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SQLinjection

SQL injection问题在ASP上可是闹得沸沸扬扬当然还有不少国内外著名的PHP程序“遇难”。至于SQL injection的详情,网上的文章太多了,在此就不作介绍。
如果你网站空间的php.ini文件里的magic_quotes_gpc设成了off,那么PHP就不会在敏感字符前加上反斜杠(\),由于表单提交的内容可能含有敏感字符,如单引号('),就导致了SQL injection的漏洞。在这种情况下,我们可以用addslashes()来解决问题,它会自动在敏感字符前添加反斜杠。
但是,上面的方法只适用于magic_quotes_gpc=Off的情况。作为一个开发者,你不知道每个用户的magic_quotes_gpc是On还是Off,如果把全部的数据都用上addslashes(),那不是“滥杀无辜”了?假如magic_quotes_gpc=On,并且又用了addslashes()函数,那让我们来看看:
//如果从表单提交一个变量$_POST['message'],内容为 Tom's book
//这此加入连接MySQL数据库的代码,自己写吧
//在$_POST['message']的敏感字符前加上反斜杠
$_POST['message'] = addslashes($_POST['message']);

//由于magic_quotes_gpc=On,所以又一次在敏感字符前加反斜杠
$sql = "INSERT INTO msg_table VALUE('$_POST[message]');";

//发送请求,把内容保存到数据库内
$query = mysql_query($sql);

//如果你再从数据库内提取这个记录并输出,就会看到 Tom\'s book
?>


这样的话,在magic_quotes_gpc=On的环境里,所有输入的单引号(')都会变成(\')……
其实我们可以用get_magic_quotes_gpc()函数轻易地解决这个问题。当magic_quotes_gpc=On时,该函数返回TRUE;当magic_quotes_gpc=Off时,返回FALSE。至此,肯定已经有不少人意识到:问题已经解决。请看代码:
//如果magic_quotes_gpc=Off,那就为提单提交的$_POST['message']里的敏感字符加反斜杠
//magic_quotes_gpc=On的情况下,则不加
if (!get_magic_quotes_gpc()) {
$_POST['message'] = addslashes($_POST['message']);
} else {}
?>

其实说到这里,问题已经解决。下面再说一个小技巧。
有时表单提交的变量不止一个,可能有十几个,几十个。那么一次一次地复制/粘帖addslashes(),是否麻烦了一点?由于从表单或URL获取的数据都是以数组形式出现的,如$_POST、$_GET)那就自定义一个可以“横扫千军”的函数:
function quotes($content)
{
//如果magic_quotes_gpc=Off,那么就开始处理
if (!get_magic_quotes_gpc()) {
//判断$content是否为数组
if (is_array($content)) {
//如果$content是数组,那么就处理它的每一个单无
foreach ($content as $key=>$value) {
$content[$key] = addslashes($value);
}
} else {
//如果$content不是数组,那么就仅处理一次
addslashes($content);
}
} else {
//如果magic_quotes_gpc=On,那么就不处理
}
//返回$content
return $content;
}
?>

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