[src/trunk]: src/sys/kern Avoid undefined behavior in mq_recv1()

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

details:   https://anonhg.NetBSD.org/src/rev/37c09770af8a
branches:  trunk
changeset: 323873:37c09770af8a
user:      kamil <kamil%NetBSD.org@localhost>
date:      Wed Jul 04 17:39:12 2018 +0000

description:
Avoid undefined behavior in mq_recv1()

Do not shift a signed integer causing change of the signed bit.

sys/kern/sys_mqueue.c:712:24, left shift of 1 by 31 places cannot be represented in type 'int'

Detected with Kernel Undefined Behavior Sanitizer.

Reported by <Harry Pantazis>

diffstat:

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

diffs (27 lines):

diff -r 957f115d3187 -r 37c09770af8a sys/kern/sys_mqueue.c
--- a/sys/kern/sys_mqueue.c     Wed Jul 04 15:38:46 2018 +0000
+++ b/sys/kern/sys_mqueue.c     Wed Jul 04 17:39:12 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: sys_mqueue.c,v 1.40 2017/11/30 20:25:55 christos Exp $ */
+/*     $NetBSD: sys_mqueue.c,v 1.41 2018/07/04 17:39:12 kamil Exp $    */
 
 /*
  * Copyright (c) 2007-2011 Mindaugas Rasiukevicius <rmind at NetBSD org>
@@ -43,7 +43,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_mqueue.c,v 1.40 2017/11/30 20:25:55 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_mqueue.c,v 1.41 2018/07/04 17:39:12 kamil Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -709,7 +709,7 @@
        /* Unmark the bit, if last message. */
        if (__predict_true(idx) && TAILQ_EMPTY(&mq->mq_head[idx])) {
                KASSERT((MQ_PQSIZE - idx) == msg->msg_prio);
-               mq->mq_bitmap &= ~(1 << --idx);
+               mq->mq_bitmap &= ~(1U << --idx);
        }
 
        /* Decrement the counter and signal waiter, if any */