文件上载安全漏洞

我的代码中是否存在文件上传安全漏洞？我在服务器端使用apache。php.ini文件中启用了文件上载。

<?php
if ($_FILES["file"]["size"] < 100000)//maximum upload size is 100 kb
{
    if ($_FILES["file"]["error"] > 0)
    {
      echo "Return Code: " . $_FILES["file"]["error"] . "<br />";
    }
    else
    {
    if (file_exists("upload/" . $_FILES["file"]["name"]))
    {
      echo $_FILES["file"]["name"] . " already exists. ";
    }
    else
    {
      move_uploaded_file($_FILES["file"]["tmp_name"],"upload/" . $_FILES["file"]["name"]);
$var="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
$samp=str_shuffle($var);
$pass=substr($samp,0,20);// creating a random text for file name.
$ext = pathinfo($_FILES["file"]["name"], PATHINFO_EXTENSION);
$ext=".{$ext}";
$newfilename="upload/".$pass.$ext;
rename("upload/".$_FILES["file"]["name"],$newfilename );
    echo "Stored in: " . $newfilename;
echo "<br>extension : ".$ext;
  }
}
}
else
  echo "File size is too large..";
?>