Subject: Re: [PATCH net] netfilter: do not hold dev in ipt_CLUSTERIP

From: Pablo Neira Ayuso <[email-masked]>
Date: Tue, 23 May 2017 23:26:07 +0200

On Sat, May 20, 2017 at 05:08:06PM +0800, Xin Long wrote:
> It's a terrible thing to hold dev in iptables target. When the dev is
> being removed, unregister_netdevice has to wait for the dev to become
> free. dmesg will keep logging the err:
> 
>   kernel:unregister_netdevice: waiting for veth0_in to become free. \
>   Usage count = 1
> 
> until iptables rules with this target are removed manually.
> 
> The worse thing is when deleting a netns, a virtual nic will be deleted
> instead of reset to init_net in default_device_ops exit/exit_batch. As
> it is earlier than to flush the iptables rules in iptable_filter_net_ops
> exit, unregister_netdevice will block to wait for the nic to become free.
> 
> As unregister_netdevice is actually waiting for iptables rules flushing
> while iptables rules have to be flushed after unregister_netdevice. This
> 'dead lock' will cause unregister_netdevice to block there forever. As
> the netns is not available to operate at that moment, iptables rules can
> not even be flushed manually either.
> 
> The reproducer can be:
> 
>   # ip netns add test
>   # ip link add veth0_in type veth peer name veth0_out
>   # ip link set veth0_in netns test
>   # ip netns exec test ip link set lo up
>   # ip netns exec test ip link set veth0_in up
>   # ip netns exec test iptables -I INPUT -d 1.2.3.4 -i veth0_in -j \
>     CLUSTERIP --new --clustermac 89:d4:47:eb:9a:fa --total-nodes 3 \
>     --local-node 1 --hashmode sourceip-sourceport
>   # ip netns del test
> 
> This issue can be triggered by all virtual nics with ipt_CLUSTERIP.
> 
> This patch is to fix it by not holding dev in ipt_CLUSTERIP, but only
> save dev->ifindex instead of dev. When removing the mc from the dev,
> it will get dev by c->ifindex through dev_get_by_index.
> 
> Note that it doesn't save dev->name but dev->ifindex, as a dev->name
> can be changed, it will confuse ipt_CLUSTERIP.
> 
> Reported-by: Jianlin Shi <[email-masked]>
> Signed-off-by: Xin Long <[email-masked]>

OK. Let's fix this finally... One comment below.

>  net/ipv4/netfilter/ipt_CLUSTERIP.c | 31 ++++++++++++++++++-------------
>  1 file changed, 18 insertions(+), 13 deletions(-)
> 
> diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
> index 038f293..d1adb2f 100644
> --- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
> +++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
> @@ -47,7 +47,7 @@ struct clusterip_config {
>  
>  	__be32 clusterip;			/* the IP address */
>  	u_int8_t clustermac[ETH_ALEN];		/* the MAC address */
> -	struct net_device *dev;			/* device */
> +	int ifindex;				/* device ifindex */
>  	u_int16_t num_total_nodes;		/* total number of nodes */
>  	unsigned long local_nodes;		/* node number array */
>  
> @@ -98,19 +98,23 @@ clusterip_config_put(struct clusterip_config *c)
>   * entry(rule) is removed, remove the config from lists, but don't free it
>   * yet, since proc-files could still be holding references */
>  static inline void
> -clusterip_config_entry_put(struct clusterip_config *c)
> +clusterip_config_entry_put(struct net *net, struct clusterip_config *c)
>  {
> -	struct net *net = dev_net(c->dev);
>  	struct clusterip_net *cn = net_generic(net, clusterip_net_id);
>  
>  	local_bh_disable();
>  	if (refcount_dec_and_lock(&c->entries, &cn->lock)) {
> +		struct net_device *dev;
> +
>  		list_del_rcu(&c->list);
>  		spin_unlock(&cn->lock);
>  		local_bh_enable();
>  
> -		dev_mc_del(c->dev, c->clustermac);
> -		dev_put(c->dev);
> +		dev = dev_get_by_index(net, c->ifindex);
> +		if (dev) {
> +			dev_mc_del(dev, c->clustermac);
> +			dev_put(dev);
> +		}
>  
>  		/* In case anyone still accesses the file, the open/close
>  		 * functions are also incrementing the refcount on their own,
> @@ -182,7 +186,7 @@ clusterip_config_init(const struct ipt_clusterip_tgt_info *i, __be32 ip,
>  	if (!c)
>  		return ERR_PTR(-ENOMEM);
>  
> -	c->dev = dev;
> +	c->ifindex = dev->ifindex;
>  	c->clusterip = ip;
>  	memcpy(&c->clustermac, &i->clustermac, ETH_ALEN);
>  	c->num_total_nodes = i->num_total_nodes;
> @@ -427,12 +431,14 @@ static int clusterip_tg_check(const struct xt_tgchk_param *par)
>  			}
>  
>  			config = clusterip_config_init(cipinfo,
> -							e->ip.dst.s_addr, dev);
> +						       e->ip.dst.s_addr, dev);
>  			if (IS_ERR(config)) {
>  				dev_put(dev);
>  				return PTR_ERR(config);
>  			}
> -			dev_mc_add(config->dev, config->clustermac);
> +
> +			dev_mc_add(dev, config->clustermac);
> +			dev_put(dev);
>  		}
>  	}
>  	cipinfo->config = config;
> @@ -458,7 +464,7 @@ static void clusterip_tg_destroy(const struct xt_tgdtor_param *par)
>  
>  	/* if no more entries are referencing the config, remove it
>  	 * from the list and destroy the proc entry */
> -	clusterip_config_entry_put(cipinfo->config);
> +	clusterip_config_entry_put(par->net, cipinfo->config);
>  
>  	clusterip_config_put(cipinfo->config);
>  
> @@ -558,10 +564,9 @@ arp_mangle(void *priv,
>  	 * addresses on different interfacs.  However, in the CLUSTERIP case
>  	 * this wouldn't work, since we didn't subscribe the mcast group on
>  	 * other interfaces */
> -	if (c->dev != state->out) {
> -		pr_debug("not mangling arp reply on different "
> -			 "interface: cip'%s'-skb'%s'\n",
> -			 c->dev->name, state->out->name);
> +	if (c->ifindex != state->out->ifindex) {

I'm missing the code to register_netdevice_notifier() so we can
refresh c->ifindex.

Just like we do in net/netfilter/xt_TEE.c