Memory leaks when opcache preloading non-exist file

[YuanchengJiang]

Description

The following command:

USE_ZEND_ALLOC=1 /php-src/sapi/cli/php  -n -c '/php-src/tmp-php.ini' -d "extension_dir=/php-src/modules/" -d "zend_extension=/php-src/modules/opcache.so" -d "opcache.enable_cli=1" -d "opcache.preload=non_exist_file"

Resulted in this output:

Warning: PHP Startup: Failed to open stream: No such file or directory in Unknown on line 0

Fatal error: Failed opening required 'non_exist_file' (include_path='.:') in Unknown on line 0

=================================================================
==2657753==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 3040 byte(s) in 95 object(s) allocated from:
    #0 0x557630088c0e in malloc (/php-src/sapi/cli/php+0x1c88c0e) (BuildId: 41fa132f3fca034615336154396bda4da9dab77f)
    #1 0x5576321d7ab8 in zend_register_functions /php-src/Zend/zend_API.c:3030:19
    #2 0x5576321d039b in zend_register_module_ex /php-src/Zend/zend_API.c:2548:27
    #3 0x5576321da059 in zend_register_internal_module /php-src/Zend/zend_API.c:2564:9
    #4 0x557631cf3578 in php_register_extensions /php-src/main/main.c:2004:8
    #5 0x5576330c1184 in php_register_internal_extensions /php-src/main/internal_functions_cli.c:86:9
    #6 0x557631cf4186 in php_module_startup /php-src/main/main.c:2204:6
    #7 0x5576330c8ee8 in php_cli_startup /php-src/sapi/cli/php_cli.c:410:9
    #8 0x5576330c2876 in main /php-src/sapi/cli/php_cli.c:1307:6
    #9 0x7f9ef5718d8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
...
Indirect leak of 40 byte(s) in 1 object(s) allocated from:
    #0 0x557630088c0e in malloc (/php-src/sapi/cli/php+0x1c88c0e) (BuildId: 41fa132f3fca034615336154396bda4da9dab77f)
    #1 0x5576321d862e in zend_register_functions /php-src/Zend/zend_API.c:3056:30
    #2 0x5576321e862f in do_register_internal_class /php-src/Zend/zend_API.c:3382:3
    #3 0x5576321e7836 in zend_register_internal_class /php-src/Zend/zend_API.c:3446:9
    #4 0x5576321e77e8 in zend_register_internal_class_ex /php-src/Zend/zend_API.c:3409:19
    #5 0x55763156f891 in register_class_FilesystemIterator /php-src/ext/spl/spl_directory_arginfo.h:513:16
    #6 0x55763156acfb in zm_startup_spl_directory /php-src/ext/spl/spl_directory.c:2770:30
    #7 0x55763146d74e in zm_startup_spl /php-src/ext/spl/php_spl.c:728:2
    #8 0x5576321ca596 in zend_startup_module_ex /php-src/Zend/zend_API.c:2342:7
    #9 0x5576321cf431 in zend_startup_module_zval /php-src/Zend/zend_API.c:2357:10
    #10 0x557632277e94 in zend_hash_apply /php-src/Zend/zend_hash.c:2080:13
    #11 0x5576321ce68f in zend_startup_modules /php-src/Zend/zend_API.c:2480:2
    #12 0x557631cf4231 in php_module_startup /php-src/main/main.c:2222:2
    #13 0x5576330c8ee8 in php_cli_startup /php-src/sapi/cli/php_cli.c:410:9
    #14 0x5576330c2876 in main /php-src/sapi/cli/php_cli.c:1307:6
    #15 0x7f9ef5718d8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16

SUMMARY: AddressSanitizer: 26088 byte(s) leaked in 815 allocation(s).

PHP Version

PHP 8.4.0-dev

Operating System

ubuntu 22.04

[iluuu1994]

Hi @YuanchengJiang! Thanks for the report.

This is a known issue.

When the script is executed with user root, preloading forks the process to run the preload script with de-escalated permissions. I believe this is done for environments other than CLI (e.g. FPM) that may be run as root, but will spawn worker processes that run under a different user. Since the preloading script runs when FPM starts, we want to avoid running the script with root privileges. (If this is wrong, @bukka can correct me)

When that process terminates, it intentionally does not clean up after itself, I'm assuming to avoid accidental modifications to the shared memory region that is needed by the main process.

Note though that I'm not very familiar with the details. Anyway, since this is known, and the leak is just cosmetic (the process always terminates, there's no real leak), I'm closing this issue.