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

[Lino Sanfilippo]

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@xxxxxxxxxxxxxxx
>> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@xxxxxx>
>
> Thank you.
>
> Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
>
> 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.

Regards,
Lino