry_last = frag_entry_curr;
+	}
+
+	/* Reached the end of the list, so insert after 'frag_entry_last'. */
+	if (likely(frag_entry_last)) {
+		hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);
+
+		if (check_add_overflow(chain->size, data_len, &chain->size))
+			overflow = true;
+
+		chain->timestamp = jiffies;
+		ret = true;
+	}
+
+out:
+	if (overflow || chain->size > batadv_frag_size_limit() ||
+	    chain->total_size != ntohs(frag_packet->total_size) ||
+	    chain->total_size > batadv_frag_size_limit()) {
+		/* Clear chain if total size of either the list or the packet
+		 * exceeds the maximum size of one merged packet. Don't allow
+		 * packets to have different total_size.
+		 */
+		batadv_frag_clear_chain(&chain->fragment_list, true);
+		chain->size = 0;
+	} else if (ntohs(frag_packet->total_size) == chain->size) {
+		/* All fragments received. Hand over chain to caller. */
+		hlist_move_list(&chain->fragment_list, chain_out);
+		chain->size = 0;
+	}
+
+err_unlock:
+	spin_unlock_bh(&chain->lock);
+
+err:
+	if (!ret) {
+		kfree(frag_entry_new);
+		kfree_skb(skb);
+	}
+
+	return ret;
+}
+
+/**
+ * batadv_frag_merge_packets() - merge a chain of fragments
+ * @chain: head of chain with fragments
+ *
+ * Expand the first skb in the chain and copy the content of the remaining
+ * skb's into the expanded one. After doing so, clear the chain.
+ *
+ * Return: the merged skb or NULL on error.
+ */
+static struct sk_buff *
+batadv_frag_merge_packets(struct hlist_head *chain)
+{
+	int hdr_size = sizeof(struct batadv_frag_packet);
+	struct batadv_frag_list_entry *entry;
+	struct batadv_frag_packet *packet;
+	struct sk_buff *skb_out;
+	bool dropped = false;
+	int size;
+
+	/* Remove first entry, as this is the destination for the rest of the
+	 * fragments.
+	 */
+	entry = hlist_entry(chain->first, struct batadv_frag_list_entry, list);
+	hlist_del(&entry->list);
+	skb_out = entry->skb;
+	kfree(entry);
+
+	packet = (struct batadv_frag_packet *)skb_out->data;
+	size = ntohs(packet->total_size) + hdr_size;
+
+	/* Make room for the rest of the fragments. */
+	if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
+		kfree_skb(skb_out);
+		skb_out = NULL;
+		dropped = true;
+		goto free;
+	}
+
+	/* Move the existing MAC header to just before the payload. (Override
+	 * the fragment header.)
+	 */
+	skb_pull(skb_out, hdr_size);
+	skb_out->ip_summed = CHECKSUM_NONE;
+	memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
+	skb_set_mac_header(skb_out, -ETH_HLEN);
+	skb_reset_network_header(skb_out);
+	skb_reset_transport_header(skb_out);
+
+	/* Copy the payload of the each fragment into the last skb */
+	hlist_for_each_entry(entry, chain, list) {
+		size = entry->skb->len - hdr_size;
+		skb_put_data(skb_out, entry->skb->data + hdr_size, size);
+	}
+
+free:
+	/* Locking is not needed, because 'chain' is not part of any orig. */
+	batadv_frag_clear_chain(chain, dropped);
+	return skb_out;
+}
+
+/**
+ * batadv_skb_is_frag() - check if newly merged skb contains unicast fragment
+ * @skb: newly merged skb
+ *
+ * Return: true if the newly merged skb is of type BATADV_UNICAST_FRAG, false
+ *  otherwise
+ */
+static bool batadv_skb_is_frag(struct sk_buff *skb)
+{
+	struct batadv_ogm_packet *batadv_ogm_packet;
+
+	/* packet should hold at least type and version */
+	if (unlikely(!pskb_may_pull(skb, 2)))
+		return false;
+
+	batadv_ogm_packet = (struct batadv_ogm_packet *)skb->data;
+
+	if (batadv_ogm_packet->version != BATADV_COMPAT_VERSION)
+		return false;
+
+	if (batadv_ogm_packet->packet_type != BATADV_UNICAST_FRAG)
+		return false;
+
+	return true;
+}
+
+/**
+ * batadv_frag_skb_buffer() - buffer fragment for later merge
+ * @skb: skb to buffer
+ * @orig_node_src: originator that the skb is received from
+ *
+ * Add fragment to buffer and merge fragments if possible.
+ *
+ * There are three possible outcomes: 1) Packet is merged: Return true and
+ * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
+ * to NULL; 3) Error: Return false and free skb.
+ *
+ * Return: true when the packet is merged or buffered, false when skb is not
+ * used.
+ */
+bool batadv_frag_skb_buffer(struct sk_buff **skb,
+			    struct batadv_orig_node *orig_node_src)
+{
+	struct hlist_head head = HLIST_HEAD_INIT;
+	struct sk_buff *skb_out = NULL;
+	bool ret = false;
+
+	/* Add packet to buffer and table entry if merge is possible. */
+	if (!batadv_frag_insert_packet(orig_node_src, *skb, &head))
+		goto out_err;
+
+	/* Leave if more fragments are needed to merge. */
+	if (hlist_empty(&head))
+		goto out;
+
+	skb_out = batadv_frag_merge_packets(&head);
+	if (!skb_out)
+		goto out_err;
+
+	/* fragment in fragment is not allowed. otherwise it is possible
+	 * to exhaust the stack when receiving a matryoshka-style
+	 * "fragments in a fragment packet"
+	 */
+	if (batadv_skb_is_frag(skb_out)) {
+		kfree_skb(skb_out);
+		skb_out = NULL;
+		goto out_err;
+	}
+
+out:
+	ret = true;
+out_err:
+	*skb = skb_out;
+	return ret;
+}
+
+/**
+ * batadv_frag_skb_fwd() - forward fragments that would exceed MTU when merged
+ * @skb: skb to forward
+ * @recv_if: interface that the skb is received on
+ * @orig_node_src: originator that the skb is received from
+ * @rx_result: set to NET_RX_SUCCESS when the fragment was forwarded and
+ *  NET_RX_DROP when it was dropped; only valid when true is returned
+ *
+ * Look up the next-hop of the fragments payload and check if the merged packet
+ * will exceed the MTU towards the next-hop. If so, the fragment is forwarded
+ * without merging it.
+ *
+ * Return: true if the fragment is consumed/forwarded, false otherwise.
+ */
+bool batadv_frag_skb_fwd(struct sk_buff *skb,
+			 struct batadv_hard_iface *recv_if,
+			 struct batadv_orig_node *orig_node_src,
+			 int *rx_result)
+{
+	struct batadv_priv *bat_priv = netdev_priv(recv_if->mesh_iface);
+	struct batadv_neigh_node *neigh_node = NULL;
+	struct batadv_frag_packet *packet;
+	bool ret = false;
+	u16 total_size;
+
+	packet = (struct batadv_frag_packet *)skb->data;
+
+	neigh_node = batadv_orig_to_router(bat_priv, packet->dest, recv_if);
+	if (!neigh_node)
+		goto out;
+
+	/* Forward the fragment, if the merged packet would be too big to
+	 * be assembled.
+	 */
+	total_size = ntohs(packet->total_size);
+	if (total_size > neigh_node->if_incoming->net_dev->mtu) {
+		if (packet->ttl < 2) {
+			kfree_skb(skb);
+			*rx_result = NET_RX_DROP;
+			ret = true;
+			goto out;
+		}
+
+		if (skb_cow(skb, ETH_HLEN) < 0) {
+			kfree_skb(skb);
+			*rx_result = NET_RX_DROP;
+			ret = true;
+			goto out;
+		}
+
+		packet = (struct batadv_frag_packet *)skb->data;
+
+		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
+		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
+				   skb->len + ETH_HLEN);
+
+		packet->ttl--;
+		batadv_send_unicast_skb(skb, neigh_node);
+		*rx_result = NET_RX_SUCCESS;
+		ret = true;
+	}
+
+out:
+	batadv_neigh_node_put(neigh_node);
+	return ret;
+}
+
+/**
+ * batadv_frag_create() - create a fragment from skb
+ * @net_dev: outgoing device for fragment
+ * @skb: skb to create fragment from
+ * @frag_head: header to use in new fragment
+ * @fragment_size: size of new fragment
+ *
+ * Split the passed skb into two fragments: A new one with size matching the
+ * passed mtu and the old one with the rest. The new skb contains data from the
+ * tail of the old skb.
+ *
+ * Return: the new fragment, NULL on error.
+ */
+static struct sk_buff *batadv_frag_create(struct net_device *net_dev,
+					  struct sk_buff *skb,
+					  struct batadv_frag_packet *frag_head,
+					  unsigned int fragment_size)
+{
+	unsigned int ll_reserved = LL_RESERVED_SPACE(net_dev);
+	unsigned int tailroom = net_dev->needed_tailroom;
+	unsigned int header_size = sizeof(*frag_head);
+	struct sk_buff *skb_fragment;
+	unsigned int mtu;
+
+	mtu = fragment_size + header_size;
+	skb_fragment = dev_alloc_skb(ll_reserved + mtu + tailroom);
+	if (!skb_fragment)
+		goto err;
+
+	skb_fragment->priority = skb->priority;
+
+	/* Eat the last mtu-bytes of the skb */
+	skb_reserve(skb_fragment, ll_reserved + header_size);
+	skb_split(skb, skb_fragment, skb->len - fragment_size);
+
+	/* Add the header */
+	skb_push(skb_fragment, header_size);
+	memcpy(skb_fragment->data, frag_head, header_size);
+
+err:
+	return skb_fragment;
+}
+
+/**
+ * batadv_frag_send_packet() - create up to 16 fragments from the passed skb
+ * @skb: skb to create fragments from
+ * @orig_node: final destination of the created fragments
+ * @neigh_node: next-hop of the created fragments
+ *
+ * Return: the netdev tx status or a negative errno code on a failure
+ */
+int batadv_frag_send_packet(struct sk_buff *skb,
+			    struct batadv_orig_node *orig_node,
+			    struct batadv_neigh_node *neigh_node)
+{
+	struct net_device *net_dev = neigh_node->if_incoming->net_dev;
+	struct batadv_hard_iface *primary_if = NULL;
+	struct batadv_frag_packet frag_header;
+	unsigned int mtu = net_dev->mtu;
+	unsigned int max_fragment_size;
+	struct batadv_priv *bat_priv;
+	struct sk_buff *skb_fragment;
+	unsigned int num_fragments;
+	unsigned int header_size;
+	int ret;
+
+	header_size = sizeof(frag_header);
+
+	/* To avoid merge and refragmentation at next-hops we never send
+	 * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
+	 */
+	mtu = min_t(unsigned int, mtu, BATADV_FRAG_MAX_FRAG_SIZE);
+	max_fragment_size = mtu - header_size;
+
+	if (skb->len == 0 || max_fragment_size == 0) {
+		ret = -EINVAL;
+		goto free_skb;
+	}
+
+	num_fragments = (skb->len - 1) / max_fragment_size + 1;
+	max_fragment_size = (skb->len - 1) / num_fragments + 1;
+
+	/* Don't even try to fragment, if we need more than 16 fragments */
+	if (num_fragments > BATADV_FRAG_MAX_FRAGMENTS) {
+		ret = -EAGAIN;
+		goto free_skb;
+	}
+
+	bat_priv = orig_node->bat_priv;
+	primary_if = batadv_primary_if_get_selected(bat_priv);
+	if (!primary_if) {
+		ret = -EINVAL;
+		goto free_skb;
+	}
+
+	/* GRO might have added fragments to the fragment list instead of
+	 * frags[]. But this is not handled by skb_split and must be
+	 * linearized to avoid incorrect length information after all
+	 * batman-adv fragments were created and submitted to the
+	 * hard-interface
+	 */
+	if (skb_has_frag_list(skb) && __skb_linearize(skb)) {
+		ret = -ENOMEM;
+		goto put_primary_if;
+	}
+
+	/* Create one header to be copied to all fragments */
+	frag_header.packet_type = BATADV_UNICAST_FRAG;
+	frag_header.version = BATADV_COMPAT_VERSION;
+	frag_header.ttl = BATADV_TTL;
+	frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
+	frag_header.reserved = 0;
+	frag_header.no = 0;
+	frag_header.total_size = htons(skb->len);
+
+	/* skb->priority values from 256->263 are magic values to
+	 * directly indicate a specific 802.1d priority.  This is used
+	 * to allow 802.1d priority to be passed directly in from VLAN
+	 * tags, etc.
+	 */
+	if (skb->priority >= 256 && skb->priority <= 263)
+		frag_header.priority = skb->priority - 256;
+	else
+		frag_header.priority = 0;
+
+	ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
+	ether_addr_copy(frag_header.dest, orig_node->orig);
+
+	/* Eat and send fragments from the tail of skb */
+	while (skb->len > max_fragment_size) {
+		/* The initial check in this function should cover this case */
+		if (unlikely(frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)) {
+			ret = -EINVAL;
+			goto put_primary_if;
+		}
+
+		skb_fragment = batadv_frag_create(net_dev, skb, &frag_header,
+						  max_fragment_size);
+		if (!skb_fragment) {
+			ret = -ENOMEM;
+			goto put_primary_if;
+		}
+
+		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
+		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
+				   skb_fragment->len + ETH_HLEN);
+		ret = batadv_send_unicast_skb(skb_fragment, neigh_node);
+		if (ret != NET_XMIT_SUCCESS) {
+			ret = NET_XMIT_DROP;
+			goto put_primary_if;
+		}
+
+		frag_header.no++;
+	}
+
+	/* make sure that there is at least enough head for the fragmentation
+	 * and ethernet headers
+	 */
+	ret = skb_cow_head(skb, ETH_HLEN + header_size);
+	if (ret < 0)
+		goto put_primary_if;
+
+	skb_push(skb, header_size);
+	memcpy(skb->data, &frag_header, header_size);
+
+	/* Send the last fragment */
+	batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
+	batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
+			   skb->len + ETH_HLEN);
+	ret = batadv_send_unicast_skb(skb, neigh_node);
+	/* skb was consumed */
+	skb = NULL;
+
+put_primary_if:
+	batadv_hardif_put(primary_if);
+free_skb:
+	kfree_skb(skb);
+
+	return ret;
+}