batman-adv: Avoid probe ELP information leak

commit 88d0895d upstream.

The probe ELPs for WiFi interfaces are expanded to contain at least
BATADV_ELP_MIN_PROBE_SIZE bytes. This is usually a lot more than the
number of bytes which the template ELP packet requires.

These extra padding bytes were not initialized and thus could contain data
which were previously stored at the same location. It is therefore required
to set it to some predefined or random values to avoid leaking private
information from the system transmitting these kind of packets.

Fixes: e4623c913508 ("batman-adv: Avoid probe ELP information leak")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Acked-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/batman-adv/bat_v_elp.c

@@ -191,6 +191,7 @@ batadv_v_elp_wifi_neigh_probe(struct batadv_hardif_neigh_node *neigh)
 	struct sk_buff *skb;
 	int probe_len, i;
 	int elp_skb_len;
+	void *tmp;
 
 	/* this probing routine is for Wifi neighbours only */
 	if (!batadv_is_wifi_netdev(hard_iface->net_dev))
@@ -222,7 +223,8 @@ batadv_v_elp_wifi_neigh_probe(struct batadv_hardif_neigh_node *neigh)
 		 * the packet to be exactly of that size to make the link
 		 * throughput estimation effective.
 		 */
-		skb_put(skb, probe_len - hard_iface->bat_v.elp_skb->len);
+		tmp = skb_put(skb, probe_len - hard_iface->bat_v.elp_skb->len);
+		memset(tmp, 0, probe_len - hard_iface->bat_v.elp_skb->len);
 
 		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
 			   "Sending unicast (probe) ELP packet on interface %s to %pM\n",