[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/net/ipv4/arp.c b/net/ipv4/arp.c
index 78dd344..bde1297 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -932,6 +932,9 @@
 {
 	struct arphdr *arp;
 
+	if (dev->nd_net != &init_net)
+		goto freeskb;
+
 	/* ARP header, plus 2 device addresses, plus 2 IP addresses.  */
 	if (!pskb_may_pull(skb, (sizeof(struct arphdr) +
 				 (2 * dev->addr_len) +
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index 9706939..41d8964 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -382,6 +382,9 @@
 	struct iphdr *iph;
 	u32 len;
 
+	if (dev->nd_net != &init_net)
+		goto drop;
+
 	/* When the interface is in promisc. mode, drop all the crap
 	 * that it receives, do not try to analyse it.
 	 */
diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index 5ae4849..08ff623 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -426,6 +426,9 @@
 	unsigned char *sha, *tha;		/* s for "source", t for "target" */
 	struct ic_device *d;
 
+	if (dev->nd_net != &init_net)
+		goto drop;
+
 	if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL)
 		return NET_RX_DROP;
 
@@ -835,6 +838,9 @@
 	struct ic_device *d;
 	int len, ext_len;
 
+	if (dev->nd_net != &init_net)
+		goto drop;
+
 	/* Perform verifications before taking the lock.  */
 	if (skb->pkt_type == PACKET_OTHERHOST)
 		goto drop;