Re: [PATCH v2] tpm: fix potential NULL pointer access in tpm_del_char_device

[Jarkko Sakkinen <jarkko@kernel.org>]

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@vger.kernel.org
> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>

Thank you.

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR,
Jarkko