Re: [PATCH v3] kasan/quarantine: fix bugs on qlist_move_cache()

[Dmitry Vyukov <dvyukov@google.com>]

On Fri, Jul 1, 2016 at 4:02 PM,  <js1304@gmail.com> wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@lge.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@lge.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;
>                 struct kmem_cache *obj_cache = qlink_to_cache(qlink);
>
> -               if (obj_cache == cache) {
> -                       if (unlikely(from->head == qlink)) {
> -                               from->head = curr->next;
> -                               prev = curr;
> -                       } else
> -                               prev->next = curr->next;
> -                       if (unlikely(from->tail == qlink))
> -                               from->tail = curr->next;
> -                       from->bytes -= cache->size;
> -                       qlist_put(to, qlink, cache->size);
> -               } else {
> -                       prev = curr;
> -               }
>                 curr = curr->next;
> +
> +               if (obj_cache == cache)
> +                       qlist_put(to, qlink, cache->size);
> +               else
> +                       qlist_put(from, qlink, cache->size);

This line is wrong. If obj_cache != cache, object size != cache->size.
Quarantine contains objects of different sizes.

>         }
>  }
>
> --
> 1.9.1
>

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