Catching Button Tampering By a User C#

Question

Login Error

As you can see, I want to catch the exception if the user is tampering the Login Button if there are no values in the fields or if it doesn't match info in the database.

For example: The field has no values and I click Login button once, it says the error. After I clicked OK button, I click Login button again and now it says, "ExecuteReader requires an open and available Connection. The connection's current state is closed."

I use 3 tier Architecture Windows Application.

BEL:

    public SqlDataReader Login(BELLogin bellog)
    {
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = Con.getcon();
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "SELECT username,password FROM tbl_login WHERE username = @Username AND password = @Password";
        cmd.Parameters.AddWithValue("@Username", bellog.Acctname);
        cmd.Parameters.AddWithValue("@Password", bellog.Password);
        SqlDataReader dr = cmd.ExecuteReader();
        return dr;
    }

BAL:

public class BELLogin
{
    public string Acctname { get; set; }
    public string Password { get; set; }
}

DBConnection:

public SqlConnection getcon()
    {
        if (con.State == System.Data.ConnectionState.Closed)
            con.Open();
        else if (con.State == System.Data.ConnectionState.Open)
            con.Close();
        return con;
    }

    public DataTable ExeReader(SqlCommand cmd)
    {
        getcon();
        cmd.Connection = getcon();
        SqlDataReader dr = cmd.ExecuteReader();
        DataTable dt = new DataTable();
        dt.Load(dr);
        return dt;
    }

GUI:

private void btn_login_Click(object sender, EventArgs e)
    {
        BELog.Acctname = txb_accName.Text;
        BELog.Password = txb_password.Text;

        SqlDataReader dr;
        dr = BALog.Login(BELog);

        if (txb_accName.Text == "" || txb_password.Text == "")
        {
            MessageBox.Show("Some fields are empty. Please fill up all fields before clicking LOGIN button.", "Login Status", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
        else
        {
            if (dr.HasRows == true)
            {
                dr.Read();
                Inventory Inv = new Inventory();
                Inv.Show();
                this.Hide();
            }
            else
            {
                MessageBox.Show("You have entered your password or account name incorrectly. Please check your password and account name and try again.", "Login Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
        dr.Close();
}

Logging in is ok but what if the user tampering the button? Thank you for helping me :D

Answer 1

You need to change your code in gui like this:

//Put code to get the reader inside else clause and close the reader in the same else clause. Also ideally you should return if you encounter. I have added it and commented it.

//Off course you would need to put more effort to make this code better. You will get to that as you get more experience. For now this should make your app work.

private void btn_login_Click(object sender, EventArgs e)
{
     BELog.Acctname = txb_accName.Text;
     BELog.Password = txb_password.Text;

     if (txb_accName.Text == "" || txb_password.Text == "")
     {
         MessageBox.Show("Some fields are empty. Please fill up all fields before clicking LOGIN button.", "Login Status", MessageBoxButtons.OK, MessageBoxIcon.Error);
         //return;
     }
     else
     {
         SqlDataReader dr;
         dr = BALog.Login(BELog);

         if (dr.HasRows == true)
         {
             dr.Read();
             Inventory Inv = new Inventory();
             Inv.Show();
             this.Hide();
         }
         else
         {
             MessageBox.Show("You have entered your password or account name incorrectly. Please check your password and account name and try again.", "Login Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
         }

          dr.Close();
    }
}

Answer 2

1. Do not reuse connections like this, it is bad practice and unnecessary.
2. Wrap all type instances that implement IDisposable in using blocks so the resources are released. In your case SqlConnection, SqlCommand, SqlDataReader, DataTable.
3. From a security standpoint you should never store your user passwords (anywhere, not DB, not files, not registry, etc. just do not store them). You need to store the hash, not the password, and compare hashes

4. Adhere to loose the coupling / high cohesion principle. Essentially expose as little as possible (especially implementation details) from your methods / classes so they can be easily reused and changed. Currently you are passing around and sharing DB objects, this will make your code brittle and very difficult to track down where problems are. Here is your code with a little bit of refactoring, notice that if you have another issue with a connection during login it would now be very easy to figure out where that might be.

   // place in new code file public class UserManager{ public BELLogin FindLogin(string userName, string password){ if(string.IsNullOrEmpty(userName) || string.IsNullOrEmpty(password)) return null;

       using(var connection = new SqlConnection("connectionStringPointerFromAppConfigHere"))
       using(SqlCommand cmd = new SqlCommand("SELECT username,password FROM tbl_login WHERE username = @Username AND password = @Password", connection))
       {
           connection.Open();
           cmd.Parameters.AddWithValue("@Username", bellog.Acctname).SqlDbType = SqlDbType.VarChar;
   
           // BAD practice! Use a secure hash instead and store that not the password!
           cmd.Parameters.AddWithValue("@Password", bellog.Password).SqlDbType = SqlDbType.VarChar;
           using(SqlDataReader dr = cmd.ExecuteReader())
           {
               if(dr.Read())
                   return new BELLogin() {Acctname = dr.GetString(0), Password = dr.GetString(1)}; // passed in is same as in datareader
           }
       }
       return null;
   }
   

   }

From your login form class

private void btn_login_Click(object sender, EventArgs e)
{
    if (string.IsNullOrEmpty(txb_accName.Text) || string.IsNullOrEmpty(txb_password.Text))
    {
        MessageBox.Show("Some fields are empty. Please fill up all fields before clicking LOGIN button.", "Login Status", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
    else
    {
        var manager = new UserManager();
        var user = manager.FindLogin(txb_accName.Text, txb_password.Text);

        if (user != null)
        {
            Inventory Inv = new Inventory();
            Inv.Show();
            this.Hide();
        }
        else
        {
            MessageBox.Show("You have entered your password or account name incorrectly. Please check your password and account name and try again.", "Login Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }
}

Answer 3

Your btn_login_Click method appears to call BALog.Login(BELog) prior to checking if there are any valid values in the username and password textboxes. Simply move the validation to the top of btn_login_Click method, and return if the fields are empty:

    if (txb_accName.Text == "" || txb_password.Text == "")
    {
        MessageBox.Show("Some fields are empty. Please fill up all fields before clicking LOGIN button.", "Login Status", MessageBoxButtons.OK, MessageBoxIcon.Error);
        return;
    }

The code in the else portion of that if statement can stay where it is, just not inside an else. The method will exit due to return statement if there are no valid values in the username and password textboxes.

As others have suggested, you should review your code to ensure you really want this structure; but if you do want to keep it that way, this simple fix will solve your problem.

Answer 4

Just get rid of your DBConnection object, it's not really doing anything and just making your structure complex:

public BELLogin Login(BELLogin bellog)
{
    SqlConnection conn = new SqlConnection(connectionsString);
    try
    { 
        using (SqlCommand cmd = new SqlCommand())
        {
           conn.Open();
           cmd.Connection = conn;
           cmd.CommandType = CommandType.Text;
           cmd.CommandText = "SELECT username,password FROM tbl_login WHERE username = @Username AND password = @Password";
           cmd.Parameters.AddWithValue("@Username", bellog.Acctname);
           cmd.Parameters.AddWithValue("@Password", bellog.Password);
           //really this should be in a using as well. 
           //You be better off reading your data 
           //into a class and returnig the class not the reader.
           using (SqlDataReader dr = cmd.ExecuteReader())
           {
               BELLogin obj = new BELLogin();
               while(dr.Read())
               {
                    //populate obj
               }
               return obj;
           }
       }
   }
   finally
   {
       conn.Close();
       conn.Dispose();
   }
}

also the way you use it can cause memory leaks as your not explicitly disposing and closing your connections. Always dispose Sql objects in C#. Be wary of exceptions too. Any exceptions in your code will not close the connection, etc. This will result in memory leaks and connections locking