linux-kernel - Re: [PATCH][next] wifi: mac80211: ieee80211_i: Avoid dozens of -Wflex-array-member-not-at-end warnings

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Message-ID: <192eb05afffd37bd13ff9bc1fc9b044b347b5dc4.camel@sipsolutions.net>
Date: Fri, 25 Oct 2024 22:48:30 +0200
From: Johannes Berg <johannes@...solutions.net>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>, "Gustavo A. R. Silva"
	 <gustavoars@...nel.org>
Cc: linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-hardening@...r.kernel.org, Aditya Kumar Singh <quic_adisi@...cinc.com>
Subject: Re: [PATCH][next] wifi: mac80211: ieee80211_i: Avoid dozens of
 -Wflex-array-member-not-at-end warnings

On Fri, 2024-10-25 at 14:36 -0600, Gustavo A. R. Silva wrote:
> > > 
> > > Yeah, I was actually going to mention this commit, as it's the one that introduced
> > > that `bool radar_detected` to the flex struct. However, it wasn't obvious to me
> > > how `struct ieee80211_chanctx_conf conf` could overwrite `radar_detected` as I didn't
> > > see `conf->drv_priv` being accessed through `struct struct ieee80211_chanctx_conf`.
> > 
> > You have to look at the drivers, see hwsim_clear_chanctx_magic() for
> > example; I wonder why hwsim_check_chanctx_magic() never caught this.
> 
> Sorry, I actually meant through `struct ieee80211_chanctx`. Something like:
> 
> struct ieee80211_chanctx *foo;
> ...
> 
> foo->conf.drv_priv[i] = something;
> 
> or
> 
> struct bar *ptr = (void *)foo->conf->drv_priv;
> then write something into *ptr...
> 
> In the above cases the code will indeed overwrite `radar_detected`.

Right, that's what it does though, no? Except it doesn't have, in the
driver, "foo->conf." because mac80211 only gives it a pointer to conf,
so it's only "conf->drv_priv" (and it's the "struct bar" example.)

So yeah, pretty sure it will overwrite that, and I do wonder why it
wasn't caught. I guess no radar detection tests with MLO yet.

johannes