Re: [PATCH 4/5] mac80211: run late dequeue late tx handlers without holding fq->lock

[Wen Gong <quic_wgong@quicinc.com>]

Hi Johannes,

do you know it?

On 12/5/2022 5:46 PM, Wen Gong wrote:
> On 3/17/2019 1:06 AM, Felix Fietkau wrote:
>> Reduces lock contention on enqueue/dequeue of iTXQ packets
>>
>> Signed-off-by: Felix Fietkau <nbd@nbd.name>
>> ---
>>   net/mac80211/tx.c | 10 ++++++++--
>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
>> index 8127e43e12b1..f85344c9af62 100644
>> --- a/net/mac80211/tx.c
>> +++ b/net/mac80211/tx.c
>> @@ -3544,6 +3544,7 @@ struct sk_buff *ieee80211_tx_dequeue(struct 
>> ieee80211_hw *hw,
>>       ieee80211_tx_result r;
>>       struct ieee80211_vif *vif = txq->vif;
>>   +begin:
>>       spin_lock_bh(&fq->lock);
> Maybe use-after-free will happened?
>
> You can see ieee80211_tx_dequeue() in tx.c as below, after 
> ieee80211_free_txskb(), it will goto begin,
> If goto out happened in below check, then the skb which is freed will 
> be returned, and use-after-free will happen.
>
> https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/tree/net/mac80211/tx.c?id=ded4698b58cb23c22b0dcbd829ced19ce4e6ce02#n3538 
>
> begin:
>     spin_lock_bh(&fq->lock);
>
>     if (test_bit(IEEE80211_TXQ_STOP, &txqi->flags) ||
>         test_bit(IEEE80211_TXQ_STOP_NETIF_TX, &txqi->flags))
>         goto out;
>
>     if (vif->txqs_stopped[ieee80211_ac_from_tid(txq->tid)]) {
>         set_bit(IEEE80211_TXQ_STOP_NETIF_TX, &txqi->flags);
>         goto out;
>     }
>
>     /* Make sure fragments stay together. */
>     skb = __skb_dequeue(&txqi->frags);
>     if (skb)
>         goto out;
>
>     skb = fq_tin_dequeue(fq, tin, fq_tin_dequeue_func);
>     if (!skb)
>         goto out;
>
>     spin_unlock_bh(&fq->lock);
>
> Maybe "skb = NULL;" should be added after "begin:".
>
> ...
>