[CVE-2016-4486][Precise] net: fix infoleak in rtnetlink

[Luis Henriques]

From: Kangjie Lu <kangjielu at gmail.com>

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 at gatech.edu>
Signed-off-by: David S. Miller <davem at davemloft.net>
(backported from commit 5f8e44741f9f216e33736ea4ec65ca9ac03036e6)
[ luis:
  - this kernel version has this code in function rtnl_fill_ifinfo(),
    changed to rtnl_fill_link_ifmap() with commit b22b941b2c25 ]
CVE-2016-4486
BugLink: https://bugs.launchpad.net/bugs/1578497
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/core/rtnetlink.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index e77373a44847..37a09046aa0a 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -920,14 +920,16 @@ 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);
 	}