Problems in Hooking SendHandler (NDIS Hooks)

Hello,
I wonder if anybody watching this list can give me some hint about the following problem :

I write NDIS hooking driver which modifies export table of NDIS.sys for NdisDe/RegisterProtocol, NdisOpen/CloseAdapter functions. The driver loads between ndis.sys and tcpip.sys.

In NdisOpenAdapter handler, after calling original handler and getting NDIS_STATUS_SUCCESS(In case of pending I do handle the case exectly the same in completion routine), I get pointer to NDIS_OPEN_BLOCK structure modify SendHandler,SendPacketsHandler, and TransferDataHandler addresses with my own equivalents.

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Version 1(NdisOpenAdapter Hook)

---

NDIS_OPEN_BLOCK pOpenBlock;
…..
pOpenBlock = *NdisBindingHandle;
…..
InterlockedExchangePointer(&pOpenBlock->SendPacketsHandler,
(SEND_PACKETS_HANDLER)pAdapterCtx->OSSendPacketsHandler);

InterlockedExchangePointer(&pOpenBlock->SendHandler,
(SEND_HANDLER)pAdapterCtx->OSSendHandler);
….
In the first version of my code, I hook handlers without copying original NDIS_OPEN_BLOCK(i.e *NdisBindingHandle) into my own m_OpenBlock structure.

Now 1st problem : This hooking works most of the time. Namely I can see sending attempts. But sometimes, it is not called even the original handler adresses are modified. For example, When I enable a network connection for the first time, SendHandlers are not called. When I disble and re-enable it, they are called properly. On a connection using a wireless LAN card, SendHandlers are never called.

Later I modified the code to keep my own NDIS_OPEN_BLOCK structure , m_OpenBlock and copied original open block into this and modified it. Then I modified NdisBindingHandle to point to it.

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Version 2(NdisOpenAdapter Hook)

---

…
NDIS_OPEN_BLOCK pOpenBlock;
…..
NdisMoveMemory(&pAdapterCtx->m_OpenBlock,*NdisBindingHandle,sizeof(NDIS_OPEN_BLOCK));

*NdisBindingHandle = &pAdapterCtx->m_OpenBlock;

pOpenBlock = *NdisBindingHandle;
…..
InterlockedExchangePointer(&pOpenBlock->SendPacketsHandler,
(SEND_PACKETS_HANDLER)pAdapterCtx->OSSendPacketsHandler);

InterlockedExchangePointer(&pOpenBlock->SendHandler,
(SEND_HANDLER)pAdapterCtx->OSSendHandler);
…..

---

This time, the hook never works! For example, when I try to enable a network connection network cable unplugged is reported. 🙂

Is there any point I am missing? Are there some possible race conditions between hooked calls which may cause this error so that I should handle?Should I also hook BindAdapter routines?(BindAdapterHandler and NdisCompleteBindAdapter)

I use Windows XP SP1 DDK on Windows XP SP2.

If somebody could comment on this, I would appreciate.

Thanks in advance,

Egemen Tas