Re: [PATCH v2 3/3] kasan: initialise array in kasan_memcmp test

Dmitry Vyukov
2020-01-16T08:07:45Z

On Thu, Jan 16, 2020 at 7:26 AM Daniel Axtens <dja@axtens.net> wrote:
>
> memcmp may bail out before accessing all the memory if the buffers
> contain differing bytes. kasan_memcmp calls memcmp with a stack array.
> Stack variables are not necessarily initialised (in the absence of a
> compiler plugin, at least). Sometimes this causes the memcpy to bail
> early thus fail to trigger kasan.
>
> Make sure the array initialised to zero in the code.
>
> No other test is dependent on the contents of an array on the stack.
>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Daniel Axtens <dja@axtens.net>

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

> ---
> lib/test_kasan.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index a130d75b9385..519b0f259e97 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -619,7 +619,7 @@ static noinline void __init kasan_memcmp(void)
> {
> char *ptr;
> size_t size = 24;
> - int arr[9];
> + int arr[9] = {};
>
> pr_info("out-of-bounds in memcmp\n");
> ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
> --
> 2.20.1
>
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