[PATCH] wifi: mac80211: change initialize for sk_buff in ieee80211_tx_dequeue()

[Guenter Roeck]

On 1/9/23 06:05, Alexander Wetzel wrote:
> On 05.01.23 06:26, Guenter Roeck wrote:
>> On Mon, Dec 12, 2022 at 03:36:07AM -0500, Wen Gong wrote:
>>> The sk_buff is only set to NULL when initialize, sometimes it will goto
>>> label "begin" after ieee80211_free_txskb(), then it points to a sk_buff
>>> which is already freed. If it run into the "goto out" after arrived to
>>> label "begin", then it will return a sk_buff which is freed, it is a
>>> risk for use-after-free.
>>>
>>> Fixes: ded4698b58cb ("mac80211: run late dequeue late tx handlers without holding fq->lock")
>>> Signed-off-by: Wen Gong <quic_wgong at quicinc.com>
>>
>> I don't see any progress on this patch. Is there a problem with it ?
>> Did it get lost ?
>>
> 
> Looks ok for me. But I just noticed that my patch
> https://patchwork.kernel.org/project/linux-wireless/patch/20221230121850.218810-1-alexander@wetzel-home.de/
> 
> should also fix the issue as an unintended side effect.
> 

Unless I am missing something, there is still a path

begin:
	...
	
	if (unlikely(test_bit(IEEE80211_TXQ_STOP, &txqi->flags)))
  		goto out;
	...
	skb = ...
	...
                         ieee80211_free_txskb(&local->hw, skb);
                         goto begin;

after your patch is applied. Unless the IEEE80211_TXQ_STOP can never be true
after the first iteration I don't see how your patch would fix the problem.

Guenter

> Alexander
> 
>> Thanks,
>> Guenter
>>
>>> ---
>>>   net/mac80211/tx.c | 4 +++-
>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>>
>>> base-commit: 922932ca02191a390f7f52fb6e21c44b50e14025
>>>
>>> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
>>> index 2171cd1ca807..0b23cc9ab9c7 100644
>>> --- a/net/mac80211/tx.c
>>> +++ b/net/mac80211/tx.c
>>> @@ -3776,7 +3776,7 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
>>>       struct ieee80211_local *local = hw_to_local(hw);
>>>       struct txq_info *txqi = container_of(txq, struct txq_info, txq);
>>>       struct ieee80211_hdr *hdr;
>>> -    struct sk_buff *skb = NULL;
>>> +    struct sk_buff *skb;
>>>       struct fq *fq = &local->fq;
>>>       struct fq_tin *tin = &txqi->tin;
>>>       struct ieee80211_tx_info *info;
>>> @@ -3790,6 +3790,8 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
>>>           return NULL;
>>>   begin:
>>> +    skb = NULL;
>>> +
>>>       spin_lock_bh(&fq->lock);
>>>       if (test_bit(IEEE80211_TXQ_STOP, &txqi->flags) ||
>