vti6: fix uninit when using x-netns

commit 092a29a4 upstream.

When the kernel deleted a vti6 interface, this interface was not removed from
the tunnels list. Thus, when the ip6_vti module was removed, this old interface
was found and the kernel tried to delete it again. This was leading to a kernel
panic.

Fixes: 61220ab3 ("vti6: Enable namespace changing")
Signed-off-by: Yao Xiwei <xiwei.yao@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/ipv6/ip6_vti.c

@@ -267,8 +267,7 @@ static struct ip6_tnl *vti6_locate(struct net *net, struct __ip6_tnl_parm *p,
 static void vti6_dev_uninit(struct net_device *dev)
 {
 	struct ip6_tnl *t = netdev_priv(dev);
-	struct net *net = dev_net(dev);
-	struct vti6_net *ip6n = net_generic(net, vti6_net_id);
+	struct vti6_net *ip6n = net_generic(t->net, vti6_net_id);
 
 	if (dev == ip6n->fb_tnl_dev)
 		RCU_INIT_POINTER(ip6n->tnls_wc[0], NULL);