// decodepkt1.c
// $ gcc -Wall decodepkt1.c -o decodepkt

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <sys/user.h>
#include <sys/syscall.h>

#define TEXT_ADDRESS  0x400e70
#define FUNC_ADDRESS  0x401e9e


unsigned char g_request[0xd0] = {
	0x3b, 0x68, 0x1c, 0x94, 0xfa, 0x5c, 0x56, 0x4e, 
	0xa5, 0x70, 0x9f, 0xc4, 0xec, 0x64, 0x09, 0xc0, 
	0x49, 0x4a, 0x26, 0x7e, 0xe7, 0xc8, 0xb0, 0x69, 
	0xdb, 0x3a, 0x04, 0x1f, 0x91, 0x84, 0x09, 0xe2, 
	0x6a, 0x57, 0x2c, 0xf3, 0x61, 0x09, 0x9c, 0xc8, 
	0x31, 0xa6, 0x9c, 0xe5, 0x20, 0xd2, 0xa9, 0x68, 
	0x62, 0xf9, 0xd6, 0xc4, 0x7b, 0x06, 0x58, 0x73, 
	0xa6, 0x59, 0xa5, 0xc1, 0x9d, 0xa0, 0x6a, 0x9f, 
	0xb4, 0x78, 0x72, 0x39, 0x85, 0xc9, 0x94, 0x83, 
	0xeb, 0x0a, 0xd6, 0x51, 0xa6, 0xc9, 0xb4, 0x9e, 
	0xb1, 0x46, 0xda, 0xee, 0x4f, 0x4b, 0xfe, 0x08, 
	0x7a, 0x60, 0xf1, 0xcc, 0x7a, 0x61, 0x9c, 0xe1, 
	0x7e, 0xca, 0x8b, 0x96, 0xc7, 0x2c, 0x63, 0x39, 
	0xf3, 0x72, 0x41, 0xf4, 0xef, 0x1c, 0x24, 0x5a, 
	0xe8, 0xa9, 0xae, 0x8e, 0x33, 0x0d, 0x13, 0xda, 
	0xee, 0x5a, 0xfb, 0xfd, 0x42, 0x1b, 0xb6, 0xcd, 
	0xd5, 0xcd, 0xb1, 0xd8, 0x49, 0xcc, 0x12, 0x10, 
	0x7c, 0xb8, 0xfc, 0xc0, 0x00, 0xdb, 0xae, 0xd6, 
	0xeb, 0x88, 0x2c, 0xd8, 0x1f, 0x4b, 0x4e, 0x01, 
	0x9d, 0x76, 0xa6, 0x03, 0x7a, 0x02, 0xec, 0x5e, 
	0x51, 0x67, 0x70, 0x17, 0xf1, 0x83, 0xbf, 0x00, 
	0xa0, 0x71, 0x31, 0x8e, 0x8a, 0x5f, 0xe0, 0xa4, 
	0xd0, 0xe4, 0x8f, 0x9c, 0xf6, 0x76, 0xc3, 0x91, 
	0x2e, 0xfa, 0x62, 0x77, 0x89, 0xd9, 0x50, 0x51, 
	0x5e, 0xd5, 0x09, 0x31, 0x66, 0xc3, 0x63, 0x5b, 
	0x3f, 0x3f, 0x4c, 0x47, 0x61, 0xca, 0x0a, 0x00
};

void err(char *str)
{
	fprintf(stderr, "ERROR: %s\n", str);
}

void target(char *argv[], char *argp[])
{
	if(ptrace(PTRACE_TRACEME, 0, NULL, NULL) != -1)
		execve(argv[0], argv, NULL);
	else
		err("PTRACE_TRACEME");
	exit(0);
}

void print_data(void)
{
	int i;
	for(i=0; i < 0xd0; i++)
		printf("%c", g_request[i]);
}

void read_data(int pid, unsigned long addr, unsigned long *data, int len)
{
	int i;
	for(i=0; i < len; i++)
		data[i] = ptrace(PTRACE_PEEKDATA, pid, addr + (i * 8), NULL);
}

void write_data(int pid, unsigned long addr, unsigned long data)
{
	ptrace(PTRACE_POKEDATA, pid, addr, data);
}

void write_data2(int pid, unsigned long addr, unsigned long *data, int len)
{
	int i;
	for(i=0; i < len; i++)
		ptrace(PTRACE_POKEDATA, pid, addr + (i * 8), data[i]);
}

int control(int pid)
{
	int status;
	struct user_regs_struct regs;
	unsigned long flag = 0;

	while(1){
		waitpid(pid, &status, 0);
		if(WIFEXITED(status))
			break;
		ptrace(PTRACE_GETREGS, pid, 0, &regs);
		if(TEXT_ADDRESS == regs.rip){
			switch(flag)
			{
			case 0:
				flag = 1;
				write_data(pid, regs.rsp, TEXT_ADDRESS);
				write_data2(pid, regs.rsp + 8, (unsigned long *)g_request, 0x0d);
				regs.rdi = regs.rsp + 8 + 2;
				regs.rsi = 4;
				regs.rdx = regs.rsp + 0x0e;
				regs.rcx = regs.rsp + 0x0e;
				regs.r8  = 0xca;
				regs.rip = FUNC_ADDRESS;
				ptrace(PTRACE_SETREGS, pid, 0, &regs);
				break;
			case 1:
				flag = 2;
				regs.rsp -= 8;
				read_data(pid, regs.rsp + 8, (unsigned long *)g_request, 0x0d);
				// print_data();
				g_request[0x0a] = 0xaa;
				write_data(pid, regs.rsp, TEXT_ADDRESS);
				write_data2(pid, regs.rsp + 8, (unsigned long *)g_request, 0x0d);
				regs.rdi = regs.rsp + 0x10;
				regs.rsi = 8;
				regs.rdx = regs.rsp + 0x18;
				regs.rcx = regs.rsp + 0x18;
				regs.r8  = 0x14;
				regs.rip = FUNC_ADDRESS;
				ptrace(PTRACE_SETREGS, pid, 0, &regs);
				break; 
			case 2:
				regs.rsp -= 8;
				read_data(pid, regs.rsp + 8, (unsigned long *)g_request, 0x0d);
				print_data();
				return 0;
			}
		}
		ptrace(PTRACE_SINGLESTEP, pid, 0, NULL);
	}

	return 0;
}

int exec_prog(char *argv[], char *argp[])
{
	int pid;

	switch(pid = fork())
	{
	case 0:
		target(argv, argp);
		break;
	case -1:
		err("ERROR");
		break;
	default:
		control(pid);
		break;
	}
	return 0;
}

int main(int argc, char *argv[], char *argp[])
{
	if(argc < 2){
		fprintf(stderr, "%s <args>\n", argv[0]);
		return 1;
	}
	argv++;
	exec_prog(argv, argp);
	return 0;
}