linux-kernel - Re: [PATCH] [PATCH v2] fsi: fix bogus error returns from cfam_read and cfam

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Message-ID: <a5e2570f-222b-5633-af67-6cf5650a741f@canonical.com>
Date:   Fri, 29 Nov 2019 09:03:50 +0000
From:   Colin Ian King <colin.king@...onical.com>
To:     Jeremy Kerr <jk@...abs.org>, Joel Stanley <joel@....id.au>,
        Alistar Popple <alistair@...ple.id.au>,
        Eddie James <eajames@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-fsi@...ts.ozlabs.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [PATCH v2] fsi: fix bogus error returns from cfam_read
 and cfam_write

On 29/11/2019 03:24, Jeremy Kerr wrote:
> Based on a static analysis report and original patch from Colin Ian King
> <colin.king@...onical.com>.
> 
> Currently, we may drop error values from cfam_read and cfam_write. This
> change returns the actual error on failure, but a partial read/write will
> take precedence.
> 
> Addresses-Coverity: ("Unused value")
> Fixes: d1dcd6782576 ("fsi: Add cfam char devices")
> Reported-by: Colin Ian King <colin.king@...onical.com>
> Signed-off-by: Jeremy Kerr <jk@...abs.org>
> 
> ---
> Colin: thanks for the report and patch. I think this is a more complete
> fix, as we want to preseve any partial read/write status if a failure
> happens mid-way through an operation. Let me know if you (or the
> coverity analysis) have any feedback.

Looks good to me. Thanks Jeremy.



> 
> ---
> 
>  drivers/fsi/fsi-core.c | 32 ++++++++++++++++++++++----------
>  1 file changed, 22 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c
> index 71c6f9fef648..3158a78c2e94 100644
> --- a/drivers/fsi/fsi-core.c
> +++ b/drivers/fsi/fsi-core.c
> @@ -699,6 +699,8 @@ static ssize_t cfam_read(struct file *filep, char __user *buf, size_t count,
>  	if (off > 0xffffffff || count > 0xffffffff || off + count > 0xffffffff)
>  		return -EINVAL;
>  
> +	rc = 0;
> +
>  	for (total_len = 0; total_len < count; total_len += read_len) {
>  		__be32 data;
>  
> @@ -707,18 +709,22 @@ static ssize_t cfam_read(struct file *filep, char __user *buf, size_t count,
>  
>  		rc = fsi_slave_read(slave, off, &data, read_len);
>  		if (rc)
> -			goto fail;
> +			break;
>  		rc = copy_to_user(buf + total_len, &data, read_len);
>  		if (rc) {
>  			rc = -EFAULT;
> -			goto fail;
> +			break;
>  		}
>  		off += read_len;
>  	}
> -	rc = count;
> - fail:
> +
> +	/* if we've read any data, we want that to be returned in
> +	 * preference to an error state */
> +	if (total_len)
> +		rc = total_len;
> +
>  	*offset = off;
> -	return count;
> +	return rc;
>  }
>  
>  static ssize_t cfam_write(struct file *filep, const char __user *buf,
> @@ -736,6 +742,8 @@ static ssize_t cfam_write(struct file *filep, const char __user *buf,
>  	if (off > 0xffffffff || count > 0xffffffff || off + count > 0xffffffff)
>  		return -EINVAL;
>  
> +	rc = 0;
> +
>  	for (total_len = 0; total_len < count; total_len += write_len) {
>  		__be32 data;
>  
> @@ -745,17 +753,21 @@ static ssize_t cfam_write(struct file *filep, const char __user *buf,
>  		rc = copy_from_user(&data, buf + total_len, write_len);
>  		if (rc) {
>  			rc = -EFAULT;
> -			goto fail;
> +			break;
>  		}
>  		rc = fsi_slave_write(slave, off, &data, write_len);
>  		if (rc)
> -			goto fail;
> +			break;
>  		off += write_len;
>  	}
> -	rc = count;
> - fail:
> +
> +	/* if we've written any data, we want to indicate that partial write
> +	 * instead of any mid-stream error */
> +	if (total_len)
> +		rc = total_len;
> +
>  	*offset = off;
> -	return count;
> +	return rc;
>  }
>  
>  static loff_t cfam_llseek(struct file *file, loff_t offset, int whence)
>