php / php/php-src

Assertion failure in gc with invalid variable (OOM)

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#16,835 3 comments 0 reactions 0 assignees View on GitHub

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Bug Category: Engine Status: Verified
Dominant language
C
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Avg merge
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Merged PRs (30d)
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Description

Description

The following code:

<?php
$cls = new finfo();
class foo {
    public $x;
    static public $y;
    public function a() {
        return $this->x;
    }
    static public function b() {
        return self::$y;
    }
}
$foo = new foo;
$h = $foo->a()[0]->a;
$h = foo::b()[1]->b;
var_dump($h);
$fusion = $h;
$base = curl_init('http://www.google.com/');
curl_setopt($base, CURLOPT_RETURNTRANSFER, true);
$mh = curl_multi_init();
for ($i = 0; $fusion < 2; ++$i) {
    $ch = curl_copy_handle($base);
    curl_setopt($ch, CURLOPT_HTTPHEADER, ['Foo: Bar']);
    curl_multi_add_handle($mh, $ch);
}
?>

Resulted in this output:

php: Zend/zend_types.h:1346: uint32_t zend_gc_delref(zend_refcounted_h *): Assertion `p->refcount > 0' failed.
Aborted (core dumped)
PHP Version

nightly

Operating System

ubuntu 22.04

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the supplied PHP reproducer with a nightly build on Ubuntu 22.04, then inspect the assertion in Zend/zend_types.h at line 1346. Trace the invalid variable and reference-count changes through the reproducer; done means the script no longer aborts with the zend_gc_delref assertion.

Written by the indexing model from the issue text.

Assessment

Tech stack
c, php
Domain
backend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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