CTF: pwn02

pwn02.c

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

int main()
{
  FILE *fp;
  char pass_stdin[32];
  char pass_file[32];
  int ret;

  setvbuf(stdout, NULL, _IONBF, 0);
  setvbuf(stdin, NULL, _IONBF, 0);

  fp = fopen("flag.txt", "r");
  fgets(pass_file, 32, fp);
  ret = strlen(pass_file);
  pass_file[ret - 1] = 0;
  fclose(fp);

  puts("Welcome to Pwn02!!!");
  puts("password: ");
  gets(pass_stdin);

  if(strcmp(pass_file, pass_stdin) == 0){
    puts("login success!!!");
    system("/bin/sh");
  }else{
    puts("login failed\n");
  }
}