ptp: check gettime64 return code in PTP_SYS_OFFSET ioctl

If a gettime64 call fails, return the error and avoid copying data back
to user.

Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: NMiroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/ptp/ptp_chardev.c

@@ -228,7 +228,9 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 			pct->sec = ts.tv_sec;
 			pct->nsec = ts.tv_nsec;
 			pct++;
-			ptp->info->gettime64(ptp->info, &ts);
+			err = ptp->info->gettime64(ptp->info, &ts);
+			if (err)
+				goto out;
 			pct->sec = ts.tv_sec;
 			pct->nsec = ts.tv_nsec;
 			pct++;
@@ -281,6 +283,7 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 		break;
 	}
 
+out:
 	kfree(sysoff);
 	return err;
 }