系统：centos 7
准备：安装libnetfilter_queue模块，可以yum安装，也可以网上下载rpm包安装
简介：使用iptables在NAT表上创建DNAT与SNAT规则，对数据包进行转发；在MANGLE表上的FORWARD链上创建NF_QUEUE规则对数据进行勾取并修改；（iptables只有mangle表可以修改数据）
示例规则：
//把到本机 50.24 8889端口的数据包，nat到50.4的8889端口
iptables -t nat -A PREROUTING -p udp -d 192.168.50.24 --dport 8889 -j DNAT --to 192.168.50.4
iptables -t nat -A POSTROUTING -p udp -d 192.168.50.4 --dport 8889 -j SNAT --to 192.168.50.24
//把目的地址50.4，目的端口8889的数据包，入队列 1
iptables -t mangle -A FORWARD -d 192.168.50.4 -p udp --dport 8889 -j NFQUEUE --queue-num 1
示例代码：
主线程DoListenIptablesThread负责对QUEUE队列数据的读取，读取到的数据通过回调PacketHandler方法解析处理，传入参数为 queue的 ID号
static void *DoListenIptablesThread(void *pData)
{
struct nfq_handle *h;
struct nfq_q_handle *qh;
struct nfnl_handle *nh;
int fd;
int rv;
int i;
pthread_t RecvPth[PthNUM];
char buf[QUEUE_BUFSIZE];
TCLEANFUNCT struTmp;
int nTmpError = -1;
int nNum = *(int *)pData;
free(pData);
pthread_detach(pthread_self()); memset(&struTmp, 0, sizeof(struTmp));
zlog_debug(cat,"opening library handle, nNum[%d]", nNum);
h = nfq_open();
if (!h)
{
nTmpError = errno;
zlog_debug(cat,"error during nfq_open(), nNum[%d]", nNum);
zlog_debug(cat,"nfq_open() errno[%d][%s]", nTmpError, strerror(nTmpError));
pthread_exit(0);
}
zlog_debug(cat,"unbinding existing nf_queue handler for AF_INET (if any), nNum[%d]", nNum);
if (nfq_unbind_pf(h, AF_INET) < 0)
{
nTmpError = errno;
zlog_debug(cat,"error during nfq_unbind_pf(), nNum[%d]", nNum);
zlog_debug(cat,"nfq_unbind_pf() errno[%d][%s]", nTmpError, strerror(nTmpError));
nfq_close(h);
pthread_exit(0);
}
zlog_debug(cat,"binding nfnetlink_queue as nf_queue handler for AF_INET, nNum[%d]", nNum);
if (nfq_bind_pf(h, AF_INET) < 0)
{
nTmpError = errno;
zlog_debug(cat,"error during nfq_bind_pf(), nNum[%d]", nNum);
zlog_debug(cat,"nfq_bind_pf() errno[%d][%s]", nTmpError, strerror(nTmpError));
nfq_close(h);
pthread_exit(0);
}
zlog_debug(cat,"binding this socket to queue [%d]", nNum);
qh = nfq_create_queue(h, nNum, &PacketHandler, &nNum);
if (!qh)
{
nTmpError = errno;
zlog_debug(cat,"error during nfq_create_queue(), nNum[%d]", nNum);
zlog_debug(cat,"nfq_create_queue() errno[%d][%s]", nTmpError, strerror(nTmpError));
nfq_close(h);
pthread_exit(0);
}
zlog_debug(cat,"setting copy_packet mode, nNum[%d]", nNum);
if (nfq_set_mode(qh, NFQNL_COPY_PACKET, 0xffff) < 0)
{
nTmpError = errno;
zlog_debug(cat,"can't set packet_copy mode, nNum[%d]", nNum);
zlog_debug(cat,"nfq_set_mode() errno[%d][%s]", nTmpError, strerror(nTmpError));
nfq_destroy_queue(qh);
nfq_close(h);
pthread_exit(0);
}
nh = nfq_nfnlh(h);
fd = nfnl_fd(nh);
struTmp.qh = qh;
struTmp.h = h;
for(i = 0;i<PthNUM;i++){
pthread_create(&RecvPth[i], NULL, DoRecvPacketThread,(void*)&struTmp);
struTmp.RecvPth[i] = RecvPth[i];
}
pthread_cleanup_push(FreePorcessResource, (void*)&struTmp);
zlog_debug(cat,"Waitting for message ..., nNum[%d]", nNum);
while ((rv = recv(fd, buf, sizeof(buf), 0)) && rv >= 0)
{
// 开始处理数据
//zlog_debug(cat,"-- New packet received -- rv[%d]", rv);
nfq_handle_packet(h, buf, rv);
memset(buf,0x00,sizeof(buf)); }
if (rv < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR) {
zlog_debug(cat, "error: [%s], wait for next event.", strerror(errno));
} else {
// recv error, free conncetion.
zlog_error(cat,"recv error: [%s]",strerror(errno));
}
}
pthread_cleanup_pop(0);
zlog_error(cat,"-- New packet received -- rv[%d] fd = [%d]", rv,fd);
zlog_debug(cat,"Exit DoNetFilter");
}
static int PacketHandler(struct nfq_q_handle *qh, struct nfgenmsg *nfmsg,struct nfq_data *nfa, void *data)
{
int id = 0;
struct nfqnl_msg_packet_hdr *ph;
u_int32_t mark,ifi;
struct iphdr *iph;
int iphdr_size;
int ret;char *nf_packet;
unsigned int nAppProto = -1;
int nReturnValue = 0;
char szHost[30] = {0};
ph = nfq_get_msg_packet_hdr(nfa);
if (ph)
{
id = ntohl(ph->packet_id);
}
mark = nfq_get_nfmark(nfa);
if (mark)
{
// DEBUG_LOG("mark=%u ", mark);
}
ifi = nfq_get_indev(nfa);
if (ifi)
{
// DEBUG_LOG("indev=%u ", ifi);
}
ifi = nfq_get_outdev(nfa);
if (ifi)
{
// DEBUG_LOG("outdev=%u ", ifi);
}
ret = nfq_get_payload(nfa, (unsigned char**)&nf_packet);
if ((ret >= 0))
{
//DEBUG_LOG("payload_len=%d bytes", ret);
//fputc('\n', stdout);
}
// parse the packet headers
iph = ((struct iphdr *) nf_packet);
iphdr_size = iph->ihl << 2;
if (iph->protocol == TCP_PRO)
{
struct tcphdr *tcp;
int tcphdr_size;
int clen;
tcp = ((struct tcphdr *) (nf_packet + (iph->ihl << 2)));
tcphdr_size = (tcp->doff << 2);
clen = ret - iphdr_size - tcphdr_size;
if(clen > 0)
{
//在此处修改数据包，修改数据包后执行下面两行代码，重新对数据进行校验，然后通知内核放行修改后的数据包 //set_tcp_checksum1(iph);
//return nfq_set_verdict(qh, id, NF_ACCEPT,(u_int32_t)ret, nf_packet); }
}
// if protocol is udp
if(iph->protocol == UDP_PRO)
{
int clen;
struct udphdr *udp;
udp = ((struct udphdr *) (nf_packet + (iph->ihl << 2)));
clen = ret - iphdr_size - UDP_HEADER_LEN;
if(clen > 0)
{
char* c;
PACKETINFO packinfo;
memset(&packinfo,0x00, sizeof(struct PACKETINFO));
c = nf_packet + iphdr_size + UDP_HEADER_LEN;
//在此处修改数据包，修改数据包后执行下面两行代码，重新对数据进行校验，然后通知内核放行修改后的数据包 //set_udp_checksum1(iph);
//return nfq_set_verdict(qh, id, NF_ACCEPT,(u_int32_t)ret, nf_packet);
}
}
return nfq_set_verdict(qh, id, NF_ACCEPT,0, NULL);
}
线程退出时资源释放代码：
主线程DoListenIptablesThread中recv的行为为阻塞，所以强制通过其他方式强制退出时，无法有效关闭并释放资源，通过FreePorcessResource对其资源进行关闭回收，并杀掉其开辟的线程；
void FreePorcessResource(void *pData)
{
TCLEANFUNCT *pTmp = NULL;
int i;
int kill_rc;
pTmp = (TCLEANFUNCT *)pData;
for(i = 0;i<PthNUM;i++){
if(!pTmp->RecvPth[i]) continue;
kill_rc = pthread_kill(pTmp->RecvPth[i], 0);
if (kill_rc == ESRCH)
{
zlog_debug(cat,"the specified thread did not exists or already quit --- ");
}
else if (kill_rc == EINVAL)
{
zlog_debug(cat,"signal is invalid --- ");
}
else
{
zlog_debug(cat,"the specified thread is alive --- ");
// 杀死该线程
pthread_cancel(pTmp->RecvPth[i]);
//pthread_join(m->second, NULL);
usleep(50*1000);
// 检测该线程是否存在
kill_rc = pthread_kill(pTmp->RecvPth[i], 0);
if (kill_rc == ESRCH)
{
zlog_debug(cat,"the specified thread did not exists or already quit +++ ");
}
else if (kill_rc == EINVAL)
{
zlog_debug(cat,"signal is invalid +++ ");
}
else
{
zlog_debug(cat,"signal is alive +++ ");
}
}
}
nfq_destroy_queue(pTmp->qh);
nfq_close(pTmp->h);
zlog_debug(cat,"closing pthread handle\n");
}
主线程DoListenIptablesThread创建的数据读取线程：(多核设备时，内核会通过多核接收数据，单线程recv数据时，系统接收缓存区会由于应用层recv过慢造成缓存区没有足够的空间，所以该处需要多线程recv处理)
static void *DoRecvPacketThread(void *pData){
TCLEANFUNCT *pTmp = NULL;
int rv;
int fd;
char buf[QUEUE_BUFSIZE];
struct nfnl_handle *nh;
pthread_detach(pthread_self());
pTmp = (TCLEANFUNCT *)pData;
nh = nfq_nfnlh(pTmp->h);
fd = nfnl_fd(nh);
while ((rv = recv(fd, buf, sizeof(buf), 0)) && rv >= 0)
{
// 开始处理数据
//zlog_debug(cat,"-- New packet received -- rv[%d]", rv);
nfq_handle_packet(pTmp->h, buf, rv);
memset(buf,0x00,sizeof(buf)); }
if (rv < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR) {
zlog_debug(cat, "error: [%s], wait for next event.", strerror(errno));
} else {
// recv error, free conncetion.
zlog_error(cat,"recv error: [%s]",strerror(errno));
}
}
zlog_error(cat,"-- New packet received -- rv[%d] fd = [%d]", rv,fd);
}
TCP与UDP数据修改后重新校验实现：
static u_int16_t checksum(u_int32_t init, u_int8_t *addr, size_t count){
/* Compute Internet Checksum for "count" bytes * beginning at location "addr". */
u_int32_t sum = init;
while( count > 1 ) {
/* This is the inner loop */
sum += ntohs(* (u_int16_t*) addr);
addr += 2;
count -= 2;
} /* Add left-over byte, if any */
if( count > 0 )
sum += ntohs(* (u_int8_t*) addr); /* Fold 32-bit sum to 16 bits */
while (sum>>16)
sum = (sum & 0xffff) + (sum >> 16);
return (u_int16_t)~sum;
}
static u_int16_t tcp_checksum2(struct iphdr* iphdrp, struct tcphdr* tcphdrp){
size_t tcplen = ntohs(iphdrp->tot_len) - (iphdrp->ihl<<2);
u_int32_t cksum = 0;
cksum += ntohs((iphdrp->saddr >> 16) & 0x0000ffff);
cksum += ntohs(iphdrp->saddr & 0x0000ffff);
cksum += ntohs((iphdrp->daddr >> 16) & 0x0000ffff);
cksum += ntohs(iphdrp->daddr & 0x0000ffff);
cksum += iphdrp->protocol & 0x00ff;
cksum += tcplen;
return checksum(cksum, (u_int8_t*)tcphdrp, tcplen);
}
static u_int16_t tcp_checksum1(struct iphdr* iphdrp){
struct tcphdr *tcphdrp = (struct tcphdr*)((u_int8_t*)iphdrp + (iphdrp->ihl<<2));
return tcp_checksum2(iphdrp, tcphdrp);
}
static void set_tcp_checksum2(struct iphdr* iphdrp, struct tcphdr* tcphdrp){
tcphdrp->check = 0;
tcphdrp->check = htons(tcp_checksum2(iphdrp, tcphdrp));
}
static void set_tcp_checksum1(struct iphdr* iphdrp){
struct tcphdr *tcphdrp = (struct tcphdr*)((u_int8_t*)iphdrp + (iphdrp->ihl<<2));
set_tcp_checksum2(iphdrp, tcphdrp);
}
static u_int16_t udp_checksum2(struct iphdr* iphdrp, struct udphdr* udphdrp){
size_t udplen = ntohs(iphdrp->tot_len) - (iphdrp->ihl<<2);
u_int32_t cksum = 0;
cksum += ntohs((iphdrp->saddr >> 16) & 0x0000ffff);
cksum += ntohs(iphdrp->saddr & 0x0000ffff);
cksum += ntohs((iphdrp->daddr >> 16) & 0x0000ffff);
cksum += ntohs(iphdrp->daddr & 0x0000ffff);
cksum += iphdrp->protocol & 0x00ff;
cksum += udplen;
return checksum(cksum, (u_int8_t*)udphdrp, udplen);
}
static u_int16_t udp_checksum1(struct iphdr* iphdrp){
struct udphdr *udphdrp = (struct udphdr*)((u_int8_t*)iphdrp + (iphdrp->ihl<<2));
return udp_checksum2(iphdrp, udphdrp);
}
static void set_udp_checksum2(struct iphdr* iphdrp, struct udphdr* udphdrp){
udphdrp->check = 0;
udphdrp->check = htons(udp_checksum2(iphdrp, udphdrp));
}
static void set_udp_checksum1(struct iphdr* iphdrp){
struct udphdr *udphdrp = (struct udphdr*)((u_int8_t*)iphdrp + (iphdrp->ihl<<2));
set_udp_checksum2(iphdrp, udphdrp);
}
程序内部宏定义整理：
#define MAC_LEN 12
#define UDP_PRO 17
#define TCP_PRO 6
#define VXLAN_HEADER_LEN 8
#define UDP_HEADER_LEN 8
#define TCP_HEADER_NO_OPERATION_LEN 20
#define QUEUE_BUFSIZE 8192
#define PthNUM 10
typedef struct __CleanFunct
{
struct nfq_q_handle *qh;
struct nfq_handle *h;
pthread_t RecvPth[PthNUM];
}TCLEANFUNCT;
程序需要头文件：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <netinet/in.h>
#include <linux/types.h>
#include <pthread.h>
#include <zlog.h>
#include <assert.h>
#include <linux/netfilter.h>
#include <libnetfilter_queue/libnetfilter_queue.h>
代码编译需要链接内容：
-lpthread -lnfnetlink -lnetfilter_queue
整理不易，转载请注明出处；