[patch] adjtimex() modes argument checking

[Michael Kerrisk <mtk.manpages@gmail.com>]

Hi Roman,

I see you added a number of new modes to adtimex() in 2.6.26-rc.
Since these are userspace-visible changes, please CC me, so
that they stand a chance of getting documented in man-pages.
(I discovered these changes only by accident.)

I also have some changes to suggest for argument checking, which,
if I understand the code correctly, prevent obvious screw-ups by
callers of adjtimex().  What do you think of the patch below?

Cheers,

Michael

--- linux-2.6.26-rc6/kernel/time/ntp.c        2008-06-22 09:05:05.000000000 +0200
+++ linux-2.6.26-rc6-p/kernel/time/ntp.c       2008-06-22 09:04:31.000000000 +0200
@@ -292,6 +292,16 @@
                         return -EINVAL;
         }

+       /* These modes are the converse of one another  */
+
+       if ((txc->modes & ADJ_MICRO) && (txc->modes & ADJ_NANO))
+               return -EINVAL;
+
+       /* Both of the following want to use txc->constant */
+
+       if ((txc->modes & ADJ_TIMECONST) && (txc->modes & ADJ_TAI))
+               return -EINVAL;
+
         /* if the quartz is off by more than 10% something is VERY wrong ! */
         if (txc->modes & ADJ_TICK)
                 if (txc->tick <  900000/USER_HZ ||