From: Daniel Lezcano <dlezcano@fr.ibm.com>

When a packet is outgoing, the namespace source is stored
into the skbuff. Because it is the loopback address, the
source == destination, so when the packet is incoming, it
has already the namespace destination set into the packet.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>

---
 include/linux/net_namespace.h |   13 +++++++++++--
 include/linux/skbuff.h        |    5 ++++-
 net/core/net_namespace.c      |   32 +++++++++++++++++++++++++++-----
 net/ipv4/ip_input.c           |    2 +-
 net/ipv4/ip_output.c          |    1 +
 5 files changed, 44 insertions(+), 9 deletions(-)

Index: 2.6.20-rc4-mm1/include/linux/skbuff.h
===================================================================
--- 2.6.20-rc4-mm1.orig/include/linux/skbuff.h
+++ 2.6.20-rc4-mm1/include/linux/skbuff.h
@@ -225,6 +225,7 @@
  *	@dma_cookie: a cookie to one of several possible DMA operations
  *		done by skb DMA functions
  *	@secmark: security marking
+ *      @net_ns: namespace destination
  */
 
 struct sk_buff {
@@ -309,7 +310,9 @@
 #ifdef CONFIG_NETWORK_SECMARK
 	__u32			secmark;
 #endif
-
+#ifdef CONFIG_NET_NS
+ 	struct net_namespace    *net_ns;
+#endif
 	__u32			mark;
 
 	/* These elements must be at the end, see alloc_skb() for details.  */
Index: 2.6.20-rc4-mm1/net/ipv4/ip_input.c
===================================================================
--- 2.6.20-rc4-mm1.orig/net/ipv4/ip_input.c
+++ 2.6.20-rc4-mm1/net/ipv4/ip_input.c
@@ -396,7 +396,7 @@
 
 	iph = skb->nh.iph;
 
-	dst_net_ns = net_ns_find_from_dest_addr(iph->daddr);
+	dst_net_ns = net_ns_find_from_dest_addr(skb);
 	if (dst_net_ns && !net_ns_match(net_ns, dst_net_ns))
 		push_net_ns(dst_net_ns);
 	/*
Index: 2.6.20-rc4-mm1/net/ipv4/ip_output.c
===================================================================
--- 2.6.20-rc4-mm1.orig/net/ipv4/ip_output.c
+++ 2.6.20-rc4-mm1/net/ipv4/ip_output.c
@@ -272,6 +272,7 @@
 
 	IP_INC_STATS(IPSTATS_MIB_OUTREQUESTS);
 
+	net_ns_tag_sk_buff(skb);
 	skb->dev = dev;
 	skb->protocol = htons(ETH_P_IP);
 
Index: 2.6.20-rc4-mm1/include/linux/net_namespace.h
===================================================================
--- 2.6.20-rc4-mm1.orig/include/linux/net_namespace.h
+++ 2.6.20-rc4-mm1/include/linux/net_namespace.h
@@ -8,6 +8,7 @@
 #include <linux/types.h>
 
 struct in_ifaddr;
+struct sk_buff;
 
 struct net_namespace {
 	struct kref		kref;
@@ -101,10 +102,13 @@
 extern __be32 net_ns_select_source_address(const struct net_device *dev,
 					   u32 dst, int scope);
 
-extern struct net_namespace *net_ns_find_from_dest_addr(u32 daddr);
+extern struct net_namespace
+*net_ns_find_from_dest_addr(const struct sk_buff *skb);
 
 extern int net_ns_ifa_is_visible(const struct in_ifaddr *ifa);
 
+extern void net_ns_tag_sk_buff(struct sk_buff *skb);
+
 #define SELECT_SRC_ADDR net_ns_select_source_address
 
 #else /* CONFIG_NET_NS */
@@ -173,7 +177,8 @@
 	return 0;
 }
 
-static inline struct net_namespace *net_ns_find_from_dest_addr(u32 daddr)
+static inline struct net_namespace
+*net_ns_find_from_dest_addr(const struct sk_buff *skb)
 {
 	return NULL;
 }
@@ -183,6 +188,10 @@
 	return 1;
 }
 
+static inline void net_ns_tag_sk_buff(struct sk_buff *skb)
+{
+	;
+}
 #define SELECT_SRC_ADDR inet_select_addr
 
 #endif /* !CONFIG_NET_NS */
Index: 2.6.20-rc4-mm1/net/core/net_namespace.c
===================================================================
--- 2.6.20-rc4-mm1.orig/net/core/net_namespace.c
+++ 2.6.20-rc4-mm1/net/core/net_namespace.c
@@ -13,6 +13,9 @@
 #include <linux/in.h>
 #include <linux/netdevice.h>
 #include <linux/inetdevice.h>
+#include <linux/skbuff.h>
+#include <linux/ip.h>
+
 #include <net/ip_fib.h>
 
 struct net_namespace init_net_ns = {
@@ -389,18 +392,25 @@
 /*
  * This function finds the network namespace destination deduced from
  * the destination address. The network namespace is retrieved from
- * the ifaddr owned by a network namespace
- * @daddr  : destination
+ * the ifaddr owned by a network namespace. If the packet is for the
+ * loopback address so we assume the destination address is already filled
+ * by the sender which is the same as the receiver.
+ * @skb : the packet to be delivered
  * Returns : the network namespace destination or NULL if not found
  */
-struct net_namespace *net_ns_find_from_dest_addr(u32 daddr)
+struct net_namespace *net_ns_find_from_dest_addr(const struct sk_buff *skb)
 {
 	struct net_namespace *net_ns = NULL;
 	struct net_device *dev;
 	struct in_device *in_dev;
+  	struct iphdr *iph;
+  	__be32 daddr;
+
+  	iph = skb->nh.iph;
+  	daddr = iph->daddr;
 
-	if (LOOPBACK(daddr))
-		return current_net_ns;
+   	if (LOOPBACK(daddr))
+  		return skb->net_ns;
 
 	read_lock(&dev_base_lock);
 	rcu_read_lock();
@@ -442,4 +452,16 @@
  	return 0;
 }
 
+/*
+ * This function allows to isolation the loopback. Because we are
+ * using the 127.0.0.1, we assume the source network namespace is
+ * the same as the destination network namespace. So setting the
+ * source, we have directly the destination when receiving the packet
+ * @skb : the packet to be tagged with the network namespace
+ */
+void net_ns_tag_sk_buff(struct sk_buff *skb)
+{
+	struct net_namespace *net_ns = current_net_ns;
+	skb->net_ns = net_ns;
+}
 #endif /* CONFIG_NET_NS */

-- 
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