[IPV6]: Fix potential net leak and oops in ipv6 routing code.

The commits f3db485 ([NETNS][IPV6] ip6_fib - fib6_clean_all handle several 
network namespaces) and 69ddb80 ([NETNS][IPV6] route6 - Make proc entry 
/proc/net/rt6_stats per namespace) made some proc files per net.

Both of them introduced potential OOPS - get_proc_net can return NULL, but
this check is lost - and a struct net leak - in case single_open() fails the
previously got net is not put.

Kill all these bugs with one patch.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -2390,10 +2390,18 @@ static int ipv6_route_show(struct seq_file *m, void *v)
 
 static int ipv6_route_open(struct inode *inode, struct file *file)
 {
+	int err;
 	struct net *net = get_proc_net(inode);
 	if (!net)
 		return -ENXIO;
-	return single_open(file, ipv6_route_show, net);
+
+	err = single_open(file, ipv6_route_show, net);
+	if (err < 0) {
+		put_net(net);
+		return err;
+	}
+
+	return 0;
 }
 
 static int ipv6_route_release(struct inode *inode, struct file *file)
@@ -2429,8 +2437,18 @@ static int rt6_stats_seq_show(struct seq_file *seq, void *v)
 
 static int rt6_stats_seq_open(struct inode *inode, struct file *file)
 {
+	int err;
 	struct net *net = get_proc_net(inode);
-	return single_open(file, rt6_stats_seq_show, net);
+	if (!net)
+		return -ENXIO;
+
+	err = single_open(file, rt6_stats_seq_show, net);
+	if (err < 0) {
+		put_net(net);
+		return err;
+	}
+
+	return 0;
 }
 
 static int rt6_stats_seq_release(struct inode *inode, struct file *file)