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: <8152a551-1813-4d44-a203-45d30f2ac671@embeddedor.com>
Date: Fri, 25 Oct 2024 14:36:44 -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 14:25, Johannes Berg wrote:
> On Fri, 2024-10-25 at 14:22 -0600, Gustavo A. R. Silva wrote:
>>
>>>> -	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`.
> 
> 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`.

> 
>>> please? Or I can do it myself I guess, but ...
>>
>> Sure thing. I can CC stable as well.
> 
> Thanks!
> 
> No need for stable, it got introduced in 6.12-rc1 only.

OK

--
Gustavo