Re: [PATCH] net: clear iflink when moving to a new netns

From: Cong Wang <redacted>

BZ: https://bugzilla.kernel.org/show_bug.cgi?id=66691

macvlan and vlan both use iflink to identify its lower device,
however, after such device is moved to the new netns, its iflink
would become meaningless as ifindex is per netns. So, instead of
forbid them moving to another netns, just clear this field so that
it will not be dumped at least.

Cc: David S. Miller <davem@davemloft.net>
Cc: Eric W. Biederman <redacted>
Cc: Eric Dumazet <redacted>
Cc: Hannes Frederic Sowa <redacted>,
Signed-off-by: Cong Wang <redacted>
Signed-off-by: Cong Wang <redacted>
---
 net/core/dev.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 4ad1b78..5e88b0c2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -6608,12 +6608,11 @@ int dev_change_net_namespace(struct net_device *dev, struct net *net, const char
 	dev_net_set(dev, net);
 
 	/* If there is an ifindex conflict assign a new one */
-	if (__dev_get_by_index(net, dev->ifindex)) {
-		int iflink = (dev->iflink == dev->ifindex);
+	if (__dev_get_by_index(net, dev->ifindex))
 		dev->ifindex = dev_new_index(net);
-		if (iflink)
-			dev->iflink = dev->ifindex;
-	}
+
+	/* Old iflink is meaningless in the new namespace */
+	dev->iflink = dev->ifindex;
 
 	/* Send a netdev-add uevent to the new namespace */
 	kobject_uevent(&dev->dev.kobj, KOBJ_ADD);