/*
* 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) 2002-2018 OpenVPN 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; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 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";
VOID NETIOAPI_API_
InitializeIpInterfaceEntry(PMIB_IPINTERFACE_ROW Row);
/*
* 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;
}
/*
* Return interface metric value for the specified interface index.
*
* Arguments:
* index : The index of TAP adapter.
* family : Address family (AF_INET for IPv4 and AF_INET6 for IPv6).
* is_auto : On return set to true if automatic metric is in use.
* Unused if NULL.
*
* Returns positive metric value or -1 on error.
*/
int
get_interface_metric(const NET_IFINDEX index, const ADDRESS_FAMILY family, int *is_auto)
{
DWORD err = 0;
MIB_IPINTERFACE_ROW ipiface;
InitializeIpInterfaceEntry(&ipiface);
ipiface.Family = family;
ipiface.InterfaceIndex = index;
if (is_auto)
{
*is_auto = 0;
}
err = GetIpInterfaceEntry(&ipiface);
/* On Windows metric is never > INT_MAX so return value of int is ok.
* But we check for overflow nevertheless.
*/
if (err == NO_ERROR && ipiface.Metric <= INT_MAX)
{
if (is_auto)
{
*is_auto = ipiface.UseAutomaticMetric;
}
return (int)ipiface.Metric;
}
return -1;
}
/*
* Sets interface metric value for specified interface index.
*
* Arguments:
* index : The index of TAP adapter.
* family : Address family (AF_INET for IPv4 and AF_INET6 for IPv6).
* metric : Metric value. 0 for automatic metric.
* Returns 0 on success, a non-zero status code of the last failed action on failure.
*/
DWORD
set_interface_metric(const NET_IFINDEX index, const ADDRESS_FAMILY family,
const ULONG metric)
{
DWORD err = 0;
MIB_IPINTERFACE_ROW ipiface;
InitializeIpInterfaceEntry(&ipiface);
ipiface.Family = family;
ipiface.InterfaceIndex = index;
err = GetIpInterfaceEntry(&ipiface);
if (err == NO_ERROR)
{
if (family == AF_INET)
{
/* required for IPv4 as per MSDN */
ipiface.SitePrefixLength = 0;
}
ipiface.Metric = metric;
if (metric == 0)
{
ipiface.UseAutomaticMetric = TRUE;
}
else
{
ipiface.UseAutomaticMetric = FALSE;
}
err = SetIpInterfaceEntry(&ipiface);
if (err == NO_ERROR)
{
return 0;
}
}
return err;
}
#endif /* ifdef _WIN32 */