Refuse closing a MySQL connection another fiber is suspended in

mysqli_close(), mysqli_stmt_close() and a reconnect would free the
connection under the parked call; they throw while its stream is busy.

Author: bukka

ext/mysqli/mysqli_api.c

@@ -275,6 +275,12 @@ PHP_FUNCTION(mysqli_close)
 
 	MYSQLI_FETCH_RESOURCE_CONN(mysql, mysql_link, MYSQLI_STATUS_INITIALIZED);
 
+	/* Another fiber is suspended in a call on it, which the close would free */
+	if (mysql->mysql && mysqlnd_conn_is_busy(mysql->mysql->data)) {
+		zend_throw_error(NULL, "Concurrent access to a MySQL connection");
+		RETURN_THROWS();
+	}
+
 	php_mysqli_close(mysql, MYSQLI_CLOSE_EXPLICIT, ((MYSQLI_RESOURCE *)(Z_MYSQLI_P(mysql_link))->ptr)->status);
 	((MYSQLI_RESOURCE *)(Z_MYSQLI_P(mysql_link))->ptr)->status = MYSQLI_STATUS_UNKNOWN;
 
@@ -1470,6 +1476,11 @@ PHP_FUNCTION(mysqli_stmt_close)
 	}
 	MYSQLI_FETCH_RESOURCE_STMT(stmt, mysql_stmt, MYSQLI_STATUS_VALID);
 
+	if (stmt->stmt->data && mysqlnd_conn_is_busy(stmt->stmt->data->conn)) {
+		zend_throw_error(NULL, "Concurrent access to a MySQL connection");
+		RETURN_THROWS();
+	}
+
 	mysqli_stmt_close(stmt->stmt, false);
 	stmt->stmt = NULL;
 	php_clear_stmt_bind(stmt);

ext/mysqli/mysqli_nonapi.c

@@ -140,6 +140,10 @@ void mysqli_common_connect(INTERNAL_FUNCTION_PARAMETERS, bool is_real_connect, b
 	if (mysql->mysql && mysqli_resource &&
 		(mysqli_resource->status > MYSQLI_STATUS_INITIALIZED))
 	{
+		if (mysqlnd_conn_is_busy(mysql->mysql->data)) {
+			zend_throw_error(NULL, "Concurrent access to a MySQL connection");
+			RETURN_THROWS();
+		}
 		/* already connected, we should close the connection */
 		php_mysqli_close(mysql, MYSQLI_CLOSE_IMPLICIT, mysqli_resource->status);
 		/* the link is not connected anymore, even if the new connection fails */

ext/mysqli/tests/io_hooks_close_busy.phpt

@@ -0,0 +1,43 @@
+--TEST--
+IO hooks: closing a connection another fiber is suspended in throws instead of freeing it
+--EXTENSIONS--
+mysqli
+--SKIPIF--
+<?php
+require_once 'skipifconnectfailure.inc';
+?>
+--FILE--
+<?php
+require_once 'connect.inc';
+include __DIR__ . '/../../standard/tests/streams/hooks/scheduler.inc';
+
+$db = my_mysqli_connect($host, $user, $passwd, $db, $port, $socket);
+$stmt = $db->prepare('SELECT 1');
+$scheduler = new Scheduler();
+Io\Hooks\set_hooks($scheduler);
+
+$scheduler->spawn(function () use ($db) {
+    echo "A: query\n";
+    $r = $db->query('SELECT SLEEP(0.5) AS s');
+    echo "A: ", $r->fetch_assoc()['s'], "\n";
+});
+$scheduler->spawn(function () use ($db, $stmt) {
+    foreach ([fn () => $db->close(), fn () => $stmt->close(), fn () => $db->real_connect()] as $close) {
+        try {
+            $close();
+        } catch (Error $e) {
+            echo "B: ", $e->getMessage(), "\n";
+        }
+    }
+});
+$scheduler->loop();
+Io\Hooks\set_hooks(null);
+var_dump($db->close());
+?>
+--EXPECT--
+A: query
+B: Concurrent access to a MySQL connection
+B: Concurrent access to a MySQL connection
+B: Concurrent access to a MySQL connection
+A: 0
+bool(true)

ext/mysqlnd/mysqlnd.h

@@ -97,6 +97,9 @@ PHPAPI MYSQLND * mysqlnd_connection_connect(MYSQLND * conn,
 
 PHPAPI void mysqlnd_debug(const char *mode);
 
+/* An operation of another flow is on the connection's stream */
+PHPAPI bool mysqlnd_conn_is_busy(const MYSQLND_CONN_DATA *conn);
+
 /* Query */
 #define mysqlnd_fetch_into(result, flags, ret_val)	(result)->m.fetch_into((result), (flags), (ret_val) ZEND_FILE_LINE_CC)
 #define mysqlnd_fetch_row_c(result)						(result)->m.fetch_row_c((result))

ext/mysqlnd/mysqlnd_connection.c

@@ -27,6 +27,7 @@
 #include "mysqlnd_debug.h"
 #include "mysqlnd_ext_plugin.h"
 #include "zend_smart_str.h"
+#include "main/php_io_hooks.h"
 
 
 extern MYSQLND_CHARSET *mysqlnd_charsets;
@@ -2337,3 +2338,10 @@ mysqlnd_connection_init(const size_t client_flags, const bool persistent, MYSQLN
 	DBG_RETURN(ret);
 }
 /* }}} */
+
+PHPAPI bool mysqlnd_conn_is_busy(const MYSQLND_CONN_DATA *conn)
+{
+	MYSQLND_VIO *vio = conn ? conn->vio : NULL;
+	php_stream *stream = vio ? vio->data->m.get_stream(vio) : NULL;
+	return stream && php_io_stream_busy(stream);
+}