standard/syslog: the request shutdown hook calls closelog() even when the request never opened syslog #24308

Description

ext/standard/syslog.c installs an unconditional request shutdown hook:

PHP_RSHUTDOWN_FUNCTION(syslog)
{
	php_closelog();
	if (BG(syslog_device)) {
		free(BG(syslog_device));
		BG(syslog_device) = NULL;
	}
	return SUCCESS;
}

php_closelog() runs after every request, whether or not this request opened syslog. In a SAPI that serves more than one request per process, that closes a process-wide handle the request may not own, and the next request opens it again.

Note that the state to avoid this already exists: php_openlog() sets PG(have_called_openlog) = 1 and php_closelog() clears it (main/php_syslog.c:74-84), and php_module_startup() resets it to 0 (main/main.c:2317). The shutdown hook simply does not look at it.

Expected

A request that never calls openlog(), closelog() or syslog() should leave the process syslog handle alone. If the handle was opened outside PHP, for example by the embedding application or by a library in the same process, PHP should not close it.

Actual

Embedded SAPI, PHP 8.5.11 (Alpine 3.24.2, musl 1.2.6, OpenSSL 3.5.9), one worker process serving three requests with error_log = syslog and a script that only calls error_log("request"). strace of the worker:

1080  connect(15, {sa_family=AF_UNIX, sun_path="/dev/log"}, 12) = 0
1080  sendto(15, "<13>Oct 13 21:57:46 php: request\n", 33, 0, NULL, 0) = 33
1080  connect(14, {sa_family=AF_UNIX, sun_path="/dev/log"}, 12) = 0
1080  sendto(14, "<13>Oct 13 21:57:46 php: request\n", 33, 0, NULL, 0) = 33
1080  connect(14, {sa_family=AF_UNIX, sun_path="/dev/log"}, 12) = 0
1080  sendto(14, "<13>Oct 13 21:57:46 php: request\n", 33, 0, NULL, 0) = 33

Three requests, three connects: the handle does not survive a request boundary. In the same process, a host that opened syslog before running PHP loses it when the first request ends. php-fpm works around this by calling php_closelog() itself when it takes over the child, with the comment "ensure to close syslog not to interrupt with PHP syslog code" (sapi/fpm/fpm/fpm_stdio.c:144), which is the same interaction seen from the other side.

Suggested fix

Check the existing flag before closing:

PHP_RSHUTDOWN_FUNCTION(syslog)
{
	if (PG(have_called_openlog)) {
		php_closelog();
	}
	...
}

That keeps the per-request BG(syslog_device) cleanup, closes the handle when this request opened it, and leaves a host-owned handle alone.

Version

PHP 8.5.11, and the same code is in the current PHP-8.5 and master branches.