[PATCH wireless v3 2/3] wifi: mt76: mt7915: clear cipher state on key removal for WED offload

[Joshua Klinesmith <joshuaklinesmith@gmail.com>]

When switching from WPA-PSK/SAE to open/no encryption, the
DISABLE_KEY path never resets mvif->mt76.cipher back to zero.
The stale cipher value is sent to the WA firmware via BSS_INFO
updates, causing the firmware to keep the protection bit set on
WED-offloaded packets. The hardware then drops all plaintext
frames, resulting in zero throughput.

Reset mvif->mt76.cipher to zero and notify the firmware via
mt7915_mcu_add_bss_info() when the last group key is removed.
The clearing is guarded by checking that both hw_key_idx and
hw_key_idx2 are unset (-1) so that GTK rotation (where the new
key is installed before the old one is removed) and BIGTK
removal while another group key is active do not trigger a
premature zero-cipher BSS update.

Fixes: 3fd2dbd6a1d3 ("mt76: mt7915: update bss_info with cipher after setting the group key")
Cc: stable@vger.kernel.org
Signed-off-by: Joshua Klinesmith <joshuaklinesmith@gmail.com>
---
 drivers/net/wireless/mediatek/mt76/mt7915/main.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7915/main.c b/drivers/net/wireless/mediatek/mt76/mt7915/main.c
index 116dff49c104..2365d1ccf23d 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7915/main.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7915/main.c
@@ -414,6 +414,19 @@ static int mt7915_set_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
 	} else {
 		if (idx == *wcid_keyidx)
 			*wcid_keyidx = -1;
+
+		/* Clear BSS cipher only when the last group key is removed;
+		 * during GTK rotation the new key is installed before the old
+		 * one is removed, so hw_key_idx still points at the new key
+		 * and this condition stays false.
+		 */
+		if (!sta && mvif->mt76.cipher &&
+		    wcid->hw_key_idx == (u8)-1 &&
+		    wcid->hw_key_idx2 == (u8)-1) {
+			mvif->mt76.cipher = 0;
+			mt7915_mcu_add_bss_info(phy, vif, true);
+		}
+
 		goto out;
 	}
 
-- 
2.43.0