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

[long.wanglong]

On 2015/9/9 17:40, Andrey Ryabinin wrote:
> 2015-09-09 6:59 GMT+03:00 Wang Long <long.wanglong@xxxxxxxxxx>:
>> 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@xxxxxxxxxx>
>> ---
>>  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.


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


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