Re: [PATCH v3 04/16] tpm: call tpm2_flush_space() on error in tpm_try_transmit()

[Stefan Berger <stefanb@linux.ibm.com>]

On 11/4/18 8:45 PM, Jarkko Sakkinen wrote:
> Always call tpm2_flush_space() on failure in tpm_try_transmit() so that
> the volatile memory of the TPM gets cleared. If /dev/tpm0 does not have
> sufficient permissions (usually it has), this could leak to the leakage

leak ->lead


> of TPM objects. Through /dev/tpmrm0 this issue does not raise new
> security concerns.
>
> Cc: stable@vger.kernel.org
> Fixes: 745b361e989a ("tpm:tpm: infrastructure for TPM spaces")
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> ---
>   drivers/char/tpm/tpm-interface.c | 28 +++++++++++++++++-----------
>   drivers/char/tpm/tpm.h           |  1 +
>   drivers/char/tpm/tpm2-space.c    |  2 +-
>   3 files changed, 19 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 64510ed81b46..ecda6f96cde0 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -224,14 +224,14 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip,
>
>   	rc = tpm2_prepare_space(chip, space, ordinal, buf);
>   	if (rc)
> -		goto out;
> +		goto out_idle;
>
>   	rc = chip->ops->send(chip, buf, count);
>   	if (rc < 0) {
>   		if (rc != -EPIPE)
>   			dev_err(&chip->dev,
>   				"%s: tpm_send: error %d\n", __func__, rc);
> -		goto out;
> +		goto out_space;
>   	}
>
>   	if (chip->flags & TPM_CHIP_FLAG_IRQ)
> @@ -247,7 +247,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip,
>   		if (chip->ops->req_canceled(chip, status)) {
>   			dev_err(&chip->dev, "Operation Canceled\n");
>   			rc = -ECANCELED;
> -			goto out;
> +			goto out_space;
>   		}
>
>   		tpm_msleep(TPM_TIMEOUT_POLL);
> @@ -257,7 +257,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip,
>   	chip->ops->cancel(chip);
>   	dev_err(&chip->dev, "Operation Timed out\n");
>   	rc = -ETIME;
> -	goto out;
> +	goto out_space;
>
>   out_recv:
>   	len = chip->ops->recv(chip, buf, bufsiz);
> @@ -265,22 +265,28 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip,
>   		rc = len;
>   		dev_err(&chip->dev,
>   			"tpm_transmit: tpm_recv: error %d\n", rc);
> -		goto out;
> +		goto out_idle;

Why not jump to out_space here and in 2 instances below?


>   	} else if (len < TPM_HEADER_SIZE) {
>   		rc = -EFAULT;
> -		goto out;
> +		goto out_idle;
>   	}
>
>   	if (len != be32_to_cpu(header->length)) {
>   		rc = -EFAULT;
> -		goto out;
> +		goto out_idle;
>   	}
>
> -	rc = tpm2_commit_space(chip, space, ordinal, buf, &len);
> -	if (rc)
> -		dev_err(&chip->dev, "tpm2_commit_space: error %d\n", rc);
> +out_space:
> +	if (rc) {
> +		tpm2_flush_space(chip);
> +	} else {
> +		rc = tpm2_commit_space(chip, space, ordinal, buf, &len);
> +		if (rc)
> +			dev_err(&chip->dev, "tpm2_commit_space: error %d\n",
> +				rc);
> +	}
>
> -out:
> +out_idle:
>   	/* may fail but do not override previous error value in rc */
>   	tpm_go_idle(chip, flags);
>
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index 49bca4d1e786..229ac42b644e 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -579,6 +579,7 @@ int tpm2_probe(struct tpm_chip *chip);
>   int tpm2_find_cc(struct tpm_chip *chip, u32 cc);
>   int tpm2_init_space(struct tpm_space *space);
>   void tpm2_del_space(struct tpm_chip *chip, struct tpm_space *space);
> +void tpm2_flush_space(struct tpm_chip *chip);
>   int tpm2_prepare_space(struct tpm_chip *chip, struct tpm_space *space, u32 cc,
>   		       u8 *cmd);
>   int tpm2_commit_space(struct tpm_chip *chip, struct tpm_space *space,
> diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
> index 1131a8e7b79b..d53c882268ff 100644
> --- a/drivers/char/tpm/tpm2-space.c
> +++ b/drivers/char/tpm/tpm2-space.c
> @@ -162,7 +162,7 @@ static int tpm2_save_context(struct tpm_chip *chip, u32 handle, u8 *buf,
>   	return 0;
>   }
>
> -static void tpm2_flush_space(struct tpm_chip *chip)
> +void tpm2_flush_space(struct tpm_chip *chip)
>   {
>   	struct tpm_space *space = &chip->work_space;
>   	int i;