On Tuesday 24 November 2009 09:51:19 Patrick McHardy wrote:

quoted

+     skb_dst_drop(skb);
+     skb->tstamp.tv64 = 0;
+     skb->pkt_type = PACKET_HOST;
+     skb->protocol = eth_type_trans(skb, dev);
+     skb->mark = 0;

skb->mark clearing should stay private to veth since its usually
supposed to stay intact. The only exception is packets crossing
namespaces, where they should appear like a freshly received skbs.

But isn't that what we want in macvlan as well when we're
forwarding from one downstream interface to another?

I did all my testing with macvlan interfaces in separate namespaces
communicating with each other, so I'd assume that we should always
clear skb->mark and skb->dst in this function. Maybe I should make
the documentation clearer?

---
net: clarify documentation of dev_forward_skb

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -1433,6 +1433,10 @@ static inline void net_timestamp(struct sk_buff *skb)
  * dev_forward_skb can be used for injecting an skb from the
  * start_xmit function of one device into the receive queue
  * of another device.
+ *
+ * The receiving device may be in another namespace, so
+ * we have to clear all information in the skb that could
+ * impact namespace isolation.
  */
 int dev_forward_skb(struct net_device *dev, struct sk_buff *skb)
 {