xuAmigo，来问个加密

最近看到很多人做加密解密，我也很感兴趣。来问一问。
我今天想实现在WRITE中得到内容，然后加密并把密文保存到DISK，然后恢复内存中的明文。我参照以前的文章写，但是怎么就总蓝屏呢？代码如下：请多指教
NTSTATUS
SfWrite(
    IN PDEVICE_OBJECT DeviceObject,
    IN PIRP Irp
    )
{PIO_STACK_LOCATION     irpSp = IoGetCurrentIrpStackLocation(Irp);
PREAD_WRITE_COMPLETION_CONTEXT CompletionCtx = NULL;
NTSTATUS               status;
PFILE_OBJECT           file  = irpSp->FileObject;
UNICODE_STRING         name;
UNICODE_STRING         dosname={0};
WCHAR nameBuf[512];
PVOID OldBuffer = NULL;//Original content
PVOID MyBuffer = NULL;
ULONG Length = 0;
ULONG Offset = 0;
PAGED_CODE();

if (!(Irp->Flags & (IRP_NOCACHE | IRP_PAGING_IO | IRP_SYNCHRONOUS_PAGING_IO)))
{
return SfPassThrough(DeviceObject,Irp);
}
do{
DbgPrint(\"SfWrite:Begin\");
if (Irp->MdlAddress)
OldBuffer = MmGetSystemAddressForMdl(Irp->MdlAddress);
else
OldBuffer = Irp->UserBuffer;
if(!OldBuffer)
{
DbgPrint(\"SfWriet:OldBuffer==NULL\");
status = STATUS_INVALID_PARAMETER;
break;
}
Length = irpSp->Parameters.Write.Length
DbgPrint(\"%d,%s\",Length,OldBuffer);
MyBuffer = ExAllocatePool(NonPagedPool,Length);
if (!MyBuffer)
{
DbgPrint(\"sfilter!SfWrite: STATUS_INSUFFICIENT_RESOURCES\\n\");
status = STATUS_INSUFFICIENT_RESOURCES;
break;
}
RtlCopyMemory(MyBuffer,OldBuffer,Length);
CompletionCtx=ExAllocatePool(NonPagedPool,sizeof(READ_WRITE_COMPLETION_CONTEXT));
if(!CompletionCtx)
{
DbgPrint(\"sfilter!SfWrite: STATUS_INSUFFICIENT_RESOURCES\\n\");
status = STATUS_INSUFFICIENT_RESOURCES;
break;
}
DbgPrint(\"Allocate OK!\");
CompletionCtx->OldMdl = Irp->MdlAddress;
CompletionCtx->OldUserBuffer = Irp->UserBuffer;
CompletionCtx->OldSystemBuffer = Irp->AssociatedIrp.SystemBuffer;
CompletionCtx->OldBuffer = OldBuffer;
CompletionCtx->MyBuffer = MyBuffer;
CompletionCtx->Length = Length;
for(Offset=0;Offset<Length;++Offset)
((PUCHAR) OldBuffer)[Offset] = ~((PUCHAR) MyBuffer)[Offset];
DbgPrint(\"OldBuffer after encrypt:%s\",OldBuffer);
IoCopyCurrentIrpStackLocationToNext(Irp);
IoSetCompletionRoutine(Irp, SfWriteCompletion, CompletionCtx, TRUE, TRUE,TRUE);
return IoCallDriver( ((PSFILTER_DEVICE_EXTENSION) DeviceObject->DeviceExtension)->AttachedToDeviceObject, Irp );
}while(FALSE);
Irp->IoStatus.Status = status;
IoCompleteRequest(Irp, IO_NO_INCREMENT);
return status;

}

NTSTATUS
SfWriteCompletion(
IN PDEVICE_OBJECT DeviceObject,
IN PIRP Irp,
IN PVOID Context
)
{
PREAD_WRITE_COMPLETION_CONTEXT CompletionCtx = (PREAD_WRITE_COMPLETION_CONTEXT) Context;
ULONG Offset = 0;
UNREFERENCED_PARAMETER(DeviceObject);
if (Irp->PendingReturned)
IoMarkIrpPending(Irp);
IoFreeMdl(Irp->MdlAddress);
Irp->MdlAddress = CompletionCtx->OldMdl;
Irp->UserBuffer = CompletionCtx->OldUserBuffer;
Irp->AssociatedIrp.SystemBuffer = CompletionCtx->OldSystemBuffer;
ExFreePoolWithTag(CompletionCtx->MyBuffer, SFLT_POOL_TAG);
return STATUS_SUCCESS;
}

我的就是重新启动以后才能看到密文，确实是缓存的问题，你按你的要求改就行

我还是直接COPY到OLDBUFFER的。
我想按照你们的思路修改一下，但是，加密以后只有重新启动才能看到密文。而我直接替换OLDBUFFER的话就可以，怎么回事？

难道是CACHE？？

我下了几个断点，终于可以了。主要是几个内存用的不小心。
还有就是IoFreeMdl(Irp->MdlAddress);不能要。

但是我的加密完了以后密文的长度会变的，比如以前length=4096，我加密以后变成了5000，怎么办？

能不能自己把这个5000的密文分两次写下去？

谢谢？

RtlCopyMemory(MyBuffer,OldBuffer,Length);
这句不要，
for(Offset=0;Offset<Length;++Offset)
((PUCHAR) OldBuffer)[Offset] = ~((PUCHAR) MyBuffer)[Offset];
这句改为
Irp->MdlAddress = IoAllocateMdl(MyBuffer,Length,FALSE,TRUE,NULL);
for(Offset=0;Offset<Length;++Offset)
((PUCHAR) MyBuffer)[Offset] = ~((PUCHAR) OldBuffer)[Offset];
MmBuildMdlForNonPagedPool(Irp->MdlAddress);
Irp->UserBuffer = MmGetMdlVirtualAddress(Irp->MdlAddress);
你试试看，OldBuffer是系统缓冲区

IoFreeMdl(Irp->MdlAddress);
Irp->MdlAddress = CompletionCtx->OldMdl;
Irp->UserBuffer = CompletionCtx->OldUserBuffer;
Irp->AssociatedIrp.SystemBuffer = CompletionCtx->OldSystemBuffer
不要这个IoFreeMdl(Irp->MdlAddress);，因为两个都是同一个mdl
释放掉了，而完成例程返回时，会自动释放掉irp的mdl的

感觉你的代码问题很多，你重新改写下