[PATCH v2] wifi: mt76: mt7996: fix reading zeroed info->control.flags after mt76_tx_status_skb_add()

[Lorenzo Bianconi]

mt76_tx_status_skb_add() zeroes the mt76_tx_cb struct stored at
info->status.status_driver_data via memset(). Since info->control and
info->status are members of the same union in ieee80211_tx_info,
this overwrites info->control.flags.
In mt7996_tx_prepare_skb(), mt76_tx_status_skb_add() is called before
mt7996_mac_write_txwi(), which re-reads info->control.flags to extract
IEEE80211_TX_CTRL_MLO_LINK. Because the field has been zeroed, the
link_id always resolves to 0 for frames using global_wcid, leading to
incorrect TXWI configuration.
Fix this by passing link_id as an explicit parameter to
mt7996_mac_write_txwi(). In mt7996_tx_prepare_skb(), the link_id is
already extracted from info->control.flags before the destructive
mt76_tx_status_skb_add() call. For the beacon and inband discovery
callers in mcu.c, use link_conf->link_id directly.

Fixes: f0b0b239b8f36 ("wifi: mt76: mt7996: rework mt7996_mac_write_txwi() for MLO support")
Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
---
Changes in v2:
- Do not use link_id in mt7996_mac_write_txwi if it is IEEE80211_LINK_UNSPECIFIED
- In mt7996_mac_write_txwi() rely on link_id calculated in
  mt7996_tx_prepare_skb().
- Link to v1: https://lore.kernel.org/r/20260530-mt76_tx_status_skb_add-overwrite-fix-v1-1-e2c3151c391a@xxxxxxxxxx
---
 drivers/net/wireless/mediatek/mt76/mt7996/mac.c    | 14 ++++----------
 drivers/net/wireless/mediatek/mt76/mt7996/mcu.c    |  5 +++--
 drivers/net/wireless/mediatek/mt76/mt7996/mt7996.h |  3 ++-
 3 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
index c98446057282..95b3078d9667 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
@@ -856,7 +856,8 @@ mt7996_mac_write_txwi_80211(struct mt7996_dev *dev, __le32 *txwi,
 void mt7996_mac_write_txwi(struct mt7996_dev *dev, __le32 *txwi,
 			   struct sk_buff *skb, struct mt76_wcid *wcid,
 			   struct ieee80211_key_conf *key, int pid,
-			   enum mt76_txq_id qid, u32 changed)
+			   enum mt76_txq_id qid, u32 changed,
+			   unsigned int link_id)
 {
 	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
@@ -866,7 +867,6 @@ void mt7996_mac_write_txwi(struct mt7996_dev *dev, __le32 *txwi,
 	bool is_8023 = info->flags & IEEE80211_TX_CTL_HW_80211_ENCAP;
 	struct mt76_vif_link *mlink = NULL;
 	struct mt7996_vif *mvif;
-	unsigned int link_id;
 	u16 tx_count = 15;
 	u32 val;
 	bool inband_disc = !!(changed & (BSS_CHANGED_UNSOL_BCAST_PROBE_RESP |
@@ -874,17 +874,11 @@ void mt7996_mac_write_txwi(struct mt7996_dev *dev, __le32 *txwi,
 	bool beacon = !!(changed & (BSS_CHANGED_BEACON |
 				    BSS_CHANGED_BEACON_ENABLED)) && (!inband_disc);
 
-	if (wcid != &dev->mt76.global_wcid)
-		link_id = wcid->link_id;
-	else
-		link_id = u32_get_bits(info->control.flags,
-				       IEEE80211_TX_CTRL_MLO_LINK);
-
 	mvif = vif ? (struct mt7996_vif *)vif->drv_priv : NULL;
 	if (mvif) {
 		if (wcid->offchannel)
 			mlink = rcu_dereference(mvif->mt76.offchannel_link);
-		if (!mlink)
+		if (!mlink && link_id != IEEE80211_LINK_UNSPECIFIED)
 			mlink = rcu_dereference(mvif->mt76.link[link_id]);
 	}
 
@@ -1096,7 +1090,7 @@ int mt7996_tx_prepare_skb(struct mt76_dev *mdev, void *txwi_ptr,
 	/* Transmit non qos data by 802.11 header and need to fill txd by host*/
 	if (!is_8023 || pid >= MT_PACKET_ID_FIRST)
 		mt7996_mac_write_txwi(dev, txwi_ptr, tx_info->skb, wcid, key,
-				      pid, qid, 0);
+				      pid, qid, 0, link_id);
 
 	/* MT7996 and MT7992 require driver to provide the MAC TXP for AddBA
 	 * req
diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mcu.c b/drivers/net/wireless/mediatek/mt76/mt7996/mcu.c
index 8be40d60ad29..a14c63438923 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7996/mcu.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7996/mcu.c
@@ -3103,7 +3103,7 @@ mt7996_mcu_beacon_cont(struct mt7996_dev *dev,
 
 	buf = (u8 *)bcn + sizeof(*bcn);
 	mt7996_mac_write_txwi(dev, (__le32 *)buf, skb, wcid, NULL, 0, 0,
-			      BSS_CHANGED_BEACON);
+			      BSS_CHANGED_BEACON, link_conf->link_id);
 
 	memcpy(buf + MT_TXD_SIZE, skb->data, skb->len);
 }
@@ -3249,7 +3249,8 @@ int mt7996_mcu_beacon_inband_discov(struct mt7996_dev *dev,
 
 	buf = (u8 *)tlv + sizeof(*discov);
 
-	mt7996_mac_write_txwi(dev, (__le32 *)buf, skb, wcid, NULL, 0, 0, changed);
+	mt7996_mac_write_txwi(dev, (__le32 *)buf, skb, wcid, NULL, 0, 0,
+			      changed, link_conf->link_id);
 
 	memcpy(buf + MT_TXD_SIZE, skb->data, skb->len);
 
diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mt7996.h b/drivers/net/wireless/mediatek/mt76/mt7996/mt7996.h
index 0dc4198fcf8b..0d6488522ba7 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7996/mt7996.h
+++ b/drivers/net/wireless/mediatek/mt76/mt7996/mt7996.h
@@ -874,7 +874,8 @@ void mt7996_mac_enable_nf(struct mt7996_dev *dev, u8 band);
 void mt7996_mac_write_txwi(struct mt7996_dev *dev, __le32 *txwi,
 			   struct sk_buff *skb, struct mt76_wcid *wcid,
 			   struct ieee80211_key_conf *key, int pid,
-			   enum mt76_txq_id qid, u32 changed);
+			   enum mt76_txq_id qid, u32 changed,
+			   unsigned int link_id);
 void mt7996_mac_update_beacons(struct mt7996_phy *phy);
 void mt7996_mac_set_coverage_class(struct mt7996_phy *phy);
 void mt7996_mac_work(struct work_struct *work);

---
base-commit: 4913f44167cf35a9536e9eec7352e15b2de0c573
change-id: 20260530-mt76_tx_status_skb_add-overwrite-fix-85818a9bb31f

Best regards,
-- 
Lorenzo Bianconi <lorenzo@xxxxxxxxxx>