Re: [PATCH] Add TPM hardware enablement driver

[Jeff Garzik <jgarzik@pobox.com>]

Greg KH wrote:
> On Tue, Mar 22, 2005 at 09:02:24PM -0500, Jeff Garzik wrote:
>
> > Kylene Hall wrote:
> >
> > > > what is the purpose of this pci_dev_get/put?  attempting to prevent 
> > > > hotplug or
> > > > something?
> > >
> > >
> > > Seems that since there is a refernce to the device in the chip structure 
> > > and I am making the file private data pointer point to that chip structure 
> > > this is another reference that must be accounted for. If you remove it 
> > > with it open and attempt read or write bad things will happen.  This isn't 
> > > really hotpluggable either as the TPM is on the motherboard.
> >
> > My point was that there will always be a reference -anyway-, AFAICS. 
> > There is a pci_dev reference assigned to the pci_driver when the PCI 
> > driver is loaded, and all uses by the TPM generic code of this pointer 
> > are -inside- the pci_driver's pci_dev object lifetime.
>
>
> Think of the following situation:
> 	- driver is bound to device.
> 	- userspace opens char dev node.
> 	- device is removed from the system (using fakephp I can do this
> 	  to _any_ pci device, even if it is on the motherboard.)
> 	- userspace writes to char dev node
> 	- driver attempts to access pci device structure that is no
> 	  longer present in memory.
>
> Because of this open needs to get a reference to the pci device to
> prevent oopses, or the driver needs to be aware of "device is now gone"
> in some other manner.

Thanks for explaining; agreed.

However, there appear to still be massive bugs in this area:

Consider the behavior of the chrdev if a PCI device has been unplugged. 
 It's still actively messing with the non-existent hardware, and never 
checks for dead h/w AFAICS.

	Jeff


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