Re: [PATCH] kasan/quarantine: fix NULL pointer dereference bug

From: Andrey Ryabinin
Date: Fri Jul 01 2016 - 07:52:42 EST




On 07/01/2016 01:55 PM, Kuthonuzo Luruo wrote:
> On Fri, Jul 1, 2016 at 1:41 PM, Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote:
>>
>>
>> On 07/01/2016 10:53 AM, js1304@xxxxxxxxx wrote:
>>> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
>>>
>>> If we move an item on qlist's tail, we need to update qlist's tail
>>> properly. curr->next can be NULL since it is singly linked list
>>> so it is invalid for tail. curr is scheduled to be moved so
>>> using prev would be correct.
>>
>> Hmm.. prev may be the element that moved in 'to' list. We need to assign the last element
>> from which is in ther 'from' list.
>
> something like this should handle qlink == head == tail:
>
> --- a/mm/kasan/quarantine.c
> +++ b/mm/kasan/quarantine.c
> @@ -251,11 +251,11 @@ static void qlist_move_cache(struct qlist_head *from,
> if (obj_cache == cache) {
> if (unlikely(from->head == qlink)) {
> from->head = curr->next;
> - prev = curr;
> + prev = from->head;

This will break 'to' list.

> } else
> prev->next = curr->next;
> if (unlikely(from->tail == qlink))
> - from->tail = curr->next;
> + from->tail = prev;
> from->bytes -= cache->size;
> qlist_put(to, qlink, cache->size);
> } else {
>
>