Re: [PATCH v2 net-next] ptp: only allow phase values lower than 1 period

[Jacob Keller <jacob.e.keller@intel.com>]

On 8/4/2020 4:43 PM, Vladimir Oltean wrote:
> The way we define the phase (the difference between the time of the
> signal's rising edge, and the closest integer multiple of the period),
> it doesn't make sense to have a phase value larger than 1 period.
> 
> So deny these settings coming from the user.
> 
> Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
> ---
> Changes in v2:
> Be sure to also deny the case where the period is equal to the phase.
> This represents a 360 degree offset, which is equivalent to a phase of
> zero, so it should be rejected on the grounds of having a modulo
> equivalent as well.
> 
>  drivers/ptp/ptp_chardev.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
> index e0e6f85966e1..ee48eb61b49c 100644
> --- a/drivers/ptp/ptp_chardev.c
> +++ b/drivers/ptp/ptp_chardev.c
> @@ -218,6 +218,19 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
>  					break;
>  				}
>  			}
> +			if (perout->flags & PTP_PEROUT_PHASE) {
> +				/*
> +				 * The phase should be specified modulo the
> +				 * period, therefore anything larger than 1
> +				 * period is invalid.
> +				 */

A nit: this could read "therefore anything equal or larger than 1 period
is invalid"? a number modulo itself is 0, right? and we use ">=" below
as well now.

I do think it's relatively clear from context so it probably isn't worth
a re-roll.


> +				if (perout->phase.sec > perout->period.sec ||
> +				    (perout->phase.sec == perout->period.sec &&
> +				     perout->phase.nsec >= perout->period.nsec)) {
> +					err = -ERANGE;
> +					break;
> +				}
> +			}
>  		} else if (cmd == PTP_PEROUT_REQUEST) {
>  			req.perout.flags &= PTP_PEROUT_V1_VALID_FLAGS;
>  			req.perout.rsv[0] = 0;
>