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Unserialize and Autoload in php

Jul 25, 2016 am 09:03 AM

  1. $string = 'O:6:"Foobar":2:{s:3:"foo";s:1:"1";s:3: "bar";s:1:"2";}';

  2. $result = unserialize($string);
  3. var_dump($result);

  4. /*

  5. object(__PHP_Incomplete_Class)[ 1]
  6. public '__PHP_Incomplete_Class_Name' => string 'Foobar' (length=6)
  7. public 'foo' => string '1' (length=1)
  8. public 'bar' => string '2' (length =1)
  9. */
  10. ?>
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When deserializing an object, if the object’s class definition does not exist, then PHP will introduce an unfinished class Concept, namely: __PHP_Incomplete_Class. Although we have successfully deserialized at this time, we still cannot access the data in the object, otherwise the following error message will appear: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition.

This is not difficult, just do a forced type conversion and turn it into an array:

  1. $string = 'O:6:"Foobar":2:{s:3:"foo";s:1:"1";s:3 :"bar";s:1:"2";}';
  2. $result = (array)unserialize($string);
  3. var_dump($result);

  4. /*

  5. array
  6. '__PHP_Incomplete_Class_Name' => string 'Foobar' (length=6)
  7. 'foo' => string '1' (length=1)
  8. 'bar' => string '2' (length=1)
  9. * /
  10. ?>

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But if the system has Autoload activated, the situation will become more complicated. By the way: PHP actually provides a configuration option called unserialize_callback_func, but its meaning is similar to autoload. I won’t introduce it here. Let’s just talk about autoload. The example is as follows:

  1. spl_autoload_register(function($name) {
  2. var_dump($name);
  3. });
  4. $string = 'O:6:"Foobar":2:{s:3: "foo"; s: 1: "1"; s: 3: "bar"; s: 1: "2"; }';
  5. $result = (array)unserialize($string);
  6. var_dump($result) ;
  7. ?>
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Execute the above code and you will find that spl_autoload_register is triggered. Most of the time this makes sense, but if you encounter an improperly defined spl_autoload_register, it will be tragic, such as the following This code:

  1. spl_autoload_register(function($name) {
  2. include "/path/to/{$name}.php";
  3. });
  4. $string = 'O:6:"Foobar ": 2: {s: 3: "foo"; s: 1: "1"; s: 3: "bar"; s: 1: "2"; }';
  5. $result = (array)unserialize($ string);
  6. var_dump($result);
  7. ?>
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No doubt, because the class definition file cannot be found, an error is reported! It is definitely possible to change spl_autoload_register, but the premise is that you can change it. If third-party code is involved, we cannot make the decision without authorization. At this time, we need a way to allow unserialize to bypass autoload. The simplest way is to add the class we need FAKE out:

  1. spl_autoload_register(function($name) {
  2. include “/path/to/{$name}.php”;
  3. });
  4. class Foobar {} // Oh, Shit!
  5. $string = 'O:6:"Foobar":2:{s:3:"foo";s:1:"1";s:3:"bar";s:1:"2";}' ;
  6. $result = (array)unserialize($string);
  7. var_dump($result);
  8. ?>
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I have to say that the above code is really rubbish. To provide you with one person I wrote:

  1. spl_autoload_register(function($name) {
  2. include “/path/to/{$name}.php”;
  3. });

  4. $string = 'O:6:"Foobar":2:{s:3:"foo";s:1:"1";s:3:"bar";s:1:"2" ;}';

  5. $functions = spl_autoload_functions();
  6. foreach ($functions as $function) {
  7. spl_autoload_unregister($function);
  8. }

  9. $result = (array)unserialize($ string);

  10. foreach ($functions as $function) {

  11. spl_autoload_register($function);
  12. }
  13. var_dump($result);
  14. ?>
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Although there is a bit more code, at least there is no FAKE class, which makes it look more comfortable.



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