php / php/php-src

Timer leaks on pcntl_fork in ZTS build

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#12,298 8 comments 0 reactions 0 assignees View on GitHub

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Bug Extension: pcntl Status: Needs Triage
Dominant language
C
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Description

Description

The following code:

<?php
pcntl_fork();

Resulted in this output (in child process):

=================================================================
==58097==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 8 byte(s) in 1 object(s) allocated from:
    #0 0xffffa37f943b in malloc (/usr/lib/aarch64-linux-gnu/libasan.so.5+0xcf43b)
    #1 0xffffa3622aaf in timer_create ../sysdeps/unix/sysv/linux/timer_create.c:59
    #2 0xaaaacd663a6b in zend_max_execution_timer_init /usr/local/src/php/Zend/zend_max_execution_timer.c:46
    #3 0xaaaacd2913c7 in init_executor /usr/local/src/php/Zend/zend_execute_API.c:202
    #4 0xaaaacd2e3497 in zend_activate /usr/local/src/php/Zend/zend.c:1257
    #5 0xaaaacd0b09c3 in php_request_startup /usr/local/src/php/main/main.c:1758
    #6 0xaaaacd7b92db in do_cli /usr/local/src/php/sapi/cli/php_cli.c:934
    #7 0xaaaacd7bbd57 in main /usr/local/src/php/sapi/cli/php_cli.c:1340
    #8 0xffffa08c7da3 in __libc_start_main ../csu/libc-start.c:308
    #9 0xaaaacbea50f3  (/opt/php/debug-zts-asan/bin/php+0x5b50f3)

There's an explicit comment that this shouldn't be freed after a fork:

void zend_max_execution_timer_shutdown(void) /* {{{ */
{
	/* Don't try to delete a timer created before a call to fork() */
	if (EG(pid) != getpid()) {
		return;
	}

So paging @dunglas who wrote that comment.

PHP Version

PHP 8.3

Operating System

No response

Contributor guide

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First steps

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  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

Reproduce the PHP 8.3 ZTS case with pcntl_fork under AddressSanitizer, then read zend_max_execution_timer.c alongside the initialization and shutdown paths shown in the report. Use the child-process leak trace as the baseline; done means the reproducer no longer reports the leaked timer without regressing timer handling in the parent process.

Written by the indexing model from the issue text.

Assessment

Tech stack
c, php
Domain
backend, operating-systems
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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