Add check_key_exists registry function

MSF side has been attempting to open keys to see if they exist, which isn't
fantastic as it results in an error. This change adds a function which indicates
to the caller if the given reg key exists.

c/meterpreter/source/extensions/stdapi/server/stdapi.c

@@ -87,6 +87,7 @@ Command customCommands[] =
 	COMMAND_REQ( "stdapi_sys_process_thread_set_regs", request_sys_process_thread_set_regs ),
 
 	// Registry
+	COMMAND_REQ( "stdapi_registry_check_key_exists", request_registry_check_key_exists ),
 	COMMAND_REQ( "stdapi_registry_load_key", request_registry_load_key ),
 	COMMAND_REQ( "stdapi_registry_unload_key", request_registry_unload_key ),
 	COMMAND_REQ( "stdapi_registry_open_key", request_registry_open_key ),
@@ -121,10 +122,7 @@ Command customCommands[] =
 	COMMAND_REQ( "stdapi_net_config_get_netstat", request_net_config_get_netstat ),
 
 #ifdef WIN32
-	{ "stdapi_net_config_get_proxy",
+	COMMAND_REQ( "stdapi_net_config_get_proxy", request_net_config_get_proxy_config),
-	  { request_net_config_get_proxy_config,			  { 0 }, 0 },
-	  { EMPTY_DISPATCH_HANDLER                                     },
-	},
 	// Resolve
 	COMMAND_REQ( "stdapi_net_resolve_host", request_resolve_host ),
 	COMMAND_REQ( "stdapi_net_resolve_hosts", request_resolve_hosts ),

c/meterpreter/source/extensions/stdapi/server/sys/registry/registry.c

@@ -3,6 +3,51 @@
 
 DWORD request_registry_create_key(Remote *remote, Packet *packet);
 
+/*!
+ * @brief Check to see if a registry key exists.
+ * @param remote Pointer to the \c Remote instance.
+ * @param packet Pointer to the request \c Packet instance.
+ * @returns Always returns \c ERROR_SUCCESS.
+ */
+DWORD request_registry_check_key_exists(Remote *remote, Packet *packet)
+{
+	Packet *response = packet_create_response(packet);
+	LPCTSTR baseKey = NULL;
+	HKEY rootKey = NULL;
+	HKEY resultKey = NULL;
+	BOOL exists = FALSE;
+	DWORD result;
+
+	rootKey = (HKEY)packet_get_tlv_value_uint(packet, TLV_TYPE_ROOT_KEY);
+	baseKey = packet_get_tlv_value_string(packet, TLV_TYPE_BASE_KEY);
+
+	if (rootKey && baseKey)
+	{
+		result = RegOpenKeyA(rootKey, baseKey, &resultKey);
+		if (result == ERROR_SUCCESS)
+		{
+			dprintf("[REG] Key found");
+			RegCloseKey(resultKey);
+			exists = TRUE;
+		}
+
+		dprintf("[REG] Key exists? %s", exists ? "TRUE" : "FALSE");
+		packet_add_tlv_bool(response, TLV_TYPE_BOOL, exists);
+		result = ERROR_SUCCESS;
+	}
+	else
+	{
+		dprintf("[REG] Invalid parameter");
+		result = ERROR_INVALID_PARAMETER;
+	}
+
+	dprintf("[REG] Returning result: %u %x", result, result);
+	packet_transmit_response(result, remote, response);
+
+	dprintf("[REG] done.");
+	return ERROR_SUCCESS;
+}
+
 /*
  * Opens a registry key and returns the associated HKEY to the caller if the
  * operation succeeds.  Right now this is just a wrapper around create_key

c/meterpreter/source/extensions/stdapi/server/sys/registry/registry.h

@@ -17,5 +17,6 @@ DWORD request_registry_enum_value(Remote *remote, Packet *packet);
 DWORD request_registry_delete_value(Remote *remote, Packet *packet);
 DWORD request_registry_load_key(Remote *remote, Packet *packet);
 DWORD request_registry_unload_key(Remote *remote, Packet *packet);
+DWORD request_registry_check_key_exists(Remote *remote, Packet *packet);
 
 #endif