ptp: Validate requests to enable time stamping of external signals.

Commit 415606588c61 ("PTP: introduce new versions of IOCTLs")
introduced a new external time stamp ioctl that validates the flags.
This patch extends the validation to ensure that at least one rising
or falling edge flag is set when enabling external time stamps.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
index 67d01998..cbbe123 100644
--- a/drivers/ptp/ptp_chardev.c
+++ b/drivers/ptp/ptp_chardev.c
@@ -149,11 +149,19 @@
 			err = -EFAULT;
 			break;
 		}
-		if (((req.extts.flags & ~PTP_EXTTS_VALID_FLAGS) ||
-			req.extts.rsv[0] || req.extts.rsv[1]) &&
-			cmd == PTP_EXTTS_REQUEST2) {
-			err = -EINVAL;
-			break;
+		if (cmd == PTP_EXTTS_REQUEST2) {
+			/* Make sure no reserved bit is set. */
+			if ((req.extts.flags & ~PTP_EXTTS_VALID_FLAGS) ||
+			    req.extts.rsv[0] || req.extts.rsv[1]) {
+				err = -EINVAL;
+				break;
+			}
+			/* Ensure one of the rising/falling edge bits is set. */
+			if ((req.extts.flags & PTP_ENABLE_FEATURE) &&
+			    (req.extts.flags & PTP_EXTTS_EDGES) == 0) {
+				err = -EINVAL;
+				break;
+			}
 		} else if (cmd == PTP_EXTTS_REQUEST) {
 			req.extts.flags &= PTP_EXTTS_V1_VALID_FLAGS;
 			req.extts.rsv[0] = 0;
diff --git a/include/uapi/linux/ptp_clock.h b/include/uapi/linux/ptp_clock.h
index 59e89a1..304059b 100644
--- a/include/uapi/linux/ptp_clock.h
+++ b/include/uapi/linux/ptp_clock.h
@@ -31,6 +31,7 @@
 #define PTP_ENABLE_FEATURE (1<<0)
 #define PTP_RISING_EDGE    (1<<1)
 #define PTP_FALLING_EDGE   (1<<2)
+#define PTP_EXTTS_EDGES    (PTP_RISING_EDGE | PTP_FALLING_EDGE)
 
 /*
  * flag fields valid for the new PTP_EXTTS_REQUEST2 ioctl.