[src/trunk]: src/sys/kern ntp(9): Avoid left shift of negative.

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

details:   https://anonhg.NetBSD.org/src/rev/49994d8144b4
branches:  trunk
changeset: 363477:49994d8144b4
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sun Mar 13 12:57:33 2022 +0000

description:
ntp(9): Avoid left shift of negative.

Kinda silly that this is UB at all...

Reported-by: syzbot+baf29c7f0756293b8257%syzkaller.appspotmail.com@localhost

diffstat:

 sys/kern/kern_ntptime.c |  9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diffs (30 lines):

diff -r e613360206ae -r 49994d8144b4 sys/kern/kern_ntptime.c
--- a/sys/kern/kern_ntptime.c   Sun Mar 13 12:49:36 2022 +0000
+++ b/sys/kern/kern_ntptime.c   Sun Mar 13 12:57:33 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_ntptime.c,v 1.62 2022/03/13 12:30:47 riastradh Exp $      */
+/*     $NetBSD: kern_ntptime.c,v 1.63 2022/03/13 12:57:33 riastradh Exp $      */
 
 /*-
  * Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -60,7 +60,7 @@
 
 #include <sys/cdefs.h>
 /* __FBSDID("$FreeBSD: src/sys/kern/kern_ntptime.c,v 1.59 2005/05/28 14:34:41 rwatson Exp $"); */
-__KERNEL_RCSID(0, "$NetBSD: kern_ntptime.c,v 1.62 2022/03/13 12:30:47 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_ntptime.c,v 1.63 2022/03/13 12:57:33 riastradh Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ntp.h"
@@ -383,7 +383,10 @@
                ntv->offset = L_GINT(time_offset);
        else
                ntv->offset = L_GINT(time_offset) / 1000; /* XXX rounding ? */
-       ntv->freq = L_GINT((time_freq / 1000LL) << 16);
+       if (time_freq < 0)
+               ntv->freq = L_GINT(-((-time_freq / 1000LL) << 16));
+       else
+               ntv->freq = L_GINT((time_freq / 1000LL) << 16);
        ntv->maxerror = time_maxerror;
        ntv->esterror = time_esterror;
        ntv->status = time_status;