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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, Denis Kirjanov <kda@linux-powerpc.org>,
        "Simon Wunderlich" <sw@simonwunderlich.de>,
        "Sven Eckelmann" <sven@narfation.org>
Date:   Fri, 24 Apr 2020 00:04:48 +0100
Message-ID: <lsq.1587683028.842404845@decadent.org.uk>
Subject: [PATCH 3.16 061/245] batman-adv: Fix DAT candidate selection on
 little endian systems
In-Reply-To: <lsq.1587683027.831233700@decadent.org.uk>
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3.16.83-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sven Eckelmann <sven@narfation.org>

commit 4cc4a1708903f404d2ca0dfde30e71e052c6cbc9 upstream.

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, this 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: be1db4f6615b ("batman-adv: make the Distributed ARP Table vlan aware")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/batman-adv/distributed-arp-table.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -207,9 +207,11 @@ static uint32_t batadv_hash_dat(const vo
 {
 	uint32_t hash = 0;
 	const struct batadv_dat_entry *dat = data;
+	__be16 vid;
 
 	hash = batadv_hash_bytes(hash, &dat->ip, sizeof(dat->ip));
-	hash = batadv_hash_bytes(hash, &dat->vid, sizeof(dat->vid));
+	vid = htons(dat->vid);
+	hash = batadv_hash_bytes(hash, &vid, sizeof(vid));
 
 	hash += (hash << 3);
 	hash ^= (hash >> 11);