[NET]: Make packet reception network namespace safe

This patch modifies every packet receive function
registered with dev_add_pack() to drop packets if they
are not from the initial network namespace.

This should ensure that the various network stacks do
not receive packets in a anything but the initial network
namespace until the code has been converted and is ready
for them.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/wan/syncppp.c b/drivers/net/wan/syncppp.c
index 67fc67c..5c71af6 100644
--- a/drivers/net/wan/syncppp.c
+++ b/drivers/net/wan/syncppp.c
@@ -51,6 +51,7 @@
 #include <linux/spinlock.h>
 #include <linux/rcupdate.h>
 
+#include <net/net_namespace.h>
 #include <net/syncppp.h>
 
 #include <asm/byteorder.h>
@@ -1445,6 +1446,11 @@
 
 static int sppp_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *p, struct net_device *orig_dev)
 {
+	if (dev->nd_net != &init_net) {
+		kfree_skb(skb);
+		return 0;
+	}
+
 	if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL)
 		return NET_RX_DROP;
 	sppp_input(dev,skb);