NetInjector/tcp.c at master · JPGuillemin/NetInjector · GitHub

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/*
 * name: tcp.c
 * this file is part of the "Net-Injector" project. It defines the write_tcp() function
 * Copyright (C) 2002 by Jean Philippe GUILLEMIN <jp.guillemin@free.fr>
 * license: This software is under GPL license
 * date: 04 17 2003
 * rev: 0.8


		 0                   1                   2                   3
		 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		|          Source Port          |       Destination Port        |
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		|                        Sequence Number                        |
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		|                    Acknowledgment Number                      |
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		|  Data |           |U|A|P|R|S|F|                               |
		| Offset| Reserved  |R|C|S|S|Y|I|            Window             |
		|       |           |G|K|H|T|N|N|                               |
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		|           Checksum            |         Urgent Pointer        |
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		|                    Options                    |    Padding    |
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
		|                             data                              |
		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

*/

#include "neti.h"

/* function that create the TCP header and data field
the result is a pointer (*tcp_packet) to the begining of TCP header
*/

int write_tcp(char *tcp_packet, int size, u_int32_t ip_saddr, u_int32_t ip_daddr){

	struct tcphdr *tcph;
	struct pseudohdr *pseudoh;
	unsigned char *tstamp;

	size = TCPHDR_SIZE + myhdr->tcp_opt_size + myhdr->data_size;

	pseudoh = (struct pseudohdr*) tcp_packet;		/* address of pseudo-header */
	tcph =  (struct tcphdr*) (tcp_packet+PSEUDOHDR_SIZE);	/* address of tcp-header */
	tstamp = (unsigned char*) (tcp_packet+PSEUDOHDR_SIZE+TCPHDR_SIZE); /* address of timestamp */
	data = (char*) (tcp_packet+PSEUDOHDR_SIZE+TCPHDR_SIZE+myhdr->tcp_opt_size);	/* address of begining of payload */

	memset(data, 0, myhdr->data_size);
	memset(tcp_packet, 0, PSEUDOHDR_SIZE+size);

	memcpy (data, payload, myhdr->data_size);

	/*filling TCP header */
	tcph->syn=myhdr->syn;
	tcph->ack=myhdr->ack;
	tcph->psh=myhdr->psh;
	tcph->rst=myhdr->rst;
	tcph->fin=myhdr->fin;
	tcph->urg=myhdr->urg;
	tcph->source = myhdr->inet_src_port;
	tcph->dest = myhdr->inet_dst_port;
	tcph->seq = random ();
	tcph->ack_seq = random ();
	/*tcph->th_x2 = 0;    not used */
	tcph->doff = 5 + myhdr->tcp_opt_size/4; 						/* size of TCP header in x32 bits */
	tcph->window = htons (myhdr->window); 	/* max window */
	tcph->check = 0;   						/* checksum will be set later */
	tcph->urg_ptr = 0;

	/*filling PSEUDO header */
	memcpy(&pseudoh->saddr, &ip_saddr, 4);
	memcpy(&pseudoh->daddr, &ip_daddr, 4);
	pseudoh->protocol	= 6; 	/* layer 4 protocole */
	pseudoh->lenght = htons(size);

	if (myhdr->tcp_opt_size) {
		u_int32_t randts = rand() ^ (rand() << 16);
		tstamp[0] = tstamp[1] = 1; /* NOOP */
		tstamp[2] = 8;
		tstamp[3] = 10; /* 10 bytes, kind+len+T1+T2 */
		memcpy(tstamp+4, &randts, 4); /* random */
		memset(tstamp+8, 0, 4); /* zero */
	}

	tcph->check = sum((u_int16_t *) tcp_packet, PSEUDOHDR_SIZE + size);

	return EXIT_SUCCESS;
}