[src/trunk]: src/sys/kern adjtime(2): Handle negative tv_sec and tv_usec.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/d1f69b2ecf58
branches:  trunk
changeset: 366131:d1f69b2ecf58
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sun May 15 16:20:10 2022 +0000

description:
adjtime(2): Handle negative tv_sec and tv_usec.

Previously I clamped these to avoid dangerous arithmetic overflow.
But I assumed sensible values should be nonnegative.

For tv_sec, this assumption was just wrong -- the adjustment may be
negative.

For tv_usec, this assumption is...not wrong, but also not right.
tv_usec is not _supposed_ to be negative (by POSIX, the type need
only represent values in [-1, 1000000]; semantically the member is
supposed to be a nonnegative number of microseconds below 1000000),
but ntp abuses it to hold negative values, for reasons unclear -- the
same effect could be had by subtracting one from tv_sec, and adding
1000000 to the negative tv_usec.  However, let's not break existing
ntp userlands...

diffstat:

 sys/kern/kern_time.c |  10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diffs (32 lines):

diff -r 34cfebadc11e -r d1f69b2ecf58 sys/kern/kern_time.c
--- a/sys/kern/kern_time.c      Sun May 15 16:12:52 2022 +0000
+++ b/sys/kern/kern_time.c      Sun May 15 16:20:10 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_time.c,v 1.213 2022/03/13 12:21:28 riastradh Exp $        */
+/*     $NetBSD: kern_time.c,v 1.214 2022/05/15 16:20:10 riastradh Exp $        */
 
 /*-
  * Copyright (c) 2000, 2004, 2005, 2007, 2008, 2009, 2020
@@ -62,7 +62,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_time.c,v 1.213 2022/03/13 12:21:28 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_time.c,v 1.214 2022/05/15 16:20:10 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/resourcevar.h>
@@ -625,9 +625,11 @@
                 */
                if (delta->tv_sec > INT64_MAX/1000000 - 1) {
                        time_adjtime = INT64_MAX;
+               } else if (delta->tv_sec < INT64_MIN/1000000 + 1) {
+                       time_adjtime = INT64_MIN;
                } else {
-                       time_adjtime = MAX(0, delta->tv_sec) * 1000000
-                           + MAX(0, MIN(999999, delta->tv_usec));
+                       time_adjtime = delta->tv_sec * 1000000
+                           + MAX(-999999, MIN(999999, delta->tv_usec));
                }
 
                if (time_adjtime) {