/*
   * netfilter module to limit the number of parallel tcp
   * connections per IP address.
   *   (c) 2000 Gerd Knorr <kraxel@bytesex.org>
   *   Nov 2002: Martin Bene <martin.bene@icomedias.com>:
   *		only ignore TIME_WAIT or gone connections

   *   (C) CC Computer Consultants GmbH, 2007

   *
   * based on ...
   *
   * Kernel module to match connection tracking information.
   * GPL (C) 1999  Rusty Russell (rusty@rustcorp.com.au).
   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #include <linux/in.h>
  #include <linux/in6.h>
  #include <linux/ip.h>
  #include <linux/ipv6.h>
  #include <linux/jhash.h>

  #include <linux/slab.h>

  #include <linux/list.h>
  #include <linux/module.h>
  #include <linux/random.h>
  #include <linux/skbuff.h>
  #include <linux/spinlock.h>
  #include <linux/netfilter/nf_conntrack_tcp.h>
  #include <linux/netfilter/x_tables.h>
  #include <linux/netfilter/xt_connlimit.h>
  #include <net/netfilter/nf_conntrack.h>
  #include <net/netfilter/nf_conntrack_core.h>
  #include <net/netfilter/nf_conntrack_tuple.h>

  #include <net/netfilter/nf_conntrack_zones.h>

  
  /* we will save the tuples of all connections we care about */
  struct xt_connlimit_conn {
  	struct list_head list;
  	struct nf_conntrack_tuple tuple;
  };
  
  struct xt_connlimit_data {
  	struct list_head iphash[256];
  	spinlock_t lock;
  };

  static u_int32_t connlimit_rnd __read_mostly;
  static bool connlimit_rnd_inited __read_mostly;

  static inline unsigned int connlimit_iphash(__be32 addr)

  {

  	return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;

  }
  
  static inline unsigned int

  connlimit_iphash6(const union nf_inet_addr *addr,
                    const union nf_inet_addr *mask)

  {

  	union nf_inet_addr res;

  	unsigned int i;

  	for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
  		res.ip6[i] = addr->ip6[i] & mask->ip6[i];

  	return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;

  }
  
  static inline bool already_closed(const struct nf_conn *conn)
  {

  	if (nf_ct_protonum(conn) == IPPROTO_TCP)

  		return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
  		       conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;

  	else
  		return 0;
  }
  
  static inline unsigned int

  same_source_net(const union nf_inet_addr *addr,
  		const union nf_inet_addr *mask,

  		const union nf_inet_addr *u3, u_int8_t family)

  {

  	if (family == NFPROTO_IPV4) {

  		return (addr->ip & mask->ip) == (u3->ip & mask->ip);
  	} else {

  		union nf_inet_addr lh, rh;

  		unsigned int i;
  
  		for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
  			lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
  			rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
  		}
  
  		return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
  	}
  }

  static int count_them(struct net *net,
  		      struct xt_connlimit_data *data,

  		      const struct nf_conntrack_tuple *tuple,

  		      const union nf_inet_addr *addr,
  		      const union nf_inet_addr *mask,

  		      u_int8_t family)

  {

  	const struct nf_conntrack_tuple_hash *found;

  	struct xt_connlimit_conn *conn;
  	struct xt_connlimit_conn *tmp;

  	struct nf_conn *found_ct;

  	struct list_head *hash;
  	bool addit = true;
  	int matches = 0;

  	if (family == NFPROTO_IPV6)

  		hash = &data->iphash[connlimit_iphash6(addr, mask)];
  	else
  		hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];

  	rcu_read_lock();

  
  	/* check the saved connections */
  	list_for_each_entry_safe(conn, tmp, hash, list) {

  		found    = nf_conntrack_find_get(net, NF_CT_DEFAULT_ZONE,
  						 &conn->tuple);

  		found_ct = NULL;
  
  		if (found != NULL)
  			found_ct = nf_ct_tuplehash_to_ctrack(found);
  
  		if (found_ct != NULL &&
  		    nf_ct_tuple_equal(&conn->tuple, tuple) &&
  		    !already_closed(found_ct))
  			/*
  			 * Just to be sure we have it only once in the list.
  			 * We should not see tuples twice unless someone hooks
  			 * this into a table without "-p tcp --syn".
  			 */
  			addit = false;
  
  		if (found == NULL) {
  			/* this one is gone */
  			list_del(&conn->list);
  			kfree(conn);
  			continue;
  		}
  
  		if (already_closed(found_ct)) {
  			/*
  			 * we do not care about connections which are
  			 * closed already -> ditch it
  			 */

  			nf_ct_put(found_ct);

  			list_del(&conn->list);
  			kfree(conn);
  			continue;
  		}

  		if (same_source_net(addr, mask, &conn->tuple.src.u3, family))

  			/* same source network -> be counted! */
  			++matches;

  		nf_ct_put(found_ct);

  	}

  	rcu_read_unlock();

  
  	if (addit) {
  		/* save the new connection in our list */
  		conn = kzalloc(sizeof(*conn), GFP_ATOMIC);
  		if (conn == NULL)
  			return -ENOMEM;
  		conn->tuple = *tuple;
  		list_add(&conn->list, hash);
  		++matches;
  	}
  
  	return matches;
  }

  static bool

  connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)

  {

  	struct net *net = dev_net(par->in ? par->in : par->out);

  	const struct xt_connlimit_info *info = par->matchinfo;

  	union nf_inet_addr addr;

  	struct nf_conntrack_tuple tuple;
  	const struct nf_conntrack_tuple *tuple_ptr = &tuple;
  	enum ip_conntrack_info ctinfo;
  	const struct nf_conn *ct;
  	int connections;
  
  	ct = nf_ct_get(skb, &ctinfo);
  	if (ct != NULL)
  		tuple_ptr = &ct->tuplehash[0].tuple;
  	else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),

  				    par->family, &tuple))

  		goto hotdrop;

  	if (par->family == NFPROTO_IPV6) {

  		const struct ipv6hdr *iph = ipv6_hdr(skb);
  		memcpy(&addr.ip6, &iph->saddr, sizeof(iph->saddr));

  	} else {
  		const struct iphdr *iph = ip_hdr(skb);
  		addr.ip = iph->saddr;

  	}
  
  	spin_lock_bh(&info->data->lock);

  	connections = count_them(net, info->data, tuple_ptr, &addr,

  	                         &info->mask, par->family);

  	spin_unlock_bh(&info->data->lock);
  
  	if (connections < 0) {
  		/* kmalloc failed, drop it entirely */

  		par->hotdrop = true;

  		return false;
  	}
  
  	return (connections > info->limit) ^ info->inverse;
  
   hotdrop:

  	par->hotdrop = true;

  	return false;
  }

  static int connlimit_mt_check(const struct xt_mtchk_param *par)

  {

  	struct xt_connlimit_info *info = par->matchinfo;

  	unsigned int i;

  	int ret;

  	if (unlikely(!connlimit_rnd_inited)) {
  		get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
  		connlimit_rnd_inited = true;
  	}

  	ret = nf_ct_l3proto_try_module_get(par->family);
  	if (ret < 0) {

  		pr_info("cannot load conntrack support for "
  			"address family %u
  ", par->family);

  		return ret;

  	}
  
  	/* init private data */
  	info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
  	if (info->data == NULL) {

  		nf_ct_l3proto_module_put(par->family);

  		return -ENOMEM;

  	}
  
  	spin_lock_init(&info->data->lock);
  	for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
  		INIT_LIST_HEAD(&info->data->iphash[i]);

  	return 0;

  }

  static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)

  {

  	const struct xt_connlimit_info *info = par->matchinfo;

  	struct xt_connlimit_conn *conn;
  	struct xt_connlimit_conn *tmp;
  	struct list_head *hash = info->data->iphash;
  	unsigned int i;

  	nf_ct_l3proto_module_put(par->family);

  
  	for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
  		list_for_each_entry_safe(conn, tmp, &hash[i], list) {
  			list_del(&conn->list);
  			kfree(conn);
  		}
  	}
  
  	kfree(info->data);
  }

  static struct xt_match connlimit_mt_reg __read_mostly = {
  	.name       = "connlimit",
  	.revision   = 0,
  	.family     = NFPROTO_UNSPEC,
  	.checkentry = connlimit_mt_check,
  	.match      = connlimit_mt,
  	.matchsize  = sizeof(struct xt_connlimit_info),
  	.destroy    = connlimit_mt_destroy,
  	.me         = THIS_MODULE,

  };

  static int __init connlimit_mt_init(void)

  {

  	return xt_register_match(&connlimit_mt_reg);

  }

  static void __exit connlimit_mt_exit(void)

  {

  	xt_unregister_match(&connlimit_mt_reg);

  }

  module_init(connlimit_mt_init);
  module_exit(connlimit_mt_exit);

  MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");

  MODULE_DESCRIPTION("Xtables: Number of connections matching");

  MODULE_LICENSE("GPL");
  MODULE_ALIAS("ipt_connlimit");
  MODULE_ALIAS("ip6t_connlimit");