batman-adv: add broadcast duplicate check

When multiple backbone gateways relay the same broadcast from the
backbone into the mesh, other nodes in the mesh may receive this
broadcast multiple times. To avoid this, the crc checksums of
received broadcasts are recorded and new broadcast packets with
the same content may be dropped if received by another gateway.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>

1 files changed, 75 insertions, 0 deletions

diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c
index 6186f6e92e3..4f6b44a5b12 100644
--- a/net/batman-adv/bridge_loop_avoidance.c
+++ b/net/batman-adv/bridge_loop_avoidance.c
@@ -1041,8 +1041,16 @@ out:
 /* initialize all bla structures */
 int bla_init(struct bat_priv *bat_priv)
 {
+	int i;
+
 	bat_dbg(DBG_BLA, bat_priv, "bla hash registering\n");
 
+	/* initialize the duplicate list */
+	for (i = 0; i < DUPLIST_SIZE; i++)
+		bat_priv->bcast_duplist[i].entrytime =
+			jiffies - msecs_to_jiffies(DUPLIST_TIMEOUT);
+	bat_priv->bcast_duplist_curr = 0;
+
 	if (bat_priv->claim_hash)
 		return 1;
 
@@ -1060,6 +1068,73 @@ int bla_init(struct bat_priv *bat_priv)
 
 /**
  * @bat_priv: the bat priv with all the soft interface information
+ * @bcast_packet: originator mac address
+ * @hdr_size: maximum length of the frame
+ *
+ * check if it is on our broadcast list. Another gateway might
+ * have sent the same packet because it is connected to the same backbone,
+ * so we have to remove this duplicate.
+ *
+ * This is performed by checking the CRC, which will tell us
+ * with a good chance that it is the same packet. If it is furthermore
+ * sent by another host, drop it. We allow equal packets from
+ * the same host however as this might be intended.
+ *
+ **/
+
+int bla_check_bcast_duplist(struct bat_priv *bat_priv,
+			    struct bcast_packet *bcast_packet,
+			    int hdr_size)
+{
+	int i, length, curr;
+	uint8_t *content;
+	uint16_t crc;
+	struct bcast_duplist_entry *entry;
+
+	length = hdr_size - sizeof(*bcast_packet);
+	content = (uint8_t *)bcast_packet;
+	content += sizeof(*bcast_packet);
+
+	/* calculate the crc ... */
+	crc = crc16(0, content, length);
+
+	for (i = 0 ; i < DUPLIST_SIZE; i++) {
+		curr = (bat_priv->bcast_duplist_curr + i) % DUPLIST_SIZE;
+		entry = &bat_priv->bcast_duplist[curr];
+
+		/* we can stop searching if the entry is too old ;
+		 * later entries will be even older
+		 */
+		if (has_timed_out(entry->entrytime, DUPLIST_TIMEOUT))
+			break;
+
+		if (entry->crc != crc)
+			continue;
+
+		if (compare_eth(entry->orig, bcast_packet->orig))
+			continue;
+
+		/* this entry seems to match: same crc, not too old,
+		 * and from another gw. therefore return 1 to forbid it.
+		 */
+		return 1;
+	}
+	/* not found, add a new entry (overwrite the oldest entry) */
+	curr = (bat_priv->bcast_duplist_curr + DUPLIST_SIZE - 1) % DUPLIST_SIZE;
+	entry = &bat_priv->bcast_duplist[curr];
+	entry->crc = crc;
+	entry->entrytime = jiffies;
+	memcpy(entry->orig, bcast_packet->orig, ETH_ALEN);
+	bat_priv->bcast_duplist_curr = curr;
+
+	/* allow it, its the first occurence. */
+	return 0;
+}
+
+
+
+/**
+ * @bat_priv: the bat priv with all the soft interface information
  * @orig: originator mac address
  *
  * check if the originator is a gateway for any VLAN ID.