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

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Date:	Fri, 1 Jul 2016 16:25:32 +0530
From:	Kuthonuzo Luruo <poll.stdin@...il.com>
To:	Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:	js1304@...il.com, 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,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH] kasan/quarantine: fix NULL pointer dereference bug

On Fri, Jul 1, 2016 at 1:41 PM, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
>
>
> 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.

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;
                        } 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 {

>>
>> 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 {
>>
>
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