diff options
Diffstat (limited to 'src/openvpn/block_dns.c')
| -rw-r--r-- | src/openvpn/block_dns.c | 332 |
1 files changed, 332 insertions, 0 deletions
diff --git a/src/openvpn/block_dns.c b/src/openvpn/block_dns.c new file mode 100644 index 0000000..cb3ce88 --- /dev/null +++ b/src/openvpn/block_dns.c @@ -0,0 +1,332 @@ +/* + * OpenVPN -- An application to securely tunnel IP networks + * over a single TCP/UDP port, with support for SSL/TLS-based + * session authentication and key exchange, + * packet encryption, packet authentication, and + * packet compression. + * + * Copyright (C) 2002-2010 OpenVPN Technologies, Inc. <sales@openvpn.net> + * 2015-2016 <iam@valdikss.org.ru> + * 2016 Selva Nair <selva.nair@gmail.com> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 + * as published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program (see the file COPYING included with this + * distribution); if not, write to the Free Software Foundation, Inc., + * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#ifdef HAVE_CONFIG_H +#include "config.h" +#elif defined(_MSC_VER) +#include "config-msvc.h" +#endif +#ifdef HAVE_CONFIG_VERSION_H +#include "config-version.h" +#endif + +#include "syshead.h" + +#ifdef _WIN32 + +#include <fwpmu.h> +#include <initguid.h> +#include <fwpmtypes.h> +#include <winsock2.h> +#include <ws2ipdef.h> +#include <iphlpapi.h> +#include "block_dns.h" + +/* + * WFP-related defines and GUIDs not in mingw32 + */ + +#ifndef FWPM_SESSION_FLAG_DYNAMIC +#define FWPM_SESSION_FLAG_DYNAMIC 0x00000001 +#endif + +// c38d57d1-05a7-4c33-904f-7fbceee60e82 +DEFINE_GUID( + FWPM_LAYER_ALE_AUTH_CONNECT_V4, + 0xc38d57d1, + 0x05a7, + 0x4c33, + 0x90, 0x4f, 0x7f, 0xbc, 0xee, 0xe6, 0x0e, 0x82 +); + +// 4a72393b-319f-44bc-84c3-ba54dcb3b6b4 +DEFINE_GUID( + FWPM_LAYER_ALE_AUTH_CONNECT_V6, + 0x4a72393b, + 0x319f, + 0x44bc, + 0x84, 0xc3, 0xba, 0x54, 0xdc, 0xb3, 0xb6, 0xb4 +); + +// d78e1e87-8644-4ea5-9437-d809ecefc971 +DEFINE_GUID( + FWPM_CONDITION_ALE_APP_ID, + 0xd78e1e87, + 0x8644, + 0x4ea5, + 0x94, 0x37, 0xd8, 0x09, 0xec, 0xef, 0xc9, 0x71 +); + +// c35a604d-d22b-4e1a-91b4-68f674ee674b +DEFINE_GUID( + FWPM_CONDITION_IP_REMOTE_PORT, + 0xc35a604d, + 0xd22b, + 0x4e1a, + 0x91, 0xb4, 0x68, 0xf6, 0x74, 0xee, 0x67, 0x4b +); + +// 4cd62a49-59c3-4969-b7f3-bda5d32890a4 +DEFINE_GUID( + FWPM_CONDITION_IP_LOCAL_INTERFACE, + 0x4cd62a49, + 0x59c3, + 0x4969, + 0xb7, 0xf3, 0xbd, 0xa5, 0xd3, 0x28, 0x90, 0xa4 +); + +/* UUID of WFP sublayer used by all instances of openvpn + 2f660d7e-6a37-11e6-a181-001e8c6e04a2 */ +DEFINE_GUID( + OPENVPN_BLOCK_OUTSIDE_DNS_SUBLAYER, + 0x2f660d7e, + 0x6a37, + 0x11e6, + 0xa1, 0x81, 0x00, 0x1e, 0x8c, 0x6e, 0x04, 0xa2 +); + +static WCHAR *FIREWALL_NAME = L"OpenVPN"; + +/* + * Default msg handler does nothing + */ +static inline void +default_msg_handler (DWORD err, const char *msg) +{ + return; +} + +#define CHECK_ERROR(err, msg) \ + if (err) { msg_handler (err, msg); goto out; } + +/* + * Add a persistent sublayer with specified uuid. + */ +static DWORD +add_sublayer (GUID uuid) +{ + FWPM_SESSION0 session; + HANDLE engine = NULL; + DWORD err = 0; + FWPM_SUBLAYER0 sublayer; + + memset (&session, 0, sizeof(session)); + memset (&sublayer, 0, sizeof(sublayer)); + + err = FwpmEngineOpen0 (NULL, RPC_C_AUTHN_WINNT, NULL, &session, &engine); + if (err != ERROR_SUCCESS) + goto out; + + sublayer.subLayerKey = uuid; + sublayer.displayData.name = FIREWALL_NAME; + sublayer.displayData.description = FIREWALL_NAME; + sublayer.flags = 0; + sublayer.weight = 0x100; + + /* Add sublayer to the session */ + err = FwpmSubLayerAdd0 (engine, &sublayer, NULL); + +out: + if (engine) + FwpmEngineClose0 (engine); + return err; +} + +/* + * Block outgoing port 53 traffic except for + * (i) adapter with the specified index + * OR + * (ii) processes with the specified executable path + * The firewall filters added here are automatically removed when the process exits or + * on calling delete_block_dns_filters(). + * Arguments: + * engine_handle : On successful return contains the handle for a newly opened fwp session + * in which the filters are added. + * May be closed by passing to delete_block_dns_filters to remove the filters. + * index : The index of adapter for which traffic is permitted. + * exe_path : Path of executable for which traffic is permitted. + * msg_handler : An optional callback function for error reporting. + * Returns 0 on success, a non-zero status code of the last failed action on failure. + */ + +DWORD +add_block_dns_filters (HANDLE *engine_handle, + int index, + const WCHAR *exe_path, + block_dns_msg_handler_t msg_handler + ) +{ + FWPM_SESSION0 session = {0}; + FWPM_SUBLAYER0 *sublayer_ptr = NULL; + NET_LUID tapluid; + UINT64 filterid; + FWP_BYTE_BLOB *openvpnblob = NULL; + FWPM_FILTER0 Filter = {0}; + FWPM_FILTER_CONDITION0 Condition[2] = {0}; + DWORD err = 0; + + if (!msg_handler) + msg_handler = default_msg_handler; + + /* Add temporary filters which don't survive reboots or crashes. */ + session.flags = FWPM_SESSION_FLAG_DYNAMIC; + + *engine_handle = NULL; + + err = FwpmEngineOpen0 (NULL, RPC_C_AUTHN_WINNT, NULL, &session, engine_handle); + CHECK_ERROR (err, "FwpEngineOpen: open fwp session failed"); + msg_handler (0, "Block_DNS: WFP engine opened"); + + /* Check sublayer exists and add one if it does not. */ + if (FwpmSubLayerGetByKey0 (*engine_handle, &OPENVPN_BLOCK_OUTSIDE_DNS_SUBLAYER, &sublayer_ptr) + == ERROR_SUCCESS) + { + msg_handler (0, "Block_DNS: Using existing sublayer"); + FwpmFreeMemory0 ((void **)&sublayer_ptr); + } + else + { /* Add a new sublayer -- as another process may add it in the meantime, + do not treat "already exists" as an error */ + err = add_sublayer (OPENVPN_BLOCK_OUTSIDE_DNS_SUBLAYER); + + if (err == FWP_E_ALREADY_EXISTS || err == ERROR_SUCCESS) + msg_handler (0, "Block_DNS: Added a persistent sublayer with pre-defined UUID"); + else + CHECK_ERROR (err, "add_sublayer: failed to add persistent sublayer"); + } + + err = ConvertInterfaceIndexToLuid (index, &tapluid); + CHECK_ERROR (err, "Convert interface index to luid failed"); + + err = FwpmGetAppIdFromFileName0 (exe_path, &openvpnblob); + CHECK_ERROR (err, "Get byte blob for openvpn executable name failed"); + + /* Prepare filter. */ + Filter.subLayerKey = OPENVPN_BLOCK_OUTSIDE_DNS_SUBLAYER; + Filter.displayData.name = FIREWALL_NAME; + Filter.weight.type = FWP_UINT8; + Filter.weight.uint8 = 0xF; + Filter.filterCondition = Condition; + Filter.numFilterConditions = 2; + + /* First filter. Permit IPv4 DNS queries from OpenVPN itself. */ + Filter.layerKey = FWPM_LAYER_ALE_AUTH_CONNECT_V4; + Filter.action.type = FWP_ACTION_PERMIT; + + Condition[0].fieldKey = FWPM_CONDITION_IP_REMOTE_PORT; + Condition[0].matchType = FWP_MATCH_EQUAL; + Condition[0].conditionValue.type = FWP_UINT16; + Condition[0].conditionValue.uint16 = 53; + + Condition[1].fieldKey = FWPM_CONDITION_ALE_APP_ID; + Condition[1].matchType = FWP_MATCH_EQUAL; + Condition[1].conditionValue.type = FWP_BYTE_BLOB_TYPE; + Condition[1].conditionValue.byteBlob = openvpnblob; + + err = FwpmFilterAdd0(*engine_handle, &Filter, NULL, &filterid); + CHECK_ERROR (err, "Add filter to permit IPv4 port 53 traffic from OpenVPN failed"); + + /* Second filter. Permit IPv6 DNS queries from OpenVPN itself. */ + Filter.layerKey = FWPM_LAYER_ALE_AUTH_CONNECT_V6; + + err = FwpmFilterAdd0(*engine_handle, &Filter, NULL, &filterid); + CHECK_ERROR (err, "Add filter to permit IPv6 port 53 traffic from OpenVPN failed"); + + msg_handler (0, "Block_DNS: Added permit filters for exe_path"); + + /* Third filter. Block all IPv4 DNS queries. */ + Filter.layerKey = FWPM_LAYER_ALE_AUTH_CONNECT_V4; + Filter.action.type = FWP_ACTION_BLOCK; + Filter.weight.type = FWP_EMPTY; + Filter.numFilterConditions = 1; + + err = FwpmFilterAdd0(*engine_handle, &Filter, NULL, &filterid); + CHECK_ERROR (err, "Add filter to block IPv4 DNS traffic failed"); + + /* Forth filter. Block all IPv6 DNS queries. */ + Filter.layerKey = FWPM_LAYER_ALE_AUTH_CONNECT_V6; + + err = FwpmFilterAdd0(*engine_handle, &Filter, NULL, &filterid); + CHECK_ERROR (err, "Add filter to block IPv6 DNS traffic failed"); + + msg_handler (0, "Block_DNS: Added block filters for all interfaces"); + + /* Fifth filter. Permit IPv4 DNS queries from TAP. + * Use a non-zero weight so that the permit filters get higher priority + * over the block filter added with automatic weighting */ + + Filter.weight.type = FWP_UINT8; + Filter.weight.uint8 = 0xE; + Filter.layerKey = FWPM_LAYER_ALE_AUTH_CONNECT_V4; + Filter.action.type = FWP_ACTION_PERMIT; + Filter.numFilterConditions = 2; + + Condition[1].fieldKey = FWPM_CONDITION_IP_LOCAL_INTERFACE; + Condition[1].matchType = FWP_MATCH_EQUAL; + Condition[1].conditionValue.type = FWP_UINT64; + Condition[1].conditionValue.uint64 = &tapluid.Value; + + err = FwpmFilterAdd0(*engine_handle, &Filter, NULL, &filterid); + CHECK_ERROR (err, "Add filter to permit IPv4 DNS traffic through TAP failed"); + + /* Sixth filter. Permit IPv6 DNS queries from TAP. + * Use same weight as IPv4 filter */ + Filter.layerKey = FWPM_LAYER_ALE_AUTH_CONNECT_V6; + + err = FwpmFilterAdd0(*engine_handle, &Filter, NULL, &filterid); + CHECK_ERROR (err, "Add filter to permit IPv6 DNS traffic through TAP failed"); + + msg_handler (0, "Block_DNS: Added permit filters for TAP interface"); + +out: + + if (openvpnblob) + FwpmFreeMemory0 ((void **)&openvpnblob); + + if (err && *engine_handle) + { + FwpmEngineClose0 (*engine_handle); + *engine_handle = NULL; + } + + return err; +} + +DWORD +delete_block_dns_filters (HANDLE engine_handle) +{ + DWORD err = 0; + /* + * For dynamic sessions closing the engine removes all filters added in the session + */ + if (engine_handle) + { + err = FwpmEngineClose0(engine_handle); + } + return err; +} + +#endif |