Re: [dpdk-dev] [dpdk-stable] [PATCH] net/tap: ipc add check for number of messages received

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 4/19/2019 5:39 PM, Lipiec, Herakliusz wrote:
> On 4/18/2019 7:13, Ferruh Yigit worte:
>> On 4/18/2019 6:19 PM, Herakliusz Lipiec wrote:
>>> A sucessfull call to rte_mp_request_sync does not guarantee that there
>>> are valid messages in the buffer, and this should be checked for
>>> before accessing data in the message.
>>>
>>> Fixes: c9aa56edec8e ("net/tap: access primary process queues from
>>> secondary")
>>> Cc: rasland@mellanox.com
>>> Cc: stable@dpdk.org
>>> Signed-off-by: Herakliusz Lipiec <herakliusz.lipiec@intel.com>
>>> ---
>>>  drivers/net/tap/rte_eth_tap.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/tap/rte_eth_tap.c
>>> b/drivers/net/tap/rte_eth_tap.c index e9fda8cf6..a619a8850 100644
>>> --- a/drivers/net/tap/rte_eth_tap.c
>>> +++ b/drivers/net/tap/rte_eth_tap.c
>>> @@ -2101,7 +2101,7 @@ tap_mp_attach_queues(const char *port_name,
>> struct rte_eth_dev *dev)
>>>  	request.len_param = sizeof(*request_param);
>>>  	/* Send request and receive reply */
>>>  	ret = rte_mp_request_sync(&request, &replies, &timeout);
>>> -	if (ret < 0) {
>>> +	if (ret < 0 || replies.n_receieved != 1) {
>>
>> The API documentation says:
>>
>> ||   * @return
>>
>>
>>
>> ||   *  - On success, return 0.
>>
>>
>>
>> ||   *  - On failure, return -1, and the reason will be stored in rte_errno.
>>
>> So if the API returns 0, why the reply is not valid, also if reply is not valid how
>> can you rely on a value in 'replies'
>>
>> What do you think updating the 'rte_mp_request_sync()' API to return error
>> whenever the reply is not valid?
> The reply is not valid, because there is no valid msg pointer in replies.msg (should be null)
> replies.nb_received should be either 0 (if replies carries no message) or 1 (if there is a message).
> 
> There are two other code paths that can return a success, but have no (valid) message.
> In rte_mp_request_sync there is a call to mp_request_sync which may return 0 with no message in case of:
> - failure to send the message on behalf of remote
> - the caller not caring about reply message.
> I propose to add a check for nb_received to net/tap since this seems to be done in everywhere 
> else when rte_mp_request_sync is called (this will do no harm), and also I think that return codes should be fixed,
> but that can be done irrelevant of this. 
> 

I see, "replies.nb_received" can be relied on since it is set in the begging of
the 'rte_mp_request_sync()'

And I can see you have created a defect for the API fix [1], it is OK to get tap
fix for rc2, but for next release it would be appreciated if you own the defect
you have submitted.

Thanks,
ferruh

[1]
https://bugs.dpdk.org/show_bug.cgi?id=257