[B.A.T.M.A.N.] [PATCH] batman-adv: Fix broadcast packet CRC calculation

["Linus Lüssing" <linus.luessing@web.de>]

So far the crc16 checksum for a batman-adv broadcast data packet, received
on a batman-adv hard interface, was calculated over zero bytes of its
content leading to many incoming broadcast data packets wrongly being
dropped.

This patch fixes this issue by calculating the crc16 over the actual,
complete broadcast payload.

The issue is a regrission introduced by
e5cf86d30a9b32feccb6b866a3f23b0e0483a3b0.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
---
It led to about 60-80% broadcast packet loss to a direct neighbor
with a ping6 with a 1s interval in our scenario, but about no
packet loss with an interval smaller than 0.2s.

Also see: https://projects.universe-factory.net/issues/65 (German)

 bridge_loop_avoidance.c |    8 ++++----
 routing.c               |    8 +++++++-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/bridge_loop_avoidance.c b/bridge_loop_avoidance.c
index 6705d35..e7b5777 100644
--- a/bridge_loop_avoidance.c
+++ b/bridge_loop_avoidance.c
@@ -1205,8 +1205,8 @@ int batadv_bla_init(struct batadv_priv *bat_priv)
 /**
  * batadv_bla_check_bcast_duplist
  * @bat_priv: the bat priv with all the soft interface information
- * @bcast_packet: originator mac address
- * @hdr_size: maximum length of the frame
+ * @bcast_packet: encapsulated broadcast frame plus batman header
+ * @bcast_packet_len: length of encapsulated broadcast frame plus batman header
  *
  * check if it is on our broadcast list. Another gateway might
  * have sent the same packet because it is connected to the same backbone,
@@ -1219,14 +1219,14 @@ int batadv_bla_init(struct batadv_priv *bat_priv)
  */
 int batadv_bla_check_bcast_duplist(struct batadv_priv *bat_priv,
 				   struct batadv_bcast_packet *bcast_packet,
-				   int hdr_size)
+				   int bcast_packet_len)
 {
 	int i, length, curr;
 	uint8_t *content;
 	uint16_t crc;
 	struct batadv_bcast_duplist_entry *entry;
 
-	length = hdr_size - sizeof(*bcast_packet);
+	length = bcast_packet_len - sizeof(*bcast_packet);
 	content = (uint8_t *)bcast_packet;
 	content += sizeof(*bcast_packet);
 
diff --git a/routing.c b/routing.c
index bc2b88b..f861b7c 100644
--- a/routing.c
+++ b/routing.c
@@ -1136,8 +1136,14 @@ int batadv_recv_bcast_packet(struct sk_buff *skb,
 
 	spin_unlock_bh(&orig_node->bcast_seqno_lock);
 
+	/* keep skb linear for crc calculation */
+	if (skb_linearize(skb) < 0)
+		goto out;
+
+	bcast_packet = (struct batadv_bcast_packet *)skb->data;
+
 	/* check whether this has been sent by another originator before */
-	if (batadv_bla_check_bcast_duplist(bat_priv, bcast_packet, hdr_size))
+	if (batadv_bla_check_bcast_duplist(bat_priv, bcast_packet, skb->len))
 		goto out;
 
 	/* rebroadcast packet */
-- 
1.7.10.4