wifi: mt76: Fix possible oob access in mt76_connac2_mac_write_txwi_80211()

Check frame length before accessing the mgmt fields in
mt76_connac2_mac_write_txwi_80211 in order to avoid a possible oob
access.

Fixes: 577dbc6 ("mt76: mt7915: enable offloading of sequence number assignment")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260226-mt76-addba-req-oob-access-v1-3-b0f6d1ad4850@kernel.org
[fix check to also cover mgmt->u.action.u.addba_req.capab,
correct Fixes tag]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: LorenzoBianconi

drivers/net/wireless/mediatek/mt76/mt76_connac_mac.c

@@ -413,6 +413,7 @@ mt76_connac2_mac_write_txwi_80211(struct mt76_dev *dev, __le32 *txwi,
 	u32 val;
 
 	if (ieee80211_is_action(fc) &&
+	    skb->len >= IEEE80211_MIN_ACTION_SIZE + 1 + 1 + 2 &&
 	    mgmt->u.action.category == WLAN_CATEGORY_BACK &&
 	    mgmt->u.action.u.addba_req.action_code == WLAN_ACTION_ADDBA_REQ) {
 		u16 capab = le16_to_cpu(mgmt->u.action.u.addba_req.capab);