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

[syzbot]

From: Slawomir Stepien <s...@poczta.fm>

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-3.5-flash Gemini:gemini-3.1-pro-preview syzbot
Reported-by: syzbot+9bdc0c...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9bdc0c5998ab45b05030
Link: https://syzkaller.appspot.com/ai_job?id=64f3e3ae-e43e-4917-b403-f9b7799fe1bc
Signed-off-by: Slawomir Stepien <s...@poczta.fm>

---
diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index 3b58af59f..830c9fc95 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -2148,8 +2148,13 @@ 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))
+ return -EINVAL;
+
rate_control_rate_init_all_links(sta);
+ }

ret = sta_info_move_state(sta, IEEE80211_STA_ASSOC);
if (ret)


base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
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[Johannes Berg]

On Thu, 2026-07-23 at 08:11 +0000, syzbot wrote:
> From: Slawomir Stepien <s...@poczta.fm>

I'm a bit confused? Did syzbot just pick up another patch?

> dereferences the NULL chanctx_conf, triggering a WARN_ON:

That can't be right?

> 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).

That's a proxy for "AP is started", but not a good one, I think we
actually have a flag or so somewhere? Maybe even reject it in cfg80211?

> Exempt Multi-Link Operation (MLO) interfaces from this check, as they
> handle chanctx_conf per-link rather than globally on the VIF.

Feels like that's only necessary because the proxy is bad.

Also maybe a similar issue arises if an MLO AP is only half-started, and
stations are added to all links, or so?

johannes