linux-kernel - Re: [PATCH v2] tpm: fix potential NULL pointer access in tpm_del_char

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Date:   Wed, 29 Dec 2021 03:46:36 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     peterhuewe@....de, jgg@...pe.ca, p.rosenberger@...bus.com,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] tpm: fix potential NULL pointer access in
 tpm_del_char_device

On Wed, Dec 29, 2021 at 02:41:52AM +0100, Lino Sanfilippo wrote:
> Hi,
> 
> On 29.12.21 at 01:13, Jarkko Sakkinen wrote:
> > On Mon, Dec 20, 2021 at 04:06:35PM +0100, Lino Sanfilippo wrote:
> >> Some SPI controller drivers unregister the controller in the shutdown
> >> handler (e.g. BCM2835). If such a controller is used with a TPM 2 slave
> >> chip->ops may be accessed when it is already NULL:
> >>
> >> At system shutdown the pre-shutdown handler tpm_class_shutdown() shuts down
> >> TPM 2 and sets chip->ops to NULL. Then at SPI controller unregistration
> >> tpm_tis_spi_remove() is called and eventually calls tpm_del_char_device()
> >> which tries to shut down TPM 2 again. Thereby it accesses chip->ops again:
> >> (tpm_del_char_device calls tpm_chip_start which calls tpm_clk_enable which
> >> calls chip->ops->clk_enable).
> >>
> >> Avoid the NULL pointer access by testing if chip->ops is valid and skipping
> >> the TPM 2 shutdown procedure in case it is NULL.
> >>
> >> Fixes: dcbeab1946454 ("tpm: fix crash in tpm_tis deinitialization")
> >> Cc: stable@...r.kernel.org
> >> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@....de>
> >
> > Thank you.
> >
> > Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
> >
> > BR,
> > Jarkko
> >
> 
> Thanks a lot for the review. Please note that the latest version is v3 which
> contains one more Fixes tag and also a tag for the review by Stefan. I also
> adjusted the source code comment in that version which I somehow messed up in v2.

Since there is no functional difference, I rather do not swap it.

I fixed a glitch:

+
+       /*

A multi-line commit needs to have this as the very first line.
You can check if the all tags were pulled by b4.

/Jarkko