[PATCH] ACS: always discard DFS channels when DFS isn't allowed

[Nicolas Escande]

On Sun May 8, 2022 at 12:42 PM CEST, Nicolas Escande wrote:
> On Tue Apr 19, 2022 at 11:18 AM CEST, Nicolas Escande wrote:
> > On Sun Apr 17, 2022 at 11:18 AM CEST, Jouni Malinen wrote:
> > > Why is this removing the use of WPA_DRIVER_FLAGS_DFS_OFFLOAD completely
> > > here? I'm not completely sure I understood what kind of a case could
> > > have allowed ACS to select a DFS channel incorrectly. Maybe that is
> > > something that should be addressed in the ACS implementation instead?
> > >
> > > Please note that the DFS offload cases might use different style for
> > > configuring the DFS operations, so it is not clear whether the
> > > ieee80211h parameter is really applicable in all such cases and this
> > > type of a change could result in breaking something that is already
> > > deployed.
> >
> > So this code fetches the channels supported by the hardware and applies
> > flags on it depending on whether or not we can use them and under what
> > conditions. So for a regular driver (one that does not sets the
> > WPA_DRIVER_FLAGS_DFS_OFFLOAD flag), when DFS is disabled by hostapd conf,
> > any DFS channel will be flagged as disabled. This gets bypassed when the
> > driver sets WPA_DRIVER_FLAGS_DFS_OFFLOAD.
> >
> > From what I understood, the DFS offload flag means that the driver
> > itself should react to DFS events and handle things like CAC wait times.
> > It shouldn't imply anything for the rest of the code, it shouldn't hide
> > the fact that this channel shouldn't be used for example.
> >
> > This is problematic when doing ACS because we usually do not take into
> > account any channel that is flagged as disabled. So this applies to DFS
> > channels when the conf doesn't allow them.
> >
> > This lead me to cases where a conf that explicitely doesn't allow DFS
> > channel (ieee80211h=0) to be used with ACS still enabled, still selected
> > a DFS channel because the driver handles DFS itself with
> > WPA_DRIVER_FLAGS_DFS_OFFLOAD flag, but doesn't bypass our ACS
> > implementation with WPA_DRIVER_FLAGS_ACS_OFFLOAD.
> >
> > I understand that this could have implications but for me the "right"
> > behaviour should be :
> > - non usable channels should be flagged as such (so when conf doesn't
> >   allow them exclude them)
> > - hostapd's ACS implem should select a "usable" channels from the list
> >   (unless ACS is offloaded with WPA_DRIVER_FLAGS_ACS_OFFLOAD in which
> >   case all bets are off)
> >
> > What do you think ?	 
> >
> > > -- 
> > > Jouni Malinen                                            PGP id EFC895FA
>
> Hi Jouni,
> Any new input on this ?

Hi there,
As I see some older stuff gets reviewed, any chance this gets another look at ?