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

[Richard Cochran]

On Mon, Aug 03, 2020 at 10:49:21PM +0300, Vladimir Oltean wrote:
> @@ -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.
> +                              */
> +                             if (perout->phase.sec > perout->period.sec ||
> +                                 (perout->phase.sec == perout->period.sec &&
> +                                  perout->phase.nsec > perout->period.nsec)) 
> {
> +                                     err = -ERANGE;
> +                                     break;
> +                             }

So if perout->period={1,0} and perout->phase={1,0} then the phase has
wrapped 360 degrees back to zero.

Shouldn't this code catch that case as well?

So why not test for (perout->phase.nsec >= perout->period.nsec) instead?

Thanks,
Richard