linux-kernel - Re: [PATCH 01/32] kasan: check KASAN_NO_FREE_META in __kasan_metadata

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Date:   Mon, 20 Jun 2022 15:39:25 +0200
From:   Marco Elver <elver@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com, Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Florian Mayer <fmayer@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH 01/32] kasan: check KASAN_NO_FREE_META in __kasan_metadata_size

On Mon, 13 Jun 2022 at 22:15, <andrey.konovalov@...ux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@...gle.com>
>
> __kasan_metadata_size() calculates the size of the redzone for objects
> in a slab cache.
>
> When accounting for presence of kasan_free_meta in the redzone, this
> function only compares free_meta_offset with 0. But free_meta_offset could
> also be equal to KASAN_NO_FREE_META, which indicates that kasan_free_meta
> is not present at all.
>
> Add a comparison with KASAN_NO_FREE_META into __kasan_metadata_size().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>

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


> ---
>
> This is a minor fix that only affects slub_debug runs, so it is probably
> not worth backporting.
> ---
>  mm/kasan/common.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index c40c0e7b3b5f..968d2365d8c1 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -223,8 +223,9 @@ size_t __kasan_metadata_size(struct kmem_cache *cache)
>                 return 0;
>         return (cache->kasan_info.alloc_meta_offset ?
>                 sizeof(struct kasan_alloc_meta) : 0) +
> -               (cache->kasan_info.free_meta_offset ?
> -               sizeof(struct kasan_free_meta) : 0);
> +               ((cache->kasan_info.free_meta_offset &&
> +                 cache->kasan_info.free_meta_offset != KASAN_NO_FREE_META) ?
> +                sizeof(struct kasan_free_meta) : 0);
>  }
>
>  struct kasan_alloc_meta *kasan_get_alloc_meta(struct kmem_cache *cache,
> --
> 2.25.1
>
> --
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