Re: [PATCH wireless v2 1/2] wifi: mac80211: Update skb's control block key in ieee80211_tx_dequeue()

[Remi Pommarel <repk@triplefau.lt>]

Hi Bert,

On Thu, Apr 10, 2025 at 11:55:26PM +0200, Bert Karwatzki wrote:
> This commit breaks the mediatek mt7921 wireless driver. In linux-next-20250410
> my mt7921e Wi-Fi controller is no longer able to connect to a network.
> I bisected this to commit a104042e2bf6 ("wifi: mac80211: Update skb's control
> block key in ieee80211_tx_dequeue()").
> 
> Hardware:
> 04:00.0 Network controller: MEDIATEK Corp. MT7921K (RZ608) Wi-Fi 6E 80MHz
> 
> This debugging patch reveals that the change causes key to be NULL in
> mt7921_tx_prepare_skb().
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/pci_mac.c b/drivers/net/wireless/mediatek/mt76/mt7921/pci_mac.c
> index 881812ba03ff..3b8552a1055c 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt7921/pci_mac.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt7921/pci_mac.c
> @@ -13,6 +13,7 @@ int mt7921e_tx_prepare_skb(struct mt76_dev *mdev, void *txwi_ptr,
>         struct mt792x_dev *dev = container_of(mdev, struct mt792x_dev, mt76);
>         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(tx_info->skb);
>         struct ieee80211_key_conf *key = info->control.hw_key;
> +       dev_info(mdev->dev, "%s: key = %px\n", __func__, key);
>         struct mt76_connac_hw_txp *txp;
>         struct mt76_txwi_cache *t;
>         int id, pid;
> 
> 
> So why is info->control.hw_key not updated by ieee80211_tx_h_select_key()?
> 
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index 34f229a6eab0..2510e3533d13 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -631,8 +631,10 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
>  		case WLAN_CIPHER_SUITE_WEP40:
>  		case WLAN_CIPHER_SUITE_WEP104:
>  		case WLAN_CIPHER_SUITE_TKIP:
> -			if (!ieee80211_is_data_present(hdr->frame_control))
> +			if (!ieee80211_is_data_present(hdr->frame_control)) {
> +				printk(KERN_INFO "%s %d: setting tx->key = NULL\n", __func__, __LINE__);
>  				tx->key = NULL;
> +			}
>  			break;
>  		case WLAN_CIPHER_SUITE_CCMP:
>  		case WLAN_CIPHER_SUITE_CCMP_256:
> @@ -641,19 +643,23 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
>  			if (!ieee80211_is_data_present(hdr->frame_control) &&
>  			    !ieee80211_use_mfp(hdr->frame_control, tx->sta,
>  					       tx->skb) &&
> -			    !ieee80211_is_group_privacy_action(tx->skb))
> +			    !ieee80211_is_group_privacy_action(tx->skb)) {
> +				printk(KERN_INFO "%s %d: setting tx->key = NULL\n", __func__, __LINE__);
>  				tx->key = NULL;
> -			else
> +			} else {
>  				skip_hw = (tx->key->conf.flags &
>  					   IEEE80211_KEY_FLAG_SW_MGMT_TX) &&
>  					ieee80211_is_mgmt(hdr->frame_control);
> +			}
>  			break;
>  		case WLAN_CIPHER_SUITE_AES_CMAC:
>  		case WLAN_CIPHER_SUITE_BIP_CMAC_256:
>  		case WLAN_CIPHER_SUITE_BIP_GMAC_128:
>  		case WLAN_CIPHER_SUITE_BIP_GMAC_256:
> -			if (!ieee80211_is_mgmt(hdr->frame_control))
> +			if (!ieee80211_is_mgmt(hdr->frame_control)) {
> +				printk(KERN_INFO "%s %d: setting tx->key = NULL\n", __func__, __LINE__);
>  				tx->key = NULL;
> +			}
>  			break;
>  		}
> 
> @@ -662,9 +668,13 @@ ieee80211_tx_h_select_key(struct ieee80211_tx_data *tx)
>  			     tx->skb->protocol != tx->sdata->control_port_protocol)
>  			return TX_DROP;
> 
> +		printk(KERN_INFO "%s: skip_hw=%d tx->key=%px\n",
> +				__func__, skip_hw, tx->key);
>  		if (!skip_hw && tx->key &&
> -		    tx->key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE)
> +		    tx->key->flags & KEY_FLAG_UPLOADED_TO_HARDWARE) {
>  			info->control.hw_key = &tx->key->conf;
> +			printk(KERN_INFO "%s: info->control.hw_key = %px\n", __func__, info->control.hw_key);
> +		}
>  	} else if (ieee80211_is_data_present(hdr->frame_control) && tx->sta &&
>  		   test_sta_flag(tx->sta, WLAN_STA_USES_ENCRYPTION)) {
>  		return TX_DROP;
> @@ -3894,6 +3904,8 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
>  	 * The key can be removed while the packet was queued, so need to call
>  	 * this here to get the current key.
>  	 */
> +	printk(KERN_INFO "%s: info->control.hw_key = %px, setting to NULL\n",
> +			__func__, info->control.hw_key);
>  	info->control.hw_key = NULL;
>  	r = ieee80211_tx_h_select_key(&tx);
>  	if (r != TX_CONTINUE) {
> 
> This patch reveals that tx->key is set to NULL (in the @@ -641,19 +643,23 @@ chunk)
> and so the updating of info->contro.hw_key is skipped:
> 
> [   17.411298] [   T1232] ieee80211_tx_h_select_key 647: setting tx->key = NULL

That means that we are trying to send non management frames using
AES_CMAC, or BIP_* cipher, aren't those ciphers used only for group
management frames ?

> [   17.411300] [   T1232] ieee80211_tx_h_select_key: skip_hw=0 tx->key=0000000000000000
> [   17.411307] [   T1232] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key = 0000000000000000
> 
> If I revert commit a104042e2bf6 while keeping the debug patches it shows that
> the for mt7921e the key is never updated in ieee80211_tx_h_select_key(), mt7921e
> relies on the key your patch is setting to NULL.
> 
> Is this a problem with your patch or with the mt7921e driver that just got
> revealed by your patch?

Not sure yet, do you happen to know which kind of frame mt7921e is
trying to be sent using this NULL key ?

Thanks,

-- 
Remi