Otherwise it is impossible to use it for something else, as it will break
userspace that puts garbage there.

The same check should be done in other structures, but the fact that
data in reserved fields is ignored is already part of the kernel ABI.

Signed-off-by: Eugene Syromiatnikov <redacted>
---
 drivers/ptp/ptp_chardev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c
index 797fab3..7cbea79 100644
--- a/drivers/ptp/ptp_chardev.c
+++ b/drivers/ptp/ptp_chardev.c

@@ -224,7 +224,8 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 			extoff = NULL;
 			break;
 		}
-		if (extoff->n_samples > PTP_MAX_SAMPLES) {
+		if (extoff->n_samples > PTP_MAX_SAMPLES
+		    || extoff->rsv[0] || extoff->rsv[1] || extoff->rsv[2]) {
 			err = -EINVAL;
 			break;
 		}

-- 
2.1.4