linux-kernel - Re: [PATCH v4 2/2] kasan: add double-free tests

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Date:	Tue, 7 Jun 2016 16:02:34 +0200
From:	Alexander Potapenko <glider@...gle.com>
To:	Kuthonuzo Luruo <kuthonuzo.luruo@....com>
Cc:	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Dmitriy Vyukov <dvyukov@...gle.com>,
	Christoph Lameter <cl@...ux.com>, penberg@...nel.org,
	rientjes@...gle.com, Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	kasan-dev <kasan-dev@...glegroups.com>,
	LKML <linux-kernel@...r.kernel.org>, ynorov@...iumnetworks.com
Subject: Re: [PATCH v4 2/2] kasan: add double-free tests

On Sun, May 29, 2016 at 6:17 PM, Kuthonuzo Luruo
<kuthonuzo.luruo@....com> wrote:
> This patch adds new tests for KASAN double-free error detection when the
> same slab object is concurrently deallocated.
>
> Signed-off-by: Kuthonuzo Luruo <kuthonuzo.luruo@....com>
> ---
>
> Changes in v4:
> - There are *no* changes for v4.
>
> Changes in v3:
> - concurrent double-free test simplified to use on_each_cpu_mask() instead
>   of custom threads.
> - reduced #threads and removed CONFIG_SMP guards per suggestion from Dmitry
>   Vyukov.
>
> ---
>
>  lib/test_kasan.c |   47 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 47 insertions(+), 0 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 5e51872..0f589e7 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -411,6 +411,49 @@ static noinline void __init copy_user_test(void)
>         kfree(kmem);
>  }
>
> +#ifdef CONFIG_SLAB
> +static void try_free(void *p)
> +{
> +       kfree(p);
> +}
> +
> +static void __init kasan_double_free_concurrent(void)
> +{
> +#define MAX_THREADS 3
> +       char *p;
> +       int cpu, cnt = num_online_cpus();
> +       cpumask_t mask = { CPU_BITS_NONE };
> +       size_t size = 4097;     /* must be <= KMALLOC_MAX_CACHE_SIZE/2 */
Can you please explicitly calculate |size| from KMALLOC_MAX_CACHE_SIZE?
> +
> +       if (cnt == 1)
> +               return;
> +       cnt = cnt < MAX_THREADS ? cnt : MAX_THREADS;
> +       pr_info("concurrent double-free (%d threads)\n", cnt);
> +       p = kmalloc(size, GFP_KERNEL);
> +       if (!p)
> +               return;
> +       for_each_online_cpu(cpu) {
> +               cpumask_set_cpu(cpu, &mask);
> +               if (!--cnt)
> +                       break;
> +       }
> +       on_each_cpu_mask(&mask, try_free, p, 0);
> +}
> +
> +static noinline void __init kasan_double_free(void)
> +{
> +       char *p;
> +       size_t size = 2049;
Please avoid using magic constants.
> +
> +       pr_info("double-free\n");
> +       p = kmalloc(size, GFP_KERNEL);
> +       if (!p)
> +               return;
> +       kfree(p);
> +       kfree(p);
> +}
> +#endif
> +
>  static int __init kmalloc_tests_init(void)
>  {
>         kmalloc_oob_right();
> @@ -436,6 +479,10 @@ static int __init kmalloc_tests_init(void)
>         kasan_global_oob();
>         ksize_unpoisons_memory();
>         copy_user_test();
> +#ifdef CONFIG_SLAB
> +       kasan_double_free();
> +       kasan_double_free_concurrent();
> +#endif
>         return -EAGAIN;
>  }
>
> --
> 1.7.1
>



-- 
Alexander Potapenko
Software Engineer

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