[[질문]winsock을 사용하여 rawsocket으로 syn 패킷 보내기

#include <winsock2.h>
#include <stdio.h>
#include "ws2tcpip.h"  //IP_HDRINCL is here
 
struct ip_hdr
{
	unsigned char ip_ver;	//4bit ipv4 version
							//4bit ip header length
	unsigned char ip_tos;	//ip tos
	unsigned short ip_totallength;	//total length
	unsigned short ip_id;	//id
	unsigned short ip_off;	//offset
	unsigned char ip_ttl;	//ttl
	unsigned char ip_protocol;	//protocol
	unsigned short sum;			//checksum
	unsigned int ip_srcaddr;	//source
	unsigned int ip_destaddr;	//dest
};
 
 
struct tcp_hdr
{
	unsigned short th_sport;	//src port
	unsigned short th_dport;	//dest   port
	unsigned long	seq;		//sequence number
	unsigned long	ack;		//acknowledgement number
	unsigned char	data;		//offset
	unsigned char	flag;		//flag
	unsigned short  win;		//window
	unsigned short	sum;		//checksum
	unsigned short urgptr;		//urgent pointer
};
 
struct pseudohdr 
{
	unsigned int saddr;
	unsigned int daddr;
	unsigned char useless;
	unsigned char protocol;
	unsigned short tcplength;
};
 
unsigned short in_chksum(unsigned short *addr, int len)
{
	int sum = 0;
	int nleft = len;
	u_short *w=addr;
	u_short answer = 0;
	while(nleft >1)
	{
		sum +=*w++;
		nleft -= 2;
	}
	if(nleft == 1)
	{
		*(u_char *)(&answer) = *(u_char *)w;
		sum += answer;
	}
	sum = (sum >> 16) + (sum & 0xffff);
	sum += (sum >> 16);
	answer = ~sum;
	return (answer);
}
 
int main()
{
	struct sockaddr_in target_addr;
	struct sockaddr_in your_addr;
	ip_hdr *iphdr;
	tcp_hdr *tcphdr;
	pseudohdr * pe;
	SOCKET s;
	WSADATA wsaData;
    WORD wVersionRequested = MAKEWORD(2,2);
	char buf[1500], *data;
 
	int optval, nRet;
	int payload;
	payload = 1500;
 
	// Init WinSock
    nRet = WSAStartup(wVersionRequested, &wsaData);
    if (nRet)
    {
        fprintf(stderr,"\nError initializing WinSock\n");
        return 0;
    }
	// Check version
    if (wsaData.wVersion != wVersionRequested)
    {
        fprintf(stderr,"\nWinSock version not supported\n");
        return 0;
    }
 
	target_addr.sin_family = AF_INET;
	target_addr.sin_addr.s_addr = inet_addr("192.168.10.102");
	target_addr.sin_port = htons(1500);
	your_addr.sin_addr.s_addr = inet_addr("192.168.10.101");
	your_addr.sin_port = htons(1500);
 
	iphdr = (struct ip_hdr *)buf;
	tcphdr = (struct tcp_hdr *)&buf[sizeof(struct ip_hdr)];
	pe = (struct pseudohdr *)((char*)tcphdr-sizeof(struct pseudohdr));
 
	pe->saddr = your_addr.sin_addr.s_addr;
	pe->daddr = target_addr.sin_addr.s_addr;
	pe->protocol = IPPROTO_TCP; 
	pe->tcplength = htons(sizeof(struct tcp_hdr)); 
 
	iphdr->ip_ver = (4<<4) | (sizeof(ip_hdr) /sizeof(ULONG));
	iphdr->ip_tos = 0;
	iphdr->ip_totallength = htons(sizeof(ip_hdr) + sizeof(tcp_hdr) + payload);
	iphdr->ip_id = rand()%0xffff;
	iphdr->ip_off = 0;
	iphdr->ip_ttl = 8;
	iphdr->ip_protocol = IPPROTO_TCP;
	iphdr->sum = 0;
	iphdr->ip_srcaddr = inet_addr("192.168.10.101");
	iphdr->ip_destaddr = inet_addr("192.168.10.102");
	iphdr->sum = in_chksum((u_short *)&iphdr, sizeof(ip_hdr));
 
	tcphdr->th_sport = htons(1500);
	tcphdr->th_dport = htons(80);
	tcphdr->flag = 0x02;	//syn패킷
	tcphdr->data = 0;
	tcphdr->seq = htonl(100);
	tcphdr->ack = htonl(0);
	tcphdr->win = htons(512);
	tcphdr->urgptr = 0;
	tcphdr->sum = in_chksum((u_short *)pe,(sizeof(struct pseudohdr)+sizeof(struct tcp_hdr)));
 
	data = &buf[sizeof(ip_hdr) + sizeof(tcp_hdr)];
	memset(data,'@',payload);
 
	s = socket(AF_INET,SOCK_RAW,IPPROTO_RAW);
	optval = 1;
	setsockopt(s,IPPROTO_IP,IP_HDRINCL, (char *) &optval, sizeof(optval));
 
	sendto(s,buf,sizeof(ip_hdr) + sizeof(tcp_hdr)+payload, 0, (SOCKADDR *)&target_addr, sizeof(target_addr));
	// Free WinSock
    WSACleanup();
 
	return 0;
}