From: Sven Eckelmann <sven@narfation.org>
Date: Thu, 28 Nov 2019 12:43:49 +0100
Subject: batman-adv: Fix DAT candidate selection on little endian systems

The distributed arp table is using a DHT to store and retrieve MAC address
information for an IP address. This is done using unicast messages to
selected peers. The potential peers are looked up using the IP address and
the VID.

While the IP address is always stored in big endian byte order, it is not
the case of the VID. It can (depending on the host system) either be big
endian or little endian. The host must therefore always convert it to big
endian to ensure that all devices calculate the same peers for the same
lookup data.

Fixes: 3e26722bc9f2 ("batman-adv: make the Distributed ARP Table vlan aware")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Acked-by: Antonio Quartulli <a@unstable.cc>

Origin: upstream, https://git.open-mesh.org/batman-adv.git/commit/728aea06f38e0e4d70f4f7d43698187f7f7055c5

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index b0af3a11d4069cb7e44419d4494f20dd653dbca8..ec7bf5a4a9fc724b63da7bfd7ece79f32b104d99 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -285,6 +285,7 @@ static u32 batadv_hash_dat(const void *data, u32 size)
 	u32 hash = 0;
 	const struct batadv_dat_entry *dat = data;
 	const unsigned char *key;
+	__be16 vid;
 	u32 i;
 
 	key = (const unsigned char *)&dat->ip;
@@ -294,7 +295,8 @@ static u32 batadv_hash_dat(const void *data, u32 size)
 		hash ^= (hash >> 6);
 	}
 
-	key = (const unsigned char *)&dat->vid;
+	vid = htons(dat->vid);
+	key = (__force const unsigned char *)&vid;
 	for (i = 0; i < sizeof(dat->vid); i++) {
 		hash += key[i];
 		hash += (hash << 10);