Fix GH-9589: dl() segfaults when module is already loaded

As of PHP 8.2.0, `zend_module_entry` structures are no longer copied,
so when a module is permanently loaded, and users try to dynamically
load that module again, the structure is corrupted[1], causing a
segfault on shutdown.

We catch that by checking whether any dynamically loaded module is
already loaded, and bailing out in that case without modifying the
`zend_module_entry` structure.

[1] <#9589 (comment)>

Closes GH-9689.

Author: cmb69

NEWS

@@ -5,6 +5,8 @@ PHP                                                                        NEWS
 - Core:
   . Fixed bug GH-9655 (Pure intersection types cannot be implicitly nullable)
     (Girgias)
+  . Fixed bug GH-9589 (dl() segfaults when module is already loaded). (cmb,
+    Arnaud)
 
 - Streams:
   . Fixed bug GH-9590 (stream_select does not abort upon exception or empty

ext/standard/dl.c

@@ -205,6 +205,11 @@ PHPAPI int php_load_extension(const char *filename, int type, int start_now)
 		return FAILURE;
 	}
 	module_entry = get_module();
+	if (zend_hash_str_exists(&module_registry, module_entry->name, strlen(module_entry->name))) {
+		DL_UNLOAD(handle);
+		zend_error(E_CORE_WARNING, "Module \"%s\" is already loaded", module_entry->name);
+		return FAILURE;
+	}
 	if (module_entry->zend_api != ZEND_MODULE_API_NO) {
 			php_error_docref(NULL, error_type,
 					"%s: Unable to initialize module\n"

ext/standard/tests/general_functions/gh9589.phpt

@@ -0,0 +1,10 @@
+--TEST--
+dl() segfaults when module is already loaded
+--EXTENSIONS--
+dl_test
+--FILE--
+<?php
+dl("dl_test");
+?>
+--EXPECT--
+Warning: Module "dl_test" is already loaded in Unknown on line 0