[src/trunk]: src/sys/kern ts2timo(9): refactor TIMER_ABSTIME handling

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

details:   https://anonhg.NetBSD.org/src/rev/9f2065fa4a8c
branches:  trunk
changeset: 953712:9f2065fa4a8c
user:      nia <nia%NetBSD.org@localhost>
date:      Thu Mar 18 14:01:18 2021 +0000

description:
ts2timo(9): refactor TIMER_ABSTIME handling

- only use *start for output of the original time.
  for clarity purposes, use the temporary variable for everything else.
- add a check for integer underflow

Reported-by: syzbot+17b5072d5ed262a966d3%syzkaller.appspotmail.com@localhost

diffstat:

 sys/kern/subr_time.c |  21 ++++++++++++---------
 1 files changed, 12 insertions(+), 9 deletions(-)

diffs (46 lines):

diff -r 7c76a5caa8de -r 9f2065fa4a8c sys/kern/subr_time.c
--- a/sys/kern/subr_time.c      Thu Mar 18 13:45:15 2021 +0000
+++ b/sys/kern/subr_time.c      Thu Mar 18 14:01:18 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: subr_time.c,v 1.28 2021/03/18 13:45:15 nia Exp $       */
+/*     $NetBSD: subr_time.c,v 1.29 2021/03/18 14:01:18 nia Exp $       */
 
 /*
  * Copyright (c) 1982, 1986, 1989, 1993
@@ -33,7 +33,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_time.c,v 1.28 2021/03/18 13:45:15 nia Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_time.c,v 1.29 2021/03/18 14:01:18 nia Exp $");
 
 #include <sys/param.h>
 #include <sys/kernel.h>
@@ -332,17 +332,20 @@
        if (ts->tv_nsec < 0 || ts->tv_nsec >= 1000000000L)
                return EINVAL;
 
-       if (start == NULL)
-               start = &tsd;
-
-       if (flags != TIMER_RELTIME || start != &tsd) {
-               error = clock_gettime1(clock_id, start);
+       if (flags == TIMER_ABSTIME || start != NULL) {
+               error = clock_gettime1(clock_id, &tsd);
                if (error != 0)
                        return error;
+               if (start != NULL)
+                       *start = tsd;
        }
 
-       if (flags != TIMER_RELTIME)
-               timespecsub(ts, start, ts);
+       if (flags == TIMER_ABSTIME) {
+               if ((tsd.tv_sec > 0 && ts->tv_sec < LLONG_MIN + tsd.tv_sec) ||
+                   (tsd.tv_sec < 0 && ts->tv_sec > LLONG_MAX + tsd.tv_sec))
+                       return EINVAL;
+               timespecsub(ts, &tsd, ts);
+       }
 
        error = itimespecfix(ts);
        if (error != 0)