Re: [PATCH v2] kasan: avoid overflowing quarantine size on low memory systems

[Andrey Ryabinin]

On 08/11/2016 04:42 PM, Alexander Potapenko wrote:
> On Thu, Aug 11, 2016 at 12:50 AM, Andrew Morton
> <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>> On Tue,  2 Aug 2016 12:27:00 +0200 Alexander Potapenko <glider@xxxxxxxxxx> wrote:
>>
>>> If the total amount of memory assigned to quarantine is less than the
>>> amount of memory assigned to per-cpu quarantines, |new_quarantine_size|
>>> may overflow. Instead, set it to zero.
>>>
>>> ...
>>>
>>> --- a/mm/kasan/quarantine.c
>>> +++ b/mm/kasan/quarantine.c
>>> @@ -196,7 +196,7 @@ void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
>>>
>>>  void quarantine_reduce(void)
>>>  {
>>> -     size_t new_quarantine_size;
>>> +     size_t new_quarantine_size, percpu_quarantines;
>>>       unsigned long flags;
>>>       struct qlist_head to_free = QLIST_INIT;
>>>       size_t size_to_free = 0;
>>> @@ -214,7 +214,9 @@ void quarantine_reduce(void)
>>>        */
>>>       new_quarantine_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) /
>>>               QUARANTINE_FRACTION;
>>> -     new_quarantine_size -= QUARANTINE_PERCPU_SIZE * num_online_cpus();
>>> +     percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
>>> +     new_quarantine_size = (new_quarantine_size < percpu_quarantines) ?
>>> +             0 : new_quarantine_size - percpu_quarantines;
>>>       WRITE_ONCE(quarantine_size, new_quarantine_size);
>>>
>>>       last = global_quarantine.head;
>>
>> Confused.  Which kernel version is this supposed to apply to?
> This is the second version of the patch which should've been applied
> to the mainline instead of v1.
> But since v1 has already hit upstream, this patch makes sense no more.
> If WARN_ONCE (which is currently present in this code) is a big deal,
> I can send a new patch that removes it.
> 

Probably not a big deal, but please, send the patch anyway.