标签：iptables stateless nat nat linux cisco
使用iptables配置stateless NAT？我没有搞错。
xt_STATIC-2-WAY-NAT.c：这是一个内核模块，实现了NAT的核心逻辑和iptables target接口
/*
*
* procfs接口的用法(已经禁用)：
* 对目标地址为1.2.1.2的数据包做目标地址转换，目标转为192.168.1.8
* echo +1.2.1.2 192.168.1.8 dst >/proc/net/static_nat
* 上述命令会同时添加一条反向的SNAT映射
*
* 上述命令添加协议支持：
* echo +1.2.1.2 192.168.1.8 dst tcp >/proc/net/static_nat
*
* 继续增加端口映射的支持：
* echo +1.2.1.2 192.168.1.8 dst tcp port-map 1234 80 >/proc/net/static_nat
*
* 请解释：
* echo +192.168.184.250 192.168.184.154 src >/proc/net/static_nat
*
* iptables接口的用法：
* 见下面的详细注释。
*
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ctype.h>
#include <net/ip.h>
#include <net/netfilter/nf_conntrack.h>
#include <linux/netfilter/x_tables.h>
#include "xt_STATIC-2-WAY-NAT.h"
static __be16 skip_atos(const char *s)
{
__be16 i = 0;
while (isdigit(*s)) {
i = i * 10 + *((s)++) - ‘0‘;
}
return i;
}
#define DIRMASK 0x11
#define BUCKETS 1024
#define ENTRY_ADD 0x10
#define ENTRY_DEL 0x20
#define NAT_OPT_DEL 0x01
#define NAT_OPT_FIND 0x04
#define NAT_OPT_ACCT_BIT 0x02
/*
* 记录统计信息
*/
struct nat_account {
u32 nat_packets;
u32 nat_bytes;
};
/*
* 这个entry数据结构的设计有两个选择：
* 1.复杂模式：
* 即将所有的信息都展现于entry本身，skb匹配过程根据skb本身的IP地址信息作为key，
* 找到entry后再匹配第四层协议。
* 2.简单模式：
* 即设置多张保存简单entry(仅仅保存IP地址映射信息)的hlist，每个协议一张表，匹配
* 时仅仅需要匹配从skb中取出的protocol相关的hlist即可。
* 很明显，第二种效率更高，但是也更松散，本实现采用第一种，日后补充实现第二种。
*/
struct static_nat_entry {
__be32 addr[DIR_NUM];
/* 该entry适用的第四层协议 */
u_int8_t proto;
union {
__be16 all[DIR_NUM];
struct {
__be16 port[DIR_NUM];
} tcp;
struct {
__be16 port[DIR_NUM];
} udp;
/* ...... */
} u;
enum nat_dir type;
struct net_device *dev;
struct nat_account acct[DIR_NUM];
struct hlist_node node[DIR_NUM];
};
/*
* 返回查询结果
*/
struct map_result {
__be32 addr;
__be16 port;
};
static DEFINE_SPINLOCK(nat_lock);
/* 保存SNAT映射 */
struct hlist_head *src_list;
/* 保存DNAT映射 */
struct hlist_head *dst_list;
/*
* 用一个IP地址(对于PREROUTING是daddr，对于POSTROUTING是saddr)作为key来获取value。
*/
static unsigned int get_address_from_map(unsigned int dir,
__be32 addr_key,
__be16 port_key,
u8 proto_key,
unsigned int opt,
struct map_result *res,
unsigned int datalen,
const struct net_device *dev)
{
unsigned int ret = -1;
/* 首先匹配明细协议，然后再匹配通配协议 */
int try = 1;
__be32 cmp_key, ret_addr;
u32 hash;
struct hlist_head *list;
struct hlist_node *iter, *tmp;
struct static_nat_entry *ent;
/* 将协议作为hash计算的一部分，可以让来自同一地址的连接散列效果更好，
* 但是代价就是如果匹配不成功，则需要将协议设置为缺省通配协议，重新
* 匹配一次。
*
* 我的第一个版本在计算hash时并没有指定proto字段，第二个版本指定了，
* 因为经过我模拟的压力测试表明，对于配置明细协议的规则而言，匹配
* 会更加迅速。也就是说，这个效率和iptables是一样的，和你配置的规则
* 有关，即：最好配置带有明细协议的规则，而不是配置通配规则(你考虑
* 的少了，机器就要多考虑，反过来想让机器不考虑那么多，你自己就要
* 多考虑！)
*/
try_agin:
hash = jhash_2words(addr_key, (__be32)proto_key, 1);
hash = hash%BUCKETS;
spin_lock(&nat_lock);
if (dir == DIR_DNAT) {
list = &dst_list[hash];
} else if (dir == DIR_SNAT) {
list = &src_list[hash];
} else {
spin_unlock(&nat_lock);
goto out;
}
hlist_for_each_safe(iter, tmp, list) {
ent = hlist_entry(iter, struct static_nat_entry, node[dir]);
/* 注意反转 */
cmp_key = (ent->type == dir) ?
ent->addr[0]:ent->addr[1];
ret_addr = (ent->type == dir) ?
ent->addr[1]:ent->addr[0];
if (addr_key == cmp_key) {
__be16 cmp_port = (ent->type == dir) ?
ent->u.all[0]:ent->u.all[1];
__be16 ret_port = (ent->type == dir) ?
ent->u.all[1]:ent->u.all[0];
if (ent->proto != IPPROTO_MAX - 1 && ent->proto != proto_key) {
continue;
}
/* 如果addr比较不通过，就无需下面的了 */
if (cmp_port) {
/* 如果port不参与比较，就无需下面的了 */
if (cmp_port != port_key) {
continue;
}
}
if (dev && ent->dev && dev != ent->dev) {
continue;
}
/* 实际上，上面的嵌套if完全可以用C的布尔逻辑搞定，但是那样的话if条件会很长 */
ret = 0;
res->addr = ret_addr;
res->port = ret_port;
try = try - 1;
if (opt == NAT_OPT_DEL) {
if (dir == ent->type) {
hlist_del(&ent->node[0]);
hlist_del(&ent->node[1]);
if (ent->dev) {
dev_put(ent->dev);
}
kfree(ent);
} else {
ret = -1;
}
}
if (opt & NAT_OPT_ACCT_BIT) {
ent->acct[dir].nat_packets ++;
ent->acct[dir].nat_bytes += datalen;
}
break;
}
}
spin_unlock(&nat_lock);
if (try > 0) {
try = try - 1;
proto_key = IPPROTO_MAX - 1;
goto try_agin;
}
out:
return ret;
}
/*
* 处理第七层的函数
* 它处理第七层协议中携带地址端口信息的情况。
* 作为一个简单的例子，我用一个自定义的协议来举例：
* ...||layer3||layer4||saddr|daddr||
*/
static int process_l7(struct sk_buff *skb, unsigned int dir, __be32 newaddr, __be16 newport)
{
int ret = 0;
goto out;
out:
return ret;
}
static u8 get_l4_proto(struct sk_buff *skb)
{
u8 ret = IPPROTO_MAX - 1;
struct iphdr *iph = ip_hdr(skb);
switch (iph->protocol) {
case IPPROTO_TCP:
ret = IPPROTO_TCP;
break;
case IPPROTO_UDP:
ret = IPPROTO_UDP;
break;
default:
ret= IPPROTO_MAX - 1;
break;
}
return ret;
}
static s16 get_l4_port(struct sk_buff *skb, unsigned int dir)
{
struct iphdr *iph = ip_hdr(skb);
void *transport_hdr = (void *)iph + ip_hdrlen(skb);
struct tcphdr *tcph;
struct udphdr *udph;
__be16 ret = 0;
switch (iph->protocol) {
case IPPROTO_TCP:
tcph = transport_hdr;
if (dir == DIR_SNAT) {
ret = tcph->source;
} else if(dir == DIR_DNAT) {
ret = tcph->dest;
} else {
ret = 0;
}
break;
case IPPROTO_UDP:
case IPPROTO_UDPLITE:
udph = transport_hdr;
if (dir == DIR_SNAT) {
ret = udph->source;
} else if(dir == DIR_DNAT) {
ret = udph->dest;
} else {
ret = 0;
}
break;
default:
ret = 0;
}
return ret;
}
static void set_l4_port(struct sk_buff *skb, unsigned int dir, __be16 port)
{
struct iphdr *iph = ip_hdr(skb);
void *transport_hdr = (void *)iph + ip_hdrlen(skb);
struct tcphdr *tcph;
struct udphdr *udph;
switch (iph->protocol) {
case IPPROTO_TCP:
tcph = transport_hdr;
if (dir == DIR_SNAT) {
tcph->source = port;
} else if(dir == DIR_DNAT) {
tcph->dest = port;
}
break;
case IPPROTO_UDP:
case IPPROTO_UDPLITE:
udph = transport_hdr;
if (dir == DIR_SNAT) {
udph->source = port;
} else if(dir == DIR_DNAT) {
udph->dest = port;
}
break;
}
}
/*
* 更新第四层的校验码信息
*/
static void nat4_update_l4(struct sk_buff *skb,
__be32 oldip, __be32 newip,
__be16 oldport, __be16 newport)
{
struct iphdr *iph = ip_hdr(skb);
void *transport_hdr = (void *)iph + ip_hdrlen(skb);
struct tcphdr *tcph;
struct udphdr *udph;
bool cond;
switch (iph->protocol) {
case IPPROTO_TCP:
tcph = transport_hdr;
inet_proto_csum_replace4(&tcph->check, skb, oldip, newip, 1);
if (newport) {
inet_proto_csum_replace2(&tcph->check, skb, oldport, newport, 0);
}
break;
case IPPROTO_UDP:
case IPPROTO_UDPLITE:
udph = transport_hdr;
cond = udph->check != 0;
cond |= skb->ip_summed == CHECKSUM_PARTIAL;
if (cond) {
inet_proto_csum_replace4(&udph->check, skb, oldip, newip, 1);
if (newport) {
inet_proto_csum_replace2(&udph->check, skb, oldport, newport, 0);
}
if (udph->check == 0) {
udph->check = CSUM_MANGLED_0;
}
}
break;
}
}
/*
* 在POSTROUTING上执行源地址转换：
* 1.正向源地址转换；
* 2.目标地址转换的逆向源地址转换
*/
static unsigned int ipv4_nat_out(unsigned int hooknum,
struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
int (*okfn)(struct sk_buff *))
{
unsigned int ret = NF_ACCEPT, res = 0;
struct map_result mres;
struct iphdr *hdr = ip_hdr(skb);
__be16 port = 0;
u8 proto;
port = get_l4_port(skb, DIR_SNAT);
proto = get_l4_proto(skb);
memset(&mres, 0, sizeof(mres));
res = get_address_from_map(DIR_SNAT, hdr->saddr, port, proto, NAT_OPT_FIND|NAT_OPT_ACCT_BIT, &mres, skb->len, out);
if (res) {
goto out;
}
if (hdr->saddr == mres.addr) {
goto out;
}
/* 执行SNAT */
if (process_l7(skb, DIR_DNAT, mres.addr, mres.port)) {
/* 如果第七层发生了改变，则重新计算相关校验码 */
}
csum_replace4(&hdr->check, hdr->saddr, mres.addr);
nat4_update_l4(skb, hdr->saddr, mres.addr, port, mres.port);
if (mres.port) {
set_l4_port(skb, DIR_SNAT, mres.port);
}
hdr->saddr = mres.addr;
out:
return ret;
}
/*
* 在PREROUTING上执行目标地址转换：
* 1.正向目标地址转换；
* 2.源地址转换的逆向目标地址转换
*/
static unsigned int ipv4_nat_in(unsigned int hooknum,
struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
int (*okfn)(struct sk_buff *))
{
unsigned int ret = NF_ACCEPT, res = 0;
struct map_result mres;
struct iphdr *hdr = ip_hdr(skb);
__be16 port = 0;
u8 proto;
port = get_l4_port(skb, DIR_DNAT);
proto = get_l4_proto(skb);
if (skb->nfct && skb->nfct != &nf_conntrack_untracked.ct_general) {
goto out;
}
memset(&mres, 0, sizeof(mres));
res = get_address_from_map(DIR_DNAT, hdr->daddr, port, proto, NAT_OPT_FIND|NAT_OPT_ACCT_BIT, &mres, skb->len, in);
if (res) {
goto out;
}
if (hdr->daddr == mres.addr) {
goto out;
}
/* 执行DNAT */
if (process_l7(skb, DIR_DNAT, mres.addr, mres.port)) {
/* 如果第七层发生了改变，则重新计算相关校验码 */
}
csum_replace4(&hdr->check, hdr->daddr, mres.addr);
nat4_update_l4(skb, hdr->daddr, mres.addr, port, mres.port);
if (mres.port) {
set_l4_port(skb, DIR_DNAT, mres.port);
}
hdr->daddr = mres.addr;
/*
* 设置一个notrack 防止其被track以及nat.
* 这是绝对合适的，因为既然是static的stateless NAT
* 我们就不希望它被状态左右
**/
/*
* 其实，并不是主要避开基于conntrack的NAT就可以了，因为
* conntrack本身就不容你对两个方向的tuple进行随意修改
*/
if (!skb->nfct) {
skb->nfct = &nf_conntrack_untracked.ct_general;
skb->nfctinfo = IP_CT_NEW;
nf_conntrack_get(skb->nfct);
}
out:
return ret;
}
static struct nf_hook_ops ipv4_nat_ops[] __read_mostly = {
{
.hook = ipv4_nat_in,
.owner = THIS_MODULE,
.pf = NFPROTO_IPV4,
.hooknum = NF_INET_PRE_ROUTING,
.priority = NF_IP_PRI_RAW + 1,
},
{
.hook = ipv4_nat_out,
.owner = THIS_MODULE,
.pf = NFPROTO_IPV4,
.hooknum = NF_INET_POST_ROUTING,
.priority = NF_IP_PRI_CONNTRACK + 1,
},
};
static char *parse_addr(const char *input, __be32 *from, __be32 *to)
{
char *p1, *p2;
size_t length = strlen(input);
if (!(p1 = memchr(input, ‘ ‘, length))) {
return NULL;
}
if (!(p2 = memchr(p1 + 1, ‘ ‘, length - (p1 + 1 - input)))) {
return NULL;
}
if (!(in4_pton(input, p1 - input, (u8 *)from, ‘ ‘, NULL))
|| !(in4_pton(p1 + 1, p2 - p1 - 1, (u8 *)to, ‘ ‘, NULL))) {
return NULL;
}
return ++p2;
}
static char *parse_port(char *input, __be16 *from, __be16 *to)
{
char *p1;
size_t length = strlen(input);
size_t delta = 0;
char tmp[8] = {0};
__be16 res;
/*portfrom portto*/
if (!(p1 = memchr(input, ‘ ‘, length))) {
return NULL;
}
delta = p1 - input;
memcpy(tmp, input, delta);
res = skip_atos(tmp);
if (!res) {
return NULL;
}
*from = htons(res);
memset(tmp, 0, sizeof(tmp));
memcpy(tmp, p1+1, length-delta);
res = skip_atos(tmp);
if (!res) {
return NULL;
}
*to = htons(res);
return p1;
}
static int add_remove_nat_entry(struct static_nat_entry *ent,
__be32 from, __be32 to,
__be16 from_port, __be16 to_port,
u8 dir,
u8 proto,
struct net_device *dev,
u8 opt)
{
int ret = 0;
__be32 normal, reverse;
struct map_result mres;
if (opt == ENTRY_ADD) {
if (!ent) {
ret = -EINVAL;
goto out;
}
ent->proto = proto;
/* 计算原始项的hash桶位置 */
normal = jhash_2words(from, (__be32)proto, 1);
normal = normal%BUCKETS;
/* 计算反转位置的hash桶位置 */
reverse = jhash_2words(to, (__be32)proto, 1);
reverse = reverse%BUCKETS;
/*
* 设置key/value对
* 注意，反转类型的hnode其key/value也要反转
*/
ent->addr[0] = from;
ent->addr[1] = to;
ent->u.all[0] = from_port;
ent->u.all[1] = to_port;
/* 这是这个entry的type，用来区分生成的两条配置项 */
ent->type = dir;
ent->dev = dev;
/* 初始化链表节点 */
INIT_HLIST_NODE(&ent->node[DIR_SNAT]);
INIT_HLIST_NODE(&ent->node[DIR_DNAT]);
if (dir == DIR_SNAT) { /* 添加SNAT项，自动生成DNAT项 */
/* 首先判断是否已经存在了 */
if (!get_address_from_map(DIR_SNAT, from, from_port, proto, NAT_OPT_FIND, &mres, 0, dev) ||
!get_address_from_map(DIR_SNAT, to, to_port, proto, NAT_OPT_FIND, &mres, 0, dev)) {
ret = -EEXIST;
goto out;
}
/* 落实到链表 */
spin_lock(&nat_lock);
hlist_add_head(&ent->node[DIR_SNAT], &src_list[normal]);
hlist_add_head(&ent->node[DIR_DNAT], &dst_list[reverse]);
spin_unlock(&nat_lock);
} else if(dir == DIR_DNAT) { /* 添加DNAT项，自动生成SNAT项 */
/* 首先判断是否已经存在了 */
struct map_result mres;
if (!get_address_from_map(DIR_DNAT, from, from_port, proto, NAT_OPT_FIND, &mres, 0, dev) ||
!get_address_from_map(DIR_DNAT, to, to_port, proto, NAT_OPT_FIND, &mres, 0, dev)){
ret = -EEXIST;
goto out;
}
/* 落实到链表 */
spin_lock(&nat_lock);
hlist_add_head(&ent->node[DIR_DNAT], &dst_list[normal]);
hlist_add_head(&ent->node[DIR_SNAT], &src_list[reverse]);
spin_unlock(&nat_lock);
} else {
ret = -EINVAL;
goto out;
}
} else if (opt == ENTRY_DEL) {
u32 r1;
if (dir == DIR_SNAT) {
r1 = get_address_from_map(DIR_SNAT, from, from_port, proto, NAT_OPT_DEL, &mres, 0, dev);
if (r1) {
ret = -ENOENT;
goto out;
}
} else if(dir == DIR_DNAT) {
r1 = get_address_from_map(DIR_DNAT, from, from_port, proto, NAT_OPT_DEL, &mres, 0, dev);
if (r1) {
ret = -ENOENT;
goto out;
}
} else {
ret = -EINVAL;
goto out;
}
} else {
ret = -EINVAL;
goto out;
}
out:
return ret;
}
static ssize_t static_nat_config_write(struct file *file, const char *buffer, size_t count, loff_t *unused)
{
int ret = 0;
size_t length = count;
__be32 from, to;
__be16 from_port = 0, to_port = 0;
u8 proto = 0;
char *buf = NULL;
char *p, *pport, *last;
struct static_nat_entry *ent;
struct net_device *dev = NULL;
if (length) {
char *pp = (char *)(buffer + (length - 1));
for (; (*pp < (char)32) || (*pp > (char)126); pp--) {
if (length <= 0) {
ret = -EINVAL;
goto out;
}
length--;
}
} else {
goto out;
}
buf = kzalloc((length + 1), GFP_ATOMIC);
if (!buf) {
ret = -ENOMEM;
goto out;
}
memcpy(buf, buffer, length);
if (!(p = parse_addr(buf + 1, &from, &to))) {
ret = -EINVAL;
goto out;
}
/*
* dev = dev_get_by_name(&init_net, $待解析的dev名字);
* */
if (strstr(p, "tcp") && !strstr(p, "udp")) {
proto = IPPROTO_TCP;
} else if (strstr(p, "udp") && !strstr(p, "tcp")) {
proto = IPPROTO_UDP;
} else {
/* 支持IPIP以及所有协议 */
proto = IPPROTO_MAX - 1;
}
if (((pport = strstr(p, "port-map")) != NULL) &&
((last = parse_port(pport + strlen("port-map") + 1, &from_port, &to_port)) == NULL)) {
ret = -EINVAL;
goto out;
}
if (‘+‘ == *buf) {
ent = (struct static_nat_entry *)kzalloc(sizeof(struct static_nat_entry), GFP_KERNEL);
if (!ent) {
ret = -EFAULT;
goto out;
}
if (strstr(p, "src")) { /* 添加SNAT项，自动生成DNAT项 */
ret = add_remove_nat_entry(ent, from, to, from_port, to_port, DIR_SNAT, proto, dev, ENTRY_ADD);
if (ret) {
kfree(ent);
goto out;
}
} else if(strstr(p, "dst")) { /* 添加DNAT项，自动生成SNAT项 */
ret = add_remove_nat_entry(ent, from, to, from_port, to_port, DIR_DNAT, proto, dev, ENTRY_ADD);
if (ret) {
kfree(ent);
goto out;
}
} else {
ret = -EFAULT;
kfree(ent);
goto out;
}
} else if (‘-‘ ==*buf) {
if (strstr(p, "src")) {
ret = add_remove_nat_entry(NULL, from, to, from_port, to_port, DIR_SNAT, proto, dev, ENTRY_DEL);
if (ret) {
goto out;
}
} else if(strstr(p, "dst")) {
ret = add_remove_nat_entry(NULL, from, to, from_port, to_port, DIR_DNAT, proto, dev, ENTRY_DEL);
if (ret) {
goto out;
}
} else {
ret = -EINVAL;
goto out;
}
} else {
ret = -EINVAL;
goto out;
}
ret = count;
out:
kfree(buf);
return ret;
}
static ssize_t static_nat_config_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
int len = 0;
static int done = 0;
int i;
char from[15], to[15];
char from_port[8], to_port[8];
char *kbuf_to_avoid_user_space_memory_page_fault = NULL;
/* 每一行的最大长度 */
#define MAX_LINE_CHARS 128
if (done) {
done = 0;
goto out;
}
/*
* 分配一块内核内存，为了避免直接操作用户内存而引发页面调度，
* 页面调度会导致睡眠切换，而我们操作的内容处在自旋锁的保护
* 下，所以不能切换！
*/
/*
* 问题：
* 我这里仅仅分配count大小的内存，是因为这个版本不支持多次读，
* 只能一次读完。也许我应该学学seq read的方法。
*/
kbuf_to_avoid_user_space_memory_page_fault = kzalloc(count, GFP_KERNEL);
if (!kbuf_to_avoid_user_space_memory_page_fault) {
len = -ENOMEM;
done = 1;
goto out;
}
spin_lock(&nat_lock);
len += sprintf(kbuf_to_avoid_user_space_memory_page_fault + len, "Source trans table:\n");
if (len + MAX_LINE_CHARS > count) {
goto copy_now;
}
for (i = 0; i < BUCKETS; i++) {
struct hlist_node *iter, *tmp;
struct static_nat_entry *ent;
hlist_for_each_safe(iter, tmp, &src_list[i]) {
ent = hlist_entry(iter, struct static_nat_entry, node[DIR_SNAT]);
sprintf(from, "%pI4", (ent->type == DIR_SNAT)? &ent->addr[0]:&ent->addr[1]);
sprintf(to, "%pI4", (ent->type == DIR_SNAT)? &ent->addr[1]:&ent->addr[0]);
if (ent->u.all[0] && ent->u.all[1]) {
sprintf(from_port, "%d", ntohs((ent->type == DIR_SNAT)? ent->u.all[0]:ent->u.all[1]));
sprintf(to_port, "%d", ntohs((ent->type == DIR_SNAT)? ent->u.all[1]:ent->u.all[0]));
len += sprintf(kbuf_to_avoid_user_space_memory_page_fault + len,
"From:%-15s To:%-15s [%s %s] Port map[From:%-5s To:%-5s] [%s] [Bytes:%u Packet:%u]\n",
from,
to,
(ent->proto == IPPROTO_TCP)?
"TCP":
(ent->proto == IPPROTO_UDP)?"UDP":"ALL",
(ent->type == DIR_SNAT)?"STATIC":"AUTO",
from_port,
to_port,
(ent->dev == NULL)?"all":ent->dev->name,
ent->acct[DIR_SNAT].nat_bytes,
ent->acct[DIR_SNAT].nat_packets);
} else {
len += sprintf(kbuf_to_avoid_user_space_memory_page_fault + len,
"From:%-15s To:%-15s [%s %s] [%s] [Bytes:%u Packet:%u]\n",
from,
to,
(ent->proto == IPPROTO_TCP)?
"TCP":
(ent->proto == IPPROTO_UDP)?"UDP":"ALL",
(ent->type == DIR_SNAT)?"STATIC":"AUTO",
(ent->dev == NULL)?"all":ent->dev->name,
ent->acct[DIR_SNAT].nat_bytes,
ent->acct[DIR_SNAT].nat_packets);
}
if (len + MAX_LINE_CHARS > count) {
goto copy_now;
}
}
}
len += sprintf(kbuf_to_avoid_user_space_memory_page_fault + len, "\nDestination trans table:\n");
if (len + MAX_LINE_CHARS > count) {
goto copy_now;
}
for (i = 0; i < BUCKETS; i++) {
struct hlist_node *iter, *tmp;
struct static_nat_entry *ent;
hlist_for_each_safe(iter, tmp, &dst_list[i]) {
ent = hlist_entry(iter, struct static_nat_entry, node[DIR_DNAT]);
sprintf(from, "%pI4", (ent->type == DIR_DNAT)? &ent->addr[0]:&ent->addr[1]);
sprintf(to, "%pI4", (ent->type == DIR_DNAT)? &ent->addr[1]:&ent->addr[0]);
if (ent->u.all[0] && ent->u.all[1]) {
sprintf(from_port, "%d", ntohs((ent->type == DIR_DNAT)? ent->u.all[0]:ent->u.all[1]));
sprintf(to_port, "%d", ntohs((ent->type == DIR_DNAT)? ent->u.all[1]:ent->u.all[0]));
len += sprintf(kbuf_to_avoid_user_space_memory_page_fault + len,
"From:%-15s To:%-15s [%s %s] Port map[From:%-5s To:%-5s] [%s] [Bytes:%u Packet:%u]\n",
from,
to,
(ent->proto == IPPROTO_TCP)?
"TCP":
(ent->proto == IPPROTO_UDP)?"UDP":"ALL",
(ent->type == DIR_DNAT)?"STATIC":"AUTO",
from_port,
to_port,
(ent->dev == NULL)?"all":ent->dev->name,
ent->acct[DIR_DNAT].nat_bytes,
ent->acct[DIR_DNAT].nat_packets);
} else {
len += sprintf(kbuf_to_avoid_user_space_memory_page_fault + len,
"From:%-15s To:%-15s [%s %s] [%s] [Bytes:%u Packet:%u]\n",
from,
to,
(ent->proto == IPPROTO_TCP)?
"TCP":
(ent->proto == IPPROTO_UDP)?"UDP":"ALL",
(ent->type == DIR_DNAT)?"STATIC":"AUTO",
(ent->dev == NULL)?"all":ent->dev->name,
ent->acct[DIR_DNAT].nat_bytes,
ent->acct[DIR_DNAT].nat_packets);
}
if (len + MAX_LINE_CHARS > count) {
goto copy_now;
}
}
}
copy_now:
spin_unlock(&nat_lock);
done = 1;
/* 这里已经解除自旋锁 */
if (copy_to_user(buf, kbuf_to_avoid_user_space_memory_page_fault, len)) {
len = EFAULT;
goto out;
}
out:
if (kbuf_to_avoid_user_space_memory_page_fault) {
kfree(kbuf_to_avoid_user_space_memory_page_fault);
}
return len;
}
static const struct file_operations static_nat_file_ops = {
.owner = THIS_MODULE,
.read = static_nat_config_read,
/* 由于有了iptables接口，为了不产生两个写接口的联动问题，特意封掉了procfs的write接口
* .write = static_nat_config_write,
*/
};
/***************************************************************************************************************************/
/* 以下就是iptables接口了，我只是为了迎合它的语法而已，事实上static 2-way nat的规则中，matches完全不起作用，
* 甚至就连PREROUTING/POSTROUTING都完全不起作用，我的目的仅仅是将其设置进内核而已。因此起作用的只有target。
* 这是有原因的，因为我只是做一个纯粹的，无状态德，理所当然的，匹配地址端口即无条件转换的NAT，如果使用match
* 将达不到这个要求，试想，如果有-i参数匹配网卡，那么反向的包怎么匹配，你不得不写两条规则，xtables-addons里面
* 的RAWNAT似乎不是很完全，因此我要自己搞一个。
* 事实上，我只是利用了target结构体的checkentry/destroy回调函数，在checkentry中添加规则，在destroy中删除规则，
* 而所谓的规则也并不是指iptables规则，iptables只是起到一个stub的作用。
* 以下是一些规则样例：
* 1.做源地址转换，将源IP地址为192.168.184.1的包的源地址转换为192.168.184.2，反方向的包自动完成目标地址转换：
* iptables -t nat -A PREROUTING -j STATIC-2-WAY-NAT --mapaddr 192.168.184.1-192.168.184.2 --type src
* 2.做目标地址转换，仅限于UDP协议，将目标IP地址为192.168.184.3的包的目标地址转换为192.168.184.4，反方向包自动做源地址转换：
* iptables -t nat -A PREROUTING -j STATIC-2-WAY-NAT --mapaddr 192.168.184.3-192.168.184.4 --type dst --proto udp
* 3.做目标地址转换，仅限于TCP协议，解释同上，添加了一个端口映射：
* iptables -t nat -A PREROUTING -j STATIC-2-WAY-NAT --mapaddr 1.1.1.5-1.6.8.6 --type dst --proto tcp * --mapport 1234-80
* 4.以下规则的所有matches无效，起不到限制规则匹配的作用：
* iptables -t nat -A PREROUTING -i eth0 -p icmp -d 1.2.3.4 -j STATIC-2-WAY-NAT ...
*/
/***************************************************************************************************************************/
/* 该链表保存了所有的当前iptales static nat规则 */
LIST_HEAD(curr_entrys);
DEFINE_SPINLOCK(curr_entrys_lock);
/*
* 引入下面的数据结构加入curr_entrys是有超级原因的。这是因为我必须维护两个链表。
* src_list/dst_list维护的是查找node，而entrys维护的则是iptables的规则node，为什么
* iptables的规则node不能重用src_list/dst_list呢？因为iptables允许添加两条多条相同
* 的规则。
* 因此必须采用引用计数的方式。关于这么做的原因还有一个因素，那就是iptables添加删除
* 规则时背后的操作：
* 添加规则：
* 1.开辟一块新的可以容纳新规则的内存空间(比原来的同一target空间大一个entry)；
* 2.将老的规则全部copy到新的内存空间，新规则append到最后或者insert到中间(copy老规则时需预留间隙)；
* 3.依次调用新内存空间所有entry的checkentry回调函数(失败则回退，略)；
* 4.如果成功则调用老规则内存空间所有entry的destroy回调函数；
* 5.释放老规则的内存空间；
*
* 各个步骤示意图如下所示(o:old n:new)：
*
* 老规则空间： o -1- -2- -3-
*
* 新规则空间： ALLOC
* n --- --- --- ---
*
* 拷贝老规则到新空间： n -1- -2- -3- ---
*
* 设置新规则： n -1- -2- -3- -4-
*
* 调用1-4的checkentry： ->chk->chk->chk->chk
* n -1- -2- -3- -4-
*
* destroy老空间的规则： ->dsy->dsy->dsy
* o -1- -2- -3-
*
* 释放老规则空间： FREE
* o -1- -2- -3-
* 删除规则：
* 和添加规则一样。
*
* 之所以每次添加规则都要触动统一target所有的既有规则，是因为iptables规则在内存中是连续存放的，
* 一开始的时候并不知道数量，因此只能在每次添加新规则的时候重新分配大一个entry的空间，然后拷贝，
* 最终释放老地址空间。
*/
struct entry_node {
struct list_head list;
atomic_t refcnt;
struct net_device *dev;
__be32 from, to;
__be16 port_from, port_to;
u8 proto;
u8 dir;
};
static void entry_insert(struct entry_node *enode)
{
spin_lock_bh(&curr_entrys_lock);
list_add_tail(&enode->list, &curr_entrys);
spin_unlock_bh(&curr_entrys_lock);
}
static struct entry_node *entry_alloc(__be32 from, __be32 to,
__be16 port_from, __be16 port_to,
u8 proto,
u8 dir,
struct net_device *dev)
{
struct entry_node *node = kzalloc(sizeof(struct entry_node), GFP_KERNEL);
if (!node) {
return NULL;
}
if (dev) {
dev_hold(dev);
}
node->dev = dev;
node->from = from;
node->to = to;
node->port_from = port_from;
node->port_to = port_to;
node->proto = proto;
node->dir = dir;
INIT_LIST_HEAD(&node->list);
atomic_set(&node->refcnt, 1);
return node;
}
static bool check_and_use(__be32 from, __be32 to,
__be16 port_from, __be16 port_to,
u8 proto,
u8 dir,
struct net_device *dev)
{
bool ret = false;
struct entry_node *i;
spin_lock_bh(&curr_entrys_lock);
if (!list_empty(&curr_entrys)) {
list_for_each_entry(i, &curr_entrys, list) {
if (i->from == from &&
i->to == to &&
i->port_from == port_from &&
i->port_to == port_to &&
i->proto == proto &&
i->dir == dir &&
i->dev == dev) {
atomic_inc(&i->refcnt);
ret = true;
}
}
}
spin_unlock_bh(&curr_entrys_lock);
return ret;
}
static bool check_and_put(__be32 from, __be32 to,
__be16 port_from, __be16 port_to,
u8 proto,
u8 dir,
struct net_device *dev)
{
bool ret = false;
struct entry_node *i, *tmp;
spin_lock_bh(&curr_entrys_lock);
if (!list_empty(&curr_entrys)) {
list_for_each_entry_safe(i, tmp, &curr_entrys, list) {
if (i->from == from &&
i->to == to &&
i->port_from == port_from &&
i->port_to == port_to &&
i->proto == proto &&
i->dir == dir &&
i->dev == dev) {
if (atomic_dec_and_test(&i->refcnt)) {
list_del(&i->list);
if (dev) {
dev_put(dev);
}
kfree(i);
ret = true;
}
}
}
}
spin_unlock_bh(&curr_entrys_lock);
return ret;
}
/*
* 理论上讲，下面这个函数应该是iptables的一条规则中所有match都匹配到之后要调用的函数，
* 但是，你可以看到，在我的static 2-way nat中，它并不起任何作用。
* 但是等等！
* 它事实上取消了排在这个规则后面的statefull NAT的执行，因为它直接在nat表中ACCEPT了，
* 这是什么，这是一个副作用，这个副作用竟然如此有用，以至于它已经可以模拟Cisco/H3C设备的
* NAT了：静态NAT优先执行！
*
* 看来这是iptables相比procfs接口的一个特别有用的副作用了！
*/
static unsigned int
do_nothing(struct sk_buff *skb, const struct xt_target_param *par)
{
return NF_ACCEPT;
}
static bool do_all_things_add(const struct xt_tgchk_param *par)
{
int ret = true;
__be32 from = 0, to = 0;
__be16 from_port = 0, to_port = 0;
u8 proto;
u8 dir;
struct static_nat_entry *ent = NULL;
const struct xt_static_nat_tginfo *info = par->targinfo;
struct net_device *dev;
/*
* struct xt_static_nat_tginfo {
* __be32 addr[DIR_NUM];
* __be16 port[DIR_NUM];
* u_int8_t proto;
* u_int8_t dir;
* };
*/
from = info->addr[0];
to = info->addr[1];
from_port = info->port[0];
to_port = info->port[1];
proto = info->proto;
dir = info->dir;
dev = dev_get_by_name(&init_net, info->dev);
/* 只有在链表中没有该entry的情况下才添加 */
if (!check_and_use(from, to, from_port, to_port, proto, dir, dev)) {
struct entry_node *enode = entry_alloc(from, to, from_port, to_port, proto, dir, dev);
if (enode) {
entry_insert(enode);
ent = (struct static_nat_entry *)kzalloc(sizeof(struct static_nat_entry), GFP_KERNEL);
if (!ent) {
ret = false;
goto out;
}
ret = add_remove_nat_entry(ent, from, to, from_port, to_port, dir, proto, dev, ENTRY_ADD);
if (ret) {
ret = false;
kfree(ent);
check_and_put(from, to, from_port, to_port, proto, dir, dev);
goto out;
}
} else {
ret = false;
goto out;
}
} else if (dev) {
dev_put(dev);
}
ret = true;
out:
return ret;
}
static void do_all_things_del(const struct xt_tgdtor_param *par)
{
int ret = 0;
__be32 from = 0, to = 0;
__be16 from_port = 0, to_port = 0;
u8 proto;
u8 dir;
const struct xt_static_nat_tginfo *info = par->targinfo;
struct net_device *dev = NULL;
from = info->addr[0];
to = info->addr[1];
from_port = info->port[0];
to_port = info->port[1];
proto = info->proto;
dir = info->dir;
dev = dev_get_by_name(&init_net, info->dev);
if (check_and_put(from, to, from_port, to_port, proto, dir, dev)) {
ret = add_remove_nat_entry(NULL, from, to, from_port, to_port, dir, proto, dev, ENTRY_DEL);
if (ret) {
goto out;
}
}
out:
if (dev) {
dev_put(dev);
}
return;
}
static struct xt_target static_nat_tg_reg[] __read_mostly = {
{
.name = "STATIC-2-WAY-NAT",
.family = NFPROTO_IPV4,
.target = do_nothing,
.table = "nat",
.targetsize = XT_ALIGN(sizeof(struct xt_static_nat_tginfo)),
.checkentry = do_all_things_add,
.destroy = do_all_things_del,
.hooks = (1 << NF_INET_POST_ROUTING) |
(1 << NF_INET_PRE_ROUTING),
.me = THIS_MODULE,
},
};
static int __init nf_static_nat_init(void)
{
int ret = 0;
int i;
src_list = kzalloc(sizeof(struct hlist_head) * BUCKETS, GFP_KERNEL);
if (!src_list) {
ret = -ENOMEM;
goto out;
}
dst_list = kzalloc(sizeof(struct hlist_head) * BUCKETS, GFP_KERNEL);
if (!dst_list) {
ret = -ENOMEM;
goto out;
}
ret = nf_register_hooks(ipv4_nat_ops, ARRAY_SIZE(ipv4_nat_ops));
if (ret < 0) {
printk("nf_nat_ipv4: can‘t register hooks.\n");
goto out;
}
ret = xt_register_targets(static_nat_tg_reg, ARRAY_SIZE(static_nat_tg_reg));
if (ret < 0) {
printk("nf_nat_ipv4: can‘t register targets.\n");
goto out;
}
if (!proc_create("static_nat", 0644, init_net.proc_net, &static_nat_file_ops)) {
ret = -ENOMEM;
goto out;
}
for (i = 0; i < BUCKETS; i++) {
INIT_HLIST_HEAD(&src_list[i]);
INIT_HLIST_HEAD(&dst_list[i]);
}
return ret;
out:
if (src_list) {
kfree(src_list);
}
if (dst_list) {
kfree(dst_list);
}
return ret;
}
static void __exit nf_static_nat_fini(void)
{
int i;
remove_proc_entry("static_nat", init_net.proc_net);
xt_unregister_targets(static_nat_tg_reg, ARRAY_SIZE(static_nat_tg_reg));
nf_unregister_hooks(ipv4_nat_ops, ARRAY_SIZE(ipv4_nat_ops));
spin_lock(&nat_lock);
for (i = 0; i < BUCKETS; i++) {
struct hlist_node *iter, *tmp;
struct static_nat_entry *ent;
hlist_for_each_safe(iter, tmp, &src_list[i]) {
ent = hlist_entry(iter, struct static_nat_entry, node[0]);
hlist_del(&ent->node[DIR_SNAT]);
hlist_del(&ent->node[DIR_DNAT]);
kfree(ent);
}
}
spin_unlock(&nat_lock);
if (src_list) {
kfree(src_list);
}
if (dst_list) {
kfree(dst_list);
}
}
module_init(nf_static_nat_init);
module_exit(nf_static_nat_fini);
MODULE_DESCRIPTION("STATIC two-way NAT");
MODULE_AUTHOR("marywangran@126.com");
MODULE_LICENSE("GPL");libxt_STATIC-2-WAY-NAT.c：这是用户态的iptables target模块的实现文件
/*
* 根据Netfilter/iptables社区的友好相权，逼出来一个iptables接口。
* 相比procfs要友好多了
*
* 起初，我就是嫌iptables模块写起来太麻烦，后来写过procfs接口之后才发现，
* 原来最麻烦的不是例行公事的调用，而是字符串解析。使用iptables框架的好处
* 在于它已经有了很多可重用的字符串解析以及到IP地址，端口的转换接口
*/
#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <xtables.h>
#include "xt_STATIC-2-WAY-NAT.h"
#undef XT_ALIGN
#define XT_ALIGN(s) (((s) + (__alignof__(struct _xt_align)-1)) & ~(__alignof__(struct _xt_align)-1))
/* 枚举规则解析状态机的当前状态 */
enum {
ADDR_OK = (1<<0),
TYPE_OK = (1<<1),
PROTO_OK = (1<<2),
PORT_OK = (1<<3),
DEV_OK = (1<<4),
};
/* 规则命令定义 */
static const struct option static_2_way_nat_tg_opts[] = {
{.name = "mapaddr", .has_arg = true, .val = ‘a‘},
{.name = "mapport", .has_arg = true, .val = ‘o‘},
{.name = "proto", .has_arg = true, .val = ‘p‘},
/* 本来想将type设置成source/destination的，但UNIX短名称传统更适合Linux */
{.name = "type", .has_arg = true, .val = ‘t‘},
/* 本来想为dev设置inside/outside属性的，但是还是用Linux术语吧 */
{.name = "dev", .has_arg = true, .val = ‘d‘},
{},
};
static void static_2_way_nat_tg_help(void)
{
printf(
"STATIC-2-WAY-NAT target options:\n"
" --mapaddr from-to --type [src|dst] --dev [ethX] --proto [tcp|udp|all] --mapport from_port-to_port\n"
);
}
/* 从字符串解析IP地址 */
static void parse_addr(const char *orig_arg, struct xt_static_nat_tginfo *info)
{
char *arg, *dash;
size_t delta, len;
u_int32_t from, to;
arg = strdup(orig_arg);
if (arg == NULL) {
xtables_error(RESOURCE_PROBLEM, "strdup");
}
len = strlen(arg);
dash = strchr(arg, ‘-‘);
if (!dash) {
xtables_error(RESOURCE_PROBLEM, "invalid argument.");
}
delta = dash - arg;
arg[delta] = 0;
from = inet_addr(arg);
if (from == INADDR_NONE){
xtables_error(RESOURCE_PROBLEM, "invalid from address.");
}
info->addr[0] = from;
arg += delta + 1;
to = inet_addr(arg);
if (to == INADDR_NONE){
xtables_error(RESOURCE_PROBLEM, "invalid to address.");
}
info->addr[1] = to;
}
/* 从字符串解析端口信息 */
static void parse_port(const char *orig_arg, struct xt_static_nat_tginfo *info)
{
char *arg, *dash;
size_t delta, len;
u_int16_t from, to;
arg = strdup(orig_arg);
if (arg == NULL) {
xtables_error(RESOURCE_PROBLEM, "strdup");
}
len = strlen(arg);
dash = strchr(arg, ‘-‘);
if (!dash) {
xtables_error(RESOURCE_PROBLEM, "invalid argument.");
}
delta = dash - arg;
arg[delta] = 0;
from = atoi(arg);
if (from == 0){
xtables_error(RESOURCE_PROBLEM, "invalid from port.");
}
info->port[0] = htons(from);
arg += delta + 1;
to = atoi(arg);
if (to == 0){
xtables_error(RESOURCE_PROBLEM, "invalid to port.");
}
info->port[1] = htons(to);
}
/* iptables框架内的规则命令解析回调函数实现 */
static int
static_2_way_nat_tg_parse(int c, char **argv, int invert, unsigned int *flags,
const void *entry, struct xt_entry_target **target)
{
int ret = false;
struct xt_static_nat_tginfo *info = (void *)(*target)->data;
switch (c) {
case ‘a‘:
if (*flags & ADDR_OK) {
xtables_error(PARAMETER_PROBLEM, "STATIC-2-WAY-NAT: multi addrmap.");
}
parse_addr(optarg, info);
/* 如果没有携带或者还没有解析到协议参数，则设置默认值 */
if (!(*flags & PROTO_OK)) {
info->proto = IPPROTO_MAX - 1;
}
/* 如果没有携带或者还没有解析到端口参数，则设置默认值 */
if (!(*flags & PORT_OK)) {
info->port[0] = 0;
info->port[1] = 0;
}
/* 如果没有携带或者还没有解析到网卡参数，则设置默认值 */
if (!(*flags & DEV_OK)) {
memset(&info->dev[0], 0, MAX_DEV_NAME);
strcpy(info->dev, "");
}
*flags |= ADDR_OK;
ret = true;
break;
case ‘o‘:
if (*flags & PORT_OK) {
xtables_error(PARAMETER_PROBLEM, "STATIC-2-WAY-NAT: multi portmap.");
}
parse_port(optarg, info);
*flags |= PORT_OK;
ret = true;
break;
case ‘p‘:
if (*flags & PROTO_OK) {
xtables_error(PARAMETER_PROBLEM, "STATIC-2-WAY-NAT: multi protocol.");
}
if (!strcmp (optarg, "tcp")) {
info->proto = IPPROTO_TCP;
} else if (!strcmp (optarg, "udp")) {
info->proto = IPPROTO_UDP;
} else {
xtables_error(PARAMETER_PROBLEM, "STATIC-2-WAY-NAT: invalid type.");
}
*flags |= PROTO_OK;
ret = true;
break;
case ‘t‘:
if (*flags & TYPE_OK) {
xtables_error(PARAMETER_PROBLEM, "STATIC-2-WAY-NAT: multi type.");
}
if (!strcmp (optarg, "src")) {
info->dir = DIR_SNAT;
} else if (!strcmp (optarg, "dst")) {
info->dir = DIR_DNAT;
} else {
xtables_error(PARAMETER_PROBLEM, "STATIC-2-WAY-NAT: invalid type.");
}
*flags |= TYPE_OK;
ret = true;
break;
case ‘d‘:
if (*flags & DEV_OK) {
xtables_error(PARAMETER_PROBLEM, "STATIC-2-WAY-NAT: multi device.");
}
strncpy(info->dev, optarg, MAX_DEV_NAME);
*flags |= DEV_OK;
ret = true;
break;
}
return ret;
}
/* iptables框架内的规则命令解析完毕检查回调函数实现 */
static void static_2_way_nat_tg_check(unsigned int flags)
{
/* 地址转换信息和类型[SNAT|DNAT]是必须要设置的 */
if (!(flags & ADDR_OK) || !(flags & TYPE_OK)) {
xtables_error(PARAMETER_PROBLEM, "STATIC-2-WAY-NAT: "
"\"--mapaddr a.b.c.d-A.B.C.D and --type [src|dst]\" is required.");
}
}
static void
static_2_way_nat_tg_print(const void *entry, const struct xt_entry_target *target,
int numeric)
{
u_int32_t addr;
const struct xt_static_nat_tginfo *info = (const void *)target->data;
if (!info) {
return;
}
addr = info->addr[0];
printf(" --mapaddr %s-", xtables_ipaddr_to_numeric((struct in_addr *)&addr));
addr = info->addr[1];
printf("%s --type %s --proto %s --mapport %d-%d --dev %s",
xtables_ipaddr_to_numeric((struct in_addr *)&addr),
(info->dir == DIR_SNAT)?"src":"dst",
(info->proto == IPPROTO_TCP)?"tcp":
((info->proto == IPPROTO_UDP)?"udp":"all"),
ntohs(info->port[0]),
ntohs(info->port[1]),
!strcmp(info->dev, "")?"all":info->dev);
}
/* iptables-save将按照该函数的实现来罗列规则 */
static void
static_2_way_nat_tg_save(const void *entry, const struct xt_entry_target *target)
{
u_int32_t addr;
const struct xt_static_nat_tginfo *info = (const void *)target->data;
if (!info) {
return;
}
addr = info->addr[0];
printf(" --mapaddr %s-", xtables_ipaddr_to_numeric((struct in_addr *)&addr));
addr = info->addr[1];
printf("%s --type %s --proto %s --mapport %d-%d --dev %s",
xtables_ipaddr_to_numeric((struct in_addr *)&addr),
(info->dir == DIR_SNAT)?"src":"dst",
(info->proto == IPPROTO_TCP)?"tcp":
((info->proto == IPPROTO_UDP)?"udp":"all"),
ntohs(info->port[0]),
ntohs(info->port[1]),
!strcmp(info->dev, "")?"all":info->dev);
}
static struct xtables_target static_2_way_nat_tg_reg = {
.version = XTABLES_VERSION,
.name = "STATIC-2-WAY-NAT",
.family = NFPROTO_IPV4,
.size = XT_ALIGN(sizeof(struct xt_static_nat_tginfo)),
.userspacesize = XT_ALIGN(sizeof(struct xt_static_nat_tginfo)),
.help = static_2_way_nat_tg_help,
.parse = static_2_way_nat_tg_parse,
.final_check = static_2_way_nat_tg_check,
.print = static_2_way_nat_tg_print,
.save = static_2_way_nat_tg_save,
.extra_opts = static_2_way_nat_tg_opts,
};
static __attribute__((constructor)) void static_2_way_nat_tg_ldr(void)
{
xtables_register_target(&static_2_way_nat_tg_reg);
}xt_STATIC-2-WAY.h：这是一个头文件，内核模块和用户态文件公用
#ifndef _LINUX_NETFILTER_XT_TARGET_STATICNAT
#define _LINUX_NETFILTER_XT_TARGET_STATICNAT 1
#define MAX_DEV_NAME 8
enum nat_dir {
DIR_SNAT,
DIR_DNAT,
DIR_NUM = 2
};
struct xt_static_nat_tginfo {
u_int32_t addr[DIR_NUM];
u_int16_t port[DIR_NUM];
u_int8_t proto;
u_int8_t dir;
char dev[MAX_DEV_NAME];
};
#endif /* _LINUX_NETFILTER_XT_TARGET_STATICNAT */obj-m += xt_STATIC-2-WAY-NAT.o
all: module xtlib
@true
module:
make -C /lib/modules/`uname -r`/build SUBDIRS=`pwd` modules
@rm -rf *.o .tmp_versions .*.mod.o .*.o.cmd *.mod.c .*.ko.cmd Module.symvers modules.order *.oo
xtlib:
gcc libxt_STATIC-2-WAY-NAT.c -fPIC -shared -o libxt_STATIC-2-WAY-NAT.so -L/usr/local/lib -lxtables
@rm -rf *.o .tmp_versions .*.mod.o .*.o.cmd *.mod.c .*.ko.cmd Module.symvers modules.order *.oo
clean:
rm -rf *.ko *.o .tmp_versions .*.mod.o .*.o.cmd *.mod.c .*.ko.cmd Module.symvers modules.order *.so *.oo如果你在寻找Linux上配置诸如Cisco设备上的static双向NAT的方法，这个或许就是你想要的； what？你觉得它完不成PAT？是的，它不行。但是想做PAT为何不使用现有的iptables实现呢？它可以自动为你解决元组唯一性问题。不要从概念上分析，事实上，static双向NAT是完全对称的，一对一的 ，也只有在BOX两边的网络在拓扑级别是完全对等的情形下，这种NAT或许才是有用的，Cisco设备经常处在这样的位置，比如一个很大的stub节点的出口位置，比如两个domain的中间位置... 我将名字取为STATIC-2-WAY-NAT，比较长也比较怪，完全不符合UNIX的小写短名传统，我的想法是：这样可以少写很多的帮助信息，因为名字就是自解释的。
一个可以直接使用的可用iptables配置的stateless NAT实现
标签：iptables stateless nat nat linux cisco
原文地址：http://blog.csdn.net/dog250/article/details/42196919
