From: Tom Hughes <tom@compton.nu>
Date: Thu, 28 Oct 2004 08:09:05 +0000 (+0000)
Subject: Fixed get_height to ensure that SK_MAXHEIGHT-1 is the maximum level we
X-Git-Tag: svn/VALGRIND_3_0_0~1435
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=8e98a4127a18f37dfd2190bf96483e4dc9745462;p=thirdparty%2Fvalgrind.git

Fixed get_height to ensure that SK_MAXHEIGHT-1 is the maximum level we
will allocate for a skip list entry as many routines use arrays of
size SK_MAXHEIGHT to hold a set of level pointers which means that a
level of SK_MAXHEIGHT is not valid due to C arrays being zero based.

This led to a number of subtle and hard to locate problems caused by
stack based arrays being overflowed by one entry when a node was
allocated with the maximum level. As each node only has a one in two
million or so chance of getting a level of SK_MAXHEIGHT this didn't
actually happen all that often.

BUG: 91028


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@2862
---

diff --git a/coregrind/vg_skiplist.c b/coregrind/vg_skiplist.c
index a02fb65d0a..1ff3fc319d 100644
--- a/coregrind/vg_skiplist.c
+++ b/coregrind/vg_skiplist.c
@@ -112,7 +112,7 @@ static inline Int get_height(void)
 {
    UInt ret = 0;
 
-   while((ret < SK_MAXHEIGHT) && (random() & 1))
+   while((ret < SK_MAXHEIGHT - 1) && (random() & 1))
       ret++;
 
    return ret;