batman-adv: Receive fragmented packets and merge

Fragments arriving at their destination are buffered for later merge.
Merged packets are passed to the main receive function as had they never
been fragmented.

Fragments are forwarded without merging if the MTU of the outgoing
interface is smaller than the size of the merged packet.

Signed-off-by: Martin Hundebøll <[email protected]>
Signed-off-by: Marek Lindner <[email protected]>
Signed-off-by: Antonio Quartulli <[email protected]>

Author: hundeboll

net/batman-adv/Makefile

@@ -24,6 +24,7 @@ batman-adv-y += bitarray.o
 batman-adv-$(CONFIG_BATMAN_ADV_BLA) += bridge_loop_avoidance.o
 batman-adv-y += debugfs.o
 batman-adv-$(CONFIG_BATMAN_ADV_DAT) += distributed-arp-table.o
+batman-adv-y += fragmentation.o
 batman-adv-y += gateway_client.o
 batman-adv-y += gateway_common.o
 batman-adv-y += hard-interface.o

net/batman-adv/fragmentation.c

@@ -0,0 +1,370 @@
+/* Copyright (C) 2013 B.A.T.M.A.N. contributors:
+ *
+ * Martin Hundebøll <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA
+ */
+
+#include "main.h"
+#include "fragmentation.h"
+#include "send.h"
+#include "originator.h"
+#include "routing.h"
+#include "hard-interface.h"
+#include "soft-interface.h"
+
+
+/**
+ * batadv_frag_clear_chain - delete entries in the fragment buffer chain
+ * @head: head of chain with entries.
+ *
+ * Free fragments in the passed hlist. Should be called with appropriate lock.
+ */
+static void batadv_frag_clear_chain(struct hlist_head *head)
+{
+	struct batadv_frag_list_entry *entry;
+	struct hlist_node *node;
+
+	hlist_for_each_entry_safe(entry, node, head, list) {
+		hlist_del(&entry->list);
+		kfree_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;
+	uint8_t i;
+
+	for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
+		chain = &orig_node->fragments[i];
+		spin_lock_bh(&orig_node->fragments[i].lock);
+
+		if (!check_cb || check_cb(chain)) {
+			batadv_frag_clear_chain(&orig_node->fragments[i].head);
+			orig_node->fragments[i].size = 0;
+		}
+
+		spin_unlock_bh(&orig_node->fragments[i].lock);
+	}
+}
+
+/**
+ * batadv_frag_size_limit - maximum possible size of packet to be fragmented
+ *
+ * Returns the maximum size of payload that can be fragmented.
+ */
+static int batadv_frag_size_limit(void)
+{
+	int 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.
+ *
+ * Returns true if chain is empty and 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,
+				   uint16_t seqno)
+{
+	if (chain->seqno == seqno)
+		return false;
+
+	if (!hlist_empty(&chain->head))
+		batadv_frag_clear_chain(&chain->head);
+
+	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.
+ *
+ * Returns 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_table_entry *chain;
+	struct batadv_frag_list_entry *frag_entry_new = NULL, *frag_entry_curr;
+	struct batadv_frag_packet *frag_packet;
+	uint8_t bucket;
+	uint16_t seqno, hdr_size = sizeof(struct batadv_frag_packet);
+	bool ret = false;
+
+	/* 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;
+	seqno = ntohs(frag_packet->seqno);
+	bucket = seqno % BATADV_FRAG_BUFFER_COUNT;
+
+	frag_entry_new = kmalloc(sizeof(*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->head);
+		chain->size = skb->len - hdr_size;
+		chain->timestamp = jiffies;
+		ret = true;
+		goto out;
+	}
+
+	/* Find the position for the new fragment. */
+	hlist_for_each_entry(frag_entry_curr, &chain->head, 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);
+			chain->size += skb->len - hdr_size;
+			chain->timestamp = jiffies;
+			ret = true;
+			goto out;
+		}
+	}
+
+	/* Reached the end of the list, so insert after 'frag_entry_curr'. */
+	if (likely(frag_entry_curr)) {
+		hlist_add_after(&frag_entry_curr->list, &frag_entry_new->list);
+		chain->size += skb->len - hdr_size;
+		chain->timestamp = jiffies;
+		ret = true;
+	}
+
+out:
+	if (chain->size > batadv_frag_size_limit() ||
+	    ntohs(frag_packet->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.
+		 */
+		batadv_frag_clear_chain(&chain->head);
+		chain->size = 0;
+	} else if (ntohs(frag_packet->total_size) == chain->size) {
+		/* All fragments received. Hand over chain to caller. */
+		hlist_move_list(&chain->head, chain_out);
+		chain->size = 0;
+	}
+
+err_unlock:
+	spin_unlock_bh(&chain->lock);
+
+err:
+	if (!ret)
+		kfree(frag_entry_new);
+
+	return ret;
+}
+
+/**
+ * batadv_frag_merge_packets - merge a chain of fragments
+ * @chain: head of chain with fragments
+ * @skb: packet with total size of skb after merging
+ *
+ * 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.
+ *
+ * Returns the merged skb or NULL on error.
+ */
+static struct sk_buff *
+batadv_frag_merge_packets(struct hlist_head *chain, struct sk_buff *skb)
+{
+	struct batadv_frag_packet *packet;
+	struct batadv_frag_list_entry *entry;
+	struct sk_buff *skb_out = NULL;
+	int size, hdr_size = sizeof(struct batadv_frag_packet);
+
+	/* Make sure incoming skb has non-bogus data. */
+	packet = (struct batadv_frag_packet *)skb->data;
+	size = ntohs(packet->total_size);
+	if (size > batadv_frag_size_limit())
+		goto free;
+
+	/* 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);
+
+	/* Make room for the rest of the fragments. */
+	if (pskb_expand_head(skb_out, 0, size - skb->len, GFP_ATOMIC) < 0) {
+		kfree_skb(skb_out);
+		skb_out = NULL;
+		goto free;
+	}
+
+	/* Move the existing MAC header to just before the payload. (Override
+	 * the fragment header.)
+	 */
+	skb_pull_rcsum(skb_out, hdr_size);
+	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;
+		memcpy(skb_put(skb_out, size), entry->skb->data + hdr_size,
+		       size);
+	}
+
+free:
+	/* Locking is not needed, because 'chain' is not part of any orig. */
+	batadv_frag_clear_chain(chain);
+	return skb_out;
+}
+
+/**
+ * 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 leave skb as is.
+ */
+bool batadv_frag_skb_buffer(struct sk_buff **skb,
+			    struct batadv_orig_node *orig_node_src)
+{
+	struct sk_buff *skb_out = NULL;
+	struct hlist_head head = HLIST_HEAD_INIT;
+	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, *skb);
+	if (!skb_out)
+		goto out_err;
+
+out:
+	*skb = skb_out;
+	ret = true;
+out_err:
+	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
+ *
+ * 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.
+ *
+ * Returns 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)
+{
+	struct batadv_priv *bat_priv = netdev_priv(recv_if->soft_iface);
+	struct batadv_orig_node *orig_node_dst = NULL;
+	struct batadv_neigh_node *neigh_node = NULL;
+	struct batadv_frag_packet *packet;
+	uint16_t total_size;
+	bool ret = false;
+
+	packet = (struct batadv_frag_packet *)skb->data;
+	orig_node_dst = batadv_orig_hash_find(bat_priv, packet->dest);
+	if (!orig_node_dst)
+		goto out;
+
+	neigh_node = batadv_find_router(bat_priv, orig_node_dst, 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) {
+		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
+		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
+				   skb->len + ETH_HLEN);
+
+		packet->header.ttl--;
+		batadv_send_skb_packet(skb, neigh_node->if_incoming,
+				       neigh_node->addr);
+		ret = true;
+	}
+
+out:
+	if (orig_node_dst)
+		batadv_orig_node_free_ref(orig_node_dst);
+	if (neigh_node)
+		batadv_neigh_node_free_ref(neigh_node);
+	return ret;
+}