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

[Andrey Konovalov <andreyknvl@gmail.com>]

On Fri, Nov 19, 2021 at 3:22 PM Marco Elver <elver@google.com> wrote:
>
> 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:
> https://lkml.kernel.org/r/0000000000003f654905c168b09d@google.com
> , which was not detectable by software KASAN modes.
>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
>  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)))
>                 return;
>
>         cpus_read_lock();
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>

Thanks!