linux-kernel - Re: [lvc-project] [PATCH] wifi: nl80211: override all other flags if MONITOR_FLAG_COOK

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Message-ID: <49fe46c6a158873cdc6593b0d5630b62a59ed059.camel@sipsolutions.net>
Date: Thu, 30 Jan 2025 22:13:14 +0100
From: Johannes Berg <johannes@...solutions.net>
To: Fedor Pchelkin <pchelkin@...ras.ru>
Cc: Vitaliy Shevtsov <v.shevtsov@...integration.ru>, 
	lvc-project@...uxtesting.org, Michael Wu <flamingice@...rmilk.net>, 
	linux-wireless@...r.kernel.org, "John W. Linville"
 <linville@...driver.com>, 	linux-kernel@...r.kernel.org, 
	syzbot+2e5c1e55b9e5c28a3da7@...kaller.appspotmail.com
Subject: Re: [lvc-project] [PATCH] wifi: nl80211: override all other flags
 if MONITOR_FLAG_COOK_FRAMES is set

On Thu, 2025-01-30 at 22:23 +0300, Fedor Pchelkin wrote:
> 
> Do you suggest rejecting to set MONITOR_FLAG_COOK_FRAMES overall?

No and yes :)

No for the context of this patch. Yes in general.

> 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@sipsolutions.net

tl;dr: only ancient hostapd versions will actually _use_ it, and they
have to fall into a relatively narrow range (April 2009 - Dec 2011.)

> 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.

> Btw, the fragment [2] says the cooked flag overrides the other ones.
> But it was written a long time ago so many things have changed I guess.

Indeed, that doesn't really make sense (certainly not any longer.)

> [1]: https://w1.fi/cgit/hostap/tree/src/drivers/driver_nl80211.c#n6209

And that was almost certainly the only user that ever existed, and can
only set the flag by itself.

johannes