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From:   Marco Elver <elver@google.com>
Date:   Thu, 12 Aug 2021 10:50:30 +0200
Message-ID: <CANpmjNOf=XzX1xhjaz7+SBN2HYq+9jH4EcHi4gfwjSyTa3q00w@mail.gmail.com>
Subject: Re: [PATCH 8/8] kasan: test: avoid corrupting memory in kasan_rcu_uaf
To:     andrey.konovalov@linux.dev
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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On Wed, 11 Aug 2021 at 21:34, <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@gmail.com>
>
> kasan_rcu_uaf() writes to freed memory via kasan_rcu_reclaim(), which is
> only safe with the GENERIC mode (as it uses quarantine). For other modes,
> this test corrupts kernel memory, which might result in a crash.
>
> Turn the write into a read.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>

Reviewed-by: Marco Elver <elver@google.com>


> ---
>  lib/test_kasan_module.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c
> index fa73b9df0be4..7ebf433edef3 100644
> --- a/lib/test_kasan_module.c
> +++ b/lib/test_kasan_module.c
> @@ -71,7 +71,7 @@ static noinline void __init kasan_rcu_reclaim(struct rcu_head *rp)
>                                                 struct kasan_rcu_info, rcu);
>
>         kfree(fp);
> -       fp->i = 1;
> +       ((volatile struct kasan_rcu_info *)fp)->i;
>  }
>
>  static noinline void __init kasan_rcu_uaf(void)
> --
> 2.25.1
>