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POraw sockets in c - bogus header length
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copied!<pre><code>#include<stdlib.h> #include<netinet/ip.h> #include<netinet/tcp.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netinet/in.h> #include<stdio.h> #include<unistd.h> #include<string.h> #include<sys/types.h> #define P 5000 /* lets flood the port */ unsigned short /* this function generates header checksums */ csum (unsigned short *buf, int nwords) { unsigned long sum; for (sum = 0; nwords > 0; nwords--) sum += *buf++; sum = (sum >> 16) + (sum & 0xffff); sum += (sum >> 16); return ~sum; } int main (void) { char ipp[10] = "1.2.3.4"; int s = socket (PF_INET, SOCK_RAW, IPPROTO_TCP); /* open raw socket */ char datagram[4096]; /* this buffer will contain ip header, tcp header, and payload. we'll point an ip header structure at its beginning, and a tcp header structure after that to write the header values into it */ struct ip *iph = (struct ip *) datagram; struct tcphdr *tcph = (struct tcphdr *) datagram + sizeof (struct ip); struct sockaddr_in sin; /* the sockaddr_in containing the dest. address is used in sendto() to determine the datagrams path */ sin.sin_family = AF_INET; sin.sin_port = htons (P);/* you byte-order >1byte header values to network byte order (not needed on big endian machines) */ sin.sin_addr.s_addr = inet_addr ("192.168.1.12"); memset (datagram, 0, 4096); /* zero out the buffer */ /* we'll now fill in the ip/tcp header values, see above for explanations */ iph->ip_hl = 5; iph->ip_v = 4; iph->ip_tos = 0; iph->ip_len = sizeof (struct ip) + sizeof (struct tcphdr); /* no payload */ iph->ip_id = htonl (54321); /* the value doesn't matter here */ iph->ip_off = 0; iph->ip_ttl = 255; iph->ip_p = 6; iph->ip_sum = 0; /* set it to 0 before computing the actual checksum later */ iph->ip_src.s_addr = inet_addr (ipp);/* SYN's can be blindly spoofed */ iph->ip_dst.s_addr = sin.sin_addr.s_addr; tcph->source = htons (1234); /* arbitrary port */ tcph->dest = htons (P); tcph->seq = random ();/* in a SYN packet, the sequence is a random */ tcph->ack_seq = 0;/* number, and the ack sequence is 0 in the 1st packet */ tcph->doff = 0; /* first and only tcp segment */ tcph->syn = 1; tcph->window = htonl (65535); /* maximum allowed window size */ tcph->check = 0;/* if you set a checksum to zero, your kernel's IP stack should fill in the correct checksum during transmission */ tcph->urg_ptr = 0; iph->ip_sum = csum ((unsigned short *) datagram, iph->ip_len >> 1); /* finally, it is very advisable to do a IP_HDRINCL call, to make sure that the kernel knows the header is included in the data, and doesn't insert its own header into the packet before our data */ { /* lets do it the ugly way.. */ int one = 1; const int *val = &one; if (setsockopt (s, IPPROTO_IP, IP_HDRINCL, val, sizeof (one)) < 0) printf ("Warning: Cannot set HDRINCL!\n"); } int i1=49; char i2 = 49; int cc = 0; int r1; while (cc<99) { ipp[6] = i1; ipp[7] = i2; if(i1 == 57) { break; } if(i2 == 57 ) { i2 = 48; i1++; } i2++; cc++; iph->ip_src.s_addr = inet_addr (ipp); if (sendto (s, /* our socket */ datagram, /* the buffer containing headers and data */ iph->ip_len, /* total length of our datagram */ 0, /* routing flags, normally always 0 */ (struct sockaddr *) &sin, /* socket addr, just like in */ sizeof (sin)) < 0) /* a normal send() */ printf ("error\n"); else printf ("sent \n"); } return 0; } </code></pre> <p>the code creates a raw socket with proper ip address and the source addrewss is 192.168.1.12...port 5000 ... the problem is that when i try to capture the packets sent using wireshark, it says something like bogus tcp headee length...should be atleast 20 ... how can i correct this error ... P.S. you can refer <a href="http://mixter.void.ru/rawip.html" rel="nofollow">link</a> for the code explanation if you find the code lengthy ... </p>

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