add_fullconenat.diff

diff --git a/arch/arm64/configs/nanopi-r2_linux_defconfig b/arch/arm64/configs/nanopi-r2_linux_defconfig
index 240a9bf57..9f8f37ca7 100644
--- a/arch/arm64/configs/nanopi-r2_linux_defconfig
+++ b/arch/arm64/configs/nanopi-r2_linux_defconfig
@@ -1665,3 +1665,4 @@ CONFIG_SCHEDSTATS=y
 CONFIG_DEBUG_SPINLOCK=y
 CONFIG_FUNCTION_TRACER=y
 CONFIG_BLK_DEV_IO_TRACE=y
+CONFIG_IP_NF_TARGET_FULLCONENAT=y
diff --git a/net/ipv4/netfilter/Kconfig b/net/ipv4/netfilter/Kconfig
index f17b40211..99f691a67 100644
--- a/net/ipv4/netfilter/Kconfig
+++ b/net/ipv4/netfilter/Kconfig
@@ -239,6 +239,15 @@ config IP_NF_TARGET_NETMAP
 	(e.g. when running oldconfig). It selects
 	CONFIG_NETFILTER_XT_TARGET_NETMAP.

+config IP_NF_TARGET_FULLCONENAT
+	tristate "FULLCONENAT target support"
+	depends on NETFILTER_ADVANCED
+	select NETFILTER_XT_TARGET_FULLCONENAT
+	---help---
+	This is a backwards-compat option for the user's convenience
+	(e.g. when running oldconfig). It selects
+	CONFIG_NETFILTER_XT_TARGET_FULLCONENAT.
+
 config IP_NF_TARGET_REDIRECT
 	tristate "REDIRECT target support"
 	depends on NETFILTER_ADVANCED
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 91efae88e..17f5c748a 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -956,6 +956,14 @@ config NETFILTER_XT_TARGET_NETMAP

 	To compile it as a module, choose M here. If unsure, say N.

+config NETFILTER_XT_TARGET_FULLCONENAT
+	tristate '"FULLCONENAT" target support'
+	depends on NF_NAT
+	---help---
+	Full Cone NAT
+
+	To compile it as a module, choose M here. If unsure, say N.
+
 config NETFILTER_XT_TARGET_NFLOG
 	tristate '"NFLOG" target support'
 	default m if NETFILTER_ADVANCED=n
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 4fc075b61..2b588d5a5 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -209,3 +209,6 @@ obj-$(CONFIG_IP_SET) += ipset/

 # IPVS
 obj-$(CONFIG_IP_VS) += ipvs/
+
+# Full cone NAT
+obj-$(CONFIG_NETFILTER_XT_TARGET_FULLCONENAT) += xt_FULLCONENAT.o
diff --git a/net/netfilter/xt_FULLCONENAT.c b/net/netfilter/xt_FULLCONENAT.c
new file mode 100644
index 000000000..8555b54e2
--- /dev/null
+++ b/net/netfilter/xt_FULLCONENAT.c
@@ -0,0 +1,733 @@
+/*
+ * Copyright (c) 2018 Chion Tang <tech@chionlab.moe>
+ *
+ * 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/kernel.h>
+#include <linux/module.h>
+#include <linux/version.h>
+#include <linux/types.h>
+#include <linux/list.h>
+#include <linux/hashtable.h>
+#include <linux/netdevice.h>
+#include <linux/inetdevice.h>
+#include <linux/workqueue.h>
+#ifdef CONFIG_NF_CONNTRACK_CHAIN_EVENTS
+#include <linux/notifier.h>
+#endif
+#include <linux/netfilter.h>
+#include <linux/netfilter_ipv4.h>
+#include <linux/netfilter/x_tables.h>
+#include <net/netfilter/nf_nat.h>
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_zones.h>
+#include <net/netfilter/nf_conntrack_tuple.h>
+#include <net/netfilter/nf_conntrack_core.h>
+#include <net/netfilter/nf_conntrack_ecache.h>
+
+#define HASH_2(x, y) ((x + y) / 2 * (x + y + 1) + y)
+
+#define HASHTABLE_BUCKET_BITS 10
+
+#ifndef NF_NAT_RANGE_PROTO_RANDOM_FULLY
+#define NF_NAT_RANGE_PROTO_RANDOM_FULLY (1 << 4)
+#endif
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+
+static inline int nf_ct_netns_get(struct net *net, u8 nfproto) { return 0; }
+
+static inline void nf_ct_netns_put(struct net *net, u8 nfproto) {}
+
+static inline struct net_device *xt_in(const struct xt_action_param *par) {
+  return par->in;
+}
+
+static inline struct net_device *xt_out(const struct xt_action_param *par) {
+  return par->out;
+}
+
+static inline unsigned int xt_hooknum(const struct xt_action_param *par) {
+  return par->hooknum;
+}
+
+#endif
+
+struct nat_mapping_original_tuple {
+  struct nf_conntrack_tuple tuple;
+
+  struct list_head node;
+};
+
+struct nat_mapping {
+  uint16_t port;     /* external UDP port */
+  int ifindex;       /* external interface index*/
+
+  __be32 int_addr;   /* internal source ip address */
+  uint16_t int_port; /* internal source port */
+
+  int refer_count;   /* how many references linked to this mapping
+                      * aka. length of original_tuple_list */
+
+  struct list_head original_tuple_list;
+
+  struct hlist_node node_by_ext_port;
+  struct hlist_node node_by_int_src;
+
+};
+
+struct tuple_list {
+  struct nf_conntrack_tuple tuple_original;
+  struct nf_conntrack_tuple tuple_reply;
+  struct list_head list;
+};
+
+#ifdef CONFIG_NF_CONNTRACK_CHAIN_EVENTS
+struct notifier_block ct_event_notifier;
+#else
+struct nf_ct_event_notifier ct_event_notifier;
+#endif
+int tg_refer_count = 0;
+int ct_event_notifier_registered = 0;
+
+static DEFINE_MUTEX(nf_ct_net_event_lock);
+
+static DEFINE_HASHTABLE(mapping_table_by_ext_port, HASHTABLE_BUCKET_BITS);
+static DEFINE_HASHTABLE(mapping_table_by_int_src, HASHTABLE_BUCKET_BITS);
+
+static DEFINE_SPINLOCK(fullconenat_lock);
+
+static LIST_HEAD(dying_tuple_list);
+static DEFINE_SPINLOCK(dying_tuple_list_lock);
+static void gc_worker(struct work_struct *work);
+static struct workqueue_struct *wq __read_mostly = NULL;
+static DECLARE_DELAYED_WORK(gc_worker_wk, gc_worker);
+
+static char tuple_tmp_string[512];
+/* non-atomic: can only be called serially within lock zones. */
+static char* nf_ct_stringify_tuple(const struct nf_conntrack_tuple *t) {
+  snprintf(tuple_tmp_string, sizeof(tuple_tmp_string), "%pI4:%hu -> %pI4:%hu",
+         &t->src.u3.ip, be16_to_cpu(t->src.u.all),
+         &t->dst.u3.ip, be16_to_cpu(t->dst.u.all));
+  return tuple_tmp_string;
+}
+
+static struct nat_mapping* allocate_mapping(const __be32 int_addr, const uint16_t int_port, const uint16_t port, const int ifindex) {
+  struct nat_mapping *p_new;
+  u32 hash_src;
+
+  p_new = kmalloc(sizeof(struct nat_mapping), GFP_ATOMIC);
+  if (p_new == NULL) {
+    pr_debug("xt_FULLCONENAT: ERROR: kmalloc() for new nat_mapping failed.\n");
+    return NULL;
+  }
+  p_new->port = port;
+  p_new->int_addr = int_addr;
+  p_new->int_port = int_port;
+  p_new->ifindex = ifindex;
+  p_new->refer_count = 0;
+  (p_new->original_tuple_list).next = &(p_new->original_tuple_list);
+  (p_new->original_tuple_list).prev = &(p_new->original_tuple_list);
+
+  hash_src = HASH_2(int_addr, (u32)int_port);
+
+  hash_add(mapping_table_by_ext_port, &p_new->node_by_ext_port, port);
+  hash_add(mapping_table_by_int_src, &p_new->node_by_int_src, hash_src);
+
+  pr_debug("xt_FULLCONENAT: new mapping allocated for %pI4:%d ==> %d\n",
+    &p_new->int_addr, p_new->int_port, p_new->port);
+
+  return p_new;
+}
+
+static void add_original_tuple_to_mapping(struct nat_mapping *mapping, const struct nf_conntrack_tuple* original_tuple) {
+  struct nat_mapping_original_tuple *item = kmalloc(sizeof(struct nat_mapping_original_tuple), GFP_ATOMIC);
+  if (item == NULL) {
+    pr_debug("xt_FULLCONENAT: ERROR: kmalloc() for nat_mapping_original_tuple failed.\n");
+    return;
+  }
+  memcpy(&item->tuple, original_tuple, sizeof(struct nf_conntrack_tuple));
+  list_add(&item->node, &mapping->original_tuple_list);
+  (mapping->refer_count)++;
+}
+
+static struct nat_mapping* get_mapping_by_ext_port(const uint16_t port, const int ifindex) {
+  struct nat_mapping *p_current;
+
+  hash_for_each_possible(mapping_table_by_ext_port, p_current, node_by_ext_port, port) {
+    if (p_current->port == port && p_current->ifindex == ifindex) {
+      return p_current;
+    }
+  }
+
+  return NULL;
+}
+
+static struct nat_mapping* get_mapping_by_int_src(const __be32 src_ip, const uint16_t src_port) {
+  struct nat_mapping *p_current;
+  u32 hash_src = HASH_2(src_ip, (u32)src_port);
+
+  hash_for_each_possible(mapping_table_by_int_src, p_current, node_by_int_src, hash_src) {
+    if (p_current->int_addr == src_ip && p_current->int_port == src_port) {
+      return p_current;
+    }
+  }
+
+  return NULL;
+}
+
+static void kill_mapping(struct nat_mapping *mapping) {
+  struct list_head *iter, *tmp;
+  struct nat_mapping_original_tuple *original_tuple_item;
+
+  if (mapping == NULL) {
+    return;
+  }
+
+  list_for_each_safe(iter, tmp, &mapping->original_tuple_list) {
+    original_tuple_item = list_entry(iter, struct nat_mapping_original_tuple, node);
+    list_del(&original_tuple_item->node);
+    kfree(original_tuple_item);
+  }
+
+  hash_del(&mapping->node_by_ext_port);
+  hash_del(&mapping->node_by_int_src);
+  kfree(mapping);
+}
+
+static void destroy_mappings(void) {
+  struct nat_mapping *p_current;
+  struct hlist_node *tmp;
+  int i;
+
+  spin_lock_bh(&fullconenat_lock);
+
+  hash_for_each_safe(mapping_table_by_ext_port, i, tmp, p_current, node_by_ext_port) {
+    kill_mapping(p_current);
+  }
+
+  spin_unlock_bh(&fullconenat_lock);
+}
+
+/* check if a mapping is valid.
+ * possibly delete and free an invalid mapping.
+ * the mapping should not be used anymore after check_mapping() returns 0. */
+static int check_mapping(struct nat_mapping* mapping, struct net *net, const struct nf_conntrack_zone *zone) {
+  struct list_head *iter, *tmp;
+  struct nat_mapping_original_tuple *original_tuple_item;
+  struct nf_conntrack_tuple_hash *tuple_hash;
+  struct nf_conn *ct;
+
+  if (mapping == NULL) {
+    return 0;
+  }
+
+  if (mapping->port == 0 || mapping->int_addr == 0 || mapping->int_port == 0 || mapping->ifindex == -1) {
+    return 0;
+  }
+
+  /* for dying/unconfirmed conntrack tuples, an IPCT_DESTROY event may NOT be fired.
+   * so we manually kill one of those tuples once we acquire one. */
+
+  list_for_each_safe(iter, tmp, &mapping->original_tuple_list) {
+    original_tuple_item = list_entry(iter, struct nat_mapping_original_tuple, node);
+
+    tuple_hash = nf_conntrack_find_get(net, zone, &original_tuple_item->tuple);
+
+    if (tuple_hash == NULL) {
+      pr_debug("xt_FULLCONENAT: check_mapping(): tuple %s dying/unconfirmed. free this tuple.\n", nf_ct_stringify_tuple(&original_tuple_item->tuple));
+
+      list_del(&original_tuple_item->node);
+      kfree(original_tuple_item);
+      (mapping->refer_count)--;
+    } else {
+      ct = nf_ct_tuplehash_to_ctrack(tuple_hash);
+      if (ct != NULL)
+        nf_ct_put(ct);
+    }
+
+  }
+
+  /* kill the mapping if need */
+  pr_debug("xt_FULLCONENAT: check_mapping() refer_count for mapping at ext_port %d is now %d\n", mapping->port, mapping->refer_count);
+  if (mapping->refer_count <= 0) {
+    pr_debug("xt_FULLCONENAT: check_mapping(): kill dying/unconfirmed mapping at ext port %d\n", mapping->port);
+    kill_mapping(mapping);
+    return 0;
+  } else {
+    return 1;
+  }
+}
+
+static void handle_dying_tuples(void) {
+  struct list_head *iter, *tmp, *iter_2, *tmp_2;
+  struct tuple_list *item;
+  struct nf_conntrack_tuple *ct_tuple;
+  struct nat_mapping *mapping;
+  __be32 ip;
+  uint16_t port;
+  struct nat_mapping_original_tuple *original_tuple_item;
+
+  spin_lock_bh(&fullconenat_lock);
+  spin_lock_bh(&dying_tuple_list_lock);
+
+  list_for_each_safe(iter, tmp, &dying_tuple_list) {
+    item = list_entry(iter, struct tuple_list, list);
+
+    /* we dont know the conntrack direction for now so we try in both ways. */
+    ct_tuple = &(item->tuple_original);
+    ip = (ct_tuple->src).u3.ip;
+    port = be16_to_cpu((ct_tuple->src).u.udp.port);
+    mapping = get_mapping_by_int_src(ip, port);
+    if (mapping == NULL) {
+      ct_tuple = &(item->tuple_reply);
+      ip = (ct_tuple->src).u3.ip;
+      port = be16_to_cpu((ct_tuple->src).u.udp.port);
+      mapping = get_mapping_by_int_src(ip, port);
+      if (mapping != NULL) {
+        pr_debug("xt_FULLCONENAT: handle_dying_tuples(): INBOUND dying conntrack at ext port %d\n", mapping->port);
+      }
+    } else {
+      pr_debug("xt_FULLCONENAT: handle_dying_tuples(): OUTBOUND dying conntrack at ext port %d\n", mapping->port);
+    }
+
+    if (mapping == NULL) {
+      goto next;
+    }
+
+    /* look for the corresponding out-dated tuple and free it */
+    list_for_each_safe(iter_2, tmp_2, &mapping->original_tuple_list) {
+      original_tuple_item = list_entry(iter_2, struct nat_mapping_original_tuple, node);
+
+      if (nf_ct_tuple_equal(&original_tuple_item->tuple, &(item->tuple_original))) {
+        pr_debug("xt_FULLCONENAT: handle_dying_tuples(): tuple %s expired. free this tuple.\n",
+          nf_ct_stringify_tuple(&original_tuple_item->tuple));
+        list_del(&original_tuple_item->node);
+        kfree(original_tuple_item);
+        (mapping->refer_count)--;
+      }
+    }
+
+    /* then kill the mapping if needed*/
+    pr_debug("xt_FULLCONENAT: handle_dying_tuples(): refer_count for mapping at ext_port %d is now %d\n", mapping->port, mapping->refer_count);
+    if (mapping->refer_count <= 0) {
+      pr_debug("xt_FULLCONENAT: handle_dying_tuples(): kill expired mapping at ext port %d\n", mapping->port);
+      kill_mapping(mapping);
+    }
+
+next:
+    list_del(&item->list);
+    kfree(item);
+  }
+
+  spin_unlock_bh(&dying_tuple_list_lock);
+  spin_unlock_bh(&fullconenat_lock);
+}
+
+static void gc_worker(struct work_struct *work) {
+  handle_dying_tuples();
+}
+
+/* conntrack destroy event callback function */
+#ifdef CONFIG_NF_CONNTRACK_CHAIN_EVENTS
+static int ct_event_cb(struct notifier_block *this, unsigned long events, void *ptr) {
+  struct nf_ct_event *item = ptr;
+#else
+static int ct_event_cb(unsigned int events, struct nf_ct_event *item) {
+#endif
+  struct nf_conn *ct;
+  struct nf_conntrack_tuple *ct_tuple_reply, *ct_tuple_original;
+  uint8_t protonum;
+  struct tuple_list *dying_tuple_item;
+
+  ct = item->ct;
+  /* we handle only conntrack destroy events */
+  if (ct == NULL || !(events & (1 << IPCT_DESTROY))) {
+    return 0;
+  }
+
+  ct_tuple_original = &(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
+
+  ct_tuple_reply = &(ct->tuplehash[IP_CT_DIR_REPLY].tuple);
+
+  protonum = (ct_tuple_original->dst).protonum;
+  if (protonum != IPPROTO_UDP) {
+    return 0;
+  }
+
+  dying_tuple_item = kmalloc(sizeof(struct tuple_list), GFP_ATOMIC);
+
+  if (dying_tuple_item == NULL) {
+    pr_debug("xt_FULLCONENAT: warning: ct_event_cb(): kmalloc failed.\n");
+    return 0;
+  }
+
+  memcpy(&(dying_tuple_item->tuple_original), ct_tuple_original, sizeof(struct nf_conntrack_tuple));
+  memcpy(&(dying_tuple_item->tuple_reply), ct_tuple_reply, sizeof(struct nf_conntrack_tuple));
+
+  spin_lock_bh(&dying_tuple_list_lock);
+
+  list_add(&(dying_tuple_item->list), &dying_tuple_list);
+
+  spin_unlock_bh(&dying_tuple_list_lock);
+
+  if (wq != NULL)
+    queue_delayed_work(wq, &gc_worker_wk, msecs_to_jiffies(100));
+
+  return 0;
+}
+
+static __be32 get_device_ip(const struct net_device* dev) {
+  struct in_device* in_dev;
+  struct in_ifaddr* if_info;
+  __be32 result;
+
+  if (dev == NULL) {
+    return 0;
+  }
+
+  rcu_read_lock();
+  in_dev = dev->ip_ptr;
+  if (in_dev == NULL) {
+    rcu_read_unlock();
+    return 0;
+  }
+  if_info = in_dev->ifa_list;
+  if (if_info) {
+    result = if_info->ifa_local;
+    rcu_read_unlock();
+    return result;
+  } else {
+    rcu_read_unlock();
+    return 0;
+  }
+}
+
+static uint16_t find_appropriate_port(struct net *net, const struct nf_conntrack_zone *zone, const uint16_t original_port, const int ifindex, const struct nf_nat_ipv4_range *range) {
+  uint16_t min, start, selected, range_size, i;
+  struct nat_mapping* mapping = NULL;
+
+  if (range->flags & NF_NAT_RANGE_PROTO_SPECIFIED) {
+    min = be16_to_cpu((range->min).udp.port);
+    range_size = be16_to_cpu((range->max).udp.port) - min + 1;
+  } else {
+    /* minimum port is 1024. same behavior as default linux NAT. */
+    min = 1024;
+    range_size = 65535 - min + 1;
+  }
+
+  if ((range->flags & NF_NAT_RANGE_PROTO_RANDOM)
+    || (range->flags & NF_NAT_RANGE_PROTO_RANDOM_FULLY)) {
+    /* for now we do the same thing for both --random and --random-fully */
+
+    /* select a random starting point */
+    start = (uint16_t)(prandom_u32() % (u32)range_size);
+  } else {
+
+    if ((original_port >= min && original_port <= min + range_size - 1)
+      || !(range->flags & NF_NAT_RANGE_PROTO_SPECIFIED)) {
+      /* 1. try to preserve the port if it's available */
+      mapping = get_mapping_by_ext_port(original_port, ifindex);
+      if (mapping == NULL || !(check_mapping(mapping, net, zone))) {
+        return original_port;
+      }
+    }
+
+    /* otherwise, we start from zero */
+    start = 0;
+  }
+
+  for (i = 0; i < range_size; i++) {
+    /* 2. try to find an available port */
+    selected = min + ((start + i) % range_size);
+    mapping = get_mapping_by_ext_port(selected, ifindex);
+    if (mapping == NULL || !(check_mapping(mapping, net, zone))) {
+      return selected;
+    }
+  }
+
+  /* 3. at least we tried. override a previous mapping. */
+  selected = min + start;
+  mapping = get_mapping_by_ext_port(selected, ifindex);
+  kill_mapping(mapping);
+
+  return selected;
+}
+
+static unsigned int fullconenat_tg(struct sk_buff *skb, const struct xt_action_param *par)
+{
+  const struct nf_nat_ipv4_multi_range_compat *mr;
+  const struct nf_nat_ipv4_range *range;
+
+  const struct nf_conntrack_zone *zone;
+  struct net *net;
+  struct nf_conn *ct;
+  enum ip_conntrack_info ctinfo;
+  struct nf_conntrack_tuple *ct_tuple, *ct_tuple_origin;
+
+  struct net_device *net_dev;
+
+  struct nat_mapping *mapping, *src_mapping;
+  unsigned int ret;
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 18, 0)
+  struct nf_nat_range2 newrange;
+#else
+  struct nf_nat_range newrange;
+#endif
+
+  __be32 new_ip, ip;
+  uint16_t port, original_port, want_port;
+  uint8_t protonum;
+  int ifindex;
+
+  ip = 0;
+  original_port = 0;
+  src_mapping = NULL;
+
+  mr = par->targinfo;
+  range = &mr->range[0];
+
+  mapping = NULL;
+  ret = XT_CONTINUE;
+
+  ct = nf_ct_get(skb, &ctinfo);
+  net = nf_ct_net(ct);
+  zone = nf_ct_zone(ct);
+
+  memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
+  memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
+  newrange.flags       = mr->range[0].flags | NF_NAT_RANGE_MAP_IPS;
+  newrange.min_proto   = mr->range[0].min;
+  newrange.max_proto   = mr->range[0].max;
+
+  if (xt_hooknum(par) == NF_INET_PRE_ROUTING) {
+    /* inbound packets */
+    ifindex = xt_in(par)->ifindex;
+
+    ct_tuple_origin = &(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
+
+    protonum = (ct_tuple_origin->dst).protonum;
+    if (protonum != IPPROTO_UDP) {
+      return ret;
+    }
+    ip = (ct_tuple_origin->dst).u3.ip;
+    port = be16_to_cpu((ct_tuple_origin->dst).u.udp.port);
+
+    /* get the corresponding ifindex by the dst_ip (aka. external ip of this host),
+     * in case the packet needs to be forwarded from another inbound interface. */
+    net_dev = ip_dev_find(net, ip);
+    if (net_dev != NULL) {
+      ifindex = net_dev->ifindex;
+      dev_put(net_dev);
+    }
+
+    spin_lock_bh(&fullconenat_lock);
+
+    /* find an active mapping based on the inbound port */
+    mapping = get_mapping_by_ext_port(port, ifindex);
+    if (mapping == NULL) {
+      spin_unlock_bh(&fullconenat_lock);
+      return ret;
+    }
+    if (check_mapping(mapping, net, zone)) {
+      newrange.flags = NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED;
+      newrange.min_addr.ip = mapping->int_addr;
+      newrange.max_addr.ip = mapping->int_addr;
+      newrange.min_proto.udp.port = cpu_to_be16(mapping->int_port);
+      newrange.max_proto = newrange.min_proto;
+
+      pr_debug("xt_FULLCONENAT: <INBOUND DNAT> %s ==> %pI4:%d\n", nf_ct_stringify_tuple(ct_tuple_origin), &mapping->int_addr, mapping->int_port);
+
+      ret = nf_nat_setup_info(ct, &newrange, HOOK2MANIP(xt_hooknum(par)));
+
+      if (ret == NF_ACCEPT) {
+        add_original_tuple_to_mapping(mapping, ct_tuple_origin);
+        pr_debug("xt_FULLCONENAT: fullconenat_tg(): INBOUND: refer_count for mapping at ext_port %d is now %d\n", mapping->port, mapping->refer_count);
+      }
+    }
+    spin_unlock_bh(&fullconenat_lock);
+    return ret;
+
+
+  } else if (xt_hooknum(par) == NF_INET_POST_ROUTING) {
+    /* outbound packets */
+    ifindex = xt_out(par)->ifindex;
+
+    ct_tuple_origin = &(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
+    protonum = (ct_tuple_origin->dst).protonum;
+
+    spin_lock_bh(&fullconenat_lock);
+
+    if (protonum == IPPROTO_UDP) {
+      ip = (ct_tuple_origin->src).u3.ip;
+      original_port = be16_to_cpu((ct_tuple_origin->src).u.udp.port);
+
+      src_mapping = get_mapping_by_int_src(ip, original_port);
+      if (src_mapping != NULL && check_mapping(src_mapping, net, zone)) {
+
+        /* outbound nat: if a previously established mapping is active,
+         * we will reuse that mapping. */
+
+        newrange.flags = NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED;
+        newrange.min_proto.udp.port = cpu_to_be16(src_mapping->port);
+        newrange.max_proto = newrange.min_proto;
+
+      } else {
+
+        /* if not, we find a new external port to map to.
+         * the SNAT may fail so we should re-check the mapped port later. */
+        want_port = find_appropriate_port(net, zone, original_port, ifindex, range);
+
+        newrange.flags = NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED;
+        newrange.min_proto.udp.port = cpu_to_be16(want_port);
+        newrange.max_proto = newrange.min_proto;
+
+        src_mapping = NULL;
+
+      }
+    }
+
+    if(mr->range[0].flags & NF_NAT_RANGE_MAP_IPS) {
+      newrange.min_addr.ip = mr->range[0].min_ip;
+      newrange.max_addr.ip = mr->range[0].max_ip;
+    } else {
+      new_ip = get_device_ip(skb->dev);
+      newrange.min_addr.ip = new_ip;
+      newrange.max_addr.ip = new_ip;
+    }
+
+    /* do SNAT now */
+    ret = nf_nat_setup_info(ct, &newrange, HOOK2MANIP(xt_hooknum(par)));
+
+    if (protonum != IPPROTO_UDP || ret != NF_ACCEPT) {
+      /* for non-UDP packets and failed SNAT, bailout */
+      spin_unlock_bh(&fullconenat_lock);
+      return ret;
+    }
+
+    /* the reply tuple contains the mapped port. */
+    ct_tuple = &(ct->tuplehash[IP_CT_DIR_REPLY].tuple);
+    /* this is the resulted mapped port. */
+    port = be16_to_cpu((ct_tuple->dst).u.udp.port);
+
+    pr_debug("xt_FULLCONENAT: <OUTBOUND SNAT> %s ==> %d\n", nf_ct_stringify_tuple(ct_tuple_origin), port);
+
+    /* save the mapping information into our mapping table */
+    mapping = src_mapping;
+    if (mapping == NULL || !check_mapping(mapping, net, zone)) {
+      mapping = allocate_mapping(ip, original_port, port, ifindex);
+    }
+    if (mapping != NULL) {
+      add_original_tuple_to_mapping(mapping, ct_tuple_origin);
+      pr_debug("xt_FULLCONENAT: fullconenat_tg(): OUTBOUND: refer_count for mapping at ext_port %d is now %d\n", mapping->port, mapping->refer_count);
+    }
+
+    spin_unlock_bh(&fullconenat_lock);
+    return ret;
+  }
+
+  return ret;
+}
+
+static int fullconenat_tg_check(const struct xt_tgchk_param *par)
+{
+  mutex_lock(&nf_ct_net_event_lock);
+
+  tg_refer_count++;
+
+  pr_debug("xt_FULLCONENAT: fullconenat_tg_check(): tg_refer_count is now %d\n", tg_refer_count);
+
+  if (tg_refer_count == 1) {
+    nf_ct_netns_get(par->net, par->family);
+#ifdef CONFIG_NF_CONNTRACK_CHAIN_EVENTS
+    ct_event_notifier.notifier_call = ct_event_cb;
+#else
+    ct_event_notifier.fcn = ct_event_cb;
+#endif
+
+    if (nf_conntrack_register_notifier(par->net, &ct_event_notifier) == 0) {
+      ct_event_notifier_registered = 1;
+      pr_debug("xt_FULLCONENAT: fullconenat_tg_check(): ct_event_notifier registered\n");
+    } else {
+      printk("xt_FULLCONENAT: warning: failed to register a conntrack notifier. Disable active GC for mappings.\n");
+    }
+
+  }
+
+  mutex_unlock(&nf_ct_net_event_lock);
+
+  return 0;
+}
+
+static void fullconenat_tg_destroy(const struct xt_tgdtor_param *par)
+{
+  mutex_lock(&nf_ct_net_event_lock);
+
+  tg_refer_count--;
+
+  pr_debug("xt_FULLCONENAT: fullconenat_tg_destroy(): tg_refer_count is now %d\n", tg_refer_count);
+
+  if (tg_refer_count == 0) {
+    if (ct_event_notifier_registered) {
+      nf_conntrack_unregister_notifier(par->net, &ct_event_notifier);
+      ct_event_notifier_registered = 0;
+
+      pr_debug("xt_FULLCONENAT: fullconenat_tg_destroy(): ct_event_notifier unregistered\n");
+
+    }
+    nf_ct_netns_put(par->net, par->family);
+  }
+
+  mutex_unlock(&nf_ct_net_event_lock);
+}
+
+static struct xt_target tg_reg[] __read_mostly = {
+ {
+  .name       = "FULLCONENAT",
+  .family     = NFPROTO_IPV4,
+  .revision   = 0,
+  .target     = fullconenat_tg,
+  .targetsize = sizeof(struct nf_nat_ipv4_multi_range_compat),
+  .table      = "nat",
+  .hooks      = (1 << NF_INET_PRE_ROUTING) |
+                (1 << NF_INET_POST_ROUTING),
+  .checkentry = fullconenat_tg_check,
+  .destroy    = fullconenat_tg_destroy,
+  .me         = THIS_MODULE,
+ },
+};
+
+static int __init fullconenat_tg_init(void)
+{
+  wq = create_singlethread_workqueue("xt_FULLCONENAT");
+  if (wq == NULL) {
+    printk("xt_FULLCONENAT: warning: failed to create workqueue\n");
+  }
+
+  return xt_register_targets(tg_reg, ARRAY_SIZE(tg_reg));
+}
+
+static void fullconenat_tg_exit(void)
+{
+  xt_unregister_targets(tg_reg, ARRAY_SIZE(tg_reg));
+
+  if (wq) {
+    cancel_delayed_work_sync(&gc_worker_wk);
+    flush_workqueue(wq);
+    destroy_workqueue(wq);
+  }
+
+  handle_dying_tuples();
+  destroy_mappings();
+}
+
+module_init(fullconenat_tg_init);
+module_exit(fullconenat_tg_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Xtables: implementation of RFC3489 full cone NAT");
+MODULE_AUTHOR("Chion Tang <tech@chionlab.moe>");
+MODULE_ALIAS("ipt_FULLCONENAT");