/* netfilter.c: look after the filters for various protocols.

   * Heavily influenced by the old firewall.c by David Bonn and Alan Cox.
   *
   * Thanks to Rob `CmdrTaco' Malda for not influencing this code in any
   * way.
   *
   * Rusty Russell (C)2000 -- This code is GPL.

   * Patrick McHardy (c) 2006-2012

   */

  #include <linux/kernel.h>
  #include <linux/netfilter.h>
  #include <net/protocol.h>
  #include <linux/init.h>
  #include <linux/skbuff.h>
  #include <linux/wait.h>
  #include <linux/module.h>
  #include <linux/interrupt.h>
  #include <linux/if.h>
  #include <linux/netdevice.h>
  #include <linux/inetdevice.h>
  #include <linux/proc_fs.h>

  #include <linux/mutex.h>

  #include <linux/slab.h>

  #include <net/net_namespace.h>

  #include <net/sock.h>
  
  #include "nf_internals.h"

  static DEFINE_MUTEX(afinfo_mutex);

  const struct nf_afinfo __rcu *nf_afinfo[NFPROTO_NUMPROTO] __read_mostly;

  EXPORT_SYMBOL(nf_afinfo);

  const struct nf_ipv6_ops __rcu *nf_ipv6_ops __read_mostly;
  EXPORT_SYMBOL_GPL(nf_ipv6_ops);

  int nf_register_afinfo(const struct nf_afinfo *afinfo)

  {

  	int err;
  
  	err = mutex_lock_interruptible(&afinfo_mutex);
  	if (err < 0)
  		return err;

  	RCU_INIT_POINTER(nf_afinfo[afinfo->family], afinfo);

  	mutex_unlock(&afinfo_mutex);

  	return 0;
  }
  EXPORT_SYMBOL_GPL(nf_register_afinfo);

  void nf_unregister_afinfo(const struct nf_afinfo *afinfo)

  {

  	mutex_lock(&afinfo_mutex);

  	RCU_INIT_POINTER(nf_afinfo[afinfo->family], NULL);

  	mutex_unlock(&afinfo_mutex);

  	synchronize_rcu();
  }
  EXPORT_SYMBOL_GPL(nf_unregister_afinfo);

  struct list_head nf_hooks[NFPROTO_NUMPROTO][NF_MAX_HOOKS] __read_mostly;

  EXPORT_SYMBOL(nf_hooks);

  
  #if defined(CONFIG_JUMP_LABEL)

  struct static_key nf_hooks_needed[NFPROTO_NUMPROTO][NF_MAX_HOOKS];

  EXPORT_SYMBOL(nf_hooks_needed);
  #endif

  static DEFINE_MUTEX(nf_hook_mutex);

  
  int nf_register_hook(struct nf_hook_ops *reg)
  {

  	struct nf_hook_ops *elem;

  	int err;

  	err = mutex_lock_interruptible(&nf_hook_mutex);
  	if (err < 0)
  		return err;

  	list_for_each_entry(elem, &nf_hooks[reg->pf][reg->hooknum], list) {
  		if (reg->priority < elem->priority)

  			break;
  	}

  	list_add_rcu(&reg->list, elem->list.prev);

  	mutex_unlock(&nf_hook_mutex);

  #if defined(CONFIG_JUMP_LABEL)

  	static_key_slow_inc(&nf_hooks_needed[reg->pf][reg->hooknum]);

  #endif

  	return 0;
  }
  EXPORT_SYMBOL(nf_register_hook);
  
  void nf_unregister_hook(struct nf_hook_ops *reg)
  {

  	mutex_lock(&nf_hook_mutex);

  	list_del_rcu(&reg->list);

  	mutex_unlock(&nf_hook_mutex);

  #if defined(CONFIG_JUMP_LABEL)

  	static_key_slow_dec(&nf_hooks_needed[reg->pf][reg->hooknum]);

  #endif

  	synchronize_net();
  }
  EXPORT_SYMBOL(nf_unregister_hook);

  int nf_register_hooks(struct nf_hook_ops *reg, unsigned int n)
  {
  	unsigned int i;
  	int err = 0;
  
  	for (i = 0; i < n; i++) {
  		err = nf_register_hook(&reg[i]);
  		if (err)
  			goto err;
  	}
  	return err;
  
  err:
  	if (i > 0)
  		nf_unregister_hooks(reg, i);
  	return err;
  }
  EXPORT_SYMBOL(nf_register_hooks);
  
  void nf_unregister_hooks(struct nf_hook_ops *reg, unsigned int n)
  {

  	while (n-- > 0)
  		nf_unregister_hook(&reg[n]);

  }
  EXPORT_SYMBOL(nf_unregister_hooks);

  unsigned int nf_iterate(struct list_head *head,

  			struct sk_buff *skb,

  			unsigned int hook,

  			const struct net_device *indev,
  			const struct net_device *outdev,

  			struct nf_hook_ops **elemp,

  			int (*okfn)(struct sk_buff *),
  			int hook_thresh)
  {
  	unsigned int verdict;
  
  	/*
  	 * The caller must not block between calls to this
  	 * function because of risk of continuing from deleted element.
  	 */

  	list_for_each_entry_continue_rcu((*elemp), head, list) {
  		if (hook_thresh > (*elemp)->priority)

  			continue;
  
  		/* Optimization: we don't need to hold module

  		   reference here, since function can't sleep. --RR */

  repeat:

  		verdict = (*elemp)->hook(hook, skb, indev, outdev, okfn);

  		if (verdict != NF_ACCEPT) {
  #ifdef CONFIG_NETFILTER_DEBUG
  			if (unlikely((verdict & NF_VERDICT_MASK)
  							> NF_MAX_VERDICT)) {
  				NFDEBUG("Evil return from %p(%u).
  ",

  					(*elemp)->hook, hook);

  				continue;
  			}
  #endif

  			if (verdict != NF_REPEAT)

  				return verdict;

  			goto repeat;

  		}
  	}
  	return NF_ACCEPT;
  }
  
  
  /* Returns 1 if okfn() needs to be executed by the caller,
   * -EPERM for NF_DROP, 0 otherwise. */

  int nf_hook_slow(u_int8_t pf, unsigned int hook, struct sk_buff *skb,

  		 struct net_device *indev,
  		 struct net_device *outdev,
  		 int (*okfn)(struct sk_buff *),
  		 int hook_thresh)
  {

  	struct nf_hook_ops *elem;

  	unsigned int verdict;
  	int ret = 0;
  
  	/* We may already have this, but read-locks nest anyway */
  	rcu_read_lock();

  	elem = list_entry_rcu(&nf_hooks[pf][hook], struct nf_hook_ops, list);

  next_hook:

  	verdict = nf_iterate(&nf_hooks[pf][hook], skb, hook, indev,

  			     outdev, &elem, okfn, hook_thresh);
  	if (verdict == NF_ACCEPT || verdict == NF_STOP) {
  		ret = 1;

  	} else if ((verdict & NF_VERDICT_MASK) == NF_DROP) {

  		kfree_skb(skb);

  		ret = NF_DROP_GETERR(verdict);

  		if (ret == 0)
  			ret = -EPERM;

  	} else if ((verdict & NF_VERDICT_MASK) == NF_QUEUE) {

  		int err = nf_queue(skb, elem, pf, hook, indev, outdev, okfn,
  						verdict >> NF_VERDICT_QBITS);

  		if (err < 0) {
  			if (err == -ECANCELED)

  				goto next_hook;

  			if (err == -ESRCH &&

  			   (verdict & NF_VERDICT_FLAG_QUEUE_BYPASS))
  				goto next_hook;

  			kfree_skb(skb);
  		}

  	}

  	rcu_read_unlock();
  	return ret;
  }
  EXPORT_SYMBOL(nf_hook_slow);

  int skb_make_writable(struct sk_buff *skb, unsigned int writable_len)

  {

  	if (writable_len > skb->len)

  		return 0;
  
  	/* Not exclusive use of packet?  Must copy. */

  	if (!skb_cloned(skb)) {
  		if (writable_len <= skb_headlen(skb))
  			return 1;
  	} else if (skb_clone_writable(skb, writable_len))
  		return 1;
  
  	if (writable_len <= skb_headlen(skb))
  		writable_len = 0;
  	else
  		writable_len -= skb_headlen(skb);
  
  	return !!__pskb_pull_tail(skb, writable_len);

  }
  EXPORT_SYMBOL(skb_make_writable);

  #if IS_ENABLED(CONFIG_NF_CONNTRACK)

  /* This does not belong here, but locally generated errors need it if connection
     tracking in use: without this, connection may not be in hash table, and hence
     manufactured ICMP or RST packets will not be associated with it. */

  void (*ip_ct_attach)(struct sk_buff *, struct sk_buff *) __rcu __read_mostly;

  EXPORT_SYMBOL(ip_ct_attach);
  
  void nf_ct_attach(struct sk_buff *new, struct sk_buff *skb)
  {
  	void (*attach)(struct sk_buff *, struct sk_buff *);

  	if (skb->nfct) {
  		rcu_read_lock();
  		attach = rcu_dereference(ip_ct_attach);
  		if (attach)
  			attach(new, skb);
  		rcu_read_unlock();

  	}
  }
  EXPORT_SYMBOL(nf_ct_attach);

  void (*nf_ct_destroy)(struct nf_conntrack *) __rcu __read_mostly;

  EXPORT_SYMBOL(nf_ct_destroy);
  
  void nf_conntrack_destroy(struct nf_conntrack *nfct)
  {
  	void (*destroy)(struct nf_conntrack *);
  
  	rcu_read_lock();
  	destroy = rcu_dereference(nf_ct_destroy);
  	BUG_ON(destroy == NULL);
  	destroy(nfct);
  	rcu_read_unlock();
  }
  EXPORT_SYMBOL(nf_conntrack_destroy);

  struct nfq_ct_hook __rcu *nfq_ct_hook __read_mostly;

  EXPORT_SYMBOL_GPL(nfq_ct_hook);

  struct nfq_ct_nat_hook __rcu *nfq_ct_nat_hook __read_mostly;
  EXPORT_SYMBOL_GPL(nfq_ct_nat_hook);

  #endif /* CONFIG_NF_CONNTRACK */

  #ifdef CONFIG_NF_NAT_NEEDED
  void (*nf_nat_decode_session_hook)(struct sk_buff *, struct flowi *);
  EXPORT_SYMBOL(nf_nat_decode_session_hook);
  #endif

  static int __net_init netfilter_net_init(struct net *net)
  {
  #ifdef CONFIG_PROC_FS
  	net->nf.proc_netfilter = proc_net_mkdir(net, "netfilter",
  						net->proc_net);

  	if (!net->nf.proc_netfilter) {
  		if (!net_eq(net, &init_net))
  			pr_err("cannot create netfilter proc entry");

  		return -ENOMEM;
  	}
  #endif
  	return 0;
  }
  
  static void __net_exit netfilter_net_exit(struct net *net)
  {
  	remove_proc_entry("netfilter", net->proc_net);
  }
  
  static struct pernet_operations netfilter_net_ops = {
  	.init = netfilter_net_init,
  	.exit = netfilter_net_exit,
  };

  void __init netfilter_init(void)
  {
  	int i, h;

  	for (i = 0; i < ARRAY_SIZE(nf_hooks); i++) {

  		for (h = 0; h < NF_MAX_HOOKS; h++)
  			INIT_LIST_HEAD(&nf_hooks[i][h]);
  	}

  	if (register_pernet_subsys(&netfilter_net_ops) < 0)

  		panic("cannot create netfilter proc entry");

  	if (netfilter_log_init() < 0)
  		panic("cannot initialize nf_log");
  }