Subject: Re: [PATCH] wifi: mt76: mt7996: Fix possible token leak in mt7996_tx_prepare_skb()

From: Lorenzo Bianconi <[email-masked]>
Date: Wed, 3 Jun 2026 09:09:15 +0200

> Hi Lore,

Hi Dylan,

> 
> We have been seeing the token memory leak in our custom kernel. After
> pulling your patch in, we are still getting the leak (validated with
> kmemleak). How did you figure out where this potential leak was? I want to
> determine if we are leaking because of our changes or if there's more areas
> for token leakage.

Can you please try to run kmemleak on Felix's tree to check if there are any
leftover leaks not fixed yet?

Regards,
Lorenzo

> 
> -- Dylan
> 
> On 5/31/26 2:10 AM, Lorenzo Bianconi wrote:
> > If link_conf or link_sta lookup fails in mt7996_tx_prepare_skb routine,
> > mt7996 driver leaks an already allocated tx token. Fix the issue
> > releasing the token in case of error.
> > 
> > Fixes: 7ef0c7ad735b0 ("wifi: mt76: mt7996: Implement MLD address translation for EAPOL")
> > Signed-off-by: Lorenzo Bianconi <[email-masked]>
> > ---
> >   drivers/net/wireless/mediatek/mt76/mt7996/mac.c | 8 ++++++--
> >   drivers/net/wireless/mediatek/mt76/tx.c         | 2 +-
> >   2 files changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
> > index c98446057282..8c56344d211b 100644
> > --- a/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
> > +++ b/drivers/net/wireless/mediatek/mt76/mt7996/mac.c
> > @@ -1067,11 +1067,11 @@ int mt7996_tx_prepare_skb(struct mt76_dev *mdev, void *txwi_ptr,
> >   		link_conf = rcu_dereference(vif->link_conf[wcid->link_id]);
> >   		if (!link_conf)
> > -			return -EINVAL;
> > +			goto error_relase_token;
> >   		link_sta = rcu_dereference(sta->link[wcid->link_id]);
> >   		if (!link_sta)
> > -			return -EINVAL;
> > +			goto error_relase_token;
> >   		dma_sync_single_for_cpu(mdev->dma_dev, tx_info->buf[1].addr,
> >   					tx_info->buf[1].len, DMA_TO_DEVICE);
> > @@ -1176,6 +1176,10 @@ int mt7996_tx_prepare_skb(struct mt76_dev *mdev, void *txwi_ptr,
> >   	tx_info->nbuf = MT_CT_DMA_BUF_NUM;
> >   	return 0;
> > +
> > +error_relase_token:
> > +	mt76_token_release(mdev, id, NULL);
> > +	return -EINVAL;
> >   }
> >   u32 mt7996_wed_init_buf(void *ptr, dma_addr_t phys, int token_id)
> > diff --git a/drivers/net/wireless/mediatek/mt76/tx.c b/drivers/net/wireless/mediatek/mt76/tx.c
> > index 22f9690634c9..f96d9c471853 100644
> > --- a/drivers/net/wireless/mediatek/mt76/tx.c
> > +++ b/drivers/net/wireless/mediatek/mt76/tx.c
> > @@ -933,7 +933,7 @@ mt76_token_release(struct mt76_dev *dev, int token, bool *wake)
> >   #endif
> >   	}
> > -	if (dev->token_count < dev->token_size - MT76_TOKEN_FREE_THR &&
> > +	if (wake && dev->token_count < dev->token_size - MT76_TOKEN_FREE_THR &&
> >   	    dev->phy.q_tx[0]->blocked)
> >   		*wake = true;
> > 
> > ---
> > base-commit: 4913f44167cf35a9536e9eec7352e15b2de0c573
> > change-id: 20260531-mt7996_tx_prepare_skb-token-leack-82e240d8c66f
> > 
> > Best regards,
>