[PATCH wireless] wifi: mt76: mt7615: do not tear down BSS/STA state for monitor vifs

[Devin Wittmayer <lucid_duck@justthetip.ca>]

From: Mark Anthony Agarro <markanthonyagarro@gmail.com>

Tearing down a monitor interface oopses:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:mt76_connac_mcu_uni_add_bss+0x144/0x370 [mt76_connac_lib]
  Call Trace:
   mt7615_remove_interface+0x6a/0x200 [mt7615_common]
   drv_remove_interface+0x60/0x140 [mac80211]
   ieee80211_del_virtual_monitor+0x8f/0xc0 [mac80211]
   ieee80211_do_open+0x550/0x7d0 [mac80211]
   ieee80211_open+0xaa/0xb0 [mac80211]
   __dev_open+0x11b/0x280

mt7615_remove_interface() tears down BSS and STA state for every vif type.
On MT7663 with offload firmware that reaches mt76_connac_mcu_uni_add_bss(),
which has no monitor case in its iftype switch. It takes WARN_ON(1), then
copies ETH_ALEN from vif->bss_conf.bssid, which is NULL for a monitor vif.

mt76_connac_mcu_bss_basic_tlv() in the same file handles this. It has an
NL80211_IFTYPE_MONITOR case and it copies phy->macaddr in place of the
bssid. The uni variant has neither.

There is nothing to tear down. mt7615_add_interface() only calls
mt7615_mcu_add_dev_info(). The BSS and STA state comes from beacon enable
in mt7615_bss_info_changed(), from mt7615_set_key() and from
mt7615_mac_sta_add(), so a monitor vif never has any.

Reported on mt7615e going from monitor back to managed, and on mt7663u on
an "ip link set down", both through ieee80211_del_virtual_monitor().

Fixes: d9852ab2f362 ("mt76: mt7615: keep mcu_add_bss_info enabled till interface removal")
Cc: stable@vger.kernel.org
Reported-by: Orly Orge <orlyorge2004@gmail.com>
Closes: https://lore.kernel.org/linux-wireless/CANj5C4mTOHs6riyWee=dFdkE5p=714J8xs-x3hq3ewQ+r6O_Nw@mail.gmail.com/
Reported-by: Inanix <contact@inanix.fr>
Closes: https://github.com/morrownr/mt76/issues/79
Tested-by: Inanix <contact@inanix.fr>
Signed-off-by: Mark Anthony Agarro <markanthonyagarro@gmail.com>
Signed-off-by: Devin Wittmayer <lucid_duck@justthetip.ca>
---
 drivers/net/wireless/mediatek/mt76/mt7615/main.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7615/main.c b/drivers/net/wireless/mediatek/mt76/mt7615/main.c
index fc619ac..986fde1 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7615/main.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7615/main.c
@@ -254,8 +254,10 @@ static void mt7615_remove_interface(struct ieee80211_hw *hw,
 
 	mt7615_mutex_acquire(dev);
 
-	mt7615_mcu_add_bss_info(phy, vif, NULL, false);
-	mt7615_mcu_sta_add(phy, vif, NULL, false);
+	if (vif->type != NL80211_IFTYPE_MONITOR) {
+		mt7615_mcu_add_bss_info(phy, vif, NULL, false);
+		mt7615_mcu_sta_add(phy, vif, NULL, false);
+	}
 
 	mt76_testmode_reset(phy->mt76, true);
 	if (vif == phy->monitor_vif)
-- 
2.55.0