lkdtm/heap: Avoid edge and middle of slabs

Har har, after I moved the slab freelist pointer into the middle of the
slab, now it looks like the contents are getting poisoned. Adjust the
test to avoid the freelist pointer again.

Change-Id: I46ac60db28cc3e0b6feb6ef3d07973c5eb237893
Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200625203704.317097-3-keescook@chromium.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: e12145cf1c3a8077e6d9f575711e38dd7d8a3ebc
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


Signed-off-by: Prateek Sood <prsood@codeaurora.org>