Re: [PATCH RFC v3] wifi: mac80211: reject station association if AP is not started

[Slawomir Stepien <sst@poczta.fm>]

On lip 16, 2026 08:22, 'syzbot' via syzkaller-upstream-moderation wrote:
> If an interface is changed to AP mode but not started, its channel context
> configuration (chanctx_conf) remains NULL. If a station is then added to
> this interface, the kernel may automatically set the
> NL80211_STA_FLAG_ASSOCIATED flag for compatibility with older userspace
> applications.
> 
> When this flag is set, sta_apply_auth_flags() attempts to initialize rate
> control for the station by calling rate_control_rate_init_all_links(). This
> eventually leads to rate_control_rate_init(), which dereferences the NULL
> chanctx_conf, triggering a WARN_ON:
> 
> WARNING: net/mac80211/rate.c:51 at rate_control_rate_init+0x5a6/0x630
> ...
> Call Trace:
>  <TASK>
>  rate_control_rate_init_all_links+0xf4/0x190 net/mac80211/rate.c:84
>  sta_apply_auth_flags+0x1bc/0x430 net/mac80211/cfg.c:2152
>  sta_apply_parameters+0x126d/0x1b10 net/mac80211/cfg.c:2618
>  ieee80211_add_station+0x3de/0x700 net/mac80211/cfg.c:2684
>  rdev_add_station+0xfc/0x290 net/wireless/rdev-ops.h:201
>  nl80211_new_station+0x1b4e/0x1fd0 net/wireless/nl80211.c:9505
> 
> Fix this by rejecting the addition or modification of a station to the
> associated state if the AP has not been started (chanctx_conf is NULL).
> Exempt Multi-Link Operation (MLO) interfaces from this check, as they
> handle chanctx_conf per-link rather than globally on the VIF.
> 
> Fixes: 55de908ab292 ("mac80211: use channel contexts")
> Assisted-by: Gemini:gemini-3.1-pro-preview Gemini:gemini-3-flash-preview syzbot
> Reported-by: syzbot+9bdc0c5998ab45b05030@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=9bdc0c5998ab45b05030
> Link: https://syzkaller.appspot.com/ai_job?id=0c474d56-8871-480a-8ac4-9a9658930b46
> To: "Johannes Berg" <johannes@sipsolutions.net>
> To: <linux-wireless@vger.kernel.org>
> Cc: <linux-kernel@vger.kernel.org>
> 
> ---
> v3:
> - Added an empty line after the newly added code block for better readability.
> 
> v2:
> - Moved the chanctx_conf check inside the WLAN_STA_RATE_CONTROL check block.
> - Removed a phrase from the commit description as requested by reviewers.
> https://lore.kernel.org/all/79cbf145-6652-4e15-be67-f7974ebc29cb@mail.kernel.org/T/
> 
> v1:
> https://lore.kernel.org/all/8e8a5122-a09e-43b2-b42f-4c73b021b173@mail.kernel.org/T/
> ---
> diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
> index 3b58af59f..d4331fbae 100644
> --- a/net/mac80211/cfg.c
> +++ b/net/mac80211/cfg.c
> @@ -2148,8 +2148,14 @@ static int sta_apply_auth_flags(struct ieee80211_local *local,
>  		 * well. Some drivers require rate control initialized
>  		 * before drv_sta_state() is called.
>  		 */
> -		if (!test_sta_flag(sta, WLAN_STA_RATE_CONTROL))
> +		if (!test_sta_flag(sta, WLAN_STA_RATE_CONTROL)) {
> +			if (!ieee80211_vif_is_mld(&sta->sdata->vif) &&
> +			    !rcu_access_pointer(
> +				    sta->sdata->vif.bss_conf.chanctx_conf))

Don't worry about 80 column limit (it is 100 for some time now in scripts/checkpatch.pl). Make this
a one line please: !rcu_access_pointer(sta->sdata->vif.bss_conf.chanctx_conf))

> +				return -EINVAL;
> +
>  			rate_control_rate_init_all_links(sta);
> +		}
>  
>  		ret = sta_info_move_state(sta, IEEE80211_STA_ASSOC);
>  		if (ret)
> 
> 
> base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482

-- 
Slawomir Stepien