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

[Alexander Potapenko]

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.


-- 
Alexander Potapenko
Software Engineer

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