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[PATCH] kasan/quarantine: fix NULL pointer dereference bug

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  [PATCH] kasan/quarantine: fix NULL pointer dereference bug js1304@gmail.com - 2016-07-01 10:00 +0200
    Re: [PATCH] kasan/quarantine: fix NULL pointer dereference bug Kuthonuzo Luruo <poll.stdin@gmail.com> - 2016-07-01 13:20 +0200
    Re: [PATCH] kasan/quarantine: fix NULL pointer dereference bug Joonsoo Kim <js1304@gmail.com> - 2016-07-01 16:00 +0200

#1435101 — [PATCH] kasan/quarantine: fix NULL pointer dereference bug

From: Joonsoo Kim <iamjoonsoo.kim@lge.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.

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@lge.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 {
-- 
1.9.1

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#1435262

On Fri, Jul 1, 2016 at 1:41 PM, Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
>
>
> On 07/01/2016 10:53 AM, js1304@gmail.com wrote:
>> From: Joonsoo Kim <iamjoonsoo.kim@lge.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@lge.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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#1435347

2016-07-01 17:11 GMT+09:00 Andrey Ryabinin <aryabinin@virtuozzo.com>:
>
>
> On 07/01/2016 10:53 AM, js1304@gmail.com wrote:
>> From: Joonsoo Kim <iamjoonsoo.kim@lge.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.

You're right. Also, I find another bug on this function.
I manage them on v2 and sent.

Thanks.

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