Code Review - SQL and Insertion Attacks (Warning: Not for Newbs)

Posted on 16th Feb 2014 by admin

Hey guys,

Its been a while, I know. Use to love coming here to answer peoples questions, but work and school have been keeping me too busy but do anything but lurk. I usually write all my code/apps by hand and over the past couple years created a common set of PHP functions that I implement on every site. This code continues to grow, and may become a framework one day (http://ryan.crawford.com/framework/default/). I wanted to present some of the crux functions for your consideration. Specifically I'd like to know what your best practices are in relation to preventing SQL insertion attacks, looking at the functions I use to control it:

Code: private $chars = array(
";" => "{00sc}", "'" => "{01sq}",
"!" => "{02ex}", "$" => "{03dl}",
"%" => "{04pr}", "<" => "{05ls}",
">" => "{06gt}", "=" => "{07eq}",
"&" => "{08an}", "#" => "{09pd}",
"," => "{10cm}", "/" => "{11fs}",
"*" => "{12as}", "\"=> "{13bs}"
);

/*
* Func: inject($str) - aptly named :)
* Desc: We'll be the only people doing SQL injection here
*/
function inject($str) {
return str_replace(array_keys($this->chars),
array_values($this->chars),$str);
}

/*
* Func: extract($str)
* Desc: Opposite of inject
*/
function extract($str) {
$str = str_replace(array_values($this->depc),
array_keys($this->depc),$str);

return str_replace(array_values($this->chars),
array_keys($this->chars),$str);
}

/*
* Func: query($query_data)
* Desc: Make a query on the database (SELECT)
* Note: If a log directory is defined, we will track queries
*/
function query($qdata) {
$result = mysql_query($qdata) or die("
Query: ".$qdata."

Issue: " . mysql_error());

// set the condition for the switch statement
$c = substr($qdata,0,strpos($qdata,' '));

if($c == "DELETE"||$c == "INSERT"||$c == "UPDATE") {
if(is_dir($this->cfg['logdir']))
$this->logLine($qdata,$this->cfg['qlog']);
return true;
}
if(mysql_num_rows($result)==0)
return false;

while($line = mysql_fetch_array($result,MYSQL_ASSOC)) {
$array_result[]=$this->extract($line);
}
return $array_result;
}

/*
* Func: iquery($array,$table)
* Desc: Insert data into the db(using just $_POST)
*/
function iquery($arr,$table) {
if(!$dataArr = $this->againstTable($arr,$table))
return false;
$n = 1;
// Loop to create SQL query
foreach($dataArr as $key => $value) {
$insertNames .= (sizeof($dataArr)==$n)? $key : $key.",";
$insertValues.= (sizeof($dataArr)==$n)? "'".$value."'" : "'".$value."',";
$n++;
}
$this->query("INSERT INTO ".$table." (".$insertNames.") VALUES (".$insertValues.");");
}


Basically, if you look at the array $chars, for inserted data I am searching for the keys and converting them to the values before insertion. It is a function I run all my inserts through. The query() function is what I do all my SELECTS with and it converts the characters back (the inject function encrypts, extract decrypts for lack of a better term). These are written object oriented so I still have access to PHP's extract if ever needed.

Question now being, what do you think of the effectiveness of this technique in terms of protecting against SQL injection? Are there ways to beat it? Are there better methods? Is this efficient? I'm not sure what algorithm PHP is using for str_replace, but the best ones don't run any faster than O(n). I don't think this runs any worse.