bearer mbim: ipv6_config set to dhcp when no ipv6 is available

[Andreas Fett]

Hi,

On Sat, Oct 06, 2018 at 02:49:32PM +0200, Aleksander Morgado wrote:
> > I could be mis-remembering, but I don't think this was intentional and
> > if MBIM says IPv6 isn't available, then MM shouldn't say it's available
> > either.
> > 
> > Bjorn or Aleksander, do you have more experience here that you could
> > share?
> 
> I agree that this could be a bug, so the patch would be very welcome.

I reread the mbim specification and things seem to be a bit more
complicated than I imagined, as they always are :-) So sorry for not
doing the reading before sending my first mail.

Essentially the standard says in 10.5.20 (MBIM_CID_IP_CONFIGURATION)
That the ip info can be aquired either via the ip configuration message
or via "the hosts ip stack" which would dhcp or SLAAC in the v6 case.
For DNS it allows a combination of the two.

So the code in ip_configuration_query_ready() seems to be correct
in advertising MM_BEARER_IP_METHOD_DHCP even when none of the bits in
ipv6configurationavailable are set.

There seems however to be a problem with the way the context ip type
is represented in the bearer. It just reflects the attribute as send in
MBIM_SET_CONNECT (10.5.12.4).

There is however an MBIM_CONNECT_INFO (10.5.12.6) which seems to report
the available ip type back. If I'm not mistaken that one is parsed
in connect_set_ready() using mbim_message_connect_response_parse().
The ip_type there however is ignored. A comment in the same function
mentions that it is only relevant for MBIM_CONTEXT_IP_TYPE_DEFAULT but
I wonder if that is true for ip4+ipv6 contexts.

Any thoughts on this?

Andreas

-- 
The three chief virtues of a programmer are:
Laziness, Impatience and Hubris. -- Larry Wall
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