batman-adv: fix header size check in batadv_dbg_arp()

[ Upstream commit 6f27d2c2a8c236d296201c19abb8533ec20d212b ]

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: be1db4f6615b ("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>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index e257efdc5d0374cdb13ad8c3282269049eeb4d16..df7c6a08018854e9a4a54a3dbcbe59c826b395e0 100644 (file)
--- 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;