Re: [lvc-project] [PATCH] wifi: nl80211: override all other flags if MONITOR_FLAG_COOK_FRAMES is set

[Jouni Malinen]

On Thu, Jan 30, 2025 at 10:13:14PM +0100, Johannes Berg wrote:
> On Thu, 2025-01-30 at 22:23 +0300, Fedor Pchelkin wrote:
> > Wouldn't it break existing userspace, especially in context of systems
> > running old stable kernels where the patch is also needed?
> > 
> > There is still some usage of this flag in hostap [1].
> 
> Theoretically, but I just commented on that here:
> 
> https://lore.kernel.org/r/a49e58998553c45953a30243ad1957c06ce6db8c.camel@xxxxxxxxxxxxxxxx
> 
> tl;dr: only ancient hostapd versions will actually _use_ it, and they
> have to fall into a relatively narrow range (April 2009 - Dec 2011.)

How did you determine that commit a11241fa1149 ("nl80211: Use nl80211
for mgmt TX/RX in AP mode") ends this use? Support for monitor mode
interface is still in hostap.git and it is even tested as part of the
hwsim test cases.. Both hostapd and wpa_supplicant can still be
configured to use the monitor interface.

It would be another question to ask whether there is any good reason to
use this anymore now that a better approach has been available for 13
years and the answer to that is likely "no". Anyway, this is a kernel
interface that has a user even in the current snapshot of user space
programs. If we are about to break that use, it would make sense to
first remove such users. I don't think I would really care about this
anymore and it would be nice to get rid of all that unlikely to be used
much, if at all, code.

> > Or your suggestion is to explicitly reject setting MONITOR_FLAG_COOK_FRAMES
> > only when it is passed combined with some other flags which it is
> > incompatible with?
> 
> Yes.

Though, this seems to imply that the case used by hostapd/wpa_supplicant
would not be broken.

-- 
Jouni Malinen                                            PGP id EFC895FA