[src/trunk]: src/sys/ufs/ffs Avoid Undefined Behavior in ffs_clusteracct()

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

details:   https://anonhg.NetBSD.org/src/rev/4b8e0bcc607a
branches:  trunk
changeset: 991247:4b8e0bcc607a
user:      kamil <kamil%NetBSD.org@localhost>
date:      Wed Jul 04 02:02:15 2018 +0000

description:
Avoid Undefined Behavior in ffs_clusteracct()

Change the type of 'bit' variable from int to unsigned int and use unsigned
values consistently.

sys/ufs/ffs/ffs_subr.c:336:10, shift exponent -1 is negative

Detected with Kernel Undefined Behavior Sanitizer.

Reported by <Harry Pantazis>

diffstat:

 sys/ufs/ffs/ffs_subr.c |  13 +++++++------
 1 files changed, 7 insertions(+), 6 deletions(-)

diffs (55 lines):

diff -r e628e418962a -r 4b8e0bcc607a sys/ufs/ffs/ffs_subr.c
--- a/sys/ufs/ffs/ffs_subr.c    Wed Jul 04 01:42:37 2018 +0000
+++ b/sys/ufs/ffs/ffs_subr.c    Wed Jul 04 02:02:15 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: ffs_subr.c,v 1.49 2016/05/07 11:59:08 maxv Exp $       */
+/*     $NetBSD: ffs_subr.c,v 1.50 2018/07/04 02:02:15 kamil Exp $      */
 
 /*
  * Copyright (c) 1982, 1986, 1989, 1993
@@ -36,7 +36,7 @@
 #endif
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: ffs_subr.c,v 1.49 2016/05/07 11:59:08 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: ffs_subr.c,v 1.50 2018/07/04 02:02:15 kamil Exp $");
 
 #include <sys/param.h>
 
@@ -287,7 +287,8 @@
        int32_t *sump;
        int32_t *lp;
        u_char *freemapp, *mapp;
-       int i, start, end, forw, back, map, bit;
+       int i, start, end, forw, back, map;
+       unsigned int bit;
        const int needswap = UFS_FSNEEDSWAP(fs);
 
        /* KASSERT(mutex_owned(&ump->um_lock)); */
@@ -312,7 +313,7 @@
                end = ufs_rw32(cgp->cg_nclusterblks, needswap);
        mapp = &freemapp[start / NBBY];
        map = *mapp++;
-       bit = 1 << (start % NBBY);
+       bit = 1U << (start % NBBY);
        for (i = start; i < end; i++) {
                if ((map & bit) == 0)
                        break;
@@ -333,7 +334,7 @@
                end = -1;
        mapp = &freemapp[start / NBBY];
        map = *mapp--;
-       bit = 1 << (start % NBBY);
+       bit = 1U << (start % NBBY);
        for (i = start; i > end; i--) {
                if ((map & bit) == 0)
                        break;
@@ -341,7 +342,7 @@
                        bit >>= 1;
                } else {
                        map = *mapp--;
-                       bit = 1 << (NBBY - 1);
+                       bit = 1U << (NBBY - 1);
                }
        }
        back = start - i;