RE: [PATCH rtw-next v5 2/4] wifi: rtw89: avoid possible TX wait initialization race

[Ping-Ke Shih <pkshih@realtek.com>]

Fedor Pchelkin <pchelkin@ispras.ru> wrote:
> The value of skb_data->wait indicates whether skb is passed on to the
> core mac80211 stack or released by the driver itself.  Make sure that by
> the time skb is added to txwd queue and becomes visible to the completing
> side, it has already allocated and initialized TX wait related data (in
> case it's needed).
> 
> This is found by code review and addresses a possible race scenario
> described below:
> 
>       Waiting thread                          Completing thread
> 
> rtw89_core_send_nullfunc()
>   rtw89_core_tx_write_link()
>     ...
>     rtw89_pci_txwd_submit()
>       skb_data->wait = NULL
>       /* add skb to the queue */
>       skb_queue_tail(&txwd->queue, skb)
> 
>   /* another thread (e.g. rtw89_ops_tx) performs TX kick off for the same queue */
> 
>                                             rtw89_pci_napi_poll()
>                                             ...
>                                               rtw89_pci_release_txwd_skb()
>                                                 /* get skb from the queue */
>                                                 skb_unlink(skb, &txwd->queue)
>                                                 rtw89_pci_tx_status()
>                                                   rtw89_core_tx_wait_complete()
>                                                   /* use incorrect skb_data->wait */
>   rtw89_core_tx_kick_off_and_wait()
>   /* assign skb_data->wait but too late */
> 
> Found by Linux Verification Center (linuxtesting.org).
> 
> Fixes: 1ae5ca615285 ("wifi: rtw89: add function to wait for completion of TX skbs")
> Cc: stable@vger.kernel.org
> Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>

Acked-by: Ping-Ke Shih <pkshih@realtek.com>