Fix bug #81719: mysqlnd/pdo password buffer overflow

Author: smalyshev

ext/mysqlnd/mysqlnd_wireprotocol.c

@@ -776,7 +776,8 @@ php_mysqlnd_change_auth_response_write(MYSQLND_CONN_DATA * conn, void * _packet)
 	MYSQLND_VIO * vio = conn->vio;
 	MYSQLND_STATS * stats = conn->stats;
 	MYSQLND_CONNECTION_STATE * connection_state = &conn->state;
-	zend_uchar * const buffer = pfc->cmd_buffer.length >= packet->auth_data_len? pfc->cmd_buffer.buffer : mnd_emalloc(packet->auth_data_len);
+	size_t total_packet_size = packet->auth_data_len + MYSQLND_HEADER_SIZE;
+	zend_uchar * const buffer = pfc->cmd_buffer.length >= total_packet_size? pfc->cmd_buffer.buffer : mnd_emalloc(total_packet_size);
 	zend_uchar * p = buffer + MYSQLND_HEADER_SIZE; /* start after the header */
 
 	DBG_ENTER("php_mysqlnd_change_auth_response_write");