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;
}
}
