Windows8核心态网络过滤研究

Windows 8是微软公司推出的最新的客户端操作系统，内部名称Windows NT 80。相对于Windows NT 5.x，其网络结构变化非常大，原有的TDI，NDIS系统挂接方法不再适用。在Windows8系统中，微软引入了两种新的网络过滤系统，WFP和NDISfilter。

 WFP (Windows Filtering Platform)

其包含从用户态到核心态的一系列应用层，根据需要可以在某一层设置回调函数拦截数据。

1、  callout

callout是WFP系统提供的扩展其功能的一种机制，callout由一组callout函数组成，每组有三种函数，

ClassifyFunction，处理收到的网络数据，例如端口号IP地址等。NotifyFunction，处理加载、删除callout事件。

FlowDeleteFunction，删除层与层之间关联的上下文。

callout由callout驱动具体实现，每个驱动可以注册多个callout。

2、WFP的层和层数据

WFP有很多层,每一层分成若干子层，具体有哪些请参阅微软文档,我以FWPM_LAYER_ALE_FLOW_ESTABLISHED_V4层为例进行讲解。这层位于ALE层，是其子层之一。面向连接的应用程序准备连接，面向无连接的程序准备通信，都发生在这一层。如果在这里拒绝了上述操作，应用程序就不能访问网络，这类似以前的TDI程序的Create事件，就是应用程序访问网络的请求刚到协议栈还没有处理。WFP每一层都有其特定的数据，根据这些数据又有特定的过滤条件，例如这层包括FWPS_METADATA_FIELD_PROCESS_ID类型数据，这个类型由UINT64类型数据定义，表示和本次网络访问请求相关的进程ID，可是FWPS_LAYER_INBOUND_IPPACKET_V4层就不包括这一类型的数据，其实FWPS_LAYER_INBOUND_IPPACKET_V4已经到了IP层，这里进程ID已经没用了。因此在FWPM_LAYER_ALE_FLOW_ESTABLISHED_V4蹭可以以进程ID作为过滤条件，而到了FWPS_LAYER_INBOUND_IPPACKET_V4层就不能用进程ID作为过滤条件了。每一层都有哪些数据类型，根据这些数据有哪些过滤条件可用，请参阅微软的WFP文档层标识符等章节。

综上，WFP系统很像一个已经有了数据过滤引擎的防火墙，但是没有规则。我们编写用户层的程序给WFP引擎设置规则，编写核心态的callout驱动处理WFP抓到的网络数据包。根据微软的文档所示，WFP能够到达IP层，如果我们想进行MAC层的处理，就必须利用NDISfilter驱动。

3、应用WFP实现应用程序访问网络时提示

这是个人防火墙的基本功能之一，当有应用程序访问网络时询问用户是否允许。首先我们编写一个callout驱动，用来处理WFP抓到的网络数据。由于WFP抓到的数据只送到callout驱动不会送到用户层程序，所以这里必须用驱动根据数据判定放行还是阻止。Callout驱动向系统注册callout函数，

    FWPS_CALLOUT0 sCallout;

    sCallout.calloutKey = *calloutKey;

    sCallout.flags = flags;

    sCallout.classifyFn = ClassifyFunction; //在实例代码中是MonitorCoFlowEstablishedCalloutV4

    sCallout.notifyFn = NotifyFunction;

    sCallout.flowDeleteFn = FlowDeleteFunction;

status = FwpsCalloutRegister0(deviceObject, &sCallout, calloutId);

FWPS_CALLOUT0结构用来组织一组callout函数，之后用FwpsCalloutRegister0函数注册。这里详细介绍下ClassifyFunction函数，这个函数主要处理网络数据包，

 

NTSTATUS MonitorCoFlowEstablishedCalloutV4(

   IN const FWPS_INCOMING_VALUES0* inFixedValues,//WFP传进来的本层特有的数据

   IN const FWPS_INCOMING_METADATA_VALUES0* inMetaValues,//本层相关的扩展数据

   IN VOID* packet,

   IN const FWPS_FILTER0* filter,

   IN UINT64 flowContext,

   OUT FWPS_CLASSIFY_OUT0* classifyOut//用这个结构里的字段告知WFP对数据包做出处理

)

{

   NTSTATUS status = STATUS_SUCCESS;

   UINT64   flowHandle;

   UINT64   flowContextLocal;

   UINT32   index;

   UINT32   LocalIPADDRv4,remoteIPADDRv4;

   USHORT   LocalPort,remotePort;

 

   UNREFERENCED_PARAMETER(packet);

   UNREFERENCED_PARAMETER(filter);

   UNREFERENCED_PARAMETER(flowContext);

 

   index = FWPS_FIELD_ALE_FLOW_ESTABLISHED_V4_IP_LOCAL_ADDRESS;

   LocalIPADDRv4 = inFixedValues->incomingValue[index].value.uint32;

 

   index = FWPS_FIELD_ALE_FLOW_ESTABLISHED_V4_IP_LOCAL_PORT;

   LocalPort = inFixedValues->incomingValue[index].value.uint16;

 

   index = FWPS_FIELD_ALE_FLOW_ESTABLISHED_V4_IP_REMOTE_ADDRESS;

   remoteIPADDRv4 = inFixedValues->incomingValue[index].value.uint32;

 

   index = FWPS_FIELD_ALE_FLOW_ESTABLISHED_V4_IP_REMOTE_PORT;

   remotePort = inFixedValues->incomingValue[index].value.uint16;

 

   DbgPrint("BaseTDI: LocalIP %lx LocalPort %d \n remoteIP %lx remotePort %d",LocalIPADDRv4,LocalPort,

       remoteIPADDRv4,remotePort);

   DbgPrint("BaseTDI: PID %d ,PID's PATH %s",inMetaValues->processId,inMetaValues->processPath->data);

   DbgPrint("\n");

 

   if (monitoringEnabled)

   {

        //访问规则代码，在这里通知用户态程序

        AskUser(LocalIP, LocalPort, remoteIP, remotePort,PID);

        If 允许

          classifyOut->actionType = FWP_ACTION_PERMIT; //允许发送或接收

        else

          classifyOut->actionType = FWP_ACTION_BLOCK; //不允许发送或接收

   }

  return status;

}

在完成callout驱动后，下面介绍用户态程序如何设置WFP系统。

设置的大体流程如下，

主要代码讲解，

//向WFP系统添加callout

DWORD WFPAppAddCallouts()

{

    FWPM_CALLOUT0 callout;

    DWORD result;

    FWPM_DISPLAY_DATA0 displayData;

    HANDLE engineHandle = NULL;

    FWPM_SESSION0 session;

    //初始化一次会话

    RtlZeroMemory(&session, sizeof(FWPM_SESSION0));

    session.displayData.name = L"TEMP WFP Session";

    session.displayData.description = L"For Adding callouts";

   

    //创建WFP引擎句柄

    result =  FwpmEngineOpen0(

        NULL,

        RPC_C_AUTHN_WINNT,

        NULL,

        &session,

        &engineHandle

        );

    if (NO_ERROR != result)

    {goto cleanup;}

    //开始与引擎交互

    result = FwpmTransactionBegin0(engineHandle, 0);

    if (NO_ERROR != result)

    {goto abort;    }

////////////////////////////////////////////////////////////////ADD CALLOUT

    RtlZeroMemory(&callout, sizeof(FWPM_CALLOUT0));

    displayData.description = MONITOR_FLOW_ESTABLISHED_CALLOUT_DESCRIPTION;

    displayData.name = MONITOR_FLOW_ESTABLISHED_CALLOUT_NAME;

 

    callout.calloutKey = TEMP_MONITOR_FLOW_ESTABLISHED_CALLOUT_V4;

    callout.displayData = displayData;

    callout.applicableLayer = FWPM_LAYER_ALE_FLOW_ESTABLISHED_V4;

    callout.flags = FWPM_CALLOUT_FLAG_PERSISTENT; //flags置这个标志表示callout始终被WFP加载

 

    result = FwpmCalloutAdd0(engineHandle, &callout, NULL, NULL);

    if (NO_ERROR != result)

    {goto abort;    }

//////////////////////////////////////////////////////////结束本次会话

    result = FwpmTransactionCommit0(engineHandle);

    if (NO_ERROR == result)

    {;}

    goto cleanup;

abort:

   

    //说明本次会话失败

    result = FwpmTransactionAbort0(engineHandle);

    if (NO_ERROR == result)

    {;}

cleanup:

    //关闭引擎

    if (engineHandle)

    {

        FwpmEngineClose0(engineHandle);

    }

    return result;

}

//向WFP系统添加filter

DWORD

WFPAppAddFilters(IN  HANDLE engineHandle/*,IN FWP_BYTE_BLOB* applicationPath*/)                

{

    DWORD result = NO_ERROR;

    FWPM_SUBLAYER0 monitorSubLayer;

    FWPM_FILTER0 filter;

    FWPM_FILTER_CONDITION0 filterConditions[1]; //需要几条规则就定义几条

 

    //初始化过滤条件

    RtlZeroMemory(filterConditions, sizeof(filterConditions));

    filterConditions[0].fieldKey = FWPM_CONDITION_IP_PROTOCOL;//所有IP协议数据

    filterConditions[0].matchType = FWP_MATCH_GREATER_OR_EQUAL;//匹配度，大于，小于，大于等于…

    filterConditions[0].conditionValue.type = FWP_UINT8;

    filterConditions[0].conditionValue.uint8 = IPPROTO_IP;

 

    //初始化子层

    RtlZeroMemory(&monitorSubLayer, sizeof(FWPM_SUBLAYER0));

    monitorSubLayer.subLayerKey = TEMP_MONITOR_SUBLAYER;

    monitorSubLayer.displayData.name = L"TEMP Monitor Sub layer";

    monitorSubLayer.displayData.description = L"TEMP Monitor Sub layer";

    monitorSubLayer.flags = 0;//FWMP_SUBLAYER_FLAG_PERSISTENT;

    // We don't really mind what the order of invocation is.

    monitorSubLayer.weight = 0;

 

    //与WFP引擎开始一次会话

    result = FwpmTransactionBegin0(engineHandle, 0);

    if (NO_ERROR != result)

    {goto abort;}

    //增加一个子层

    result = FwpmSubLayerAdd0(engineHandle, &monitorSubLayer, NULL);

    if (NO_ERROR != result)

    {goto abort;}

 

////////////////////////////////////////////FWPM_LAYER_ALE_FLOW_ESTABLISHED_V4

    RtlZeroMemory(&filter, sizeof(FWPM_FILTER0));

 

    filter.layerKey = FWPM_LAYER_ALE_FLOW_ESTABLISHED_V4;

    filter.displayData.name = L"Flow established filter.";

    filter.displayData.description = L"Sets up flow for traffic that we are interested in.";

    filter.action.type = FWP_ACTION_CALLOUT_INSPECTION; //表示把符合条件数据包交给callout处理

    filter.action.calloutKey = TEMP_MONITOR_FLOW_ESTABLISHED_CALLOUT_V4;

    filter.filterCondition = filterConditions;

    filter.subLayerKey = monitorSubLayer.subLayerKey;

    filter.weight.type = FWP_EMPTY; //系统自动设置weight。weight值越大加载越靠前

 

    filter.numFilterConditions = 1;//过滤条件数

 

    result = FwpmFilterAdd0(engineHandle,

        &filter,

        NULL,

        &(filterID[0]));

 

    if (NO_ERROR != result)

    {goto abort;}

 

//结束本次会话

    result = FwpmTransactionCommit0(engineHandle);

    if (NO_ERROR == result)

    {;}

    goto cleanup;

abort:

//说明本次会话失败

    result = FwpmTransactionAbort0(engineHandle);

    if (NO_ERROR == result)

    {;}

cleanup:

    return result;

}

二、NDISfilter

NDISfilter是利用系统提供的NDIS过滤引擎，获得MAC级别的网络数据包(这里可以看出WFP，NDISfilter，还有本文未提到的FileSystemMiniFilter，他们都是利用了微软提供的过滤引擎，向其注册回调函数，得到数据后处理)。关键代码说明，其中的详细数据结构请参阅微软文档NDISfilter一节，

 

NDIS_FILTER_DRIVER_CHARACTERISTICS      FChars;

 

 NdisZeroMemory(&FChars, sizeof(NDIS_FILTER_DRIVER_CHARACTERISTICS));

        FChars.Header.Type = NDIS_OBJECT_TYPE_FILTER_DRIVER_CHARACTERISTICS;

        FChars.Header.Size = sizeof(NDIS_FILTER_DRIVER_CHARACTERISTICS);

        FChars.Header.Revision = NDIS_FILTER_CHARACTERISTICS_REVISION_1;

        FChars.MajorNdisVersion = FILTER_MAJOR_NDIS_VERSION;

        FChars.MinorNdisVersion = FILTER_MINOR_NDIS_VERSION;

        FChars.MajorDriverVersion = 1;

        FChars.MinorDriverVersion = 0;

        FChars.Flags = 0;

 

        FChars.FriendlyName = FriendlyName;

        FChars.UniqueName = UniqueName;

        FChars.ServiceName = ServiceName;

 

        FChars.SetOptionsHandler = FilterRegisterOptions;       

        FChars.AttachHandler = FilterAttach;//如果是我们想挂接的网络介质,就在这里通知系统挂接

        FChars.DetachHandler = FilterDetach;

        FChars.RestartHandler = FilterRestart;

        FChars.PauseHandler = FilterPause;

        FChars.SetFilterModuleOptionsHandler = FilterSetModuleOptions;          

        FChars.OidRequestHandler = FilterOidRequest;

        FChars.OidRequestCompleteHandler = FilterOidRequestComplete;

        FChars.CancelOidRequestHandler = FilterCancelOidRequest;

       

        FChars.SendNetBufferListsHandler = FilterSendNetBufferLists;//发送回调函数    

        FChars.ReturnNetBufferListsHandler = FilterReturnNetBufferLists;

        FChars.SendNetBufferListsCompleteHandler = FilterSendNetBufferListsComplete;

        FChars.ReceiveNetBufferListsHandler = FilterReceiveNetBufferLists;//接收回调函数

        FChars.DevicePnPEventNotifyHandler = FilterDevicePnPEventNotify;

        FChars.NetPnPEventHandler = FilterNetPnPEvent;

        FChars.StatusHandler = FilterStatus;

        FChars.CancelSendNetBufferListsHandler = FilterCancelSendNetBufferLists;

 

NDIS_FILTER_DRIVER_CHARACTERISTICS这个结构用来组织NDISfilter功能函数供NDIS系统回调，例如FilterSendNetBufferLists，发送数据回调函数，NDIS发送MAC帧时回调这个函数，相应数据可以在这个函数里得到处理，之后还给NDIS系统继续处理。

VOID

FilterSendNetBufferLists(

        IN  NDIS_HANDLE         FilterModuleContext,

        IN  PNET_BUFFER_LIST    NetBufferLists,

        IN  NDIS_PORT_NUMBER    PortNumber,

        IN  ULONG               SendFlags

        )

{

    PMS_FILTER          pFilter = (PMS_FILTER)FilterModuleContext;

    NDIS_STATUS         Status = NDIS_STATUS_SUCCESS;

    PNET_BUFFER_LIST    CurrNbl;

BOOLEAN             DispatchLevel;

 

//这里开始分析PNET_BUFFER_LIST指向的网络数据,并显示如何获得MAC地址

    PNET_BUFFER_LIST      pNetBufList,pNextNetBufList;

    PMDL                  pMdl;

    PNDISPROT_ETH_HEADER  pEthHeader = NULL;

    ULONG                 TotalLength,Offset,BufferLength;

 

    pNetBufList = NetBufferLists;

 

    while (pNetBufList != NULL)

    {

        pNextNetBufList = NET_BUFFER_LIST_NEXT_NBL (pNetBufList);

        //得到当前和包相关的MDL,MDL里即MAC帧,详细的NET_BUFFER_LIST结构请参阅微软相关文档

        pMdl = NET_BUFFER_CURRENT_MDL(NET_BUFFER_LIST_FIRST_NB(pNetBufList));  

        TotalLength = NET_BUFFER_DATA_LENGTH(NET_BUFFER_LIST_FIRST_NB(pNetBufList));

        Offset = NET_BUFFER_CURRENT_MDL_OFFSET(NET_BUFFER_LIST_FIRST_NB(pNetBufList));

        BufferLength = 0;

        do

        {

            ASSERT(pMdl != NULL);

            if (pMdl)

            {

                NdisQueryMdl(

                    pMdl,

                    &pEthHeader,

                    &BufferLength,

                    NormalPagePriority);

            }

 

            if (pEthHeader == NULL)

            {

                BufferLength = 0;

                break;

            }

 

            if (BufferLength == 0)

            {

                break;

            }

            ASSERT(BufferLength > Offset);

 

            BufferLength -= Offset;

            pEthHeader = (PNDISPROT_ETH_HEADER)((PUCHAR)pEthHeader + Offset);

 

            DbgPrint("DstMAC %x-%x-%x-%x-%x-%x",pEthHeader->DstAddr[0],

                pEthHeader->DstAddr[1],pEthHeader->DstAddr[2],

                pEthHeader->DstAddr[3],pEthHeader->DstAddr[4],

                pEthHeader->DstAddr[5]);

 

            DbgPrint("srcMAC %x-%x-%x-%x-%x-%x",pEthHeader->SrcAddr[0],

                pEthHeader->SrcAddr[1],pEthHeader->SrcAddr[2],

                pEthHeader->SrcAddr[3],pEthHeader->SrcAddr[4],

                pEthHeader->SrcAddr[5]);

            DbgPrint("\n");

 

            if (BufferLength < sizeof(NDISPROT_ETH_HEADER))

            {

                break;

            }

        }while (FALSE);

        pNetBufList = pNextNetBufList;

    }

}