linux-kernel - Re: [PATCH v4] kasan/quarantine: fix bugs on qlist_move

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Date:	Mon, 4 Jul 2016 12:49:08 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	<js1304@...il.com>, Andrew Morton <akpm@...ux-foundation.org>
CC:	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	<kasan-dev@...glegroups.com>,
	Kuthonuzo Luruo <poll.stdin@...il.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v4] kasan/quarantine: fix bugs on qlist_move_cache()



On 07/04/2016 07:31 AM, 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.
> 
> v4: fix cache size bug s/cache->size/obj_cache->size/
> 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..b2e1827 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;

Nit: Wouldn't be more appropriate to swap 'curr' and 'qlink' variable names?
Because now qlink is acts as a "current" pointer.

> +
> +		if (obj_cache == cache)
> +			qlist_put(to, qlink, obj_cache->size);
> +		else
> +			qlist_put(from, qlink, obj_cache->size);
>  	}
>  }
>  
>