linux-kernel - Re: [PATCH 2/2] kasan: Fix a type conversion error

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Date:	Wed, 9 Sep 2015 12:40:13 +0300
From:	Andrey Ryabinin <ryabinin.a.a@...il.com>
To:	Wang Long <long.wanglong@...wei.com>
Cc:	Andrey Konovalov <adech.fo@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, wanglong@...qinren.net,
	peifeiyue@...wei.com, morgan.wang@...wei.com
Subject: Re: [PATCH 2/2] kasan: Fix a type conversion error

2015-09-09 6:59 GMT+03:00 Wang Long <long.wanglong@...wei.com>:
> The current KASAN code can find the following out-of-bounds
> bugs:
>         char *ptr;
>         ptr = kmalloc(8, GFP_KERNEL);
>         memset(ptr+7, 0, 2);
>
> the cause of the problem is the type conversion error in
> *memory_is_poisoned_n* function. So this patch fix that.
>
> Signed-off-by: Wang Long <long.wanglong@...wei.com>
> ---
>  mm/kasan/kasan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
> index 7b28e9c..5d65d06 100644
> --- a/mm/kasan/kasan.c
> +++ b/mm/kasan/kasan.c
> @@ -204,7 +204,7 @@ static __always_inline bool memory_is_poisoned_n(unsigned long addr,
>                 s8 *last_shadow = (s8 *)kasan_mem_to_shadow((void *)last_byte);
>
>                 if (unlikely(ret != (unsigned long)last_shadow ||
> -                       ((last_byte & KASAN_SHADOW_MASK) >= *last_shadow)))
> +                       ((long)(last_byte & KASAN_SHADOW_MASK) >= *last_shadow)))

Is there any problem if we just define last_byte as 'long' instead of
'unsigned long' ?

>                         return true;
>         }
>         return false;
> --
> 1.8.3.4
>
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