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

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Date:	Mon, 4 Jul 2016 13:36:48 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Andrey Ryabinin <aryabinin@...tuozzo.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 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.

Thanks.