linux-kernel - Re: [PATCH v3] kasan/quarantine: fix bugs on qlist_move

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Date:	Mon, 4 Jul 2016 12:43:44 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	<kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] kasan/quarantine: fix bugs on qlist_move_cache()



On 07/04/2016 07:36 AM, Joonsoo Kim wrote:
> On Fri, Jul 01, 2016 at 05:17:10PM +0300, Andrey Ryabinin wrote:
>>
>>
>> On 07/01/2016 05:02 PM, js1304@...il.com wrote:
>>> From: Joonsoo Kim <iamjoonsoo.kim@....com>
>>>
>>> There are two bugs on qlist_move_cache(). One is that qlist's tail
>>> isn't set properly. curr->next can be NULL since it is singly linked
>>> list and NULL value on tail is invalid if there is one item on qlist.
>>> Another one is that if cache is matched, qlist_put() is called and
>>> it will set curr->next to NULL. It would cause to stop the loop
>>> prematurely.
>>>
>>> These problems come from complicated implementation so I'd like to
>>> re-implement it completely. Implementation in this patch is really
>>> simple. Iterate all qlist_nodes and put them to appropriate list.
>>>
>>> Unfortunately, I got this bug sometime ago and lose oops message.
>>> But, the bug looks trivial and no need to attach oops.
>>>
>>> v3: fix build warning
>>>
>>> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>>> ---
>>>  mm/kasan/quarantine.c | 21 +++++++--------------
>>>  1 file changed, 7 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
>>> index 4973505..cf92494 100644
>>> --- a/mm/kasan/quarantine.c
>>> +++ b/mm/kasan/quarantine.c
>>> @@ -238,30 +238,23 @@ static void qlist_move_cache(struct qlist_head *from,
>>>  				   struct qlist_head *to,
>>>  				   struct kmem_cache *cache)
>>>  {
>>> -	struct qlist_node *prev = NULL, *curr;
>>> +	struct qlist_node *curr;
>>>  
>>>  	if (unlikely(qlist_empty(from)))
>>>  		return;
>>>  
>>>  	curr = from->head;
>>> +	qlist_init(from);
>>>  	while (curr) {
>>>  		struct qlist_node *qlink = curr;
>>
>> Can you please also get rid of either qlink or curr.
>> Those are essentially the same pointers.
> 
> Hello,
> 
> Before putting the qlist_node to the list, we need to calculate
> curr->next and remember it to iterate the list. I use curr
> for this purpose so qlink and curr are not the same pointer.
> 

Right, I missed the fact that qlist_put() changes ->next pointer, thus we  can't fetch ->next after qlist_put().

> Thanks.
>