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

[Vladimir Oltean <olteanv@gmail.com>]

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.
+				 */
+				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