Re: [PATCH v4 3/8] tpm: validate event log access before tpm_bios_log_setup

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Fri, Oct 07, 2016 at 01:41:29AM +0530, Nayna wrote:
> Are we trying to say that, once the teardown() is started, no more opening
> of files are allowed, even if they are visible ?

Yes.

> But if open() has happened first, and then teardown(), in that case private
> data is already passed to seq_open().

Yes.

> That means here the behaviour will still be same as existing..

No, the crucial difference is that the 'get_device' is now safe. It
either acquires a kref or it returns ENODEV. Since we have safely done
get_device, and hold a kref, we know the log cannot become freed since you
will move the log free to the tpm_dev_release function.

tpm_dev_release is called when the chip kref count goes to 0.

> opened files continue to access the data, and teardown will not be
> waiting for opened files to be closed() ? Is this correct
> understanding of what we are trying to do ?

Right, no waiting. Instead we defer kfree(chip) until all users are
done, including open user files. This is the same approach we use in
other parts of the subsystem.

Jason

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