drop_monitor: add missing call to genlmsg_end

BugLink: http://bugs.launchpad.net/bugs/1656876

[ Upstream commit 4200462d ]

Update nlmsg_len field with genlmsg_end to enable userspace processing
using nlmsg_next helper. Also adds error handling.
Signed-off-by: Reiter Wolfgang <wr0112358@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/core/drop_monitor.c

@@ -80,6 +80,7 @@ static struct sk_buff *reset_per_cpu_data(struct per_cpu_dm_data *data)
 	struct nlattr *nla;
 	struct sk_buff *skb;
 	unsigned long flags;
+	void *msg_header;
 
 	al = sizeof(struct net_dm_alert_msg);
 	al += dm_hit_limit * sizeof(struct net_dm_drop_point);
@@ -87,17 +88,31 @@ static struct sk_buff *reset_per_cpu_data(struct per_cpu_dm_data *data)
 
 	skb = genlmsg_new(al, GFP_KERNEL);
 
-	if (skb) {
-		genlmsg_put(skb, 0, 0, &net_drop_monitor_family,
-				0, NET_DM_CMD_ALERT);
-		nla = nla_reserve(skb, NLA_UNSPEC,
-				  sizeof(struct net_dm_alert_msg));
-		msg = nla_data(nla);
-		memset(msg, 0, al);
-	} else {
-		mod_timer(&data->send_timer, jiffies + HZ / 10);
+	if (!skb)
+		goto err;
+
+	msg_header = genlmsg_put(skb, 0, 0, &net_drop_monitor_family,
+				 0, NET_DM_CMD_ALERT);
+	if (!msg_header) {
+		nlmsg_free(skb);
+		skb = NULL;
+		goto err;
+	}
+	nla = nla_reserve(skb, NLA_UNSPEC,
+			  sizeof(struct net_dm_alert_msg));
+	if (!nla) {
+		nlmsg_free(skb);
+		skb = NULL;
+		goto err;
 	}
+	msg = nla_data(nla);
+	memset(msg, 0, al);
+	genlmsg_end(skb, msg_header);
+	goto out;
 
+err:
+	mod_timer(&data->send_timer, jiffies + HZ / 10);
+out:
 	spin_lock_irqsave(&data->lock, flags);
 	swap(data->skb, skb);
 	spin_unlock_irqrestore(&data->lock, flags);