Add per-extension child initialization hooks

UPGRADING.INTERNALS

@@ -14,6 +14,12 @@ PHP 8.7 INTERNALS UPGRADE NOTES
 1. Internal API changes
 ========================
 
+- Added zend_module_entry.child_init_func, an optional void callback invoked by
+  php_child_init() in the child process after core child initialization. It runs
+  in module dependency order for started modules and may run before a request
+  starts or during an active request. Use
+  STANDARD_MODULE_PROPERTIES_EX_WITH_CHILD_INIT(callback) to initialize it.
+  Modules without a callback continue to use STANDARD_MODULE_PROPERTIES_EX.
 - Removed the ZEND_LOG_XOR() macro.
 - Removed the ZEND_TRUTH() macro.
 - Removed zend_execute_scripts(). Manually call zend_execute_script() in a loop

Zend/zend_modules.h

@@ -30,7 +30,7 @@
 #define ZEND_MODULE_INFO_FUNC_ARGS zend_module_entry *zend_module
 #define ZEND_MODULE_INFO_FUNC_ARGS_PASSTHRU zend_module
 
-#define ZEND_MODULE_API_NO 20260925
+#define ZEND_MODULE_API_NO 20261024
 #ifdef ZTS
 #define USING_ZTS 1
 #else
@@ -45,7 +45,11 @@
 
 #define ZEND_MODULE_BUILD_ID "API" ZEND_TOSTR(ZEND_MODULE_API_NO) ZEND_BUILD_TS ZEND_BUILD_DEBUG ZEND_BUILD_SYSTEM ZEND_BUILD_EXTRA
 
-#define STANDARD_MODULE_PROPERTIES_EX 0, 0, NULL, 0, ZEND_MODULE_BUILD_ID
+#define STANDARD_MODULE_PROPERTIES_EX_WITH_CHILD_INIT(child_init) \
+	0, 0, NULL, 0, ZEND_MODULE_BUILD_ID, child_init
+
+#define STANDARD_MODULE_PROPERTIES_EX \
+	STANDARD_MODULE_PROPERTIES_EX_WITH_CHILD_INIT(NULL)
 
 #define NO_MODULE_GLOBALS 0, NULL, NULL, NULL
 
@@ -96,6 +100,7 @@ struct _zend_module_entry {
 	void *handle;
 	int module_number;
 	const char *build_id;
+	void (*child_init_func)(void);
 };
 
 #define MODULE_DEP_REQUIRED		1

ext/session/php_session.h

@@ -183,8 +183,6 @@ typedef struct _php_ps_globals {
 	bool mod_user_is_open;
 	bool mod_user_uses_object_methods_as_handlers;
 	bool use_trans_sid; /* contains the INI value of whether to use trans-sid */
-	bool random_seeded;
-
 	bool in_rfc1867_update;    /* php_session_rfc1867_update() is running */
 } php_ps_globals;
 

ext/session/session.c

@@ -400,18 +400,6 @@ static zend_long php_session_gc(bool immediate)
 	if ((PS(mod_data) || PS(mod_user_implemented))) {
 		/* Use probability-based GC if not forced and probability is configured */
 		if (!collect && PS(gc_probability) > 0) {
-			/* Seed lazily on first GC draw per process. */
-			if (UNEXPECTED(!PS(random_seeded))) {
-				php_random_uint128_t seed;
-				if (php_random_bytes_silent(&seed, sizeof(seed)) == FAILURE) {
-					seed = php_random_uint128_constant(
-						php_random_generate_fallback_seed(),
-						php_random_generate_fallback_seed()
-					);
-				}
-				php_random_pcgoneseq128xslrr64_seed128(PS(random).state, seed);
-				PS(random_seeded) = true;
-			}
 			collect = php_random_range(PS(random), 0, PS(gc_divisor) - 1) < PS(gc_probability);
 		}
 
@@ -3010,7 +2998,15 @@ static PHP_GINIT_FUNCTION(ps)
 		.algo = &php_random_algo_pcgoneseq128xslrr64,
 		.state = &ps_globals->random_state,
 	};
-	ps_globals->random_seeded = false;
+
+	php_random_uint128_t seed;
+	if (php_random_bytes_silent(&seed, sizeof(seed)) == FAILURE) {
+		seed = php_random_uint128_constant(
+			php_random_generate_fallback_seed(),
+			php_random_generate_fallback_seed()
+		);
+	}
+	php_random_pcgoneseq128xslrr64_seed128(ps_globals->random.state, seed);
 }
 
 /* Interfaces extending the given one are not flattened into ce->interfaces before they are
@@ -3445,6 +3441,13 @@ static zend_result php_session_rfc1867_callback(unsigned int event, void *event_
 	return retval;
 }
 
+static void php_session_child_init(void)
+{
+	/* Give each child a distinct, widely separated GC sequence without requesting new entropy. */
+	uint64_t advance = (uint64_t) getpid() << 32;
+	php_random_pcgoneseq128xslrr64_advance(PS(random).state, advance);
+}
+
 zend_module_entry session_module_entry = {
 	STANDARD_MODULE_HEADER,
 	"session",
@@ -3457,7 +3460,7 @@ zend_module_entry session_module_entry = {
 	PHP_GINIT(ps),
 	NULL,
 	NULL,
-	STANDARD_MODULE_PROPERTIES_EX
+	STANDARD_MODULE_PROPERTIES_EX_WITH_CHILD_INIT(php_session_child_init)
 };
 
 #ifdef COMPILE_DL_SESSION

ext/session/tests/gh22616.phpt

@@ -0,0 +1,99 @@
+--TEST--
+GH-22616: Session GC randomness is independent after a fork
+--EXTENSIONS--
+session
+pcntl
+--INI--
+session.gc_probability=1
+session.gc_divisor=2
+session.use_cookies=0
+session.cache_limiter=
+--FILE--
+<?php
+$handler = new class implements SessionHandlerInterface, SessionIdInterface, SessionUpdateTimestampHandlerInterface {
+    public bool $collected = false;
+
+    public function create_sid(): string { return 'gh22616'; }
+    public function validateId(string $id): bool { return true; }
+    public function updateTimestamp(string $id, string $data): bool { return true; }
+    public function open(string $path, string $name): bool { return true; }
+    public function close(): bool { return true; }
+    public function read(string $id): string|false { return ''; }
+    public function write(string $id, string $data): bool { return true; }
+    public function destroy(string $id): bool { return true; }
+    public function gc(int $max_lifetime): int|false {
+        $this->collected = true;
+        return 0;
+    }
+};
+session_set_save_handler($handler);
+session_id('gh22616');
+
+function sequence(): string {
+    global $handler;
+    if (session_status() === PHP_SESSION_ACTIVE) {
+        session_write_close();
+    }
+    $result = '';
+    for ($i = 0; $i < 256; $i++) {
+        $handler->collected = false;
+        session_start();
+        session_write_close();
+        $result .= (int) $handler->collected;
+    }
+    return $result;
+}
+
+$results = [];
+foreach (['unseeded', 'seeded', 'active'] as $state) {
+    if ($state === 'active') {
+        session_start();
+    }
+    $file1 = tempnam(sys_get_temp_dir(), 'gh22616');
+    $pid1 = pcntl_fork();
+    if ($pid1 === -1) {
+        throw new Exception('fork failed');
+    }
+    if ($pid1 === 0) {
+        file_put_contents($file1, sequence());
+        exit;
+    }
+
+    $file2 = tempnam(sys_get_temp_dir(), 'gh22616');
+    $pid2 = pcntl_fork();
+    if ($pid2 === -1) {
+        throw new Exception('fork failed');
+    }
+    if ($pid2 === 0) {
+        file_put_contents($file2, sequence());
+        exit;
+    }
+
+    $parent = sequence();
+    pcntl_waitpid($pid1, $status1);
+    pcntl_waitpid($pid2, $status2);
+    $child1 = file_get_contents($file1);
+    $child2 = file_get_contents($file2);
+    unlink($file1);
+    unlink($file2);
+    $results[$state] = pcntl_wifexited($status1)
+        && pcntl_wexitstatus($status1) === 0
+        && pcntl_wifexited($status2)
+        && pcntl_wexitstatus($status2) === 0
+        && strlen($child1) === 256
+        && strlen($child2) === 256
+        && $parent !== $child1
+        && $parent !== $child2
+        && $child1 !== $child2;
+}
+var_dump($results);
+?>
+--EXPECT--
+array(3) {
+  ["unseeded"]=>
+  bool(true)
+  ["seeded"]=>
+  bool(true)
+  ["active"]=>
+  bool(true)
+}

ext/zend_test/php_test.h

@@ -29,6 +29,7 @@ ZEND_TSRMLS_CACHE_EXTERN()
 #endif
 
 ZEND_BEGIN_MODULE_GLOBALS(zend_test)
+	zend_long child_init_count;
 	int observer_enabled;
 	int observer_show_output;
 	int observer_observe_all;

ext/zend_test/test.c

@@ -1603,6 +1603,13 @@ static PHP_INI_MH(OnUpdateZendTestObserveOplineInZendMM)
 	return OnUpdateBool(entry, new_value, mh_arg1, mh_arg2, mh_arg3, stage);
 }
 
+static ZEND_FUNCTION(zend_test_child_init_count)
+{
+	ZEND_PARSE_PARAMETERS_NONE();
+
+	RETURN_LONG(ZT_G(child_init_count));
+}
+
 static ZEND_FUNCTION(zend_test_fill_packed_array)
 {
 	HashTable *parameter;
@@ -2495,6 +2502,11 @@ PHP_MINFO_FUNCTION(zend_test)
 	DISPLAY_INI_ENTRIES();
 }
 
+static void zend_test_child_init(void)
+{
+	ZT_G(child_init_count)++;
+}
+
 zend_module_entry zend_test_module_entry = {
 	STANDARD_MODULE_HEADER,
 	"zend_test",
@@ -2509,7 +2521,7 @@ zend_module_entry zend_test_module_entry = {
 	PHP_GINIT(zend_test),
 	PHP_GSHUTDOWN(zend_test),
 	NULL,
-	STANDARD_MODULE_PROPERTIES_EX
+	STANDARD_MODULE_PROPERTIES_EX_WITH_CHILD_INIT(zend_test_child_init)
 };
 
 #ifdef COMPILE_DL_ZEND_TEST

ext/zend_test/test.stub.php

@@ -280,6 +280,8 @@ function zend_test_nodiscard(): int {}
     #[\NoDiscard(message: "custom message 2")]
     function zend_test_deprecated_nodiscard(): int {}
 
+    function zend_test_child_init_count(): int {}
+
     /** @alias zend_test_void_return */
     function zend_test_aliased(): void {}
 

ext/zend_test/tests/child_init.phpt

@@ -0,0 +1,39 @@
+--TEST--
+GH-22616: Extension child initialization runs once per fork in the child
+--EXTENSIONS--
+zend_test
+pcntl
+--FILE--
+<?php
+var_dump(zend_test_child_init_count());
+$pid = pcntl_fork();
+if ($pid === -1) {
+    throw new Exception('fork failed');
+}
+if ($pid === 0) {
+    var_dump(zend_test_child_init_count());
+    $pid = pcntl_fork();
+    if ($pid === -1) {
+        throw new Exception('fork failed');
+    }
+    if ($pid === 0) {
+        var_dump(zend_test_child_init_count());
+        exit;
+    }
+    pcntl_waitpid($pid, $status);
+    var_dump(pcntl_wifexited($status) && pcntl_wexitstatus($status) === 0);
+    var_dump(zend_test_child_init_count());
+    exit;
+}
+pcntl_waitpid($pid, $status);
+var_dump(pcntl_wifexited($status) && pcntl_wexitstatus($status) === 0);
+var_dump(zend_test_child_init_count());
+?>
+--EXPECT--
+int(0)
+int(1)
+int(2)
+bool(true)
+int(1)
+bool(true)
+int(0)