ptp: use memdup_user().

Use memdup_user to duplicate a memory region from user-space to
kernel-space, instead of open coding using kmalloc & copy_from_user.

Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/ptp/ptp_chardev.c

@@ -208,14 +208,9 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 		break;
 
 	case PTP_SYS_OFFSET:
-		sysoff = kmalloc(sizeof(*sysoff), GFP_KERNEL);
+		sysoff = memdup_user((void __user *)arg, sizeof(*sysoff));
-		if (!sysoff) {
+		if (IS_ERR(sysoff)) {
-			err = -ENOMEM;
+			err = PTR_ERR(sysoff);
-			break;
-		}
-		if (copy_from_user(sysoff, (void __user *)arg,
-				   sizeof(*sysoff))) {
-			err = -EFAULT;
 			break;
 		}
 		if (sysoff->n_samples > PTP_MAX_SAMPLES) {