net: fix infoleak in rtnetlink

The stack object “map” has a total size of 32 bytes. Its last 4
bytes are padding generated by compiler. These padding bytes are
not initialized and sent out via “nla_put”.
Signed-off-by: Kangjie Lu <kjlu@gatech.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 5f8e4474)
CVE-2016-4486
BugLink: https://bugs.launchpad.net/bugs/1578497Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Christopher Arges <chris.j.arges@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

net/core/rtnetlink.c

@@ -1175,14 +1175,16 @@ static noinline_for_stack int rtnl_fill_vfinfo(struct sk_buff *skb,
 
 static int rtnl_fill_link_ifmap(struct sk_buff *skb, struct net_device *dev)
 {
-	struct rtnl_link_ifmap map = {
-		.mem_start   = dev->mem_start,
-		.mem_end     = dev->mem_end,
-		.base_addr   = dev->base_addr,
-		.irq         = dev->irq,
-		.dma         = dev->dma,
-		.port        = dev->if_port,
-	};
+	struct rtnl_link_ifmap map;
+
+	memset(&map, 0, sizeof(map));
+	map.mem_start   = dev->mem_start;
+	map.mem_end     = dev->mem_end;
+	map.base_addr   = dev->base_addr;
+	map.irq         = dev->irq;
+	map.dma         = dev->dma;
+	map.port        = dev->if_port;
+
 	if (nla_put(skb, IFLA_MAP, sizeof(map), &map))
 		return -EMSGSIZE;