Re: [PATCH v4 1/2] kasan: detect negative size in memory operation function

[Andrey Ryabinin]

On 11/21/19 4:02 PM, Walter Wu wrote:
> On Thu, 2019-11-21 at 15:26 +0300, Andrey Ryabinin wrote:
>>
>> On 11/12/19 9:53 AM, Walter Wu wrote:
>>
>>> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
>>> index 6814d6d6a023..4bfce0af881f 100644
>>> --- a/mm/kasan/common.c
>>> +++ b/mm/kasan/common.c
>>> @@ -102,7 +102,8 @@ EXPORT_SYMBOL(__kasan_check_write);
>>>  #undef memset
>>>  void *memset(void *addr, int c, size_t len)
>>>  {
>>> -	check_memory_region((unsigned long)addr, len, true, _RET_IP_);
>>> +	if (!check_memory_region((unsigned long)addr, len, true, _RET_IP_))
>>> +		return NULL;
>>>  
>>>  	return __memset(addr, c, len);
>>>  }
>>> @@ -110,8 +111,9 @@ void *memset(void *addr, int c, size_t len)
>>>  #undef memmove
>>>  void *memmove(void *dest, const void *src, size_t len)
>>>  {
>>> -	check_memory_region((unsigned long)src, len, false, _RET_IP_);
>>> -	check_memory_region((unsigned long)dest, len, true, _RET_IP_);
>>> +	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
>>> +	    !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
>>> +		return NULL;
>>>  
>>>  	return __memmove(dest, src, len);
>>>  }
>>> @@ -119,8 +121,9 @@ void *memmove(void *dest, const void *src, size_t len)
>>>  #undef memcpy
>>>  void *memcpy(void *dest, const void *src, size_t len)
>>>  {
>>> -	check_memory_region((unsigned long)src, len, false, _RET_IP_);
>>> -	check_memory_region((unsigned long)dest, len, true, _RET_IP_);
>>> +	if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) ||
>>> +	    !check_memory_region((unsigned long)dest, len, true, _RET_IP_))
>>> +		return NULL;
>>>  
>>
>> I realized that we are going a wrong direction here. Entirely skipping mem*() operation on any
>> poisoned shadow value might only make things worse. Some bugs just don't have any serious consequences,
>> but skipping the mem*() ops entirely might introduce such consequences, which wouldn't happen otherwise.
>>
>> So let's keep this code as this, no need to check the result of check_memory_region().
>>
>>
> Ok, we just need to determine whether size is negative number. If yes
> then KASAN produce report and continue to execute mem*(). right?
> 

Yes.