Re: [PATCH] cfg80211: fix sband iftype data lookup for AP_VLAN

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2023-06-22 at 18:50 +0200, Felix Fietkau wrote:
> On 22.06.23 18:41, Johannes Berg wrote:
> > On Thu, 2023-06-22 at 18:25 +0200, Felix Fietkau wrote:
> > > On 22.06.23 18:07, Johannes Berg wrote:
> > > > On Thu, 2023-06-22 at 18:05 +0200, Felix Fietkau wrote:
> > > > > Since AP_VLAN interfaces are not pushed to the driver, 
> > > > > 
> > > > That's a mac80211 thing though.
> > > > 
> > > > > the driver should not
> > > > > be expected to register iftype data for them.
> > > > > Map them to the regular AP iftype on lookup.
> > > > 
> > > > And this is in cfg80211 - not sure that seems right?
> > > > 
> > > > OTOH I'd expect no callers with VLAN here, it doesn't really make sense
> > > > since they're not a standalone mode that actually has HE/EHT, but still,
> > > > seems odd this way?
> > > > 
> > > > What's actually calling it? I'm guessing somewhere in mac80211?
> > > 
> > > Yes, I guess only mac80211 is affected. I put in the cfg80211 prefix
> > > because that's what the header file belongs to.
> > > 
> > > I made the patch in response to this:
> > > https://patchwork.kernel.org/project/linux-wireless/patch/20230605152141.17434-4-shayne.chen@mediatek.com/
> > 
> > OK, sure, that also doesn't really make sense.
> > 
> > > I found that there are several calls to ieee80211_get_he_iftype_cap and
> > > ieee80211_get_eht_iftype_cap, which could be affected by this issue.
> > > I thought dealing with this in a single place would be better than playing
> > > whac-a-mole by fixing it at the call sites.
> > > 
> > 
> > I replaced almost all of them with ieee80211_get_he_iftype_cap_vif() so
> > it shouldn't be that bad? Looks like I forgot some though.
> 
> I guess one advantage in using my fix would be that it's way easier to 
> backport.
> How about using my fix initially (with a changed prefix if you prefer), 
> and then replace it once the call sites have been switched over to 
> ieee80211_get_he_iftype_cap_vif?
> 

Actually, I don't even mind the fix itself that much, I just think the
description is a bit misleading :-)

How about just describing it as something like "AP_VLAN is virtual so it
doesn't really exist as a type for capabilities; surely AP was
intended"?

I can kind of see how this might happen too, you have a STA, check the
interface, etc.

johannes