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

[Ryder Lee <Ryder.Lee@mediatek.com>]

On Sat, 2026-05-30 at 17:25 +0200, Lorenzo Bianconi wrote:
> 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@kernel.org>
> ---
>  drivers/net/wireless/mediatek/mt76/mt7996/mac.c    | 9 +++------
>  drivers/net/wireless/mediatek/mt76/mt7996/mcu.c    | 5 +++--
>  drivers/net/wireless/mediatek/mt76/mt7996/mt7996.h | 3 ++-
>  3 files changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
> b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
> index c98446057282..2d3f80b3e41a 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 |
> @@ -876,9 +876,6 @@ void mt7996_mac_write_txwi(struct mt7996_dev
> *dev, __le32 *txwi,
>  
>  	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) {
> @@ -1096,7 +1093,7 @@ 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);

The reason we didn't make the same change is because we use other
control flags (IEEE80211_TX_CTRL*) of info->control.flags not just MLO
one. So with this change we still need to copy over the other flags and
pass them in as well.

Ryder
> 
> ---
> base-commit: 4913f44167cf35a9536e9eec7352e15b2de0c573
> change-id: 20260530-mt76_tx_status_skb_add-overwrite-fix-85818a9bb31f
> 
> Best regards,