登录密码比对疑问

数据库保存字段是md5（密码）,表单接收处理的密码是md5(密码+后缀)，这两个判断返回的逻辑值是true吗？为什么我昨晚试了，返回账户密码不正确，但是ajax返回值是ok，如果全部乱输入，则ajax返回的是null。如果密码不匹配为什么ajax返回ok？如果匹配为什么返回密码不正确？问题出在哪里？
1.IndexController.class.php:

<code><?php namespace Home\Controller;
use Think\Controller;
class IndexController extends Controller {
  public function index(){
    $this->display();
  }
  public function checkUserName(){
    if(!IS_AJAX){
      $data=array('errMsg' => '非法访问方式');
    }
    $userName=I('username','','htmlspecialchars');
    $userPass=I('userpass','','htmlspecialchars');
    $userInfo=D("Stuser")->getUserInfo($userName);
    if($userInfo['userpass']!=handleMd5Pass($userPass)){
      //echo $userInfo['userpass']."<br>";
      //echo handleMd5Pass($userPass);
      echo "用户名或密码不正确";
      //var_dump(handleMd5Pass($userPass));
    }
    if($userInfo){
      //$userInfo->where(array('id' => $userInfo['id']))->save($errMsg);
      session('userId',$userInfo['id']);
      $data=array(
        'info' => 'ok',
        'callback' => U('/stfjzd-13/index.php/Home/Index/index')
      );
    }
    $this->ajaxReturn($data);
  }

}
</code>

2.StuserModel.class.php

<code><?php namespace Home\Model;
  use Think\Model;
  //用户表模型
  class StuserModel extends Model{
    private $DB="";
    public function __construct(){
      //构造函数创建模型
      $this->DB=M("Stuser");
    }
    //数据库中检索用户数据，find()检索一条->Index
    public function getUserInfo($userName){
      //$res=$this->DB->field('username','userpass')->where('username="'.$userName.'"')->find();
      $userInfo=$this->DB->where('username="'.$userName.'"')->find();
      echo $this->DB->getLastSql();
      return $userInfo;
    }
  }
?>
</code>

3.Login.js

<code>$('.search_sub').click(function(event){
  event.preventDefault();
  var userName=$("#username").val();
  var userPass=$("#userpass").val();
  if(userPass=="" || userName==""){
    alert("登陆名称与密码不能为空");
    $("#username").focus();
    return false;
  }else{
    var url="/stfjzd-13/index.php/Home/Index/checkUserName";
    //var url="{U('/stfjzd-13/index.php/Home/Index/checkUserName')}";
    $.post(url,{username:userName,userpass:userPass},function(msg){
      if(msg.errMsg=="ok"){
        window.location.href=msg.callback;
      }else{
        alert(msg.errMsg);
      }
    },"JSON")
  }
})
</code>

回复内容：

数据库保存字段是md5（密码）,表单接收处理的密码是md5(密码+后缀)，这两个判断返回的逻辑值是true吗？为什么我昨晚试了，返回账户密码不正确，但是ajax返回值是ok，如果全部乱输入，则ajax返回的是null。如果密码不匹配为什么ajax返回ok？如果匹配为什么返回密码不正确？问题出在哪里？
1.IndexController.class.php:

<code><?php namespace Home\Controller;
use Think\Controller;
class IndexController extends Controller {
  public function index(){
    $this->display();
  }
  public function checkUserName(){
    if(!IS_AJAX){
      $data=array('errMsg' => '非法访问方式');
    }
    $userName=I('username','','htmlspecialchars');
    $userPass=I('userpass','','htmlspecialchars');
    $userInfo=D("Stuser")->getUserInfo($userName);
    if($userInfo['userpass']!=handleMd5Pass($userPass)){
      //echo $userInfo['userpass']."<br>";
      //echo handleMd5Pass($userPass);
      echo "用户名或密码不正确";
      //var_dump(handleMd5Pass($userPass));
    }
    if($userInfo){
      //$userInfo->where(array('id' => $userInfo['id']))->save($errMsg);
      session('userId',$userInfo['id']);
      $data=array(
        'info' => 'ok',
        'callback' => U('/stfjzd-13/index.php/Home/Index/index')
      );
    }
    $this->ajaxReturn($data);
  }

}
</code>

2.StuserModel.class.php

<code><?php namespace Home\Model;
  use Think\Model;
  //用户表模型
  class StuserModel extends Model{
    private $DB="";
    public function __construct(){
      //构造函数创建模型
      $this->DB=M("Stuser");
    }
    //数据库中检索用户数据，find()检索一条->Index
    public function getUserInfo($userName){
      //$res=$this->DB->field('username','userpass')->where('username="'.$userName.'"')->find();
      $userInfo=$this->DB->where('username="'.$userName.'"')->find();
      echo $this->DB->getLastSql();
      return $userInfo;
    }
  }
?>
</code>

3.Login.js

<code>$('.search_sub').click(function(event){
  event.preventDefault();
  var userName=$("#username").val();
  var userPass=$("#userpass").val();
  if(userPass=="" || userName==""){
    alert("登陆名称与密码不能为空");
    $("#username").focus();
    return false;
  }else{
    var url="/stfjzd-13/index.php/Home/Index/checkUserName";
    //var url="{U('/stfjzd-13/index.php/Home/Index/checkUserName')}";
    $.post(url,{username:userName,userpass:userPass},function(msg){
      if(msg.errMsg=="ok"){
        window.location.href=msg.callback;
      }else{
        alert(msg.errMsg);
      }
    },"JSON")
  }
})
</code>

<code>    if($userInfo['userpass']!=handleMd5Pass($userPass)){
        //此处只echo了错误，但是没有返回到前端。
      echo "用户名或密码不正确";
      //var_dump(handleMd5Pass($userPass));
    }
    if($userInfo){
        //你的代码运行到这里，用户名对，所以查出了userInfo，所以返回了ok。正确应该在密码验证错误的时候就返回给前端，不再往后运行
      session('userId',$userInfo['id']);
      $data=array(
        'info' => 'ok',
        'callback' => U('/stfjzd-13/index.php/Home/Index/index')
      );
    }
    $this->ajaxReturn($data);</code>

在注释中

echo "用户名或密码不正确";

这里 return