[OpenWrt-Devel] [PATCH] runqueue: Fix the callbacks order in runqueue_task_kill()

[John Crispin]

On 01/07/2019 16:23, Alban wrote:
> On Mon, 1 Jul 2019 15:48:47 +0200
> John Crispin <john at phrozen.org> wrote:
>
>> On 21/06/2019 17:38, Alban Bedel wrote:
>>> Since commit 11e8afea (runqueue should cal the complete handler from
>>> more places) the call to the complete() callback has been moved to
>>> runqueue_task_complete().  However in runqueue_task_kill()
>>> runqueue_task_complete() is called before the kill() callback.
>>> This will result in a use after free if the complete() callback free
>>> the task struct.
>>>
>>> Furthermore runqueue_start_next() is already called at the end of
>>> runqueue_task_complete(), so there is no need to call it again in
>>> runqueue_task_kill().
>>>
>>> Signed-off-by: Alban Bedel <albeu at free.fr>
>>> ---
>>>    runqueue.c | 4 +---
>>>    1 file changed, 1 insertion(+), 3 deletions(-)
>>>
>>> diff --git a/runqueue.c b/runqueue.c
>>> index a1d0133..4c621aa 100644
>>> --- a/runqueue.c
>>> +++ b/runqueue.c
>>> @@ -196,11 +196,9 @@ void runqueue_task_kill(struct runqueue_task
>>> *t) if (!t->queued)
>>>    		return;
>>>    
>>> -	runqueue_task_complete(t);
>>>    	if (running && t->type->kill)
>>>    		t->type->kill(q, t);
>>> -
>>> -	runqueue_start_next(q);
>>> +	runqueue_task_complete(t);
>>>    }
>>>    
>>>    void runqueue_stop(struct runqueue *q)
>> Hi,
>>
>> runqueue_task_complete() will decrement running which, if called
>> after the kill clause might not even trigger the kill() call. I am
>> assuming you are running a custom runqueue_task_type ?
> No, TBH I haven't tested this, but as there is no documentation I had
> to go through the code and noticed this suspicious construct. I then
> saw commit 6a7fb7d8d (runqueue: fix use-after-free bug) which confirmed
> that complete() is expected to free the task struct, which with the
> above code will clearly lead to an access after free.
>
> But I don't really see what you mean, 'running' is a boolean so it
> can't be decremented. Did you mean 'running_tasks'?
>
> Alban


i did actually mean running_task, I'll have another look later on today

     John


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