linux-kernel - Re: [PATCH] tpm: avoid accessing cleared ops during shutdown

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Message-ID: <20200714113205.GA1461506@linux.intel.com>
Date:   Tue, 14 Jul 2020 14:32:18 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Andrey Pronin <apronin@...omium.org>
Cc:     peterhuewe@....de, jgg@...pe.ca, linux-integrity@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Guenter Roeck <groeck@...omium.org>
Subject: Re: [PATCH] tpm: avoid accessing cleared ops during shutdown

On Fri, Jul 10, 2020 at 11:25:44AM -0700, Andrey Pronin wrote:
> > Why does not tpm_del_char_device need this?
> 
> "Not" is a typo in the sentence above, right? tpm_del_char_device *does*
> need the fix. When tpm_class_shutdown is called it sets chip->ops to
> NULL. If tpm_del_char_device is called after that, it doesn't check if
> chip->ops is NULL (normal kernel API and char device API calls go
> through tpm_try_get_ops, but tpm_del_char_device doesn't) and proceeds to
> call tpm2_shutdown(), which tries sending the command and dereferences
> chip->ops.

It's a typo, yes. Sorry about that.

tpm_class_shutdown() is essentially tail of tpm_del_char_device().

To clean things up, I'd suggest dropping tpm_del_char_device() and
call tpm_class_shutdown() in tpm_chip_unregisters() along, and open
coding things that prepend it in tpm_del_char_device().

/Jarkko