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

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Date:	Fri, 1 Jul 2016 11:11:56 +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>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH] kasan/quarantine: fix NULL pointer dereference bug



On 07/01/2016 10:53 AM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> 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.
> 
> Unfortunately, I got this bug sometime ago and lose oops message.
> But, the bug looks trivial and no need to attach oops.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> ---
>  mm/kasan/quarantine.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
> index 4973505..9a132fd 100644
> --- a/mm/kasan/quarantine.c
> +++ b/mm/kasan/quarantine.c
> @@ -255,7 +255,7 @@ static void qlist_move_cache(struct qlist_head *from,
>  			} 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 {
>