On Fri, Apr 11, 2025 at 01:10:02PM +0200, Bert Karwatzki wrote:
> Am Freitag, dem 11.04.2025 um 12:06 +0200 schrieb Remi Pommarel:
> > 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 ?
Thanks for the debug.
I completely miscalculated the line here sorry. In fact it means here
that mt7921e needs a key for null data frames or for non protected
management frames.
As a lot of your frame control dump does not make sense to me (e.g.
0xffff) maybe you could try to print the fc here at line 647. Just a
wild guess maybe mt7921e needs MT_TXD3_PROTECT_FRAME for NULL data
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,
>
> I modified my debugging patch to print mgmt->frame_control, if needed I could
> also insert a nore complicated function printing out frame types using the
> ieee80211_is_*() functions:
>
> diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/pci_mac.c
> b/drivers/net/wireless/mediatek/mt76/mt7921/pci_mac.c
> index 881812ba03ff..cfbe7e1e4713 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt7921/pci_mac.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt7921/pci_mac.c
> @@ -13,6 +13,9 @@ 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;
> + struct ieee80211_mgmt *mgmt = (void *)tx_info->skb->data;
> + __le16 fc = mgmt->frame_control;
> + dev_info(mdev->dev, "%s: key = %px fc = 0x%hx\n", __func__, key, fc);
> struct mt76_connac_hw_txp *txp;
> struct mt76_txwi_cache *t;
> int id, pid;
>
> and get this, while unsuccesfully trying to connect (also note that one time
> getting a key worked):
>
> $ dmesg | grep prepare_skb
> [ 11.775642] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0xb0
> [ 11.800047] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0x0
> [ 13.365330] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0xb0
> [ 13.370257] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0x0
> [ 16.468481] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0xb0
> [ 16.472407] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0x0
> [ 16.542017] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0x188
> [ 16.549581] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0x188
> [ 16.597120] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0xffff
Thanks again for taking time to debug that.
As said above some of those fc does not make sense to me as I am not
expected first two bits (Protocol version) to be non null.
> [ 16.612263] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> 0000000000000000 fc = 0xd0
>
> Here we actually go a key:
> [ 16.614478] [ T1227] mt7921e 0000:04:00.0: mt7921e_tx_prepare_skb: key =
> ffff89c275297230 fc = 0x4188
> [...]
--
Remi
