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wifi: mac80211: refuse to make a monitor active when it has no queue

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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: 79af1f8661 ("mac80211: avoid allocating TXQs that won't be used")
Cc: stable@vger.kernel.org
Signed-off-by: Devin Wittmayer <lucid_duck@justthetip.ca>
Link: https://patch.msgid.link/20260904200338.10829-1-lucid_duck@justthetip.ca
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This commit is contained in:
Devin Wittmayer 2026-09-04 13:03:38 -07:00 committed by Johannes Berg
parent 06f42accaf
commit 2b04d65569
1 changed files with 4 additions and 0 deletions
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4
net/mac80211/cfg.c
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@ -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) &&