/* Helper handling for netfilter. */
  
  /* (C) 1999-2001 Paul `Rusty' Russell
   * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   */
  
  #include <linux/types.h>
  #include <linux/netfilter.h>
  #include <linux/module.h>
  #include <linux/skbuff.h>
  #include <linux/vmalloc.h>
  #include <linux/stddef.h>
  #include <linux/slab.h>
  #include <linux/random.h>
  #include <linux/err.h>
  #include <linux/kernel.h>
  #include <linux/netdevice.h>

  #include <linux/rculist.h>

  #include <linux/rtnetlink.h>

  #include <net/netfilter/nf_conntrack.h>
  #include <net/netfilter/nf_conntrack_l3proto.h>

  #include <net/netfilter/nf_conntrack_l4proto.h>

  #include <net/netfilter/nf_conntrack_helper.h>
  #include <net/netfilter/nf_conntrack_core.h>

  #include <net/netfilter/nf_conntrack_extend.h>

  static DEFINE_MUTEX(nf_ct_helper_mutex);

  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 int nf_ct_helper_vmalloc;
  
  
  /* Stupid hash, but collision free for the default registrations of the
   * helpers currently in the kernel. */
  static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
  {
  	return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^

  		(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;

  }

  static struct nf_conntrack_helper *

  __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
  {

  	struct nf_conntrack_helper *helper;

  	struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };

  	struct hlist_node *n;
  	unsigned int h;

  	if (!nf_ct_helper_count)
  		return NULL;
  
  	h = helper_hash(tuple);

  	hlist_for_each_entry_rcu(helper, n, &nf_ct_helper_hash[h], hnode) {

  		if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
  			return helper;

  	}
  	return NULL;
  }

  
  struct nf_conntrack_helper *
  __nf_conntrack_helper_find_byname(const char *name)
  {
  	struct nf_conntrack_helper *h;

  	struct hlist_node *n;
  	unsigned int i;

  	for (i = 0; i < nf_ct_helper_hsize; i++) {

  		hlist_for_each_entry_rcu(h, n, &nf_ct_helper_hash[i], hnode) {

  			if (!strcmp(h->name, name))
  				return h;
  		}

  	}

  	return NULL;
  }

  EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find_byname);

  struct nf_conn_help *nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
  {
  	struct nf_conn_help *help;
  
  	help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
  	if (help)
  		INIT_HLIST_HEAD(&help->expectations);
  	else
  		pr_debug("failed to add helper extension area");
  	return help;
  }
  EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);

  int __nf_ct_try_assign_helper(struct nf_conn *ct, gfp_t flags)
  {
  	int ret = 0;
  	struct nf_conntrack_helper *helper;
  	struct nf_conn_help *help = nfct_help(ct);
  
  	helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
  	if (helper == NULL) {
  		if (help)
  			rcu_assign_pointer(help->helper, NULL);
  		goto out;
  	}
  
  	if (help == NULL) {
  		help = nf_ct_helper_ext_add(ct, flags);
  		if (help == NULL) {
  			ret = -ENOMEM;
  			goto out;
  		}
  	} else {
  		memset(&help->help, 0, sizeof(help->help));
  	}
  
  	rcu_assign_pointer(help->helper, helper);
  out:
  	return ret;
  }
  EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);

  static inline int unhelp(struct nf_conntrack_tuple_hash *i,
  			 const struct nf_conntrack_helper *me)
  {
  	struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
  	struct nf_conn_help *help = nfct_help(ct);
  
  	if (help && help->helper == me) {
  		nf_conntrack_event(IPCT_HELPER, ct);

  		rcu_assign_pointer(help->helper, NULL);

  	}
  	return 0;
  }

  void nf_ct_helper_destroy(struct nf_conn *ct)
  {
  	struct nf_conn_help *help = nfct_help(ct);
  	struct nf_conntrack_helper *helper;
  
  	if (help) {
  		rcu_read_lock();
  		helper = rcu_dereference(help->helper);
  		if (helper && helper->destroy)
  			helper->destroy(ct);
  		rcu_read_unlock();
  	}
  }

  int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
  {

  	unsigned int h = helper_hash(&me->tuple);

  	BUG_ON(me->expect_policy == NULL);
  	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);

  	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);

  	mutex_lock(&nf_ct_helper_mutex);
  	hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);

  	nf_ct_helper_count++;

  	mutex_unlock(&nf_ct_helper_mutex);

  
  	return 0;
  }

  EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);

  static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
  					     struct net *net)

  {

  	struct nf_conntrack_tuple_hash *h;

  	struct nf_conntrack_expect *exp;

  	const struct hlist_node *n, *next;

  	const struct hlist_nulls_node *nn;

  	unsigned int i;

  	/* Get rid of expectations */

  	for (i = 0; i < nf_ct_expect_hsize; i++) {
  		hlist_for_each_entry_safe(exp, n, next,

  					  &net->ct.expect_hash[i], hnode) {

  			struct nf_conn_help *help = nfct_help(exp->master);
  			if ((help->helper == me || exp->helper == me) &&
  			    del_timer(&exp->timeout)) {
  				nf_ct_unlink_expect(exp);
  				nf_ct_expect_put(exp);
  			}

  		}
  	}
  
  	/* Get rid of expecteds, set helpers to NULL. */

  	hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)

  		unhelp(h, me);
  	for (i = 0; i < nf_conntrack_htable_size; i++) {

  		hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)

  			unhelp(h, me);
  	}

  }
  
  void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
  {
  	struct net *net;
  
  	mutex_lock(&nf_ct_helper_mutex);
  	hlist_del_rcu(&me->hnode);
  	nf_ct_helper_count--;
  	mutex_unlock(&nf_ct_helper_mutex);
  
  	/* Make sure every nothing is still using the helper unless its a
  	 * connection in the hash.
  	 */
  	synchronize_rcu();

  	rtnl_lock();

  	spin_lock_bh(&nf_conntrack_lock);
  	for_each_net(net)
  		__nf_conntrack_helper_unregister(me, net);

  	spin_unlock_bh(&nf_conntrack_lock);

  	rtnl_unlock();

  }

  EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);

  static struct nf_ct_ext_type helper_extend __read_mostly = {

  	.len	= sizeof(struct nf_conn_help),
  	.align	= __alignof__(struct nf_conn_help),
  	.id	= NF_CT_EXT_HELPER,
  };

  int nf_conntrack_helper_init(void)

  {

  	int err;
  
  	nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
  	nf_ct_helper_hash = nf_ct_alloc_hashtable(&nf_ct_helper_hsize,

  						  &nf_ct_helper_vmalloc, 0);

  	if (!nf_ct_helper_hash)
  		return -ENOMEM;
  
  	err = nf_ct_extend_register(&helper_extend);
  	if (err < 0)
  		goto err1;
  
  	return 0;
  
  err1:
  	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_vmalloc,
  			     nf_ct_helper_hsize);
  	return err;

  }

  void nf_conntrack_helper_fini(void)

  {
  	nf_ct_extend_unregister(&helper_extend);

  	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_vmalloc,
  			     nf_ct_helper_hsize);

  }