Socket raw, can't get response from tcp server in tcp handshake - c

Question

I'm trying to send tcp SYN packet using socket raw with special structure sockaddr_ll, but my packet is ignored. My program should send SYN tcp packet and receive SYN/ACK packet. I tried to find a mistake and found that my packet has the wrong checksum and I fixed it, but nothing changed. How to fix it?
My packet:
My code:
int main(int argc, char *argv[])
{
int sockfd;
struct ifreq if_idx;
struct ifreq if_mac;
struct ifreq ifreq_ip;
int tx_len = 0;
unsigned char* sendbuf;
sendbuf=(unsigned char*)malloc(64);
memset(sendbuf,0,64);
struct ether_header *eh = (struct ether_header *) sendbuf;
struct iphdr *iph = (struct iphdr *) (sendbuf + sizeof(struct ether_header));
struct tcphdr *tcph = (struct tcphdr *) (sendbuf + sizeof(struct ether_header) + sizeof(struct tcphdr));
struct sockaddr_ll socket_address;
char ifName[IFNAMSIZ];
/* Get interface name */
if (argc > 1)
strcpy(ifName, argv[1]);
else
strcpy(ifName, DEFAULT_IF);
/* Open RAW socket to send on */
if ((sockfd = socket(AF_PACKET, SOCK_RAW, IPPROTO_TCP)) == -1) {
perror("socket");
}
/* Get the index of the interface to send on */
memset(&if_idx, 0, sizeof(struct ifreq));
strncpy(if_idx.ifr_name, ifName, IFNAMSIZ-1);
if (ioctl(sockfd, SIOCGIFINDEX, &if_idx) < 0)
perror("SIOCGIFINDEX");
/* Get the MAC address of the interface to send on */
memset(&if_mac, 0, sizeof(struct ifreq));
strncpy(if_mac.ifr_name, ifName, IFNAMSIZ-1);
if (ioctl(sockfd, SIOCGIFHWADDR, &if_mac) < 0)
perror("SIOCGIFHWADDR");
/* get ip */
memset(&ifreq_ip,0,sizeof(ifreq_ip));
strncpy(ifreq_ip.ifr_name,ifName,IFNAMSIZ-1);
if(ioctl(sockfd,SIOCGIFADDR,&ifreq_ip)<0)
{
printf("error in SIOCGIFADDR \n");
}
/* Construct the Ethernet header */
/* Ethernet header */
eh->ether_shost[0] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[0];
eh->ether_shost[1] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[1];
eh->ether_shost[2] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[2];
eh->ether_shost[3] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[3];
eh->ether_shost[4] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[4];
eh->ether_shost[5] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[5];
eh->ether_dhost[0] = MY_DEST_MAC0;
eh->ether_dhost[1] = MY_DEST_MAC1;
eh->ether_dhost[2] = MY_DEST_MAC2;
eh->ether_dhost[3] = MY_DEST_MAC3;
eh->ether_dhost[4] = MY_DEST_MAC4;
eh->ether_dhost[5] = MY_DEST_MAC5;
/* Ethertype field */
eh->ether_type = htons(ETH_P_IP);
tx_len += sizeof(struct ether_header);
/* ip header */
iph->ihl = 5;
iph->version = 4;
iph->tos = 0;
iph->tot_len = htons(sizeof (struct iphdr) + sizeof(struct tcphdr));
iph->id = htonl (01); //Id of this packet
iph->frag_off = 0;
iph->ttl = 64;
iph->protocol = IPPROTO_TCP;
iph->check = 0;
iph->saddr = inet_addr(inet_ntoa((((struct sockaddr_in *)&(ifreq_ip.ifr_addr))->sin_addr)));
iph->daddr = inet_addr ( "127.0.0.1" );
//Ip checksum
iph->check = 0xce7c;//csum ((unsigned short *) sendbuf, iph->tot_len);
tx_len += sizeof(struct iphdr);
//tcp
tcph->source = htons (20);
tcph->dest = htons (43521);
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 (8192);
tcph->check = 0; //leave checksum 0 now, filled later by pseudo header
tcph->urg_ptr = 0;
//Now the TCP checksum
struct pseudo_header psh;
char* pseudogram;
psh.source_address = inet_addr(inet_ntoa((((struct sockaddr_in *)&(ifreq_ip.ifr_addr))->sin_addr)));
psh.dest_address = inet_addr ( "127.0.0.1" );
psh.placeholder = 0;
psh.protocol = IPPROTO_TCP;
psh.tcp_length = htons(sizeof(struct tcphdr));
int psize = sizeof(struct pseudo_header) + sizeof(struct tcphdr);
pseudogram = (char*)malloc(psize);
memcpy(pseudogram , (char*) &psh , sizeof (struct pseudo_header));
memcpy(pseudogram + sizeof(struct pseudo_header) , tcph , sizeof(struct tcphdr));
tcph->check = csum( (unsigned short*) pseudogram , psize);
tx_len+= sizeof(struct tcphdr);
/* Index of the network device */
socket_address.sll_ifindex = if_idx.ifr_ifindex;
/* Address length*/
socket_address.sll_halen = ETH_ALEN;
/* Destination MAC */
socket_address.sll_addr[0] = MY_DEST_MAC0;
socket_address.sll_addr[1] = MY_DEST_MAC1;
socket_address.sll_addr[2] = MY_DEST_MAC2;
socket_address.sll_addr[3] = MY_DEST_MAC3;
socket_address.sll_addr[4] = MY_DEST_MAC4;
socket_address.sll_addr[5] = MY_DEST_MAC5;
socket_address.sll_family = AF_PACKET;
/* Send packet */
if (sendto(sockfd, sendbuf, tx_len, 0, (struct sockaddr*)&socket_address, sizeof(struct sockaddr_ll)) < 0)
printf("Send failed\n");
return 0;
}