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

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

On 09/09/2015 01:22 PM, long.wanglong wrote:
> On 2015/9/9 17:40, Andrey Ryabinin wrote:
>> 2015-09-09 6:59 GMT+03:00 Wang Long <long.wanglong@huawei.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@huawei.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' ?
> 
> yes, I think it is not OK, because on my test, if we define last_byte as 'long'
> instead of 'unsigned long', the bug we talk about can not be found.
> 

Ah, right, even if we declare last_byte as signed, 'last_byte & KASAN_SHADOW_MASK' still will
be unsigned, so this won't work.

So, please, fix up changelog according to Vladimir,
and you may consider this patch

	Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>