Preventing SQL Injection in ASP.Net

Question

I have this code

UPDATE OPENQUERY (db,'SELECT * FROM table WHERE ref = ''"+ Ref +"'' AND bookno = ''"+ Session("number") +"'' ') 

How would I prevent SQL Injections on this?

UPDATE

Here's what i'm trying

SqlCommand cmd = new SqlCommand("Select * from Table where ref=@ref", con); 
cmd.Parameters.AddWithValue("@ref", 34);

For some reason everything I try and add it doesn't seem to work I keep getting SQL Command mentioned below.

The error is this

'SqlCommand' is a type and cannot be used as an expression

I'm taking over someone else's work so this is all new to me and I would like do things the right way so if anyone can provide any more help on how to make my query above safe from SQL injections then please do.

UPDATE NO 2

I added in the code as VasilP said like this

Dim dbQuery As [String] = "SELECT * FROM table WHERE ref = '" & Tools.SQLSafeString(Ref) & "' AND bookno = '" & Tools.SQLSafeString(Session("number")) & "'"

But I get an error Tools is not declared do I need to specify a certain namespace for it to work?

UPDATE

Has anyone got any ideas on the best of getting my query safe from SQL injection without the errors that i'm experiencing?

UPDATE

I now have it so it work without the parameters bit here's my updated source code any idea why it won't add the parameter value?

Dim conn As SqlConnection = New SqlConnection("server='server1'; user id='w'; password='w'; database='w'; pooling='false'")
   conn.Open()


Dim query As New SqlCommand("Select * from openquery (db, 'Select * from table where investor = @investor ') ", conn)
query.Parameters.AddWithValue("@investor", 69836)

dgBookings.DataSource = query.ExecuteReader
dgBookings.DataBind()

It works like this

Dim conn As SqlConnection = New SqlConnection("server='server1'; user id='w'; password='w'; database='w'; pooling='false'")
   conn.Open()


Dim query As New SqlCommand("Select * from openquery (db, 'Select * from table where investor = 69836') ", conn)

dgBookings.DataSource = query.ExecuteReader
dgBookings.DataBind()

The error i'm getting is this

An error occurred while preparing a query for execution against OLE DB provider 'MSDASQL'. 

And it's because it isn't replacing the @investor with the 69836

Any ideas?

SOLUTION

Here is how I solved my problem

Dim conn As SqlConnection = New SqlConnection("server='h'; user id='w'; password='w'; database='w'; pooling='false'")

conn.Open()

Dim query As New SqlCommand("DECLARE @investor varchar(10), @sql varchar(1000) Select @investor = 69836 select @sql = 'SELECT * FROM OPENQUERY(db,''SELECT * FROM table WHERE investor = ''''' + @investor + ''''''')' EXEC(@sql)", conn)

dgBookings.DataSource = query.ExecuteReader
dgBookings.DataBind()

Now I can write queries without the worry of SQL injection

Answer 1

Try using a parameterized query here is a link http://www.aspnet101.com/2007/03/parameterized-queries-in-asp-net/

Also, do not use OpenQuery... use the this to run the select

SELECT * FROM db...table WHERE ref = @ref AND bookno = @bookno

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More articles describing some of your options:

http://support.microsoft.com/kb/314520

What is the T-SQL syntax to connect to another SQL Server?

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Edited

Note: Your original question was asking about distributed queries and Linked servers. This new statement does not reference a distributed query. I can only assume you are directly connecting to the database now. Here is an example that should work. Here is another reference site for using SqlCommand.Parameters

SqlCommand cmd = new SqlCommand("Select * from Table where ref=@ref", con); 
cmd.Parameters.Add("@ref", SqlDbType.Int);
cmd.Parameters["@ref"] = 34;

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Edited:

Ok Jamie taylor I will try to answer your question again.

You are using OpenQuery becuase you are probably using a linked DB

Basically the problem is the OpenQuery Method takes a string you cannot pass a variable as part of the string you sent to OpenQuery.

You can format your query like this instead. The notation follows servername.databasename.schemaname.tablename. If you are using a linked server via odbc then omit databasename and schemaname, as illustrated below

    Dim conn As SqlConnection = New SqlConnection("your SQL Connection String")
    Dim cmd As SqlCommand = conn.CreateCommand()
    cmd.CommandText = "Select * db...table where investor = @investor"
    Dim parameter As SqlParameter = cmd.CreateParameter()
    parameter.DbType = SqlDbType.Int
    parameter.ParameterName = "@investor"
    parameter.Direction = ParameterDirection.Input
    parameter.Value = 34