Re: [PATCH] kasan/test: only do kmalloc_double_kzfree for generic mode

[Andrey Konovalov]

On Sun, May 17, 2026 at 9:17 AM Wang Wensheng <wsw9603@xxxxxxx> wrote:
>
> kmalloc_double_kzfree() would corrupt kernel memory when the just
> freed memory were allocated by another thread before the second
> call to kfree_sensitive().
>
> This could not happen in GENERIC mode as it uses quarantine.

Quite unfortunate to disable this test for HW_TAGS, but I don't see an
easy way to resolve the issue otherwise.

>
> Signed-off-by: Wang Wensheng <wsw9603@xxxxxxx>
> ---
>  mm/kasan/kasan_test_c.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
> index 32d06cbf6a31..02e43ccc9f21 100644
> --- a/mm/kasan/kasan_test_c.c
> +++ b/mm/kasan/kasan_test_c.c
> @@ -874,6 +874,12 @@ static void kmalloc_double_kzfree(struct kunit *test)
>         char *ptr;
>         size_t size = 16;
>
> +       /*
> +        * Only generic KASAN uses quarantine, which could prevent the just freed
> +        * memory from being allocated soon.
> +        */

Let's reword this to:

With the tag-based KASAN modes, if the memory happens to be
reallocated between the two frees and the new allocation tag happens
to match the old one, the second free will cause a memory corruption.
Resolving https://bugzilla.kernel.org/show_bug.cgi?id=212177 would
help to deal with this. With Generic KASAN, it's effectively
impossible for the memory to get reallocated due to the quarantine.

> +       KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC);
> +
>         ptr = kmalloc(size, GFP_KERNEL);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> --
> 2.43.0
>
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With the comment rewording:

Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>