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

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

[Vladimir Oltean]

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>
---
 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..02fcd5e8b998 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.
+				 */
+				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;
-- 
2.25.1

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

[David Miller]

From: Vladimir Oltean <olteanv@gmail.com>
Date: Mon,  3 Aug 2020 22:49:21 +0300

> 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>

Richard, please review.

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

[David Miller]

From: Vladimir Oltean <olteanv@gmail.com>
Date: Mon,  3 Aug 2020 22:49:21 +0300

> 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>

Richard, I need your review on this patch.

Thank you.

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

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

[Vladimir Oltean]

On Tue, Aug 04, 2020 at 04:23:35PM -0700, Richard Cochran wrote:
> 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

Oof, I guess this is what one would call 'brain fart'. In my mind,
checking for equality between period and phase required an extra 'if',
which I was reluctant to add (or to even think about, it seems). I
converted the nsec check to >= and it works as it should (I checked with
a modified ts2phc).

ts2phc[326.764]: config item /dev/ptp1.ts2phc.perout_phase is 1000000000
ts2phc[326.764]: config item /dev/ptp1.ts2phc.pulsewidth is 500000000
ts2phc[326.764]: PTP_PEROUT_REQUEST2 failed: Numerical result out of range

I'm sending a v2 with your change very soon.

Thanks.
-Vladimir