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Date: Thu, 20 Nov 2014 16:24:30 +0800
From: Jason Wang <jasowang@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 4/4] rtl8139: fix Pointer to local outside
 scope
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To: Gonglei <arei.gonglei@huawei.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "stefanha@redhat.com" <stefanha@redhat.com>, "Huangpeng (Peter)" <peter.huangpeng@huawei.com>

On 11/20/2014 04:18 PM, Gonglei wrote:
> On 2014/11/20 16:11, Jason Wang wrote:
>
>> On 11/20/2014 04:05 PM, Gonglei wrote:
>>> On 2014/11/20 15:50, Jason Wang wrote:
>>>
>>>>>> Maybe just initialize iov unconditionally at the beginning and check
>>>>>>>> dot1q_buf instead of iov for the rest of the functions. (Need deal with
>>>>>>>> size < ETHER_ADDR_LEN * 2)
>>>>>> More complicated, because we can't initialize iov when
>>>>>>  "size < ETHER_ADDR_LEN * 2".
>>>>>>
>>>>>> Best regards,
>>>>>> -Gonglei
>>>>>>
>>>> Probably not: you can just do something like:
>>>>
>>>>     if (dot1q_buf && size < ETHER_ADDR_LEN * 2) {
>>>>         dot1q_buf = NULL;
>>>>     }
>>>>
>>>> and check dot1q_buf afterwards. Or just drop the packet since its size
>>>> was less than mininum frame length that Ethernet allows.
>>> Sorry, I don't understand. But,
>>> what's your meaning "initialize iov unconditionally at the beginning"?
>> Something like:
>>
>> @@ -1774,7 +1774,12 @@ static uint32_t
>> rtl8139_RxConfig_read(RTL8139State *s)
>>  static void rtl8139_transfer_frame(RTL8139State *s, uint8_t *buf, int size,
>>      int do_interrupt, const uint8_t *dot1q_buf)
>>  {
>> -    struct iovec *iov = NULL;
>> +    struct iovec iov[3] = {
>> +        { .iov_base = buf, .iov_len = ETHER_ADDR_LEN * 2 },
>> +        { .iov_base = (void *) dot1q_buf, .iov_len = VLAN_HLEN },
>> +        { .iov_base = buf + ETHER_ADDR_LEN * 2,
>> +          .iov_len = size - ETHER_ADDR_LEN * 2 },
>> +    };
>>
>> and assign dot1q_buf to NULL is size is not ok.
>>
> If "size <  ETHER_ADDR_LEN * 2", .iov_len = size - ETHER_ADDR_LEN * 2 will be
> negative value;
> and if dot1q_buf is NULL, .iov_base = (void *) dot1q_buf will be NULL too. Any side-effect?

Then you need check dot1q_buf instead of iov after. Iov won't be used if
dot1q_buf is NULL.
>
>> Just a suggestion, your call.
> Thanks, Jason :)
>
> Best regards,
> -Gonglei
>