From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Fri, 16 Mar 2018 11:29:10 +0100
Subject: batman-adv: fix header size check in batadv_dbg_arp()

Checking for 0 is insufficient: when an SKB without a batadv header, but
with a VLAN header is received, hdr_size will be 4, making the following
code interpret the Ethernet header as a batadv header.

Fixes: 3e26722bc9f2 ("batman-adv: make the Distributed ARP Table vlan aware")
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
Signed-off-by: Sven Eckelmann <sven@narfation.org>

Origin: upstream, https://git.open-mesh.org/batman-adv.git/commit/7dfe729b169b1217f47744edbd1616f473340fda

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index 4d982e63a3ab269e3d3b1e7a9d5f205638051603..fcd38e48a6ea74bd91b0bdd874cb5e88e661e729 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -391,7 +391,7 @@ static void batadv_dbg_arp(struct batadv_priv *bat_priv, struct sk_buff *skb,
 		   batadv_arp_hw_src(skb, hdr_size), &ip_src,
 		   batadv_arp_hw_dst(skb, hdr_size), &ip_dst);
 
-	if (hdr_size == 0)
+	if (hdr_size < sizeof(struct batadv_unicast_packet))
 		return;
 
 	unicast_4addr_packet = (struct batadv_unicast_4addr_packet *)skb->data;