[PATCH 5.7 22/79] lkdtm/heap: Avoid edge and middle of slabs

Greg Kroah-Hartman
2020-08-10T15:23:02Z

From: Kees Cook <keescook@chromium.org>

commit e12145cf1c3a8077e6d9f575711e38dd7d8a3ebc upstream.

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.

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>

---
drivers/misc/lkdtm/heap.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/misc/lkdtm/heap.c
+++ b/drivers/misc/lkdtm/heap.c
@@ -58,11 +58,12 @@ void lkdtm_READ_AFTER_FREE(void)
int *base, *val, saw;
size_t len = 1024;
/*
- * The slub allocator uses the first word to store the free
- * pointer in some configurations. Use the middle of the
- * allocation to avoid running into the freelist
+ * The slub allocator will use the either the first word or
+ * the middle of the allocation to store the free pointer,
+ * depending on configurations. Store in the second word to
+ * avoid running into the freelist.
*/
- size_t offset = (len / sizeof(*base)) / 2;
+ size_t offset = sizeof(*base);

base = kmalloc(len, GFP_KERNEL);
if (!base) {