@hacky02:~$ cat /Uebungen/Aufgabenblatt01/Aufgabe03/heap.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>


#define SECRETFILE "/Uebungen/Aufgabenblatt01/Aufgabe03/secret"
#define PASSFILE "/Uebungen/Aufgabenblatt01/Aufgabe03/pass"
#define ROOT_USER 1337



void loadsecret(char *file, char *data, int len) {
        FILE *fp;
        fp = fopen(file, "r");
   if (fp){
        fgets(data, len, fp);
           fclose(fp);
   } else {
      printf("Error opening %s\n", file);
      exit(-1);
   }
}

void usage(char *app) {
        printf("Usage: %s username password\n\n", app);
        exit(-1);
}


int main(int argc, char **argv) {

        /* Allocating space on the heap for preventing overwrite of SEIP */
        char *username = malloc(64);
        char *password = malloc(64);
        char *secret = malloc(128);

        /* Checking for arguments */
        if (argc < 3) usage(argv[0]);

        /* Loading password from file */
        loadsecret(PASSFILE, password, 20);
        loadsecret(SECRETFILE, secret, 128);

        /* Dropping privs, so nobody can get root */
        /*setresuid(getuid(),getuid(),getuid());
        setresgid(getgid(),getgid(),getgid());*/
   setresuid(ROOT_USER,ROOT_USER,ROOT_USER);
   setresgid(ROOT_USER,ROOT_USER,ROOT_USER);


        strcpy(username, argv[1]);

        if ( strncmp(password, argv[2],20) == 0 ) {
                printf("Welcome %s!\n",username);
                printf("The secret data for today is:\n%s\n",secret);
                /* beeing paranoid and deleting the data from memory */
                free(secret);
        }
}