Re: [Qemu-devel] [PATCH] filter-buffer: fix segfault while start qemu with status=off property

[Jason Wang]

On 04/01/2016 05:33 PM, Hailiang Zhang wrote:
> On 2016/4/1 17:10, Wen Congyang wrote:
>> On 04/01/2016 04:24 PM, Hailiang Zhang wrote:
>>> On 2016/4/1 15:39, Jason Wang wrote:
>>>>
>>>>
>>>> On 04/01/2016 03:08 PM, zhanghailiang wrote:
>>>>> After commit 338d3f, we support 'status' property for filter object.
>>>>> The segfault can be triggered by starting qemu with 'status=off'
>>>>> property
>>>>> for filter, when the s->incoming_queue is NULL, we reference it
>>>>> directly
>>>>> in qemu_net_queue_flush().
>>>>>
>>>>> Let's check the value of 's->incoming_queue' before calling
>>>>> qemu_net_queue_flush().
>>>>>
>>>>> Signed-off-by: zhanghailiang <address@hidden>
>>>>> ---
>>>>>    net/filter-buffer.c | 2 +-
>>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/net/filter-buffer.c b/net/filter-buffer.c
>>>>> index cc6bd94..79e2ce3 100644
>>>>> --- a/net/filter-buffer.c
>>>>> +++ b/net/filter-buffer.c
>>>>> @@ -34,7 +34,7 @@ static void filter_buffer_flush(NetFilterState *nf)
>>>>>    {
>>>>>        FilterBufferState *s = FILTER_BUFFER(nf);
>>>>>
>>>>> -    if (!qemu_net_queue_flush(s->incoming_queue)) {
>>>>> +    if (s->incoming_queue &&
>>>>> !qemu_net_queue_flush(s->incoming_queue)) {
>>>>>            /* Unable to empty the queue, purge remaining packets */
>>>>>            qemu_net_queue_purge(s->incoming_queue, nf->netdev);
>>>>>        }
>>>>
>>>> We'd better handle this at generic layer and don't let a specific net
>>>> filter need to worry about this.
>>>>
>>>> Looks like the issue is we may trigger status_changed() too early
>>>> (even
>>>> before the the filter was initialized).
>>>>
>>>
>>> Yes ~
>>>
>>>> How about not call status_changed() if the initialization is not done?
>>>>
>>>
>>> But seems that it is difficult to confirm if the filter is initialized
>>> or not ...
>>
>> If nfc->setup() is not called, nf->netdev is NULL.
>>
>
> Yes, you right, Jason, what's opinion ?
>
> Thanks,
> hailiang

Looks good. Please also add a comment of this in the patch.

Thanks

>
>> Thanks
>> Wen Congyang
>>
>>>
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