[PATCH 1/2] wifi: mac80211: recheck the IBSS station limit before insertion

[Zhao Li <enderaoelyther@gmail.com>]

Frames from successive unknown IBSS peers can make the deferred worker
install more than 128 stations.

The receive path checks local->num_sta before allocating each station,
but pending stations are not included in that count. Several allocations
can therefore pass before the worker inserts any of them, and the worker
then drains the list without rechecking the limit.

Recheck the installed-station limit in the worker under the wiphy mutex
and free entries that no longer fit.

LLM assistance was used to find the bug and review.

Fixes: 8bf11d8d0811 ("mac80211: delay IBSS station insertion")
Cc: stable@vger.kernel.org
Signed-off-by: Zhao Li <enderaoelyther@gmail.com>
---
Validation: A W=1 module build with MODPOST passed. The
insertion recheck was not exercised separately; the two-patch series was
run as described in patch 2. A reproducer is available on request.
Sparse C=2 passed. Targeted Smatch introduced no new diagnostics.

 net/mac80211/ibss.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/ibss.c b/net/mac80211/ibss.c
index d74b66426349..bd7dbaa942fa 100644
--- a/net/mac80211/ibss.c
+++ b/net/mac80211/ibss.c
@@ -1626,8 +1626,12 @@ void ieee80211_ibss_work(struct ieee80211_sub_if_data *sdata)
 		list_del(&sta->list);
 		spin_unlock_bh(&ifibss->incomplete_lock);
 
-		ieee80211_ibss_finish_sta(sta);
-		rcu_read_unlock();
+		if (sdata->local->num_sta >= IEEE80211_IBSS_MAX_STA_ENTRIES) {
+			sta_info_free(sdata->local, sta);
+		} else {
+			ieee80211_ibss_finish_sta(sta);
+			rcu_read_unlock();
+		}
 		spin_lock_bh(&ifibss->incomplete_lock);
 	}
 	spin_unlock_bh(&ifibss->incomplete_lock);
-- 
2.56.0