linux-kernel - Re: [PATCH v2 1/4] tpm_tis: Explicitly check for error code

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Message-Id: <CT5VIPKR029R.Z1XFDV427X1V@suppilovahvero>
Date:   Wed, 07 Jun 2023 00:09:21 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Alexander Steffen" <Alexander.Steffen@...ineon.com>,
        <linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] tpm_tis: Explicitly check for error code

On Mon Jun 5, 2023 at 8:59 PM EEST, Alexander Steffen wrote:
> recv_data either returns the number of received bytes, or a negative value
> representing an error code. Adding the return value directly to the total
> number of received bytes therefore looks a little weird, since it might add
> a negative error code to a sum of bytes.
>
> The following check for size < expected usually makes the function return
> ETIME in that case, so it does not cause too many problems in practice. But
> to make the code look cleaner and because the caller might still be
> interested in the original error code, explicitly check for the presence of
> an error code and pass that through.
>

Cc: stable@...r.kernel.org
Fixes: cb5354253af2 ("[PATCH] tpm: spacing cleanups 2")

> Signed-off-by: Alexander Steffen <Alexander.Steffen@...ineon.com>
> ---
>  drivers/char/tpm/tpm_tis_core.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 558144fa707a..aaaa136044ae 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -363,8 +363,13 @@ static int tpm_tis_recv(struct tpm_chip *chip, u8 *buf, size_t count)
>  		goto out;
>  	}
>  
> -	size += recv_data(chip, &buf[TPM_HEADER_SIZE],
> -			  expected - TPM_HEADER_SIZE);
> +	rc = recv_data(chip, &buf[TPM_HEADER_SIZE],
> +		       expected - TPM_HEADER_SIZE);
> +	if (rc < 0) {
> +		size = rc;
> +		goto out;
> +	}
> +	size += rc;
>  	if (size < expected) {
>  		dev_err(&chip->dev, "Unable to read remainder of result\n");
>  		size = -ETIME;
> -- 
> 2.34.1

BR, Jarkko