[PATCH 1/2] kasan: add ability to detect double-kmem_cache_destroy()

From: Marco Elver
Date: Fri Nov 19 2021 - 09:22:40 EST

Because mm/slab_common.c is not instrumented with software KASAN modes,
it is not possible to detect use-after-free of the kmem_cache passed
into kmem_cache_destroy(). In particular, because of the s->refcount--
and subsequent early return if non-zero, KASAN would never be able to
see the double-free via kmem_cache_free(kmem_cache, s). To be able to
detect a double-kmem_cache_destroy(), check accessibility of the
kmem_cache, and in case of failure return early.

While KASAN_HW_TAGS is able to detect such bugs, by checking
accessibility and returning early we fail more gracefully and also
avoid corrupting reused objects (where tags mismatch).

A recent case of a double-kmem_cache_destroy() was detected by KFENCE:
, which was not detectable by software KASAN modes.

Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
mm/slab_common.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index e5d080a93009..4bef4b6a2c76 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -491,7 +491,7 @@ void kmem_cache_destroy(struct kmem_cache *s)
int err;

- if (unlikely(!s))
+ if (unlikely(!s || !kasan_check_byte(s)))