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: <3471e59f-a414-479f-8fb0-aa1a26aecf16@embeddedor.com>
Date: Fri, 25 Oct 2024 14:22:58 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Johannes Berg <johannes@...solutions.net>,
 "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 25/10/24 14:14, Johannes Berg wrote:
> On Fri, 2024-10-25 at 14:10 -0600, Gustavo A. R. Silva wrote:
>> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
>> getting ready to enable it, globally.
>>
>> Move the conflicting declaration to the end of the structure and add
>> a code comment. Notice that `struct ieee80211_chanctx_conf` is a
>> flexible structure --a structure that contains a flexible-array member.
>>
>> Fix 50 of the following warnings:
>>
>> net/mac80211/ieee80211_i.h:895:39: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>> ---
>>   net/mac80211/ieee80211_i.h | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
>> index e7815ffeaf30..c65adbdf2166 100644
>> --- a/net/mac80211/ieee80211_i.h
>> +++ b/net/mac80211/ieee80211_i.h
>> @@ -892,9 +892,10 @@ struct ieee80211_chanctx {
>>   	/* temporary data for search algorithm etc. */
>>   	struct ieee80211_chan_req req;
>>   
>> -	struct ieee80211_chanctx_conf conf;
>> -
>>   	bool radar_detected;
>> +
>> +	/* MUST be last - ends in a flexible-array member. */
>> +	struct ieee80211_chanctx_conf conf;
>>   };
> 
> Oi. That's not just a warnings problem, that's actually a pretty stupid
> bug, this will surely get used and radar_detected will alias stuff that
> the driver puts there - at least for drivers using chanctx_data_size,
> which is a couple: ath9k, iwlmvm, mt792x, rwt89 and hwsim.
> 
> Could you resend with a description that this is a bugfix and
> 
> Fixes: bca8bc0399ac ("wifi: mac80211: handle ieee80211_radar_detected() for MLO")

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`.

> 
> please? Or I can do it myself I guess, but ...

Sure thing. I can CC stable as well.

> 
> This shouldn't go to next, it should go to 6.12 since that broke it...

OK, in that case I just remove the `[next]` part from the subject line.

Thanks
--
Gustavo