Bug #66052 [Com]: Serialized value ids are shared between nested serialization operations
Edit report at https://bugs.php.net/bug.php?id=66052&edit=1
ID: 66052
Comment by: adrien dot brault at gmail dot com
Reported by: crog at gustavus dot edu
Summary: Serialized value ids are shared between nested
serialization operations
Status: Open
Type: Bug
Package: *General Issues
PHP Version: 5.4.21
Block user comment: N
Private report: N
New Comment:
Another failing test case http://3v4l.org/JbqmH
Previous Comments:
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[2013-11-19 19:40:21] adrien dot brault at gmail dot com
Modified the test case and found another issue
http://3v4l.org/UCNin
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[2013-11-07 20:09:01] crog at gustavus dot edu
Description:
------------
The current serialization format does not specify value ids and instead relies on a count from the
beginning of the data. While this works fine for "standard" serialization, it breaks
horribly when custom serialization (via Serializable) is thrown into the mix.
In the case in which we first discovered this issue, we have an object which saves and loads its
data to a file, database or whatever (depending on the current implementation of the save() method).
It can then be saved/loaded via the save()/load() methods respectively, and this works fine.
To ensure that we weren't wasting time/resources, we also implemented the Serializable
interface and a serialize method which simply calls save() and returns a single string which can be
used to identify the location of our data (a filename if stored on the file system, row id if in the
database, etc.). Conversely, unserialize sets the source and calls load(). This, again, works fine
if used in isolation.
Now, where the problems arise is when the two are mixed. Our current file system implementation of
save() does its own serialization. If we call save() to save our data, but then load through it
through the unserialize operation, the serialized data's reference counts are all off by one
(as the original serialization didn't go through serialize). The same off-by-one bug shows up
if this is done in reverse (saved through serialize(), loaded through load()).
The effects of this bug are one of two things:
- The values simply point to the wrong variables. Very hard to debug and incredibly confusing to
anyone unfamiliar with the serialization format.
- The values point to non-existent values (-1 or max +1). This causes an error which reports the
byte offset into the serialized data where the error occurred.
The test below is rather convoluted for a test case, but demonstrates the problem as it relates to
the code in which we discovered it. I can, if necessary, attempt to provide further explanation or
additional details.
Test script:
---------------
class ObjectWithReferences {
protected $var1;
protected $var2;
protected $var3;
public function __construct() {
$this->var1 = new StdClass();
$this->var2 = null;
$this->var3 = $this->var1;
}
}
class WrapperObject implements Serializable
{
static $tempstorage;
protected $obj;
public function setObject($obj) {
$this->obj = $obj;
}
public function getObject() {
if (is_string($this->obj)) {
$this->obj = unserialize($this->obj);
}
return $this->obj;
}
public function save() {
$archive = (object) [
'object' => is_string($this->obj) ? $this->obj :
serialize($this->obj),
];
static::$tempstorage = json_encode($archive);
var_dump("Serialized:", static::$tempstorage);
}
public function load() {
$archive = json_decode(static::$tempstorage);
$this->obj = $archive->object;
}
public function serialize() {
$this->save(false);
return "wrapper!"; // Doesn't actually matter here.
}
public function unserialize($serialized) {
$this->load();
}
}
$owr = new ObjectWithReferences();
$wrapper = new WrapperObject();
$wrapper->setObject($owr);
$wrapper->save();
$wrapper->load();
var_dump($wrapper->getObject());
$serialized = serialize($wrapper);
$wrapper = unserialize($serialized);
var_dump($wrapper->getObject());
Expected result:
----------------
string 'Serialized:' (length=11)
string
'{"object":"O:20:\"ObjectWithReferences\":3:{s:7:\"\u0000*\u0000var1\";O:8:\"stdClass\":0:{}s:7:\"\u0000*\u0000var2\";N;s:7:\"\u0000*\u0000var3\";r:2;}"}'
(length=152)
object(ObjectWithReferences)[9]
protected 'var1' =>
object(stdClass)[10]
protected 'var2' => null
protected 'var3' =>
object(stdClass)[10]
string 'Serialized:' (length=11)
string
'{"object":"O:20:\"ObjectWithReferences\":3:{s:7:\"\u0000*\u0000var1\";O:8:\"stdClass\":0:{}s:7:\"\u0000*\u0000var2\";N;s:7:\"\u0000*\u0000var3\";r:3;}"}'
(length=152)
object(ObjectWithReferences)[8]
protected 'var1' =>
object(stdClass)[9]
protected 'var2' => null
protected 'var3' =>
object(stdClass)[9]
Actual result:
--------------
string 'Serialized:' (length=11)
string
'{"object":"O:20:\"ObjectWithReferences\":3:{s:7:\"\u0000*\u0000var1\";O:8:\"stdClass\":0:{}s:7:\"\u0000*\u0000var2\";N;s:7:\"\u0000*\u0000var3\";r:2;}"}'
(length=152)
object(ObjectWithReferences)[9]
protected 'var1' =>
object(stdClass)[10]
protected 'var2' => null
protected 'var3' =>
object(stdClass)[10]
string 'Serialized:' (length=11)
string
'{"object":"O:20:\"ObjectWithReferences\":3:{s:7:\"\u0000*\u0000var1\";O:8:\"stdClass\":0:{}s:7:\"\u0000*\u0000var2\";N;s:7:\"\u0000*\u0000var3\";r:3;}"}'
(length=152)
object(ObjectWithReferences)[8]
protected 'var1' =>
object(stdClass)[9]
protected 'var2' => null
protected 'var3' => null
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