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

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Message-ID: <CABXOdTcAZjG8aQvs+M72CFe9rAdBKZH+6x=C1Ha2aX_w0gXiHw@mail.gmail.com>
Date:   Tue, 14 Jul 2020 08:48:38 -0700
From:   Guenter Roeck <groeck@...gle.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Andrey Pronin <apronin@...omium.org>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <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 Tue, Jul 14, 2020 at 4:32 AM Jarkko Sakkinen
<jarkko.sakkinen@...ux.intel.com> wrote:
>
> 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().
>

Personally I would have preferred two separate patches, one to fix the
immediate problem (with Cc: stable) and one for the cleanup, but I
guess merging both into one is ok as long as it is marked for stable.

Thanks,
Guenter