Filter驱动：过滤(修改)接受数据包

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驱动开发

数据结构 .net 防火墙 IDEA

Filter驱动可以实现简单的防火墙功能。它可以过滤所有接收到的包，然后进行分析处理，最后根据情况决定是否网上传递给Protocol层，最后给应用程。

我们的原则是不能在接收到的NBL修改数据，因为后面我们还会需要这个完整的包结构，尤其是在调用NdisFReturnNetBufferLists释放NBL的owership的时候。所以第一步要做的就是拷贝数据：拷贝NetBufferList数据

拷贝好了数据之后，我们需要做的是：

首先通知底层驱动，可能是Miniport driver，意思是：Filter已经收到数据，现在归还NBL的所有权，甚至说Miniport Driver可以继续往NBL写数据了。

 //Call return function to info the underlying driver of releasing ownership of NBL
        NDIS_SET_RETURN_FLAG(ReturnFlags, NDIS_RETURN_FLAGS_DISPATCH_LEVEL);
        NdisFReturnNetBufferLists(pFilter->FilterHandle, NetBufferLists, ReturnFlags);

其次就是把自己刚才拷贝好的数据，根据需要更改数据，比如更改port number等。

发送已经更改好的NBL

 NdisFIndicateReceiveNetBufferLists(
            pFilter->FilterHandle,
            pCopyNetBufferLists,
            PortNumber,
            NumberOfNetBufferLists,
            ReceiveFlags);

最后一步，别忘记了，往上发自己创建的NBL，是不能调用NdisFReturnNetBufferLists的，因为这个是Filter创建的，不是由底层发上来的，如果调用了，就会出错了。所以在FilterReturnNetBufferLists中拦截销毁自己定义的NBL，因为这是protocol已经把NBL中的数据拷贝好了~

 if(NetBufferLists->SourceHandle == pFilter->FilterHandle)
    {
        //Please just free this NBL
        ReadNetBuffer(NetBufferLists);//print out something...
        result = FreeMdlAndNetBufferList(NetBufferLists);
        if(result == TRUE)
        {
            DEBUGP(DL_TEST, ("Free my own NBL ======ReturnNetBufferLists\n"));
        }
    }
    else
    {
        NdisFReturnNetBufferLists(pFilter->FilterHandle, NetBufferLists, ReturnFlags);
    }

关于释放NBL，这里贴出来：

BOOLEAN
FreeMdlAndNetBufferList
(
    PNET_BUFFER_LIST NetBufferLists
)
{
    BOOLEAN result = FALSE;
    PNET_BUFFER_LIST	CurrNbl,nextNbl= NULL;
    PNET_BUFFER			Currbuff;
    PMDL				mdl,pMdl;
    UINT                BufferLength;
    PUCHAR              pCopyData = NULL;
//Free all the NBLs allocate by myself
    CurrNbl = NetBufferLists;
    while(CurrNbl)
    {
        Currbuff =NET_BUFFER_LIST_FIRST_NB(CurrNbl);
        while(Currbuff)
        {
            pMdl = NET_BUFFER_FIRST_MDL(Currbuff);

            FILTER_ASSERT(pMdl != NULL);
            NdisQueryMdl(
                pMdl,
                (PVOID *)&pCopyData,
                &BufferLength,
                NormalPagePriority);
            FILTER_ASSERT(pCopyData != NULL);
            NdisFreeMdl(pMdl);//Free MDL
            pCopyData = NULL;
            Currbuff = NET_BUFFER_NEXT_NB(Currbuff);
        }
        nextNbl = NET_BUFFER_LIST_NEXT_NBL(CurrNbl);//get Next MBL
        NdisFreeNetBufferList(CurrNbl);//Free CurrentNBL
        CurrNbl = nextNbl;
    }
    result =  TRUE;
    return result;
}

展示运行结果：

首先是拷贝数据结构：

写道

00000066 10.77174854 ===============>copyNetBufferList
00000067 10.77175713 NDISLWF:
00000068 10.77176189 ==============>allocateNetBuffAndNetBufferList
00000069 10.77177429 NDISLWF:
00000070 10.77178001 <==============allocateNetBuffAndNetBufferList
00000071 10.77178478 NDISLWF:
00000072 10.77179432 newBufferLength is 231, mdlOffset is 18 and Current mdl offset 18
00000073 10.77179909 NDISLWF:
00000074 10.77180481 There are 1 NB in this list---_---
00000075 10.77180958 NDISLWF:
00000076 10.77181625 There are 1 NBLs
00000077 10.77182007 <============copyNetBufferList

最后是往上发送的：

写道

00000079 10.77193928 ===>ReturnNetBufferLists, NetBufferLists is 890D5540.
00000080 10.77194309 NDISLWF:
00000081 10.77194786 ==============>ReadNetBuffer
00000082 10.77195263 NDISLWF:
00000083 10.77195644 ---Read From NBL: Ethernet Header info:
00000084 10.77198792 NDISLWF:
00000085 10.77200031 00-19-e0-e0-2d-30 -> 00-1d-0f-af-50-b0 Mac地址
00000086 10.77200699 NDISLWF:
00000087 10.77201366 DestIPAddr: 221.5.88.88 -> 192.168.1.105 ip地址
00000088 10.77201843 NDISLWF:
00000089 10.77202225 <==============ReadNetBuffer
00000090 10.77202702 NDISLWF:
00000091 10.77203274 Free my own NBL ======ReturnNetBufferLists销毁数据

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