TCP Packet Sender errors - c

Question

I have been trying to create a tcp packet sender in c with the following code
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
int main(void){
char buffer[1024];
int packetsize[100];
char* source_ip = "192.168.2.1";
struct sockaddr_in serv;
struct iphdr *iph;
struct tcphdr *tcph;
int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);
serv.sin_family = AF_INET;
serv.sin_port = htons(80);
serv.sin_addr.s_addr = inet_addr ("8.8.8.8");
struct tcp_pseudo
{
uint32_t src_addr;
uint32_t dst_addr;
uint8_t zero;
uint8_t proto;
uint16_t length;
} pseudohead;
struct help_checksum
{
struct tcp_pseudo pshd;
struct tcphdr tcphd;
char tcpdata[1024];
} tcp_chk_construct;
// Create Packet Header
iph.ihl = 5;
iph.version = 4;
iph.tos = 0;
iph.tot_len = sizeof(struct iphdr) + packetsize;
iph.id = rand_cmwc();
iph.frag_off = 0;
iph.ttl = MAXTTL;
iph.protocol = IPPROTO_TCP;
iph.check = 0;
iph.saddr = source_ip;
iph.daddr = serv.sin_addr.s_addr;
// Create TCP Header
tcph.source = htons (1234);
tcph.dest = htons (80);
tcph.seq = 0;
tcph.ack_seq = 0;
tcph.doff = 5;
tcph.fin=0;
tcph.syn=1;
tcph.rst=0;
tcph.psh=0;
tcph.ack=0;
tcph.urg=0;
tcph.window = htons (5840);
tcph.check = 0;
tcph.urg_ptr = 0;
pseudohead.src_addr = iph->saddr;
pseudohead.dst_addr = iph->daddr;
pseudohead.dummy = 0;
pseudohead.proto = iph->protocol;
pseudohead.length = htons(sizeof(struct tcphdr) + packetsize);
tcp_chk_construct.pshd = pseudohead;
tcp_chk_construct.tcphd = tcph;
memcpy(tcp_chk_construct.tcpdata, buffer, packetsize);
tcph->check = in_cksum((unsigned short *) &tcp_chk_construct,
sizeof(struct tcp_pseudo) + sizeof(struct tcphdr) + packetsize);
memcpy(packetsize, (char *) &iph
, sizeof(iphdr));
memcpy(packetsize + sizeof(iphdr), (char *) &tcph
, sizeof(tcphdr));
memcpy(packetsize + sizeof(iphdr) + sizeof(tcphdr, buffer, packetsize);
if (sendto (sockfd, /* our socket */
buffer, /* the buffer containing headers and data */
iph->tot_len, /* total length of our datagram */
0, /* routing flags, normally always 0 */
(struct sockaddr *) &serv, /* socket addr, just like in */
sizeof (serv)) < 0) /* a normal send() */
{
printf ("error\n");
}
else
{
printf ("Packet Send \n");
}
}
I use the netinet/ip.h and netinet/tcp.h to make the actual tcp packet but I get the following errors when compiling my code:
error: variable has incomplete type 'struct iphdr'
struct iphdr iph;
forward declaration of 'struct iphdr'
struct iphdr iph;
error: invalid application of 'sizeof' to an incomplete type 'struct iphdr'
iph.tot_len = sizeof(struct iphdr) + packetsize;
error: no member named 'source' in 'struct tcphdr'
tcph.source = htons (1234);
error: no member named 'dest' in 'struct tcphdr'
tcph.dest = htons (80);
and so on for the tcp header.

Answer 1

One at a time.
warning: incompatible pointer to integer conversion initializing 'char' with an expression of type 'char [12]' [-Wint-conversion] char source_ip = "192.168.2.1";
This is due to the fact that you are trying to save a string literal in a char variable. Change the line to
char* source_ip = "192.168.2.1";
warning: implicit declaration of function 'inet_addr' is invalid in C99 [-Wimplicit-function-declaration] serv.sin_addr.s_addr = inet_addr ("8.8.8.8");
For this, include the header #include <arpa/inet.h>

Answer 2

Only compilation error resolved version of your original code. Not guaranteed to run.
[Compiler used - gcc 4.9.2 on Ubuntu 15.04]
Some code is commented since I could not understand its usage or found it ambiguous (e.g. use of 'packetsize' array variable - it is 'int' array but used in expression to calculate length using base address of array).
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
int main(void)
{
char buffer[1024];
int packetsize[100];
char *source_ip = "192.168.2.1";
struct sockaddr_in serv;
struct iphdr iph;
struct tcphdr tcph;
int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);
serv.sin_family = AF_INET;
serv.sin_port = htons(80);
serv.sin_addr.s_addr = inet_addr ("8.8.8.8");
struct tcp_pseudo
{
uint32_t src_addr;
uint32_t dst_addr;
uint8_t zero;
uint8_t proto;
uint16_t length;
} pseudohead;
struct help_checksum
{
struct tcp_pseudo pshd;
struct tcphdr tcphd;
char tcpdata[1024];
} tcp_chk_construct;
// Create Packet Header
iph.ihl = 5;
iph.version = 4;
iph.tos = 0;
//iph.tot_len = sizeof(struct iphdr) + packetsize;
iph.tot_len = sizeof(struct iphdr) + sizeof(struct tcphdr);
iph.id = rand_cmwc();
iph.frag_off = 0;
iph.ttl = MAXTTL;
iph.protocol = IPPROTO_TCP;
iph.check = 0;
iph.saddr = inet_addr(source_ip);
iph.daddr = serv.sin_addr.s_addr;
// Create TCP Header
tcph.source = htons (1234);
tcph.dest = htons (80);
tcph.seq = 0;
tcph.ack_seq = 0;
tcph.doff = 5;
tcph.fin=0;
tcph.syn=1;
tcph.rst=0;
tcph.psh=0;
tcph.ack=0;
tcph.urg=0;
tcph.window = htons (5840);
tcph.check = 0;
tcph.urg_ptr = 0;
//pseudohead.src_addr = iph.saddr;
//pseudohead.dst_addr = iph.daddr;
//pseudohead.dummy = 0;
//pseudohead.proto = iph.protocol;
//pseudohead.length = htons(sizeof(struct tcphdr) + packetsize);
//tcp_chk_construct.pshd = pseudohead;
//tcp_chk_construct.tcphd = tcph;
//memcpy(tcp_chk_construct.tcpdata, buffer, packetsize);
//tcph.check = in_cksum((unsigned short *) &tcp_chk_construct, sizeof(struct tcp_pseudo) + sizeof(struct tcphdr) + packetsize);
memcpy((void *)buffer, (void *) &iph , sizeof(struct iphdr));
memcpy((void *)buffer + sizeof(struct iphdr), (void *) &tcph , sizeof(struct tcphdr));
//memcpy(packetsize + sizeof(struct iphdr) + sizeof(struct tcphdr), buffer, packetsize);
if (sendto (sockfd, buffer, iph.tot_len, 0, (struct sockaddr *) &serv, sizeof (serv)) < 0)
{
printf ("error\n");
}
else
{
printf ("Packet Send \n");
}
return 0;
}