conntrack: add /proc entry to disable helper by default

This patch give the user different methods to disable
the attachment of helper to all connections on a given
port. The idea is to allow the user to choose with the CT target
the helper assignement he wants to have.

First method it to use the 'no_helper_assign' option on the
nf_conntrack module. As this is a constraint to do this at the time
of the loading, a /proc entry is also available.
Setting sys/net/netfilter/nf_conntrack_no_helper_assign to 1 will
disable the automatic assignement of the helper. The user will
---
 include/net/netfilter/nf_conntrack_helper.h |    3 +
 include/net/netns/conntrack.h               |    2 +
 net/netfilter/nf_conntrack_core.c           |    6 ++
 net/netfilter/nf_conntrack_helper.c         |   79 ++++++++++++++++++++++++++-
 4 files changed, 88 insertions(+), 2 deletions(-)

Hi Eric,

On Tue, Mar 27, 2012 at 12:05:02AM +0200, Eric Leblond wrote:
> This patch give the user different methods to disable
> the attachment of helper to all connections on a given
> port. The idea is to allow the user to choose with the CT target
> the helper assignement he wants to have.
> 
> First method it to use the 'no_helper_assign' option on the
> nf_conntrack module.

Could you rename this to nf_conntrack_helper and set it to 1?

That means current automatic helper assignation is enabled.

Moreover, we should spot a warning message telling that automatic
helper assignation will be disabled soon.

Please, also fix minor glitches below.

Thanks for taking care of this Eric.

> As this is a constraint to do this at the time
> of the loading, a /proc entry is also available.
> Setting sys/net/netfilter/nf_conntrack_no_helper_assign to 1 will
> disable the automatic assignement of the helper. The user will
> ---
>  include/net/netfilter/nf_conntrack_helper.h |    3 +
>  include/net/netns/conntrack.h               |    2 +
>  net/netfilter/nf_conntrack_core.c           |    6 ++
>  net/netfilter/nf_conntrack_helper.c         |   79 ++++++++++++++++++++++++++-
>  4 files changed, 88 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/netfilter/nf_conntrack_helper.h b/include/net/netfilter/nf_conntrack_helper.h
> index f1c1311..abd2fc83 100644
> --- a/include/net/netfilter/nf_conntrack_helper.h
> +++ b/include/net/netfilter/nf_conntrack_helper.h
> @@ -63,6 +63,9 @@ static inline struct nf_conn_help *nfct_help(const struct nf_conn *ct)
>  extern int nf_conntrack_helper_init(void);
>  extern void nf_conntrack_helper_fini(void);
>  
> +extern int nf_conntrack_helper_init_net(struct net *net);
> +extern void nf_conntrack_helper_fini_net(struct net *net);
> +
>  extern int nf_conntrack_broadcast_help(struct sk_buff *skb,
>  				       unsigned int protoff,
>  				       struct nf_conn *ct,
> diff --git a/include/net/netns/conntrack.h b/include/net/netns/conntrack.h
> index 7a911ec..2395288 100644
> --- a/include/net/netns/conntrack.h
> +++ b/include/net/netns/conntrack.h
> @@ -26,11 +26,13 @@ struct netns_ct {
>  	int			sysctl_tstamp;
>  	int			sysctl_checksum;
>  	unsigned int		sysctl_log_invalid; /* Log invalid packets */
> +	int			sysctl_no_helper_assign;

I'd say, call this variable "sysctl_auto_helper_assign_enabled" or
something similar. You also have to change the logic: 1 is enabled, 0
is disabled.

Probably I'm proposing a too long name, but I like names that evoke
what the thing do, it's intuitive.

>  #ifdef CONFIG_SYSCTL
>  	struct ctl_table_header	*sysctl_header;
>  	struct ctl_table_header	*acct_sysctl_header;
>  	struct ctl_table_header	*tstamp_sysctl_header;
>  	struct ctl_table_header	*event_sysctl_header;
> +	struct ctl_table_header	*helper_sysctl_header;
>  #endif
>  	char			*slabname;
>  };
> diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
> index 76613f5..5faeb75 100644
> --- a/net/netfilter/nf_conntrack_core.c
> +++ b/net/netfilter/nf_conntrack_core.c
> @@ -1301,6 +1301,7 @@ static void nf_conntrack_cleanup_net(struct net *net)
>  	nf_conntrack_tstamp_fini(net);
>  	nf_conntrack_acct_fini(net);
>  	nf_conntrack_expect_fini(net);
> +	nf_conntrack_helper_fini_net(net);
>  	kmem_cache_destroy(net->ct.nf_conntrack_cachep);
>  	kfree(net->ct.slabname);
>  	free_percpu(net->ct.stat);
> @@ -1528,9 +1529,14 @@ static int nf_conntrack_init_net(struct net *net)
>  	ret = nf_conntrack_ecache_init(net);
>  	if (ret < 0)
>  		goto err_ecache;
> +	ret = nf_conntrack_helper_init_net(net);
> +	if (ret < 0)
> +		goto err_helper;
>  
>  	return 0;
>  
> +err_helper:
> +	nf_conntrack_helper_fini_net(net);
>  err_ecache:
>  	nf_conntrack_tstamp_fini(net);
>  err_tstamp:
> diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
> index bbe23ba..9663494 100644
> --- a/net/netfilter/nf_conntrack_helper.c
> +++ b/net/netfilter/nf_conntrack_helper.c
> @@ -34,6 +34,67 @@ static struct hlist_head *nf_ct_helper_hash __read_mostly;
>  static unsigned int nf_ct_helper_hsize __read_mostly;
>  static unsigned int nf_ct_helper_count __read_mostly;
>  
> +static bool nf_ct_no_helper_assign __read_mostly;
> +module_param_named(no_helper_assign, nf_ct_no_helper_assign, bool, 0644);
> +MODULE_PARM_DESC(no_helper_assign, "Do not assign helper to connection based on port.");
> +
> +#ifdef CONFIG_SYSCTL
> +static struct ctl_table helper_sysctl_table[] = {
> +	{
> +		.procname	= "nf_conntrack_no_helper_assign",
> +		.data		= &init_net.ct.sysctl_no_helper_assign,
> +		.maxlen		= sizeof(unsigned int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec,
> +	},
> +	{}
> +};
> +
> +static int nf_conntrack_helper_init_sysctl(struct net *net)
> +{
> +	struct ctl_table *table;
> +
> +	table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
> +			GFP_KERNEL);
> +	if (!table)
> +		goto out;
> +
> +	table[0].data = &net->ct.sysctl_no_helper_assign;
> +
> +	net->ct.helper_sysctl_header = register_net_sysctl_table(net,
> +			nf_net_netfilter_sysctl_path, table);
> +	if (!net->ct.helper_sysctl_header) {
> +		printk(KERN_ERR "nf_conntrack_helper: can't register to sysctl.\n");
> +		goto out_register;
> +	}
> +	return 0;
> +
> +out_register:
> +	kfree(table);
> +out:
> +	return -ENOMEM;
> +}
> +
> +static void nf_conntrack_helper_fini_sysctl(struct net *net)
> +{
> +	struct ctl_table *table;
> +
> +	table = net->ct.helper_sysctl_header->ctl_table_arg;
> +	unregister_net_sysctl_table(net->ct.helper_sysctl_header);
> +	kfree(table);
> +}
> +#else
> +static int nf_conntrack_helper_init_sysctl(struct net *net)
> +{
> +	return 0;
> +}
> +
> +static void nf_conntrack_helper_fini_sysctl(struct net *net)
> +{
> +}
> +#endif /* CONFIG_SYSCTL */
> +
> +
>  
>  /* Stupid hash, but collision free for the default registrations of the
>   * helpers currently in the kernel. */
> @@ -118,6 +179,7 @@ int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
>  {
>  	struct nf_conntrack_helper *helper = NULL;
>  	struct nf_conn_help *help;
> +	struct net *net = nf_ct_net(ct);
>  	int ret = 0;
>  
>  	if (tmpl != NULL) {
> @@ -127,8 +189,10 @@ int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
>  	}
>  
>  	help = nfct_help(ct);
> -	if (helper == NULL)
> +
> +	if ((helper == NULL) && !net->ct.sysctl_no_helper_assign)
            ^              ^
You can remove these. I also thinkg it's better check if helper
assignment is enabled before check helper == NULL.

>  		helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
> +
>  	if (helper == NULL) {
>  		if (help)
>  			RCU_INIT_POINTER(help->helper, NULL);
> @@ -273,7 +337,6 @@ int nf_conntrack_helper_init(void)
>  	err = nf_ct_extend_register(&helper_extend);
>  	if (err < 0)
>  		goto err1;
> -
  ^^^
don't remove this line removal, please.

>  	return 0;
>  
>  err1:
> @@ -281,8 +344,20 @@ err1:
>  	return err;
>  }
>  
> +int nf_conntrack_helper_init_net(struct net *net)
> +{
> +	net->ct.sysctl_no_helper_assign = nf_ct_no_helper_assign;
> +
> +	return nf_conntrack_helper_init_sysctl(net);
> +}
> +
>  void nf_conntrack_helper_fini(void)
>  {
>  	nf_ct_extend_unregister(&helper_extend);
>  	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
>  }
> +
> +void nf_conntrack_helper_fini_net(struct net *net)
> +{
> +	nf_conntrack_helper_fini_sysctl(net);
> +}
> -- 
> 1.7.9.1
> 
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