[PATCH linux dev-4.13 v2] fsi: occ: Add check for OCC response checksum

[Andrew Jeffery]

On Wed, 2 May 2018, at 00:21, Eddie James wrote:
> The OCC specification indicates that it is an error scenario if the
> response checksum doesn't match the sum of the bytes of the response.
> The driver needs to perform this calculation and check, and return an
> error if it's a mismatch.
> 
> Signed-off-by: Eddie James <eajames at linux.vnet.ibm.com>

Acked-by: Andrew Jeffery <andrew at aj.id.au>

> ---
> Changes since v1:
>  - rename occ_check_sum() to occ_verify_checksum()
>  - remove checksum field from occ_response and instead add two bytes to data
>    field, with comment
>  - add comment to fetching checksum from response data
> 
>  drivers/fsi/fsi-occ.c | 26 ++++++++++++++++++++++++--
>  1 file changed, 24 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/fsi/fsi-occ.c b/drivers/fsi/fsi-occ.c
> index 45ae13c..8df1c64 100644
> --- a/drivers/fsi/fsi-occ.c
> +++ b/drivers/fsi/fsi-occ.c
> @@ -58,8 +58,7 @@ struct occ_response {
>  	u8 cmd_type;
>  	u8 return_status;
>  	__be16 data_length;
> -	u8 data[OCC_RESP_DATA_BYTES];
> -	__be16 checksum;
> +	u8 data[OCC_RESP_DATA_BYTES + 2];	/* two bytes checksum */
>  } __packed;
>  
>  /*
> @@ -427,6 +426,27 @@ static int occ_release(struct inode *inode, struct 
> file *file)
>  	.release = occ_release,
>  };
>  
> +static int occ_verify_checksum(struct occ_response *resp, u16 data_length)
> +{
> +	u16 i;
> +	u16 checksum;
> +	/* Fetch the two bytes after the data for the checksum. */
> +	u16 checksum_resp = get_unaligned_be16(&resp->data[data_length]);
> +
> +	checksum = resp->seq_no;
> +	checksum += resp->cmd_type;
> +	checksum += resp->return_status;
> +	checksum += (data_length >> 8) + (data_length & 0xFF);
> +
> +	for (i = 0; i < data_length; ++i)
> +		checksum += resp->data[i];
> +
> +	if (checksum != checksum_resp)
> +		return -EBADMSG;
> +
> +	return 0;
> +}
> +
>  static int occ_write_sbefifo(struct sbefifo_client *client, const char *buf,
>  			     ssize_t len)
>  {
> @@ -692,6 +712,8 @@ static void occ_worker(struct work_struct *work)
>  
>  	xfr->resp_data_length = resp_data_length + 7;
>  
> +	rc = occ_verify_checksum(resp, resp_data_length);
> +
>  done:
>  	mutex_unlock(&occ->occ_lock);
>  
> -- 
> 1.8.3.1
>