linux-kernel - Re: [PATCH 3/4] tpm: in tpm2_del_space check if ops pointer is still valid

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Date:   Sun, 17 Jan 2021 20:13:27 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     peterhuewe@....de, jgg@...pe.ca, stefanb@...ux.vnet.ibm.com,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        p.rosenberger@...bus.com, Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH 3/4] tpm: in tpm2_del_space check if ops pointer is still
 valid

On Sat, Jan 16, 2021 at 02:22:40AM +0100, Lino Sanfilippo wrote:
> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
> 
> In tpm2_del_space() the sessions are flushed by means of the tpm_chip
> operations. However the concerning operations pointer my already be NULL at
> this time in case that the chip has been unregistered (see
> tpm_chip_unregister() which calls tpm_del_char_device() which sets
> chip->ops to NULL).
> Avoid the NULL pointer access by first calling tpm_try_get_ops() to check
> if the operations pointer is still valid and skipping the session flushing
> in case of an unregistered chip.
> 
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
> ---
>  drivers/char/tpm/tpm2-space.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
> index 784b8b3..ea6eee9 100644
> --- a/drivers/char/tpm/tpm2-space.c
> +++ b/drivers/char/tpm/tpm2-space.c
> @@ -59,7 +59,7 @@ int tpm2_init_space(struct tpm_space *space, unsigned int buf_size)
>  void tpm2_del_space(struct tpm_chip *chip, struct tpm_space *space)
>  {
>  	mutex_lock(&chip->tpm_mutex);
> -	if (!tpm_chip_start(chip)) {
> +	if (!tpm_try_get_ops(chip) && !tpm_chip_start(chip)) {
>  		tpm2_flush_sessions(chip, space);
>  		tpm_chip_stop(chip);
>  	}
> -- 
> 2.7.4
> 

I have hard time to believe that any of these patches are based on
actual regressions.

/Jarko