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"

Bug: 28620102

Change-Id: I13da380c6fe8abca49e3cf9f05293c02b44d2e5e
Signed-off-by: kangjie <kangjielu@gmail.com>
(cherry picked from commit d7bd06d4e7f6b8f9019bb993fd41dc361154abc3)

net/core/rtnetlink.c

@@ -924,14 +924,14 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
 		NLA_PUT_STRING(skb, IFLA_IFALIAS, dev->ifalias);
 
 	if (1) {
-		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;
 		NLA_PUT(skb, IFLA_MAP, sizeof(map), &map);
 	}