From 2b04d6556964ae9f89819b86a0a7801e39c3aae5 Mon Sep 17 00:00:00 2001 From: Devin Wittmayer Date: Fri, 4 Sep 2026 13:03:38 -0700 Subject: [PATCH] wifi: mac80211: refuse to make a monitor active when it has no queue A monitor interface only gets a TXQ if it's created active, and one can't be added later. Setting the flag on a down interface is still allowed, so the driver is handed a monitor with no queue. ath9k dereferences it: BUG: kernel NULL pointer dereference, address: 0000000000000066 RIP: 0010:ath_tx_node_init+0x49/0x170 [ath9k] ath9k_add_interface+0x10c/0x140 [ath9k] drv_add_interface+0x54/0x250 [mac80211] ieee80211_do_open+0x32f/0x800 [mac80211] Reached with CAP_NET_ADMIN by "iw dev X set monitor active" followed by "ip link set X up". RTNL is held, so netlink operations block behind it. Refuse the flag when there is no queue to give. Fixes: 79af1f866193 ("mac80211: avoid allocating TXQs that won't be used") Cc: stable@vger.kernel.org Signed-off-by: Devin Wittmayer Link: https://patch.msgid.link/20260904200338.10829-1-lucid_duck@justthetip.ca Signed-off-by: Johannes Berg --- net/mac80211/cfg.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c index d3558f0c7550..a1753335eb9d 100644 --- a/net/mac80211/cfg.c +++ b/net/mac80211/cfg.c @@ -115,6 +115,10 @@ static int ieee80211_set_mon_options(struct ieee80211_sub_if_data *sdata, return -EBUSY; } + /* TXQs are reserved in ieee80211_if_add() and cannot be added later */ + if ((params->flags & MONITOR_FLAG_ACTIVE) && !sdata->vif.txq) + return -EOPNOTSUPP; + /* validate whether MU-MIMO can be configured */ if (!ieee80211_hw_check(&local->hw, WANT_MONITOR_VIF) && !ieee80211_hw_check(&local->hw, NO_VIRTUAL_MONITOR) &&