[PATCH v11 14/20] tpm: Protect against locality counter underflow

[Jarkko Sakkinen]

On Fri Sep 13, 2024 at 11:05 PM EEST, Ross Philipson wrote:
> From: "Daniel P. Smith" <dpsmith at apertussolutions.com>
>
> Commit 933bfc5ad213 introduced the use of a locality counter to control when a
> locality request is allowed to be sent to the TPM. In the commit, the counter
> is indiscriminately decremented. Thus creating a situation for an integer
> underflow of the counter.
>
> Signed-off-by: Daniel P. Smith <dpsmith at apertussolutions.com>
> Signed-off-by: Ross Philipson <ross.philipson at oracle.com>
> Reported-by: Kanth Ghatraju <kanth.ghatraju at oracle.com>

Remove reported-by.

> ---
>  drivers/char/tpm/tpm_tis_core.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index fdef214b9f6b..a6967f312837 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -180,7 +180,10 @@ static int tpm_tis_relinquish_locality(struct tpm_chip *chip, int l)
>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>  
>  	mutex_lock(&priv->locality_count_mutex);
> -	priv->locality_count--;
> +	if (priv->locality_count > 0)
> +		priv->locality_count--;
> +	else
> +		pr_info("Invalid: locality count dropped below zero\n");

Explain the context.

>  	if (priv->locality_count == 0)
>  		__tpm_tis_relinquish_locality(priv, l);
>  	mutex_unlock(&priv->locality_count_mutex);

BR, Jarkko