Re: [PATCH 09/11] kasan: fix memory corruption in kasan_bitops_tags test

[Alexander Potapenko]

On Tue, Jan 5, 2021 at 7:28 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> Since the hardware tag-based KASAN mode might not have a redzone that
> comes after an allocated object (when kasan.mode=prod is enabled), the
> kasan_bitops_tags() test ends up corrupting the next object in memory.
>
> Change the test so it always accesses the redzone that lies within the
> allocated object's boundaries.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Link: https://linux-review.googlesource.com/id/I67f51d1ee48f0a8d0fe2658c2a39e4879fe0832a
> ---
>  lib/test_kasan.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index b67da7f6e17f..3ea52da52714 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -771,17 +771,17 @@ static void kasan_bitops_tags(struct kunit *test)
>
>         /* This test is specifically crafted for the tag-based mode. */
>         if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> -               kunit_info(test, "skipping, CONFIG_KASAN_SW_TAGS required");
> +               kunit_info(test, "skipping, CONFIG_KASAN_SW/HW_TAGS required");
>                 return;
>         }
>
> -       /* Allocation size will be rounded to up granule size, which is 16. */
> -       bits = kzalloc(sizeof(*bits), GFP_KERNEL);
> +       /* kmalloc-64 cache will be used and the last 16 bytes will be the redzone. */
> +       bits = kzalloc(48, GFP_KERNEL);

I think it might make sense to call ksize() here to ensure we have
these spare bytes.