php / php/php-src

HashTable use-after-destroy during lazy proxy __get() with dynamic properties

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#20,612 1 comment 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
#[AllowDynamicProperties]
class RealInstance {
    public $_;
    public function __get($name) {
        global $obj;
        $obj->foo ??= $obj->$$a[] =&$$a;
        $a[] =$$a; 
        $x[!0] =$$a;
        return $this->name;
    }
}
class Proxy extends RealInstance {
    public function r_get($name) {
        return $this->$name;
    }
}
$rc = new ReflectionClass(Proxy::class);
$obj = $rc->newLazyProxy(function () {
    return new RealInstance;
});
$real = $rc->initializeLazyObject($obj);
var_dump($real->prop);

Resulted in this output:

/path/to/php-src/Zend/zend_hash.c(2699) : ht=0x7f6a9f802900 is already destroyed
php: /path/to/php-src/Zend/zend_hash.c:73: void _zend_is_inconsistent(const HashTable *, const char *, int): Assertion `0' failed.
Aborted
Notes

This bug triggers the same hash table use-after-destroy assertion as #20286 but via a different execution path.

Commit:

56795d2810e

Build configuration:

CC="clang" CXX="clang++" CFLAGS="-fsanitize=address -g -O0" CXXFLAGS="-fsanitize=address -g -O0" LDFLAGS="-fsanitize=address" ./buildconf --force && ./configure --enable-debug --enable-address-sanitizer --disable-shared --with-pic --enable-mbstring --with-zlib
PHP Version
PHP 8.6.0-dev (cli) (built: Nov 29 2025 14:32:34) (NTS DEBUG)
Copyright (c) The PHP Group
Zend Engine v4.6.0-dev, Copyright (c) Zend Technologies
    with Zend OPcache v8.6.0-dev, Copyright (c), by Zend Technologies
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

Run the supplied reproducer with the documented debug and AddressSanitizer build, then inspect the assertion in zend_hash.c and the lazy proxy path through __get(), newLazyProxy(), and initializeLazyObject(). Done means the reproducer no longer reaches the HashTable use-after-destroy assertion and a regression test covers this execution path.

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
Quiet
Clarity
Mostly clear
Newbie friendliness
42/100

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