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 a02fb65d0a4f918379635b1aee64641a0e6088bf..1ff3fc319d40b09ee23af3b75ac2ba39ab242d12 100644 (file)
--- 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;