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

["Lipiec, Herakliusz" <herakliusz.lipiec@intel.com>]

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.