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

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Date:   Tue, 4 Aug 2020 16:23:35 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        jacob.e.keller@...el.com
Subject: Re: [PATCH net-next] ptp: only allow phase values lower than 1 period

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