tcp cheat

#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>


#define PACKET_LENGTH 8192


unsigned short csum(unsigned short *buf, int len)
{
        unsigned long sum;
        for(sum=0; len>0; len--){
                sum += *buf++;
        }
        sum = (sum >> 16) + (sum &0xffff);
        sum += (sum >> 16);
        return (unsigned short)(~sum);
}


int main(int argc, char *argv[])
{
        int sd;
        char buffer[PACKET_LENGTH];
        struct iphdr *ip = (struct iphdr *) buffer;
        struct tcphdr *tcp = (struct tcphdr *) (buffer + sizeof(struct iphdr));
        struct sockaddr_in sin, din;
        int one = 1;
        const int *val = &one;


        memset(buffer, '*', PACKET_LENGTH);
        if(argc != 5){
                printf("- Invalid parameters!!!\n");
                exit(-1);
        }


        sd = socket(PF_INET, SOCK_RAW, IPPROTO_TCP);
        if(sd < 0){
                perror("socket() error");
                exit(-1);
        }else{
                printf("socket()-SOCK_RAW and tcp protocol is OK.\n");
        }


        sin.sin_family = AF_INET;
        din.sin_family = AF_INET;
        sin.sin_port = htons(atoi(argv[2]));
        din.sin_port = htons(atoi(argv[4]));
        sin.sin_addr.s_addr = inet_addr(argv[1]);
        din.sin_addr.s_addr = inet_addr(argv[3]);


        ip->ihl = 5;
        ip->version = 4;
        ip->tos = 16;
        ip->tot_len = sizeof(struct iphdr) + sizeof(struct tcphdr)+200;
        ip->id = htons(54321);
        ip->frag_off = 0;
        ip->ttl = 64;
        ip->protocol = 6; // TCP
        ip->check = 0; // Done by kernel


        ip->saddr = inet_addr(argv[1]);
        ip->daddr = inet_addr(argv[3]);


        tcp->source = htons(atoi(argv[2]));
        tcp->dest = htons(atoi(argv[4]));
        tcp->seq = htonl(100);
        tcp->ack_seq = 0;
        tcp->syn = 0;
        tcp->ack = 0;
        tcp->window = htons(32767);
        tcp->check = 0; // Done by kernel
        tcp->urg_ptr = 0;
        ip->check = csum((unsigned short *) buffer, (sizeof(struct iphdr) + sizeof(struct tcphdr)));

     //告诉kernel packet中包含headers，常规编写客户端代码时，要使用connect函数，connect函数的作用就是实现与server端的三次握手，建立通信，所以在此处我们不调用connect
        if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) < 0){
                perror("setsockopt() error");
                exit(-1);
        }else{
                printf("setsockopt() is OK\n");
        }
        printf("Using :Source IP: %s port: %u, Target IP: %s port: %u.\n", argv[1], atoi(argv[2]), argv[3], atoi(argv[4]));


        unsigned int count;
        while(1){
                if(sendto(sd, buffer, ip->tot_len, 0, (struct sockaddr *)&sin, sizeof(sin)) < 0){
                        perror("sendto() error");
                        exit(-1);
                }else{
                        printf("sendto() is OK\n");
                }
                sleep(2);
        }
        close(sd);
        return 0;
}

=======================================================================================

./test 192.168.0.123 23 192.168.31.129 8008

============================================================================================================================================

接收端代码

#include <stdio.h>
#include <string.h>
#include <errno.h>  
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>  
#include <linux/in.h>
#include <linux/if_ether.h>
#include <net/if.h>
#include <sys/ioctl.h>


int main(int argc, char **argv) {
  int sock, n;
  char buffer[2048];
  unsigned char *iphead, *ethhead;
  struct ifreq ethreq;
  
  if ( (sock=socket(PF_PACKET, SOCK_RAW, 
                    htons(ETH_P_IP)))<0) {
    perror("socket");
    exit(1);
  }
#if 0
  /* Set the network card in promiscuos mode */
  strncpy(ethreq.ifr_name,"eth0",IFNAMSIZ);
  if (ioctl(sock,SIOCGIFFLAGS,?req)==-1) {
    perror("ioctl");
    close(sock);
    exit(1);
  }
  ethreq.ifr_flags|=IFF_PROMISC;
  if (ioctl(sock,SIOCSIFFLAGS,?req)==-1) {
    perror("ioctl");
    close(sock);
    exit(1);
  }
#endif  
  while (1) {
    printf("----------\n");
    n = recvfrom(sock,buffer,2048,0,NULL,NULL);
    printf("%d bytes read\n",n);


    /* Check to see if the packet contains at least 
     * complete Ethernet (14), IP (20) and TCP/UDP 
     * (8) headers.
     */
    if (n<42) {
      perror("recvfrom():");
      printf("Incomplete packet (errno is %d)\n",
             errno);
      close(sock);
      exit(0);
    }


    ethhead = buffer;
    printf("Source MAC address: "
           "%02x:%02x:%02x:%02x:%02x:%02x\n",
           ethhead[0],ethhead[1],ethhead[2],
           ethhead[3],ethhead[4],ethhead[5]);
    printf("Destination MAC address: "
           "%02x:%02x:%02x:%02x:%02x:%02x\n",
           ethhead[6],ethhead[7],ethhead[8],
           ethhead[9],ethhead[10],ethhead[11]);


    iphead = buffer+14; /* Skip Ethernet header */
    if (*iphead==0x45) { /* Double check for IPv4
                          * and no options present */
      printf("Source host %d.%d.%d.%d\n",
             iphead[12],iphead[13],
             iphead[14],iphead[15]);
      printf("Dest host %d.%d.%d.%d\n",
             iphead[16],iphead[17],
             iphead[18],iphead[19]);
      printf("Source,Dest ports %d,%d\n",
             (iphead[20]<<8)+iphead[21],
             (iphead[22]<<8)+iphead[23]);
      printf("Layer-4 protocol %d\n",iphead[9]);
    }
  }
}

================================================================================

结果：

254 bytes read
Source MAC address: 00:0c:29:5d:22:49
Destination MAC address: 00:50:56:f5:14:fa
Source host 192.168.0.123
Dest host 192.168.31.129
Source,Dest ports 23,1234
Layer-4 protocol 6