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Bug #78589 Memory leak with GC + __destruct()
Submitted: 2019-09-23 10:20 UTC Modified: 2019-09-23 10:35 UTC
From: nikic@php.net Assigned:
Status: Closed Package: Scripting Engine problem
PHP Version: 7.4Git-2019-09-23 (Git) OS:
Private report: No CVE-ID: None
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 [2019-09-23 10:20 UTC] nikic@php.net
Description:
------------
This is reduced from an OSS-Fuzz testcase involving unserialize(), but turns out to be some kind of generic GC bug. It is related to the changes to __destruct() handling in 7.4.

Test script:
---------------
class Test {
    public function __destruct() {} 
} 
 
$test = new Test; 
$test->foo = [&$test->foo];
$ary = [&$ary, $test];
unset($ary, $test);
gc_collect_cycles();

Actual result:
--------------
[Mon Sep 23 12:17:48 2019]  Script:  '/home/nikic/php-src-fuzz/t009.php'
Zend/zend_vm_execute.h(27609) :  Freeing 0x00007f8220201940 (32 bytes), script=/home/nikic/php-src-fuzz/t009.php
[Mon Sep 23 12:17:48 2019]  Script:  '/home/nikic/php-src-fuzz/t009.php'
/home/nikic/php-src-fuzz/Zend/zend_hash.c(256) :  Freeing 0x00007f82202588a0 (56 bytes), script=/home/nikic/php-src-fuzz/t009.php
[Mon Sep 23 12:17:48 2019]  Script:  '/home/nikic/php-src-fuzz/t009.php'
/home/nikic/php-src-fuzz/Zend/zend_hash.c(131) :  Freeing 0x00007f822025c280 (264 bytes), script=/home/nikic/php-src-fuzz/t009.php
=== Total 3 memory leaks detected ===


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 [2019-09-23 10:35 UTC] nikic@php.net
-Status: Open +Status: Analyzed
 [2019-09-23 10:35 UTC] nikic@php.net
The problem seems to be that we set gc_protected=1 during the zval destruction phase. However, in this case the destruction of the object wants to add the inner array to the GC buffer. (It was previously removed as nested data of the __destruct object.)
 [2019-09-24 10:19 UTC] nikic@php.net
Automatic comment on behalf of nikita.ppv@gmail.com
Revision: http://git.php.net/?p=php-src.git;a=commit;h=73115ef8730cc2466fdb039acb6b9463bc08808a
Log: Fixed bug #78589
 [2019-09-24 10:19 UTC] nikic@php.net
-Status: Analyzed +Status: Closed
 
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