Subject: Re: switching network namespace midway

From: [email-masked] (Eric W. Biederman)
Date: Thu, 01 Nov 2012 23:18:58 -0700

Benjamin LaHaise <[email-masked]> writes:

> On Thu, Oct 25, 2012 at 09:15:34AM -0700, Eric W. Biederman wrote:
>> > I've read IPv4 gre code, and it appears to do the right thing on rx, but it 
>> > does *not* appear to handle namespaces correctly on transmit.  In general, 
>> > I would expect pretty much all code to get namespace handling correct for 
>> > the rx case.  I'll have a closer look at fixing this tomorrow if nobody else 
>> > beats me to it.
>> 
>> It will be interesting to see what you come up with. 
>
> Well, I finally had some time to work on the ip_gre module a bit today, 
> and here's what I came up with.  The basic idea is to store the network 
> namespace in the ip_tunnel structure at creation time for use in sending 
> and receiving packets, allowing the gre network device to be safely moved 
> into another network namespace.  This works for me in moving a gre tunnel 
> into an lxc container, and survives module unload and namespace 
> destruction.  I'll try to spend a bit more time adding similar support to 
> the other ip_tunnel devices over the next few days.  Comments/thoughts?
>
> 		-ben

You need a per network namespace exit function to delete the tunnel when
the xmit direction goes away.  Otherwise we have a very nasty race if
the original network namespace exits.

NETNS_LOCAL may make sense on the reference device that is used to
support ioctls for creating devices.

ipgre_open ?  It looks like it needs to be handled.  Probably that
ip_route_output_gre needs to be moved.

ipv6?

Eric

> -- 
> "Thought is the essence of where you are now."
> 
> 
> diff --git a/include/net/ipip.h b/include/net/ipip.h
> index ddc077c..9cfba92 100644
> --- a/include/net/ipip.h
> +++ b/include/net/ipip.h
> @@ -19,6 +19,7 @@ struct ip_tunnel_6rd_parm {
>  struct ip_tunnel {
>  	struct ip_tunnel __rcu	*next;
>  	struct net_device	*dev;
> +	struct net		*net;		/* Namespace for packet i/o */
>  
>  	int			err_count;	/* Number of arrived ICMP errors */
>  	unsigned long		err_time;	/* Time when the last ICMP error arrived */
> diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
> index 7240f8e..705dc66 100644
> --- a/net/ipv4/ip_gre.c
> +++ b/net/ipv4/ip_gre.c
> @@ -461,6 +461,7 @@ static struct ip_tunnel *ipgre_tunnel_locate(struct net *net,
>  	dev_net_set(dev, net);
>  
>  	nt = netdev_priv(dev);
> +	nt->net = net;
>  	nt->parms = *parms;
>  	dev->rtnl_link_ops = &ipgre_link_ops;
>  
> @@ -484,8 +485,10 @@ failed_free:
>  
>  static void ipgre_tunnel_uninit(struct net_device *dev)
>  {
> -	struct net *net = dev_net(dev);
> -	struct ipgre_net *ign = net_generic(net, ipgre_net_id);
> +	struct ip_tunnel *tunnel = netdev_priv(dev);
> +	struct ipgre_net *ign;
> +
> +	ign = net_generic(tunnel->net, ipgre_net_id);
>  
>  	ipgre_tunnel_unlink(ign, netdev_priv(dev));
>  	dev_put(dev);
> @@ -837,7 +840,7 @@ static netdev_tx_t ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev
>  			tos = ipv6_get_dsfield((const struct ipv6hdr *)old_iph);
>  	}
>  
> -	rt = ip_route_output_gre(dev_net(dev), &fl4, dst, tiph->saddr,
> +	rt = ip_route_output_gre(tunnel->net, &fl4, dst, tiph->saddr,
>  				 tunnel->parms.o_key, RT_TOS(tos),
>  				 tunnel->parms.link);
>  	if (IS_ERR(rt)) {
> @@ -1010,7 +1013,7 @@ static int ipgre_tunnel_bind_dev(struct net_device *dev)
>  		struct flowi4 fl4;
>  		struct rtable *rt;
>  
> -		rt = ip_route_output_gre(dev_net(dev), &fl4,
> +		rt = ip_route_output_gre(tunnel->net, &fl4,
>  					 iph->daddr, iph->saddr,
>  					 tunnel->parms.o_key,
>  					 RT_TOS(iph->tos),
> @@ -1341,7 +1344,6 @@ static void ipgre_tunnel_setup(struct net_device *dev)
>  	dev->flags		= IFF_NOARP;
>  	dev->iflink		= 0;
>  	dev->addr_len		= 4;
> -	dev->features		|= NETIF_F_NETNS_LOCAL;
>  	dev->priv_flags		&= ~IFF_XMIT_DST_RELEASE;
>  
>  	dev->features		|= GRE_FEATURES;
> @@ -1432,6 +1434,7 @@ static void ipgre_destroy_tunnels(struct ipgre_net *ign, struct list_head *head)
>  static int __net_init ipgre_init_net(struct net *net)
>  {
>  	struct ipgre_net *ign = net_generic(net, ipgre_net_id);
> +	struct ip_tunnel *tunnel;
>  	int err;
>  
>  	ign->fb_tunnel_dev = alloc_netdev(sizeof(struct ip_tunnel), "gre0",
> @@ -1445,6 +1448,9 @@ static int __net_init ipgre_init_net(struct net *net)
>  	ipgre_fb_tunnel_init(ign->fb_tunnel_dev);
>  	ign->fb_tunnel_dev->rtnl_link_ops = &ipgre_link_ops;
>  
> +	tunnel = netdev_priv(ign->fb_tunnel_dev);
> +	tunnel->net = net;
> +
>  	if ((err = register_netdev(ign->fb_tunnel_dev)))
>  		goto err_reg_dev;
>